Oleum Rutae. - Rautenol. - Essence de Rue.
Origin. The oil of rue of commerce is obtained from several species of the genus Ruta (family Rutaceae). According to A. Birckenstockl) and to H. Carette2), Ruta graveolens, L. (Ger. Gartenraute) is distilled in France. The yield amounts to about 0,06 p.c. It is not known from which plant the Spanish oil is distilled.
In Algeria two distinct oils of rue are distilled. The one is designated summer oil of rue and is obtained from Ruta mon-tana, L.3). The other known as winter oil of rue is obtained from Ruta bracteosa, L. According to Carette, the Rue de Corse is not the R. Corsica as might be supposed, but R. bracteosa.
For commercial purposes the French, Spanish and Algerian oils come into consideration. In Germany oil of rue has been distilled only occasionally. From the dry herb of the Garten-raute (Ruta graveolens, L; R. hortensis, Mill.) H. Haensel4) obtained 0,135 p.c. of an oil that was not identical with the ordinary oil of rue. Schimmel & Co. distilled dry herb from Smyrna with a yield of 0,7 p. c. The oil obtained congealed between - 7 and - 8°, hence was rich in methyl heptyl ketone.
Composition. The two characteristic constituents of oil of rue are two ketones, viz., methyl-n-nonyl ketone and methyl1) Moniteur scientifique Quesneville 1906, 352. - Birckenstock's.opinion that Algerian oil of rue is likewise obtained from Ruta graveolens and that the differences in the two oils are due to the different stages of vegetation in which they are distilled, is erroneous. While it is true that the oils are distilled at different periods, the differences in the oils are due to different botanic origin of the respective plants.
2) Journ. de Pharm. et Chim. VI. 24 (1906), 58.
3) Comp. F. Jadin, Berichte von Roure-Bertrand Fils April 1911, 11. This article contains complete botanic descriptions, with illustrations, of the several species of Ruta subjected to distillation.
4) Pharm. Ztg. 51 (1906), 323, 1026.
/7-heptyl ketone (See vol. I, p. 434). Of the two the former was first known, its chemical constitution having been ascertained by A. Giesecke1) also by E. von Gorup-Besanez and F. Grimm2) toward the beginning of the seventies of the past century. Methyl heptyl ketone was discovered by H. Thorns3) in a commercial oil probably of French or Spanish origin. The relative amounts of the two vary greatly in individual oils. Whereas the oil examined by Thorns contained about 85 p. c. of the nonyl compound and 5 p.c. of the heptyl compound, H. von Soden and K. Henle4) also found about 90 p.c. of ketones in an Algerian oil of which 2/3 were methyl heptyl ketone and 1/3 methyl nonyl ketone. From German (?) oil of rue, ). Houben5) isolated 2,4 p.c. of heptyl and 71 p.c. of the nonyl ketone. According to F. B. Power and H. Lees") an oil of unknown origin (presumably Algerian) contained both ketones in approximately the same proportions.
Of those constituents which boil below 190° such small amounts are present in oil of rue that they are overlooked unless very large quantities of oil are subjected to investigation. The following substances were identified by Power and Lees: l-a-pinene (m. p. of nitrolpiperide 119 to 120°), cineol (m. p. of iodol compound 114 to 115°) and -limonene (m. p. of tetra-bromide 103°). All three together did not constitute one percent of the total oil. The same investigators also found the secondary alcohols corresponding to the two ketones, viz., methyl-n-heptyl carbinol and methyl-n-nonyl carbinol (See vol. I, p. 351). Their presence in the oil had been suspected by v. Soden and Henle. C. Mannich7) as well as Houben6) had shown that they can be prepared by reduction of the ketones. Both alcohols are present in the oil to the extent of 10 p.c, partly free, partly as acetic esters4)0). In addition to these Power and Lees demonstrated the presence of a valeric acid ester, probably that of ethyl alcohol. Of the acid constituents of the oil, free fatty acids should be mentioned. Among these there is one that boils at 236 to 238° that is probably identical with caprylic acid1). Salicylic acid, m. p. 156°, was likewise isolated from the saponification liquid. Presumably it occurs in the original oil as methyl ester2).
