KINETIC-STUDY ON CHEMICAL OXIDATION OF LEUCOEMERALDINE BASE POLYANILINE TO EMERALDINE BASE

Leucoemeraldine base form polyaniline, [C6H4-NH]n(PLM), dissolved in N-methylpyrrolidone undergoes oxidation promoted by O2 and H2O2 in the presence of FeCl3 and CuCl2 catalysts to give emeraldine base form polyaniline, [C6H4-NH-C6H4-NH]n[C6H4-N=C6H4=N]n (PEM), as revealed by the UV-vis spectra of the reaction mixtures. The reaction with O2 follows first-order kinetics which shows the rate constant of 6.8 X 10(-5) s-1 at 30-degrees-C. Activation energy of the reaction is determined as 50.4 kJ mol-1 from temperature dependence of the rate constants. Oxidation of PLM with H2O2 in the presence of FeCl3 proceeds smoothly to give PEM, and UV-vis spectroscopy reveals the presence of clear isosbestic points during the oxidation reaction. The initial rates of the reaction are proportional to the concentration of FeCl3 catalysts and increase with H2O2 Concentration at [H2O2] below 40 mM, while they level of fat about 40 mM of [H2O2]. Further oxidation of PEM to give fully oxidized polyaniline does not occur under the reaction conditions. CuCl2 also serves as an effective catalyst for the oxidation of PLM to PEM by H2O2, and in this case, the rate of reaction increases with increase in the concentration of H2O2 over a wide range of [H2O2] (33-490 mM). The reaction of PLM with a limited amount of dibenzoyl peroxide proceeds rapidly to give PEM, while an excess amount of dibenzoyl peroxide causes formation of uncharacterized product by further oxidation of the initially formed PEM.