Rue Oil

#### Rue Oil. **Rue**** **Oil is steam distilled from freshly harvested, blooming or fruit-bearing, wild growing plants of **Ruta Montana, **cultivated plants of **Ruta Graveolens**, or other species of **Ruth. **The plants are natives of the Mediterranean countries, and they grow wild in Spain, Morocco, Corsica, Sardinia and Algeria. Cultivation also takes place in France and Spain, to a small degree in Italy and Yugoslavia. Spain is the largest producer of rue oil, but Algerian oil has been preferred by many perfume houses until it recently became almost unobtainable. A part of all Algerian rue oil is derived from a rue species which yields a substantially different rue oil (the so-called winter rue which does not solidify at temperatures above 0°C.). Occasionally, one can find Spanish oils of this same type. **Rue Oil **is a yellow to orange-yellow material, liquid at room temperature, but solid at lower temperature; it usually solidifies at about 10°C. (see above). Its odor is sharp-herbaceous, distinctly fruity-orange-like, with a characteristic bitter- acrid undertone that makes the overall impression an unpleasant one. The flavor is equally sharp- acrid, burning. Rue oil has been used in certain types of flavor, e. g. coconut, to reproduce the peculiar fatty-fruity note in these flavor types. For most people, however, rue oil is harmful to the mucous membranes and will often irritate the skin. On account of certain haemorrhage-producing effects of the oil when taken internally, the sale of rue oil is controlled in a number of countries. For these reasons, backed up by the results of physiological and pharmacological tests, *rue oil should** **never be used in perfumery or flavor work. *The main constituent of the oil, Methyl Nonyl Ketone (in the so-called "summer rue" oil) is held responsible for the skin-irritating effect, while Methyl Umbelliferone and an alkaloid in the herb are supposed to be toxic. The two latter materials are not readily distillable with steam, but may be present in the essential oil in trace amounts. The ketone has long served as a convenient starting material for the production of Methyl Nonyl Acetaldehyde, a highly appreciated perfume chemical. The ketone is now produced synthetically, but it is interesting to note that many commercial lots of methyl nonyl acetaldehyde contain as much as 10 or 15% of the above (unreacted) ketone. The latter is responsible for the fruity-orange-like note which is a typical part of the "conventional" description of the odor of methyl nonyl acetaldehyde. This odor description —like many others—will need revision when purer lots of "MNA" become more common on the market. In view of the above, rue oil may slowly vanish from the perfume and flavor market, although it may maintain its importance as a source of natural methyl nonyl ketone for some time.