Effect of Alkanediyl‐α,ω‐Type Cationic Dimeric (Gemini) Surfactants on the Reaction Rate of Ninhydrin with [Cu(II)‐Gly‐Tyr]⁺ Complex

The effect of gemini (16‐ s ‐16, s = 4, 5, 6) surfactants on the reaction rate of ninhydrin with [Cu(II)‐Gly‐Tyr] + complex was determined using a spectrophotometric technique. The ninhydrin concentration was kept in excess in order to maintain pseudo‐first‐order conditions. The reaction followed irreversible first‐ and fractional‐order kinetics with respect to [Cu(II)‐Gly‐Tyr] + and [ninhydrin], respectively. It is found that gemini surfactants effectively catalyze the reaction. The rate constants ( k ψ ) first increase and then become relatively constant with increasing gemini surfactant concentration similar to conventional cetyltrimethylammonium bromide. At higher gemini surfactant concentration a third region of increasing k ψ is observed. The unusual third region is ascribed to changes in micellar morphology. The kinetic data has been analyzed using a micellar pseudo‐phase model.