Initial state and transition state solvation effects in the oxidation of iodide and catechol by hexachloroiridate(IV) in binary aqueous solvent mixtures

Abstract

. 61, 1361 (1983). Rate constants arc rcportcd for hexachloroiridate(IV) oxidation of iodidc in methanol-, cthanol-, t-butyl alcohol -, cthylene glycol-, glycerol-, acetone-, acetonitrile-, and dimcthyl sulphoxidc -water solvent mixtures, and for thc hcxachloroiridate(1V) oxidation of catcchol in methanol-watcr mixtures. With thc aid of ancillary solubility data and measurements, solvent effects on reactivity have been analysed into initial statc and transition statc components. In the lattcr, there arc probably both electron transfer and diffusion contributions since it is not possiblc to identify uniquely the separate kinetic steps associated with the activation process. In these redox systems, however, transition state solvation changes dominate. This conclusion is compared with initial state -transition state effects in the reaction of catechol with hexahydroxoantimonic acid, in the bromate oxidation of bromide, the peroxodisulphate oxidation of iodide, and with patterns established earlicr for substitution at inorganic centres. In view of some disagreements and uncertainties in the literature concerning the number of molecules of water of crystallisation in potassium hexachloroiridate(II1) and hexachloroiridate(1V). this matter, of considcrable importance to hexachloroiridate transfer parameter estimation, is briefly reviewed.

Electrostriction and counter ion effects in an outer-sphere electron transfer reaction. Kinetics of the reduction of hexachloroiridate(IV) by iodide ion†

“…3a, 10 The mechanism has also been discussed in an investigation of solvation influences upon the reaction. 11 A combination of thermodynamic data obtained from solubility measurements on K 2 IrCl 6 and literature values for I Ϫ , in aqueous mixtures, led to the following results and conclusions. The transition state in mixed solvents is more destabilised than are the reactants, considered together, relative to aqueous solution.…”

“…The overall analysis pointed to the redox step as rate determining. 11 In principle, the activation parameters can be used to help to distinguish between these mechanistic pathways. The measured values represent composites of contributing terms for either pathway.…”

Copper Catalysis of the Oxidation of Iodide by [FeIII(bpy)2(CN)2]+ in Acetonitrile

“…2 With [CoW 12 O 40 ] 5-, aqueous solvent mixtures again were usedsin this case, up to 40% methanol, 40% acetonitrile, and 60% dimethyl sulfoxide (DMSO). 4 With [IrCl 6 ] 2-, a variety of aqueous solvent mixtures were used, but the aqueous fraction was never <20%. 3 To our knowledge, there are no reports of kinetic data on such reactions in "pure" nonaqueous media.…”

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

“…Decreases in the rate constants for the oxidation of substituted 1,2-dihydroxybenzenes by metal complexes have been observed in other organized media, such as micelles" and microemulsions,22 as well as in aqueous-organic solvents. 20 The inclusion stability constant determined for the (H2tbc-P-cd} complex from the kinetic measurements in this study, (2.5 & 0.5) x lo3 dm3 mol-', is smaller than the corresponding values of (8)(9)(10) x lo3 dm3 mol-', calculated from 'H NMR titrations and from the kinetics of the oxidations of H,tbc by [IrCl,] ,-, bis( 1,4,7-triazacyclononane)nickel(111), and diaqua-(1,4,8,1 l-tetraazacyclotetradecane)nickel(III). 26 The rate constants for the oxidations of H,tbc by the iridium(1v) and nickel(II1) complexes were also observed to decrease more substantially ( k , / k , x 5 ) than for [OS(CN),]~-( k 2 / k 1 x 2) upon P-cd inclusion of the reductant.…”