GB809452A - Oxidation of fatty acids - Google Patents

Abstract

A mono-carboxylic acid and a dicarboxylic acid are produced by adding a dihydroxy saturated higher fatty acid, produced by the partial oxidation of an ethylenically unsaturated higher fatty acid as hereinafter defined, to a reaction liquid comprising a quantity of said unsaturated acid undergoing oxidation by reaction with oxygen, the dihydroxy acid being added in small quantities such that the concentration thereof in the reaction liquid is never high enough to stop the oxidation reaction. The unsaturated higher fatty acid referred to above is a mono-carboxylic acid containing at least 10, preferably not more than 24, carbon atoms, and also containing at least one ethylenically unsaturated linkage, there being no ethylenic linkages conjugated with the carbonyl of the carboxylic acid radical. Examples of such acids are oleic acid, palmitoleic, petroselinic, erucic and linoleic acids. The acids may be in commercially pure form or in the form of materials containing such acids, such as foots oil. The amount of dihydroxy acid added initially may be from 1 to 5 per cent by weight and subsequent additions may be successively larger until, after the reaction has been under way for some time, the concentration of dihydroxy acid in the reaction liquid is about 10 per cent. The oxidation during the addition of the dihydroxy acid may be carried out under the conditions as regards nature and concentration of catalyst, temperature and the ratio of unsaturated acid to solvent as described in Specification 809,451 except that any suitable solvent may be present in the reaction liquid, such as benzene or propanol. Advantageously the oxidation is carried out until 50 to 95 per cent, preferably 60 to 80 per cent, of the unsaturated fatty acid has been oxidized. The solvent may be removed by distillation, together with acetic and propionic acids formed when propanol is used as solvent, any esters present are saponified, as by refluxing with aqueous sodium hydroxide, the mixture is then acidified, e.g. with sulphuric acid, and the acidified mixture is extracted with ether. The ethersoluble carboxylic acids are reacted with ethyl or methyl alcohol and separated by fractional distillation under sub-atmospheric pressure. Alternatively, after distilling off the ether from the extract, the monocarboxylic acid is fractionally distilled from the mixture and the dicarboxylic acid is recovered by extracting the residue with hot water followed by cooling or evaporation to crystallise the acid therefrom. In an example, technical oleic acid in solution in propanol in the presence of cobalt naphthenate is oxidized by bubbling air through the liquid maintained at 81 DEG C. and after the oxidation has begun, 9,10-dihydroxystearic acid is added in small increments over the entire reaction period in such a manner that the concentration thereof in the mixture never exceeds 5 per cent by weight. After 140 hours the mixture is worked up to obtain pelargonic acid and azeleic acid.