GB813842A - Improvements in or relating to the production of aliphatic mono-and di-carboxylic acids - Google Patents

Abstract

Saturated mono- and di-carboxylic acids are prepared by oxidizing ethylenically unsaturated fatty acids containing at least 12 carbon atoms in a first stage by means of molecular oxygen to produce saturated mono- and di-carboxylic acids, terminating this stage while further oxidation is still possible and effecting further oxidation in a second stage with nitric acid, substantial oxidation taking place in both stages and the second stage being continued to achieve a substantial increase in yield of saturated mono-and di-carboxylic acids. The first stage may be carried out by passing air or other gas containing free oxygen, preferably under pressure, through a solution of the unsaturated fatty acid in a solvent such as acetic acid, benzene, propanol or an ester. An oxidation catalyst such as one containing Co, Mn, Cu or Cr, for example, cobalt acetate or naphthenate, may be present; alternatively, or in addition, an oxidation promotor, e.g. acetaldehyde, may be used. This oxidation may be effected at about 25-150 DEG C., preferably below 90 DEG C. It is preferably terminated when the unsaturation of the initial acid is reduced by 70-100 per cent, the oxidation products then comprising substantial amounts of mono- and di-carboxylic acids. The second stage may be effected by slowly adding the crude mixture from the first stage, freed from solvent, to nitric acid, preferably of 40-85 per cent strength and at 30-35 DEG C., followed by heating to about 100 DEG C. Nitric oxide formed may be re-oxidized with air to nitric acid either in situ or separately and reused. The final product forms an upper non-aqueous layer containing monocarboxylic acids and a lower aqueous layer of nitric acid and dicarboxylic acids. The lower layer may be chilled to crystallize the dicarboxylic acids. Preferably, the aqueous layer is extracted with, for example, cyclohexane or n-heptane to remove monocarboxylic acids; the extract and the upper non-aqueous layer are combined, extracted with water and then fractionated to recover monocarboxylic acids. The aqueous layer and the aqueous extract are combined and cooled to recover the dicarboxylic acids. In examples: (1) crude oleic acid in admixture with acetic acid, acetaldehyde and cobalt acetate is air oxidized at 65 p.s.i.g. at 54 DEG C. to reduce the unsaturation by about 96 per cent, the acetic acid is stripped off and the residue further oxidized with nitric acid and the products are worked up to recover pelargonic acid and C6-C9 dicarboxylic acids, mainly azelaic and suberic acids; small amounts of esters are also formed; (2) a mixture of oleic, linoleic and saturated acids from tall oil is similarly oxidized, yielding pelargonic acid, caproic acid and C6-C9 dicarboxylic acids; (3) as in (2) omitting the acetaldehyde; (4) crude tall oil is oxidized as in (1). Other unsaturated fatty acids mentioned are palmitoleic, petroselenic, linolenic and erucic acids acids and foots oil.