1) Zeitschr. f. Chemie 13 (1870), 428.
2) Liebigs Annalen 157 (1871), 275.
3) Berichte d. deutsch. pharm. Ges. 11 (1901), 3.
4) Pharm. Ztg. 46 (1901), 277.
5) Berl. Berichte 35 (1902), 3587.
6) Joum. chem. Soc. 81 (1902), 1585.
7) Berl. Berichte 35 (1902), 2144.
The blue fluorescence of the oil, which is occasionally observed, is traced to the presence of methyl anthranilic acid methyl ester3). However, the acid that was isolated had a melting point of 173° instead of 178 to 179°. In addition, Power and Lees isolated from a non-fluorescing oil a base with a quinoline-like odor, that was likewise devoid of fluorescence.
The highest boiling fraction (about 0,5 p.c.) boils between 250 and 320° and is blue4).
Properties. Oil of rue is a colorless to yellow liquid which in most instances fluoresces. Its a rue-like odor, pleasant only in great dilution, is intense and persistent. Its properties differ according to its botanical origin, also according to the vegetative condition of the plant at the time of distillation. All oils, however, have in common a low specific gravity, which is lower than that of most volatile oils. The congealing point differs for the several oils. Whereas French and Spanish oils, also some of the Algerian oils, congeal between +6 and +10,5°, other Algerian oils do not solidify at even - 15°, for the reasons mentioned above.
d15o0,8328 to 0,8437; aD - 0°40' to +2° 10' (the optical rotation is mostly dextrogyrate and independent of the congealing point); n])20o1,430 to 1,434; congealing point +5,8 to 10,8°, mostly above 7°; soluble in 1,5 to 3 vol of 70 p.c. alcohol (in isolated cases the diluted solution reveals opalescence or even turbidity because of the separation of paraffin).
An oil distilled in Guerrevieille (southern France) possessed somewhat different properties: d15o0,8378; aD + 0°; nD20o1,43168; soluble in 2,5 vol. or more of 70 p.c. alcohol with a decided separation of paraffin; it did not congeal above - 5°, but paraffin crystals were separated at +10°.
1) Bed. Berichte 35 (1902), 3587.
2) Journ. chem. Soc. 81 (1902), 1585.
3) Report of Schimmel & Co. October 1901, 47.
4) Journ. chem. Soc. 81 (1902), 1585.
1. The oil distilled during the summer from Ruta montana with methyl nonyl ketone as principal constituent.
d15o 0,8370 to 0,8381; aD + 0° to +0°56'; nD20o1,43058 to 1,43218; congealing point +7,3 to 10,4°; soluble in 2 to 3 vol. or more of 70 p.c. alcohol, occasionally with opalescence due to the separation of paraffin.
2. The oil distilled during the winter from Ruta bracteosa with methyl heptyl ketone as principal constituent.
d15o 0,8373 to 0,8446; aD - 1°14' to - 5°; nD20o about 1,430; the congealing point is very low; some oils not solidifying at - 15°; soluble in 2 to 3 vol. of 70 p.c. alcohol, occasionally with turbidity because of its paraffin content.
d16o0,834 to 0,847; aD - 1° to +0°30'; congealing point below 0° to +7,5°; soluble in 2 to 4 vol. of 70 p.c. alcohol.
A Syrian oil had the following constants: d15o0,8408; aD - 0°28'; nD20o1,43296; congealing point - 1,9°; soluble in 2 vol. or more of 70 p.c. alcohol with fluorescence.
Examination. Characteristic for pure oil of rue are its low specific gravity and its solubility in 70 p.c. alcohol.
Petroleum and turpentine oil are recognized by their insolubility in 70 p.c. alcohol. Turpentine oil can be identified by collecting the distillate below 200° and testing it for pinene. The pure oil does not yield more than 5 p.c. below 200°.
The amount of pinene present in pure oil is so small (see under Composition) that the natural pinene can be identified only when large quantities of oil are operated upon. Because of the possibility of preparing a mixture of proper specific gravity and solubility from alcohol and an oil soluble in 70 p.c. alcohol, it is advisable always to examine commercial oils for alcohol.
Most adulterants can be separated by treating the oil with acid sulphite solution and further study of the non-combined portion.