Heliotropin, also known as piperonal, is the methylene ether of protocatechuic aldehyde. It has been observed but once in a volatile oil and then only in minimal amount, namely in the oil from the flowers of Spiraea Ulmaria. The supposed occurrence in some varieties of vanilla bean assumed by Busse1) is still doubtful.'2) Furthermore, it is not known whether the heliotropin-like odor of certain flowers, such as the heliotrope, is due to the presence of this aldehyde or not.
1) Tiemann and Haarmann, Berl. Berichte 7 (1874), 613.
As source for the artificial preparation of piperonal, piperin was formerly used. At present it is obtained much more cheaply by the oxidation of Isosafrol.
Heliotropin constitutes colorless, lustrous crystals that have a heliotrope-like odor, that melt at 35 to 36° and that boil at 236°. It is readily soluble in alcohol, ether and similar solvents; difficultly soluble in cold water, more readily in boiling water. From hot water it can be obtained in crystals an inch long and more. In glycerin it is very sparingly soluble, somewhat more in paraffin oil, comparatively readily soluble in olive oil (about 6 p. c). At a temperature of 10° it is soluble to the extent of about 5 p. c. in 70 percent. alcohol.
As aldehyde, heliotropin combines with acid sulphite. Upon reduction piperonyl alcohol, m. p. 51°, results; upon oxidation piperonylic acid, m. p. 227,5 to 228°. Other derivatives are its monobromide, m. p. 129°, its mononitro compound, m. p. 94,5°, the anilide, m. p. 65°, the thiosemicarbazone, m. p. 185°, and the semicarbazone, m. p. 224 to 225°.
It may be mentioned that heliotropin possesses antipyretic and antiseptic properties, and that it may be used as antidote in strychnine poisoning.
Heliotropin should be stored in a cool, dark place since it turns yellow or even brown and is decomposed when exposed to light.3)
When examined for adulterants, the melting point and solubility should be determined. Its behavior toward acid sulphite with which it reacts readily may also be ascertained.
1) Arbeiten a. d. Kaiserl. Ges.-Amt 15 (1898 to 1899), 108.
2) Walbaum, Wallach-Festschrift Gottingen 1909. p. 649; Report of Schimmel & Co. October 1909, 142.
3) Report of Schimmel 8j Co. April 1904, 128.
In this connection a heterocyclic aldehyde may be mentioned, namely,