CINNAMIC ACID, or PHENYLACRYLIC ACID, C9H802

This article appears in Volume V06, Page 376 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: CHR-CLI

CINNAMIC ACID, or PHENYLACRYLIC ACID, C9H802 or C6H6CH: CHCOOH, an acid found in the form of its benzyl ester in Peru and Tolu balsams, in storax and in some gumbenzoins. It can be prepared by the reduction of phenyl propiolic acid with zinc and acetic acid, by

heating

HEATING

benzal malonic acid, by the condensation of

ethyl

ETHYL

acetate with benzaldehyde in the presence of sodium ethylate or by the so-called "

Perkin

PERKIN, SIR WILLIAM HENRY (1838-1907)

reaction "; the latter being the method commonly employed. In making the acid by this process benzaldehyde, acetic an-hydride and anhydrous sodium acetate are heated for some

hours

HOURS, CANONICAL

to about 18o C., the resulting product is made alkaline with sodium carbonate, and any excess of benzaldehyde removed by a current of steam. The residual liquor is filtered and acidified with hydrochloric acid, when cinnamic acid is precipitated, C6H5CHO+CH3000Na = C6HICH :CH COONa+H2O. It may be purified by recrystallization from hot water. Consider-able controversy has taken place as to the course pursued by this reaction, but the matter has been definitely settled by the

work

WORK

of R. Fittig and his pupils (Annalen, 1883, 216, pp. too, 115; 1885, 227, pp. 55, 119), in which it was shown that the aldehyde forms an addition compound with the sodium

salt

of the fatty acid, and that the acetic anhydride plays the

part

PART

of a dehydrating agent. Cinnamic acid crystallizes in needles or prisms, melting at 1330 C.; on reduction it gives phenyl propionic acid, C6H5.CH2CH2000H. Nitric acid oxidizes it to benzoic acid and acetic acid. Potash fusion decomposes it into benzoic and acetic acids. Being an unsaturated acid it combines directly with hydrochloric acid, hydrobromic acid, bromine, &c. On nitration it gives a mixture of ortho and para nitrocinnamic acids, the former of which is of historical importance, as by converting it into orthonitrophenyl propiolic acid A. Baeyer was enabled to carry out the complete

synthesis

SYNTHESIS (Gr. a6vOeacs, from avvrcBivac, to put together)

of indigo (q.v.). Reduction of orthonitrocinnamic acid gives orthoaminocinnamic acid, C6H4(NH2)CH:CH000H, which is of theoretical importance, as it readily gives a

quinoline

QUINOLINE (Benzopyridine), C9H7N

derivative. An isomer of cinnamic acid known as allo-cinnamic acid is also known.
For the oxy-cinnamic acids see COUMARIN.

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