Pyrocatechol

PYROCATECHOL, brenzcatechin, orthodihydroxybenzene (pyrocatechin, brenzcatechin, orthodioxy-benzol), is found in nature predominantly in the form of complex derivatives in wild grapes, plane tree bark, the wood of gum-producing trees, in various sorts of kino, in coal tar, bituminous shale, wood tar, and crude wood vinegar; pyrocatechinsulfuric acid is found along with free pyrocatechol in human pathological urine and in horse urine. Pyrocatechol is obtained by the dry distillation of catechu, kino, protocatechuic acid [C₆H₃(COOH)(OH)₂ = C₆H₄(OH)₂ + CO₂] and those tannins that give a green coloration with ferric chloride (e.g., coffee-tannin acid); industrially, pyrocatechol is obtained by the action of molten potassium hydroxide on brown coal and on resins (benzoin, guaiac resin, etc.), by heating cellulose with water to 200°, by heating guaiacol with hydrogen iodide, by the careful fusion of orthodiodophenol, C₆H₄(OH)(I), or orthophenolsulfonic acid with potassium hydroxide. Insignificant amounts of pyrocatechol are produced by the action of hydrogen peroxide on phenol or benzene in the presence of ferrous sulfate. Pyrocatechol sublimes in the form of white, shiny, bitter-tasting, faintly odorous rhombic leaflets. From solutions, pyrocatechol crystallizes in the form of short columns. Pyrocatechol melts at 104–105°, boils at 245°; it is readily soluble in water, alcohol, and ether; in aqueous solutions with ferric chloride, it gives a green coloration; upon the addition of soda, ammonia, or sodium acetate, the color shifts from violet to carmine-red. Solutions in potassium hydroxide or ammonia turn green in air, then brown and black. Lead subacetate gives a white precipitate of C₆H₄O₂Pb in aqueous solution. Pyrocatechol reduces solutions of noble metals even in the cold; copper (Fehling's solution) is reduced only upon boiling. With bromine, pyrocatechol yields tetrabromopyrocatechol, C₆Br₄(OH)₂, in the form of brown needles melting at 187°; acetyl chloride yields water-insoluble, crystallizable diacetylpyrocatechol, C₆H₄(O.C₂H₃O)₂. A derivative of pyrocatechol is guaiacol. Another very important derivative of pyrocatechol is adrenaline.

Action. The action of pyrocatechol on the organism is similar to that of phenol, but weaker; excitation of the centers of the medulla oblongata causes accelerated dyspneic respiration, an increase in blood pressure, and convulsions, followed by paralysis of the central nervous system. Death occurs under the phenomena of collapse caused by the paralysis of the respiratory and vasomotor centers. Pyrocatechol is more toxic (the lethal dose for a rabbit is 0.5 g) than its isomers—hydroquinone and resorcinol. Like other compounds of the phenol group, pyrocatechol exhibits antiseptic and antipyretic action, but being more toxic than resorcinol, it is not used in medicine. For the detection of pyrocatechol in urine, the latter is strongly acidified with hydrochloric acid, boiled for about 2 minutes, and after cooling, extracted repeatedly with ether; the residue after distilling off the ether extract is dissolved in water and filtered; the filtrate is precipitated with a slight excess of lead, the precipitate is collected, washed with a small amount of water, and upon the addition of diluted sulfuric acid, extracted again with ether; upon evaporation of the ether extract at room temperature, crystals of pyrocatechol separate, which are identified by their melting point (104–105°) and by the reaction with ferric chloride (green coloration). N. Kornilov.