Polarographic reduction of aqueous sulfur dioxide

• Published in: Polyhedron Vol. 5; no. 9; pp. 1467 - 1473
• Main Authors: Reynolds, W.L., Yuan, Yu
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 1986; New York, NY Elsevier Science
• Subjects: Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; Kinetics and mechanism of reactions; Chemical reduction; Polarography; Numerical data; PH; Aqueous solution; Electrochemical reaction; Acidic solution; Sulfur dioxide; Inorganic compound
• ISSN: 0277-5387
• DOI: 10.1016/S0277-5387(00)83508-1

Direct- and alternating-current polarograms of aqueous SO 2 · OH 2 solutions show four reduction waves, more than previously reported. Waves I and II probably result from the electroreduction of SO 2 · OH 2 and HSO − 3, respectively; these two waves completely overlap at pH 1 but are partially resolved at higher pH values due to different pH dependence. Reduction of SO 2 · OH 2 involves two electrons and two H + ions and the initial product is probably sulfoxylic acid, H 2SO 2. This product can disproportionate to S 0 and SO 2 · OH 2 in very acidic media (pH ≤ 1) and, in the limit, double the reduction current of SO 2 · OH 2. Reduction of HSO − 3 appears to occur via two paths: one is a two-electron three-H + ion path and the other is a one-electron one-H + ion path. The former dominates at pH ≤ 3 and probably produces H 2SO 2; the latter dominates at pH > 4 and may produce SO − 2. H 2SO 2 in less acidic media can react with HSO − 3 to yield dithionite species (such as H 2S 2O 4, HS 2O − 4 and S 2O 2− 4) and HSO 2 and SO − 2 by dissociation of the dithionite species. Waves III and IV are believed to result from reduction of HSO 2 and SO − 2, respectively, to H 2SO 2 species.