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

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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 pKa 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.