Artificially it is obtained by the condensation of benzaldehyde with acetic aldehyde.
It is a yellow liquid possessing a characteristic cinnamon-like odor. Products made by Schimmel & Co. revealed the following properties.
B. p. under atmospheric pressure abt. 252° with partial decomposition, 128 to 130° (20 mm.), 118 to 120° (10 mm.); d15o 1,054 to 1,058; aD + 0°; its index of refraction, nD20o1,61949/) is the highest observed in connection with volatile oils. When cooled, it congeals to a solid, light yellow mass that melts at - 7,5°. It is soluble in about 25 vols, or more of 50 p. c. alcohol, also in about 7 vols, of 60 p. c. alcohol and in 2 to 3 vols, of 70 p. c. alcohol. In petroleum ether it is practically insoluble.
Cinnamic aldehyde reacts with both acid and neutral sulphite. When it is to be separated by means of the bisulphite addition product, an excess of the bisulphite solution should be avoided since a second molecule will combine with the formation of the water-soluble C6H5 C2H3(S03Na) • CH(OH) • S03Na. Other derivatives that are suited to the identification of cinnamic aldehyde are the semicarbazone, m. p. 208°, the phenylhydrazone, m. p. 168°. Furthermore cinnamic acid, which is formed even by the action of atmospheric oxygen, and its oxidation products benzaldehyde and benzoic acid.
In connection with artificial cinnamic aldehyde care should be taken that it be free from chlorine, since the presence of chlorine is an indication of insufficient purity. For the detection of chlorine, also for the quantitative determination of cinnamic aldehyde compare the chapter "The examination of volatile oils".
1) Bruhl, Liebig's Annalen 235 (1886), 18, 31.
In addition to the aromatic aldehydes already mentioned, a number of others should be enumerated in which benzene hydrogen has been replaced by hydroxy or alkyloxy groups. Although widely distributed in the vegetable kingdom, they occur in small amounts only. In as much as they possess valuable properties as perfumes, most of them are also prepared synthetically, hence there exists an extensive patent literature.