Title of Invention	NOVEL PHOSPHINIC ACIDS AND THEIR SULFUR DERIVATIVES AND METHODS FOR THEIR PREPARATION
Abstract	The present invention provides phosphinic acids and their sulfur derivatives, in accordance with the following formula (I): wherein R<l> and R<2> are different and each of R<l> and R<2> is independently selected from an organic radical that branches at the alpha carbon and an organic radical that branches at the beta carbon, and each of X and Y is independently 0 or S, and wherein said compound is a liquid at room temperature. Compounds of formula (I) find utility for example as metal extractants. Also provided are methods for making compounds of formula (I) and their corresponding phosphine intermediates.

Title of Invention

NOVEL PHOSPHINIC ACIDS AND THEIR SULFUR DERIVATIVES AND METHODS FOR THEIR PREPARATION

Abstract

The present invention provides phosphinic acids and their sulfur derivatives, in accordance with the following formula (I): wherein R<l> and R<2> are different and each of R<l> and R<2> is independently selected from an organic radical that branches at the alpha carbon and an organic radical that branches at the beta carbon, and each of X and Y is independently 0 or S, and wherein said compound is a liquid at room temperature. Compounds of formula (I) find utility for example as metal extractants. Also provided are methods for making compounds of formula (I) and their corresponding phosphine intermediates.

