Holocellulose from aspen wood

Relatively pure xylan isolated from the holocellulose of aspen (Populus) wood is said to contain 85% of xylose residues.78 One of the characteristic properties of xylan is its ease of hydrolysis. Because it hydrolyzes much more readily than cellulose, mild acid treatment may be employed to bring about preferential hydrolysis of xylan from plant material. Xylose is ordinarily prepared in the laboratory by direct sulfuric acid hydrolysis of the native xylan in ground corn cobs.74 Hydrolysis in hydrochloric acid proceeds rapidly, but decomposition to furfural also occurs to some extent.76 A commercial method for the production of D-xylose from cottonseed hulls76 and straw77 and from corn cobs17 78 has been described. 

Woods contain a number of acyl (mainly acetyl) groups, and it is probable that these are associated with the xylan components of the hemicellulose fraction. Evidence for the original esterification of aspen-wood xylan comes from the observation that the isolated xylan (obtained by alkaline extraction) is readily cleaved by periodate, whereas only a small proportion of the D-xylose residues in the wood itself are oxidized under similar conditions.66 Hemicelluloses still containing acyl groups may be extracted from wood holocelluloses by means of dimethyl sulfoxide, and further quantities... 

Bird and Ritter isolated, from wood of white oak, a chlorine holocellu-lose which contained all of the 0-acetyl groups present in the wood. Mitchell and Ritter later extracted a chlorine holocellulose from sugar maple with water and obtained a xylan in a yield of 3.4% of the wood. This polysaccharide contained 9.2% of 0-acetyl groups. A xylan which had been obtained in the same way, from aspen, by Wise and Jones, was, on treatment with periodate, oxidized almost to completion. When the wood itself was similarly treated, most of its xylan escaped oxidation. Although it appears evident that all of the xylan in the wood could not possibly have been accessible to the aqueous reagent, it was concluded that the lack of oxidation was most probably due to the fact that the native xylan was partly 0-acetylated. After treatment of wood from Eucalyptus regnans with methanol at 150°, Stewart and coworkers obtained, on extraction with water, a xylan (in a jdeld of 3.7%) which contained 5-6% of acetate... 

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