Process for the cleavage of thiol esters of aromatic carboxylic acids

摘要

1,146,692. Clearing thiol esters by electrolysis. FARBWERKE HOECHST A.G. Feb.25, 1966 [Feb.25, 1965], No.8433/66. Heading C7B. Thiol esters of aromatic carboxylic acids are cleared to yield thiols by electrolytically reducing a compound of the formula R - CO - S - R1 where R is a phenyl radical optionally substituted by a C 1 to C 4 alkyl radical, a C 1 to C 6 alkoxy radical or halogen, and R1 is either a C 1 to C 8 alkyl radical a C 5 to C 8 cycloalkyl radical, a phenyl or phenyalkyl radical which may be substituted by a C 1 to C 4 alkyl radical or the radical of an amino acid or a peptide, in the presence of tetra-alkyl ammonium salts. The anode may be of boron carbide or another carbide or of graphite and the cathode may be of lead, iron, platinum or mercury. Typically electrolysis is effected in a cell having a layer of mercury on the bottom of the vessel as the cathode, a porous diaphragm containing a graphite anode and a cooling system being disposed at a distance of 0À5 to 1 cm from the mercury surface. The substance to be cleared e. g. 5-benzoyl- ; l -cystein together with an excess of tetra-alkyl ammonium salt e.g. (CH 3 ) 4 NCl, in methanol a mixture of water and other organic solvent e.g. dimethyl acetamide is placed in the vessel as catholyte and the space within the diaphragm surrounding the anode is filled with water and the whole is cooled, e.g. to 5‹C., electrolysis being carried out at 5 to 10‹C. with an applied potential of 20 volts at a current of 1 amp. Methods of separating the thiols from the catholyte are described.