Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF CARBOXYLIC ACIDS "

Abstract

An improved process for the preparation ofcarboxylic acids using rhenium (VII)oxide, as catalyst which comprises dissolving an aliphatic ketone, or a unsubstituted/substituted aromatic alkyl ketone having general formula 1 the drawing accompanying this specification, wherein R=alkyl and aryl, substituted aryls and R" =alkyl, rhenium(VII) oxide and an oxidant in the range of 50-100% in apola^ solvent, heating the reaction mixture at a temperature ranging between 40-1 OOo C for a period oj Jfo 30 hours, cooling the reaction mixture to ambient temperature, and separating the carboxylic acid of the general formula 2 of the drawing by filtration method^

Full Text

This invention relates to an improved process for the preparation of carboxylic acids. More particularly it relates to a process for the preparation of aliphatic or aromatic carboxylic acids using a rhenium (VII) oxide catalyst. Still more particularly, the present invention relates to a process for' the conversion of aliphatic ketones or substituted/unsubstituted aromatic alkyl ketones having general formula 1 in the drawing accompanying this specification wherein R= alkyl and aryl, substituted aryls and R = alkyl to corresponding aliphatic, substituted/unsubstituted aromatic carboxylic acids having the structural formula 2 in the drawing accompanying this specification by rhenium (VII) oxide (Re2O7) in combination with an oxidant. In the prior art, conversion of aliphatic or substituted or unsubstituted aromatic methyl or methylene ketones to aliphatic or substituted or unsubstituted aromatic acid is achieved by the following eight methods. 1. Haloform reactions in which the conversion of methyl ketones to carboxylic acids have been achieved using NaBrO2/NaBr, NaOH/Br2, NaOBr, KOC1, NaOCl as main oxidising reagents [Ref: (1) J.A.C.S. (1931), 53, 3184 ; (2) Org. Synth. Coll. Vol. (1932), 1,526; (3) Chem. Rev. (1934), 15, 275; (4) Org. Synth. Coll. Vol. (1943), 2, 428; (5) Org. Synth. Coll. Vol. (1955), 3, 302; (6) Org. Synth. Coll. Vol. (1973), 5, 8; (7)J.A.C.S.(1985),107, 2033, 5570; (8) Synthesis (1985), 674 ]. 2. p-Methylacetophenone is refluxed with dilute nitric acid, the solid formed was boiled with aqueous sodium hydroxide and treated with potassium permanganate for 2 hours and acidified with cone, sulphuric acid to give 1,4-benzene dicarboxylic acid [ Ref: Org. Synth. Coll. Vol. (1955), 3, 791]. 3. Aromatic methyl ketones and iodine are disolved in pyridine and heated on water-bath for 30 minutes, the α-keto alkylpyridinium iodide obtained was further heated with alcoholic sodium hydroxide which was acidified to give benzoic acids [Ref: J.A.C.S. (1944), 66, 894]. 4. Heating of substituted aromatic acetophenones with sodium dichromate and acetic acid or sulphuric acid to afford substituted benzoic acids constitutes the fourth method [Ref: Org. Synth. Coll. Vol. (1955), 3, 420]. 5. Conversion of acetophenones to benzoic acids using catalytic quantity of manganese triacetate in the stream of oxygen at high temperature (150 C) constitutes the fifth method [Ref: Recueil (1961), 80, 57]. 6. The conversion of cholest-4-en-3-one and 17p-acetoxyandrost-4-en-3-one to corresponding 4-seco-3-carboxylic acids by treatment of sodium metaperiodate and potassium permanganate in water or t-butanol [Ref: (1) Can. J.Chem. (1961), 39, 599; (2) J.C.S. PTI (1974), 1475]. 7. Acetophenones disolved in benzene and water were added with further addition of pentafluoroiodobenzene bis(trifluoroacetate) (3 equivalents) to get benzoic acids in 51-95 % yield after overnight stirring [Ref: Chem. Comm. (1987), 202]. 8. The oxidation of oc-amino ketones to the corresponding acids has been achieved with 30% H2O2. However, the reaction takes 14 hours to achieve moderate yields.Benzoic acids are also manufactured by liquid phase air oxidation of toluene using cobalt catalysts and NaBr as promoter. Literature survey reveals that rhenium (II), (III) and (VII) oxides are used as reducing agents at high pressures (150-258 atm) for the transformation of nitrobenzene to aniline, styrene to ethylbenzene and acetophenone to methylphenylcarbinol [Ref: (1) J.O.C. (1959), 24, 1847; (2) J.O.C. (1962), 27, 4402; (3) J.O.C. (1963), 28, 2343, 2345, 2347]. Recently dihydroxylation of olefins catalysed by Re2O7 has also been reported [Ref:(l) J. Chem. Soc. Chem Comm. 1991, 1578, (2) Ger. Offen. DE 3 902 357 (1989)]. The above mentioned processes in the prior art are known to be useful for the conversion of aliphatic or substituted or unsubstituted aromatic methyl ketones to the corresponding carboxylic acids, however they suffer from the following drawbacks. 