om the reduction of nitro or nitroso compounds by
heating them with alcoholic potash (preferably using methyl alcohol). They
may also be obtained by the oxidation of azo compounds. When reduced (in
acid solution) they yield amines; distillation with reduced iron gives azo
compounds, and warming with ammonium sulphide gives hydrazo compounds.
Concentrated sulphuric acid converts azoxybenzene into oxyazobenzene (O.
Wallach, _Ber._, 1880, 13, p. 525). Azoxybenzene, (C_6H_5N)_2O,
crystallizes from alcohol in yellow needles, which melt at 36deg C. On
distillation, it yields aniline and azobenzene. Azoxybenzene is also found
among the electro-reduction products of nitrobenzene, when the reduction is
carried out in alcoholic-alkaline solution.

The mixed azo compounds are those in which the azo group .N:N. is united
with an aromatic radical on the one hand, and with a radical of the
aliphatic series on the other. The most easily obtained mixed azo compounds
are those formed by the union of a diazonium salt with the potassium or
sodium salt of a nitroparaffin (V. Meyer, _Ber._, 1876, 9, p. 384):

C_6H_5N_2.NO_3 + CH_3.CH(NO_2)K = KNO_3 + C_6H_5N_2.CH(NO_2)CH_3.
Benzene-azo-nitro-ethane.

Those not containing a nitro group may be prepared by the oxidation of the
corresponding mixed hydrazo compounds with mercuric oxide. E. Bamberger
(_Ber._, 1898, 31, p. 455) has shown that the nitro-alkyl derivatives
behave as though they possess the constitution of hydrazones, for on
heating with dilute alkalies they split more or less readily into an
alkaline nitrite and an acid hydrazide:

C_6H_5NH.N:C(NO_2)CH_3 + NaOH = NaNO_2 + C_6H_5NH.NH.CO.CH_3.

Benzene-azo-methane, C_6H_5.N_2.CH_3, is a yellow oil which boils at 150deg
C. and is readily volatile in steam. Benzene-azo-ethane, C_6H_5.N_2.C_2H_5,
is a yellow oil which boils at about 180deg C. with more or less
decomposition. On standing with 60% sulphuric acid for some time, it is
converted into the isomeric acetaldehyde-phenylhydrazone,
C_6H_5NH.N:CH.CH_3 (_Ber._, 1896, 29, p. 794).

The diazo cyanides, C_6H_5N_2.CN, and carboxylic acids, C_6H_5.N_2.COOH,
may also be considered as mixed azo derivatives. Diazobenzenecyanide,
C_6H_5N_2.CN, is an unstable oil, formed when potassium cyanide is added to
a solution of a diazonium salt. Phenyl-azo-carboxylic acid,
C_6H_5.N_2.COOH, is obtained in the form of its potassium salt when
phenylsemica