A new and unequivocal synthesis of a ‘three-branched’ azaphenothiazine heterocycle is described. The parent compound. 15,16-dithia-3,5,10,12-tetra azabenzo[h]pentaphene was obtained by mononitration of pyridin-4[1H] one and thiation with P2S5 to give 3-nitropyridine-4[1H]-thione. Base catalysed condensation of this compound with 2,3-dichloro-1,4 naphthoquinone gave 2,3-bis(3-nitro-4-pyridylthio)-1,4-naphthoquinone which, on reduction with tin(II) chloride and glacial acetic acid, gave the parent compound, a purple-red dye. Also reported is the synthesis of a new angular diazaphenothiazine, 9-bromo-6-chloro-8,11,12-triazabenz[a]an thracen-5-one. Their intense colorations, ease of preparation in good yields and ready reduction with Na2S2O4. and reoxidalion by atmospheric oxygen make these compounds good vat dyes. These purple-red dyes and their derivatives were also found to be good colorants for paper, plastic, paint, ink, soap, polish, rubber, candle and cosmetic products.
Dyes and Pigments 12/1988; 9(6):427–442. DOI:10.1016/0143-7208(88)82002-3