Azine Dyestuffs

The azine group, with the four adjacent carbon atoms, forms a new ring, containing six atoms, so that phenazine may be regarded as containing three rings, like, anthracene. 

The azines are in some respects analogous to the quinone-anilides. 

The reaction will be easily understood from the following graphic equation — 

The simplest azines are not dyestuffs, they are slightly coloured bodies, generally yellow, and possessing weak basic properties, their salts being decomposed by water. 

The introduction of amido-groups intensifies the basic character of the azine, and increases the dyeing properties. 

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On reduction, toluylene blue gives triamidotolylphenylamine. On heating, toluylene red [4] see Azine Dyestuffs) is formed. 

The azine dyestuffs mostly possess a well-marked fluorescence this appears in some cases in the alcoholic solutions of the salts, and in others in the ethereal solution of the base. 

Toluylene red is a dimethyl derivative of a homologue of diamidophenazine, and is prepared by oxidation of dimethylpara-pbenylenediamine with metatoluylenediamine at the boil, and is also formed by heating toluylene blue (amidoindamine) [4] (see introduction to the Azine Dyestuffs). The base forms orange-red crystals, which contain four molecules of water. The water may be expelled at 150°, leaving the anhydrous compound, which is of a blood-red colour [4J. The alcoholic and ethereal solutions fluoresce strongly. 

The dyestuffs eoming under this classifieation contain four nitrogen atoms. Unlike the previous azine dyestuffs they contaiu at least three hydrocarbon chains. Although their behaviour shows them to be phenazine derivatives, they differ in many respects from those previously described. Especially noticeable is their strong basic character, which in many respects resembles that of the quaternary ammonium bases, and the characteristic bitter taste of the latter compounds is also present in the saffra-nines. Another point of difference from the rest of the azine dyestuffs is that the free base has the same colour as the monoacid salts. 

Many hydrazones and azines are colored and useful as dyestuffs. Examples are 2-hydroxynaphthazine, a yellow fluorescent dye (Lumogen LT Bright Yellow), and the pyridon—azino—quinone class of red-violet dyes. Numerous hydrazine derivatives are antioxidants and stabilizers by virtue of their reducing and chelating powers. 

Hydrazine and its derivatives find considerable use in the synthesis of biologically active materials, dyestuff intermediates and other organic derivatives. Reactions of aldehydes to form hydrazides (RCH=NNH2) and azines (RCH=NN=CHR) are well known in organic chemistry, as is the use of hydrazine and its derivatives in the synthesis of heterocyclic compounds. 

AZTNES. The products of the reaction between an aldehyde nr a ketone with hydrazine are termed azines. A number of dyestuffs and complex members of the pyridine family of compounds also are termed azines. See also Pyridine and Derivatives. 

Reduction and reoxidation tests. Reduction with hydrosulphite B X is effected by boiling the fabric in this reagent for about two minutes. Azines, thiazines, oxazines, etc., and most of the azo-dyestuffs are completely reduced in about half a minute, but insoluble azo-dyestuffs require more prolonged boiling for their complete reduction. 

These comprise a series of weak dyestuffs discovered by Caro and Wittj the type of which is obtained by heating azophenine with concentrated sulphuric acid or with zinc powder. The formation of this compound, which contains two azine rings, may be represented by the following equation —... 

Fast Black.—The commercial product bearing this name is obtained by action of nitroso-dimethylaniline on meta-oxy-diphenylamine. It contains the groups characteristic both of the oxyindamines and the azines. It is a basic dyestuff, and is fixed on cotton prepared with sumac and acetate of iron. 

Another dyestuff based on p-phenylenediamine is Safranine B Extra (C. 1.50200), an azine dye which is obtained by reaction with aniline, via an intermediate indamine stage the earlier importance of safranine dyes however has diminished. 

The development of reactive components based on azines started in 1956 with the launch of chlorottiazine dyes by ICI. The immediate success of the triazine based reactive dyes led to an intensive search for alternative reactive systems by the various dyestuff firms. Much efforts has been expended on the synthesis and evaluation of several related fluoropyrimidinyl derivatives. Out of all the patented components only 5-chloro-2,4,6-trifluoropyrimidine and 5-chloro-2,4-difluoro-6-methylpyrimidine have attained notable technical and economic significants. Figure 16 shows the relevant dyesmfifs and their manufacturers. 

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