Influence of Mercuric Nitrate on Species and Reactions Related to Chlorine Dioxide Formation

Abstract

Mercuric ions influence reactions and intermediates that are involved in forming chlorine dioxide from chlorate ions. Addition of mercuric ions to reaction solutions can aid in understanding the mechanism and kinetics of this system. Mercuric ions do not react with aqueous solutions of chlorine dioxide unless those solutions contain chlorous acid. This unusual effect has enabled us to confirm that chlorous acid is an intermediate in the formation of chlorine dioxide in the methanol−chlorate reaction. This work discusses the effect of mercuric ions on solutions containing various Cl species (chlorine, chlorine dioxide, chlorous acid, and both chlorine dioxide and chlorous acid) and on reactions that involve these same species. The work also explores the methanol−chlorate reaction in the absence of mercuric ions. In the initial stage of the process, chlorine dioxide forms after an induction period, during which an intermediate rapidly forms, maximizes in concentration, and then disappears, and a second intermediate forms and attains a steady-state concentration. We show by several methods, including mercuric ion addition, that the second intermediate is chlorous acid. We have not conclusively identified the first intermediate. The increase and decline in its concentration is accompanied by the development and disappearance of the solution color (yellow). Although the UV absorbance behavior of the system suggests that the intermediate is chlorine, the color of the solution associated with this intermediate is not characteristic of solutions containing chlorine at these concentrations.

Unexpected Phenomena in the Mercury(II)−Chlorite Ion System: Formation and Kinetic Role of the HgClO2+Complex

“…17 As an exception, the disappearance of ClO 2 was found in acidic aqueous solution of chlorite ion, chlorine dioxide, and mercury(II). 18 This phenomenon was used to confirm the formation of chlorous acid as an intermediate in the oxidation of methanol with chlorate ion. On the basis of the chemical properties of oxychlorine species and Hg(II), the decay of ClO 2 is quite an unexpected phenomenon and indicates very unique features of the Hg(II)-ClO 2 --ClO 2 system.…”

“…Redox reactions of chlorite ion are often coupled with catalytic decomposition of this species producing chlorine dioxide which is stable under acidic condition . As an exception, the disappearance of ClO 2 was found in acidic aqueous solution of chlorite ion, chlorine dioxide, and mercury(II) . This phenomenon was used to confirm the formation of chlorous acid as an intermediate in the oxidation of methanol with chlorate ion.…”

Influence of H2O2 on a chloride‐dependent reaction path to chlorine dioxide

“…Burke et al (1993) measured the rate in the absence of chloride. They correlated all of the experimental data in terms of an empirical expression, RCIO, = 1.5 X 10'" Effect of mercuric salts Indu et al (1997) used mercuric ion as a diagnostic tool in studies of chlorine dioxide formation. Mercuric ions: (1) remove chloride from solution by forming soluble HgCI,; (2) rapidly decompose chlorite ions in solution; and (3) do not react with chlorine dioxide in solution, unless chlorite ions are present.…”

“…No change in chlorine dioxide concentration indicates that chlorite is not present, or is present in very low concentration. Indu et al (1997) referred to the work of Gordon and Emmenegger (1966) who suggested that chlorite and chlorinc dioxide form a complex in solution c10, + c10; --3 Cl20, (18) Indu et al speculated that mercuric decomposes chlorine dioxide in this complex form.…”