Title of Invention

A CONTINUOUS PROCESS FOR THE SIMULTANEOUS PREPARATION OF PIVALOYL CHLORIDE AND AN AROYL CHLORIDE

Abstract

ABSTRACT The invention relates to a continuous process for the preparation of pivaloyl chloride and of aroyl chloride, in particular benzoyl chloride. Accordingly the present invention provides a process which comprises reacting pivalic acid with a trichloromethylated aromatic compound in the presence of a catalyst at a temperature of between 60oC and 180oC under reduced pressure. The products formed are continuously removed from the reaction region, the hydrogen chloride formed being treated in a washing region in which a trichloromethylated compound moves countercurrentwise. The process of the present invention provides acid chlorides of high purity and of unchanging quality with high yields of greater than 96%, complete conversion of the reactants and high productivity.

Full Text

The invention relates to a continuous process for the/preparation of pivaloyl chloride and of aroyl chloride, in particular of benzoyl chloride. Pivaloyl chloride is an important synthetic intermediate in the chemical industry. It is very widely used in the synthesis of various pharmaceutical products (antiviral agents, anti-inflammatory agents) or plant-protection products (herbicides, insecticides). It is also used in the synthesis of peresters, such as tert-butyl perpivalate and tert-amyl perpivalate, which are used in particular as initiators in radical polymerization. Aroyl chlorides are also important synthetic intermediates, used in particular in the manufacture of peroxides and peresters and in the synthesis of various colorants, insecticides or rubber additives. The main access routes to pivaloyl chloride comprise processes in which conventional reagents, such as phosgene, sulphonyl chloride, phosphorus tri- or pentachlorides, thionyl chloride or oxalyl chloride, are reacted with pivalic acid or alternatively in which carbon monoxide is reacted, in the presence of a catalyst, with tert-butyl ch-loride. However, all these processes represent complex technologies, on account of the reagents involved and the need to carry out expensive treatments of the products obtained and of the effluents, which rule out industrial production. Thus, for example in the process described by Butlerow (Justus Liebigs Ann. Chem., p. 373, 1874], which consists in reacting pivalic acid with phosphorus pentachloride according to the reaction: (CH,)iCCOOH + PCI, ' (CHJ, CCOCl + POCI3 + HCl the POCli and the pivaloyl chloride obtained have boiling temperatures which are so close (104-106°C) that it is virtually impossible to separate them. This author also added potassium pivalate to the reaction mixture obtained, in order to convert POCl to P2O5 according to the reaction: Other authors (Bull. Soc. Chim. Fr., p, 350-351, 1939], in the light of this process, have proposed to prepare pivaloyl chloride directly in a single stage by reaction of sodium pivalate with POCI3 according to the reaction; With a 25% molar excess of sodium pivalate, the molar yield of pivaloyl chloride is only 81% with respect to the POCI3 employed, which, of course, rules out an industrial process, all the more so since the price of sodium pivalate is much higher than the price of the desired pivaloyl chloride. The proposal has been made to use phosphorus trichloride in place of PCI. (J. Am. Chem. See, 54, The hydrochloric acid formed is continuously removed and the pivaloyl chloride is purified by distillation after separation by settling of the phosphorous acid, which can be advantageously recovered. However, the molar yield of pivaloyl chloride is less than 90'ri with respect to the pivalic acid employed and it is very difficult to remove the final traces of phosphorous acid (reducing product), which traces rule out the use of pivaloyl chloride in certain syntheses. One of the most frequently mentioned processes for the synthesis of pivaloyl chloride in the literature is that employing thionyl chloride according to the reaction: The reaction is generally carried out in tJie presence of a 20 to 50% molar excess of SOCl. According to these conditions, molar yields of distilled pivaloyl chloride are obtained which are close to 90%. The addition of catalysts, such as DMF, pyridine or N~metliylacetamide, makes it possible to increase the reaction kinetics and to improve the selectivity [fall in the percentage of by-products, such as the anhydride)■ However, this process has the disadvantage of resulting in a pivaloyl chloride which can comprise sulphur. In addition, in the eventuality of the use of a catalyst, the catalyst is difficult to recycle. Pivaloyl chloride can also be obtained frorti phosgene according to the reaction: or alternatively by carbonylation of tert-butyl chlofide in the presence of catalysts, such as AlCl or FeClj, according to the reaction: However, these