Full Text	NOVEL PHOSPHINIC ACIDS AND THEIR SULFUR DERIVATIVES AND METHODS FOR THEIR PREPARATION FIELD OF THE INVENTION: The present invention relates generally to the field of organic chemistry. More particularly, the present invention provides novel organic phosphinic acids and their sulfur derivatives and methods for their preparation. These novel compounds find utility as metal extractants. SUMMARY OF THE INVENTION: In one aspect, the invention provides a compound defined by formula (I): wherein: R1 and R2 are different and each of R1 and R2 is independently selected from: (a) -CH2-CHR3R4, where R3 is methyl or ethyl; and R4 is an optionally substituted alkyl or heteroalkyl; and (b) -CR3(CH2R5)R6, where R3 is methyl or ethyl; and R5 is H or an optionally substituted alkyl or heteroalkyl, and R6 is an optionally substituted alkyl or heteroalkyl; or 1 R5, R€ and the ethylene group to which they are bonded form a five or six-nembered optionally substituted cycloalkyl or heterocycloalkyl ring; and each of X and Y is independently 0 or S. Thus, in embodiments, the invention provides the following compounds of formula (I) : (a) (2,4,4-trimethylpentyl)(1,1,3,3-tetramethylbutyl) phosphinic acid; (b) (1,1,3, 3-tetratnethylbutyl) (2-ethylhexyl)phosphinic acid; (c) (2,4,4-trimethylpentyl (2-ethylhexyl)phosphinic acid; (d) (2,4,4-trimethylpentyi: (1-methyl-l-ethylpentyl) phosphinic acid; and (e) (1-methyl-l-ethylpentyl)(2-ethylhexyl)phosphinic acid; and their mono- and dithio- derivatives, and salts thereof. As described herein, compounds of formula (I) can be prepared for example by allowing a secondary phosphine of formula (II): to react with (i) an oxidizing agent, to produce the corresponding phosphinic acid; (ii) sulfur, to produce the corresponding dithiophosphini acid; or (iii) a limited amount of oxidizing agent, to produce the corresponding phosphine oxide, which is subsequently allowed to react with sulfur to produce the corresponding monothiophosphinic acid. In another aspect, the present invention provides a method for preparing a secondary phosphine of formula (II) wherein R1 and R2 are as def:.ned above and R2 is -CH2-CHR3R4, wherein the method comprises allowing a primary phosphine of formula R1PH2 to react with an olefin of formula CH2=CR3R4 under free radical conditions. In another aspect, the present invention provides a method for preparing a secondary phosphine of formula (II) wherein R1 and R2 are as defined above and R2 is -CR3 (CH2R5)R6, wherein the method comprises allowing a primary phosphine of formula R1PH2 to react in the presence of an acid catalyst with an olefin of formula HR5C=CR3R6. Some of the secondary phosphine compounds of formula (II) are novel. Thu3, in embodiments, the invention provides the following secondary phosphine compounds: (a) (2,4,4-trimethylpentyl (1,1, 3 , 3-tetramethylbutyl) phosphine; (b) (1, l,3,3-tetramethylbutyl) (2-ethylhexyl)phosphine; (c) (2,4,4-trimethylpentyl] (2-ethylhexyl)phosphine; (d) (2,4,4-trimethylpentyl)(1-methyl-l-ethylpentyl) phosphine; and (e) (l-methy-l-ethylpentyl)(2-ethylhexyl)phosphine. In another aspect, the present invention provides use of a compound of formula (I) or a salt thereof as a metal extractant. In another aspect, the invention provides a process for the extraction of a metal from a metal-bearing solution, comprising contacting said solution with a compound of formula (I), allowing the compound of formula (I) to form a complex with the metal, and recovering the complex. In embodiments, a compound of formula (I) in which X and Y are both 0, or a salt thereof, can be used to selectively extract cobalt(II) from an aqueous solution comprising cobalt(II) and rickel(II). DETAILED DESCRIPTION: Values for R1 and R2 are chosen to yield compounds of formula (I) that have low melting points. For many applications, the compound of formula (I) is used in its liquid state. Accordingly, compounds of formula (I) that are liquid at room temperature (e.g. over a temperature range of between about 15°C to about 25°C, more particularly at a temperature of about 16°C, about 20°C and about 25°C) are generally suitable for applications that are carried out at or near room temperature whereas compounds of formula (I) that melt at low temperature (for example at temperatures less than about. 30°C, about 40°C, about 50°C, about 60°C, about 80°C, about 100°C, about 150°C) are generally suitable for applications that are carried out at slightly elevated temperatures (i.e. above the melting point of the compound of formula (I)). Hence, values for R1 and R2 are chosen such that R1 and R2 are different, as the resulting asymmetry tends tc decrease the melting point of the compound. Branching is another determinant of melting point. Specifically, the melting point tends to decrease as the degree of branching of R1 and R2 increases. By definition, each of R1 and R2 is independently branched at the alpha or beta carbon, but additional branching can occur at the alpha or omega carbon or at any intermediate point. Branching at the alpha carbon and/or beta carbon may improve the ability of an organophosphinic acid to bind cobalt selectively over nickel and/or calcium, by increasing steric hindrance around the central phosphorous atom and thus favouring coordination of the phosphinic acid with cobalt(II). The presence of one or more chiral centres in R1 and R2 tends to decrease the melting point, by providing a mixture of stereoisomers. The melting point tends to increase as the number of carbon atoms in the compound increases, so R1 and R2 are typically chosen such that the compound of formula (I) contains no more than about 20 carbon atoms. However, for some purposes (such as metal extraction from aqueous solutions), compounds of formula (I) that are hydrophobic or "water immiscible" are desired. The term "water immiscible" is intended to describe compounds that form a two phase system when mixed with water, but does not exclude compounds that dissolve in water nor compounds that dissolve water, provided that the two phase system forms. For these purposes, compounds of formula (I) that have a total of about 12 carbon atoms or more can be useful. For many applications (such as metal extraction applications), R1 and R2 are chosen to yield compounds that are miscible (preferably in all proportions) with an organic solvent used in the particular application. The miscibility of compounds of formula (I) in the specified organic solvent can readily be determined (e.g. by eye), without the exercise of inventive skill. R1 and R2 can contain heteroatoms (e.g. the carbon backbone can be interrupted by one or more atoms selected from N, 0, and S) or bear additional substituents (such as hydroxyl, halo, alkoxy, alkylthio, carboxy, and acetyl groups), provided that the substituents or heteroatoms do not interfere with the preparation or utility of the compounds of the invention, as can readily be determined by routine experimentation requiring no inventive skill. However, the presence of heteroatoms and additional substituents are likely to increase costs. Therefore, for many purposes, R1 and R2 will not contain heteroatoms or bear additional substituents. Thus, for many purposes, each of R1 and R2 is independently an alkyl group or cycloalkyl group made up of hydrogen and carbon atoms only, such as: a C5-C16 alkyl group, i.e. an alkyl group that has a total of between 5 and 16 carbon atoms (i.e. 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16 carbon atoms) and often between 6 to 10 carbon atoms; or a C5-C16 cycloalkyl group, e.g. a five- or six-membered ring substituted with at least one alkyl group (i.e. R3 and optionally one or more additional alkyl groups), such that said cycloalkyl group has a total of between 6 and 16 carbon atoms (i.e. 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16) and often between 6 to 10 carbon atoms. Herein, the term "alkyl" includes straight and branched chain alkyl radicals. R3, R4, R5 and R6 are chosen to provide the desired values for R1 and R2. For example, when R1 is a C5-C16 alkyl of formula -CR3 (CH2R5) R6 and R3 and R5 are both methyl, then R6 is C1-C12 alkyl. R4, R5 and R6 may be branched. Thus, suitable values for R1 and R2 include: 2,4,4- trimethylpentyl; 1,1,3,3-tetramethylbutyl; 2-ethylhexyl; and 1-methyl-1-ethylpentyl. (I) METHODS FOR PREPARING COMPOUNDS OF FORMULA (I): Compounds of formula (I) can be prepared using known chemical reactions. Far example, a secondary phosphine of formula (II) wherein R1 and R2 are as defined above, can be prepared by adding a primary phosphine to an olefin either by way of acid-catalysed addition or under free radical conditions. Then, the secondary phosphine can be reacted with: (i) an oxidizing agent, to produce phosphinic acid; (ii) sulfur, to produce dithiophosphinic acid; or (iii) a limited amount of oxidizing agent, to produce a phosphine oxide that can subsequently be allowed to react with sulfur to prepare monothiophosphinic acid. Free radical conditions are useful for preparing a secondary phosphine that has an R group substituted at the beta carbon atom, because free radical conditions favour addition of phosphine to a primary carbon atom, such as the terminal carbon atom of a 1-alkene. Acid catalysis is useful for preparing a secondary phosphine that has an R group substituted at the alpha carbon, because acid catalysis favours addition of the phosphine to a tertiary carbon. (A) PREPARATION OF SECONDARY PHOSPHINES UNDER FREE RADICAL CONDITIONS Methods for adding phosphines to olefins under free radical conditions are known. For example, U.S. Patent Number 4,374,780 describes a method for making bis (2,4,4- trimethylpentyDphosphinic acid by free radical addition of two moles of 2,4,4-trimethylpentene-l to phosphine followed by oxidation with hydrogen peroxide. Thus, a method for preparing a secondary phosphine of formula (II): wherein R1 and R2 are as defined above and R2 is -CH2-CHR3R4, comprises, for example, allowing ci primary phosphine of formula R1PH2 to react with an olefin of formula CH2=CR3R4 under free radical conditions. Free radical initiators are known in the art and the skilled person will be able to select a suitable free radical initiator for use in the above-described reaction. Mention is made of azobis free radical initiators, such as azobisisobutylnitrile. The phosphine addition reaction is not particularly temperature limited and will take place over a wide range of temperatures Consequently, a temperature range for carrying out the reaction is generally chosen based on the half life of t.he initiator employed. For example, for azobisisobutylnitrile, the reaction can be carried out at temperatures ranging from about 40° to about 110°C, preferably about 60° to about 90° C. To reduce the production of unwanted tertiary phosphines, the reaction should be carried out with a molar excess of primary phosphine. For example, (2,4,4-trimethylpentyl)(2-ethylhexyl) phosphine can be prepared by addition of: (a) (2,4,4-trimethylpentyl)phosphine to 2-ethylhex-l-ene or (b) 2-ethylhexylphosphine to (2,4,4-trimethyl)pentene-l under free radical conditions as described above. (B) PREPARATION OF SECONDARY PHOSPHINES BY ACID-CATALYZED ADDITION Methods for adding phosphines to olefins via acid catalyzed addition have been known for some time (see for example U.S. Patent Number 2584112). For example, U.S. Patent Number 5,925,784 describes a method of making bis(l,1,3,3-tetramethylbutyl)phosphinic acid by acid- catalyzed addition of phospiine to diisobutylene, followed by oxidation with hydrogen peroxide. Thus, a method for preparing a secondary phosphine of formula (II) : wherein R1 and R2 are as defined above and R2 is -CR3 (CH2R5)R6, comprises, for example, allowing a primary phosphine of formula R1PH2 to react in the presence of an acid catalyst with an olefin of formula HR5C=CR3R6. The acid catalysed addition step can be conveniently carried out in the presence of a protonatable organic solvent (i.e. an organic solvent that contains a hydroxy (OH) group), such as a glycol or glycol ether. Examples of suitable glycol or glycol ethers for this purpose include: ethylene glycol, glycerine, and glyme. The acid catalyst can be any strong non-oxidizing acid. Alkylsulfonic acids (including but not limited to methanesulfonic acid and toluenesulfonic acid) are preferred due to their availability, low cosr and compatibility with most stainless steels (which are commonly used to make industrial reactors). However, other strong non-oxidizing acids such as HCl and H3PO4 may be used in the method of the invention, although HCl will require that the reaction be carried out in a halide resistant reactor. The molar ratio of acid catalyst to primary phosphine is about 1:1 to about 5:1, preferably about 1.5:1.0. A molar excess of acid catalyst may improve yield, but increases the cost of the process. In general, the acid-catalyzed addition step can be carried out by adding the acid catalyst to a vessel containing the primary phosphine and the olefin under an inert atmosphere (such as nitrogen) at atmospheric pressure and elevated temperature (e.g. about 50° to about 160°C, preferably about 75° to about 125°C), and allowing the reaction to proceed for between about 2 to about 88 hours (preferably between about 8 to about 2 0 hours). Elevated temperatures may improve yield and reduce reaction time. The reaction product(s) can be analyzed using standard methods, e.g. gas chromatography (GC) and/or nuclear magnetic resonance (NMR) analysis. The presence of ar excess of olefin may improve yield in the phosphine addition step but can lead to olefin dimers and trimers. The alkylphosphine may be present in excess, but the excess alkylphosphine should typically be removed prior to oxidation. Therefore, in most cases, the reaction will comprise olefin and the primary phosphine in a molar ratio ranging from abcut 0.5:1 to about 3:1, preferably about 1.5:1.0. Upon completion of the acid catalysed addition step, the reaction mixture can be worked up (e.g. by washing with aqueous base, recoverirg the organic phase, and removing any unreacted starting materials and solvent under vacuum at elevated temperature (e.g. about 80°C)), to provide a crude secondary phosphine preparation that can be used directly in the oxidation step, without further purification. The olefin can be a single species or a mixture of two related olefin species, each having a tertiary carbon double-bonded to a neighbouring carbon atom. For example, diisobutylene is ordinarily available commercially as a mixture of (2,4,4-trimethyl)pentene-l and (2,4,4-trimethyl) pentene-2. In the presence: of an acid catalyst, a primary phosphine can add to both of these species of olefin at their beta carbon, which is; tertiary. For example: (a) (2,4,4-trimethylpenty])(1,1,3,3-tetramethyl)phosphine can be prepared by allowing (2,4,4-trimethylpentyl) phosphine to react with diisobutylene in the presence of an acid catalyst; (b) (1,1,3,3-tetramethylbutyl)(2-ethylhexyl)phosphine can be prepared by allowing 2-ethylhexylphosphine to react with diisobutylene in the presence of an acid catalyst; (c) (2,4,4-trimethylpenty])(1-methyl-1-ethylpentyl) phosphine can be prepared by allowing (2,4,4-trimethyl- pentyl ) phosphine to react with 2-ethylhexene-l in the presence of an acid cetalyst; and (d) (1-methyl-l-ethylpentyl)(2-ethylhexyl)phosphine can be prepared by allowing 2-ethylhexylphosphine to react with 2-ethylhexene-l in the presence of an acid catalyst. (C) OXIDATION OF A SECONDARY PHOSPHINE The secondary phcsphines described above can be oxidized to prepare the corresponding phosphinic acids. At a molecular level, the oxidation of the secondary phosphine occurs in two steps. First, the secondary phosphine is oxidized to phosphine oxide, which is then oxidized to form the phosphinic acid. In practice, complete oxidation of the secondary phosphine can be accomplished in a single reaction. The secondary phosphine can be oxidized, for example;, by allowing it to react with an oxidizing agent (preferably hydrogen peroxide) in the presence of an acid catalyst: (e.g. sulfuric acid) and water, at atmospheric pressure and elevated temperature (e.g. about 50°C to about 110°C, preferably about 80°C to about 100°C) for about 4 to about 16 hours or until complete. Lower temperatures slow the reaction, resulting in longer reaction times. However, higher temperatures tend to remove one alkyl group, resulting in the formation of some monoalkylphosphonic ac:.d side product. The course of the reaction can be followed for example by 31P NMR. Suitable oxidizing agents include hydrogen peroxide, which is an inexpensive and convenient oxidizing agent. The stoichiometry of the oxidation reaction dictates that two equivalents of hydrogen peroxide react with one equivalent of phosphine in this reaction. However, the presence of an excess of hydrogen peroxide can improve yield (i.e. pushing the oxidation reaction towards completion) at little extra cost. So in many cases, hydrogen peroxide will be present in excess of the secondary phosphine, say in a ratio of equivalents ranging from between about 2:1 to about 4:1, preferably about 3:1. Upon completion oi: the reaction, the reaction mixture can be worked up (e.g. by washing with aqueous base (e.g. sodium hydroxide) then aqueous acid (e.g. sulfuric acid), then drying under vacuum at elevated