XANTHONE (dibenzo-y-pyrone, or diphenylene ketone oxide)

This article appears in Volume V28, Page 882 of the Encyclopedia Britannica.

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XANTHONE (dibenzo-y-pyrone, or diphenylene ketone oxide) , C13HiO2, in organic

chemistry

, a heterocyclic compound containing the ring

system

SYSTEM

shown below. It is obtained by the oxidation of xanthene (methylene diphenylene

oxide

OXIDE

) with chromic acid; by the action of phosphorus oxycliloride on disodium salicylate; by

heating

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

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 180190 C. (F. Ullmann, Ber., 1905, 38, pp. 729, 2120, 2211). It crystallizes in needles which melt at 173174 and boil at 349350 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

CAUSTIC (Gr. rcavvraubs, burning)

potash it yields phenol and salicylic acid. Mild reducing agents convert it into xanthydrol, the group > CO becoming > CHOH, whilst a strong reducing agent like hydriodic acid converts it into xanthene, the group> CO becoming> CH2. Phosphorus pentasulphide at 140150 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

HYDROXYLAMINE, NH2OH

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

CAUSTIC (Gr. rcavvraubs, burning)

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

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

ALUMINIUM (symbol Al; atomic weight 27.0)

chloride. Its tetramethyl-diamino derivative, which is formed by condensing formaldehyde with dimethyl-meta-aminophenol and subsequent elimination of water from the resulting

diphenyl

DIPHENYL (phenyl benzene), C6H5

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.
(CH3)2

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