a group of vat dyes based on benzanthrone. The benzanthrone molecule (I) consists of four condensed six-member rings. Benzanthrone itself does not have dye properties.
Benzanthrone dyes are obtained by the condensation of two molecules of benzanthrone, with the splitting-off of four hydrogen atoms and the formation of two carbon-to-carbon bonds. Depending on the condensation conditions, either di-benzanthrone (II) or isodibenzanthrone (III) is obtained. Both substances, together with their various derivatives, the vat dyes, are distinguished by their great fastness, variety, and intensity of color tone; some of them are also used as fast pigments. Dibenzanthrone, Vat Blue 20, is obtained by fusing benzanthrone with KOH or a mixture of KOH and NaOH at 225° C. The alkaline solution of the product of its reduction by hydrosulfite is a reddish-violet color. It dyes cotton a dark blue color that is highly fast against the action of light and chlorine. Dimethoxydibenzanthrone, Vat Green 1, is obtained by the oxidation of dibenzanthrone to 16,17-dioxy dibenzanthrone and the methylation of the oxy groups. [Color descriptions are from the Colour Index, vol. 3, 1957.] It dyes cotton a very vivid dark blue-green color. Dibromodimethoxydibenzanthrone, Vat Green 2, is obtained by bromination of dimethoxydibenzanthrone; it yields colors of a yellowish hue. Isodibenzanthrone is reddish-violet and is obtained by treating 3-chlorobenzanthrone or 3,3’-benzanthronyl sulfide in a medium of alcohols and KOH. The most important derivatives of isodibenzanthrone are the halogen derivatives, such as dichlorisodibenz-anthrone, Vat Violet 1. It dyes cotton a violet color. AH benzanthrone dyes are insoluble in water and are applied to fabric in the form of leuco compounds.
REFERENCE
Kogan, I. M. Khimiia krasitelei, 3rd ed. Moscow, 1956.Want to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit the webmaster's page for free fun content.
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