Electrosynthesis of sulfur-containing organic compounds from cumulene derivatives using a sacrificial sulfur-graphite electrode

Electrosynthesis of sulfur-containing organic compounds from cumulene derivatives was studied using a sacrificial sulfur-graphite electrode. 1,1-Di-p-chlorophenylbuta-1,2,3-triene (1a),1,1-di-p-chlorophenyl-4,4-di-p-methylphenylbuta-1,2,3-triene (1b), 1,1,4,4-tetraphenylbuta-1,2,3-triene (1c) and 1,1-di-p-methoxyphenyl-4,4-diphenylbuta-1,2,3-triene (Id) were used as cumulenes. With la, Lb and Ic, 7-membered ring compounds with five sulfur atoms such as pentathiepins 2a, 2b and 2c were produced as the major products accompanied with dimeric compounds 3a, 3b and 3c which had a 1,2,5,6-tetrathiocin skeleton in minor amounts, respectively. However, Id, which is the most difficult to be reduced among the cumulenes studied, did not give sulfur-containing organic compounds. Yields of 2a, 2b and 2c decreased a little by the addition of a proton donor such as benzoic acid. Main products 2 will be initiated by a Michael addition of the polysulfide anion(s) (S-8(2-) and/or S-6(2-)) produced by electroreduction of elemental sulfur. By-products 3 will be probably produced by further reaction of 2 with the polysulfide anion(s). (C) 1997 Elsevier Science Ltd.