processes exhibit the disadvantage of using highly toxic reagents which are difficult to handle and requiring the use of catalysts in order to obtain a good selectivity and yields of greater than 90%, It should be noted that, in the case of the carbonylation of tert-butyl chloride, the use of catalysts is capable of resulting in the formation of impurities or of causing the retrogression of the product formed. The access routes to aroyl chlorides, in particular to benzoyl chloride, also comprise processes in which conventional reagents, such as PCI5, COCI2 or SOCli, are reacted with aromatic acids. More specifically, benzoyl chloride is obtained industrially by partial hydrolysis of phenylchloroform or by reaction of benzoic acid with phenylchloroforin according to the reaction; The simultaneous production of pivaloyl chloride and of an aroyl chloride, more specifically of benzoyl chloride, is not described to any great extent in the literature. This simultaneous production of acid chlorides is based on the reaction; which is a chlorodehydroxylation reaction of RCOOH by Japanese Patent JP 86-021 517 B describes a process for the batchwise preparation of pivaloyl chloride and of benzoyl chloride. This process consists in reacting, in a first stage, pivalic acid and phenylchloroform in a stoichiometric amount, at atmospheric pressure, in the presence of FeCl and at a temperature ranging from OC to 150°C and then, after removal of the HCl formed, in distilling the pivaloyl chloride under reduced pressure. Subsequently, in a second stage, after introduction of a fresh charge of catalyst, the reaction mixture is heated to a temperature of between 40° and 160°C and then the benzoyl chloride formed is distilled under reduced pressure. Although this process makes it possible to obtain acceptable yields, of between 90% and 95%, of pivaloyl chloride and of benzoyl chloride, there are a number of disadvantages to this way of operating. Thus, it is necessary to remove all the pivaloyl chloride before carrying out the second stage, at the risk of decarbonylating the pivaloyl chloride In order to avoid this, the authors of the patent mentioned completed the distillation by extracting the residual pivaloyl cnloride by partial distillation under reduced pressure of the benzoyl chloride formed. Under these conditions, the distillating fraction is composed essentially of benzoyl chloride, with a few % of pivaloyl chloride and of other unidentified compounds. There is a significant disadvantage to this way of operating, when it is known that various by-products are capable of being formed as a result of side reactions, the most important of which are the following: - an equilibrium transhalogenation reaction between benzoyl chloride and pivalic acid: - the reaction of the benzoic acid formed with benzoyl chloride, to result in benzoic anhydride; These by-products formed during the first stage are difficult to avoid. The authors of the patent mentioned also, in the second stage, added a significant amount of FeCl-i in order to convert the by-products and in particular benzoic anhydride in the presence of unconverted CH.,CCli according to the reaction: (CgH,CO),0 + C,H,CC1, -' 3C5H5COCI Finally, this batch process exhibits lengthy, successive, transitcry and net very productive operations. In addition, this process is completely silent with regard to any advantageous recovery of the hydrochloric acid formed. According to the present invention, there is provided a continuous process for the simultaneous preparation of pivaloyl chloride and an aroyl chloride of formula (2) by reaction,in the presence of at least one catalyst of Friedel-Crafts type,of pivalic acid with a trichlcromethylated aromatic compound of formula (1) according to the reaction: in which the or each R, which may be the same or different, represents a halogen atorr., such as F, CI or Br, a linear or branched alkyl radical containing from 1 to 4 carbon atoms, a linear or branched perfluoroalkyl radical containing from 1 to 4 carbon atoms or a -COCl radical, m represents G, 1 or 2 and n represents 1, 2 or 3 and in which the -CCl, groups are situated on non-adjacent carbon atoms when n > 1, which process comprises: - simultaneously and continuously introducing pivalic acid, at least one trichlcromethylated aromatic compound of formula [1] and at least one catalyst of Friedel-Crafts type into a reaction region and reacting them with stirring and under reduced pressure at a temperature of between 60°c and 180°C and preferably of between 120°C and 150°C, - continuously separating the unconverted reactants from the products which form the gas flow exiting at the top of the reaction region, - partially condensing the said products into a liquid mixture comprising pivaloyl chloride and an aroyl chloride of formula (2), - treating, in a washing region in which a trichloromethylated aromatic compound of