Claus, Ber., 1873, 6, p. 723); by passing aniline vapour over lead oxide, or by the oxidation of dihydrophenazine, which is prepared by heating pyrocatechin with orthophenylene diamine (C. Ris, Ber., 1886, 19, p. 2206).
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.
Orthophenylene diamine, C 6 H 4 (NH2)2, crystallizes from water in plates, which melt at 102 -103° C. and boil at 256-258° C. When heated with io% hydrochloric acid to 180° C. it yields pyrocatechin (Jacob Meyer, Ber., 1897, 30, p. 2569).
Jour., 1901, 26, p. to) attempted to prepare this compound by the action of iodine on the lead salt of pyrocatechin suspended in chloroform.
Willstatter (Ber., 1904, 37, p. 4744), by dissolving pyrocatechin in absolute ether containing ignited sodium sulphate and then adding dry silver oxide, obtained the quinone in dark red crystalline plates which decompose between 60° and 70° C.