Page:EB1911 - Volume 19.djvu/740

 gives phenyl diazonium nitrate. With aniline and acetic acid it yields azobenzene. It combines with aromatic amines to form azocompounds, with arylhydroxylamines to form azoxy compounds, and with hydroxylamine it gives isodiazobenzene.

NITRO COMPOUNDS, in organic chemistry, compounds containing the monovalent radical −NO2 directly combined with carbon.

Aiphatic Nitro Compounds.–The nitroparaffins may be obtained by the action of the alkyl iodides on silver nitrite (V. Meyer, Ann. 1874, 171, p. 1 et seq.). When methyl iodide is used, nitromethane is the sole product, but the higher homologues give more or less of the isomeric nitrous esters. Nitroparaffins may also be obtained by the action of sodium nitrite on the -halogen fatty acids, the -nitro fatty acids first formed readily eliminating carbon dioxide (H. Kolbe, Jour. prak. Chem., 1872 [2] 5, p. 427). Tertiary nitro compounds may also be obtained by the oxidation of the corresponding amino-, hydroxylamino- and nitroso-hydrocarbons with mono per sulphuric acid (E. Bamberger, Ber., 1903, 36, p. 385):

⪫C⋅NH2→ &emsp; ⪫C⋅NHOH→ &emsp; ⪫C⋅NO→ &emsp; ⪫C⋅NO2.

The nitro compounds of the lower members of the paraffin series cannot be prepared by the direct action of nitric acid on the hydrocarbons themselves, but, in the case of some of the higher members of the series direct nitration is possible (M. Konowalow, Comptes rendus, 1892, 114, p. 26; Ber., 1895, 28, p. 1852; R. A. Worstall, Amer. Chem. Jour., 1898, 20, p. 202).

The nitro compounds are colourless, somewhat pleasant smelling liquids, which distil without decomposition and possess boiling points much higher than those of the isomeric nitrous esters. Reduction with acid-reducing agents gives amines. The primary and secondary nitro compounds (i.e. those containing the groupings ⋅CH2NO2 and >CH⋅NO2) form metallic derivatives; for example, sodium salts, which according to A. Hantzsch (Ber., 1899, 32, pp. 577 et seq.) are probably derived from the isomeric iso-nitro compounds R&#x202f;:&#x202f;NO(OH), and thus the nitro derivatives are to be looked upon as pseudo-acids. These sodium salts are crystalline solids which are readily soluble in water and are very explosive. Stannous chloride and hydrochloric acid reduce the nitroparaffins to -alkyl hydroxylamines, amines and some ammonia being simultaneously produced (V. Meyer, Ber., 1891, 24, p. 3530), whilst the primary nitro compounds on heating with hydrochloric acid yield hydroxylamine and an acid:

CH3⋅CH2⋅NO2+H2O＝CH3⋅CO2H+NH2OH

(V. Meyer, Ann., 1876, 180, p. 163). When reduced by the Sabatier and Senderens’ method (Comptes rendus, 1902, 135, p. 225) they are converted into amines, provided the temperature be kept at 150°-200° C., a higher temperature leading to the formation of paraffins and ammonia. The hydrogen in the primary and secondary nitro compounds which is attached to the same carbon atom as the nitro group is readily replaced by bromine in alkaline solution. The reactions of the nitroparaffins with nitrous acid are very characteristic and have been used as a method for discriminating between the primary, secondary and tertiary s (q.v.) (V. Meyer, Ann., 1875, 175, p. 93). The primary compounds form nitrolic acids of the type R⋅C(:NOH)NO, the secondary yield pseudo-nitrols of the type RR1: C(NO)(NO2), whilst the tertiary nitro compounds are not acted upon by nitrous acid. The primary nitroparaffins combine with nitric oxide in the presence of sodium ethylate, to form nitroalkylisonitramines, R⋅CH(NO2)⋅N2O2H (W. Traube, Ann., 1898, 300, p. 95)

Aromatic Nitro Compounds.—The aromatic nitro compounds are generally obtained by the direct action of nitric acid. Substitution takes place usually in the nucleus and only rarely in the side chain, and according to the conditions of the experiment and the nature of the compound acted upon, one or more nitro groups enter the molecule. The reaction is generally carried out in the presence of sulphuric acid, which is used to absorb the water formed during the process of nitration. Nitro compounds have also been prepared by the action of cuprous oxide on diazonium salts (T. Sandmeyer, Ber., 1887, 20, p. 1494); by the action of copper powder on the double salt formed by the addition of potassium mercuric nitrite to diazonium nitrites; and by the oxidation of primary aromatic amines (E. Bamberger, Ber., 1893, 26, p. 496). The mono-nitro compounds are stable and distil Without decomposition; they have a pale yellow colour and possess an agreeable odour. Most of the poly-nitro compounds are not volatile, but undergo decomposition on heating. The nitro group in the aromatic series is bound very firmly in the molecule and is not readily exchanged for other groups. Several different products may be obtained by the reduction of the aromatic nitro compounds, the substances formed in any particular case depending on the conditions of experiment. In acid solution, amines are obtained, in alkaline solution, azoxy, azo and hydrazo compounds, and in neutral solution hydroxylamino compounds. The electrolytic reduction of the aromatic nitro compounds gives rise to substituted hydroxylamines which are immediately transformed into aminophenols or amines.

The nitrolic acids, R⋅C(:NOH)NO2, may be prepared by the action of nitrous acid on the primary nitroparaffins; by the action of hydroxylamine on the dibromnitroparaffins; and by the action of nitrogen peroxide on the -isonitroso fatty acids (G. Ponzio, Gazz., 1903, 33 (1), p. 508). They are colourless solids which are readily soluble in water and possess the character of Weak acids. They are characterized by the deep red colour of their solutions in alkalis. When strongly heated they decompose, forming fatty acids, nitrogen peroxide and nitrogen. By passing hydrochloric acid gas into an ethereal solution of the acids, the nitro group is eliminated and the hydrochloride of an oximido-acid is obtained (A. Werner and H. Buss, Ber., 1895, 28, p. 1232): CH3⋅C(:NOH)NO2+2HCl=HNO2+CH3⋅C(:NOH)Cl⋅HCl.

When heated with water and mineral acids, the nitrolic acids are completely decomposed, yielding fatty acids and nitrous oxide.