The chemical nature of the extractives from the bark of red alder, alnus rubra, Bong Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8w32r795f

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  • The purpose of this investigation was to determine the nature of the extractives from red alder bark in an effort to discover the materials which cause the red stain in red alder wood. Samples of bark and wood were obtained and successively extracted with hexane, benzene, ether, ethanol, and hot water. The total extractive, content of the bark was 24.01 percent, while that of the wood was 8.60 percent. The hexane extract amounted to three percent of the dry weight of the bark. Sixty percent of this extract was a saponifiable fatty acid mixture with a neutral equivalent of 290 and a Hanus iodine number of 80.3. Linoleic acid was shown to be present in this mixture. Saponified alcohols and other neutral materials composed 29.1 percent of the hexane extract, and contained a phytosterol, the triterpene alcohol alnulin, and the triterpene ketone protalnulin. The ether extract amounted to .8 percent of the bark. The unsaponifiable materials amounted to 23 percent of the extract and contained the same compounds present in this fraction of the hexane extract. The yield of alcohol soluble material was nine percent of the dry bark. A water insoluble phlobaphene composed 11.7 percent of the alcohol extract. Paper partition chromatography showed that the remaining 88.3 percent of the alcohol extract contained four materials. A standard tannin analysis with hide powder indicated that 28.7 percent of the alcohol extract was a water soluble tannin fraction. Part of this tannin was obtained from the water solution of the alcohol extract by salting out with sodium chloride. It was shown to be a phlobatannin with a catechol nucleus. A reducing sugar analysis showed that 32.7 percent of the alcohol extract was free sugars. Chromatography showed these sugars to be glucose and xylose. The remaining 26.9 percent of the alcohol extract was found to be a phenolic xyloside with properties quite similar to those of the tannin fraction. This xyloside was best isolated by extracting the bark with ethyl acetate, pouring the extract into hexane, dissolving the precipitate in warm water, and adding lead acetate. The lead salts of the xyloside were then suspended in methanol and decomposed with hydrogen sulfide. Evaporating the filtered methanol solution to dryness left the xyloside as a light orange solid. It gave a green color with ferric chloride, a red precipitate when heated with acid, and an intense red color in a basic solution. Its methoxyl content was 3.66 percent. About one-third of the xyloside was removed by acid hydrolysis and shown to be xylose. The infra-red absorption spectras of the phlobaphene, tannin, and xyloside were quite similar. The hot water extract was two percent of the dry bark. It contained an alcohol insoluble tannin-carbohydrate material. A crude carbohydrate fraction was isolated by treating the extract with hide powder, concentrating it to a small volume, and pouring it into a large volume of alcohol. The resultant reddish powder gave a maximum reducing sugar value of 54 percent after a six hour hydrolysis period. Chromatographic analysis showed the presence of glucose, arabinose and a trace of xylose. A pentosan determination showed the presence of 16.93 pentosans. The materials present in the extractives from the bark of red alder which may cause the red stain in the wood are the tannin-like xyloside and the tannin fraction.
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