formula (1) moves countercurrentwise, the remaining uncondensed gaseous mixture comprising hydrogen chloride, - continuously extracting, at the bottom of the said reaction region, a liquid mixture mainly comprising the aroyl chloride of formula (2) formed and the catalyst used in the reaction region, the said mixture being treated in a so-called "reactive" distillation region, from which is extracted, at the top, the aroyl chloride of formula (2), and - isolating the pivaloyl chloride. The unconverted reactants advantageously return to the reaction region. According to the present invention, the trichloromethylated aromatic compound (1) used in the washing region can be partially or completely introduced into the reaction region after having been used in the washing region. It will preferably be completely introduced into the reaction region, so as advantageously to recycle the pivalcyl chloride absorbed by the trichloromethylated aromatic compound (1) in the washing region. According to the present invention, the mixture extracted at the bottom of the reaction region, mainly comprising aroyl chloride and also unconverted trichloromethylated aromatic compound (1), catalvst, aroyl anhydride and, optionally, small amounts of by¬products, is treated in a so-called "reactive" distillation region generally under reduced pressure at a temperature at least equal to 120°C. In addition, it is possible to use an additional amount of catalyst of Friedel-Crafts type which is identical to or different from that used in the reaction region. The complementary part of the aroyl cl'iloride formed in the process is recovered at the top. Heavy products are recovered at the bottom and are destroyed, in particular by incineration. The reaction is preferably carried out with a molar ratio: of from 0.90n to l.lOn and preferably of between In and 1.03n. According to the present invention, the reaction is preferably carried out in the reaction region under a reduced pressure at most equal to 500 mbar and preferably of between 100 mbar and 400 mbar. The catalyst of Friedel-Crafts type used may be a Lewis acid or a Bronsted acid. Mention will be made, by way of illustration of Lewis acid which can be used according to the invention, of Feci,, ZnCli, SnCl, AlCl,, SbCls, CoCl, BF, and the like. Use will preferably be made of FeCl,, Mention will be made, by way of illustration of Bronsted acid which can be used according to the present invention, of sulphuric acid, phosphoric acid, polyphosphoric acids, pyrosulphuric acid, fluorosulphonic acid or chlorosulphonic acid. Use will preferably be made of sulphuric acid. These catalysts of Friedel-Crafts type can be introduced into the reacticm region as such, in the form of aqueous solutions, in solution in one of the reactants or in solution in pivaloyl chloride or aroyl chloride. According to the present invention, use will suitably be made of a molar amount of pure Lewis acid of between 0.01% and 1% and preferably of between 0.05% and 0.2%, with respect to the amount of pivalic acid employed. According to the present invention, use will suitably be made of a molar amount of pure Eronsted acid of between 0.1% and 5 and preferably of between 0.05% and 2%, with respect to the amount of pivalic acid employed. It would not be departing from the scope of the invention if the trichloromethylated aromatic compound moving countercurrentwise in the washing region were different from that introduced into the reaction region. The pure hydrogen chloride exiting at the top of the said washing region is subsequently advantageously absorbed in water in order to result in commercial aqueous HCl solutions. The liquid mixture extracted at the top of the reaction region, composed of a mixture of pivaloyl chloride and of aroyl chloride, is advantageously subjected to a distillation under reduced pressure which makes it possible to separate the various chlorides formed. Mention will be made, by way of illustration of trichloromethylated aromatic compounds (1) which can be used according to the present invention, of: - trichloromethylbenzene or phenylchloroform, - 2-chloro-, 3-chloro- and 4-chloro-l-trichloromethylbenzenes, - 1,3- and 1,4-bis(trichloromethyl)benzenes, - 4-fluoro-1-trichloromethylbenzene. -3,4-dichIoro-]-trichIoromethyibenzene and 4-trifluoromethyM-trichloromethylben2eiie. The process of the invention appties applies very particulaiiy to the preparation of pivaloyi chloride and of benzoyl chloride from pivalic acid and phenylchlorofonn. The process exhibits the advantage of resulting in acid chlorides of high purity and of unchanging quality with high yields of greriter than 96%, complete conversion of the reactants and high productivity. In addition, the hydrogen chloride formed is directly and advantageously recovered. This process also exhibits the ad\nteg6 of generating few t-products and in particular does not produce gaseous