Correlation analysis of reactivity in the reduction of trans-chloro(RC6H4NH2)bis(1,2-diaminoethane)cobalt(III) complexes by hexacyanoferrate(II) in aqueous methanol

The structural and solvent effects on the reduction of trans-chloro(RC6H4NH2)bis(1,2-diaminoethane)cobalt(III) ion (R = H, p-Me, p-OMe, p-OEt, p-F, m-Me and m-OMe) by the hexacyanoferrate(II) complex was investigated in aqueous MeOH. The second order rate constants for these reactions were determined spectrophotometrically at three different temperatures and activation parameters have been computed. Reduction proceeding through ion-pair formation is proposed on the basis of the Laidler-Eyring and Grunwald-Winstein equations. The influence of added co-solvent on the reactivity has been analysed using multiple regression equations viz. Kamlet-Taft and Swain. The reduction rates were correlated with Hammett's substituent constants yielding a negative reaction constant.