Cyanine Dyes:- (Part 2)
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Cyanine Dyes:-
Most of the cyanine dyes however lack fastness to acids and other agencies such as light, hence they have very limiter application for textiles. A few nembers of cyanine dyes also called as polymethinedyes are useful basic or cationic dyes for textile purpose. Most of these dyes are derived from heterocyclic nitrogen system indole with pecullar structures. These dyes are also known as Astrazon colours. Astrafloxine FF and Astrazon Pink FG are two examples of the series. The key inermediate required for their synthesis is the indolenine base which is condensed with the appropriate aldehyde or the indolenine-w-aldehydewhich is condensed with the appropriate amine or active methyl group of a suitable compound. The indolenine base is obtained by the treatment of alkali on 2,3,3—trimethylindolenine methiodide which is prepared by the quarternisation of 2,3,3—trimethyl indolenine with nethyl iodide. The indolenine-w-aldehyde is prepared from the indolenine bas by direct formylation with dimethyl formamide and phosphorous oxychloride. The synthesis of Astrazon Pink FG is given below.
