The Relationship between the Chemical Constitution of Vat Dyes and their Dyeing and Fastness Behaviour

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Abstract
An outline is given of the developments in vat dyeing technique over the past twenty–five years, and an attempt is made to correlate the effects of the chemical constitution of vat dyes on dyeing and fastness properties. Present conceptions of the mechanism of vat dyeing are described, and (17 J vat dyes (mainly anthraquinonoid) are arranged in five chemical classes, which are further sub–divided into groups of closely similar constitution and properties. The hue characteristics and dyeing and fastness properties of each group are then described. The dyeing properties of vat dyes (with particular reference to a series of unsubstituted anthraquinone–carbazolo dyos) are then reviewed and some general rules are found to exist in respect of dyebath assistant requirements (caustic soda, sodium hydrosulphite, and exllausting salt) as well as for migration powers. Louco stability of the vat in respoct of over–reduction, hydrolysis, dehalogenation, and molecular rearrangement has been investigated from the point of view of the constitution of the individual dyes. Fastness properties and their relation to the constitution of the dyes have been examined from the viewpoint of resistance to light, overoxidation, bleaching, washing, and soda boiling. Finally, a simple test for the determination of the tendering powers of vat dyes on cellulose on exposure to light is proposed. A large number of dyos have been examined by a silver staining technique, and tendering has been directly related to the constitution of many dyes. Attempts to prepare inactive yellow and orange dyes by mixing active and inactive dyes proved of littlo value, but in the production of greens it has been found possible to inhibit tendering, even in the presence of a highly active yellow.