GB1318795A - Manufacture of cyclohexadiene-dioic acids - Google Patents

Abstract

1318795 Cyclohexadiene dioic acids BADISCHE ANILIN- & SODA-FABRIK AG 22 Oct 1970 [23 Oct 1969] 50117/70 Heading C2C [Also in Division C7] 3,5-Cyclohexadiene-1,2-dioic acid and 2,5- cyclohexadiene-1,4-dioic acid are prepared by the electrochemical reduction of o-phthalic acid and terephthalic acid respectively in a cell wherein the anode and cathode chambers are separated by a diaphragm, using a catholyte containing an organic solvent, the flow of electrolysis current being periodically broken and the electrolytic cell short-circuited. Typically the catholyte contains 5-25 wt. per cent phthalic acid, 40-80% of organic solvent (ethers, carboxamides, and/or nitriles, e.g. dioxane, tetrahydrofuran, glycolmonoethylether, dimethylformamide or acetonitrile), 5-40% H 2 O, and 1-20% H 2 SO 4 ; the anolyte is 2-20% H 2 SO 4 . The diaghragm may be an ion-exchange material or plastic tissue; the anode Pb, PbO 2 , graphite or a platinum metal, and the cathode Pb. A current density of 1-30 A/dm<SP>2</SP> and a temperature of 20-70‹ C. may be used, the current being interrupted and shortcircuiting taking place for 5 sec.-15 min. every 6 min.-20 hrs.; the ratio electrolysis period: no current period being 10,000 : 1 to 100 : 5. At intervals the current may be reversed at 1/100 to 1/5 of working value instead of the above-mentioned cessation. In an embodiment, six bipolar plate-shaped Pb electrodes are connected in series (and optionally water-cooled) with sulphonated polystyrene diaphragms between anodes and cathodes; the cathode chambers are connected in series to permit continuous pumping of catholyte; the product is recovered by evaporation of the organic solvent and filtration.