temperature (e.g. about 80°C)), to afford a liquid product that contains the desired phosphinic acid product. The foregoing method generally affords a liquid end product that contains the desired phosphinic acid, as well as certain side products. When the process is carried out under suitable conditions, the desired phosphinic acid product can be the major component (e.g. 80-95% or more by weight) of the liquid end product. The liquid end product of the prescribed method i can be used in metal extract ion processes without further purification, as most of the; side products are not expected to interfere with the metal extraction process. However, the oxidation step can result in the production of phosphonic acid side products (i.e. R1PO(OH)2 and R2PO(OH)2), which may for example reduce; the selectivity of the end product for cobalt over calcium and nickel. If desired, reaction conditions (especially temperature, as noted above) can be chosen to minimize the production of phosphonic acid side products. If desired, the liquid end product can be i washed with one or more alkaline water washes to reduce the level of monophosphonic acids to an acceptable level, e.g. about 1% or less. (D) REACTION OF SECONDARY PHOSPHINES OR PHOSPHINE OXIDES WITH SULFUR The secondary pho3phines described above can also be used as intermediates to prepare the corresponding monothiophosphinic acids and dithiophosphinic acids. Dithiophosphinic acids can be prepared, for example, by allowing a secondary phosphine to react with sulfur, in accordance with known methods (e.g. as described in US Patent Number 5925784 or GB902802). Secondary phosphines just defined can be reacted with sulfur, water, and a base reagent, such as ammonium hydroxide, to produce the salt of the corresponding secondary dithiophosphinic acid, such as the ammonium salt thereof. Reactions of this type are generally carried out at temperatures in the range of about 0°C to about 100°C, preferably about 15°C to about 75°C. The salt thus prepared can be reacted with an acid, such as HC1, dilute sulfuric acid, or methane sulfonic acid to produce the secondary dithiophosphinic acid. These reactions generally are made to take place at temperatures in the range of about -30°C to about 75°C, preferably about 10°C to about 50°C. Monothiophosphinic acids can be prepared, for example, by: (i) allowing a secondary phosphine to react with a limiting amount of an oxidizing agent, to produce a secondary phosphine oxide; and (ii) allowing the secondary phosphine oxide to react with sulfur to produce a monothiophosphinic acid. A suitable method for preparing monothiophosphinic acids is described in for example US Patent Number 4555368. Briefly, the secondary phosphine can be oxidized to form the corresponding diorganophosphine oxide, without forming significant amounts of the corresponding diorganophosphinic acid. To achieve this, the oxidation reaction can be performed by gradual or incremental addition of the oxidizing agent at a rate wnich provides a controlled temperature of from about 40°C to about 60°, and preferably from about 50°C to about 55°C. The amount of oxidizing agent added should be sufficient to oxidize substantially all of the secondary phosphlne and generally an equimolar amount of oxidizing agent is used. The time of addition may vary depending on the start Lng amounts of secondary phosphine used. Generally, oxidation under controlled temperature conditions can be completed with gradual or incremental addition of the oxidizing agent over a period of from about 1 to about 3 hours. The selection of a particular oxidizing agent is not critical, so long as it is effective to oxidize the secondary phosphine to the secondary phosphine oxide. Hydrogen peroxide is the preferred oxidizing agent for use herein, because it is inexpensive, readily available, and the temperature and rate of the oxidation reaction are easily controlled with its use. After substantially all of the secondary phosphine has been converted to the corresponding secondary phosphine oxide, the resulting secondary phosphine can be heated to an elevated temperature of between about 60°C to about 90°C, and preferably from about 6E°C to about 75°C, and an excess of sulfur and excess of an hydroxide compound added to convert the secondary phosph.ine oxide to the corresponding monothiophosphinate compound. The sulfurization reaction in the presence of base can be conducted at temperatures of between about 60°C to about 90°C, and allowed to proceed substantially to completion. Generally, the reaction can be completed within a period of from about 1 to about 5 hours at temperatures of 60°C to 90°C. The resulting moncthiophosphinic acid can undergo tautomerization, interconverting between the following tautomers; (II) UTILITY OP COMPOUNDS OF FORMULA I It is known in the art that organic phosphinic acids can be used for metal extraction, notably cobalt (II) extraction (see for example U.S. Patent Numbers 4373780; 4353883; 4348367; and 5925784). Organic phosphinic acids are also known to be useful for extraction of other metals, such as rare earth metals, actinides, and platinum group metals. Organic mono- and dithio-phosphinic acids have also been found to be useful as metal extractants (see for example U.S. Patent Numbers 5028403 and 4721605) . The acidity of these phosphorus-containing acids increases with increasing sulfur content, which tends to increase the ability of the acid to extract metals from solutions having low pH but also tends to ir.crease the difficulty of subsequently stripping the metal therefrom. Thus, it can be appreciated that compounds of formula (I) may be used as metal extractants (e.g. for the recovery of a variety of metals from aqueous solutions containing such metals alor.e or in combination with other less desirable metals). In. embodiments, compounds of formula (I) may be used in cobalt extraction processes. Bis(2,4,4-trimethylpentyl)-phosphinic acid (disclosed in U.S. Patent number 4374780 and marketed by Cytec Industries, Inc. under the name CYANEX 272 is widely used for separating cobalt and/or nickel from either sulfate or low chloride media. CYANEX 272 can bind cobalt selectively, while simultar.eously rejecting calcium, magnesium, and nickel, which are often present in aqueous cobalt (II)-bearing solutions. CYANEX 272 is also used for the separation of heavy rare earth metals and the selective separation of iron and zinc from cobalt solutions. However, CYANEX 272 has certain limitations and drawbacks. In particular, CYANEX 272 becomes increasingly viscous and difficult to work with when it is loaded with cobalt, and as a result, it is usually leaded to only 70-75% of its maximum theoretical capacity in industrial processes. In the examples described herein, (2,4,4-trimethylpentyl){1,3,3,3-tetramethylbutyl)phosphinic acid (which is a compound cf formula (I) exemplified herein) has been observed to have a cobalt loading capacity comparable to that of CYANEX 272, but unlike CYANEX 272, without becoming overly viscous even at maximum cobalt loading. Therefore, in embodiments, (2,4,4- trimethylpentyl)(1,1,3,3 tetramethylbutyl) phosphinic acid allows for cobalt loading of up to 100% of the theoretical capacity in industrial processes, an improvement over CYANEX 272 on the order of 25-30%, without encountering viscosity problems. An improved practical cobalt loading capacity and/or reduction in viscosity problems (as has been observed with (2,4,4-trimethylpentyl)il,1,3,3- tetramethylbutyl)phosphinic acid in the examples described herein) may improve the overall efficiency and productivity in certain applications, such as commercial cobalt (II) extraction processes. In the examples described herein, (2,4,4- trimethylpentyl) (1,1,3,3-tetramethylbutyl)phosphinic acid has also been observed to be better than CYANEX 272 at rejecting calcium. In commercial cobalt extraction processes, cobalt is typically recovered by stripping it from an organic phase with sulfuric acid. Co-extraction of calcium is undesirable because it may lead to the formation of gypsum at the interface of :he organic phase and water phase during the step of stripping cobalt from the organic phase, and so may interfere with and decrease the productivity of the stripping step. Thus, in embodiments, an improved calcium rejection (as has been observed with (2,4,4 -trimethyl-pentyl) (1,1,3,3 -1etramethylbutyl) phosphinic acid in the examples described herein) may reduce the amount of calcium that is co-extracted in cobalt extraction processes, which may improve the productivity and efficiency of the cobalt stripping step. Further, in the examples described herein, (2,4,4 -trimethylpentyl) (1,1,3,3 -tetramethylbutyl)phosphinic acid has been observed to be more selective for cobalt over nickel than CYANEX 272. U.S. Patent Number 5925784 discloses bis(1,1,3,3- tetramethylbutyl)phosphinic acid and teaches that this compound has utility as an agent for separating cobalt and/or nickel. However, certain properties of bis (1,1,3,3- tetramethylbutyl)phosphinic acid limit its industrial utility; for example it is a solid at room temperature and has limited solubility in the aromatic and aliphatic solvents commonly used in ths industry for cobalt extraction processes. In contrast, in accordance with the present invention, values of R1 and R7 can be chosen to provide compounds of formula (I) that are liquids at room temperature and/or miscible (preferably in all proportions) with the aromatic and aliphatic solvents used in cobalt extraction. The compounds of formula (I) can be used for cobalt extraction in accordance with known methods (for example, as described in U.S. Patent Numbers 5925784, 4353883, and 4348367). For example, (2,4,4-trimethyl- pentyl)(1,1,3,3-tetramethylbutyl) phosphinic acid can be directly substituted for CYANEX 272, although it may be necessary to modify the process somewhat to accommodate for differences between the chemical and physical properties of these compounds. One skilled in the art can adapt such known methods to incorporat.e the use of compounds of formula (I) using routine experimentation, without the exercise of inventive skill. All publications and patent applications cited in this specification are herein incorporated by reference as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. EXAMPLES: EXAMPLE 1; SYNTHESIS OF (2,4,4-TRIMETHYLPENTYL) (1,1,3,3- TETRAMETHYLBUTYL)PHOSPHINIC ACID The end product of this second synthesis of (2,4,4-trimethylpentyl) (1,1,3,3-tetramethylbutyl)phosphinic acid is referred to hereafter as "Batch 1". (I) Synthesis of (2, 4, 4-trirtethylpentyl) (1,1, 3, 3-tetra- methylbutyl)phosphine: 2,4,4-tritnethylper.tylphosphine (302.7 g, 99% GC, 2.07 mol, 1.0 eq.), diisobutylene (a mixture of 2,4,4- trimethyl-pentene-1 and 2,4,4-trimethyl-pentene-2; 348.3 g, 3.11 mol, 1.5 eq.) and diethyleneglycol (295 g, weight ratio -0.97) were added into a three neck flask under nitrogen. The mixture was heated to 80°C at which time methanesulfonic acid (298.9 g, 3.11 mol, 1.5 eq.) was slowly dripped into the flask through an addition funnel over 50 minutes. The mixture was further heated to reflux at 120°C and digested overnight (16 hrs.). The reaction mixture was cooled and toluene (300 ml) was added followed by slow addition of an aqueous solution of NaOH (125 g in 500 g water, 3.11 mol, 1.5 eq.) such that the temperature of the reaction remained below 60°C. After vigorous mixing the contents were transferred to a separatory funnel to allow a clear phase separation. The organic phase was then collected and the solvent and un-reacted starting materials were stripped off under vacuum at 80°C. The resulting product (452 g, 85% yield) was a clear colourless liquid and was analyzed by 31P NMR and GC. Results: 31P NMF.: 5 -23.54 (doublet); and GC/MS: retention time (m/e) 12.70 min (258). (II) Synthesis of (2,4, 4-tr:.methylpentyl) (1,1, 3,3-tetra methylbutyl)phosphinic acid. Water (500 g, 1.0 weight ratio relative to volume of dialkylphosphine) was added to a three-necked round bottom flask with a catalytic amount of sulfuric acid (5 g, 1% relative to weight of water). The flask was blanketed with nitrogen and fitted with a mechanical stirring device. The (2,4,4-trimethylpentyl) (1,1,3,3-tetramethylbutyl) phosphine (443 g, 1.7 mol, 1.0 eq.; from step (I) above) was added to the reaction vessel to form a biphasic system, in which the top layer is the organic phase. The reaction mixture was then heated to 50°C under stirring and nitrogen. The heat source was removed and an aqueous solution of ~25% hydrogen peroxide (700 g, 5.2 mol, 3.0 eq.) was slowly dripped into the reaction mixture ensuring that a slow and steady increase in temperature occurred while avoiding large and sudden temperature changes. After one equivalent of H2O2 was added (~50 min), the external heat source was applied to provide a reaction temperature of > 95°C before the second equivalent of H2O2 was added, in like fashion (-45 min) . At this point the excess H2O2 was added to ensure complete oxidation of starting material. The reaction mixture was digested at > 95°C overnight (16 hrs.) at which time a sample was extracted for 31P NMR analysis, to determine the completion of the reaction. Results: 31P NMR peak: 8 63.53. Upon completion of the reaction, toluene (~ 200ml) was added to the mixture to reduce the viscosity of the organic layer. The organic phase was then washed with an equal volume of water. The organic phase was then washed further with an aqueous solution of NaOH (100 g in 1L of water) to achieve a pH ~ 7-8. The aqueous layer was removed and the phosphinic acid was restored with an acidic wash (H2SO4 in water, lOg/L). The desired product was then stripped of water and dried under vacuum at 80°C to afford a clear colourless liquid (40fi g, 82% yield) . Example 2: SYNTHESIS OF (2,4,4-TRIMETHYLPENTYL) (1,1,3,3- TETRAMETHYLBUTYL)PHOSPHINIC ACID The end product of this second synthesis of (2,4,4-trimethylpentyl) (1,1,3,3-tetramethylbutyl) phosphinic acid is referred to hereafter as "Batch 2". (I) Synthesis of (2,4,4-triitethylpentyl) (1,1,3,3-tetra methylbutyl)phosphine: 2,4,4-trimethylpentylphosphine (412.4 g, 2.82 mol, 1.0 eq.), diisobutylene (a mixture of 2,4,4-trimethyl- pentene-1 and 2,4,4-trimethyl-pentene-2; 474.3 g, 4.23 mol, 1.5 eq.) and diethyleneglycol (413.3 g, weight ratio -1.00) were added into a three neck flask under nitrogen. The mixture was heated to 80°C a; which time methanesulfonic acid (4 07.6 g, 4.24 mol, 1.5 eq.) was slowly dripped into the flask through an addition funnel over 50 minutes. The mixture was further heated to reflux at 113°C overnight (16 hrs.). The reaction mixture was cooled down and toluene (400 ml) was added followed by slow addition of an aqueous solution of NaOH (174.8 g in 500g water, 4.37 mol, 1.5 eq.) such that the temperature of the reaction remained below 60°C. After vigorous mixing the contents were transferred to a separatory funnel with an additional 500 ml water and 300 ml toluene. Clear phase separation was observed and the aqueous layer was removed, followed by an additional wash of the organic layer with 1 L of water. The organic phase was then collected and the solvent and unreacted starting materials were stripped off under vacuum at 80°C. The resulting product (562.1 g, 77% yield) was a clear colourless liquid and was analyzed by 31P NMR and GC. Results: 31P NMR: 8 -24.76 (doublet); and GC/MS: retention time (m/e) 14.98 min (258). (II) Synthesis of (2 , 4 , 4-trinethylpentyl) (1,1, 3, 3-tetra methylbuty)phosphinic acid: Water (578 g, -1.0 weight ratio relative to volume of dialkylphosphine) was added to a three-necked round bottom flask with a catalytic amount: of sulfuric acid (5.8 g, 1% relative to weight of water). The flask was blanketed with nitrogen and fitted with a mechanical stirring device. The (2,4,4-trimethylpentyl) (1,1,3,3-tetramethylbutyl) phosphine (556.9 g, 2.16 mol, 1.0 eq.; from step (I) above) was added to the reaction vessel to form a biphasic system, in which the top layer is the organic phase. The reaction mixture was then heated to 50°C under stirring and nitrogen. The heat source was removed and an aqueous solution of -25% hydrogen peroxide (889.8 g, 6.54 mol, 3.0 eq.) was slowly dripped into the reaction mixture ensuring that a slow and steady increase in temperature occurred while avoiding large and sudden temperature changes. After one equivalent of H2O2 was added (~12 0 min), the external heat source was returned to ensure a reaction temperature of > 95°C before the second equivalent of H2O2 was added, in like fashion (~90 min). At this point the excess H2O2 was added to ensure complete oxidation of starting material. The reaction mixture was digested at > 95°C overnight (16 hrs.) at which time a sample was extracted for 31P NMR analysis, to determine the completion of the reaction. Results: 3:P NMR peak: 8 63.52. Upon completion cf the reaction, toluene (~ 500ml) was added to the mixture tc reduce the viscosity of the organic layer. The aqueous phase was removed and the organic was treated with an aqueous solution of NaOH (100 g in 1L of water) to achieve a pH - 7-8. The aqueous layer was removed and the phosphinic acid was restored with an acidic wash (H2SO4 in water, lOOg/L). The desired product was then stripped of water and dried under vacuum at 80°C to afford a clear colourless viscous liquid (551.7 g, 88% yield). A sample was taken for NMR analysis and methylated for analysis by GC/MS. Res alts: 31P NMR peak: 5 65.73; and GC/MS: retention time (m/e) 19.02 min (272). EXAMPLE 3 Two samples of the novel extractant, (2,4,4- trimethylpentyl) (1,1, 3, 3-tetramethylbutyl) phosphinic acid (Batch 1 and Batch 2) were chromatography/mass spectros;copy detector (GC/MSD) to fully characterize the active ingredient, as well as all other minor components and impurities. The acidic components were first converted to their respective methyl esters to allow for elution from the gas chromatograph column. 