efQuents. Accordingly the present invention provides a continuous process lor the simultaneous preparation of pivaloyi chloride and an aro; i chloride of formula (2) by reaction, in the presence of at least one catalyst of Friedel-Crafb type, of pivalic acid widi a trichloromethylated aromatic compound of formula (1) according to the reaction: in which the or each R, which may be the same or different represents a halogen atom, a linear or branched alkyl radical containing from 1 to 4 carbon atoms, a linear or branched perfluoroalkyl radical containing from 1 to 4 carbon atoms or a -COCl radical, m represents 0, 1 or 2 and n represents 1,2 or 3 and in which the -CCI3 groups are situated on non-adjacent carbon atoms when n > 1, which process comprises; - simultaneously and continuously introducing pivalic acid, at least one trichloromethylated aromatic compound of formula (1) and at least one catalyst of Friedel-Crafts type into a reaction region and reacting them with stirring and under below atmosphet pressure at a temperature of between 60°C to 180°c, - continuously separating the gaseous reaction products exiting at the top of said reaction region fom the unconverted reactants, - partially condensing said gaseous reaction products to a liquid consisting of pivaloyl chloride and aroyl chloride of formula (2), - washing the uncondensed gaseous reaction mixture therefrom containing gaseous hydrogen chloride countercurreatly with a trichloromethylaromatic compound of fonnula I to remove hydrochloric acid therefrom, - recycling said trichloromethyl aromatic compoud of formula I from the washing region to said reaction region, - continuously extracting a liquid mixture from the bottom of said reaction region which is subjected to reactive distillation in a known manner to separate and isolate pivaloyl chloride and the aroyl chloride therefrom in a known manner. The example which follows illustrates the invention. EXAMPLE 130 kg/h of pivalic acid, with 0.5 kg/h of a 40% by weight aqueous FeCl3 solution and 285.3 kg/h of a phenylchlorofonn flow comprising 35,5 kg/h of pivaloyl chloride, are continuously introduced, with stirring and under a pressure of 133 mbar, into a 2.5 m3 glass-lined reactor maintained at 135°C, under stabili2ed conditions, comprising a mixture which comprises benzoyl chloride, phenylchloroform and benzoic anhydride. Under these conditions, the pivaloyl chloride is immediately formed and evaporated, as well as a portion of the benzoyl chloride. The gaseous reaction products are continuously extracted at the top of the reactor and are carried into a small separating column equipped with a structured packing of 6 theoretical plates, where they are separated from the unconverted reactants. The unconverted reactants return to the reactor. After condensation of the mixture of gaseous products, extraction is continuously carried out of, on the one hand, a liquid mixture composed of 147.7 kg/h of pivaloyl chloride, of 82.8 kg/h of benzoyl chloride and of 0.9 kg/h of tert-butyl chloride, which is conveyed to a storage tank in order to be subsequently subjected to a distillation which makes it possible to recover pivaloyl chloride having a purity of greater than 99.5%, and, on the other hand, a gas flow composed of 47.8 kg/h of hydrogen chloride (HCl gas), of 35.6 kg/h of pivaloyl chloride and of 2,7 kg/h of tert-butyl chloride, which is evacuated by a liquid ejector and conveyed into a washing column packed with 9 theoretical plates, in which column the hydrogen chloride is washed countercurrentwise with 200 kg/h of phenylchloroform at 10°C. 47.5 kg/h of HCl gas are recovered at the top of this washing column and are conveyed over a falling film isothermal absorber, where they are absorbed by 95.5 kg/h of water to form 144.9 kg/h of a 33% by weight aqueous HCl solution. At the bottom of the washing region, the phenylchloroform, which has absorbed the organic compounds present in the gas flow introduced into the said washing column, is conveyed into the reactor; it forms a portion of the 285.6 kg/h of phenylchloroform employed. At the reactor bottom, 102,3 kg/h of a liquid mixture are continuously extracted, which mixture comprises 55.6 kg of benzoyl chloride, 16.9 kg of phenylchloroform, 21.3 kg of benzoic anhydride, 2.8 kg of pivaloyl chloride. 