1) In connection with oils prepared by himself, Ziegelmann observed d15o 1,1578 to 1,1786 (d25o 1,1502 to 1,171), which low densities are probably due to some extraordinary circumstance in the preparation. Oils with such low specific gravities never occur when they are distilled on a large scale.
2) Ann. de Chim. et Phys. III. 10 (1844), 327. - Liebig's Annalen 48 (1843), 60 and 52 (1844), 327.
According to F. B. Power and C. Kleber'), sweet birch oil consists of methyl salicylate2) to the extent of 99,8 p.c.3). If the oil, diluted with ether, is shaken repeatedly with 701/2 p.c. potassium hydroxide solution, the methyl salicylate passes into aqueous solution as potassium methyl salicylate, and can thus readily be separated from the other components of the oil, which remain in the ethereal solution.
The semi-solid ethereal residue can be separated, by steam distillation, into two parts. The non-volatile part congeals upon cooling. It is readily soluble in ether, difficultly in alcohol, crystallizes in laminae, is not acted upon by sulphuric or nitric acids, and consists of a paraffin, judging from its elementary analysis and its melting point, which lies at 65,5°, it should be regarded as triacontane, C30H62. The part which is volatile with water vapor is soluble in 80 p.c. alcohol, and boils at 230 to 235° (under 25 mm. pressure at about 135°). Its composition is expressed by the formula C14H2402. It is an ester which upon saponification is resolved into its components, an alcohol C8H10O and an acid C6H10O2.
Examination. Inasmuch as the oils of sweet birch and gaul-theria are the heaviest of all known oils, the presence of foreign oils or petroleum invariably produces a lowering of the specific gravity. Most adulterants also reduce the solubility of the oil in 70 p.c. alcohol. A convenient means of detecting adulteration is afforded by the property of methyl salicylate to form with potassium hydroxide, a water-soluble salt (C6H4[OK]Cooch3). The test is carried out in the following manner: To 1 cc. of either sweet birch oil or wintergreen oil to be tested, 10 cc. of a 5 p.c. potassium hydroxide solution are added and the mixture is shaken. If the oil is pure, a clear, colorless or but slightly yellow-colored liquid results. If foreign oils or petroleum, chloroform, etc. be present, the mixture becomes turbid, and after standing for some time, oily drops will separate either at the surface or at the bottom. In this manner the presence of 5 p.c. foreign, non-phenolic constituents can be detected. Inasmuch as the odor of methyl salicylate disappears completely upon saponification, the particular kind of adulterant can mostly be recognized by the odor of the saponified oil.
1) Pharm. Rundsch. (New York) 13 (1895), 228.
a) The assertion made by H. Trimble and H. J. M. Schroter (Americ. journ. Pharm. 61 , 398 and 67 , 561), that benzoic acid, ethyl alcohol and a sesquiterpene C15H24 are contained in gaultheria oil and in sweet birch oil has been proved to be wrong, as shown by Power (Pharm. Rundsch. [New York] 7 , 283), also by Power and Kleber (Ibidem 13 , 228).
") Ziegelmann (loc. cit.) found but 90,2 to 97,83 °/o ester in oils distilled by himself. These low results are presumably due to incomplete saponification.
The methyl salicylate content can be determined either by separating and weighing the salicylic acid, or volumetrically.
For the quantitative determination by weight1) 1,5 to 2 g. of oil are saponified in a flask of 50 cc. capacity with a slight excess of concentrated sodium hydroxide solution. The liquid is then transferred to a separating funnel, an excess of hydrochloric acid is added and the salicylic acid set free is shaken out with ether. In order to remove traces of sodium chloride from the ethereal solution, this is shaken out with water. The ether is evaporated from a tared dish on a water-bath. The remaining salicylic acid is weighed after it has been brought to constant weight in a desiccator over sulphuric acid.
This method of determination presupposes a pure oil, since foreign admixtures, such as sassafras oil, would also enter the ethereal solution and, upon evaporation of the ether, would be but partly volatilized and partly weighed with the salicylic acid.
The amount of salicylic acid can also be determined according to the method of ). Messinger and G. Vortmann2). It is based on the fact that, in the presence of much alkali, iodine converts salicylic acid into diiodosalicylic acid. Using an iodine solution of known strength, the excess of iodine can be titrated with volumetric thiosulphate solution. The reaction is expressed by the following equations: C6H4(OH)Cook + 3Koh + 61 = C6H2I2(OI)COOK4 3KI + 3H20.
1) B. H. Ewing, Proceed. Americ. Pharm. Assoc. 40 (1892), 196.
2) Berl. Berichte 22 (1889), 2321 and 23 (1890), 2755. As to the usefulness of the method comp. W. Fresenius and L. Grunhut, Zeitschr. f. anal. Chem. 38 (1899), 292; also J. Messinger, Journ. f. prakt. Chem. II. 61 (1900), 237.
The application of this method to wintergreen oil is recommended by E. Kremers and M. James1).
A weighed amount of oil is saponified with a normal potassium hydroxide solution, care being taken that for every molecule of methyl salicylate at least 7 mol. of potassium hydroxide are used. The liquid is then diluted with water to exactly 250 or 500 cc. Of this solution 5 or 10 cc. are transferred to a flask and heated to about 60°. Sufficient 1/10 normal iodine solution is then added until the decidedly yellow color remains permanent. Upon shaking, a deep red precipitate is produced. After cooling, the solution is acidulated with dilute sulphuric acid and diluted with water to 250 or 500 cc. In an aliquot part of the filtrate, about 100 cc, the excess of iodine is titrated with 1/10 normal sodium thiosulphate solution.
1 mol. methyl salicylate / 6 atoms iodine = 151,64 /759.2 = 0.19974314
By multiplying the amount of iodine consumed with the factor 0,19974314, the corresponding amount of methyl salicylate can be computed and from this its percentage in the oil.
The simplest way to ascertain the methyl salicylate content of the oil is to determine its ester value, from which the amount of ester can be computed (Comp. Vol.1, p. 574)2). In this connection it should be noted that the oil should be boiled with a large excess of alkali (30 cc. alcoholic half-normal potassium hydroxide to about 1,5 g. oil) for 2 hours, otherwise results that are too low are likely to be obtained.
A good oil contains at least 98 p. c. of methyl salicylate.