The Reactions of Disulphide Dyes for the Covalent Coloration of Keratin

The synthesis of one ortho‐ and three para‐azo disulphide dyes is described. Disulphide exchange between these dyes and model compounds (cysteine and thioglycollic acid) has been studied. Previously reported work has indicated that covalent binding of colouring matters to wool can occur by disulphide exchange. The present dyes were therefore applied to keratin. The lack of fastness of the ortho‐azo dye showed that no disulphide exchange leading to covalent bonding occurred. The para‐azo disulphide dyes underwent disulphide exchange, but under the conditions used, this was effective only at high concentrations ofdye. Even then, only slight covalent bonding was achieved.