salicylic acid or 2-hydroxybenzoic acid, C₆H₄(OH)CO₂H, a colorless, crystalline organic carboxylic acid that melts at 159°C;; it is soluble in ethanol and ether but is only slightly soluble in water. It is prepared commercially by heating sodium phenolate (the sodium salt of phenol) with carbon dioxide under pressure to form sodium salicylate, which is treated with sulfuric acid to liberate salicylic acid. Salicylic acid and its derivatives are toxic when consumed in large amounts. Sodium salicylate is used to a small extent as a food preservative and as an antiseptic in mouthwashes and toothpastes. The major use of salicylic acid is in the preparation of its ester derivatives; since it contains both a hydroxyl (-OH) and a carboxyl (-CO₂H) group, it can react with either an acid or an alcohol. The hydroxyl group reacts with acetic acid to form the acetate ester, acetylsalicylic acid (see aspirin). Several useful esters are formed by reaction of the carboxyl group with alcohols. The methyl ester, methyl salicylate (also called oil of wintergreen since it produces the fragrance of wintergreen), is formed with methanol; it is used in food flavorings and in liniments. The phenyl ester, phenyl salicylate, or salol, is formed with phenol; it is used in medicine as an antiseptic and antipyretic. This ester hydrolyzes, not in the acidic stomach, but in the alkaline intestines, releasing free salicylic acid. The menthyl ester, menthyl salicylate, which is used in suntan lotions, is formed with menthol.

White, crystalline solid organic compound used chiefly to make aspirin and other pharmaceutical products, including methyl salicylate (oil of wintergreen, for medicines and flavourings), phenyl salicylate (for sunburn creams and pill coatings), and salicylanilide (a cutaneous fungicide). Its molecular structure, with the formula C₆H₄(OH)COOH, consists of a six-membered aromatic ring (see aromatic compound) having a hydroxyl group (singlehorzbondOH) and a carboxyl group (singlehorzbondCOOH) bonded to adjacent carbon atoms; as such, it is both a phenol and a carboxylic acid. It and certain derivatives occur naturally in some plants, particularly species of Spiraea and Salix (willow). Large amounts are used in producing certain dyes.

Learn more about salicylic acid with a free trial on Britannica.com.