Kinetics and mechanism of oxidation of nitrilotriacetic acid by diperiodatoargentate(III)

Abstract

Diperiodatoargentate(III) oxidizes nitrilotriacetic acid in a mildly basic medium to produce formaldehyde and ammonia. This reaction follows a complex kinetic behaviour. The axial binding of NTA to silver(III) complex takes place on the millisecond time-scale with a second-order rate constant of (4.8 ± 0.5) × 103 dm3 mol−1 s−1. Two electrons are transferred from bound NTA to the silver(III) centre sequentially. At low [NTA] (<1 × 10−3 mol dm−3), the rate law follows first-order kinetics with respect to NTA but at high [NTA] it becomes independent of its concentration. The first electron is transferred to the silver(III) centre with a second-order rate constant of (7.2 ± 0.5) dm3 mol−1 s−1. The second electron is transferred subsequently in the fast step from NTA radical to the silver(II) species. The latter stages of reaction consists of a composite process involving the oxidation of NTA and its products in parallel reactions. Kinetic experiments suggest that [AgIII(H3IO6)(H2O)2]+ is the reactive silver(III) species involved. Copyright © 1999 John Wiley & Sons, Ltd.