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

The kinetics of phenylalanine (phe) oxidation by permanganate has been investigated in absence and presence of cetyltrimethylammonium bromide (CTAB) using conventional spectrophotometric technique. The rate shows first- and fractional-order dependence on [MnO(4)(-)] and [phe] in presence of CTAB. At lower values of [CTAB] (< or =10.0x10(-4)moldm(-3)), the catalytic ability of CTAB aggregates are strong. In contrast, at higher values of [CTAB] (> or =10.0x10(-4)moldm(-3)), the inhibitory effect was observed in absence of H(2)SO(4). We find that anions (Br(-), Cl(-) and NO(3)(-)) 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 MnO(4)(-), CTAB and MnO(4)(-), respectively, are presented. A mechanism consistent with kinetic results has been discussed. Complex formation constant (K(c)) and micellar binding constant (K(s)) were calculated at 30 degrees C and found to be K(c)=319mol(-1)dm(-3) and K(s)=1127mol(-1)dm(-3), respectively.