Monoazo Acid dyes:- (Part 1)
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Monoazo acid dyes containing a variety of coupling components are known. Thus, naphthols, arylamino derivatives, pyrazolones, etc. containing sufficient sulphonic acid or carboxylic acid groups are coupled with aryldiazonium salts derived from arylamino sulphonic acids. Acid orange II (41), Acid orange IV (538) and Metanil yellow (539) are typical examples.
Acid orange II (41) is prepared by the reverse diazotisation of sulphanilic acid and slow addition of the resulting diazonium salt to alkaline solution of b-naphthol containing caustic, soda ash and salt at 6-80 C. At the end of coupling temperature can be brought to 150C and pH 9.0 to 9.0. After stirring for a few hours, hydrochloric acid is added to bring pH slightly alkaline and the salted out dye is filtered and dried.