1. EXPERIMENTAL Two samples of (2,4,4-trimethylpentyl) (1,1,3,3-tetramethylbutyl) phosphinic acid (Batch 1 and Batch 2) were accurately weighed to the nearest 0.1 milligram and diluted with toluene to a final concentration of 20% by weight. A 500 /µL aliquot of the solution was allowed to react with an equal volume of methylating reagent (N,N-dimethylformamide dimethyl acetal) , and 0.2 µL of the resulting mixture was injected into the gas chromatograph. 2. RESULTS The results of GC/MSD analysis (area %) for each component of the 2 samples cf (2,4,4-trimethylpentyl) (1,1,3 , 3-tetramethylbutyl) phosphinic acid (Batch 1 and Batch 2) are shown in Table 1. 3. DISCUSSION The chromatographs for the two samples of (2,4,4- trimethylpentyl) (1,1, 3 , 3-tetramethylbutyl) phosphinic acid (Batch 1 and Batch 2) were similar in the composition of components and impurities present and slightly different in the terms of the quantities of components. Besides the major component ((2,4,4-trimethylpentyl) (1,1,3,3-tetramethylbutyl) phosphinic acid), the analysis indicated the presence of the corresponding impurities namely the dialkyl phosphinic acids, the monoalkyl phosphonic acids and the phcsphine oxides. The presence of the monoalkyl phosphonic acids must be minimized as they tend to reduce the cobalt/nickel selectivity of the extractant. EXAMPLE 4: Characterization of 2,4,4-trimethylpentyl (1,1,3,3-tetramethylbutyl)phosphinic acid The following test work involved studying the performance of the new extractant (2,4,4-trimethyl- pentyl) (1,1,3,3-tetramethylbutyl)phosphinic acid (TEST 1) and CYANEX 272. The experiments examined the extraction of single metals from sulfate solutions and their mutual selectivity as a function of pH, loading capacity of cobalt and viscosity of organic solutions as a function of cobalt loading. PART A - EXTRACTION FROM sINGLE METAL SULFATE SOLUTIONS AT VARYING pH A.1 EXPERIMENTAL The single metal aqueous solutions were prepared by dissolving a weighed amount of the respective sulfate salt and a weighed amount cf sodium sulfate salt in deionized water. The metal concentration in each solution was 0.001M, except Fe(III) which was 0.0015M. The sodium sulfate concentration was 0.5M for all solutions. The metals studied were Co(II), Ni(II), Ca(II), Mg(II), Mn(II), Zn(II), Pe(III), and Cu(II). The organic solutions were prepared by diluting (2,4,4-trimethylpentyl)(1,1,3,3-tetramethylbutyl)phosphinic acid or CYANEX 272 to 0. 1M o:: phosphinic acid with ISOPAR M diluent. ISOPAR M is an aliphatic (>99.5%) hydrocarbon diluent commercially available from Imperial Oil, Canada. Equilibrium distributions of the various metals between organic and aqueous phases as a function of pH were determined at 50°C by contacting equal volumes (300 mL) of the two phases in a jacketed beaker and mixed with mechanical stirring. The temperature of the solution during extraction was maintained at 50°C by a circulating bath. The pH was adjusted by adding a known volume of either sodium hydroxide or sulfuric acid to the aqueous phase. A contact time of 15 minutes was used between each pH adjustment. Samples of each phase were withdrawn (15 mL) and analysed. The equilibrium pH of the aqueous raffinate samples was measured using a ROSS combination pH electrode calibrated at room temperature with pH 1.00 (potassium chloride - hydrochloric acid buffer), 4.00 (potassium biphthlate buffer), and 7.00 (potassium phosphate monobasic - sodium hydroxide buffer) buffer solutions. For all experiments, the aqueous samples were analysed by Atomic Absorption Spectroscopy (AAS). The metal concentration in the organic phase for each sample was deduced by subtracting the raffinate concentration from the initial metal concentration in the feed solution. A.2 RESULTS Besides cobalt, nickel and calcium, other metals (i.e. zinc, iron, copper, magnesium and manganese) were also studied. There was however no significant difference between (2,4,4-trimethylpentyl)(1,1,3,3-tetramethylbutyl)phosphinic acid and CYANEX 272 for these metals and their numerical data are therefore not reported here. The numerical data for the extraction of cobalt, calcium and nickel as a function of pH using (2,4,4-trimethylpentyl)(1,1,3,3- tetramethylbutyl) phosphinic acid and CYANEX 272 are shown in Table 2. Table 3 shows the pH50 values for each metal using (2,4,4-trimethylpentyl) (1,1,3, 3-tetramethylbutyl) phosphinic acid ("TEST") and CYANEX 272 as well as the ApH50 (ApH50 = pH50Co - pH50metals) values, respectively. The pH50 values were determined using the log of the distribution ratio, log D, and plotting the values as a function of pH. The distribution coefficient, D, is defined as the ratio of the total metal content in the organic phase to the metal content in the aqueous phase. The results indicate selectivity for cobalt- nickel, cobalt-zinc, cobalt-Iron, and cobalt-calcium for (2,4,4-trimethylpentyl) (1,1, 3,3-tetramethylbutyl) phosphinic acid. Furthermore, (2, 4, 4-t:rimethylpentyl) (1,1,3,3-tetramethylbutyl) phosphinic acid shows a substantial increase in selectivity over CYANEX 272 for cobalt over both calcium and. nickel. This higher cobalt- calcium selectivity could have a great advantage in a solvent extraction plant by decreasing the formation of gypsum in the circuit. PART B - COBALT LOADING CAPACITY AND VISCOSITY B.1 EXPERIMENTAL FOR THE LOADING CAPACITY OF COBALT The aqueous solution was prepared by dissolving a weighed amount of cobalt sulfate salt in deionized water. The metal concentration in :he solution was 40 g/L. The organic solutions were prepared by diluting (2,4,4-tri- methylpentyl)(1,1,3,3-tetramethylbutyl)phosphinic acid extractant or CYANEX 272 to 0.14M of phosphinic acid with ISOPAR M diluent. ISOPAR M is an aliphatic (>99.5%) hydrocarbon diluent commercially available from Imperial Oil, Canada. Equilibrium distributions of cobalt between the organic and aqueous phases vas determined at 50°C by contacting an aqueous volume (250 mL) and an organic volume (50 mL) to give an aqueous to organic phase ratio of 5. The two phases were contacted in a jacketed beaker and mixed with mechanical stirring. The temperature of the solution during the extraction was maintained at 50°C by a circulating bath. The pH was adjusted by adding a known volume of sodium hydroxide to the aqueous phase. A constant pH of 6.13 ± 0.03 for a period of 15 minutes was necessary to ensure maximum loading of the metal. The phases were separated and the organic fiLtered through phase separating (P/S) paper to ensure that no entrained aqueous was present. The metal concentration in the organic was determined by stripping with 100 g/L H2SO4 using equal volumes of both phases (4 0 mL) for 5 minutes at room temperature. The strip liquor was collected in a sanple vial. An aliquot (35 mL) of the stripped organic was stripped a second time with an equal volume (35 mL) of fresh acid. This was repeated a third time using 30 mL of stripped organic and 30 mL of fresh acid. The three strip liquors were kept separate and analysed individually by ICP. The three strip liquor concentrations were summed to determine the amount of cobalt loaded. A total of three loading tests were completed (TEST 1, TEST 2, and TEST 3). The equilibrium pH of the aqueous samples was measured as previously described in section above. B.2 EXPERIMENTAL FOR THE VISCOSITY OF ORGANIC SOLUTIONS AS A FUNCTION OF COBALT LOADING The aqueous solution was prepared by dissolving a weighed amount of cobalt sulfate salt in deionized water. The metal concentration in the solution was 40 g/L. The organic solutions were prepared by diluting a weighed amount of either CYANEX 272 (200 grams, Lot# WE2060451) or (2 , 4, 4-trimet:iylpentyl) (1,1, 3 , 3-tetramethyl- buty)phosphinic acid extratant (200 grams, TEST 3) extractant to 20% (w/w) with ISOPAR M diluent. These solutions were split in two equal portions in order to prepare the different per cent cobalt loading. Equilibrium distributions of cobalt between the organic and aqueous phases were determined as previously described in the section above with the exceptions that the temperature was room temperature and the aqueous to organic phase ratio was of unity (500 mL volume for each phase). A constant pH of 5.90 ± 0.02, and pH of 6.05 ± 0.02 for CYANEX 272 and (2,4,4-trimethylpentyl) (1,1,3,3-tetramethyl- butyl) phosphinic acid extrectant (TEST 3), respectively, for a period of 15 minutes vas necessary to ensure maximum loading of the metal. Phases were separated and the organic was centrifuged for 30 minutes at 3000 rpm to ensure that no entrained aqueous or precipitate was present. Samples were next prepared by mixing 100% loaded and 0% loaded at various volumes such that viscosities of 0%, 10%, 30%, 45%, 60%, 75%, 90%, and 100% cobalt loading could be measured at varying temperatures. The samples were Tested using a TA Instruments' AR1000N rheometer. A step Flow method was used in 90 second intervals ranging 10 to 60°C. In most cases data points were collected at least eve:ry 10°C. Temperature control (+/- 0.l°C) was provided by a Peltier plate. The geometry consisted of a 60 mm cone and plate with a 2° angle. All samples were found to be Newtonian, i.e., their viscosities are independent of the shear rate. Thus tests with varying temperatures reported were all done at the same shear rate (500/s). B. 3 RESULTS The calculated cobalt concentration in the organic phase was determined for three samples of (2,4,4-trimethyl- pentyl) (1,1,3,3-tetramethylbutyDphosphinic acid (TEST 1, TEST 2,and TEST 3) and CYANEX 272 and is shown in Table 4. The results indicate a slight difference in the loading capacity of the two extractants with CYANEX 272 having a slightly higher maximum cobalt loading capacity than (2,4,4-trimethylpentyl)(1,1,3,3-tetramethylbutyl) phosphinic acid. The following two tables (5 and 6) show the viscosity of both (2, 4, 4-trimethylpentyl) (1,1, 3, 3-tetr- methylbutyl) phosphinic acid and CYANEX 272. Results indicate that the viscosity does not change much with varying cobalt solution loadings for (2,4,4-trimethylpentyl) (1,1,3,3-tetramethylbutyl) phosphinic acid. On the other hand, there is a large increase in viscosity between 75, 90, and 100% cobalt solution loading for the CYANEX 272 samples. On a practical basis, this means that 100% cobalt loading can be achieved with (2,4,4-trimethylpentyl)(1,1,3,3-tetra- methylbutyl) phosphinic acid whereas CYANEX 272 is limited to 70-75% cobalt loading to limit the viscosity issues. l i i i i i—i—i—r~~i—i jp r~ r» n f» «o -y I I i 1 1 1 1 A • • CD vo •* 3 o 2? °\ m ' ■ ■ 3 * N ■* oonoo "S-'SESSS g ° * ° ° * ° trt 5 H oo 10 • 2 — „ •o § — ° S g 5 Si 5 S 5 3 2 Sffl S S^2«;SS rt "13 ^ «g _ U JO H CN oovonin pi H B, "> • ^ "\ 3 »" ^ IT) mCNMrH d-1 Si ® ® " H. "! ^ H. ^ u -. ^o • di onH^Hp-ooooiN •yM ™ ■^ ■rjo-Hr-vor-omt^HoD «g ffjpKininmof-inr- 10 -0«>4J a.J5 .Sg5'mr»ooHinr;Hr- g 5_g fl* ^nr'o,H Z > " 2±j H — S 3 Anirt0'ONO** 5 O« 'J-H StnOi.o^ovit^i-ir- « _« .; __g 3 «i * n n " H off S O # g ''vDinMifontNH 2 — i;-^ •H -r I ^ „ ui n n IN M 5 S^J.^^^^^ ret u) — ° ^rin^HH -8 * °) °^ ^ "J • n. °t "I H U1^i««)HH 1 f CJouiowooo© '^ er-trHfNCNn"!CinU3 §'00100100000 [H'~' SorHHr>10ln^l'OVD I II I 11 II I H w CLAIMS: 1. A compound defined by formula (I): wherein: R1 and R2 are different and each of R1 and R2 is independently selected from: (a) -CH2-CHR3R4, where R3 is methyl or ethyl; and R4 is an optionally substituted alkyl or heteroalkyl; and (b) -CR3(CH2R5)R6, where R3 is methyl or etayl; and R5 is H or an optionally substituted alkyl or heteroalkyl, and R6 is an optionally substituted alkyl or heteroalkyl; or R5, R6 and the ethylene group to which they are bonded form a five or six-membered optionally substituted cycloalkyl or heterocycloalkyl ring; and each of X and Y is independently 0 or S. 2. The compound of claim 1, wherein R1 and R2 contain carbon atoms and hydrogen atoms only. 3. The compound of claim 2 which contains a total of between 12 and 2 0 carbon atoms. 4. The compound of claim 2 or 3, wherein each of R1 and R2 is independently C5-C16 alkyl or C5-C16 cycloalkyl. 5. The compound of claim 2, wherein each of R1 and R2 is independently C6-C16 alkyl. 6. The compound of claim 2, wherein each of R1 and R2 is independently C8 alkyl. 7. The compound of claim 2, wherein each of R1 and R2 is independently selected from 2,4,4-trimethylpentyl; 1,1,3,3-tetramethyl-butyl; 2-ethylhexyl; and 1-methyl-l- ethylpentyl. 8. The compound of any one of claims 1 to 7, wherein X and Y are both 0. 9. The compound of any one of claims 1 to 7, wherein one of X and Y is 0 and the other is S. 10. The compound of any one of claims 1 to 7, wherein X and Y are both S. 11. The compound (2,4,4-trimethylpentyl) (1,1,3,3- tetramethylbutyl) phosphinic acid: 12. The compound (1,1,3,3-tetramethylbutyl)(2-ethyl- hexyl)phosphinic acid. 13. The compound (2,4,4-trimethylpentyl)(2-ethylhexyl) phosphinic acid. 14. The compound (2,4,4-trimethylpentyl)(1-methyl-l- ethylpentyl)phosphinic acid. 15. The compound (1-methyl-1-ethylpentyl)(2-ethyl- hexyl)phosphinic acid. 16. The compound (2,4,4-trimethylpentyl)(1,1,3,3- tetramethylbutyl)dithiophosphinic acid. 17. The compound (2,4,4-trimethylpentyl)(1,1,3,3- tetramethylbutyl)monothiophosphinic acid. 18. The compound (1,1 3,3-tetramethylbutyl)(2-ethyl- hexyl) dithiophosphinic acid 19. The compound (1,1 3,3-tetramethylbutyl)(2-ethyl- hexyl )monothiophosphinic acid. 20. The compound (2,4,4-trimethylpentyl)(2-ethyl- hexyl )dithiophosphinic acid. 21. The compound (2,4,4-trimethylpentyl)(2-ethyl- hexyl )monothiophosphinic acid. 22. The compound (2,4,4-trimethylpentyl)(1-methyl-l- ethylpentyl)dithiophosphinic acid. 23. The compound (2,4,4-trimethylpentyl)(1-methyl-l- ethylpentyl)monothiophosphinic acid. 24. The compound (1-methyl-1-ethylpentyl)(2-ethyl- hexyl ) dithiophosphinic acid. 25. The compound (1-methyl-1-ethylpentyl)(2-ethyl- hexyl) monothiophosphinic ac:id. 26. A method for preparing a. secondary phosphine of formula (II): wherein R1 and R2 are as defined in claim 1 and R2 is -CH2-CHR3R4, wherein the method comprises allowing a primary phosphine of formula R1pH2 to react with an olefin of formula CH2=CR3R4 under free radical conditions. 27. A method for preparing a secondary phosphine of formula (II) : wherein R1 and R2 are as defined in claim 1 and R2 is -CR3(CH2R5)R6, wherein the method comprises allowing a primary phosphine of formula R1 PH2 to react in the presence of an acid catalyst with an olefin of formula HR5C=CR3R6. 28. The method of claim 27, wherein ethylene glycol is used as a solvent for carrying out the reaction. 29. The method of claim 27 or 28, wherein the acid catalyst is methanesulfonic acid. 30. The method of any one of claims 27 to 29 wherein the primary phosphine is (2,4,4-trimethylpentyl)phosphine, and the olefin is diisobutylene. 31. A method for preparing a formula (I) as defined in claim 1, the method comprising: (a) preparing a secondary phosphine according to the method of claim 26 or 27; and (b) allowing the secondary pnosphine to react with (i) an oxidizing agent, to produce the corresponding phosphinic acid; (ii) sulfur, to produce the corresponding dithiophosphinic acid; or (iii) a limited amount of oxidizing agent, to produce the corresponding phosphine oxide, which is subsequently allowed to react with sulfur to produce the corresponding monothiophosphanic acid. 32. The method of claim 31, wherein the secondary phosphine is (2,4,4-trimethy3pentyl)(1,1,3,3-tetramethyl- butyl)phosphine prepared according to the method of claim 18. 33. The method of claim 31 or 32, wherein the compound of formula (I) is a phosphinic acid and the oxidizing agent is hydrogen peroxide. 34. Use of a compound of any one of claims 1 to 25 or a salt thereof as a metal extractant, 35. Use of a compound of any one of claims 1 to 15 or a salt thereof as a metal extractant, wherein X and Y are both 0 and the metal is cobal':. 36. The compound (2,4,4-trimethylpentyl) (1,1,3,3- tetramethylbutyl)phosphine. 37. The compound (1,1,3,3-tetramethylbutyl)(2-ethyl- hexyl) phosphine. 38. The compound (2,4,4-trimethylpentyl)(2-ethylhexyl) phosphine. 39. The compound (2, ethylpentyl)phosphine. The present invention provides phosphinic acids and their sulfur derivatives, in accordance with the following formula (I): wherein R and R are different and each of R and R is independently selected from an organic radical that branches at the alpha carbon and an organic radical that branches at the beta carbon, and each of X and Y is independently 0 or S, and wherein said compound is a liquid at room temperature. Compounds of formula (I) find utility for example as metal extractants. Also provided are methods for making compounds of formula (I) and their corresponding phosphine intermediates.

