Kinetics of reduction of [Os(CN)6]3– ion by ascorbic acid and substituted 1,2- and 1,4-dihydroxybenzenes in acidic media. Effects of β-cyclodextrin inclusion of the reductant

Abstract

The kinetics of reduction of the hexacyanoosmate(III) ion by ascorbic acid and several substituted 1,2-and 1,4-dihydroxybenzenes have been investigated in acidic aqueous media. A Marcus correlation between the cross-reaction rate constants and the semiquinone or ascorbate radical reduction potentials has been constructed, yielding a [Os(CN)₆]^4–/3– self-exchange rate constant of 1.7 × 10⁴ dm³ mol^–1 s^–1, in good agreement with the directly measured value. The effects of β-cyclodextrin (β-cd) inclusion of 1,2-dihydroxybenzene and 4-tert-butyl-1,2-dihydroxybenzene on the kinetics of electron transfer have been investigated. The rate constant for 4-tert-butyl-1,2-dihydroxybenzene (K_cd= 2500 ± 500 dm³ mol^–1) decreases from 150 to 72 dm³ mol^–1 s^–1 upon β-cd inclusion. There is no observed change in the rate constant for the oxidation of 1,2-dihydroxybenzene (23 ± 1 dm³ mol^–1 s^–1) due to very weak inclusion (K_cd= 14 ± 3 dm³ mol^–1) in the β-cd cavity.