The pseudo-first-order rate constants in the absence (kobs, s−1) and presence of CTAB (kψ, s−1) were calculated up to 80% completion of the reaction using a computer program. Other details regarding pH measurements and kinetic methodology were the same as described elsewhere ( Kabir-ud-Din et al., 2000). Plots of log (absorbance) vs. time were made, keeping the fixed concentration of the reactants in aqueous and CTAB micelles (30, 40, and 50 × 10−3 mol dm−3) at temperature 70 °C and pH 5.0 ( Fig. 2).