Abstract:
The inner bark of Douglas-fir was successively extracted with ethanol-water (4:1 v/v), benzene-ethanol (2:1, v./iv), water, and 0.5% aqueous ammonium oxalate solution. The residue was reacted with acidified sodium chlorite, a commonly used reagent to separate lignin from carbohydrates. In general the reaction dissolves the lignin and leaves the carbohydrates as an insoluble "holocellulose" residue. However, a considerable amount of carbohydrates are often dissolved with the lignin. The primary objective of this work was to determine what carbohydrates were solubilized and how much was solubilized. The solubilized materials were recovered as white solids by lyophilization. The solids were high in ash content (13. 39%), but dialysis and re-precipitation did not lower the ash value. The solubilized materials did not contain sulfur, phosphorus or halogens but did have some nitrogen (0.84%). The fraction was acid hydrolyzed and paper chromatography of the hydrolyzate showed ten amino acids. The acid hydrolyzate also contained rhamnose, xylose, arabinose, mannose, galactose and glucose as shown by paper chromatography. The sugars were quantitatively analyzed by gasliquid chromatography of their alditol acetates. The monosaccharide ratios were: glucose, 59.1; arabinose, 11.9; galactose, 3.9; mannose, 3.7; xylose, 1.0; rhamnose, 1.0. Rhamnose has not been previously reported in Douglas-fir bark. Infrared spectroscopy, a carbazole-sulfuric acid color test, and paper chromatography showed the presence of uronic acids. However, the amount of uronic acids appeared less than in the starting material and it was concluded that the reaction did not result in significant oxidation of the primary hydroxyl groups on the polysaccharides to uronic acids. The materials solubilized by the acidified sodium chlorite delignification reaction were methylated to block all of the free hydroxyl groups in the polysaccharides. The methylated material was hydrolyzed and identification of the monomers is expected to aid greatly in the elucidation of the polysaccharide structures.
