Temperature Dependence of the Rate Constants for Reaction of Dihalide and Azide Radicals with Inorganic Reductants

Article abstract of DOI:10.1021/j100161a050

Rate constants for several reactions of inorganic radicals with inorganic reductants in aqueous solutions have been measured by pulse radiolysis as a function of temperature, generally between 5 and 75 deg C.The reactions studied were of the dihalide radicals, Cl2^.-, Br2^.-, and I2^.-, the (SCN)^.- radical, and the neutral radical N3^., reacting with the substitution-inert metal complexes, Fe(CN)6(4-), Mo(CN)8(4-), and W(CN)8(4-), and with the anions SO3(2-), HSO3(1-), NO2(1-), and ClO2(1-).The rate constants measured were in the range of 1E6 to 5E9 M^-1 s^-1and the calculated Arrhenius activation energies ranged from 5 to 35 kJ mol^-1.The preexponential factors also varied considerably, with log A ranging from 8.9 to 13.1.The temperature dependence of the reaction rate constant is correlated to the reaction exothermicity for the metal complexes, which apparently react by outer-sphere electron transfer.The simple anions, however, have lower activation energies, which do not correlate well with the exothermicities, suggesting that these anions probably react by inner-sphere mechanism.