Copper(II) Catalyzed Oxidation of Aliphatic Thiols (Thioglycolic Acid and 2-Mercaptoethanol) by Heteroleptic Co(III)-Bound Superoxo Complex

Abstract

In aqueous acid media (0.02-0.06 M), two aliphatic thiols (RSH) viz. thioglycolic acid (TGA) and mercapto ethanol (MERCAP) were oxidized by heteroleptic metal bound superoxo complex, [(dien)(en)CoIII(O2)CoIII(en)(dien)]5+ (1) (en = ethylenediamine, NH2CH2CH2NH2 and dien = diethylenetriamime, NH2(CH2)2NH(CH2)2NH2) to the corresponding disulphides. Complex 1 is reduced to its corresponding peroxo complex, [(dien)(en)CoIII(O2)CoIII(en)(dien)]4+ (2) in these reactions. The oxidation of both thiols were dramatically catalyzed by the presence of Cu2+ ion. The observed rate constant ko was found to be proportional to [RSH]2 and [Cu]T 2 (where [Cu]T is the analytical concentration of Cu2+). The rate of reaction decreases with increasing ionic strength (I) of the reaction media and ko is also proportional to [H+]2–. The experimental observation suggests that a 1:2 anionic complex formed between Cu2+ and RSH participates in the redox cycle.