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Oil of Eucalyptus. U.S.D. 21^st 1926
Compiled and edited by Ivor Hughes.

OLEUM EUCALYPTI. U. S., Br. OIL OF EUCALYPTUS Ol. Eucalypt
Eucalyptus Oil. The volatile oil distilled from the fresh leaves of Eucalyptus Globulus Labillardiere, and from some other species of Eucalyptus (Fam. Myrtacece). Oil of Eucalyptus yields not less than 70 per cent, of eucalyptol (cineol) C₁₀H₁₈O]. U.S.

Oil of Eucalyptus is the oil distilled from the fresh leaves of Eucalyptus Globulus, Labill., Eucalyptus dumosa, A. Cunn., and other species of Eucalyptus, and rectified. Br.

 Various species of the genus Eucalyptus, grown in Australia and Algeria, yield volatile oils in sufficient quantity to be commercial products. There are more than one hundred different kinds of eucalyptus oil known. These are classified according to the predominant constituent as follows: Eucalyptus-pinene oils of which fifty-one varieties have been described; eucalyptus-pinene oils containing no phellandrene, of which there are seven varieties; pinene-sesquiterpene oils, containing no phellandrene, of which there are fourteen varieties; oils containing aromadendral but no phellandrene of which there are nine varieties; phellandrene containing oils with piperotone present, of which there are eleven varieties; phellandrene containing oils with sesquiterpene present, of which there are twenty-two varieties and unclassified oils containing geraniol and its acetic ester, citral, citronellal, etc., of which there are four varieties.

Aromadendrol is an aldehyde-like body which. Baker and Smith reported along with australol, a phenolic compound. (Ph. Ztg., 1922, lxvii, 611.) Cryptol, a laevorotatory compound, is responsible for the optical activity of certain eucalyptus oils according to Bead and Smith. These oils differ radically in therapeutic properties (see Eucalyptus). The oils officially intended are those containing preponderating proportions of cineol. There are very few species which produce an oil as rich in cineol as required by the U. S. X (70 per cent.) but the standard of the Br. is considerably lower (55 per cent.). Oils reaching the latter figure have been distilled from the E. incinata Turcz., and E. cneorifolia DC., in addition to those named by the Pharmacopoeia. The oils from E. odorata Behr. and E. amygdalina Labill. also yield oils fairly rich in cineol but rarely, if ever, reach the proportion official.

Description and Physical Properties.� "A colorless or pale yellow liquid, having a characteristic, aromatic, somewhat camphoraceous odor, and a pungent, spicy, cooling taste.

The Oil is soluble in 4 volumes of 70 per cent, alcohol, by volume. Specific gravity: 0.905 to 0.925 at 25� C. Optical rotation: varies from -10� to +10� in a 100 mm. tube at 25� C. Refractive index: 1.4600 to 1.4690 at 20� C. A solution of the recently distilled Oil in 70 per cent, alcohol (1 in 4) is neutral to moistened litmus paper. Mix 2 cc. of Oil of Eucalyptus with 4 cc. of glacial acetic acid, and gradually add 3 cc. of a 20 per cent, aqueous solution of sodium nitrite. When the mixture is gently stirred with a glass rod, crystals of phellandrene nitrite do not form (eucalyptus oils containing large amounts of phellandrene). The Oil meets the requirements of the test for heavy metals in volatile oils.

The congealing point of Oil of Eucalyptus does not fall below -15.4� C. as determined by the method described on page 1536. Preserve it in well-stoppered amber-colored bottles in a cool place protected from light." U.S.

" Colorless or pale yellow. Aromatic, camphoraceous odor; taste pungent, leaving a sensation of cold. Specific gravity 0.910 to 0.930; optical rotation -10� to +10�. Soluble in 5 parts of alcohol (70 per cent.). Contains riot less than 55 per cent, by volume of cineol as determined by the process described under ' Oleum Cajuputi.' When 1 millilitre is mixed with 2 millilitres of glacial acetic acid and 5 millilitres of petroleum spirit, 2 millilitres of a saturated aqueous solution of sodium nitrite being added, and the mixture gently shaken, no crystalline precipitate forms in the upper layer (absence of oils containing much phellandrene)." Br.

Assay.� The assay of oil of eucalyptus for its cineol' content has long been a matter of research. The earlier methods depended upon fractional distillation, freezing the proper fraction and subsequently weighing the crystallized cineol. Later a method was used in which strong phosphoric acid was added to the oil. This produced a crystalline magma of cineol phosphate, which was collected, pressed between sheets of filter paper and subsequently decomposed with hot water in a graduated tube which enabled the proportion of separated cineol to be read off.

This was the test used in the U. S. P. VIII. This test was subsequently changed by the substitution of arsenic acid for the phosphoric acid previously used, the cineol arsenate being believed to be more easily separated and purified. This was known as Turner and Holmes' modification. (Perf, and Essent. Oil Rec., 1915, p. 21.)

Schimmel and Co. later recommended the use of a cassia flask and the absorption of the cineol by a 50 per cent, aqueous solution of resorcinol. Still another method was proposed by Dodge in which potassium permanganate was employed as the reagent. Parry reviewed the arsenic acid method and condemned it as not satisfactory as to its accuracy. The U S P. Revision Committee, finding no method of assay for cineol that can be considered reliable, has included none in the tenth revision, simply relying on the congealing point of the oil for an approximate idea of its value.