Full Text

NOVEL PHOSPHINIC ACIDS AND THEIR SULFUR DERIVATIVES AND
METHODS FOR THEIR PREPARATION
FIELD OF THE INVENTION:
The present invention relates generally to the
field of organic chemistry. More particularly, the present
invention provides novel organic phosphinic acids and their
sulfur derivatives and methods for their preparation. These
novel compounds find utility as metal extractants.
SUMMARY OF THE INVENTION:
In one aspect, the invention provides a compound
defined by formula (I):

wherein:
R1 and R2 are different and each of R1 and R2 is independently
selected from:
(a) -CH2-CHR3R4, where R3 is methyl or ethyl; and R4 is an
optionally substituted alkyl or heteroalkyl; and
(b) -CR3(CH2R5)R6, where
R3 is methyl or ethyl; and
R5 is H or an optionally substituted alkyl or
heteroalkyl, and R6 is an optionally substituted alkyl or
heteroalkyl; or
1

R5, R€ and the ethylene group to which they are
bonded form a five or six-nembered optionally substituted
cycloalkyl or heterocycloalkyl ring;
and each of X and Y is independently 0 or S.
Thus, in embodiments, the invention provides the
following compounds of formula (I) :
(a) (2,4,4-trimethylpentyl)(1,1,3,3-tetramethylbutyl)
phosphinic acid;
(b) (1,1,3, 3-tetratnethylbutyl) (2-ethylhexyl)phosphinic
acid;

(c) (2,4,4-trimethylpentyl (2-ethylhexyl)phosphinic acid;
(d) (2,4,4-trimethylpentyi: (1-methyl-l-ethylpentyl)
phosphinic acid; and
(e) (1-methyl-l-ethylpentyl)(2-ethylhexyl)phosphinic acid;
and their mono- and dithio- derivatives, and salts thereof.
As described herein, compounds of formula (I) can
be prepared for example by allowing a secondary phosphine of
formula (II):
to react with (i) an oxidizing agent, to produce the
corresponding phosphinic acid; (ii) sulfur, to produce the
corresponding dithiophosphini acid; or (iii) a limited
amount of oxidizing agent, to produce the corresponding

phosphine oxide, which is subsequently allowed to react with
sulfur to produce the corresponding monothiophosphinic acid.
In another aspect, the present invention provides
a method for preparing a secondary phosphine of formula (II)
wherein R1 and R2 are as def:.ned above and R2 is
-CH2-CHR3R4, wherein the method comprises allowing a primary
phosphine of formula R1PH2 to react with an olefin of formula
CH2=CR3R4 under free radical conditions.
In another aspect, the present invention provides
a method for preparing a secondary phosphine of formula (II)
wherein R1 and R2 are as defined above and R2 is
-CR3 (CH2R5)R6, wherein the method comprises allowing a primary
phosphine of formula R1PH2 to react in the presence of an
acid catalyst with an olefin of formula HR5C=CR3R6.
Some of the secondary phosphine compounds of
formula (II) are novel. Thu3, in embodiments, the invention
provides the following secondary phosphine compounds:
(a) (2,4,4-trimethylpentyl (1,1, 3 , 3-tetramethylbutyl)
phosphine;
(b) (1, l,3,3-tetramethylbutyl) (2-ethylhexyl)phosphine;
(c) (2,4,4-trimethylpentyl] (2-ethylhexyl)phosphine;
(d) (2,4,4-trimethylpentyl)(1-methyl-l-ethylpentyl)
phosphine; and
(e) (l-methy-l-ethylpentyl)(2-ethylhexyl)phosphine.
In another aspect, the present invention provides
use of a compound of formula (I) or a salt thereof as a
metal extractant.

In another aspect, the invention provides a
process for the extraction of a metal from a metal-bearing
solution, comprising contacting said solution with a
compound of formula (I), allowing the compound of
formula (I) to form a complex with the metal, and recovering
the complex. In embodiments, a compound of formula (I) in
which X and Y are both 0, or a salt thereof, can be used to
selectively extract cobalt(II) from an aqueous solution
comprising cobalt(II) and rickel(II).
DETAILED DESCRIPTION:
Values for R1 and R2 are chosen to yield compounds
of formula (I) that have low melting points. For many
applications, the compound of formula (I) is used in its
liquid state. Accordingly, compounds of formula (I) that
are liquid at room temperature (e.g. over a temperature
range of between about 15°C to about 25°C, more particularly
at a temperature of about 16°C, about 20°C and about 25°C)
are generally suitable for applications that are carried out
at or near room temperature whereas compounds of formula
(I) that melt at low temperature (for example at
temperatures less than about. 30°C, about 40°C, about 50°C,
about 60°C, about 80°C, about 100°C, about 150°C) are
generally suitable for applications that are carried out at
slightly elevated temperatures (i.e. above the melting point
of the compound of formula (I)). Hence, values for R1 and R2
are chosen such that R1 and R2 are different, as the
resulting asymmetry tends tc decrease the melting point of
the compound.
Branching is another determinant of melting point.
Specifically, the melting point tends to decrease as the
degree of branching of R1 and R2 increases. By definition,

each of R1 and R2 is independently branched at the alpha or
beta carbon, but additional branching can occur at the alpha
or omega carbon or at any intermediate point. Branching at
the alpha carbon and/or beta carbon may improve the ability
of an organophosphinic acid to bind cobalt selectively over
nickel and/or calcium, by increasing steric hindrance around
the central phosphorous atom and thus favouring coordination
of the phosphinic acid with cobalt(II).
The presence of one or more chiral centres in R1
and R2 tends to decrease the melting point, by providing a
mixture of stereoisomers.
The melting point tends to increase as the number
of carbon atoms in the compound increases, so R1 and R2 are
typically chosen such that the compound of formula (I)
contains no more than about 20 carbon atoms. However, for
some purposes (such as metal extraction from aqueous
solutions), compounds of formula (I) that are hydrophobic or
"water immiscible" are desired. The term "water immiscible"
is intended to describe compounds that form a two phase
system when mixed with water, but does not exclude compounds
that dissolve in water nor compounds that dissolve water,
provided that the two phase system forms. For these
purposes, compounds of formula (I) that have a total of
about 12 carbon atoms or more can be useful.
For many applications (such as metal extraction
applications), R1 and R2 are chosen to yield compounds that
are miscible (preferably in all proportions) with an organic
solvent used in the particular application. The miscibility
of compounds of formula (I) in the specified organic solvent
can readily be determined (e.g. by eye), without the
exercise of inventive skill.

R1 and R2 can contain heteroatoms (e.g. the carbon
backbone can be interrupted by one or more atoms selected
from N, 0, and S) or bear additional substituents (such as
hydroxyl, halo, alkoxy, alkylthio, carboxy, and acetyl
groups), provided that the substituents or heteroatoms do
not interfere with the preparation or utility of the
compounds of the invention, as can readily be determined by
routine experimentation requiring no inventive skill.
However, the presence of heteroatoms and additional
substituents are likely to increase costs. Therefore, for
many purposes, R1 and R2 will not contain heteroatoms or bear
additional substituents.
Thus, for many purposes, each of R1 and R2 is
independently an alkyl group or cycloalkyl group made up of
hydrogen and carbon atoms only, such as: a C5-C16 alkyl
group, i.e. an alkyl group that has a total of between 5 and
16 carbon atoms (i.e. 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
or 16 carbon atoms) and often between 6 to 10 carbon atoms;
or a C5-C16 cycloalkyl group, e.g. a five- or six-membered
ring substituted with at least one alkyl group (i.e. R3 and
optionally one or more additional alkyl groups), such that
said cycloalkyl group has a total of between 6 and 16 carbon
atoms (i.e. 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16) and
often between 6 to 10 carbon atoms. Herein, the term
"alkyl" includes straight and branched chain alkyl radicals.
R3, R4, R5 and R6 are chosen to provide the desired
values for R1 and R2. For example, when R1 is a C5-C16 alkyl
of formula -CR3 (CH2R5) R6 and R3 and R5 are both methyl, then R6
is C1-C12 alkyl. R4, R5 and R6 may be branched.

Thus, suitable values for R1 and R2 include: 2,4,4-
trimethylpentyl; 1,1,3,3-tetramethylbutyl; 2-ethylhexyl; and
1-methyl-1-ethylpentyl.
(I) METHODS FOR PREPARING COMPOUNDS OF FORMULA (I):
Compounds of formula (I) can be prepared using
known chemical reactions. Far example, a secondary
phosphine of formula (II)

wherein R1 and R2 are as defined above, can be prepared by
adding a primary phosphine to an olefin either by way of
acid-catalysed addition or under free radical conditions.
Then, the secondary phosphine can be reacted with: (i) an
oxidizing agent, to produce phosphinic acid; (ii) sulfur, to
produce dithiophosphinic acid; or (iii) a limited amount of
oxidizing agent, to produce a phosphine oxide that can
subsequently be allowed to react with sulfur to prepare
monothiophosphinic acid.
Free radical conditions are useful for preparing a
secondary phosphine that has an R group substituted at the
beta carbon atom, because free radical conditions favour
addition of phosphine to a primary carbon atom, such as the
terminal carbon atom of a 1-alkene.
Acid catalysis is useful for preparing a secondary
phosphine that has an R group substituted at the alpha

carbon, because acid catalysis favours addition of the
phosphine to a tertiary carbon.
(A) PREPARATION OF SECONDARY PHOSPHINES UNDER FREE RADICAL
CONDITIONS
Methods for adding phosphines to olefins under
free radical conditions are known. For example, U.S. Patent
Number 4,374,780 describes a method for making bis (2,4,4-
trimethylpentyDphosphinic acid by free radical addition of
two moles of 2,4,4-trimethylpentene-l to phosphine followed
by oxidation with hydrogen peroxide.
Thus, a method for preparing a secondary phosphine
of formula (II):

wherein R1 and R2 are as defined above and R2 is -CH2-CHR3R4,
comprises, for example, allowing ci primary phosphine of
formula R1PH2 to react with an olefin of formula CH2=CR3R4
under free radical conditions.
Free radical initiators are known in the art and
the skilled person will be able to select a suitable free
radical initiator for use in the above-described reaction.
Mention is made of azobis free radical initiators, such as
azobisisobutylnitrile.
The phosphine addition reaction is not
particularly temperature limited and will take place over a

wide range of temperatures Consequently, a temperature
range for carrying out the reaction is generally chosen
based on the half life of t.he initiator employed. For
example, for azobisisobutylnitrile, the reaction can be
carried out at temperatures ranging from about 40° to
about 110°C, preferably about 60° to about 90° C.
To reduce the production of unwanted tertiary
phosphines, the reaction should be carried out with a molar
excess of primary phosphine.
For example, (2,4,4-trimethylpentyl)(2-ethylhexyl)
phosphine can be prepared by addition of:
(a) (2,4,4-trimethylpentyl)phosphine to 2-ethylhex-l-ene or
(b) 2-ethylhexylphosphine to (2,4,4-trimethyl)pentene-l
under free radical conditions as described above.
(B) PREPARATION OF SECONDARY PHOSPHINES BY ACID-CATALYZED
ADDITION
Methods for adding phosphines to olefins via acid
catalyzed addition have been known for some time (see for
example U.S. Patent Number 2584112). For example, U.S.
Patent Number 5,925,784 describes a method of making
bis(l,1,3,3-tetramethylbutyl)phosphinic acid by acid-
catalyzed addition of phospiine to diisobutylene, followed
by oxidation with hydrogen peroxide.
Thus, a method for preparing a secondary phosphine
of formula (II) :

wherein R1 and R2 are as defined above and R2 is
-CR3 (CH2R5)R6, comprises, for example, allowing a primary
phosphine of formula R1PH2 to react in the presence of an
acid catalyst with an olefin of formula HR5C=CR3R6.
The acid catalysed addition step can be
conveniently carried out in the presence of a protonatable
organic solvent (i.e. an organic solvent that contains a
hydroxy (OH) group), such as a glycol or glycol ether.
Examples of suitable glycol or glycol ethers for this
purpose include: ethylene glycol, glycerine, and glyme.
The acid catalyst can be any strong non-oxidizing
acid. Alkylsulfonic acids (including but not limited to
methanesulfonic acid and toluenesulfonic acid) are preferred
due to their availability, low cosr and compatibility with
most stainless steels (which are commonly used to make
industrial reactors). However, other strong non-oxidizing
acids such as HCl and H3PO4 may be used in the method of the
invention, although HCl will require that the reaction be
carried out in a halide resistant reactor. The molar ratio
of acid catalyst to primary phosphine is about 1:1 to
about 5:1, preferably about 1.5:1.0. A molar excess of acid
catalyst may improve yield, but increases the cost of the
process.
In general, the acid-catalyzed addition step can
be carried out by adding the acid catalyst to a vessel

containing the primary phosphine and the olefin under an
inert atmosphere (such as nitrogen) at atmospheric pressure
and elevated temperature (e.g. about 50° to about 160°C,
preferably about 75° to about 125°C), and allowing the
reaction to proceed for between about 2 to about 88 hours
(preferably between about 8 to about 2 0 hours). Elevated
temperatures may improve yield and reduce reaction time.
The reaction product(s) can be analyzed using standard
methods, e.g. gas chromatography (GC) and/or nuclear
magnetic resonance (NMR) analysis.
The presence of ar excess of olefin may improve
yield in the phosphine addition step but can lead to olefin
dimers and trimers. The alkylphosphine may be present in
excess, but the excess alkylphosphine should typically be
removed prior to oxidation. Therefore, in most cases, the
reaction will comprise olefin and the primary phosphine in a
molar ratio ranging from abcut 0.5:1 to about 3:1,
preferably about 1.5:1.0.
Upon completion of the acid catalysed addition
step, the reaction mixture can be worked up (e.g. by washing
with aqueous base, recoverirg the organic phase, and
removing any unreacted starting materials and solvent under
vacuum at elevated temperature (e.g. about 80°C)), to
provide a crude secondary phosphine preparation that can be
used directly in the oxidation step, without further
purification.
The olefin can be a single species or a mixture of
two related olefin species, each having a tertiary carbon
double-bonded to a neighbouring carbon atom. For example,
diisobutylene is ordinarily available commercially as a
mixture of (2,4,4-trimethyl)pentene-l and (2,4,4-trimethyl)

pentene-2. In the presence: of an acid catalyst, a primary
phosphine can add to both of these species of olefin at
their beta carbon, which is; tertiary.
For example:
(a) (2,4,4-trimethylpenty])(1,1,3,3-tetramethyl)phosphine
can be prepared by allowing (2,4,4-trimethylpentyl)
phosphine to react with diisobutylene in the presence
of an acid catalyst;
(b) (1,1,3,3-tetramethylbutyl)(2-ethylhexyl)phosphine can
be prepared by allowing 2-ethylhexylphosphine to react
with diisobutylene in the presence of an acid catalyst;

