Sulfoxylic and Thiosulfurous Acids and their Dialkoxy Derivatives

Being potent reductants, sulfoxylic acid S(OH)2 and its salts (sulfoxylates) are intermediates in many reactions of important industrial chemicals, such as sodium hydroxymethanesulfinate (rongalite) and thiourea dioxide. Sulfoxylates contain the -O-S-O- moiety, which is isoelectronic to trioxides, -O-O-O-. However, the apparent structural and valence electron count similarity may be contrasted to significant differences in reactivity. Thiosulfurous acid H2S2O2 is a primary product of reaction between hydrogen sulfide and sulfur dioxide. Despite the central role of the S-S bond in organic, inorganic and biological chemistry, thiosulfurous acid remains one of the least studied sulfur acids together with its one sulfur counterpart–sulfoxylic acid. Here we present the first special review describing the structure, stability and reactivity of these acids and their anions. Organic derivatives of sulfoxylic and thiosulfurous acids are much more studied than the acids themselves. In this review, organic derivatives of sulfoxylic and thiosulfurous acids (dialkoxy sulfoxylates (R-O-S-O-R) and dialkoxy disulfides (R-O-S-S-O-R), which are isoelectronic to organic trioxides and tetroxides), as well as organic trisulfanes R-S-S-S-R and tetrasulfanes R-S-S-S-S-R, respectively, are also briefly discussed. Keywords: dialkoxy disulfides; dialkoxy sulfoxylates; reactivity; structure; sulfoxylic acid; thiosulfurous acid