Amino-azo-compounds

Two important classes of derivatives of the azo compounds which include some very valuable dyes are the amino azo and hydroxy azo compounds. The latter which are also called oxy azo compounds are derivatives of the azo compounds resulting from the substitution of one or more hydroxyl groups in the rings. 

The amino azo compounds are exactly analogous, having one or more amino groups in the rings. 

He found that tertiary amines like di-methyl aniline react easily, but that primary amines react in this way only when there are two such 

Diazo amino Compounds.—In the case of para primary di-amines and primary mono-amines such as aniline, the reaction does not take place in this way. It was found later, however, that primary monoamines did yield azo compounds by a molecular rearrangement of an intermediate diazo amino compound. 

Thus by means of the Griess Reaction it is possible to start with an amino compound, diazotise it and then couple up the diazo compound with an undiazotized amino compound and obtain the amino azo compound either directly or after molecular rearrangement. 

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Compounds containing two primary amino groups attached to a benzene ring can be prepared by the reduction of dinitro compounds and of nitroanilines, usually with tin or stannous chloride and hydrochloric acid or with iron and very dilute hydrochloric acid. / ara-diamines may also be obtained by the reduction of aromatic amino-azo compounds (e.g., p-aminodimethylanihne from methyl orange, see Section IV,78). p-Phenylenediamine may also be prepared from p-nitroacetanilide reduction with iron and acid yields p-amino-acetaniUde,.which may be hydrolysed to the diamine. 

If suitable amino azo compounds are coupled to iV-phenylamino-5-naphthol-7-sulfonic acid, violet, moderately lightfast paper dyes with good brilliance are obtained, e.g., C.I. Direct Violet 51, 27855 [6227-10-7] (15). 

If amino azo compounds which contain 1-naphthylamine or 1-naphthylamine-6- or -7-sulfonic acid as their middle component are coupled with 2-amino-5-naphthol-7-sulfonic acid and their derivatives blue paper dyes such as C.I. Direct Blue 71, 34140 [4399-55-5] (16) are obtained, which have good lightfastness but generally a slightly dull shade. 

In alkaline solution 2-methylbenzotriazole (185) is reduced to the 1,3-dihydro derivative which may be reoxidized anodically to the starting material.88 In acid solution the dihydrobenzotriazole (186) forms an o-amino-azo compound (187) this does not cyclize in alkaline solution. 

Aminoazobenzene. Aminoazobenzene and many other amino-azo compounds are only slightly soluble even in hot, dilute hydrochloric acid. Again, no attempt is made to dissolve the base completely, and a procedure similar to example 4 is used except that it is not necessary to cool the mixture while the base is being ground with hydrochloric acid. 

Constitution.— Both of these reactions of preparation establish the constitution of the amino azo compounds and also of the hydroxy azo compounds as we have represented them. While three isomers are possible in each case, depending on whether the azo group and the amino or hydroxyl group are in the ortho, meta or para positions in relation to each other, yet in fact only ortho and para compounds are known in most instances. The full constitution of the ortho and para amino azo benzene is then. 

The ortho and para amino azo compounds differ in certain reactions and the view is held by some that two different formulas represent them. We shall not take up the discussion of this question however. 

Amino azo compounds are in general yellow or brown crystalline substances insoluble or difficultly soluble in water, but soluble in alcohol or ether. They are basic compounds readily forming salts which usually possess a distinctly different color from that of the free bases. As amino compounds they are able to be diazotized and converted into still more complicated azo compounds in which two azo groups are present in the molecule and which are known as dis-azo compounds. 

The most important derivatives of the amino azo compounds are the sulphonic acids of which mono- and di-sulphonic acids are known. 

This is the simplest amino azo compound and is known in the para form. It is a yellow-brown crystalline substance melting at 126°, and boiling at 360°. It is soluble in alcohol and slightly in hot water. 

Butter Yellow.—The di-methyl derivative of amino azo benzene which we have referred to in our discussion of the general method for the formation of amino azo compounds by the Griess reaction (p. 569), is also a dye known as butter yellow It is insoluble in water, but soluble in oils and, therefore, is used to color butter. 

Both di-amino and tri-amino azo compounds are known. In these compounds in which two amino groups are in the same ring the azo group cannot be para to both and it is found that the most common form is the one in which one amino group is ortho and the other para. 

The important tri-amino azo compound is the one in which two amino groups are in one ring, ortho and para to the azo group and one amino group meta to the azo group in the other ring. The constitution of the compound is proven by its preparation from meta-phenylene di-amine, we/a-di-amino benzene. This is diazotized so that only one... 

Such a reaction agrees perfectly with the new formula which has been generally accepted as expressing the constitution of the free diazo base and the salts. The base thus takes the name benzene diazonium hydroxide and the salts, e.g., the chloride, benzene diazonium chloride signifying their ammonium character. The new formula does not, however, fit the reactions by which diazo. compounds are converted into azo or amino azo compounds nor the reduction of diazo benzene to phenyl hydrazine. Thus we have two formulas neither of which... 

The formation of the diazotate from the diazonium salt by means of alkalies is explained by the reverse of the first reaction. This makes clear the reaction by which the diazonium salts yield azo compounds (p. 569). The reaction takes place best in neutral or alkaline solution and under these conditions the diazonium salt would yield the diazo hydroxide compound which would then couple with the amine and form the amino azo compound. 

A high yield of a fused triazole is obtained when the oxime of a 2-aminobenz-anilide is treated with nitrous acid [3048]. Cyclization of amino-azo compounds with LTA is often carried out in dichloromethane but acetic acid also gives good... 

If formed, the triazene can often be converted into the amino azo compound by even gentle warming with dilute acid this conversion is smoother if the triazene is warmed with the amine used for coupling and a small amount of its hydrochloride.368 The acid-catalysed rearrangement of triazenes involves intermediate reformation of the diazonium salt and the amine.369,370 So, if rearrangement of a triazene is carried out in the presence of a different, more readily coupling amine, the diazonium component reacts preferentially with the latter e.g., A,ALdimethyl-/ -(phenylazo)aniline is obtained from diazoaminobenzene and N,N-di-methylaniline.368... 

Purines, Pteridines, and Related Systems.— This year has seen the development, particularly by Japanese workers, of several new and modified procedures for the synthesis of purines and other fused pyrimidine ring systems. Especially useful as precursors for these syntheses are the arylidene derivatives (241 X = NH2 or OH) and the 6-amino-azo-compounds (240 X = N). The amino-azo-compounds are cyclized directly to purine derivatives (242) on fusion with arylamines, " or,... 

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