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

The kinetics of formation of N-diketohydrindylidenehistidinatocopper(II) co mplex has been investigated in the presence of cationic cetyltrimethylammon ium bromide (CTAB) surfactant in aqueous medium (pH = 5.0). Similarly in aq ueous solution, the reaction followed irreversible first-order kinetics wit h respect to [Cu(II)-histidine](+) and fractional-order with respect to [Ni nhydrin]. Although the reaction mechanism remained unaltered by micelles, a typical k(psi)[CTAB] profile was observed, that is, with a progressive inc rease in [CTAB], the reaction rate increased, reached a maximum value, and then decreased. The results are treated quantitatively in terms of the kine tic pseudo-phase model. Activation parameters were also evaluated and a lar ge decrease in Delta S# shows the formation of a well-structured activated complex. It was found that anionic sodium dodecyl sulphate (SDS) and non-io nic Triton X-100 (TX-100) surfactants have no effect on the reaction. (C) 1 999 John Wiley & Sons, Inc.