Kinetics and mechanism of the sulphamic acid–nitric acid reaction: evidence for consecutive reactions

Abstract

The title reaction occurs in three stages. The first and fast step probably involves attack of [NO₂]⁺ on sulphamic acid, while the subsequent steps involve rearrangement and elimination. The direct displacement of [SO₃H]⁺ by [NO₂]⁺ can be excluded. Dinitrogen oxide and sulphate are produced in the third (and slowest) stage, for which the kinetics have been studied over the range [HNO₃]= 0.274–14.8 mol dm^–3. This third stage is first order in both [NH₃SO₃H] and [NO₃^–], and approximately second order with respect to the acidity function H₀, indicative of involvement of a [NO₂]⁺ group in the transition state. The second stage of the reaction is retarded by HNO₃. Several alternative mechanisms are discussed.