Organosulfur oxoacids. Part 1. Synthesis, structure, and reactivity of dimethylaminoiminomethanesulfinic acid (DMAIMSA)

Abstract

One of the major metabolites of dimethylthiourea, dimethylaminoiminomethanesulfinic acid (DMAIMSA), was synthesized by controlled oxidation of dimethylthiourea using hydrogen peroxide. The crystal structure was determined by X-ray crystallography. It is a zwitterionic species in its solid form, with a positive charge delocalized around an sp2-hybridized carbon center and two nitrogen atoms. It crystallizes in the triclinic P[Formula: see text] space group. The C—S bond, at 1.880(2) Å, is much longer than a typical C—S single bond length of 1.79 Å. It is also longer than the one observed in thiourea trioxide, a comparable sulfonic acid. This C—S bond is stable in acidic conditions and is easily cleaved in basic conditions or in the presence of suitable nucleophiles that can attack the positively disposed carbon center. DMAIMSA is highly reactive and easily decomposes in basic conditions to yield dithionite in the presence of oxygen, whereas in strictly anaerobic conditions it gives a mixture of sulfite and sulfide. The precursor to dithionite, SO2·–, is formed from the one-electron oxidation of the sulfoxylate anion, SO22–, which results from an initial heterolytic cleavage of the C—S bond in DMAIMSA. The sulfur center is oxidized, even by mild oxidants such as aqueous iodine, to sulfate. Key words: thiourea metabolites, synthesis, structure, reactivity.