Micellar effects on the reduction of tris(acetylacetonato)cobalt (III) by 1-benzyl-1,4-dihydronicotinamide with ionic surfactants
The reduction of tris(acetylacetonato)cobalt(III)[Co(acac)3] by 1-benzyl-1,4-dihydronicotinamide (BNAH) has been studied in 4–100%(v/v) methanol-borate buffer with or without surfactants of anionic sodium dodecylsulphate (SDS) or cationic dodecyltrimethylammonium chloride (DTAC) micelles. The second-order reaction rate decreases on increased methanol content of the solvent system and in the presence of the surfactant micelles in the reaction system; it is retarded in the order of DTAC > SDS > none, and the rate constants of the electron transfer in the micellar pseudophase are 15–70 times smaller than that in the bulk aqueous phase. The binding constants of BNAH to SDS and DTAC micelles were determined to be 236 and 102 mol–1 dm3, respectively, at 30 °C by fluorescence measurements. It was also well reflected, by the estimated values of the activation parameters, that the micellar reaction of both the incorporated reactants [BNAH and Co(acac)3] proceeded at the water-micelle interface, in which low polar environments suppress the reaction through the unfavourable orientation of the reactants and the destabilization of the transition state of the reaction.