GB1342961A - Processes for preparing aromatic tetracarboxylic acids or anhydrides thereof - Google Patents

Abstract

1342961 Aromatic tetracarboxylic acids and anhydrides thereof FURUKAWA ELECTRIC CO Ltd 19 April 1971 [13 March 1970 14 Mareh 1970 4 April 1970 26 Oct 1970 5 Nov 1970 10 Dec 1970] 23879/71 Heading C2C An aromatic tetracarboxylic acid or an anhydride thereof is obtained by oxidizing with molecular oxygen an appropriate tetraalkylbenzene or derivative thereof in a medium of a C 2 to C 8 carboxylic acid, in the liquid phase and in the presence of a catalyst consisting of a heavy metal (present either as the free element or combined in a compound) and bromine (present either as the free element or combined in a compound), the catalyst containing from 8 to 40 parts by wt. promine (calculated as Br) and from 3 to 25 parts by wt. heavy metal (calculated as the metal) per 100 parts by wt. of the raw material to be oxidized. Examples of tetraalkyl benzenes are durene, isodurene, prehnitene, trimethylisopropylbenzene and dimethyldiisopropylbenzene. Examples of derivatives of tetraalkyl benzenes are 2,3-dimethyltetrahydronaphthalene, octahydroanthracene, a bis(chloromethy)xylene, a chloromethylpseudocumene, a chloromethylmesitylene, a bis(hydroxymethyl) xylene, a hydroxymethylpseudocumene, a monoformyltrimethylbenzene, a dimethylisophthalic acid or a trimethylbenzoic acid. Specified heavy metals are Co, Mn, Ni, Cr, V, Mo, W and Ce. Preferably the reaction temperature is maintained at 95‹ to 180‹ C. until the starting material is converted at least to monocarboxylic acid, and thereafter raising the temperature to 180‹ to 240‹ C. for further oxidation. Similarly the catalyst may be added to the reaction mixture in two stages, namely 10 to 60% in the first stage for formation of at least the monocarboxylic acid and the remainder for further oxidation. The heavy metal salts of the aromatic tetracarboxylic acids are suitably removed from the product by treating the reaction mixture with an aqueous solution of a strong acid, e.g. by boiling the reaction mixture, then cooling it by adding it to aqueous acid and collecting the precipitate of free aromatic tetracarboxylic acid. Examples are given for the preparation of pyromellitic acid, prehnitic acid, mellophanic acid and pyromellite dianhydride.