(c) (2,4,4-trimethylpenty])(1-methyl-1-ethylpentyl)
phosphine can be prepared by allowing (2,4,4-trimethyl-
pentyl ) phosphine to react with 2-ethylhexene-l in the
presence of an acid cetalyst; and
(d) (1-methyl-l-ethylpentyl)(2-ethylhexyl)phosphine can be
prepared by allowing 2-ethylhexylphosphine to react
with 2-ethylhexene-l in the presence of an acid
catalyst.
(C) OXIDATION OF A SECONDARY PHOSPHINE
The secondary phcsphines described above can be
oxidized to prepare the corresponding phosphinic acids.
At a molecular level, the oxidation of the
secondary phosphine occurs in two steps. First, the
secondary phosphine is oxidized to phosphine oxide, which is
then oxidized to form the phosphinic acid. In practice,
complete oxidation of the secondary phosphine can be
accomplished in a single reaction. The secondary phosphine

can be oxidized, for example;, by allowing it to react with
an oxidizing agent (preferably hydrogen peroxide) in the
presence of an acid catalyst: (e.g. sulfuric acid) and water,
at atmospheric pressure and elevated temperature
(e.g. about 50°C to about 110°C, preferably about 80°C to
about 100°C) for about 4 to about 16 hours or until
complete. Lower temperatures slow the reaction, resulting
in longer reaction times. However, higher temperatures tend
to remove one alkyl group, resulting in the formation of
some monoalkylphosphonic ac:.d side product. The course of
the reaction can be followed for example by 31P NMR.
Suitable oxidizing agents include hydrogen
peroxide, which is an inexpensive and convenient oxidizing
agent. The stoichiometry of the oxidation reaction dictates
that two equivalents of hydrogen peroxide react with one
equivalent of phosphine in this reaction. However, the
presence of an excess of hydrogen peroxide can improve yield
(i.e. pushing the oxidation reaction towards completion) at
little extra cost. So in many cases, hydrogen peroxide will
be present in excess of the secondary phosphine, say in a
ratio of equivalents ranging from between about 2:1 to
about 4:1, preferably about 3:1.
Upon completion oi: the reaction, the reaction
mixture can be worked up (e.g. by washing with aqueous base
(e.g. sodium hydroxide) then aqueous acid (e.g. sulfuric
acid), then drying under vacuum at elevated temperature
(e.g. about 80°C)), to afford a liquid product that contains
the desired phosphinic acid product.
The foregoing method generally affords a liquid
end product that contains the desired phosphinic acid, as
well as certain side products. When the process is carried

out under suitable conditions, the desired phosphinic acid
product can be the major component (e.g. 80-95% or more by
weight) of the liquid end product.
The liquid end product of the prescribed method
i can be used in metal extract ion processes without further
purification, as most of the; side products are not expected
to interfere with the metal extraction process. However,
the oxidation step can result in the production of
phosphonic acid side products (i.e. R1PO(OH)2 and R2PO(OH)2),
which may for example reduce; the selectivity of the end
product for cobalt over calcium and nickel. If desired,
reaction conditions (especially temperature, as noted above)
can be chosen to minimize the production of phosphonic acid
side products. If desired, the liquid end product can be
i washed with one or more alkaline water washes to reduce the
level of monophosphonic acids to an acceptable level, e.g.
about 1% or less.
(D) REACTION OF SECONDARY PHOSPHINES OR PHOSPHINE OXIDES
WITH SULFUR
The secondary pho3phines described above can also
be used as intermediates to prepare the corresponding
monothiophosphinic acids and dithiophosphinic acids.
Dithiophosphinic acids can be prepared, for
example, by allowing a secondary phosphine to react with
sulfur, in accordance with known methods (e.g. as described
in US Patent Number 5925784 or GB902802). Secondary
phosphines just defined can be reacted with sulfur, water,
and a base reagent, such as ammonium hydroxide, to produce
the salt of the corresponding secondary dithiophosphinic
acid, such as the ammonium salt thereof. Reactions of this
type are generally carried out at temperatures in the range

of about 0°C to about 100°C, preferably about 15°C to
about 75°C. The salt thus prepared can be reacted with an
acid, such as HC1, dilute sulfuric acid, or methane sulfonic
acid to produce the secondary dithiophosphinic acid. These
reactions generally are made to take place at temperatures
in the range of about -30°C to about 75°C, preferably
about 10°C to about 50°C.
Monothiophosphinic acids can be prepared, for
example, by:
(i) allowing a secondary phosphine to react with a
limiting amount of an oxidizing agent, to produce a
secondary phosphine oxide; and
(ii) allowing the secondary phosphine oxide to react with
sulfur to produce a monothiophosphinic acid.
A suitable method for preparing monothiophosphinic acids is
described in for example US Patent Number 4555368. Briefly,
the secondary phosphine can be oxidized to form the
corresponding diorganophosphine oxide, without forming
significant amounts of the corresponding diorganophosphinic
acid. To achieve this, the oxidation reaction can be
performed by gradual or incremental addition of the
oxidizing agent at a rate wnich provides a controlled
temperature of from about 40°C to about 60°, and preferably
from about 50°C to about 55°C. The amount of oxidizing
agent added should be sufficient to oxidize substantially
all of the secondary phosphlne and generally an equimolar
amount of oxidizing agent is used. The time of addition may
vary depending on the start Lng amounts of secondary
phosphine used. Generally, oxidation under controlled
temperature conditions can be completed with gradual or

incremental addition of the oxidizing agent over a period of
from about 1 to about 3 hours.
The selection of a particular oxidizing agent is
not critical, so long as it is effective to oxidize the
secondary phosphine to the secondary phosphine oxide.
Hydrogen peroxide is the preferred oxidizing agent for use
herein, because it is inexpensive, readily available, and
the temperature and rate of the oxidation reaction are
easily controlled with its use.
After substantially all of the secondary phosphine
has been converted to the corresponding secondary phosphine
oxide, the resulting secondary phosphine can be heated to an
elevated temperature of between about 60°C to about 90°C,
and preferably from about 6E°C to about 75°C, and an excess
of sulfur and excess of an hydroxide compound added to
convert the secondary phosph.ine oxide to the corresponding
monothiophosphinate compound. The sulfurization reaction in
the presence of base can be conducted at temperatures of
between about 60°C to about 90°C, and allowed to proceed
substantially to completion. Generally, the reaction can be
completed within a period of from about 1 to about 5 hours
at temperatures of 60°C to 90°C.
The resulting moncthiophosphinic acid can undergo
tautomerization, interconverting between the following
tautomers;

(II) UTILITY OP COMPOUNDS OF FORMULA I
It is known in the art that organic phosphinic
acids can be used for metal extraction, notably cobalt (II)
extraction (see for example U.S. Patent Numbers 4373780;
4353883; 4348367; and 5925784). Organic phosphinic acids
are also known to be useful for extraction of other metals,
such as rare earth metals, actinides, and platinum group
metals.
Organic mono- and dithio-phosphinic acids have
also been found to be useful as metal extractants (see for
example U.S. Patent Numbers 5028403 and 4721605) . The
acidity of these phosphorus-containing acids increases with
increasing sulfur content, which tends to increase the
ability of the acid to extract metals from solutions having
low pH but also tends to ir.crease the difficulty of
subsequently stripping the metal therefrom.
Thus, it can be appreciated that compounds of
formula (I) may be used as metal extractants (e.g. for the
recovery of a variety of metals from aqueous solutions
containing such metals alor.e or in combination with other
less desirable metals). In. embodiments, compounds of
formula (I) may be used in cobalt extraction processes.
Bis(2,4,4-trimethylpentyl)-phosphinic acid
(disclosed in U.S. Patent number 4374780 and marketed by
Cytec Industries, Inc. under the name CYANEX 272 is widely
used for separating cobalt and/or nickel from either sulfate
or low chloride media. CYANEX 272 can bind cobalt
selectively, while simultar.eously rejecting calcium,
magnesium, and nickel, which are often present in aqueous
cobalt (II)-bearing solutions. CYANEX 272 is also used for
the separation of heavy rare earth metals and the selective

separation of iron and zinc from cobalt solutions. However,
CYANEX 272 has certain limitations and drawbacks. In
particular, CYANEX 272 becomes increasingly viscous and
difficult to work with when it is loaded with cobalt, and as
a result, it is usually leaded to only 70-75% of its maximum
theoretical capacity in industrial processes.
In the examples described herein,
(2,4,4-trimethylpentyl){1,3,3,3-tetramethylbutyl)phosphinic
acid (which is a compound cf formula (I) exemplified herein)
has been observed to have a cobalt loading capacity
comparable to that of CYANEX 272, but unlike CYANEX 272,
without becoming overly viscous even at maximum cobalt
loading. Therefore, in embodiments, (2,4,4-
trimethylpentyl)(1,1,3,3 tetramethylbutyl) phosphinic acid
allows for cobalt loading of up to 100% of the theoretical
capacity in industrial processes, an improvement over CYANEX
272 on the order of 25-30%, without encountering viscosity
problems. An improved practical cobalt loading capacity
and/or reduction in viscosity problems (as has been observed
with (2,4,4-trimethylpentyl)il,1,3,3-
tetramethylbutyl)phosphinic acid in the examples described
herein) may improve the overall efficiency and productivity
in certain applications, such as commercial cobalt (II)
extraction processes.
In the examples described herein, (2,4,4-
trimethylpentyl) (1,1,3,3-tetramethylbutyl)phosphinic acid
has also been observed to be better than CYANEX 272 at
rejecting calcium. In commercial cobalt extraction
processes, cobalt is typically recovered by stripping it
from an organic phase with sulfuric acid. Co-extraction of
calcium is undesirable because it may lead to the formation
of gypsum at the interface of :he organic phase and water

phase during the step of stripping cobalt from the organic
phase, and so may interfere with and decrease the
productivity of the stripping step. Thus, in embodiments,
an improved calcium rejection (as has been observed with
(2,4,4 -trimethyl-pentyl) (1,1,3,3 -1etramethylbutyl)
phosphinic acid in the examples described herein) may reduce
the amount of calcium that is co-extracted in cobalt
extraction processes, which may improve the productivity and
efficiency of the cobalt stripping step.
Further, in the examples described herein,
(2,4,4 -trimethylpentyl) (1,1,3,3 -tetramethylbutyl)phosphinic
acid has been observed to be more selective for cobalt over
nickel than CYANEX 272.
U.S. Patent Number 5925784 discloses bis(1,1,3,3-
tetramethylbutyl)phosphinic acid and teaches that this
compound has utility as an agent for separating cobalt
and/or nickel. However, certain properties of bis (1,1,3,3-
tetramethylbutyl)phosphinic acid limit its industrial
utility; for example it is a solid at room temperature and
has limited solubility in the aromatic and aliphatic
solvents commonly used in ths industry for cobalt extraction
processes. In contrast, in accordance with the present
invention, values of R1 and R7 can be chosen to provide
compounds of formula (I) that are liquids at room
temperature and/or miscible (preferably in all proportions)
with the aromatic and aliphatic solvents used in cobalt
extraction.
The compounds of formula (I) can be used for
cobalt extraction in accordance with known methods (for
example, as described in U.S. Patent Numbers 5925784,
4353883, and 4348367). For example, (2,4,4-trimethyl-

pentyl)(1,1,3,3-tetramethylbutyl) phosphinic acid can be
directly substituted for CYANEX 272, although it may be
necessary to modify the process somewhat to accommodate for
differences between the chemical and physical properties of
these compounds. One skilled in the art can adapt such
known methods to incorporat.e the use of compounds of formula
(I) using routine experimentation, without the exercise of
inventive skill.
All publications and patent applications cited in
this specification are herein incorporated by reference as
if each individual publication or patent application were
specifically and individually indicated to be incorporated
by reference.
The citation of any publication is for its
disclosure prior to the filing date and should not be
construed as an admission that the present invention is not
entitled to antedate such publication by virtue of prior
invention.

