Micellar effects on the rates of the condensation reaction between copper(II)-histidine complex and ninhydrin

Abstract

The kinetics of formation of N-diketohydrindylidenehistidinatocopper(II) complex has been investigated in the presence of cationic cetyltrimethylammonium bromide (CTAB) surfactant in aqueous medium (pH = 5.0). Similarly in aqueous solution, the reaction followed irreversible first-order kinetics with respect to [Cu(II)-histidine]+ and fractional-order with respect to [Ninhydrin]. Although the reaction mechanism remained unaltered by micelles, a typical kψ-[CTAB] profile was observed, that is, with a progressive increase in [CTAB], the reaction rate increased, reached a maximum value, and then decreased. The results are treated quantitatively in terms of the kinetic pseudo-phase model. Activation parameters were also evaluated and a large decrease in ΔS# shows the formation of a well-structured activated complex. It was found that anionic sodium dodecyl sulphate (SDS) and non-ionic Triton X-100 (TX-100) surfactants have no effect on the reaction.