Abstract
WHEAT STRAW HEMICELLULOSE:
1. The hemicellulose ( xylan) was extracted from defatted,
delignified wheat straw with dilute alkali. It contained
xylose, and arabinose (6.2%) together with some uronic acid.
2. Complete removal of arabinose by purification through
the copper complex was found to be impossible. Purification
was finally effected by fractional solubility in aqueous
ethanol.
3. The purified xylan had xylose, 87.9%; arabinose, 9.6%;
uronic anhydride, '3.2 %; methoxyl, 0.4% and ash, 0.7 %. The
xylose residues held in combination with uronic anhydride
as aldobiuronic acid are not taken into account in these
figures.
4. The reducing power determined by alkaline hypoiodite
indicated a D.P. of 164, and by 3:5-dinitro salicylic acid, 43. Neither method is completely reliable.
5. The fully methylated xylan had a viscosity in m. cresol
corresponding to a D.P. of 26-7.
6. The methylated xylan on hydrolysis and estimation with
alkaline hypoiodite yielded the following molar ratios;
trimethyl pentose, 2.8%; 2:3-dimethyl xylose, 94.3 %;
monomethyl xylose, 2.9%. The uronic acid was not estimated.
7. The hydrolysate of the methylated xylan was separated
on a cellulose column. The following were identified,
calculated as 100% total pentose; 2:3:4-trimethyl xylose, 2.4%; 2:3-dimethyl xylose, 94.5%; 2-methyl xylose, 3.4 %.
8. In addition to the above, there was obtained a uronic
acid identified as 2-methyl-3- (2:3:4-trimethylαD glucuronosido) D xylose.
9. Unmethylated xylan was hydrolysed, the aldobiuronic
acid separated as the barium salt, and rehydrolysed.
Glucuronic acid and glucurone were detected, but no
4-methyl glucuronic acid was found.
10. On the basis of the above results, and the results
of periodate oxidation, a probable structure is suggested
for the hemicellulose.
II. BEECHWOOD HEMICELLULOSE A.
1. The hemicellulose ( xylan) was extracted with dilute
alkali from pre-extracted beechwood.
2. The xylan gave on hydrolysis, xylose, 81.6%; rhamnose,
0.40 %; and had uronic anhydride 9.5%; methoxyl, 1.7%; and total lignin, 1.9%.
3. The reducing power, by alkaline hypoiodite, indicated
a D.P. of 130-144, and by Meyer's method, 167-197.
4. The viscosity of the fully methylated xylan in
m.cresol indicated a D.P. of 50.
5. The hydrolysate of the methylated xylan was separated
on a cellulose column. The following molar ratios were
obtained:- 2:3:4-trimethyl xylose, 1.34%; 2:3-dirnethyl xylose, 78.l6%; monomethyl xylose, 10.08%. No rhamnose
derivatives were obtained. The monomethyl xylose contained
3-methyl xylose and 2-methyl xylose in ratio 20:1 approx.
6. In addition to the above, 10.49% (mol.) of a methylated
aldobiuronic acid was obtained from the column and identified
as 3-methyl-2- (2:3:4-trimethylαD glucuronosido) D xylose.
7. The unmethylated xylan was hydrolysed and a monomethyl
aldobiuronic acid was isolated as the barium salt. Reduction
and hydrolysis of the acid yielded 4-methyl D glucose.
8. Periodate oxidation of the unmethylated polysaccharide
gave an uptake of 1.0 mol. periodate per C₅H₈O₄ unit. The formic acid released did not reach a constant value.
9. On the basis of the above results, a probable structure is suggested for the hemicellulose.