Is hydrazoic acid (HN3) an intermediate in the destruction of hydrazine by excess nitrous acid?

Abstract

The kinetics of the decomposition of NH₂NNOH, the intermediate absorbing at 225 nm formed in the nitrous acid–hydrazine reaction have been studied by stopped-flow spectrophotometry at acidities up to 1 mol dm^–3 H⁺. A substantial amount of protonation occurs at high acidities, and the pK_a of NH₃⁺NNOH is 0.57. In excess hydrazine decomposition occurs to form hydrazoic acid (HN₃), but in excess nitrous acid a rapid second nitrosation occurs by a diffusion-controlled reaction between NO⁺ and NH₂NNOH which can bypass this pathway, though the possibility of some hydrazoic acid formation cannot be ruled out. Spectrophotometric evidence has been obtained for the formation of a relatively stable species, probably a very minor component, a product of the double-nitrosation reaction.