Quinones polycyclic dyes

Anthraquinone, its derivatives, and a series of polycyclic quinones (Vat dyes) are reduced with an alkaline solution of sodium dithionite heated to 80 °C to dihydroxy derivatives. Solutions of alkaline salts of quinones are usually of a different color (for example, red for anthraquinone). After dropping the sample on filter paper the original color returns slowly in consequence of air oxidation. 

Vat cotton, rayon, and wool water-insoluble dyes solubilized by reducing with sodium hydrogensulfite, then exhausted on fiber and reoxidized anthraquinone (including polycyclic quinones) and indigoids... 

Vat dyes. The vat dyes are insoluble complex polycyclic molecules based on the quinone structure (keto-forms). They are reduced with sodium hydrosulfite in a strongly alkaline medium to give soluble leuco forms that have a great affinity for cellulose. After the reduced dye has been absorbed on the fiber, the leuco forms are reoxidized to the insoluble keto forms. The dyeings produced in this way have high wash and light-fastness. An example of a vat dye is vat blue 4 (indan-threne) [5]. 

Isoviolanthrone is described as a highly anellated polycyclic quinone system , essentially two benzanthrone molecules joined asymmetrically. This compound was first synthesised in 1907 and has long been known as a vat dye. However, it is the dichloro-derivative which is best known as a pigment, affording the reddish violet colour known as isoviolanthrone violet. Cl Pigment Violet 31 Colour Index, 1971 Wich, 1973 Herbst and Hunger, 1997). 

The vast majority of colored organic compounds are based on donor-acceptor chromogens, and with the exception of the polycyclic quinones and the phthalo-cyanines, all the commercially important synthetic dyes are of this type [34, 35]. 

Dyes based on anthraquinone and related polycyclic aromatic quinones are of great importance. Many of the most lightfast acid, mordant, disperse, and vat dyes are of this kind. The chromophore is the carbonyl group. 

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