GB1012237A - A process for the preparation of carboxylic acids - Google Patents

Abstract

Mono or dicarboxylic acids of the general formula <FORM:1012237/C2/1> wherein R1, R2 and R3 are organic groups bound with a carbon atom to the carbon atom indicated, and n is 1 or 2 with a proviso that when n is 2 the groups R1, R2 and R3 need not be identical and that at least one of the groups may be a valency bond, are made by a process which comprises contacting a ketone having the general formula <FORM:1012237/C2/2> with molecular oxygen or a molecular oxygen containing gas in the liquid phase, and in the presence of an acid having a dissociation constant not higher than 10-3, and an oxidation catalyst which is preferably a salt or a mixture of salts of cobalt, manganese and/or cerium. One of the R groups is preferably an unsubstituted aromatic nucleus or such a nucleus substituted with one or more hydroxyl groups, alkyl groups containing up to four carbon atoms, or halogen atoms, most preferably a benzene nucleus. A further class of starting materials comprises those wherein the R groups ar halogen substituted or unsubstituted alkyl groups having up to eight carbon atoms each for example methyl, ethyl, isopropyl or octyl groups. A further suitable starting material has a general formula. <FORM:1012237/C2/3> wherein R represents a hydrogen atom, a halogen atom, a hydroxyl group or an alkyl group having up to six carbon atoms, especially a methyl, ethyl or isopropyl group. One of R groups in the first formula may have the form Ar-R1-Ar1 wherein Ar's are OH, alkyl, halogen substituted or unsubstituted aryl groups and R1 may be -O-, -CO-, -SO2-, or -C(CH3)2-, the especially suitable being symmetrical as represented by the formula <FORM:1012237/C2/4> The amount of acid used in the reaction is preferably at least n gram-equivalents of the acid per mole of the ketone, n having the same value as in the formula of the ketone use. The acid may be a halogen substituted or unsubstituted carboxylic acid having not more than 10 carbon atoms in the molecule, especially acetic acid. Other preferred features of the reaction include the use of anhydrous conditions, a temperature not higher than 200 DEG C. especially within the range of 50-160 DEG C. In the examples beta-methyl-beta-phenylbutyric acid is prepared starting from 4-methyl-4-phenyl-2-pentanone using manganese triacetate in glacial acetic acid medium. The methyl ester of the product is obtained by esterification under the influence of hydrogen chloride. As by-product 2-methyl-2-(o-carboxyphenyl) propanal is obtained. In the preparation of beta - methyl - beta - (p - tolyl)-butyric acid, from 4-methyl-4-(p-tolyl)-2-pentanone using manganese triacetate and glacial acetic acid 2 - methyl - 2 - (p - methyl - o-carboxyphenyl) propanal is obtained as by-product. Similarly 4-methyl-4-(p-bromophenyl)-2-pentanone is converted to beta-methyl-beta-(p-bromophenyl) butyric acid and 1,4-bis-(1,1-dimethyl-3-oxo-butyl) benzene is converted to 1,4 - bis - (1,1 - dimethyl - 2 - carboxyethyl)-benzene and the latter was converted to the dimethyl ester.