Although this aldehyde has not yet been found in a volatile oil, it may be mentioned here since it finds application in perfumery on account of its hyacinth-like odor. It can be prepared in one of several ways. Phenyl-a-chloro lactic acid, phenyl-a-bromo lactic acid or a-bromo styrene are commonly used as starting point.
Pure phenylacetic aldehyde is a colorless liquid of an exceedingly intensive hyacinth-like odor. In contact with the skin it colors the latter yellow. Radziszewski1) enumerates the following constants:
B. p. 205. to 207°; d 1,085.
Schimmel & Co. have determined the following constants:
B. p. abt. 75° (5 mm.); d15o1,0315 to 1,0521; aD + 0°; nD20o 1,52536 to 1,53370; soluble in about 3 vols. of 70 p. c. alcohol.
Phenylacetic aldehyde oxidizes readily to phenylacetic acid. Oxidized with nitric acid it yields benzoic acid. It manifests a decided tendency to polymerize, hence it is difficult to preserve it unchanged. It should be tested for halogen, the presence of which would indicate insufficient purification. (Compare the chapter "The examination of volatile oils", under benz-aldehyde.)
1) Berl. Berichte 9 (1876), 372.