Determination of Rate Constants for Electron Transfer from Radical Anions of Aromatic Compounds to Diaryl Disulfides

Article abstract of DOI:10.1021/ja00408a034

Rate constants for electron transfer from the radical anions of aromatic compounds to diaryl disulfides (ArSSAr) have been determined in tetrahydrofuran.By the change of the reduction potentials of the aromatic compounds from -1.04 to -1.91 V (vs.SCE), the rate constants varied from 0.015 to 2.3 * 10⁸ M^-1 s^-1; conventional spectrophotometry has been employed to measure the slow reaction rates, and the xenon-flash photolysis technique has been applied to the fast reaction systems.The reaction including the free ion or the loose ion pair of the thioxanthone sulfone radical anion, (TO-SO2)^-/., was faster than that including the tight ion pair.In the case of the (TO-SO2)^-/., Na⁺-PhSSPh system, temperature variation yielded the free energy of activation (ΔG^* = 18.7 kcal/mol) and activation enthropy (ΔS^* = -29.1 eu) at 22.4 deg C; the reduction potential of PhSSPh was estimated to be -1.80 V vs.SCE from ΔG^* value.Electron-withdrawing substituents of ArSSAr increase the rates and vice versa; the Hammett reaction constants (ρ) were estimated to be ca. +1.50 and 1.40 for electron transfer from perylene radical anion and (TO-SO2)^-/.,Na⁺ to ArSSAr, respectively.The factors controlling the rates have been examined.