Carbonyl Dyes and Pigments

Abstract

The chemical class of colorants that is second in importance to azo dyes and pigments is characterized by the presence of a carbonyl (CO) group, which may be regarded as the essential chromophoric unit. A substantial part of this chapter is devoted to anthraquinones, the most important group of carbonyl dyes and pigments. In contrast to azo dyes, carbonyl dyes are found in nature; dyes such as indigo and alizarin – an anthraquinone derivative – are amongst the most important natural dyes for textiles. Synthetic carbonyl dyes and pigments are capable of providing a wide range of colours, essentially covering the entire visible spectrum. In terms of fastness properties, carbonyl dyes and pigments are often superior to their azo counterparts, often making them the colorants of choice when high technical performance is demanded. A particular textile application class dominated by carbonyl dyes is the vat dye class, a group of dyes applied to cellulosic fibres such as cotton. The ability of the carbonyl groups to undergo reduction to a water-soluble form which is capable of transferring to the fibre, and subsequently re-oxidised to its original system, is utilized. In this chapter the characteristic structural features of the most important types of carbonyl colorants are reviewed and an overview of some of the more important synthetic routes is presented.