1. In the haloform reactions, highly alkaline conditions and high temperatures are employed. It also uses the halogenated oxidants (NaOBr, NaOCl, NaOH/Br2 etc.) which are hazardous to the environment. 2. Most of the methods in prior art are not catalytic methods, they involve the use of stoichiometric amounts of the expensive reagents. 3. In most of the stoichiometric reactions in the prior art, large amounts of waste products containing heavy metals ( Cr, Mn,etc) residues are generated in the processes that are difficult to dispose of. 4. Manganese triacetate is very expensive and is active only at high temperatures and is not reusable. 5. In one of the methods the use of large excess of expensive pentafluoroiodobenzene bis(trifluoroacetate) is not suitable for the large-scale preparation of benzoic acids. 6. Although H2O2 is a useful oxidant, it oxidises only a-amino ketones and also it takes 14 days to complete the reaction. In view of all the above disadvantages of the prior art, it is desirable to provide a process, that is, safe, inexpensive, single step and simple. The main object of the present invention is to provide an improved process of preparation of carboxylic ncids which obviates the drawbacks as detailed above. Another object of the present invention to provide a single step process for the preparation of carboxylic ncids by conversion of appropriate aliphatic, substituted/unsubstituted aromatic alkyl ketones using rhenium (VII) oxide in catalytic quantity that can easily be separated from the product and reused. Accordingly, the present invention provides an improved process for the preparation of carboxylic acids using rhenium (VII) oxide, as catalyst which comprises dissolving an aliphatic ketone, or a unsubstituted/substituted aromatic alkyl ketone having general formula 1 the drawing accompanying this specification, wherein R=alkyl and aryl, substituted aryls and R'= alkyl, rhenium (VII) oxide and an oxidant.in the range of 50-100% in a polar solvent, heating the reaction mixture at a temperature ranging between 40-100°C for a period of 3 to 30 hours, cooling the reaction mixture to ambient temperature, and separating the carboxylic acid of the general formula 2 of the drawing by filtration methods. In one of the embodiments of the present invention the oxidant used may be strong oxidising agents exemplified by tert-butyl hydroperoxide (TBHP) hydrogen or benzoyl peroxide. In yet another embodiment of the present invention the strength of the oxidant may be in the range of 50-100% preferably 60-80%. In another embodiment of the present invention the polar solvent used may be selected from organic solvents such as but not limited to methanol, ethanol, t-butanol, acetic acid, a'cetonitrile etc. In a feature of the present invention the product is isolated simply pouring the reaction mixture into water and filtering, and the solid thus precipitated, the aqueous part containing the catalyst was evaporated under reduced pressure to obtain the catalyst. In yet another feature, the catalyst could be reused for the reaction several times without affecting the catalytic property. In yet another feature, the substituents on the aromatic ring could be both electron withdrawing or electron donating groups such as methyl, OCH3, NO2 and X (Cl, Br, I) present at various positions (o-, p- and m-) on the aromatic nucleus. The process of the present invention is described herein below with reference to examples, which are illustrative only and should not be construed to limit the scope of the present invention in any manner. EX AMPLE-1 A mixture of acetophenone (25 parts), Re2O7 (2.5 parts) and 70% TBHP (150 parts) in methanol (100 parts) was heated at 55° C for 5 hours. The reaction mixture was poured into water to afford the benzoic acid, which was filtered, (yield, 21 parts). The filtrate containing catalyst was evaporated under reduced pressure to recover the catalyst. EXAMPLE - 2 A mixture of p-hydroxyacetophenone (18 parts), Re2O7 (1.7 parts) and 70%TBHP (125 parts) in methanol (100 parts) was heated at 55° C for 5 hours. The reaction mixture was poured into water to afford the solid p-hydroxy benzoic acid that was filtered, (yield, 15 parts). The filtrate containing catalyst was evaporated under reduced pressure to recover the catalyst. EXAMPLE - 3 A mixture of p-chloroacetophenone (15 parts), Re2O7 (1.3 parts) and 70%TBHP (110 part) in