Reactions of the hydroperoxyl radical (HO2) with nitrogen dioxide and tetranitromethane in aqueous solution

Abstract

HO₂ produced in a flow system by the electron beam irradiation of aerated formic acid solutions reacts with tetranitromethane (TNM) in acid solution in two stages. Rapid formation of nitroform by reaction (1) is followed by a delayed reaction with 0.5 s < t_½ < 10 min. The delayed reaction forms nearly half the total nitroform at low [TNM] and pH; it is suppressed by KCNS and is believed to be due to reduction of TNM by peroxynitric acid (HO₂NO₂) formed in the mechanism: HO₂⇌ O^–₂+ H⁺, C(NO₂)₄+^–₂→ C(NO₂)^–₃+ O₂+ NO₂, k₁= 2 × 10⁹ dm³ mol^–1 s^–1(1), HO₂+NO₂→ HO₂NO₂k₁₀= 4 × 10⁹ dm³ mol^–1 s^–1(10), 2NO₂→ N₂O₄, k₁₃= 10¹⁰ dm³ mol^–1 s^–1(13), N₂O₄+ H₂O → HNO₂+ HNO₃. Quantitative evidence for this mechanism is presented.