Catalytic Rearrangement of O, S-Dialkyl Dithiocarbonates to S, S-Dialkyl Dithiocarbonates by Pyridine N-Oxides.The Reaction Mechanism

Abstract

The reaction of O-alkyl S-methyl dithiocarbonates (xanthates) (I) with pyridine N-oxides (II) gave the corresponding S-alkyl S-methyl dithiocarbonates (dithiolcarbonate) (III) together with the symmetric S, S-dialkyl and S, S-dimethyl dithiocarbonates in good yieds. Pyridine N-oxides bearing electron-donating substituents are efficient catalysts for rearrangement of I to III.The reaction is pseudo-first-order and the apparent first-order rate constant is proportional to the concentration of II.The role of pyridine N-oxides and the reaction behavior of O, S-dialkyl dithiocarbonates are discussed on the basis of kinetic and molecular orbital calculation data.The rearrangement may proceed by nucleophilic attack of ^-SCOSR derived from a complex of I and II on the O-alkyl group of xanthates.The reaction provides a useful preparation method for alkanethiols by aminolysis of the products with ethanolamine.