AZO COMPOUNDS, organic substances of the type R N:N R' (where R = an aryl radical and R' = a substituted alkyl, or aryl radical).
The azo compounds are intensely coloured, but are not capable of being used as dyestuffs unless they contain salt-forming, acid or basic groups.
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.
It acts as a weak antiseptic. It is used for enriching coal gas, as a vermin killer, in the manufacture of certain azo dyes, and in the preparation of phthalic acid (q.v.).
Witt), and by the decomposition of ortho-anilido-(-toluidido- &c.)-azo compounds with dilute acids.
He was a pupil of Azo, and the master of Odofredus, of Hostiensis, and of Jacobus de Ravanis, the last of whom has the reputation of having first applied dialectical forms to legal science.
From the primary amines are derived the diazo compounds and azo compounds; closely related are the hydrazines (q.v.).
16, p. 2546) uses a mixture of soda-lime, stannous chloride and sulphur for nitroand azo-compounds, and C. Arnold (Ber.
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 azo-group is particularly active, both the aliphatic and aromatic compounds being coloured.
The simplest aliphatic compounds, such as diazo-methane, diazoethane, and azo-formic acid, are yellow; the diamide of the latter acid is orange-red.
Of the aromatic compounds azo-benzene is bright orange-red, and a-azonaphthalene forms red needles or small steel-blue prisms. The azogroup, however, has little or no colouring effect when present in a ring system, such as in cinnolene, phthalazine and tolazone.
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.
The quinonoid structure of many coloured compounds has been proved experimentally, as, for example, by Hewitt for the benzene-azo-phenols, and Hantzsch for triaminotriphenyl methane and acridine derivatives; but, at the same time, many substances cannot be so explained.
The acid finds considerable use in organic chemistry, being employed to discriminate between the different types of alcohols and of amines, and also in the production of diazo, azo and diazo-amino compounds.
The barons supported Azo of Liguria, the lawful successor of Herbert II.; the citizens of Le Mans set up a commune, expelled Azo's representatives and made war on the barons.
In acid solution, amines are obtained, in alkaline solution, azoxy, azo and hydrazo compounds, and in neutral solution hydroxylamino compounds.
The ortho-compounds condense to azimido benzenes, the metacompounds yield azo-dyestuffs, and the para-compounds yield bis-diazo compounds of the type XN2ï¿½C6H4ï¿½N2X.
The a-naphthylamine sulphonic acids are used for the preparation of azo dyes, these dyes possessing the important property of dyeing unmordanted cotton.
Azo-benzene, C 6 H 5 N:NC 6 H 5y discovered by E.
Amino-azo Compounds may be prepared as shown above.
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.
Triamino-azo-benzene: (meta-aminobenzene-azo-meta-phenylene diamine or Bismarck brown, phenylene brown, vesuvine, Manchester brown), NH 2.
Alkylated amino-azo-benzenes are also known, and are formed by the coupling of diazonium salts with alkylated amines, provided they contain a free para.
Methyl orange (helianthin, gold orange, Mandarin orange), (CH 3) 2 N C 6 H 4 N 2 C 6 H 4 SO 3 Na, is the sodium salt of paradimethylaminobenzene-azo-benzene sulphonic acid.
Soc., 1900, 77, pp. 99 et seq.) nitrated para-oxyazobenzene with dilute nitric acid and found that it gave a benzene-azo-ortho-nitrophenol, whereas quinone are not attacked by dilute nitric acid.
Hewitt has also attacked the problem by brominating the oxyazobenzenes, and has shown that when the hydrobromic acid produced in the reaction is allowed to remain in the system, a brombenzene-azo-phenol is formed, whilst if it be removed (by the addition of sodium acetate) bromination takes place in the phenolic nucleus; consequently the presence of the mineral acid gives the azo compound a pseudo-quinonoid character, which it does not possess if the mineral acid be removed from the sphere of the reaction.
Para-oxyazobenzene (benzene-azo-phenol), C 6 H 5 N: N (1) C6H4 011(4), is prepared by coupling diazotized aniline with phenol in alkaline solution.
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.
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.
Benzene-azo-methane, C 6 H 5 N 2 CH 3, is a yellow oil which boils at 150° C. and is readily volatile in steam.
N 2 COOH, may also be considered as mixed azo derivatives.
Phenyl-azo-carboxylic acid, C 6 H 5 N 2 Cooh, is obtained in the form of its potassium salt when phenylsemicarbazide is oxidized with potassium permanganate in alkaline solution (J.
The corresponding amide, phenyl-azo-carbonamide, C6H5N2: CONH 2, also results from the oxidation of phenylsemicarbazide (Thiele, loc. cit.), and forms reddish-yellow needles which melt at 114° C. When heated with benzaldehyde to 120° C. it yields diphenyloxytriazole, (C6H5)2CN3C(OH).
Numerous mono-, diand trisulphonic acids of a-naphthol are employed in the preparation of azo dyes.
Blagden (Ber.,1900,33,p.2544), who consider that three simultaneous reactions occur, namely, the formation of labile double salts which decompose in such a fashion that the radical attached to the copper atom wanders to the aromatic nucleus; a catalytic action, in which nitrogen is eliminated and the acid radical attaches itself to the aromatic nucleus; and finally, the formation of azo compounds.
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.