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
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 (Kcd= 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 (Kcd= 14 ± 3 dm3 mol–1) in the β-cd cavity.