Radiation-induced debromonation of 1,2-dibromotetrafluoroethane (Halon2402) in alcohols followed by Br2•− formation – A pulse radiolysis study

Abstract

Pulse radiolysis technique was used to investigate early stages of radiation-induced reactions in alcohols (methanol and 2-propanol) containing a halogenated compound, Halon2402, and it was found that repetition of irradiation leads to accumulation of a transient species having absorption around 360 nm, which is attributed to dibromine radical anion (Br2•−). The alcohols containing bromide anion (Br−) were also investigated because it is reported debromonation occurs during the radiation-induced degradation, revealing that at first Br− is oxidized into bromine atom (Br•) by alkoxy radicals of the solvent alcohols, and then, Br2•− is formed by its reaction with another Br−. Since not only Br− but also acid (H+) is produced during the degradation, influence of acid was also investigated, showing that acid is essential in the oxidation of Br− into Br• in the alcohols. In addition, deuteration of the solvent alcohols resulted in significant increase in the amount of Br2•− production, implying it is alkoxy radicals of the solvent alcohols that oxidize Br− into Br•. Difference in the Br− oxidation between methanol and 2-propanol was also discussed in relevance to difference in redox potentials of the transient species.