Kinetics and Mechanism of Oxidation of L-Ascorbic Acid by Pt(IV)(aq) in Aqueous Hydrochloric Acid Medium

[摘要] Reduction of [PtCl6]2−by L-ascorbic acid (H2ASc) in 0.1 M aqueous acid medium has been investigated spectrophotometrically under pseudo-first order condition at [PtCl6]2−= 0.005–0.007 mol dm−3, 0.05 ≤ [H2ASc]/mol dm−3≤ 0.3, 298 K ≤T≤ 308 K, [H+] = 0.14 mol dm−3,I=0.5 mol dm−3. The redox reaction follows the rate law:d[Pt(IV)]/dt=k[H2ASc][Pt(IV)], wherekis the second-order rate constant and [H2ASc] is the total concentration of ascorbic acid. Electron transfer from [H2ASc] to Pt(IV) center leading to the release of two halide ions and formation of the reaction products, square planner Pt(II) halide complex, and dehydrated ascorbic acid is suggested. This redox reaction follows an outersphere mechanism as Pt(IV) complex is substituted inert. Activation parameters were calculated corresponding to rate of electron transfer reactionk. Activation parameters favor the electron transfer reaction.

[学科分类] 物理化学和理论化学