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OLEUM ROSAE. Br. OIL OF ROSE. U.S.D. 1926.
Compiled by Ivor Hughes.

Fats and oils saturated with the rose perfume have been used since the earliest times. Of the seven thousand or more cultivated varieties of rose only a few are used for the production of oil. The chief of these is Rosa damascena or damask rose, a shrub whose habitat is unknown but which was introduced to Europe from Asia Minor in the 16th century.

It attains a height of 5 feet and is further characterized by possessing stems covered with many stout, hooked prickles and glandular bristles, imparipinnate leaves with 5 to 7 ovate-oblong, serrate leaflets, pubescent on their lower surfaces, prickly petioles, red, pink or white flowers, borne in corymbs, and obovate hip fruits.

The volatile oil from this species is commonly called attar, otto, or essence of roses. It is prepared on a large scale in Europe, especially in the Balkan Mountains, in Egypt, Persia, Cashmere, India, and other countries of the East, but European and American commerce is at present supplied chiefly from the region constituting the southern slope of the Balkans in Bulgaria, the town of Kizanlik being the most important center of production.

The roses are gathered in May, and are distilled with the green leaves of the calyx. From thirty to sixty pounds are put into a tinned copper boiler, of the capacity of about 150 pounds, nearly filled with water. The heat is applied over an open fire, and a boiling temperature is continued for two hours, when the first part of the distilled fluid is returned to the boiler, and the process is continued to completion. The oil collects on the top of the water in the receiver, when, it is removed from time to time as it accumulates. In the south of France a small quantity of oil of rose is prepared by distilling the petals with water and separating the oil which floats to the surface. The annual output of oil is small, most of it being marketed in the form of rose water.

The quantity of oil yielded by roses is very small, from 150 to 300 pounds being required to produce a single ounce of the oil. The price is correspondingly high; at present (1924) it is about $20 to $30 an ounce.

The experiments of Schimmel are said to indicate that the oil of rose can be prepared from German-grown flowers with commercial success. It is affirmed that the product is superior to the Turkish oil in fineness and strength of aroma, and also that it differs in having a higher congealing point, German oil solidifying at 32� C., Turkish oil at 20� C. For an account of its production, see P. J., 1893, 262; also J. S. C. I., 1919, xxxix, 43A.

For accounts of the modern rose industry see Tschirch, Seifenseider Ztg., 1921, xlviii,

and Chipkoff, Bull. So. Pharm., 1921, xxviii, 389. Srivastava and Sinha give an account of the manufacture of otto from Indian rose. (Per/. & Ess. Oil Bee., 1921, xii, 14.) Lorgues (C. D., 1920, xciii, 1629) describes the French rose industry.

Oil of rose is nearly colorless, or presents some shade of green, yellow, or red, but, according to Polier, the color is no criterion of its value. Its odor is very powerful and diffusive. Alcohol dissolves it, although not freely when cold. Although described by the Br, as a " semi-solid," at the temperatures ordinarily met with in the United States it is liquid.

" A pale yellow or yellowish-green crystalline mass, semi-solid at ordinary temperatures. Strong, fragrant, rose-like odor; taste sweetish. Specific gravity at 30� C. (compared with water at 15.5� C.) 0.854 to 0.862; optical rotation -2� to -4�; refractive index at 25� C. 1.456 to 1.465; melting point 20� to 23� C." Br.

Oil of rose consists of two portions, one liquid, the other solid at ordinary temperatures. These may be separated by freezing the oil and compressing it between folds of blotting paper, which absorbs the liquid oil and leaves the concrete stearopten. The liquid portion is oxygenated, while the solid portion, which is odorless when pure, consists of a mixture of several hydrocarbons, one of which melts at from 35.5� to 36.5� C., and is a paraffin of the formula C₁₆H₃₄.

"The addition of 70 per cent, alcohol precipitates the paraffin hydrocarbons of the oil, but forms a clear solution with its other constituents, the solution being slightly acid to litmus T.S." U. S. VIII.

The oxygenated portion consists .of the two alcohols, geraniol, and citronellol, together constituting 75 per cent, of the oil. The rhodinol of Eckart was a mixture of these two alcohols. (Schim. Rep., April, 1898, 40.) While these two alcohols are mainly found in rose oil in the free state, esters of the same are also present in amounts varying from 2.5 to 3.5 per cent. (Gildemeister and Hoffmann, Aetherische Oele, p. 565.) Linalool, citral and phenyl ethyl alcohol are also present in small amounts as are also nerol, farnesol, eugenol, linalol and nonylic aldehyde. The U. S. P. VIII considered the saponification value as of sufficient importance to incorporate it as an official test, as follows:

Assay.� " Place in a weighing-bottle about 2 cc. of the Oil of Rose, and weigh accurately. Transfer it, with the aid of a little alcohol, to a 100 cc. flask, and add 20 cc. of half-normal alcoholic potassium hydroxide V.S. Connect the flask with a reflux condenser, and boil the mixture during thirty minutes on a water-bath. When cool, add 50 cc. of distilled water and a few drops of phenolphthalein T.S., and titrate with half-normal sulphuric acid V.S. Subtract the number of cc. of half-normal sulphuric acid V.S. required, from 20 (the 20 cc. of half-normal alcoholic potassium hydroxide V.S. taken), multiply the difference by 27.87, and divide by the weight of the Oil to obtain the saponification value." U. S. VIII.

