The effect of added halide and thiocyanate ions on the nitroamine–nitrous acid reaction. The oxidation of nitroamine by halogens

Abstract

The nitrous acid–nitroamine reaction is catalysed by added thiocyanate ion or chloride ion, with a rate law –d(HNO₂)/dt=k₃[HNO₂][NH₂NO₂][X^–], where X^–= SCN^– or Cl^–, which may be re-expressed as –d(HNO₂)/dt=k₅[NOX][NHNO₂^–]. This rate law corresponds to a rate-determining attack of the covalent nitrosyl compound upon the deprotonated nitroamine molecule : for thiocyanate, k₅= 1.3 × 10⁴ dm³ mol^–1 s^–1 at I= 0.25 mol dm^–3 and 0 °C. The addition of bromide results in a small catalytic effect, but after an induction period there is rapid increase in the rate of loss of nitrous acid, with a change in stoicheiometry. It is suggested that the reaction is initiated by the attack of bromine or bromine atoms (formed by decomposition of nitrosyl bromide) on nitroamine to give a species that reacts with nitrous acid.