2-Xanthenes, hydroxy-substituted

For uniformity with the stmctures given in the Colourindex the ammonium radical (9) is used for the amino-substituted xanthenes and the keto form for the hydroxy derivatives. The xanthene dyes may be classified into two main groups diphenylmethane derivatives, called pyronines, and triphenylmethane derivatives (eg, (4)), which are mainly phthaleins made from phthaUc anhydride condensations. A third much smaller group of rosamines (9-phenylxanthenes) is prepared from substituted ben2aldehydes. The phthaleins may be further subdivided into the following fluoresceins (hydroxy-substituted) rhodamines (amino-substituted), eg, (6) and mixed hydroxy/amino-substituted. 

Sahin, Nieger, and Brdse have reported also the oxidative coupling of various hexahydro-xanthenols. The application of an iron complex as oxidant converted the 2-hydroxy-substituted xanthenes 1056 (Scheme 13.26) to the 3,3- t S-coupled biaryl 1057 (565). It appears that these two papers ((564) and (674)) represent the only chemical studies published on the topic of xanthone or xanthene biaiyl-coupUng. 

The propensity of hydroxy-substituted biphenyls to undergo photodehydration in a manner like the hydroxybenzyl alcohols above (to give biphenyl-type quinone methides) was discovered during an investigation into the photoisomerization of xanthene (91) to 6H-dibenzo[fc,d]pyran (92) °... 

The co-condensation of 4 -acetylphenol-2,4-dinitrophenylhydrazone and substituted aminobenzoic acids such as2-aminobenzoic acid or acetyloxy-benzoic acid with methanal occurs under acid catalysis. But, the co-condensation of 4 -acetylphenol-2,4-dinitrophenylhydrazone, methanal, and any of the following benzoic acids 3-methylbenzoic acid, 4-aminobenzoic acid, and 2-(6-hydroxy-3-oxo-3H- xanthen-9-yl)-benzoic acid (phenolphthalein), occurs under base catalyst. These products generally have lower decomposition temperatures than those containing 3-(8 -pentadecenyl)phenol. 

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