KINETICS AND MECHANISM OF REDUCTION OF BROMOTHALLIUM(III) COMPLEXES BY HYDROGEN-PEROXIDE IN PERCHLORIC-ACID MEDIA

The thallium(III)-H2O2 reaction was found to be catalysed by bromide i on and the maximum rate observed at a bromide to thallium(III) ratio, R, of 2:1; the rate decreased at higher values of R. The reactivity of various bromothallium(III) species follows the order [TlBr]2+ < [TlBr 2]+ > TlBr3 > [TlBr4]-. The complicated rate law of the reaction is as in equation (i) where k1, k2, k3 and k4 are the rate constants for -d [Tl(III)]/dt = (kK[Tl3+] [H2O2] + k1K1[TlBr2+]+ k2K2[TlBr2+] + k3K3[Ti Br3] + k4K4[TlBr4-])[H2O2]/[H+] (i) the steps involving [TlBr(O2H)] +, [TlBr2(O2H)], [TlBr3(O2H)]- and [TiBr4(O2H)]2- and K1, K2, K3 and K4 the respective formation constants, and k and K are the rate and forma tion constants for the steps representing the bromide-ion independent path.