The assay process of the U. S. IX was as follows: " Measure 10 mils of the Oil, from a pipette, into a round-bottom glass dish of 50 mils capacity, which is embedded in finely broken ice. Add 10 mils of arsenic acid T.S. and stir until precipitation is complete. When the mixture ceases to congeal further, allow it to stand for ten minutes in the ice bath. (If at this point a hard mass is formed, add 5 mils of purified petroleum benzin, and mix the mass well before proceeding with the assay.) Then transfer it immediately to a hardened filter paper, about 18.5 cm. in diameter, by means of a pliable horn spatula; spread it evenly over the surface of the paper and lay a second hardened filter paper over the top. Wrap several thicknesses of absorbent or filter paper around the hardened niters, and place the whole between the plates of a press and bring to bear all the pressure possible for about one minute. Change the outside absorbent papers and press again, repeating the operation, if necessary, until the eucalyptol arsenate is apparently dry, and separates readily when touched with a spatula. The pressing is not complete until a hard mass remains which is broken up with difficulty; and usually two changes of filter paper are required, pressing each time for about two minutes; if left too long in the press the compound may decompose.

Now, transfer the compound completely by means of the horn spatula to a glass funnel inserted into a 100 mil cassia flask with a neck graduated to 10 mils into tenths. Wash the last portions of the precipitate into the flask with a stream of hot distilled water from a wash bottle, assisting the disintegration with a glass rod, place the flask in boiling water and rotate it until the compound is thoroughly broken up. Then add enough distilled water to cause the eucalyptol to rise into the neck of the flask, cool it to room temperature and read its volume. This volume, multiplied by 10, shows the percentage of eucalyptol (cineol) in the Oil." U. S. IX.

Power has modified the test for phellandrene so as to make it more delicate. According to his directions, 1 cc. of the oil is mixed with 5 cc. of petroleum benzin, 1 or 2 cc. of a concentrated solution of sodium nitrite added, and subsequently glacial acetic acid added, a drop or two at a time, with vigorous agitation after each addition. If phellandrene is present in any considerable amount, its crystalline nitrosite, C₁₀H₁₆(NO)N0₂, will separate from the benzin solution.

The oil from Eucalyptus Globulus contains pinene, C₁₀H₁₆, and eucalyptol (or cineol). Schimmel & Co. also state (B. Chem. G., April, 1888) that they have obtained several of the aldehydes of the fatty series, notably valeraldehyde, and probably butyraldehyde and capronaldehyde, in their distillation of the oil from Eucalyptus Globulus. Eudesmol, C₁₀H₁₆O (possibly a ketone), is the name given to a crystalline camphor obtained from the oil from E. piperita Smith, by H. G. Smith and R. T. Baker. It also occurs in the oil from E. Globulus. It is isomeric with camphor, but has its oxygen atom combined in a different way. Whether or not the medicinal virtues of the official oil are due entirely to its cineol is uncertain, but many prefer to use the pure eucalyptol to the oil itself.

Uses. � Oil of eucalyptus is an active germicide, although surpassed in power by many of the other volatile oils. Cineol is probably a less efficient antibacterial agent than oil of eucalyptus. It is absorbed from the intestinal tract, eliminated partially through the breath to which it imparts its odor, and also, as an oxidation product, through the urine to which it gives an odor resembling that of violets.

A number of cases of poisoning from oil of eucalyptus have been reported. Barker and Rowntree (J. H. H. B., 1918, xxix, 215) have collated 29 eases of eucalyptus poisoning of which 7 were fatal. The smallest fatal dose was 3.5 cc. (57 minims), but doses of 5 fluid-drachms and in one case 1 fluidounce were recovered from. The most common symptoms were epigastric burning with nausea and usually vomiting; dizziness and muscular weakness also occurred almost uniformly. The skin was pale, or sometimes cyanotic, the extremities cold, pulse rapid and small, pupils generally much contracted; the intellection almost always affected, in most instances the patients were dazed and usually drowsy. In the very severe types delirium was common and occasionally associated with convulsions. One of the earliest symptoms is a feeling of suffocation. The odor of the drug was strong on the breath, often remaining for one or two days, and was sometimes also perceptible in the urine and feces. There are some people with idiosyncrasies in whom ordinary therapeutic doses give rise to dermatitis.

The oil of eucalyptus is used locally as an antiseptic, especially in the treatment of infections of the upper respiratory tract and in certain forms of skin disease. Internally it is used as a stimulating expectorant in chronic bronchitis and tuberculosis. In these conditions it is also frequently given by inhalation; a few drops of the oil may be added to boiling water and the mixed vapors and steam inhaled. It has been especially praised in asthma, given internally or preferably by inhalation by means of cigarettes, which may be made by rolling up the dried leaves, or the vapor from boiling water containing the oil may be inhaled. It is also used as a remedy against the hookworm, but is probably of inferior value. It possesses also some antiperiodic power and may be used in malarial fever when for any reason quinine or methylthionine are not available.

Dose, three to ten minims (0.2-0.6 cc.), best administered in emulsion.
Off. Prep.� Unguentum Eucalypti, Br.; Curatio Paraffini, N.F.

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