PYROCATECHIN, or PYROCATECHOL  , ortho-dioxybenzene, C6H4(OH)2, first prepared in 1839 by H . Reinsch on distilling catechin (the juice of Mimosa catechu); occurs free in kino and in beechwood tar; its sulphonic acid is present in the urine of the horse and man . It results in the alkaline fusion of many resins, and may be prepared by fusing ortho-phenolsulphonic acid, o-chlorphenol, o-bromphenol, and o-phenoldisulphonic acid with potash, or, better, by heating its methyl ether, guaiacol, C6H4(OH) (OCH3), a constituent of beechwood tar, with hydriodic acid . Pyrocatechin crystallizes in white rhombic prisms, which melt at 104° and boil at 245°; it is readily soluble in water, alcohol and ether . Ferric chloride gives a green coloration with the aqueous solution, whilst the alkaline solution rapidly changes to a green and finally to a black colour on exposure to the air . It reduces silver solutions in the cold and alkaline copper on heating . Guaiacol may be obtained directly from beechwood tar, from pyrocatechin by methylation with potash and potassium methyl sulphate at 18o°, or from anisol by nitration, reduction of the ortho-nitroanisol to amino-anisol, which is then diazotized and boiled with water . It melts at 28° and boils at 25o° . It is employed in medicine as an expectorant . The dimethyl ether or veratrol i phosphate (PbCl)Pb4(PO4)3, sometimes occurring in sufficient is also used in medicine . Many other pyrocatechin derivatives have abundance to be mined as an ore of lead. been suggested for therapeutic application . Guaiacol carbonate is known as duotal, the phosphate as phosphatol, the phosphite as guaiaco-phosphal; phosphotal is a mixture of the phosphites of creosote phenols .

The valerianic ester of guaiacol is known as geosote, the benzoic as benzosol, the salicylic as guaiacolsalol, while the

glycerin ether appears as guaiamar . Pyrocatechin readily condenses to form heterocyclic compounds; cyclic esters are formed by phosphorus trichloride and oxychloride, carbonyl chloride, sulphuryl chloride, &c.; whilst ortho-phenylenediamine, o-aminophenol, and o-aminothiophenol give phenazine, phenoxazine and thiodiphenylamine .