Kinetics and Mechanism of the Periodate Oxidation of Malachite Green in Acidic Medium
S. O. Idris *
Department of Chemistry, Ahmadu Bello University, Zaria, Nigeria.
H. Hassan
Department of Chemistry, Ahmadu Bello University, Zaria, Nigeria.
J. F. Iyun
Department of Chemistry, Ahmadu Bello University, Zaria, Nigeria.
Y. Mohammed
Department of Chemistry, Nasarawa State University, Keffi, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
The kinetics of the periodate (IO4–) oxidation of malachite green (MG+) have been studied in aqueous acidic medium. The observed results at [H+] = 1 x 10–4 mol dm–3 (HCl), ionic strength of reaction medium, I = 0.5 mol dm–3 and T = 25.5±0.3°C are consistent with the rate law:
−d[MG+]/dt = k2[MG+][IO4-]
where k2 = (k7 + k6K5[H+])
The reaction was catalysed by increase in [H+] and added anions but displayed a negative BrØnsted–Debye salt effect. Spectrophotometric test showed the absence of intermediate complex formation. Based on these findings, a plausible mechanism is proposed.
Keywords: Kinetics, mechanism, outersphere, malachite green, periodate