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CROTONIC ACID (C4H6O2)

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Originally appearing in Volume V07, Page 511 of the 1911 Encyclopedia Britannica.
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CROTONIC See also:

ACID (C4H6O2) . Three acids of this empirical See also:formula are known, viz. crotonic acid, isocrotonic acid and methacrylic acid; the constitutional formulae are HC•CH3H' CHsCH ' See also:CH2. C0 H' Crotonic Acid. Isocrotonic Acid. Methacrylic Acid. The See also:isomerism of crotonic and isocrotonic acids is to be explained on the See also:assumption of a different spatial arrangement of the atoms in the See also:molecule (see STEREOCIEMISTRY). Crotonic acid, so named from the fact that it was erroneously supposed to be a saponification product of croton oil, may be prepared by the oxidation of croton-aldehyde, CH3• CH:CH• CHO, obtained by dehydrating aldol, or by treating See also:acetylene successively with sulphuric acid and See also:water; by boilhig allyl See also:cyanide with See also:caustic potash; by the See also:distillation of 0-oxybutyric acid; by See also:heating See also:paraldehyde with malonic acid and acetic acid to 100° C. (T. Komnenos, See also:Ann., 1883, 218, p. 149). CH2(000H)2+CH 3CHO->CH 3 • CH: C(COOH)2-> CH s• CH:CH• COOH; or by heating pyruvic acid with an excess of acetic anhydride and See also:sodium acetate to 16o-18o° C. (B.

Homolka, Ber., 1885, 18, p. 987). It crystallizes in needles (from hot water) which melt at 72° C. and See also:

boil at 180-181° C. It is moderately soluble in See also:cold water. It combines directly with See also:bromine, and, with fuming hydrobromic acid at Too° C., it gives chiefly a-brombutyric acid. With hydriodic acid it gives only 0-iodobutyric acid. Potash See also:fusion converts it into acetic acid; nitric acid oxidizes it to acetic and oxalic acids; chromic acid mixture to acetaldehyde and acetic acid, and See also:potassium permanganate to a8-dioxybutyric acid. Isocrotonic acid (Quartenylic acid) is obtained from (3-chlorisocrotonic acid, formed when acetoacetic ester is treated with See also:phosphorus pentachloride and the product poured into water, by the See also:action of sodium See also:amalgam (A. Geuther). It is an oil, possessing a See also:smell like that of butyric acid. It boils at 171.9° C., with partial See also:conversion into crotonic acid; the transformation is See also:complete when the acid is heated to 17o-18o° C. in a sealed See also:tube. Potassium permanganate oxidizes it to 0y-dioxybutyric acid.

Methacrylic acid was first obtained in the See also:

form of its See also:ethyl ester by E. See also:Frankland and B. F. Duppa (Annalen, 1865, 136, p. 12) by acting with phosphorus pentachloride on oxyisobutyric ester (See also:CH3)2•C(OH)•COOC2H5. It is, however, more readily ob-tained by boiling citra- or meso-brompyrotartaric acids with alkalis. It crystallizes in prisms, which are soluble in water, melt at 16° C., and boil at 160.5° C. When fused with an See also:alkali, it forms propionic acid; with bromine it yields a(3-dibromisobutyric acid. Sodium amalgam reduces it to isobutyric acid. A polymeric form of methacrylic acid has been described by F. Engelhorn (Ann., 188o, 200, p. 70).

End of Article: CROTONIC ACID (C4H6O2)

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