Oil of rose is frequently, one might almost say usually, adulterated with various fixed or volatile oils; among those most commonly met are spermaceti, oil of rose-geranium and oil of palmarosa. Some of these falsifications are very difficult of detection. An adulteration with a fixed oil produces a permanent greasy stain upon paper, and spermaceti is left behind on the evaporation of a few drops of the oil from a watch crystal in a water bath.. Massatsch (Ph. Ztg., 1923, Ixviii, 832) states that to be certain of the purity of rose oil, the following characters must be determined: specific gravity, optical rotation, congealing point, refractive index, stearopten content, saponification number and alcohol content.

He gives the following constants for a good oil: sp. gr. 0.849-0.862, congealing point 18 - 23.� C., acid number 0.5 � 3.0, ester number 7 -1 6, saponification number 7.5-19, alcohol content 66 . 75 per cent., stearopten 17-21 per cent.

Tedermann (Zeit. An. Chem., 1895, 5) reached the conclusion, after much experimenting that there is no reliable chemical or physical test for the adulteration of oil of rose with geranium oil The sense of smell, according to Conroy, furnishes the best means of determining the quality; he recommends the dissolving of one drop of oil of rose in twenty drops of alcohol, pouring the solution in one fluidounce of warm water, shaking, and comparing the odor with that of a standard sample treated in the same way. (P. J., 1896 474; see also C. D., 1897, 53.) For other tests which have been suggested see U. S. D., 20th ed., p. 787.

Synthetic rose oils are now manufactured and sold on a large scale. Most of them contain a certain proportion of true rose oil, for the reproduction of the odor by synthetic constituents alone has never been achieved.

Rhodinol is the trade name for the principal constituent in most of these formulas. It consists of citronellol and geraniol in the proportion of about two of the former to one of the latter. Nerol and terpeneless oil of rose are other constituents of importance. An indispensable ingredient is phenyl-ethyl alcohol C₆H₅CH₂CH₂OH (benzyl carbinol), which contributes to the similarity of the odor. Other constituents the names of which appear in formulas for synthetic rose oil, intended to imitate one or the other of special types of rose are as follows: Alpha ionone, ethyl cinnamate, benzyl acetate, isobutyl acetate, isoeugenol, cinnamic aldehyde, citronellyl acetate, nonyl aldehyde and citral.

A rose oil is said to be distilled in Germany which contains 75 per cent, of phenyl-ethyl alcohol, which is present in only small proportions in ordinary rose oil, in which it ordinarily occurs as a benzoic ester or combined with phenyl acetic acid. Hjort and Kaufman (J. P. Ex. T., 1920, xv, 129) have shown this oil to be a powerful local anesthetic, but its instability is said to interfere with its practical usefulness.

A rose oil obtained in the yield of 0.015 per cent, by extraction of the petals with volatile solvents was found by F. Elze to have the following constants: Sp. gr. 0.9844 at 20� C., specific rotation +0.6�; acid value 3.15; ester value 2.9; acetylation value 317.5. Phenyl-ethyl alcohol was the chief constituent of this oil which also contained geraniol, citronellol, nerol, and farnesol (J. Soc. Chem. Ind., 1919, xxxix, 43A).

Oil of rhodium (Oleum ligni Rhodii, Aspalathum). This oil was attributed by Lewis to the Convolvulus Scoparius L. but according to Holmes (Perfume and Essential Oil Record, 1911, ii, p. 29) is the product of a species of Genista, either G. canariensis L. or G. virgata. Link.

It is used to adulterate oil of rose. Guaiac wood oil is also occasionally used for the same purpose. A factitious oil of rhodium is sometimes sold as a lure for rats and other animals. It is made from oil of copaiba flavored with a trace of oil of rose. The synthetic oil of rose has largely replaced that obtained by distillation.

Oil of rose may be added, as a grateful perfume, to various spirituous preparations for internal use, and to cerates and ointments. It is both too expensive and too powerful for most pharmaceutic purposes.

Off. Prep.�Unguentum Aquae Rosas, Br.

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