EXAMPLES:
EXAMPLE 1; SYNTHESIS OF (2,4,4-TRIMETHYLPENTYL) (1,1,3,3-
TETRAMETHYLBUTYL)PHOSPHINIC ACID
The end product of this second synthesis of
(2,4,4-trimethylpentyl) (1,1,3,3-tetramethylbutyl)phosphinic
acid is referred to hereafter as "Batch 1".
(I) Synthesis of (2, 4, 4-trirtethylpentyl) (1,1, 3, 3-tetra-
methylbutyl)phosphine:
2,4,4-tritnethylper.tylphosphine (302.7 g, 99% GC,
2.07 mol, 1.0 eq.), diisobutylene (a mixture of 2,4,4-
trimethyl-pentene-1 and 2,4,4-trimethyl-pentene-2; 348.3 g,
3.11 mol, 1.5 eq.) and diethyleneglycol (295 g, weight ratio
-0.97) were added into a three neck flask under nitrogen.
The mixture was heated to 80°C at which time methanesulfonic
acid (298.9 g, 3.11 mol, 1.5 eq.) was slowly dripped into
the flask through an addition funnel over 50 minutes. The
mixture was further heated to reflux at 120°C and digested
overnight (16 hrs.).
The reaction mixture was cooled and toluene (300
ml) was added followed by slow addition of an aqueous
solution of NaOH (125 g in 500 g water, 3.11 mol, 1.5 eq.)
such that the temperature of the reaction remained
below 60°C. After vigorous mixing the contents were
transferred to a separatory funnel to allow a clear phase
separation. The organic phase was then collected and the
solvent and un-reacted starting materials were stripped off
under vacuum at 80°C. The resulting product (452 g, 85%
yield) was a clear colourless liquid and was analyzed by 31P
NMR and GC. Results: 31P NMF.: 5 -23.54 (doublet); and GC/MS:
retention time (m/e) 12.70 min (258).

(II) Synthesis of (2,4, 4-tr:.methylpentyl) (1,1, 3,3-tetra
methylbutyl)phosphinic acid.
Water (500 g, 1.0 weight ratio relative to volume
of dialkylphosphine) was added to a three-necked round
bottom flask with a catalytic amount of sulfuric acid (5 g,
1% relative to weight of water). The flask was blanketed
with nitrogen and fitted with a mechanical stirring device.
The (2,4,4-trimethylpentyl) (1,1,3,3-tetramethylbutyl)
phosphine (443 g, 1.7 mol, 1.0 eq.; from step (I) above) was
added to the reaction vessel to form a biphasic system, in
which the top layer is the organic phase. The reaction
mixture was then heated to 50°C under stirring and nitrogen.
The heat source was removed and an aqueous solution of ~25%
hydrogen peroxide (700 g, 5.2 mol, 3.0 eq.) was slowly
dripped into the reaction mixture ensuring that a slow and
steady increase in temperature occurred while avoiding large
and sudden temperature changes. After one equivalent of H2O2
was added (~50 min), the external heat source was applied to
provide a reaction temperature of > 95°C before the second
equivalent of H2O2 was added, in like fashion (-45 min) . At
this point the excess H2O2 was added to ensure complete
oxidation of starting material. The reaction mixture was
digested at > 95°C overnight (16 hrs.) at which time a
sample was extracted for 31P NMR analysis, to determine the
completion of the reaction. Results: 31P NMR peak: 8 63.53.
Upon completion of the reaction, toluene (~ 200ml)
was added to the mixture to reduce the viscosity of the
organic layer. The organic phase was then washed with an
equal volume of water. The organic phase was then washed
further with an aqueous solution of NaOH (100 g in 1L of
water) to achieve a pH ~ 7-8. The aqueous layer was removed
and the phosphinic acid was restored with an acidic wash

(H2SO4 in water, lOg/L). The desired product was then
stripped of water and dried under vacuum at 80°C to afford a
clear colourless liquid (40fi g, 82% yield) .
Example 2: SYNTHESIS OF (2,4,4-TRIMETHYLPENTYL) (1,1,3,3-
TETRAMETHYLBUTYL)PHOSPHINIC ACID
The end product of this second synthesis of
(2,4,4-trimethylpentyl) (1,1,3,3-tetramethylbutyl)
phosphinic acid is referred to hereafter as "Batch 2".
(I) Synthesis of (2,4,4-triitethylpentyl) (1,1,3,3-tetra
methylbutyl)phosphine:
2,4,4-trimethylpentylphosphine (412.4 g, 2.82 mol,
1.0 eq.), diisobutylene (a mixture of 2,4,4-trimethyl-
pentene-1 and 2,4,4-trimethyl-pentene-2; 474.3 g, 4.23 mol,
1.5 eq.) and diethyleneglycol (413.3 g, weight ratio -1.00)
were added into a three neck flask under nitrogen. The
mixture was heated to 80°C a; which time methanesulfonic
acid (4 07.6 g, 4.24 mol, 1.5 eq.) was slowly dripped into
the flask through an addition funnel over 50 minutes. The
mixture was further heated to reflux at 113°C overnight (16
hrs.).
The reaction mixture was cooled down and toluene
(400 ml) was added followed by slow addition of an aqueous
solution of NaOH (174.8 g in 500g water, 4.37 mol, 1.5 eq.)
such that the temperature of the reaction remained below
60°C. After vigorous mixing the contents were transferred
to a separatory funnel with an additional 500 ml water and
300 ml toluene. Clear phase separation was observed and the
aqueous layer was removed, followed by an additional wash of
the organic layer with 1 L of water. The organic phase was
then collected and the solvent and unreacted starting

materials were stripped off under vacuum at 80°C. The
resulting product (562.1 g, 77% yield) was a clear
colourless liquid and was analyzed by 31P NMR and GC.
Results: 31P NMR: 8 -24.76 (doublet); and GC/MS: retention
time (m/e) 14.98 min (258).
(II) Synthesis of (2 , 4 , 4-trinethylpentyl) (1,1, 3, 3-tetra
methylbuty)phosphinic acid:
Water (578 g, -1.0 weight ratio relative to volume
of dialkylphosphine) was added to a three-necked round
bottom flask with a catalytic amount: of sulfuric acid
(5.8 g, 1% relative to weight of water). The flask was
blanketed with nitrogen and fitted with a mechanical
stirring device. The (2,4,4-trimethylpentyl)
(1,1,3,3-tetramethylbutyl) phosphine (556.9 g, 2.16 mol,
1.0 eq.; from step (I) above) was added to the reaction
vessel to form a biphasic system, in which the top layer is
the organic phase. The reaction mixture was then heated to
50°C under stirring and nitrogen. The heat source was
removed and an aqueous solution of -25% hydrogen peroxide
(889.8 g, 6.54 mol, 3.0 eq.) was slowly dripped into the
reaction mixture ensuring that a slow and steady increase in
temperature occurred while avoiding large and sudden
temperature changes. After one equivalent of H2O2 was added
(~12 0 min), the external heat source was returned to ensure
a reaction temperature of > 95°C before the second equivalent
of H2O2 was added, in like fashion (~90 min). At this point
the excess H2O2 was added to ensure complete oxidation of
starting material. The reaction mixture was digested at
> 95°C overnight (16 hrs.) at which time a sample was
extracted for 31P NMR analysis, to determine the completion
of the reaction. Results: 3:P NMR peak: 8 63.52.

Upon completion cf the reaction, toluene (~ 500ml)
was added to the mixture tc reduce the viscosity of the
organic layer. The aqueous phase was removed and the
organic was treated with an aqueous solution of NaOH (100 g
in 1L of water) to achieve a pH - 7-8. The aqueous layer
was removed and the phosphinic acid was restored with an
acidic wash (H2SO4 in water, lOOg/L). The desired product
was then stripped of water and dried under vacuum at 80°C to
afford a clear colourless viscous liquid (551.7 g, 88%
yield). A sample was taken for NMR analysis and methylated
for analysis by GC/MS. Res alts: 31P NMR peak: 5 65.73; and
GC/MS: retention time (m/e) 19.02 min (272).
EXAMPLE 3
Two samples of the novel extractant, (2,4,4-
trimethylpentyl) (1,1, 3, 3-tetramethylbutyl) phosphinic acid
(Batch 1 and Batch 2) were chromatography/mass spectros;copy detector (GC/MSD) to fully
characterize the active ingredient, as well as all other
minor components and impurities. The acidic components were
first converted to their respective methyl esters to allow
for elution from the gas chromatograph column.
1. EXPERIMENTAL
Two samples of (2,4,4-trimethylpentyl)
(1,1,3,3-tetramethylbutyl) phosphinic acid (Batch 1 and
Batch 2) were accurately weighed to the nearest 0.1
milligram and diluted with toluene to a final concentration
of 20% by weight. A 500 /µL aliquot of the solution was
allowed to react with an equal volume of methylating reagent
(N,N-dimethylformamide dimethyl acetal) , and 0.2 µL of the
resulting mixture was injected into the gas chromatograph.

2. RESULTS
The results of GC/MSD analysis (area %) for each
component of the 2 samples cf (2,4,4-trimethylpentyl)
(1,1,3 , 3-tetramethylbutyl) phosphinic acid (Batch 1 and
Batch 2) are shown in Table 1.

3. DISCUSSION
The chromatographs for the two samples of (2,4,4-
trimethylpentyl) (1,1, 3 , 3-tetramethylbutyl) phosphinic acid
(Batch 1 and Batch 2) were similar in the composition of
components and impurities present and slightly different in
the terms of the quantities of components. Besides the
major component ((2,4,4-trimethylpentyl)
(1,1,3,3-tetramethylbutyl) phosphinic acid), the analysis
indicated the presence of the corresponding impurities
namely the dialkyl phosphinic acids, the monoalkyl
phosphonic acids and the phcsphine oxides. The presence of
the monoalkyl phosphonic acids must be minimized as they
tend to reduce the cobalt/nickel selectivity of the
extractant.
EXAMPLE 4: Characterization of 2,4,4-trimethylpentyl
(1,1,3,3-tetramethylbutyl)phosphinic acid
The following test work involved studying the
performance of the new extractant (2,4,4-trimethyl-
pentyl) (1,1,3,3-tetramethylbutyl)phosphinic acid (TEST 1)
and CYANEX 272. The experiments examined the extraction of
single metals from sulfate solutions and their mutual
selectivity as a function of pH, loading capacity of cobalt
and viscosity of organic solutions as a function of cobalt
loading.

PART A - EXTRACTION FROM sINGLE METAL SULFATE SOLUTIONS AT
VARYING pH
A.1 EXPERIMENTAL
The single metal aqueous solutions were prepared
by dissolving a weighed amount of the respective sulfate
salt and a weighed amount cf sodium sulfate salt in
deionized water. The metal concentration in each solution
was 0.001M, except Fe(III) which was 0.0015M. The sodium
sulfate concentration was 0.5M for all solutions. The
metals studied were Co(II), Ni(II), Ca(II), Mg(II), Mn(II),
Zn(II), Pe(III), and Cu(II).
The organic solutions were prepared by diluting
(2,4,4-trimethylpentyl)(1,1,3,3-tetramethylbutyl)phosphinic
acid or CYANEX 272 to 0. 1M o:: phosphinic acid with ISOPAR M
diluent. ISOPAR M is an aliphatic (>99.5%) hydrocarbon
diluent commercially available from Imperial Oil, Canada.
Equilibrium distributions of the various metals
between organic and aqueous phases as a function of pH were
determined at 50°C by contacting equal volumes (300 mL) of
the two phases in a jacketed beaker and mixed with
mechanical stirring. The temperature of the solution during
extraction was maintained at 50°C by a circulating bath.
The pH was adjusted by adding a known volume of either
sodium hydroxide or sulfuric acid to the aqueous phase. A
contact time of 15 minutes was used between each pH
adjustment. Samples of each phase were withdrawn (15 mL)
and analysed.
The equilibrium pH of the aqueous raffinate
samples was measured using a ROSS combination pH electrode
calibrated at room temperature with pH 1.00 (potassium

chloride - hydrochloric acid buffer), 4.00 (potassium
biphthlate buffer), and 7.00 (potassium phosphate monobasic
- sodium hydroxide buffer) buffer solutions.
For all experiments, the aqueous samples were
analysed by Atomic Absorption Spectroscopy (AAS). The metal
concentration in the organic phase for each sample was
deduced by subtracting the raffinate concentration from the
initial metal concentration in the feed solution.
A.2 RESULTS
Besides cobalt, nickel and calcium, other metals
(i.e. zinc, iron, copper, magnesium and manganese) were also
studied. There was however no significant difference between
(2,4,4-trimethylpentyl)(1,1,3,3-tetramethylbutyl)phosphinic
acid and CYANEX 272 for these metals and their numerical
data are therefore not reported here. The numerical data for
the extraction of cobalt, calcium and nickel as a function
of pH using (2,4,4-trimethylpentyl)(1,1,3,3-
tetramethylbutyl) phosphinic acid and CYANEX 272 are shown
in Table 2. Table 3 shows the pH50 values for each metal
using (2,4,4-trimethylpentyl) (1,1,3, 3-tetramethylbutyl)
phosphinic acid ("TEST") and CYANEX 272 as well as the ApH50
(ApH50 = pH50Co - pH50metals) values, respectively. The
pH50 values were determined using the log of the distribution
ratio, log D, and plotting the values as a function of pH.
The distribution coefficient, D, is defined as the ratio of
the total metal content in the organic phase to the metal
content in the aqueous phase.
The results indicate selectivity for cobalt-
nickel, cobalt-zinc, cobalt-Iron, and cobalt-calcium for
(2,4,4-trimethylpentyl) (1,1, 3,3-tetramethylbutyl) phosphinic
acid. Furthermore, (2, 4, 4-t:rimethylpentyl)

(1,1,3,3-tetramethylbutyl) phosphinic acid shows a
substantial increase in selectivity over CYANEX 272 for
cobalt over both calcium and. nickel. This higher cobalt-
calcium selectivity could have a great advantage in a
solvent extraction plant by decreasing the formation of
gypsum in the circuit.

