Oleum Caryophylli, B.P. Oil of Cloves.
Related entries: Cloves
Oil of cloves is obtained by distillation from the unexpanded flower-heads of Eugenia caryophyllata, Thunb. (N.O. Myrtaceae), cultivated in Sumatra, Penang, the Seychelles, Zanzibar, and Pemba, and largely imported from the last two places. It is also official in the U.S.P. Oil of cloves occurs as an almost colourless or pale yellow liquid when recently distilled, gradually becoming reddish-brown; strongly refractive; odour, strongly aromatic; taste, persistently burning. Specific gravity, 1.047 (B.P., not below 1.050) to 1.065 (1.040 to 1.060 at 25°). Rotation, from 0° to -1.5°. The oil distils between 250° and 260°. Most adulterations lower the specific gravity. Turpentine may be detected by fractional distillation. Eugenol, being used in the manufacture of vanillin, is liable to be abstracted from the oil. The constants given, however, will readily detect this and other forms of fraud.
Soluble in all proportions of alcohol; in 70 per cent. alcohol (1 in 3), in 60 per cent. alcohol (1 in 60); in ether, and in strong acetic acid.
Constituents.—Oil of cloves consists chiefly of eugenol, C10H12O2, a phenol, which is present to the extent of 85 to 90 per cent. (U.S.P., not less than 80 per cent.), and is the most valuable and characteristic constituent of the oil. It boils, under ordinary pressure, with slight decomposition, at 253° to 254°. It may be obtained in a pure state by treating the oil with solution of sodium hydroxide (2 to 5 per cent.), and after shaking out the alkaline solution several times with ether to remove caryophyllene and other bodies, decomposing it with sulphuric acid. The amount present in the oil can be determined as follows:—Introduce into a flask with a long neck (graduated in decimils) 10 mils of the oil of cloves and 100 mils of solution of potassium hydroxide, and shake the mixture for five minutes. When the liquids have separated completely, add sufficient solution of potassium hydroxide to raise the lower limit of the oily layer to the zero mark of the scale, and note the volume of the residual liquid, which should not measure more than 1 to 1.5 mils, indicating the presence of 85 to 90 per cent. of eugenol (U.S.P., 2 mils = 80 per cent. of eugenol). The separation may be assisted by warming and rotating the flask. Thorn's process for the determination of this phenol depends on converting the eugenol into its benzoyl derivative, separating and weighing as such. Caryophyllene, C15H24, a sesquiterpene, is also present. Other constituents are furfural, C5H4O2, which is probably the cause of the oil becoming darker in colour; methyl- amyl-ketone, C5H11COCH3, a body which communicates the much valued fruity odour to the oil; vanillin, methyl salicylate, and about 2 per cent. of acetyleugenol.
Action and Uses.—Oil of cloves, like other volatile oils, is antiseptic and antiputrescent; it is often employed as a preservative of organic substances when its odour is unobjectionable. Externally, it is rubefacient, counter-irritant, and slightly anaesthetic; mixed with 2 parts of olive oil it may be applied to neuralgic areas; and, as Linimentum Succini Compositum, it is employed as an embrocation in bronchitis, whooping cough, and rheumatism. Internally, oil of cloves is antispasmodic and carminative; doses of 3 to 5 minims have given good results in phthisis, reducing expectoration and cough. It may be administered on sugar or in capsules to allay flatulent colic, and is added to purgative pills to prevent griping. Pills containing a large proportion of oil may be massed by the addition of a little soap. Oil of cloves is applied on cotton wool to allay pain in dental caries.
Dose.—¼ to 2 decimils (0.025 to 0.2 milliliters) (½ to 3 minims).