Angeli's salt

As first reported by Angelo Angeli in 1896, the salt is prepared by combining hydroxylamine and an organic nitrate, as a source of nitronium (): :NH2OH + RONO2 + 2 NaOR′ → ROH + 2 R′OH + Na2N2O3 The structure of the hydrate has been confirmed by X-ray crystallography. The anion is planar. Starting from the ONN end, the bond distances are 1.35 Å (N–O), 1.26 Å (N–N), 1.31 Å (N–Otrans), and 1.32 Å (N–Ocis). The negative charge is on the oxygen atoms at opposite ends of the molecule. The angles are 112.9° (Osingle–N–N), 118.4° (N–N–Otrans), and 122.5° (N–N–Ocis). This means that the nitrogen–nitrogen bond is a double bond, and that the cis oxygen is slightly repelled by the single oxygen. == Decomposition ==

Aqueous solutions of trioxodinitrate are unstable below pH 10. The rate of decomposition increases between pH 10 and 8, is essentially stable between pH 8 and 4, then accelerates again below pH 4. Between pH 8 and 4, the main decomposition mechanism is tautomerization of monoprotonated trioxodinitrate to , which decomposes reversibly to nitrite () and nitroxyl (). The resulting nitroxyl dimerizes rapidly to hyponitrous acid (), which dehydrates to nitrous oxide. : : Below pH 4, the main decomposition mechanism is tautomerization of diprotonated trioxodinitrate to reach the unstable transition state . This loses water to yield an excited state of trans-dinitrogen dioxide that, upon de-excitation, fragments to two nitric oxide molecules. : == Reactions ==

Reaction of Angeli's salt with secondary amines in the presence of a proton source results in extrusion of N2 via isodiazenes as proposed intermediates. ==References==