KINETICS AND MECHANISM OF THE OXIDATION OF SULFITE BY 2-TETRAMETHYL-1,4,8,11-TETRAAZACYCLOTETRADECANE)() (TMC=1,4,8,11)

The kinetics of the oxidation of SO32- by trans-[Ru(tmc)O-2](2+) (tmc = ,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) has been studied in aqueous solution at 25.0 degrees C. The reaction had the following stoichiometry: trans-[Ru-VI(tmc)O-2](2+) + SO32- + H2O --> trans-[Ru-I V(tmc)O(OH2)](2+) + SO42-. Sulfite and sulfur-containing products were analysed by ion chromatography. No S2O62- could be detected. The rate law is -d[Ru-VI]/dt = k/{1 + ([H+]/K)}[Ru-VI][S-IV] with k = (7.0 +/- 1.4) x 10(4) dm(3) mol(-1) s(-1) and K = (3.4 +/- 1.0) x 10(-7) mol d m(-3) at I = 1.0 mel dm(-3). The value of k is more than two orders of magnitude greater than predicted by Marcus theory, and an inner-spher e mechanism involving the intermediate [O=Ru-VI=O=SO3] is proposed. Th is may decompose by one- or two-electron pathways.