Acidum Cinnamicum. Cinnamic Acid.
C9H8O2 = 148.064.
Cinnamic acid, C6H5CH:CHCOOH, may be obtained from storax, balsam of Peru, or balsam of tolu; also by the oxidation of cinnamic aldehyde from oil of cassia, or by the interaction of benzyl dichloride and sodium acetate. The acid should contain not less than 99 per cent. of pure cinnamic acid. It occurs in colourless, odourless crystals, which are at first tasteless, but afterwards have a burning taste. Melting-point, 133°. The synthetic acid usually smells slightly of benzaldehyde, and melts at about 130°. Cinnamic acid immediately reduces an alkaline solution of potassium permanganate. It should be free from chlorides. The acid should be stored in well-stoppered, dark amber-coloured bottles.
Soluble in water (1 in 3500), readily soluble in alcohol and oils.
Action and Uses.—Cinnamic acid has an action similar to that of benzoic acid, and its use by injection has been much vaunted as a cure for tuberculosis, great emphasis being laid on its power to induce leucocytosis; it is doubtful, however, if such an effect is produced in man, but, even if it were produced, no evidence is known to show that an excess of leucocytes in the general circulation is beneficial. It is used chiefly as the sodium salt, since solutions of the acid give rise to some pain when injected hypodermically. Salts of orthohydroxycinnamic (coumaric) acid have been similarly employed. Acetocoumaric acid, or acetyl-orthocoumaric acid, C6H40COCH3CH:CHCOOH, also known under the trade-name of Tylmarin, is prepared by the interaction of salicylic aldehyde, acetic anhydride, and sodium acetate. It occurs in colourless crystals. Melting-point, 150°. It is slightly soluble in water, soluble in alcohol (1 in 19), chloroform (1 in 16), or ether (1 in 50). Acetocoumaric acid is a powerful antiseptic and has the general properties of the coal-tar derivatives. It is supposed to cause leucocytosis, but medicinal doses have no such effect in man. It has been employed in the treatment of pulmonary tuberculosis and tuberculous glands, also in cancer, and as an intestinal antiseptic. It is readily hydrolysed into orthocoumaric and acetic acids, and is best administered in cachets in doses of 3 to 6 decigrams (5 to 10 grains). It is sometimes used concurrently with hypodermic injections of sodium cinnamate. It is incompatible with alkalies.
Dose.—3 to 16 milligrams (1/20 to ¼ grain).