Douglas-fir bark : n-hexane-soluble and volatile materials Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3r074x919

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  • Douglas-fir bark was extracted with n-hexane. A light-colored "wax-like" solid was recovered from the extract by evaporation of the solvent. Chemically intact sterol esters and ferulic acid esters were isolated from the "wax" without saponification or degradation as had been necessary in former investigations. The characterization of the intact esters provides an improved understanding of the characteristics of the extracted "wax." Previous investigations had been limited to an identification of compounds from saponified and chemically fragmented "wax." The intact, undegraded sterol and ferulic acid esters were isolated by subjecting the n-hexane-soluble materials to column chromatography using Silica Gel G as stationary phase and chloroform-n-hexane (3:1 v/v) as developing solvent. The effluents were collected in different fractions and numbered from 1 to 75. Fractions 1, 2, 4, 6, 9, and 11 were tested by thin-layer chromatography using diethyl ether-n-hexane (1:4 v/v) and chloroform-carbon tetrachloride (6:1 v/v) as the solvent systems. The chromatograms showed two spots (R[subscript]f 0.96 and 0.76). Positive results for Liebermann-Burchard tests were found in all of the above fractions except fraction 11, with the most prominent color reaction in fraction 2. Thin-layer chromatographic and gas-liquid chromatographic results showed no free sterols in these fractions and the materials were thus considered to be sterol esters. Fraction 2 was then subjected to saponification since it showed the strongest Liebermann- Burchard test. The unsaponifiable fractions were tested by thin-layer chromatography and gas-liquid chromatography. The results showed the existence of campesterol and [Beta]-sitosterol. Their presence was further confirmed by combined gas-liquid chromatographic-mass spectrometry analyses. The saponifiable and diethyl ether-soluble fraction was analyzed by gas-liquid chromatography and combined gas-liquid chromatographic-mass spectrometry analyses. The results showed the existence of n-tridecanoic acid, n-hexadecanoic acid, n-heptadecanoic acid, cis-9-octadecenoic acid, n-eicosanoic acid, n-docosanoic acid, n-tetracosanoic acid and the possible existence of n-nonadecanoic acid. Any or all of these fatty acids can form esters with the two sterols. The presence of sterol esters, especially esters of odd-numbered fatty acids, has not been previously reported in Douglas-fir bark. Fractions 13 to 17 on the column chromatograph showed a dark blue coloration when exposed to ultraviolet light. The materials in these fractions were collected and purified by recrystallization and thin-layer chromatography. Infrared spectra of the purified material showed it to be an ester. A saponification reaction was then conducted to study the acid part and the alcohol part of the ester. The alcohol portion was found to be a mixture of behenyl alcohol and lignoceryl alcohol by studies of melting point, gas chromatography, and infrared and mass spectrometry. The acid part was proven to be ferulic acid by melting point test, infrared spectroscopy, field desorption mass spectrometry, and nuclear magnetic resonance spectroscopy. The infrared spectrum of the ester showed the presence of hydroxyl groups. Therefore, the ester linkage was between the carboxylic acid group of ferulic acid and the hydroxyl group of the two fatty alcohols. The ferulic acid ester was thus different from the ester found in white fir bark. The present work is the first report to show that ferulic acid does not exist in the free form in n-hexane "wax" as had been suggested earlier. It exists as an ester. The n-hexane-soluble materials were also shown to contain some terpenes, alcohols and other easily volatilized components. To avoid heavy losses, the volatile materials were collected by steam distillation of the bark rather than to attempt to separate them from the n-hexane-soluble fraction. Combined gas-liquid chromatographic-mass spectrometry analyses showed the major volatile components to be furfural, terpinene-4-ol, [alpha]-terpineol, guaiacol, 2, 5-dimethyl-3- acetylfuran, and [Beta]-cyclocitral. The presence of [alpha]-pinene, [Beta]-pinene, limonene, 1, 5-p-menthadien-7-ol, {Beta]-citronellol, and gerniol was also tentatively identified. The presence of [alpha]-terpineol is of interest to forest entomologists because it is known to be an insect attractant for bark beetles. The present work is the first report concerning the presence of furfural, terpinene-4-ol, [alpha]-terpineol, guaiacol, 2, 5-dimethyl-3-acetylfuran, and [Beta]-cyclocitral in Douglas-fir bark.
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