The seed hairs of lcapolc (Ceiba penlandra) on alkaline extraction have yielded a hcrnicellulose composed of xylose and uronic acid residues. Partial hydrolysis of the polysaccharide gave 2-0-(4-0-methyl-~-~-9-lucopyranospl~1ronic a~i t l ) -D -~y l o p y r a l~~s~, 4-0-methyl-D-glucuronic acid, and, probably, galacturonic acid. Hydrolysis of the fully methylated hemicellulose yielded a mixture of 2-0-and 3-0-meth>~l-~-sylose, 2,s-di-0-methyl-D--lose, 2,3,4-tri-o-rnethyl-~-xylose, and 2-0-(2,3,4-tri-0-methy~-a-~-~copyra1ios)~1roic acid)-3-0-methyl-D-xylopyranose in a niolar ratio of 1.1 : 38: 1: 6. The number-average D.P. of the native and the methylated polysaccharides was 177 and 124, respectively. On the basis of this and other evidence it is suggested that the average hemicellulose rnolccule contains approximately 180 1,4-linked P-D-~ylopyraII~se residues, one eighth of which carry a singlc tcrrnilial side chain of 4-0-methyl-D-glucuronic acid, attached through a n a-glycosidic bond to C ? of the sylose. The xylan frameworlc contains, on the avcrage, slightly less than two branching points per macromolecule, most of them probably originating from C3. The number of acid side chains and branches is twice as large as that of the otherwise similar 4-0-methyl glucuronosylan present in the seed hairs of rnillcweed floss.In previous investigations the general cheinical composition of the seed hairs of kapok was studied (1) as well as the molecular characteristics of their cellulose component (2, 3). The present paper is concerned with the structure and properties of the main heinicellulose constituent.
RESULTS AND DISCUSSIONThe high pentosan content (24.4Y0) of the extractive-free seed hairs indicated that the predominant he~nicellulose was based on xylose residues. The considerable amounts of acetyl (8.0%) and uronic anhydride (6.6y0) groups present as well as the forlliation of a methylated glucuronic acid on hydrolysis of the fibers suggested that the polysaccharide in its native state was a partially acetylated methyl glucuronoxylan. When kapok fibers were extracted with aqueous alkali a deacetylated product was obtained in a yield of 18.870, containing 83.3y0 pentosan and with [a]; -G8O in water. Its content of ash, methoxyl, and uroilic anhydride indicated the presence of an average of 7.8 anhydroxylose units per methylated uronic acid.Partial acid hydrolysis of the hemicell~~lose gave a mixture of sugars which was resolved into a neutral and an acidic portion on a column of anion exchange resin. The neutral part contained mostly D-xylose which crystallized but also traces of glucose, mannose, arabinose, and rhamnose. Elution of the column with dilute acetic acid yielded three sugar acids, namely a monouronic acid, chromatographically identical with galacturonic acid, an aldobiouroilic acid, and a mono-0-methyl monouronic acid.The methoxyl content and equivalent weight of the aldobiouronic acid suggested that it consisted of a methoxyuronic acid linked to a pentose residue. A portion of the acid was c...
