Xanthone dyes

According to Schweppe (1992), Bignonia chica Humb. et Bonpl. (Bignoniaceae) produces the xanthone dye carajurin. This is dye designated by the Colour Index (1971) as Cl 75180 Natural Orange 5. 

UV spectra, 3, 599 xanthone synthesis from, 3, 840 Xanthydryl chloride xanthone synthesis from, 3, 840 Xanthyletin synthesis, 3, 743, 804 Xanthylium laser dye synthesis, 3, 865 Xanthylium salts aromaticity, 3, 641 charge density calculations, 3, 576 C NMR, 3, 592 H NMR, 3, 585 mass spectra, 3, 620 reactions... 

Much of the synthetic chemistry of xanthones has arisen out of their natural occurrence, a topic which has been reviewed (61CRV591), and also as a result of their incorporation into dyes. There are only two routes of any significance to xanthones and these basically involve ring closure on to either the heterocyclic oxygen atom or the carbonyl carbon atom (Scheme 185). 

Xanthene polymethyne dyes as active laser media 81YGK1200. Xanthones, natural 82UK1753. 

Mayo et al. [422] found that methylene blue, 3-ethoxy-5-methoxy-xanthone, crystal violet and acridine red sensitize the photo-oxidation of polyisoprene in chlorobenzene on exposure to UV light. The reaction rate is highest when the concentration of the dye is 10-4 mole 1 1. The addition of 2,6-di-tert-butyl-4-methylphenol to the solution does not stop the photo-oxidation reaction but merely reduces the quantity of oxygen absorbed. It may be concluded that the oxidation cannot occur by the free radical mechanism. 

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