The nitro group has a very important action mainly on account of the readiness with which it can be introduced into the molecule, but its effect is much less than that of the azo group. The colour produced is generally yellow, which, in accordance with a general rule, is intensified with an increase in the number of groups; compare, for example, mono-, diand tri-nitrobenzene.
Nitro-phenols are readily obtained by the action of nitric acid on phenol.
By the reduction of nitro-phenols, the corresponding aminophenols are obtained, and of these, the metaand para-derivatives are the most important.
Meta-aminophenol is prepared by reducing metanitrophenol, or by heating resorcin with ammonium chloride and ammonia to 200° C. Dimethyl-meta-aminophenol is prepared by heating meta-aminophenol with methyl alcohol and hydrochloric acid in an autoclave; by sulphonation of dimethylaniline, the sulphonic acid formed being finally fused with potash; or by nitrating dimethylaniline, in the presence of sulphuric acid at 0° C. In the latter case a mixture of nitro-compounds is obtained which can be separated by the addition of sodium carbonate.
It is frequently used as a reducing agent: in acid solutions it reduces ferric to ferrous salts, arsenates to arsenites, permanganates to manganous salts, &c., whilst in alkaline solution it converts many organic nitro compounds into the corresponding amino derivatives.
For example: nitric acid and sulphuric acid readily react with benzene and its homologues with the production of nitro derivatives and sulphonic acids, while in the aliphatic series these acids exert no substituting action (in the case of the olefines, the latter acid forms an addition product); another distinction is that the benzene complex is more stable towards oxidizing agents.
This compound is readily oxidized to benzoic acid, C 6 H 5 000H, the aromatic residue being unattacked; nitric and sulphuric acids produce nitro-toluenes, C6H4 CH3 N02j and toluene sulphonic acids, C 6 H 4 CH 3 SO 3 H; chlorination may result in the formation of derivatives substituted either in the aromatic nucleus or in the side chain; the former substitution occurs most readily, chlor-toluenes, C 6 H 4 CH 3 Cl, being formed, while the latter, which needs an elevation in temperature or other auxiliary, yields benzyl chloride, C 6 H 5 CH 2 C1, and benzal chloride, C 6 11 5 CHC1 2.
From meta-brombenzoicacid two nitrobrombenzoic ac i ds are obtained on direct nitration; elimination of the bromine atom and the reduction of the nitro to an amino group in these two acids results in the formation of the same ortho-aminobenzoic acid.
Hence the positions occupied by the nitro groups in the two different nitrobrombenzoic acids must be symmetrical with respect to the carboxyl group. In 1879, Hubner (Ann., 1 95, p. 4) proved the equivalence of the second pair, viz.
Experience has shown that such mono-derivatives as nitro compounds, sulphonic acids, carboxylic acids, aldehydes, and ketones yield as a general rule chiefly the meta-compounds, and this is independent of the nature of the second group introduced; on the other hand, benzene haloids, amino-, homologous-, and hydroxy-benzenes yield principally a mixture of the orthoand para-compounds.
Benzene and its homologues, carboxylic acids, and nitro compounds are much more stable towards oxidizing agents than.
The first class includes those substances which require no preliminary treatment, and comprises the amides and ammonium compounds, pyridines, quinolines, alkaloids, albumens and related bodies; the second class requires preliminary treatment and comprises, with few exceptions, the nitro-, nitroso-, azo-, diazoand amidoazo-compounds, hydrazines, derivatives of nitric and nitrous acids, and probably cyanogen compounds.
The principal chromophores are the azo, -N = N -, azoxy, = N 2 O, nitro, - N02, nitroso, - NO, and carbonyl, = CO, groups.
The theories of colour have also been investigated by Hantzsch, who first considered the nitro-phenols.
On the chromophoreauxochrome theory (the nitro group being the chromophore, and the hydroxyl the auxochrome) it is necessary in order to explain the high colour of the metallic salts and the colourless alkyl and aryl derivatives to assume that the auxochromic action of the hydroxyl group is only brought strongly into evidence by salt formation.
Meyer, which are formed when nitrous acid acts on primary aliphatic nitro compounds.
Meyer formulated these compounds as nitroximes or nitro-isnitroso derivatives, viz.
Other substituent groups exercise morphotropic effects similar to those exhibited by the alkyl radicles; investigations have been made on halogen-, hydroxy-, and nitro-derivatives of benzene and substituted benzenes.
The nitro group behaves very similarly to the hydroxyl group. The effect of varying the position of the nitro group in the molecule is well marked, and conclusions may be drawn as to the orientation of the groups from a knowledge of the crystal form; a change in the symmetry of the chemical molecule being often attended by a loss in the symmetry of the crystal.
It combines with sulphuric acid to form nitro-sulphonic acid, SO 2 (OH) (N02).
Nitramide, NH 2 NO 2, is obtained by the action of sulphuric and nitric acids on potassium imidosulphonate, or by the action of ice-cold sulphuric acid on potassium nitro-carbamate (J.
