New and Surprising Experimental Results from the Oxidation of Sulfinic and Sulfonic Acids

Thiourea, (H 2 N) 2 C S, aminoiminomethanesulfinic acid, H 2 N(HN )CSO 2 H (AIMSA), and aminoiminomethanesulfonic acid, H 2 N(HN=)CSO 3 H (AIMSOA) are all oxidized by mild oxidizing agents to a sulfate and an organic residue. AIMSA and AIMSOA are the postulated intermediates in the oxidation pathway of thiourea to sulfate. The oxidation of AIMSOA is accompanied by a cleavage of the C−S bond to form sulfate. Surprisingly, freshly prepared solutions of AIMSOA are oxidized by the common oxidants (oxyhalogens and halogens) at rates that are much slower than oxidation rates of AIMSA by the same oxidants. These results seem to suggest that AIMSOA may be structurally different from AIMSA and that the decomposition of AIMSOA to HSO 3 - is the prerequisite to its oxidation. The oxidation pathway of AIMSA to SO 4 2- also proceeds through the formation of HSO 3 - and not predominantly through AIMSOA.