Cyanation of water-soluble disperse dyes

Dyes containing the SO2CH2COOH group (SMC) are water soluble and, in the dyeing process these dyes decarboxylate to give disperse dyes which can be absorbed by polyester fibres. Some ortho-bromo azo dyes of this type are treated with a cyanating agent to give the corresponding ortho-cyano dyes. The cyanation reaction takes place in aqueous solution preferably of pH 7¯9 at room temperature. Various factors affecting this reaction are considered. The dyes colour polyester fibres in red to blue shades with good fastness.