1.4 kg of benzoic acid, catalyst and heavy residues related to the impurities in the phenyl-chloroform employed. This liquid mixture is discharged into a storage tank and is then subjected to a reactive distillation, in a column with 20 theoretical plates, under reduced pressure at a temperature of between 120°C and 150°C and in the presence of 0.1% by weight of FeCl3 with respect to the weight of the mixture. The residual pivaloyl chloride and then benzoyl chloride with a purity of greater than 99.9%, emerge at the top of this column. The heavy products are removed by incineration. After the distillation operations, the pivaloyl chloride and benzoyl chloride yields are greater than 96.8% and 97% respectively. The hydrochloric acid obtained in this process is a 33% aqueous HCl solution of commercial grade. WE CLAIM: 1. A continuous process for the simultaneous preparation of pivaloyl chloride and an aroyl chloride of formula (2) by reaction, in the presence of at least one catalyst of Friedel-Crafts type, of pivalic acid with a trichloromethylated aromatic compound of formula (1) according to the reaction: in which the each R, which may be the same or different, represents a halogen atom, a linear or branched alkyl radical containing from 1 to 4 carbon atoms, a linear or branched perfluoroalkyl radical containing from 1 to 4 carbon atoms or a -COCl radical, m represents 0, 1 or 2 and D represents 1,2 or 3 and in which the -CCI3 groups are situated on non-adjacent carbon atoms when n > 1, which process comprises: - simultaneously and continuously introducing pivalic acid, at least one trichloromethylated aromatic compound of formula (1) and at least one catalyst of Friedel-Crafts type into a reaction region and reacting them with stirring and under below atmospheric pressure at a temperature of between 60°C to 180oc, - continuously separating the gaseous reaction products exiting at the top of said reaction region from the unconverted reactants, - partially condensing said gaseous reaction products to a liquid consisting of pivaloyl chloride and aroyl chloride of formula (2), - washing the uncondensed gaseous reaction mixture therefrom containing gaseous hydrogen chloride countercurrently with a trichloromethylaromatic compound of formula I to remove hydrochloric acid therefrom, - recycling said trichloromethyl aromatic compoud of formula I from the washing region to said reaction region, - continuously extracting a liquid mixture from the bottom of said reaction region which is subjected to reactive distillation in a known manner to separate and isolate pivaloyl chloride and the aroyl chloride therefrom in a known manner. 2. The process as claimed in claim 1, in which the or each R represents fluorine, chlorine or bromine. 3. The process as claimed in claim 1 or 2, in which the reactive distillation is carried out in the presence of an additional amount of catalyst of Friedel-Crafts type. 4. The process as claimed in any one of claims 1 to 3, in which the temperature in the reaction region is between 120oC and 150o. 5. The process as claimed in any one of the preceding claims, in which the reaction is carried out in the reaction region under a reduced pressure at most equal to 500 mbar. 6. The process as claimed in claim 5, in which the reaction is carried out in the reaction region under a reduced pressure of between 100 mbar and 400 mbar. 7. The process as claimed in any one of the preceding claims, in which the reaction is carried out with a molar ratio: 8. The process as claimed in claim 7, in which the molar ratio is between n and 1.03n. 9. The process as claimed in any one of preceding claims, in which the catalyst of Friedel-Crafts type is a Lewis acid. 10. The process as claimed in claim 9, in which the Lewis acid is FeCI3. 11. The process as claimed in claim 9 or 10, in which the molar amount of Lewis acid used is between 0.01% and 1%, with respect to the amount of pivalic acid employed. 12. The process as claimed in claim 11, in which the molar amount of Lewis acid used is between 0.05% and 0.2%, with respect to the amount of pivalic acid employed. 13. The process as claimed in any one of claims 1 to 8, in which the catalyst of Friedel-Crafts type is a Bronsted acid. 14. The process as claimed in claim 13, in which the Bronsted acid is sulphuric acid. 15. The process as claimed in claim 13 or 14, in which the molar amount of Bronsted acid used is between 0.1% and 5%, with respect to the amount of pivalic acid employed. 16. The process as claimed in any one of the preceding claims, in which the trichloromethylated aromatic compound of formula (1) used in the washing region is completely introduced into the reaction region. 17. The process as claimed in any one of the preceding claims, in which the trichloromethylated aromatic compound of formula (1) is trichloromethylbenzene (or phenylchloroform). 18. The process as claimed in any one of the preceding claims, in which the gaseous hydrogen chloride exiting the washing region is absorbed in water. 19. A continuous process for the simultaneous preparation of pivaloyt chloride and aroyl chloride substantially as herein described.

Documents:

2851-mas-1998 abstract.pdf

2851-mas-1998 claims.pdf

2851-mas-1998 correspondence others.pdf

2851-mas-1998 correspondence po.pdf

2851-mas-1998 description (complete).pdf

2851-mas-1998 form-2.pdf

2851-mas-1998 form-26.pdf

2851-mas-1998 form-3.pdf

2851-mas-1998 form-4.pdf

2851-mas-1998 form-6.pdf

2851-mas-1998 petition.pdf