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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 aspirinaspirin,
acetyl derivative of salicylic acid (see salicylate) that is used to lower fever, relieve pain, reduce inflammation, and thin the blood. Common conditions treated with aspirin include headache, muscle and joint pain, and the inflammation caused by rheumatic fever and
..... Click the link for more information. ). 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.
(o-hydroxybenzoic acid), the simplest aromatic hydroxycarboxylic acid. A colorless crystalline compound that is poorly soluble in water but readily soluble in organic solvents. Melting point, 159°C; boiling point, 211°C (at 2.66 kilonewtons per sq m).
Salicylic acid is widespread in nature, especially in the form of the glycoside of its methyl ester, methyl salicylate. It is usually produced industrially by carboxylation of phenol (the Kolbe-Schmitt reaction). Salicylic acid has weak antiseptic and irritant properties and, at high concentrations, keratolytic properties. It is used topically in salve, paste, powder, and solution form for treating skin ailments. It is an ingredient of Las-sar’s paste, galmanin powder, and corn lotion and plaster. The sodium salt of salicylic acid (sodium salicylate), the amide (sali-cylamide), and acetylsalicylic acid (aspirin) are used as antipyretic, antirheumatic, anti-inflammatory, and analgesic agents. The phenyl ester of salicylic acid is used as an antiseptic, and p-aminosalicylic acid (PAS) is used as an antituberculosis drug.
Because of its antiseptic action, salicylic acid is used in the preservation of foods. Its esters are used in the manufacture of azo dyes and odoriferous substances, and the acid itself is used for the colorimetric identification of iron and copper and for the separation of thorium from other elements.