PART B - COBALT LOADING CAPACITY AND VISCOSITY
B.1 EXPERIMENTAL FOR THE LOADING CAPACITY OF COBALT
The aqueous solution was prepared by dissolving a
weighed amount of cobalt sulfate salt in deionized water.
The metal concentration in :he solution was 40 g/L. The
organic solutions were prepared by diluting (2,4,4-tri-
methylpentyl)(1,1,3,3-tetramethylbutyl)phosphinic acid
extractant or CYANEX 272 to 0.14M of phosphinic acid with
ISOPAR M diluent. ISOPAR M is an aliphatic (>99.5%)
hydrocarbon diluent commercially available from Imperial
Oil, Canada.
Equilibrium distributions of cobalt between the
organic and aqueous phases vas determined at 50°C by
contacting an aqueous volume (250 mL) and an organic volume
(50 mL) to give an aqueous to organic phase ratio of 5. The
two phases were contacted in a jacketed beaker and mixed
with mechanical stirring. The temperature of the solution
during the extraction was maintained at 50°C by a
circulating bath. The pH was adjusted by adding a known
volume of sodium hydroxide to the aqueous phase. A constant
pH of 6.13 ± 0.03 for a period of 15 minutes was necessary
to ensure maximum loading of the metal. The phases were
separated and the organic fiLtered through phase separating
(P/S) paper to ensure that no entrained aqueous was present.
The metal concentration in the organic was determined by
stripping with 100 g/L H2SO4 using equal volumes of both
phases (4 0 mL) for 5 minutes at room temperature. The strip
liquor was collected in a sanple vial. An aliquot (35 mL)
of the stripped organic was stripped a second time with an
equal volume (35 mL) of fresh acid. This was repeated a

third time using 30 mL of stripped organic and 30 mL of
fresh acid.
The three strip liquors were kept separate and
analysed individually by ICP. The three strip liquor
concentrations were summed to determine the amount of cobalt
loaded. A total of three loading tests were completed
(TEST 1, TEST 2, and TEST 3).
The equilibrium pH of the aqueous samples was
measured as previously described in section above.
B.2 EXPERIMENTAL FOR THE VISCOSITY OF ORGANIC
SOLUTIONS AS A FUNCTION OF COBALT LOADING
The aqueous solution was prepared by dissolving a
weighed amount of cobalt sulfate salt in deionized water.
The metal concentration in the solution was 40 g/L.
The organic solutions were prepared by diluting a
weighed amount of either CYANEX 272 (200 grams, Lot#
WE2060451) or (2 , 4, 4-trimet:iylpentyl) (1,1, 3 , 3-tetramethyl-
buty)phosphinic acid extratant (200 grams, TEST 3)
extractant to 20% (w/w) with ISOPAR M diluent. These
solutions were split in two equal portions in order to
prepare the different per cent cobalt loading.
Equilibrium distributions of cobalt between the
organic and aqueous phases were determined as previously
described in the section above with the exceptions that the
temperature was room temperature and the aqueous to organic
phase ratio was of unity (500 mL volume for each phase). A
constant pH of 5.90 ± 0.02, and pH of 6.05 ± 0.02 for
CYANEX 272 and (2,4,4-trimethylpentyl) (1,1,3,3-tetramethyl-
butyl) phosphinic acid extrectant (TEST 3), respectively,
for a period of 15 minutes vas necessary to ensure maximum

loading of the metal. Phases were separated and the organic
was centrifuged for 30 minutes at 3000 rpm to ensure that no
entrained aqueous or precipitate was present.
Samples were next prepared by mixing 100% loaded
and 0% loaded at various volumes such that viscosities of
0%, 10%, 30%, 45%, 60%, 75%, 90%, and 100% cobalt loading
could be measured at varying temperatures.
The samples were Tested using a TA Instruments'
AR1000N rheometer. A step Flow method was used in 90 second
intervals ranging 10 to 60°C. In most cases data points
were collected at least eve:ry 10°C. Temperature control
(+/- 0.l°C) was provided by a Peltier plate. The geometry
consisted of a 60 mm cone and plate with a 2° angle. All
samples were found to be Newtonian, i.e., their viscosities
are independent of the shear rate. Thus tests with varying
temperatures reported were all done at the same shear rate
(500/s).
B. 3 RESULTS
The calculated cobalt concentration in the organic
phase was determined for three samples of (2,4,4-trimethyl-
pentyl) (1,1,3,3-tetramethylbutyDphosphinic acid (TEST 1,
TEST 2,and TEST 3) and CYANEX 272 and is shown in Table 4.

The results indicate a slight difference in the
loading capacity of the two extractants with CYANEX 272
having a slightly higher maximum cobalt loading capacity
than (2,4,4-trimethylpentyl)(1,1,3,3-tetramethylbutyl)
phosphinic acid.
The following two tables (5 and 6) show the
viscosity of both (2, 4, 4-trimethylpentyl) (1,1, 3, 3-tetr-
methylbutyl) phosphinic acid and CYANEX 272. Results
indicate that the viscosity does not change much with
varying cobalt solution loadings for (2,4,4-trimethylpentyl)
(1,1,3,3-tetramethylbutyl) phosphinic acid. On the other
hand, there is a large increase in viscosity between 75, 90,
and 100% cobalt solution loading for the CYANEX 272 samples.
On a practical basis, this means that 100% cobalt loading
can be achieved with (2,4,4-trimethylpentyl)(1,1,3,3-tetra-
methylbutyl) phosphinic acid whereas CYANEX 272 is limited
to 70-75% cobalt loading to limit the viscosity issues.

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CLAIMS:
1. A compound defined by formula (I):

wherein:
R1 and R2 are different and each of R1 and R2 is independently
selected from:
(a) -CH2-CHR3R4, where R3 is methyl or ethyl; and R4 is an
optionally substituted alkyl or heteroalkyl; and
(b) -CR3(CH2R5)R6, where
R3 is methyl or etayl; and
R5 is H or an optionally substituted alkyl or
heteroalkyl, and R6 is an optionally substituted alkyl or
heteroalkyl; or
R5, R6 and the ethylene group to which they are
bonded form a five or six-membered optionally substituted
cycloalkyl or heterocycloalkyl ring;
and each of X and Y is independently 0 or S.
2. The compound of claim 1, wherein R1 and R2 contain
carbon atoms and hydrogen atoms only.
3. The compound of claim 2 which contains a total of
between 12 and 2 0 carbon atoms.
4. The compound of claim 2 or 3, wherein each of R1
and R2 is independently C5-C16 alkyl or C5-C16 cycloalkyl.

5. The compound of claim 2, wherein each of R1 and R2
is independently C6-C16 alkyl.
6. The compound of claim 2, wherein each of R1 and R2
is independently C8 alkyl.
7. The compound of claim 2, wherein each of R1 and R2
is independently selected from 2,4,4-trimethylpentyl;
1,1,3,3-tetramethyl-butyl; 2-ethylhexyl; and 1-methyl-l-
ethylpentyl.
8. The compound of any one of claims 1 to 7, wherein
X and Y are both 0.
9. The compound of any one of claims 1 to 7, wherein
one of X and Y is 0 and the other is S.
10. The compound of any one of claims 1 to 7, wherein
X and Y are both S.
11. The compound (2,4,4-trimethylpentyl) (1,1,3,3-
tetramethylbutyl) phosphinic acid:

12. The compound (1,1,3,3-tetramethylbutyl)(2-ethyl-
hexyl)phosphinic acid.
13. The compound (2,4,4-trimethylpentyl)(2-ethylhexyl)
phosphinic acid.
14. The compound (2,4,4-trimethylpentyl)(1-methyl-l-
ethylpentyl)phosphinic acid.

15. The compound (1-methyl-1-ethylpentyl)(2-ethyl-
hexyl)phosphinic acid.
16. The compound (2,4,4-trimethylpentyl)(1,1,3,3-
tetramethylbutyl)dithiophosphinic acid.
17. The compound (2,4,4-trimethylpentyl)(1,1,3,3-
tetramethylbutyl)monothiophosphinic acid.
18. The compound (1,1 3,3-tetramethylbutyl)(2-ethyl-
hexyl) dithiophosphinic acid
19. The compound (1,1 3,3-tetramethylbutyl)(2-ethyl-
hexyl )monothiophosphinic acid.
20. The compound (2,4,4-trimethylpentyl)(2-ethyl-
hexyl )dithiophosphinic acid.
21. The compound (2,4,4-trimethylpentyl)(2-ethyl-
hexyl )monothiophosphinic acid.
22. The compound (2,4,4-trimethylpentyl)(1-methyl-l-
ethylpentyl)dithiophosphinic acid.
23. The compound (2,4,4-trimethylpentyl)(1-methyl-l-
ethylpentyl)monothiophosphinic acid.
24. The compound (1-methyl-1-ethylpentyl)(2-ethyl-
hexyl ) dithiophosphinic acid.
25. The compound (1-methyl-1-ethylpentyl)(2-ethyl-
hexyl) monothiophosphinic ac:id.
26. A method for preparing a. secondary phosphine of
formula (II):

wherein R1 and R2 are as defined in claim 1 and R2 is
-CH2-CHR3R4, wherein the method comprises allowing a primary
phosphine of formula R1pH2 to react with an olefin of formula
CH2=CR3R4 under free radical conditions.
27. A method for preparing a secondary phosphine of
formula (II) :

wherein R1 and R2 are as defined in claim 1 and R2 is
-CR3(CH2R5)R6, wherein the method comprises allowing a primary
phosphine of formula R1 PH2 to react in the presence of an
acid catalyst with an olefin of formula HR5C=CR3R6.
28. The method of claim 27, wherein ethylene glycol is
used as a solvent for carrying out the reaction.
29. The method of claim 27 or 28, wherein the acid
catalyst is methanesulfonic acid.
30. The method of any one of claims 27 to 29 wherein
the primary phosphine is (2,4,4-trimethylpentyl)phosphine,
and the olefin is diisobutylene.

31. A method for preparing a formula (I) as defined in
claim 1, the method comprising:
(a) preparing a secondary phosphine according to the method
of claim 26 or 27; and
(b) allowing the secondary pnosphine to react with
(i) an oxidizing agent, to produce the
corresponding phosphinic acid;
(ii) sulfur, to produce the corresponding
dithiophosphinic acid; or
(iii) a limited amount of oxidizing agent, to
produce the corresponding phosphine oxide, which is
subsequently allowed to react with sulfur to produce the
corresponding monothiophosphanic acid.
32. The method of claim 31, wherein the secondary
phosphine is (2,4,4-trimethy3pentyl)(1,1,3,3-tetramethyl-
butyl)phosphine prepared according to the method of
claim 18.
33. The method of claim 31 or 32, wherein the compound
of formula (I) is a phosphinic acid and the oxidizing agent
is hydrogen peroxide.
34. Use of a compound of any one of claims 1 to 25 or
a salt thereof as a metal extractant,
35. Use of a compound of any one of claims 1 to 15 or
a salt thereof as a metal extractant, wherein X and Y are
both 0 and the metal is cobal':.
36. The compound (2,4,4-trimethylpentyl) (1,1,3,3-
tetramethylbutyl)phosphine.

37. The compound (1,1,3,3-tetramethylbutyl)(2-ethyl-
hexyl) phosphine.
38. The compound (2,4,4-trimethylpentyl)(2-ethylhexyl)
phosphine.
39. The compound (2, ethylpentyl)phosphine.

The present invention provides phosphinic acids and
their sulfur derivatives, in accordance with the
following formula (I): wherein R and
R are different and each of R and
R is independently selected from an organic
radical that branches at the alpha carbon and an
organic radical that branches at the beta carbon, and
each of X and Y is independently 0 or S, and wherein
said compound is a liquid at room temperature.
Compounds of formula (I) find utility for example as
metal extractants. Also provided are methods for making
compounds of formula (I) and their corresponding
phosphine intermediates.

Documents:

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Patent Number

272668

Indian Patent Application Number

5022/KOLNP/2008

PG Journal Number

17/2016

Publication Date

22-Apr-2016

Grant Date

19-Apr-2016

Date of Filing

11-Dec-2008

Name of Patentee

CYTEC CANADA INC.

Applicant Address

9061 GARNER ROAD, NIAGARA FALLS, ONTARIO, L2E 6T4

Inventors:

#	Inventor's Name	Inventor's Address
1	YUEHUI ZHOU	3 DEERFORD ROAD TORONTO ONTARIO M23 3H9
2	BOBAN JAKOVLJEVIC	8040 WESTIMINSTER DRIVE NIAGARA FALLS, ONTARIO L2H 2Z2
3	CYRIL CHRISTIAN HENRI BOURGET	APT. L08, 4658 DRUMMOND ROAD, NIAGARA FALLS, ONTARIO L2E 7E1
4	ALLAN JAMES ROBERTSON	36 FOSTER AVENUE, THOROLD, ONTARIO L2V 4J5
5	DONATO NUCCIARONE	376 CELTIC DRIVE, STONEY CREEK, ONTARIO L&E 4N3
6	JEFFREY CHARLES HENRY DYCK	26 FOXHILL CRESCENT SAINT CATHARINES, ONTARIO L25 3T9

PCT International Classification Number

C07F 9/30,C07F 9/50

PCT International Application Number

PCT/CA2007/001043

PCT International Filing date

2007-06-12

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2,550,557	2006-06-14	Canada