Patent GB-1051614-A (GB)
IPC: H01M8/08
Abstract: 1,051,614. Electrochemical oxidation of organic compounds. SEIMENS-SCHUCKERTWERKE A. G. & VARTA A. G. June 4, 1963 [June 2, 1962], No. 22129/63. Heading C7B. [Also in Division H1] In converting one organic compound into another by electrochemically substituting hydrogen by another atom or functional group by means of a reaction electrode the potential of which is maintained below the reversible oxygen potential to an extent such that no evolution of free oxidizing agent occurs, the process is interrupted when the desired reaction is attained by interrupting the external circuit of the electrode when a determined change in the potential of the electrode occurs. If the starting organic compound has a plurality of successively replaceable hydrogen atoms, when the first stage in the replacement of hydrogen has been completed the process may be continued either at the same operating potential of the electrode by increasing the reaction temperature or by withdrawing a determined quantity of electrolyte and converted organic compound into another reaction cell having a reaction electrode of greater catalytic activity than in the preceding stage. As shown, a mixture of glycerol and 6N KOH is fed from a reservoir 5 into a cell 4 having a reaction electrode 8 consisting of a nickel double-skeleton catalyst electrode of the kind described in Specification 806, 644 and a silver double-skeleton catalyst oxygen electrode 7 as in Specification 907, 907 operated with air supplied via pipe 9. A calomel reference electrode 10 is provided for the electrode 8 together with monitoring voltmeter and ammeter. The operating temperature is selected as 100C. When all the glycerol has been converted to dihydroxacetone a drop in the electrode potential occurs and the external circuit is interrupted and the electrolyte and compound produced are drained from the cell via an automatically controlled magnetic valve 11 which closes again when the cell is empty. Some of the mixture is collected in a reservoir 12 and the remainder is fed into a second cell 2 where it is held at 100C and reaction is effected with a reaction electrode of the kind used in cell 1 but incorporating nickel granules and a Raney silver counter electrode operated with oxygen. A drop in the reaction potential indicates conversion of the dihydroxyacetone to hydroxyacetyl formic acid and the external circuit is again interrupted and the cell 2 automatically emptied, the contents being divided between reservoir 14 and cell 3. Cell 3 is operated at 110C with a reaction electrode formed by pouring palladinized carbon particles between small mesh gauzes, a nickel plate counter-electrode 15 and a battery 16, the product being anhydrous mesoxalic acid. For the oxidation of ethylene glycol in 5À2N KOH to glycollic acid, the temperature is 23C, the reaction electrode is a catalyst sieve electrode filled with Raney nickel, and the counter electrode is an oxygen electrode consisting of a compressed mixture of polythene and carbon with the layer adjacent the electrolyte containing silver oxide. A voltage drop from 1v. to 0À69v. indicates completion of the reaction. On increasing the temperature to 90C the electrode voltage is restored to 1v. and the glycolic acid is converted to oxalic acid. Reference is made to oxidizing nitrobenzenes, 1:2:3 triazoles, pyrrole and carboxylic acids and to the use of hydrohalic acids as electrolyte when the substitution is effected by halogen atoms. For alkaline electrolytes, catalyst materials specified in order of decreasing activity are (1) Raney nickel or palladinized carbon, (2) cobalt powder, (3) carbonyl nickel activated with boranates, (4) nickel powder; while catalysts specified for acid electrolytes are finely divided platinum or iridium, e.g. platinized carbon.