methanol (100 parts) was heated at 65° C for 5 hours. The reaction mixture was poured into water to afford the p-chlorobenzoic acid which was filtered, (yield, 8 part). The filtrate containing catalyst was evaporated under reduced pressure to recover the catalyst. EXAMPLE- 4 A mixture of p-nitroacetophenone (15 parts), Re2O7 (1.2 parts) and 70%TBHP (125 parts) in methanol (100 parts) was heated at 60° C for 5 hours. The reaction mixture was poured into water to afford the p-nitrobenzoic acid which was filtered, (yield, 7 parts). The filtrate containing catalyst was evaporated under reduced pressure to recover the catalyst. EXAMPLE -5 A mixture of 2,4-dimethoxyacetophenone (10 parts), Re2O7 (0.9 parts) and 70%TBHP (100 parts) in t-butanol (75 part) was heated at 70° C for 5 hours. The reaction mixture was poured into water to afford the 2,4-dimethoxybenzoic acid which was filtered, (yield, 8 parts). The filtrate containing catalyst was evaporated under reduced pressure to recover the catalyst. EXAMPLE - 6 A mixture of 4-isobutylacetophenone (12 parts), Re2O7 (1 parts) and 70% TBHP (125parts) in t-butanol (75 parts) was heated at 80° C for 10 hours. The reaction mixture was poured into water to afford the 4-isobutylbenzoic acid that was filtered, (yield, 8 parts). The filtrate containing catalyst was evaporated under reduced pressure to recover the catalyst. EXAMPLE - 7 A mixture of p-methoxyacetophenone (20 parts), Re2O7 (1.8 parts) and 70% TBHP (160 parts) in acetic acid (100 parts) was heated at 60° C for 10 hours. The reaction mixture was poured into water to afford the p-methoxybenzoic acid that was filtered, (yield, 15 parts). The filtrate containing catalyst was evaporated under reduced pressure to recover the catalyst. EXAMPLE - 8 A mixture of 4-phenyl-3-butene-2-one (15 parts), Re2O7 (1.7 parts) and 70% TBHP (150 parts) in acetic acid (100 parts) was heated at 50° C for 15 hours. The reaction mixture was poured into water to afford the cinnamic acid which was filtered, (yield, 9 parts). The filtrate containing catalyst was evaporated under reduced pressure to recover the catalyst. EXAMPLE - 9 A mixture of 2-acetylpyrrole (15 parts), Re2O7 (1.3 parts) and 70% TBHP (100 parts) in Icetic acid (100 parts) was heated at 80° C for 5 hours. The reaction mixture was poured into water to afford the pyrrol-2-carboxylic acid that was filtered, (yield, 12 parts). The filtrate containing catalyst was evaporated under reduced pressure to recover the catalyst. EXAMPLE -10 A mixture of 2-octanone (18 parts), Re2O7 (1.6 parts) and 70% TBHP (180 parts) in acetic acid (100 parts) was heated at 75° C for 5 hours. The reaction mixture was poured into water to afford the n-Heptanoic acid that was filtered, (yield, 14 parts). The filtrate containing catalyst was evaporated under reduced pressure to recover the catalyst. The advantages of the present invention are as follows: 1. The process is economically viable. 2. It is environmentally safe. 3. It is easy to handle. 4. It is time saving. We claim: 1. An improved process for the preparation of carboxylic acids using rhenium (VII) oxide, as catalyst which comprises dissolving an aliphatic ketone, or a unsubstituted/substituted aromatic alkyl ketone having general formula 1 the drawing accompanying this specification, wherein R=alkyl and aryl, substituted aryls and R'= alkyl, rhenium (VII) oxide and an oxidantlin the range of 50-100% in a polar solvent, heating the reaction mixture at a temperature ranging between 40-100°C for a period of 3 to 30 hours, cooling the reaction mixture to ambient temperature, and separating the carboxylic acid of the general formula 2 of the drawing by filtration methods. 2. An improved process as claimed in claim 1 wherein the oxidant used is selected from tertiary butyl hydroperoxide, hydrogen or benzoyl peroxide 3. An improved process as claimed in claims 1 and 2 wherein the strength of the oxidant is preferably in the range of 60-80%. 4. An improved process as claimed in claims 1 to 3 wherein the polar solvent used is selected from methanol, ethanol, t- butanol, acetic acid, acetonitrile. 5. An improved process for the preparation of carboxylic acid substantially as herein described with reference to examples and drawing accompanying the specification.

Documents:

2706-del-1998-abstract.pdf

2706-del-1998-claims.pdf

2706-del-1998-correspondence-others.pdf

2706-del-1998-correspondence-po.pdf

2706-del-1998-description (complete).pdf

2706-del-1998-drawings.pdf

2706-del-1998-form-1.pdf

2706-del-1998-form-19.pdf

2706-del-1998-form-2.pdf