XANTHONE (dibenzo-y-pyrone, or diphenylene ketone

See also:

• OXIDE

oxide)  , C13HiO2, in organic chemistry, a heterocyclic compound containing the ring system shown below . It is obtained by the oxidation of xanthene (methylene diphenylene oxide) with chromic acid; by the action of phosphorus oxycliloride on disodium salicylate; by heating 2.2'-dioxybenzophenone with concentrated sulphuric acid; by distilling fluoran with lime; by the oxidation of xanthydrol (R . Meyer, Ber., 1893, 26, p . 1277); by boiling diazotized 2.2'-diaininobenzophenone with water (Heyl., Ber., 1898, 31, p . 3034) ; by heating salol with concentrated sulphuric acid (C . Graebe, Ann., 1889, 254, p . 280), and by heating potassium-ortho=chlorobenzoate with sodium phenolate and a small quantity of copper powder to 180–190° C . (F . Ullmann, Ber., 1905, 38, pp . 729, 2120, 2211) . It crystallizes in needles which melt at 173–174° and boil at 349–350° C., and are volatile in steam . Its solution in concentrated sulphuric acid is of a yellow colour and shows a marked blue fluorescence .

The carbonyl

group is not ketonic in character since it yields neither an oxime nor hydrazone . When fused with caustic potash it yields phenol and salicylic acid . Mild reducing agents convert it into xanthydrol, the group > CO becoming > CH•OH, whilst a strong reducing agent like hydriodic acid converts it into xanthene, the group> CO becoming> CH2 . Phosphorus pentasulphide at 140–150° C. converts it into xanthion by transformation of > CO to >CS (R . Meyer, Ber., 1900, 33, p . 2580), and this latter compound condenses with hydroxylamine to form xanthone oxime . All four mono-hydroxyxanthones are known, and are prepared by heating salicylic acid with either resorcin, pyrocatechin or hydroquinone; they are yellow crystalline solids, which act as dyestuffs . The 1.7-di,hydroxyxanthone, known as euxanthone, is prepared by heating euxanthic acid with hydrochloric acid or by heating hydrouinone carboxylic acid with l3-resorcylic acid and acetic anhydride (S . Kostanecki, Ber., 1891, 24, p . 3983E C . Graebe, Ann., 1889, 254, p . 298) .

It is also obtained from

Indian yellow (Graebe, ibid.), formed in the urine of cows fed on mango leaves . It crystallizes in yellow needles which sublime readily . On fusion with caustic potash it decomposes with formation of tetrahydroxy-benzophenone, which then breaks up into resorcin and hydroquinone . The isomeric 1.6-dihydroxyxanthone, isoeuxanthone, is formed when 13-resorcylic acid is heated with acetic anhydride . Gentisein, or 1.3.7-trihydroxyxanthone, is found in the form of its methyl ether (gentisin) in gentian root; it is obtained synthetically by condensing phloroglucin with hydroquinone carboxylic acid . Xanthene, C15H1oO, may be synthesized by condensing phenol with ortho-cresol in the presence of aluminium chloride . Its tetramethyl-diamino derivative, which is formed by condensing formaldehyde with dimethyl-meta-aminophenol and subsequent elimination of water from the resulting diphenyl methane derivative, is the leuco base of pyronine, into which it passes by oxidation . Cl(CHa)2N/\/\ o /\% 8 7/\/CO\, /~//CH\ \/\ /\/~3 5 4 Xanthone . Pyronine .