Vat Dyes Containing Polycyclic Systems
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This subclass of vat dyes includes polycyclic systems such as dibezopyrenequinoes (665), anthanthrones (666), pyranthrones (667), dibenzanthrones (668), etc.A typical example of such dyes is caledon Jade Green XBN (669) which is a dibenzanthrone derivative. This dye (669) is prepared from benzanthrone (178). Benzanthrone (178) is fused with caustic potash in the presence of a flux such as sodium acetate and a sovent such as isobutanol and ari oxidised to get 4,4' bis-benzanthrone (670) which is subsquently treated with manganese dioxide and sulphuric acid at 350C gives 16,17-diketodibenzanthrone (671). This intermediate (671) is converted to 16, 17dihydroxydibenzanthrone (672) by the treatment with 35% aqueous sodium bisulphite solution. The subsequent methylation affords the vat dye (669) which is important for its brilliant green shade and overall excellent fastness.
