Catalytic conversion of chlorite to chlorine dioxide by non-heme complexes
The oxyanions of chlorine (ClOx-, x=1-4) have diverse applications and are used in a variety of commercial products. They are very stable in an aqueous environment leading to water contamination, thereby posing a concern for the environment and human health. At the microbial level, the enzyme perchlorate reductase catalyzes the reduction of perchlorate (ClO4-) to chlorite (ClO2-) and chlorite dismutase further reduces chlorite to innocuous chloride (Cl -) and dioxygen (O2). Two non-heme complexes [Fe III-TAML]- (Tetraamido Macrocyclic Ligand), and [Mn II-(BnTPEN)] in the presence of peracetic acid (PAA) have been studied as catalysts for chlorite dismutation under ambient conditions. Kinetic and mechanistic studies were carried out to study the reactivity of Fe III-TAML and MnII-BnTPEN in the presence of PAA with sodium chlorite in acetate buffer (pH=5.0) at ambient temperatures. The TAML complex has been proposed to catalyze the one-electron oxidation of chlorite to chlorine dioxide (ClO2), as well as the dismutation of chlorite to chloride and dioxygen, after an induction period. The [MnII-BnTPEN] + PAA reaction displayed non-linear characteristics in the form of a long quiescent induction period, followed by the sudden and rapid production of ClO2 in the presence of excess ClO2-. Herein, reaction characteristics of the two non-heme systems have been described, and a reaction mechanism has been proposed. Chlorine dioxide, a pulp bleaching agent and a disinfectant is currently produced at the point of use involving harsh conditions. Hence, the non-heme-chlorite systems offer an inexpensive, mild method to produce ClO2 for industrial applications.
Abu-Omar, Purdue University.
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