Detailed kinetics and mechanism of the oxidation of thiocyanate ion (SCN-) by peroxomonosulfate ion (HSO5(-)). Formation and subsequent oxidation of hypothiocyanite ion (OSCN-).
The haloperoxidase-catalyzed in vivo oxidation of  thiocyanate ion (SCN(-)) by H(2)O(2) is important for generation of the antimicrobial hypothiocyanite ion (OSCN(-)), which is also susceptible to oxidation by strong in vivo oxidizing agents (i.e., H(2)O(2), OCl(-), OBr(-)). We report a detailed mechanistic investigation on the multistep oxidation of excess SCN(-) with  peroxomonosulfate ion (HSO(5)(-) in the form of Oxone) in the range from pH 6.5 to 13.5. OSCN(-) was detected to be the intermediate of this reaction under the above conditions, and a kinetic model is proposed. Furthermore, by kinetic separation of the consecutive reaction steps, the rate constant of the direct oxidation of OSCN(-) by HSO(5)(-) was determined: k(2) = (1.6 ± 0.1) × 10(2) M(-1) s(-1) at pH 13.5 and k(2)(H) = (3.3 ± 0.1) × 10(3) M(-1) s(-1) at pH 6.89. A critical evaluation of the estimated activation parameters of the elementary steps revealed that the oxidations of SCN(-) as well as the consecutive OSCN(-) by HSO(5)(-) are more likely to proceed via 2e(-)-transfer steps rather than 1e(-) transfer.
Department of Inorganic and Analytical Chemistry, University of Debrecen, P.O. Box 21, Debrecen H-4010, Hungary. kalmar.jozsef@science.unideb.hu
József
J
Kalmár
Gábor
G
Lente
István
I
Fábián
D007477:Ions / Q000737:chemistry; D007700:Kinetics; D010084:Oxidation-Reduction; D010545:Peroxides / Q000737:chemistry*; D013861:Thiocyanates / Q000138:chemical synthesis* / Q000737:chemistry*
D007477:Ions; D010545:Peroxides; D013861:Thiocyanates; C038288:peroxymonosulfate