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ACETIC ACID (acidum aceticum)
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ACETIC See also:ACID (acidum aceticum) , CH3•CO2H, one of the most important organic acids. It occurs naturally in the juice of ' See See also:Gibbon, ch. xlvii. (vol. v. p. 129 in See also:Bury's ed.). many See also:plants, and as the See also:esters of n-hexyl and n-octyl See also:alcohols in the seeds of Heracleum giganteum, and in the See also:fruit of Heracleum sphondylium, but is generally obtained, on the large See also:scale, from the oxidation of spoiled wines, or from the destructive See also:distillation' of See also:wood. In the former See also:process it is obtained in the See also:form of a dilute aqueous See also:solution, in which also the colouring matters of the See also:wine, salts, &c., are dissolved; and this impure acetic acid is what we ordinarily See also:term See also:vinegar (q.v.). Acetic acid (in the form of vinegar) was known to the ancients, who obtained it by the oxidation of alcoholic liquors. Wood-vinegar was discovered in the, See also:middle ages. Towards the See also:close of the 18th See also:century, A. L. See also:Lavoisier showed that See also:air was necessary to the formation of vinegar from See also:alcohol. In 183o J. B. A. See also:Dumas converted acetic acid into trichloracetic acid, and in 1842 L. H. F. Melsens reconverted this derivative into the See also:original acetic acid by reduction with See also:sodium See also:amalgam. The See also:synthesis of trichloracetic acid from its elements was accomplished in 1843 by H. See also:Kolbe; this taken in See also:conjunction with Melsens's observation provided the first synthesis of acetic acid. An-hydrous acetic acid—glacial acetic acid—is a leafy crystalline See also:mass melting at 16.70 C., and possessing an exceedingly pungent See also:smell. It boils at 118°, giving a vapour of abnormal specific gravity. It dissolves in See also:water in all proportions with at first a contraction and afterwards an increase in See also:volume. It is detected by See also:heating with See also:ordinary alcohol and sulphuric acid, which gives rise to acetic ester or See also:ethyl acetate, recognized by its fragrant odour; or by heating with arsenious See also:oxide, which forms the pungent and poisonous cacodyl oxide. It is a monobasic acid, forming one normal and two acid See also:potassium salts, and basic salts with See also:iron, See also:aluminium, See also:lead and See also:copper. Ferrous and ferric acetates are used as mordants; normal lead acetate is known in See also:commerce as See also:sugar of lead (q.v.); basic copper acetates are known as See also:verdigris (q.v.). See also:Pharmacology and See also:Therapeutics.—Glacial acetic acid is occasionally used as a See also:caustic for corns. The dilute acid, or vinegar, may be used to bathe the skin in See also:fever, acting as a pleasant refrigerant. Acetic acid has no valuable properties for See also:internal See also:administration. Vinegar, however, which contains about 5 % acetic acid, is frequently taken as a cure for obesity, but there is no See also:warrant for this application. Its continued employment may, indeed, so injure the mucous membrane of the See also:stomach as to interfere with digestion and so cause a morbid and dangerous reduction in See also:weight. The acetates constitute a valuable See also:group of medicinal agents, the potassium See also:salt being most frequently employed. After absorption into the See also:blood, the acetates are oxidized to See also:carbonates, and therefore are remote alkalies, and are administered whenever it is desired to increase the alkalinity of. the blood or to reduce the acidity of the urine, without exerting the disturbing See also:influence of alkalies upon the See also:digestive See also:tract. The citrates See also:act in precisely similar See also:fashion, and may be substituted. They are somewhat more pleasant but more expensive. ACETO-ACETIC ESTER, C6H1003 or CH3•CO•CH2•000C2H5, a chemical substance discovered in 1863 by A. Geuther, who showed that the See also:chief product of the See also:action of sodium on ethyl acetate was a sodium See also:compound of See also:composition C6H903Na, which on treatment with acids gave a colourless, somewhat oily liquid of composition CeHlo03. E. See also:Frankland and B. F. Duppa in 1865 examined the reaction and concluded that Geuther•'s sodium salt was a derivative of the ethyl ester of See also:acetone carboxylic acid and possessed the constitution CH3CO•CHNa•000C2H5. This view was not accepted by Geuther, who looked upon his compound C6H1003 as being an acid: J. See also:Wislicenus also investigated the reaction very thoroughly and accepted the Frankland-Duppa See also:formula (Annalen, 1877, 186, p. 163; 1877, 19o, P. 257)• The substance is best prepared by drying ethyl acetate over See also:calcium chloride and treating it with sodium See also:wire, which is best introduced in one operation; the liquid boils and is then heated on a water See also:bath for some See also:hours, until the sodium all dissolves. After the reaction is completed, the liquid is acidified with dilute sulphuric acid (1:5) and then shaken with salt solution, separated from the salt solution, washed, dried and fractionated. The portion boiling between 175 and 185°C. is redistilled. The yield amounts to about 3o% of that required by theory. A. Ladenburg and J. A. Wanklyn have shown that pure ethyl acetate See also:free from alcohol will not react with sodium to produce aceto-acetic ester. L. Claisen, whose views are now accepted, studied the reactions of sodium ethylate and showed that if sodium ethylate be used in See also:place of sodium in the above re-action the same result is obtained. Additional information and CommentsThere are no comments yet for this article.
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