Patent GB-818302-A (GB)
Title: Process for the production of phthalic acids and formic acid
IPC: C07C27/12
Filed: 1955-11-07
Abstract: In a process for the production of a phthalic acid and formic acid by the oxidation in the liquid phase with molecular oxygen in the presence of a heavy metal oxidation catalyst of a dialkyl benzene having one alkyl with from 1 to 4 carbon atoms and the other alkyl with from 2 to 4 carbon atoms, the carbon atom of each alkyl attached directly to the ring having at least one hydrogen substituent, the formic acid and water formed are removed from the reaction mixture as the oxidation proceeds to an extent which at least ensures that the formic acid content of the reaction mixture is maintained below 5 per cent by weight and the water content of the reaction mixture is maintained below 10 per cent by weight. In a modification of the process the dialkyl benzene is pre-oxidized to intermediates with molecular oxygen and these intermediates are subsequently oxidized to phthalic acid with molecular oxygen in the presence of the heavy metal oxidation catalyst, formic acid and water being removed in each oxidation step to maintain the formic acid and water concentrations in the reaction mixture below 5 per cent by weight and 10 per cent by weight respectively.  The process is preferably carried out in the presence of a saturated aliphatic mono-carboxylic acid having from 2 to 6, especially 2 to 4, carbon atoms.  Catalysts specified include manganese salts, e.g. a manganese halide, e.g. the bromide or a stoichiometric mixture of manganese acetate and ammonium bromide, a manganese salt of a carboxylic acid, e.g. of a mono-carboxylic acid having from 2 to 10 carbon atoms or of the carboxylic acid formed or manganese toluene sulphonate.  Dialkyl benzenes mentioned for use as starting materials include m- and p-ethyl -, propyl -, iso - propyl, butyl and isobutyl toluenes. The starting material may contain some iso-meric materials, lower or higher homologues and saturated aliphatic or hydrocarbon materials of similar boiling ranges relatively resistant to oxidation in the process of the invention. Mixtures of hydrocarbons may be converted to mixtures of phthalic acids which may be separated by esterification and fractionation. Elevated pressures may be employed and where a lower mono-carboxylic acid is included in the reaction mixture the liquid phase should contain some of said acid.  The reaction may be carried out batchwise or continuously and liquid remaining after separation of the product may be recycled.  In examples: terephthalic acid and formic acids are obtained by treating p-cymene in the presence of acetic acid and manganese bromide with air at 180 DEG  C. under a pressure of 3-400 p.s.i.g. in a reactor fitted with a reflux condenser, the condensate from which is passed to a separatory device in which formic acid and water are removed from the condensate to be recycled to the reactor so as to maintain the concentration of each below 5 per cent by weight of the reaction mixture; the crude terephthalic acid is washed with acetic acid and water; in a comparative run, all the condensate is returned to the reactor (1); in similar processes terephthalic acid is obtained from p-diethyl benzene, p-n-propyl toluene, p-n-butyl toluene, and p-i-butyl toluene, isophthalic acid is obtained from m-cymene, m-diethyl benzene, m-n-propyl toluene, m-n-butyl toluene and m-i-butyl toluene, and phthalic acid from o-cymene, o-diethyl benzene, o-n-propyl toluene, o-n-butyl toluene and o-i-butyl toluene.  Phthalic acid may be converted to the anhydride and sublimed.  The crude phthalic acids may be esterified with an alkanol containing 1-3 carbon atoms in the presence of hydrochloric, sulphuric or phosphoric acid, e.g. in amount up to about 3 per cent of the reaction mixture or the acids may be converted to the corresponding acid chlorides and reacted with methanol.  The ester products may be fractionated or steam distilled. The dimethyl esters may be hydrolysed with aqueous acid to the free acids.  The esters may be employed in the preparation of polyester resins, e.g. by reaction with ethylene glycol or glycerol.