Oxidation of Thiols by Molecular Oxygen in Tetramethylguanidine

Abstract

THE formation of stable alkylammonium thiolate salts from the reaction of benzenethiol with p-, sec-, and tert-aliphatic amines was first observed by Gordy and Stanford1 and further substantiated by Grillot and Brooks2. Subsequent work has demonstrated that: (a) the formation of alkylammonium thiolates from the reaction or aromatic and arakyl thiols with aliphatic amines is a general reaction; (b) that aliphatic amines catalyse the oxidation of thiols by molecular oxygen in hydrocarbon solvents3. The latter suggests that the active species in these oxidations is the thiol anion (RS ⊝). Recent investigations in these laboratories have demonstrated that dipolar solvents markedly accelerate the base-catalysed oxidation of thiols4. This finding coupled with the foregoing results suggested that tetramethylguanidine (TMG) would be capable of functioning simultaneously as both a solvent and a base for thiol oxidations. This was found to be true.