By oxidizing potassium benzene iso-diazotate with alkaline potassium ferricyanide, E. Bamberger (_Ber._, 1894, 27, p. 914) obtained the _diazoic acids_, R·NH·NO2, substances which he had previously prepared by similarly oxidizing the diazonium salts, by dehydrating the nitrates of primary amines with acetic anhydride, and by the action of nitric anhydride on the primary amines. Concentrated acids convert them into the isomeric nitro-amines, the -NO2 group going into the nucleus in the ortho- or para- position to the amine nitrogen; this appears to indicate that the compounds are nitramines. They behave, however, as tautomeric substances, since their alkali salts on methylation give nitrogen ethers, whilst their silver salts yield oxygen ethers:
/--> potassium salt --> R·N(CH3)·NO2 nitramine. R·NH·NO2< \--> silver salt --> R·N:N·O·OCH3 diazoate.
_Phenyl nitramine_, C6H5NH·NO2, is a colourless crystalline solid, which melts at 46° C. Sodium amalgam in alkaline solution reduces it to phenylhydrazine.
_Constitution of the Diazo Compounds._--P. Griess (_Ann._, 1866, 137, p. 39) considered that the diazo compounds were formed by the addition of complex groupings of the type C6H4N2- to the inorganic acids; whilst A. Kekulé (_Zeit. f. Chemie_, 1866, 2, p. 308), on account of their ready condensation to form azo compounds and their easy reduction to hydrazines, assumed that they were substances of the type R·N:N·Cl. The constitution of the diazonium group -N2·X, may be inferred from the following facts:--The group C6H5N2- behaves in many respects similarly to an alkali metal, and even more so to the ammonium group, since it is capable of forming colourless neutral salts with mineral acids, which in dilute aqueous solution are strongly ionized, but do not show any trace of hydrolytic dissociation (A. Hantzsch, _Ber._, 1895, 28, p. 1734). Again, the diazonium chlorides combine with platinic chloride to form difficultly soluble double platinum salts, such as (C6H5N2Cl)2·PtCl4; similar gold salts, C6H5N2Cl·AuCl3, are known. Determinations of the electrical conductivity of the diazonium chloride and nitrate also show that the diazonium radical is strictly comparable with other quaternary ammonium ions. For these reasons, one must assume the existence of pentavalent nitrogen in the diazonium salts, in order to account for their basic properties.