A unique autocatalytic process and evidence for a concerted-stepwise mechanism transition in the dissociative electron-transfer reduction of aryl thiocyanates.
Electrochemical reduction of p-methyl-, p-methoxy-, and 3,5-dinitrophenyl thiocyanates as well as p-methyl- and p-methoxyphenyl disulfides was investigated in acetonitrile at an inert electrode. This series of compounds reveals a striking change in the reductive cleavage mechanism of the S-CN bond in thiocyanates as a function of the substituent on the aryl ring of the aryl thiocyanate. With nitro substituents, a stepwise mechanism, with an anion radical as the intermediate, takes place. When electron-donating groups (methyl and methoxy) are present, voltammetric as well as convolution analyses provide clear evidence for a transition between the concerted and stepwise mechanisms based on the magnitude of the transfer coefficient alpha. Moreover, a very interesting autocatalytic process is involved during the electrochemical reduction of these compounds. This process involves a nucleophilic substitution reaction on the initial aryl thiocyanate by the electrochemically generated arenethiolate ion. As a result of this unusual process, the electrochemical characteristics (peak potential and peak width) of the investigated series are concentration dependent.
Houmam
Abdelaziz
A
Electrochemical Technology Centre, Department of Chemistry and Biochemistry, University of Guelph, Guelph, Ontario, Canada N1G 2W1. houmam@chembio.uoguelph.ca
Hamed
Emad M
EM
Still
Ian W J
IW
D001555:Benzene Derivatives / Q000737:chemistry; D002384:Catalysis; D004220:Disulfides / Q000737:chemistry; D004563:Electrochemistry / Q000379:methods; D007700:Kinetics; D010084:Oxidation-Reduction; D013816:Thermodynamics; D013861:Thiocyanates / Q000737:chemistry*
D001555:Benzene Derivatives; D004220:Disulfides; D013861:Thiocyanates