Farmakognosi_Oleum Rosae

Otto of rose is obtained by distillation from the fresh flowers of the damask rose, Rosa damascena, Miller (N.O. Rosaceae), a plant which is cultivated largely in European Turkey, Bulgaria, Egypt, Persia, Cashmere, India, etc. It is also official in the U.S.P. Oil of rose occurs as a pale yellow, semi-solid, crystalline mass at ordinary temperatures, having the strong, fragrant odour of the damask rose, and a mild, slightly sweet taste. It yields turbid mixtures with even very large amounts of alcohol, on account of the difficultly soluble paraffins; the liquid portion of the oil forms clear solutions with 70 per cent. alcohol. Specific gravity, 0.854 to 0.862 at 30°, compared with distilled water at 15° (B.P., 0.856 to 0.860). Rotation, slightly laevorotatory, -2° to -4°. Refractive index
1.460 to 1,46,5 at 250, Saponification value, 10 to 17. Acid value, 0.5 to 3.0. Congealing point, 15° to 22°, usually about 20°. Stearoptene content, 10 to 15 per cent. One of the chief adulterants of oil of rose is palmarosa oil, from Andropogon Schoenanthus, Linn., which has the effect of lowering the melting-point, but this has been counteracted by the addition of spermaceti, stearin, paraffin wax, or the oil of Rosa alba, Linn., which contains more solid stearoptene than that of Rosa damascena; other adulterants are true geranium oil, guaiacum wood oil obtained from Bulnesia sarmienti, Lorentz, sandal wood oil, and fixed oils, the last named being detected by the fact that they leave a greasy stain when evaporated from paper. Paraffin, which is sometimes added to oil deficient in stearoptene, crystallises with a more granular structure than the normal constituent. Spermaceti and stearin as adulterants are detected by saponification, the resulting salts yielding palmitic and stearic acids respectively on decomposition with hydrochloric acid, no fatty acids being yielded on saponifying pure rose oil. Alcohol lowers the specific gravity; sandal wood oil increases it; palmarosa oil has little effect either on the density or rotation. Guaiacum wood oil increases the specific gravity and optical rotation, raises the congealing point, and on evaporation leaves a resinous residue. The great similarity of rose oil and many of its adulterants, renders detection by physical properties a matter of the greatest difficulty. Colour tests are useless. The sense of smell is one of the most useful means of assessing the value of the oil.
Constituents.—The chief constituents of the oil are the alcohols geraniol, C₁₀H₁₈O, and citronellol, C₁₀H₂₀O, the two together being present to the extent of 70 to 75 per cent., while the citronellol constitutes about one-fourth of the liquid portion of the oil. Traces of esters of these alcohols are also present, but as the characteristic odour of the oil is not due to any of these constituents, either singly or mixed, the presence of some other odorous principle is assumed. The differences in the odour of varieties of the oil appear to indicate chemical differences. Free acids, front decomposition of the esters, are also present. The solid stearoptene is a mixture of two or more odourless paraffin hydrocarbons, melting at 33° to 37°.
Uses.—Oil of rose is largely employed in perfumery. It is also used, because of its odour, in preparing lozenges, tooth powders, tooth pastes, liquid dentifrices, ointments, and articles for the toilet.