DETERMINATION OF BORNEOL ESTERS IN THE ESSENTIAL OIL OF SIBERIAN STONE PINE (PINUS SIBIRICA MAYR) AND SIBERIAN FIR (ABIES SIBIRICA LEDB)

G. G. Lykhina, L. A. Pershina, Zh. V. Plomchak

(Presented at the scientific concluding conference of the Chemical-Technological Faculty)

In carrying out an analysis of the essential oil of Siberian stone pine for the content of bornyl acetate, we observed a discrepancy between the results determined by the saponification method and by the gas–liquid chromatography method.

In the first case, 3.01% bornyl acetate is obtained; in the second, 2.06%.

The overestimated content of bornyl acetate determined by the saponification method with subsequent titration of acids can be explained by the presence of other borneol esters, primarily bornyl formate.

For this purpose we studied, by paper chromatography, the acids obtained during saponification of the essential oil.

Two ml of essential oil were dissolved in twice the volume of ethyl alcohol; then 15 ml of an alcoholic solution of caustic soda were added. The flask was closed with a stopper fitted with a reflux condenser (a glass tube 1 m long). The contents of the flask were heated on a water bath for 1.5 hours. After saponification the solution was evaporated.

The sodium salts of acids obtained in this way were used for chromatography. The sodium salts of the acids were applied to the starting line of a paper strip (rapid chromatographic paper of the Leningrad Factory No. 2 named after Volodarsky). The paper strips were placed in a cylinder with a ground-glass stopper for saturation in a solvent system: n-butanol—1.5 N ammonia in a ratio of 1:1. Saturation of the paper with the solvent took place for 6 hours; development lasted 12 hours.

Then the paper strip was dried and developed with a chlorophenol-red solution. The acids appeared as yellow spots on a violet background.

By the paper chromatography method, formic and acetic acids were detected in the saponification products of the essential oil of Siberian stone pine. Since formic and acetic acids are poorly separated during chromatography, ammoniacal silver nitrate was used as the developer; it is reduced by formic acid [1].

Compounds that reduce ammoniacal silver nitrate solution appear as brown spots.

In the saponification products of the essential oil obtained from the needles and bark of Siberian fir (Abies sibirica Ledb), formic acid was not detected.

By gas–liquid chromatography, the essential oil of Siberian stone pine was chromatographed on a KhL-4 chromatograph (Fig. 1).

As the stationary phase, sorbitan hexacyanethyl ether deposited on Inza brick was used; helium served as the mobile phase.

The analysis conditions were developed on samples of cedar oil and an artificially prepared mixture consisting of bornyl acetate (b.p.

Fig. 1. Chromatogram of the essential oil of Siberian stone pine:
1 — terpene fraction;
2 — bornyl acetate;
3 — bornyl formate;
4 — camphor; 5 — borneol

223°, \(D^{15} = 0.991\)) and bornyl formate (b.p. 225–230°, \(D^{20} = 1.016\); \(n_D^{15} = 1.470\)) and camphor. The latter served as the internal standard.

Sufficiently sharp peaks were obtained under the following analysis conditions:

On the chromatogram of the essential oil of Siberian stone pine, a peak of bornyl formate is always present alongside the peak of bornyl acetate. Calculation of the content of bornyl acetate and bornyl formate was carried out by the normalization method, with the introduction of calibration standardization coefficients, which were calculated from artificially prepared samples, and their independence from the ratio of the components in the sample was verified [2].

Thus, the essential oil of Siberian stone pine contains 2% bornyl acetate and 1% bornyl formate.

REFERENCES

1. Chromatography on Paper. Edited by I. M. Hais and K. Macek. Foreign Literature Publishing House, Moscow, 1962.
2. M. I. Goryaev. Characteristics of Chemical Compounds Included in Essential Oils. Alma-Ata, 1953.