KINETICS OF REDUCTION OF [OS(CN)6]3- ION BY ASCORBIC-ACID AND SUBSTITUTED 1,2-DIHYDROXYBENZENES AND 1,4-DIHYDROXYBENZENES IN ACIDIC MEDIA - EFFECTS OF BETA-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 x 10(4) dm3 mol-1 s-1, in good agreement with the directly measured value, The effects of beta-cyclodextrin (beta-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 beta-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 beta-cd cavity.