Kinetics of Electron-transfer Reactions of para-Substituted Phenols p-C6H4(X)OH with 3+ (phen = 1,10-phenantroline) and with 2- in Aqueous Acidic Solutions: Correlation between the Hammett Constant of X and the One-electron Redox Potential of p-C6H4(X)OH

Article abstract of DOI:10.1039/DT9840000341

Kinetic Studies of the electron-transfer reactions of p-C6H4(X)OH (X= H, OCH3, OH, NH2, or NH3⁺ with tris(1,10-phenanrtoline)iron(III), ³⁺, and with hexachloroiridate(IV), ^2-, have been made in aqueous acidic solutions.The second-order rate constants (k₀) follow the rate law -d/dt = k₀, where A is the one-electron acceptor ³⁺ or ^2-, and were determined at an ionic strength of 1.0 mol dm^-3 and 25 deg C.The order of the forward rate constants (k_f) for the one-electron transfer step, which are defined as k₀ = 2k_f for the other X, was H < NH3⁺ < CH3 < OCH3 < OH < NH2 in approximate ratio 1 : 35 : 76 : 7x1E4 : 1.5x1E5 : 1.1x1E7 in the case of ³⁺ and 1 : 150 : 75 : 4x1E4 : 7.2x1E4 : 1.0x1E8 in the case of the ^2- reactions.By applying Marcus theory to k_f, standard redox potentials for the radical cations p-C6H4(X)OH^.+ were estimated and found to be well correlated with the Hammett constants (?_p) for the para substituents X.

Full text of DOI:10.1039/DT9840000341

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