C6H6O2 = 110.048.
Pyrocatechin, C6H4(OH)2, the ortho variety of the three isomeric dihydroxybenzenes, occurs naturally in the leaves of the Virginian creeper, Ampelopsis hederacea (N.O. Vitaceae), and is found among the products of the distillation of catechu, kino, and most vegetable extracts containing tannins. It is present in crude pyroligneous acid distilled from wood. Tar on keeping acquires a granular appearance, partly owing to the formation of minute crystals of pyrocatechin. It may be prepared chemically by fusing potassium phenol-sulphonate with potassium hydroxide, also by heating guaiacol to 195° to 200°, and then passing in hydriodic acid as long as methyl iodide distils over. Pyrocatechin occurs in the form of white, glistening, short, rectangular prisms, or acicular crystals, having a slight odour and a bitter taste. Melting-point, 104°; boiling-point, 240° to 245°, but it begins to sublime below this temperature in thin laminae. It burns with a bright flame. The aqueous solution reduces silver salts in the cold, and Fehling's solution on warming; the alkaline aqueous solution rapidly absorbs oxygen, the colour changing to green and finally to black. With ferric chloride it yields a green colour, changing to violet on addition of ammonia or sodium bicarbonate. With lead acetate a white precipitate is formed. It precipitates a concentrated solution of egg albumen, but not gelatin. With nitric acid it reacts violently, forming oxalic acid. It has weak acidic properties, and should be protected from light and ammonia vapour.
Soluble in water, alcohol, ether, or hot toluene; moderately soluble in benzene or chloroform.
Uses.—Pyrocatechin is not employed in medicine. It is the starting point in the preparation of synthetic adrenine. and is also largely used as a reducing agent in photography.