In the first fractions of lemongrass oil, Barbier and Bou-veault1) found a methylheptenone which, according to their opinion, differed from the substance obtained by Wallach2) from cineolic acid. However, as demonstrated by Schimmel & Co.3), the methylheptenone isolated from lemongrass oil is identical with the ketone of Wallach and that described by Tiemann and Semmler 4).
Geraniol4), the alcohol corresponding to citral, is contained in the highest fractions of the oil, partly free, partly as ester. It was isolated by means of its calcium chloride compound (m. p. of diphenylurethane 82°).
The presence of linalool 5) in fraction 198 to 200° may be regarded as probable.
Barbier and Bouveault observed the presence of a terpene (b. p. 175°; aD - 5°48') in some oils but not in others. It formed a liquid bromide from which small amounts of a solid substance, m. p. 85°, separated. Presumably it got into lemongrass oil by adulteration.
Properties. As its name indicates, lemongrass oil has an intensive lemon-like odor and taste. It is a reddish-yellow to reddish-brown, mobile liquid; sp. gr. 0,899 to 0,905, exceptionally a density of 0,895 and up to 0,910 has been observed in otherwise good oils; aD + 1°25' to - 5°; nD20o 1,483 to 1,488; soluble in 1,5 to 3 vols, of 70 p. c. alcohol, in isolated cases slight opalescence or turbidity was observable resulting from the separation of paraffin.
Characteristic of the quality of an oil is its citral content, its principal constituent. This is determined either according to the bisulphite method (vol. I, p. 582) or according to the sulphite method (vol. I, p. 584). According to the first method, other aldehydes and a part of the methylheptenone are determined with the citral. Consequently higher results are obtained by this method than by the sulphite method.
1) Compt. rend. 118 (1894), 983.
2) Liebig's Annalen 258 (1890), 319 ff.
3) Report of Schimmel &j Co. October 1894, 33. Comp. also Tiemann & Semmler, Berl. Berichte 28 (1895), 2126, footnote.
4) Berl. Berichte 26 (1893), 2721.
5) Report of Schimmel & Co. October 1S94, 33; April 1899, 65.
6) Loc. cit.
The aldehyde content of a normal oil varies between 70 and 85 p. c. when determined according to the bisulphite method and between 65 and 80 p. c. when assayed according to the sulphite method. Hence, in recording assays, or when purchasing according to guaranteed aldehyde content, the method of assay should always be mentioned. If the same oil is assayed according to both methods, the bisulphite method gives results that are higher by 2 to 5,5 p.c.1). Upon prolonged storage the citral content is reduced2).
Adulterations. Although adulteration of lemongrass oil is not very common, unwarranted additions have been observed occasionally. Petroleum and cocoanut oil are recognized by the incomplete solubility of the oil. Upon distillation of the oil with steam, the latter remains in the flask and can readily be recognized as such 3). More difficult is the detection of citronella oil which Parry4) as well as Schimmel & Co.5) have found. The oils adulterated with citronella oil had a remarkably low citral content and after the citral had been removed the odor of citronella oil was distinctly perceptible.
Easier was the detection of an adulteration with acetone observed by Parry6). The oil in question attracted attention because of its low specific gravity, but had an apparent citral content of 76 p. c. The acetone was separated by fractional distillation. In as much as it combines with bisulphite, it apparently increased the citral content.
Production and Commerce. The principal seat of production lies in Southern India, more particularly in the province Travan-core, south of Cochin, with Trivandrum as principal collecting center. The principal port of export, however, is Cochin.
1) Report of Schimmel & Co. October 1908, 82. 2) Ibidem October 1909, 75. 3) Ibidem October 1905, 45.
4) Chemist and Druggist 06 (1905), 140.
5) Report of Schimmel & Co., April 1907, 68. 6) Chemist and Druggist 02 (1903), 768.
Calicut and Quilon also export lemongrass oil 7). The accompanying curve illustrates the exports, with the exception of 1889/90. from the beginning to the present time.
Whereas in 1884 the exports amounted to but 228 cases of 12 bottles of 22 oz. each (71/2 kg. in all), they rose materially in recent years as shown by the following table. The sudden rise in 1906 would seem to be associated with the prospective termination of the ionone patents in Germany. The exports in cases to the several ports are recorded in the following table:
7) Watt, The commercial products of India. London 1908. p. 458. Hooper, Chemist and Druggist 70 (1907), 208.
In Ceylon also some lemongrass oil is distilled, but only in isolated places and in small amount only. Statistics are not available.
In the Straits Settlements the distillation of lemongrass oil is still conducted on a small scale only. In 1903 it amounted to not more than 200 gals. (abt. 900 I.2).