GB809451A - Oxidation of fatty acids - Google Patents

Abstract

A monocarboxylic acid and a dicarboxylic acid are produced by oxidation with molecular oxygen of an ethylenically unsaturated higher fatty acid containing at least ten, preferably not more than twenty-four, carbon atoms and also containing at least one ethylenically unsaturated linkage, there being no ethylenic linkages which are conjugated with the carbonyl group of the carboxylic acid radical, wherein said fatty acid is oxidised while in solution in propanol. Suitable unsaturated acids are oleic acid, palmitic, petroselinic, erucic, and linoleic acids, which may be in pure form, or materials containing them, such as foots oil, may be used. The ratio of fatty acid to propanol may vary from 2 : 1 to 1 : 10, ratios of 1 : 2 or 1 : 3 to 1 : 5 being preferred. The oxidation is conveniently effected by passing air, or other gas containing molecular oxygen, through a solution of the fatty acid in propanol, preferably in the presence of an oxidation catalyst, such as a catalyst containing cobalt, manganese, copper or chromium, e.g. cobalt acetate or cobalt naphthenate. The oxidation may take place at temperatures of from 25 DEG to 150 DEG C., preferably between 80 and 90 DEG C. If desired, the reaction may be started at a temperature above 90 DEG C., e.g. 150 DEG C., to reduce the induction period and after the reaction has begun the temperature may be reduced to the desired range. The reaction may also be started in the presence of 5 to 20 per cent of the reaction products obtained by a previous oxidation. The oxidation is advantageously continued until about 50 to 95 per cent, preferably 60 to 80 per cent, of the unsaturated fatty acid has been oxidized. The products may be isolated by distilling off the solvent together with acetic and propionic acids formed, and saponifying any esters present by refluxing with aqueous sodium hydroxide. The mixture is then acidified, e.g. with sulphuric acid, and extracted with ether which also results in the precipitation of a dihydroxy carboxylic acid by-product. After evaporation of the ether, the carboxylic acids are reacted with ethyl or methyl alcohol and the resulting esters are fractionated under reduced pressure. Alternatively, after evaporation of ether, the mixture is fractionally distilled to recover, in the case of oleic acid oxidation, pelargonic acid and the azelaic acid may be extracted from the residue with hot water. The dihydroxy acid by-product may be further oxidized to form the same mono- and di-carboxylic acid as described in Specification 809,452. Examples describe the oxidation of oleic acid in n-propanol by passing air through the solution, in the presence or absence of cobalt naphthenate, to give pelargonic acid, azelaic acid and 9,10-dihydroxy stearic acid.