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Encyclopedia Britannica - Main :: SAC-SAR |
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SALICYLIC ACID (ortho-hydroxybenzoic acid) , an aromatic acid, C6H4(OH)(CO2H), found in the free state in the buds of Spiraea Ulmaria and, as its methyl ester, in gaultheria oil and in the essential oil of Andromeda Leschenaultii. It was discovered in 1838 by Piria as a decomposition product of salicin. It may be obtained by the oxidation of saligenin and of salicylic aldehyde; by the distillation of copper benzoate; by the decomposition of anthranilic acid with nitrous acid; by fusion of ortho-chlor or ortho-brom benzoic acid with potash; by heating orthocyanphenol with alcoholic potash; by heating a mixture of phenol, carbon tetrachloride and alcoholic potash to zoo C. (F. Tiemann and K Reimer, Ber., 1876, 9, p. 1285); and by the action of sodium on a mixture of phenol and chlorcarbenic ester (T. Wilm and G. Wischin, Zeit. f. Chemie, 1868, 6). It is manufactured by Kolbe's process or by some modification of the same. Sodium phenolate is heated in a stream of carbon dioxide in an iron retort at a temperature of 18o-22o C., when half the phenol distils over and a basic sodium salicylate is left. The sodium salt is dissolved in water and the free acid precipitated by hydrochloric acid (H. Kolbe, Ann., 186o, 115, p. 201). R. Schmitt (Jour. peak
Salicylic acid crystallizes in small colourless needles which melt at 155 C. It is sparingly soluble in cold water, but readily dissolves in hot. It sublimes, but on rapid heating decomposes into carbon dioxide and phenol. It is volatile in steam. Ferric chloride colours its aqueous solution violet. Potassium bichromate and sulphuric acid oxidize it to carbon dioxide and water; and potassium chlorate and hydrochloric acid to chloranil. On boiling with concentrated nitric acid it yields picric acid. When heated with resorcin to zoo C. it gives trioxybenzophenone. Bromine water in dilute aqueous solution gives a white precipitate of tribromophenol-bromide C6H2Br3.OBr. Sodium reduces salicylic acid in boiling amyl alcohol solution to n-pimelic acid (A. Einhorn and R. Willstatter, Ber., 1893, 26, pp. 2, 913; 1894, 27 p. 331). Potassium persulphate oxidizes it in alkaline solution, the product on boiling with acids giving hydroquinone carboxylic acid (German Patent 81,297). When boiled with calcium chloride and ammonia, salicylic acid gives a precipitate of insoluble basic calcium salicylate, C6114 a reaction which serves to distinguish it from the isomeric meta-and para-hydroxybenzoic acids. It yields both esters and ethers
Methyl Salicylate, C6H4(OH)CO2CH6, found in oil of wintergreen, in the oil of Viola tricolor and in the root of varieties of Polygala, is a pleasant-smelling liquid which boils at 222 C. On passing dry ammonia into the boiling ester, it gives salicylamide and dimethylamine. When boiled with aniline it gives methylaniline and phenol. Ethyl salicylate, C6H4(OH)CO2C2H6, is obtained by boiling salicylic acid with alcohol and a little sulphuric acid, or by dropping an alcoholic solution of salicylic acid into 13-naphthalene sulphonic acid at a temperature of 140-150 C. (German Patent 76,574). It is a pleasant-smelling liquid which boils at 233 C. It is practically unchanged when boiled with aniline. Phenyl salicylate, C6H4(OH)C02C6H6, or salol, is obtained by heating salicylic acid, phenol and phosphorus oxychloride to 120-125 C.; by heating salicylic acid to 220 C.; or by heating salicyl metaphosphoric acid and phenol to 140-150 C. (German Patent 85,565). It crystallizes in rhombic plates which melt at 42 C. and boil at 172 C. (12 mm.). Its sodium salt is transformed into the isomeric C6H4(OC6H5) CO2Na when heated to 300. When heated in air for many hours it decomposes, yielding carbon dioxide, phenol and xanthone. Acetyl-salicylic acid (salacetic acid), C5H4(O000H3)CO2H, is obtained by the action of acetyl chloride on the acid or its sodium salt (K. Kraut, Ann., 1869, 15o, p. 9). It crystallizes in needles and melts at 132 C. (with decomposition). Hydrolysis with baryta water gives acetic and salicylic acids. It is used in medicine
Applications.The addition of a little of the acid to glue renders it more tenacious; skins to be used for making leather do not undergo decomposition if steeped in a dilute solution; butter containing a small quantity of it may be kept sweet for months even in the hottest weather. It also prevents the mouldiness of preserved fruits and has been found useful in the manufacture of vinegar. The use of salicylic acid as a food preservative, was, however, condemned in the findings of the commission appointed by the government of the United States of America, in 1904. Medicine
taste .Salicylic acid and salicin (q.v.) share the properties common to the group of aromatic acids, which, as a group, are antiseptic without being toxic to mana property practically unique; are unstable in the body
Sodium salicylate circulates in the blood unchanged, decomposition occurring in the kidney, and probably in tissues suffering from the Diplococcus rheumaticus of Poynton and Paine. It used to be stated that these drugs are marked cardiac depressants; and the heart being invariably implicated in rheumatic fever, it is supposed that these drugs must be given with great
Therapeutics.Salicylic acid is used externally for the removal of corns and similar epidermic thickenings. It causes some pain, so that a sedative should be added. A common formula
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These drugs are specific for acute rheumatism (rheumatic fever). The drug is not a true specific, as quinine is for malaria, since it rarely, if ever, prevents the cardiac damage usually done by rheumatic fever; but it entirely removes the agonizing pain, shortly after its administration, and, an hour or two later, brings down the temperature to normal. In thirty-six hours no symptoms are left. If the drug be now discontinued, they will return in over 9o% of cases. In acute gonorrhoeal arthritis, simulating rheumatic fever, salicylates are useless. They may thus afford a means of diagnosis. In rheumatic hyperpyrexia, where the poison has attacked the central nervous system, salicylates almost always fail. The mode of their administration in rheumatic fever is of the utmost importance. At first 20 grains of sodium salicylate should be given every hour: the interval
Sahcylate of soda may occasionally be of use in cases of'gallstone, owing to its action on the bile. It often relieves neuralgia, especially when combined with caffeine and quinine. Salicylism, or salicylic poisoning, occurs in a good many cases of the use of these drugs. Provided the kidneys be healthy, the symptoms may be ignored. If nephritis be present, it may be seriously aggravated, and the drug must therefore be withheld. The headache, deafness, ringing in the ears and even delirium of salicylism, are practically identical with the symptoms of cinchonism. The drug must be at once withheld if haemorrhages (subcutaneous, retinal, &c.) are observed. As in the case of quinine, the administration of small doses of hydrobromic acid often relieve the milder symptoms. End of Article: SALICYLIC ACID (ortho-hydroxybenzoic acid) If you wish, you can link directly to this article.
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