Abstract
The reaction of malic acid with dichromate studied in presence and absence of manganese(II) follows a second-order kinetics with respect to [malic acid] which shifts to first-order in presence of manganese(II). The catalytic effect of manganese(II) suggests that chromium(IV) is not formed as an intermediate. In the first-order reaction (in presence of manganese(II)) malic acid is oxidized to carbon dioxide and malonic acid. The effect of cationic and anionic surfactants, was also investigated and it was found that cationic micelles catalyse the reaction while anionic micelles have no effect. The influence of different parameters such as [reactant], [surfactant], temperature and added salts was considered. For surfactant concentrations well above the ciritical micelle concentration, the rate constant-[surfactant] profiles can be interpreted in terms of distribution of both the reactants between water and the micelles, using the binding constants 121.2 and 22.5 mol(-1) dm(3) for chromium(VI) to CPB and CTAB, respectively. The catalytic effect of this reaction is greater for CPB than CTAB. This is the result of greater association of chromium(VI), not of a greater rate. constant in the micelle.