Large quantities of ground mica are used in the manufacture of wall-paper, and to produce a frosted effect on toys, stage scenery, &c. Powdered mica is also used in the manufacture of paints and paper, as a lubricant, and as an absorbent of nitro-glycerine and disinfectants.
NITRO COMPOUNDS, in organic chemistry, compounds containing the monovalent radical -NO 2 directly combined with carbon.
Aiphatic Nitro Compounds.-The nitroparaffins may be obtained by the action of the alkyl iodides on silver nitrite (V.
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.
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.
Hantzsch (Ber., 18 99, 3 2, pp. 577 et seq.) are probably derived from the isomeric iso-nitro compounds R: NO(OH), and thus the nitro derivatives are to be looked upon as pseudo-acids.
Meyer, Ber., 1891, 24, p. 3530), whilst the primary nitro cornpdunds on heating with hydrochloric acid yield hydroxylamine and an acid: CH 3 CH 2 NO 2 +H 2 0 = CH3 C02H+NH20H (V.
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 primary compounds form nitrolic acids of the type R C (: NOH) NO, the secondary yield pseudo-nitrols of the type RR': C(NO)(NO 2), whilst the tertiary nitro compounds are not acted upon by nitrous acid.
Aromatic Nitro Compounds.-The aromatic nitro compounds are generally obtained by the direct action of nitric acid.
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.
Nitro compounds have also been prepared by the action of cuprous oxide on diazonium salts (T.
The mono-nitro compounds are stable and distil without decomposition; they have a pale yellow colour and possess an agreeable odour.
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.
The electrolytic reduction of the aromatic nitro compounds gives rise to substituted hydroxylamines which are immediately transformed into aminophenols or amines.
It readily forms a sodium salt, from the aqueous solution of which on the addition of a mineral acid an isomeric solid form of the nitro compound (melting at 84° C.) is precipitated.
Ruff (Ber., 18 9 8, 3 1, p. 457) from nitro-di-isobutyl by reducing it to the corresponding hydroxylamino compound with aluminium amalgam and oxidizing this with chromic acid mixture.
The products of the action of nitric acid on cellulose are not nitro compounds in the sense that picric acid is, but are nitrates or nitric esters.
In a similar manner, formic acid and dicyanophenylhydrazine yields a phenyl-triazole carboxylic acid, in which the phenyl group may be nitrated, the nitro group reduced to the amino group, and the product oxidized to a triazole carboxylic acid, which, by elimination of carbon dioxide, yields the free triazole: HO 2 C C=N H02C C =N, NPh-> N :CH N :CH They also result when the acidylthiosemicarbazides are strongly heated, the mercapto-triazoles so formed being converted into triazoles on oxidation with hydrogen peroxide (M.
Koerner (Ber., 1884, 17, p. 203) by condensing ortho-nitrobenzaldehyde with aniline, the resulting ortho-nitro-para-diamino-triphenylmethane being reduced to the corresponding orthoamino compound, which on oxidation yields chrysaniline.
It is readily nitrated to nitrobenzene, two, and even three nitro groups being introduced if some dehydrator such as concentrated sulphuric acid be present.
The primary aromatic amines may be prepared by the reduction of the nitro-hydrocarbons, the reducing agents used being either alcoholic-ammonium sulphide (N.
Concentrated nitric acid attacks them violently, producing various oxidation products, but if the amino group be "protected" by being previously acetylated, then nitro derivatives are obtained.
Mayow perceived the similarity of the processes of respiration and combustion, and showed that one constituent of the atmosphere, which he termed spiritus nitro-aereus, was essential to combustion and life, and that the second constituent, which he termed spiritus nitri acidi, inhibited combustion and life.
It is a powerful reducing agent, and is frequently employed for this purpose in organic chemistry; thus hydroxy acids are readily reduced on heating with the concentrated acid, and nitro compounds are reduced to amino compounds, &c. It is preferable to use the acid in the presence of amorphous phosphorus, for the iodine liberated during the reduction is then utilized in forming more hydriodic acid, and consequently the original amount of acid goes much further.
They may be prepared by the reduction of nitro compounds in alkaline solution (using zinc dust and alkali, or a solution of an alkaline stannite as a reducing agent); by oxidation of hydrazo compounds; or by the coupling of a diazotized amine and any compound of a phenolic or aminic type, provided that there is a free para position in the amine or phenol.
Amino-azo-benzene, C6H5 N2 C 6 H 4 NH 2, crystallizes in yellow plates or needles and melts at 126° C. Its constitution is determined by the facts that it may be prepared by reducing nitro-azo-benzene by ammonium sulphide and that by reduction with stannous chloride it yields aniline and.
Azoxy Compounds, R N O N R', are usually yellow or red crystalline solids which result from the reduction of nitro or nitroso compounds by heating them with alcoholic potash (preferably using methyl alcohol).
Those not containing a nitro group may be prepared by the oxidation of the corresponding mixed hydrazo compounds with mercuric oxide.
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 6 H 5 NH N: C(N02)CH3+NaOH=NaN02+C6H5NH NH CO CH3.