vat dyes

  Vat dyes have been used for many decades to color cotton and other cellulose fibers. Despite their high cost and their muted colors, these dyes are extremely important for certain textiles because of their superior fastness. Very few new vat dyes have been developed over the past few years. Water-insoluble vat dyes are converted to soluble anthrahydroquinones by reducing  agents,  such  as  sodium  dithionite (hydrosulfite)  in  the  presence  of sodium  hydroxide.  The  sodium  salts  of  these  mostly  deep  colored  leuco  compounds penetrate cellulose fibers. The insoluble dye is attached firmly to the fiber after  reoxidation .  Representative  of  a  special  form  are  the water-soluble  sulfuric  acid  esters of the anthrahydroquinone compounds, namely, the leuco esters of vat dyes. On the basis of their chemical constitutions the anthraquinoid vat dyes may be classified in the following major groups: acylaminoanthraquinones, anthraqui- noneazoles, anthrimides and other linked anthraquinones, anthrimidocarbazoles,

phthaloylacridones, benzanthrone dyes, indanthrones, and other polycondensed ring systems.