Direct dyes from benzidine congeners
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It is known that benzidine and its congeners3,3'-dimethyl (benzidine, 3,3'-dimethoxy benzidine and 3,3'- dichlorobezidine are genotoxic diamines6-13 and thus there has been a relentless search for non genotoxic alternatives the synthesis of direct dyes.14 Studies have shown that mutagenicity of a arylamines can be reduced by introducing bulky ortho substituents to the amino group.15-17 Continuous efforts have been made further in these lines to synthesise non-mutagenic diamines.12,13 It has also been shown that 2,2'-dimethyl-5,5'-dipropoxybenzidine (9) is non-mutagenic18 and gives non-mutagenic azo and azomethine pigments.19 In a recent study20 the diamines 2,2'-dimethy-5,5'-dipropoxybenzidine (10) have been prepared and used to prepare direct dyes having comparable colour and fastness properties to commercial direct dyes using the traditional naphthalene intermediates like J-acid and H-acid. It has been shown that the introduction of methyl groups in the 2,2'-positions gives the expected hypsochromic shifts in disazo direct dyes, and gives favourable results with regard to staining of adjacent fabrics.20
