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LACTIC ACID (hydroxypropionic acid), ...

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Originally appearing in Volume V16, Page 56 of the 1911 Encyclopedia Britannica.
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LACTIC See also:

ACID (hydroxypropionic acid), C3H603 . Two lactic acids are known, differing from each other in the position occupied by the hydroxyl See also:group in the See also:molecule; they are known respectively as a-hydroxypropionic acid (See also:fermentation or inactivelactic acid), See also:CH3• CH(OH) . See also:CO2H, and/3-hydroxypropionic acid (hydracrylic acid), (q.v.), See also:CH2(OH)•CH2•CO2H. Although on structural grounds there should be only two hydroxypropionic acids, as a See also:matter of fact four lactic acids are known. The third isomer (sarcolactic acid) is found in See also:meat See also:extract (J. v. See also:Liebig), and may be prepared by the See also:action of Penicillium glaucum on a See also:solution of See also:ordinary ammonium lactate. It is identical with a-hydroxypropionic acid in almost every respect, except with regard to its See also:physical properties. The See also:fourth isomer, formed by the action of Bacillus laevo-lacti on See also:cane-See also:sugar, resembles sarcolactic acid in every respect, except in its action on polarized See also:light (see STEREOISOMERISM). Fermentation, or ethylidene lactic acid, was isolated by K. W. See also:Scheele (Trans. See also:Stockholm Acad.

178o) from sour See also:

milk (See also:Lat. See also:lac,lactis, milk, whence the name). About twenty-four years later See also:Bouillon Lag-range, and independently A. F. de See also:Fourcroy and L. N. See also:Vauquelin, maintained that Scheele's new acid was nothing but impure acetic acid. This notion was combated by J. See also:Berzelius, and finally refuted (in 1832) by J. v. Liebig and E. See also:Mitscherlich, who, by the elementary analyses of lactates, proved the existence of this acid as a distinct See also:compound. It may be prepared by the lactic fermentation of starches, sugars, gums, &c., the sugar being dissolved in See also:water and acidified by a small quantity of tartaric acid and then fermented by the addition of sour milk, with a little putrid See also:cheese. See also:Zinc carbonate is added to the mixture (to neutralize the acid formed), which is kept warm for some days and well stirred. On boiling and filtering the product, zinc lactate crystallizes out of the solution.

The acid may also be synthesized by the decomposition of alanine (a-aminopropionic acid) by nitrous acid (K. Strecker, See also:

Ann., 185o, 75, p. 27); by the oxidation of propylene glycol (A. See also:Wurtz) ; by boiling a-chlorpropionic acid with See also:caustic alkalis, or with See also:silver See also:oxide and water; by the reduction of pyruvic acid with See also:sodium See also:amalgam; or from acetaldehyde by the cyanhydrin reaction (J. See also:Wislicenus, Ann., 1863, I28, p. 13) CH3•CHO --i CH3.CH(OH).CN —~ CH3•CH(OH)•CO2H.decomposes on See also:distillation under ordinary atmospheric pressure; but at very See also:low pressures (about i mm.) it distils at about 85° C., and then sets to a crystalline solid, which melts at about 18° C. It possesses the properties both of an acid and of an See also:alcohol. When heated with dilute sulphuric acid to 13o° C., under pressure, it is resolved into formic acid and acetaldehyde. Chromic acid oxidizes it to acetic acid and See also:carbon dioxide; See also:potassium permanganate oxidizes it to pyruvic acid; nitric acid to oxalic acid, and a mixture of See also:manganese dioxide and sulphuric acid to acetaldehyde and carbon dioxide. Hydrobromic acid converts it into a-brompropionic acid, and hydriodic acid into propionic acid. Lactide, O< CH(CHs)•CO>O a crystalline solid, of melting-point CO•CH(CH3) 124° C., is one of the products obtained by the distillation of lactic acid.

End of Article: LACTIC ACID (hydroxypropionic acid), C3H603

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