Sub- and post-micellar catalytic and inhibitory effects of cetlytrimethylammonium bromide in the permanganate oxidation of phenylalanine

The kinetics of phenylalanine (phe) oxidation by permanganate has been investigated in absence and presence of cetlytrimethylammonium bromide (CTAB) using conventional spectrophotometric technique. The rate shows first- and fractional-order dependence on [MnO4−] and [phe] in presence of CTAB. At lower values of [CTAB] (≤10.0 × 10−4 mol dm−3), the catalytic ability of CTAB aggregates are strong. In contrast, at higher values of [CTAB] (≥10.0 × 10−4 mol dm−3), the inhibitory effect was observed in absence of H2SO4. We find that anions (Br−, Cl− and NO3−) in the form of sodium salts are strong inhibitors for the CTAB catalyzed oxidation. Kinetic and spectrophotometric evidences for the formation of an intermediate complex and an ion-pair complex between phe and MnO4−, CTAB and MnO4−, respectively, are presented. A mechanism consistent with kinetic results has been discussed. Complex formation constant (Kc) and micellar binding constant (Ks) were calculated at 30 °C and found to be Kc = 319 mol−1 dm−3 and Ks = 1127 mol−1 dm−3, respectively.