GB798619A - Oxidation of aralkyl compounds to aromatic carboxylic acids - Google Patents

Abstract

Aromatic mono and dicarboxylic acids are prepared by the oxidation of one or more alkyl radicals of an aralkyl compound (as defined below) in acetic acid, in the presence of a cobaltous catalyst, ozone being used as an initiator of the reaction and oxygen being passed through the reaction mixture, which is maintained at a temperature of from about room temperature to 130 DEG C. The term "aralkyl compound" is used to denote organic compounds containing an aromatic nucleus, e.g. benzene, naphthalene, which is substituted with one or more alkyl radicals, e.g. methyl, ethyl, propyl, butyl or octyl, and which may also be substituted with radicals containing oxygen. Specified starting materials are toluene, o-xylene, m-xylene, p-xylene, methyl benzene, mesitylene, ethyl benzene, a -methyl naphthalene, p-toluic acid, p-methoxy toluene and 5-t-butyl-m-xylene. Suitable catalysts are cobaltous acetate tetrahydrate, cobaltous propionate, cobaltous formate, cobaltous butyrate, cobaltous toluate, cobaltous terephthalate, and cobaltous naphthenate. Suitable concentrations of the catalyst are from 0.001 to 0.3 parts by weight of the cobaltous catalyst per part of acetic acid, and the starting mixture preferably contains 0.01 to 0.5 parts by weight of the aralkyl compound per part of acetic acid. The amount of ozone necessary to initiate the oxidation reaction is very minute and may be less than 0.04 parts by weight of ozone per part of the cobaltous catalyst. The rates of oxygen and ozone addition may vary within any desired limits, e.g. 0.04-0.1 parts per hour of ozone per part catalyst, and 0.01 to 1 part by weight of oxygen per hour, per part of aralkyl compound. Inert gases may be present as diluents for the oxygen, e.g. helium, neon, xenon, krypton and argon, or air alone may be used. The reaction may be carried out at subatmospheric, atmospheric or super atmospheric pressures, preferably at the reflux temperature of the reaction mixture, i.e. 110-115 DEG C. The water formed during the reaction is preferably removed, e.g. by distillation when it reaches an excess of about 0.1 part by weight per part of acetic acid. The process of the invention is carried out by adding the aralkyl compound, acetic acid and cobaltous catalyst to a suitable reaction vessel and heating to the reaction temperature when ozone and oxygen are passed into the reaction mixture. The reaction is self sustaining after the solution turns green and no more ozone need then be added. Examples are given of the preparation of terephthalic acid, p-toluic acid, iso-phthalic acid, m-toluic acid, o-phthalic acid, o-toluic acid, benzoic acid, p-methoxy benzoic acid, 5-methylisophthalic acid, 3,5-dimethyl benzoic acid, t-butyl toluic acids, and 5-t-butyl isophthalic acid.