Related entry: Caryophyllus (U. S. P.)—Cloves
A volatile oil distilled from the immature flower-buds of Eugenia aromatica (Linné), O. Kuntze (Eugenia caryophyllata, Thunberg).
"It should be kept in well-stoppered bottles, in a cool place, protected from the light"—(U. S. P.).
Preparation.—Oil of cloves is procured by submitting cloves, with water, to repeated distillation; to extract the whole of the oil from cloves, they must be subjected to repeated cohobations, The addition of common salt is often resorted to to raise the point of ebullition. On an average they yield from 17 to 22 per cent of volatile oil. At the present time nearly all the oil is produced by means of superheated steam. The bulk of the oil used in this country is distilled here from South American cloves. In Europe clove-stalks are said to furnish a portion of the oil. The yield from this source is 5.5 to 6 per cent, and the specific gravity 1.055 to 1.065 (Schimmel & Co.).
Description.—The official oil is described as "a pale-yellow, thin liquid, becoming darker and thicker by age and exposure to the air, having a strongly aromatic odor of cloves, and a pungent and spicy taste. Specific gravity, 1.060 to 1.067 at 15° C. (59° F.). Soluble in an equal volume of alcohol, this solution being slightly acid to litmus paper; also soluble in an equal volume of glacial acetic acid"—(U. S. P.). It is also dissolved by ether and the fixed oils. Nitric acid reddens it, and when the mixture is heated, oxalic acid is formed. It is one of the least volatile and most difficult to distill of all the volatile oils. It boils between 250° and 260° C. (482° and 500° F.). It sinks in water, and is sparingly soluble in it. Its optical rotation is slightly left-handed.
Chemical Composition.—The principal constituents of oil of cloves are eugenol (70 to 95 per cent), aceto-eugenol (2 to 3 per cent, Erdmann, 1897), the sesquiterpene caryophyllene constituting the remainder. Eugenol (allyl-guaiacol, C6H3.C3H5.OCH3.OH) is a faintly yellowish liquid possessing a strong clove odor and a burning taste. It is heavier than water, its specific gravity being 1.072 at 14.5° C. (58.1° F.). By oxidation it yields vanillin, which is also a constituent of the oil. Like the typical phenol (carbolic acid), eugenol dissolves in solution of caustic alkalies, forming phenolates, whereby its odor is lost; the eugenol may be liberated again by the addition of acid. On account of its being an ortho-diphenol-derivative, it turns blue in alcoholic solution with ferric chloride (compare Guaiacolum).Caryophyllene (C15H24, Church, 1875; Wallach, 1892) is a colorless liquid of a faint odor; it forms a crystallizable compound with 1 molecule of water (caryophyllene hydrate, C15H26O), melting at 96° C. (204.8° F.). Caryophyllene also occurs in oil of copaiba. Minor constituents of oil of cloves are salicylic acid (Scheuch, 1863; Erdmann, 1897), methyl alcohol, furfurol (furfur-aldehyde, C4H3O.CHO), to the presence of which is probably due the turning brown of oil of cloves upon exposure, and methyl-amyl-ketone, having an ethereal fruit odor (see Gildemeister and Hoffmann, Die Aetherischen Oele, 1899).
Tests.—The U. S. P. directs the following tests for oil of cloves: "When shaken with an equal volume of a concentrated solution of potassium hydrate, or of stronger ammonia water, it forms a semisolid, yellowish mass. If 2 drops of the oil be dissolved in 4 Cc. of alcohol, and a drop of ferric chloride T.S. added, a bright green color will be produced; and if the same test be made with a drop of dilute ferric chloride T.S., prepared by diluting the test-solution with four times its volume of water, a blue color will be produced which soon changes to yellow. If 1 Cc. of the oil be mixed with 2 Cc. of a mixture of 2 volumes of alcohol and 1 volume of water, it should form a clear and perfect solution "absence of petroleum, most fatty oils, oil of turpentine, and similar oils). If 1 Cc. of the oil be shaken with 20 Cc. of hot water, the water should show a scarcely perceptible acid reaction to litmus paper. If, after cooling, the aqueous layer be passed through a wet filter, the clear filtrate should yield, with a drop of ferric chloride T.S., only a transient grayish-green, but not a blue or violet color (absence of carbolic acid)"—(U. S. P.). A markedly lower specific gravity than that given above, points to the addition of lighter oils, as oil of turpentine, etc. Oil from clove-stalks is difficult to identify chemically; according to Gildemeister and Hoffmann (loc. cit.), it differs from oil of cloves in being devoid of aceto-eugenol.
The eugenol contents of oil of cloves may be determined quantitatively, according to H. Thorns (1891), by converting it into its benzoyl compound and weighing the latter; or, according to Umney (Pharm. Jour. Trans., Vol. XXV, 1895, p. 950), by adding a 10 per cent (better a 4 to 5 per cent) solution of caustic potash to a definite quantity of the oil, and measuring the volume of the oil above the eugenol-potassium layer.
Action, Medical Uses, and Dosage.—Oil of cloves is stimulant and irritant, and is much used as a corrector of other medicines, and as an external counterirritant. It is frequently inserted on cotton into the cavity of a carious tooth to alleviate toothache, and in the external auditory meatus to relieve earache. Its dose is from 2 to 5 drops on sugar, or in emulsion. One part of oil of cloves mixed with 3 parts of linseed oil, and given in doses of 6 or 8 drops in milk, 2 or 3 times a day, has been found useful in allaying pain, palpitation, and other annoying symptoms common to some forms of heart disease. It preserves mucilage of tragacanth prepared for adhesive purposes.
Derivatives of Eugenol.—EUGENOL-ACETAMIDE (C6H3.C3H3.OCH3.OCH2CONH2). This body is said to be obtained by the interaction of concentrated solution of ammonia and eugenol-acetic-ethyl-ether. It forms shining, crystalline needles or scales, which melt at 110° C. (230° F.). Water and alcohol dissolve it. It is reputed antiseptic and a local anaesthetic, acting somewhat like cocaine. It is a patented preparation (see Pharm. Centralhalle, 1892, p. 441).
BENZOYL-EUGENOL (C6H3.C3H5[OCH3]O.COC6H5).—This compound forms colorless, odorless, slightly bitter needles, of a neutral reaction. It fuses at 70.5° C. (158.9° F.). Water scarcely dissolves it, but it is readily dissolved by hot alcohol, acetone, ether, and chloroform. It is recommended for the treatment of tuberculous disorders. It is patented.
CINNAMYL-EUGENOL (C6H3.C3H5[OCH3]O.CO[CH]2C6H5).—Tasteless, odorless, colorless, shining needles, fusing at 90° to 91° C. (194° to 195.8° F.). Hot alcohol, ether, acetone, and chloroform dissolve it. Its uses are the same as those of the preceding drug (see Pharm. Centralhalle, 1891, p. 366).
King's American Dispensatory, 1898, was written by Harvey Wickes Felter, M.D., and John Uri Lloyd, Phr. M., Ph. D.