6533b836fe1ef96bd12a1c7b

RESEARCH PRODUCT

The electrochemical reduction of thioisonicotinamide in an aqueous medium

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Abstract The electrochemical reduction of thioisonicotinamide NRCSNH 2 has been examined in an aqueous medium between H 0 =−1 and pH=13.7. As shown by cyclic voltammetry and polarography, a global 2e − reversible transfer is followed by two successive first-order chemical reactions and a 2e − , 2H + reduction (EC 1 C 2 E process). A mechanism is proposed, beginning with the 2e − reduction of NRCSNH 2 to the formal diionized form NRC − (SH)(NH 3 + ), the first chemical reaction, C 1 , being a formal proton transfer which yields the 4- gem aminosulfanylmethylpyridine; the rate constant of this reaction is 2×10 4  s −1 in acidic medium and diminishes in neutral medium. The second process, C 2 , which is much slower, is actually made up of two reactions in parallel (with loss of NH 3 or H 2 S), whose rate constants are in the ratio 4 to 1; the thioaldehyde and the imine which result from these reactions are easier to reduce than thioisonicotinamide. A comparison of the rates of deamination and dehydrosulfuration with those of dehydration and deamination previously obtained during the reduction of isonicotinic acid, isonicotinamide and their derivatives is made.