Synonym.—Oil of Pennyroyal.
Oil of pulegium or pennyroyal is obtained by distillation from fresh pennyroyal herb, Mentha Pulegium, Linn. (N.O. Labiatae), a native of most parts of Europe. It occurs as a yellow or greenish-yellow liquid, having a strong aromatic, mint-like odour, and an aromatic taste. Specific gravity, 0.930 to 0.960; rotation, +13° to +35°. Adulteration of oil of pennyroyal with oil of turpentine may readily be detected by the diminished solubility in 70 per cent. alcohol, and also by the lowering of the specific gravity and boiling-point.
Soluble in 70 per cent. alcohol (1 in 2 or more, forming a clear solution).
Constituents.—The chief constituent of the oil is the ketone pulegone, C10H16O, forming about 80 per cent. of the oil. It is a colourless liquid, gradually becoming pale yellow, and has a peppermint-like odour. Its specific gravity is 0.936; boiling-point, 221°; rotation, +22.9°. It is identical with the pulegone obtained from Oleum Hedeomae. Pulegone may be prepared in a very pure state by forming the bisulphite compound, which separates on shaking the oil, diluted with one-fourth its volume of alcohol, with solution of sodium bisulphite. It combines with bromine to form a liquid dibromide, and with hydrochloric acid and hydrobromic acid to form crystalline addition products. Reduction with sodium in alcoholic solution yields first the alcohol pulegol, C10H17OH, then l-menthol, C10H20O. The isomer, isopulegone, which may be prepared from citronellal, differs from pulegone in not forming a crystalline compound with sodium bisulphite, and in not yielding menthol on reduction with sodium. Isopulegone shaken with barium hydroxide is completely converted into pulegone, identical with the natural substance.
Action and Uses.—Oil of pennyroyal closely resembles, in its properties, other volatile oils. It is administered on sugar, or with a draught of hot water, as an emmenagogue. During excretion it mildly irritates the kidneys and bladder, and reflexly excites uterine contractions.
Dose.—½ to 2 decimils (0.05 to 0.2 milliliters) (1 to 3 minims).
- Essentia Pulegii, B.P.C.—ESSENCE OF PULEGIUM. Syn.—Essence of Pennyroyal. 1 in 8.
- Taken on sugar, or with a draught of hot water, as an emmenagogue. Dose.—6 to 12 decimils (0.6 to 1.2 milliliters) (10 to 20 minims).