Patent GB-785072-A (GB)
Title: Improvements in or relating to the preparation of aromatic carboxylic acids
IPC: C07C51/265
Filed: 1955-05-25
Abstract: A process for preparing an aromatic carboxylic acid comprises oxidizing an alkylsubstituted aromatic hydrocarbon or an alkyl-substituted aromatic monocarboxylic acid as defined below or alkyl ester thereof in the liquid phase with molecular oxygen or a molecular oxygen-containing gas and in the presence of a saturated aliphatic hydrocarbon which is also oxidized by said molecular oxygen or molecular oxygen-containing gas wherein the proportion of saturated aliphatic hydrocarbon in the reaction mixture is at least 40 per cent by weight of the aromatic reactant present therein.  The aromatic starting materials are those compounds of the kind specified which contain one or more oxidizable substituents and derivatives thereof which contain substituents in the ring or alkyl side chain which are not themselves oxidized and which do not inhibit the oxidation of the alkyl groups.  Specific compounds mentioned include the xylenes, toluene, diethyl benzenes, cumenes, cymenes, mesitylene, prehnitene, durene, isodurene, o-, m- and p-diisopropylbenzene and derivatives thereof containing substituents such as nitro and sulphonic groups, halogen atoms, carboxyl, hydroxyl and other alkyl groups, toluic, tertiary-butyl benzoic, mesitylenic, o, m- and p-isopropyl benzoic acids and alkyl esters thereof, preferably in which the alkyl groups have not more than 8 carbon atoms.  Aliphatic hydrocarbons specified include straight and branched chain alkanes, e.g. from ethane to decane.  Mixtures of aliphatic hydrocarbons may be used such as gasoline or liquid petroleum fractions free from aromatic hydrocarbons.  Organic liquids which may be present in the reaction mixture include benzene, tert.-butylbenzene, chlor- and p-dichlorobenzene, aliphatic carboxylic acids, e.g. acetic and propionic acids and methyl and ethyl esters of such acids, aliphatic ketones such as di-isobutyl ketone, aliphatic and aromatic nitriles such as aceto- and benzonitriles.  Catalysts may be employed, e.g. compounds or complexes, either organic or inorganic, of heavy polyvalent metals, e.g. the organic or inorganic salts, oxides, chelates or complexes of polyvalent metals of atomic number from about 23 to about 82.  Specified metals of which the salts or other compounds are suitable include cobalt, manganese, vanadium and chromium.  Specific compounds mentioned include the chloride of vanadium, cobalt and manganese, acetates of ferric iron, cobalt, zinc, bismuth, manganese lead and copper, naphthenates of these metals, cobalt and barium permanganates and mixtures thereof may be employed.  Preferred catalysts include cobalt p-toluate, naphthenate, stearate, octoate, salicylate, acetonate or isovalerylacetonate. Water may be removed from the reactor during the reaction by venting vapours evolved and returning any organic component to the reactor or inert dehydrating agents may be employed in the reaction zone. Elevated temperatures and pressures may be employed.  In examples, terephthalic acid and some p-toluic acid are obtained by passing air into a heated mixture of p-xylene and n-octane (I); terephthalic acid is obtained by oxidizing a mixture of p-toluic acid, n-octane and cobalt naphthenate with air at 130 DEG  C. (II); the monomethyl ester of terephthalic acid is obtained by oxidizing at 130 DEG  C. p-methyl toluate in the presence of n-decane and cobalt stearate with air (III); and a dibasic acid is obtained in a similar process when a mixture of pseudocumene and n-decane is oxidized.