tic alkali, C. Schraube and C.
Schmidt (_Ber._, 1894, 27, p. 520) obtained an isomer of potassium
benzene diazotate. These _iso-_diazotates are formed much more readily
when the aromatic nucleus in the diazonium salt contains negative
radicals. _Potassium benzene iso-diazotate_ resembles the normal salt,
but is more stable, and is more highly ionized. Carbon dioxide
converts it into _phenyl nitrosamine_, C6H5NH.NO (A. Hantzsch). The
potassium salt of the iso-diazo hydroxide yields on methylation a
nitrogen ether, R.N(CH3).NO, whilst the silver salt yields an oxygen
ether, R.N:N.OCH3. These results point to the conclusion that the
iso-diazo hydroxide is a tautomeric substance. The same oxygen ether
is formed by the methylation of the silver salt of the normal diazo
hydroxide; this points to the conclusion that the isomeric hydroxides,
corresponding with the silver derivatives, have the same structural
formulae, namely, R.N:N.OH. These oxygen ethers contain the grouping
-N:N-, since they couple very readily with the phenols in alkaline
solution to form azo compounds (q.v.) (E. Bamberger, _Ber._, 1895, 28,
p. 225); they are also explosive.

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 deg. 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-