Pyrocatechol, often known as catechol or benzene-1,2-diol, is a benzenediol, with formula C6H4(OH)2. It was first prepared in 1839 by H. Reinsch by distilling catechin (the juice of Mimosa catechu). This colourless compound occurs naturally, but about 20000 tons are manufactured each year, mainly as precursors to pesticides, flavors, and fragrances. Its sulfonic acid is often present in the urine of many mammals. Small amounts of catechol occur naturally in fruits and vegetables, along with the enzyme polyphenol oxidase. Upon mixing the enzyme with the substrate and exposure to oxygen (as when a potato or apple is cut), the colorless catechol oxidizes to reddish-brown benzoquinone derivatives. The enzyme is inactivated by adding an acid, such as lemon juice, or by refrigeration. Excluding oxygen also prevents the browning reaction. Catechol melts at 28 oC and boils at 250 oC. It is employed in medicine as an expectorant. The dimethyl ether or veratrol is also used in medicine. Many other pyrocatechin derivatives have been suggested for therapeutic application.
