Nitration hemicelluloses

Although most polysaccharides may be acylated without degradation, acyl derivatives of xylans29 are often unsatisfactory for molecular-weight determinations owing to their poor solubility characteristics. Mixed esters of xylans143 are often superior in this respect, but there are obvious difficulties in the differential analysis of acyl groups. Hemicellulose nitrates have been used for measurements of molecular size,168 but xylan nitrates,29 like xylan acetates, are reported to have poor solubility characteristics. 

The hemicelluloses give explosive compounds on nitration, but the yields are small and stabilization difficult (Ref 1)... 

Finishing wood cellulose. The finishing process is made to obtain a higher a-cellulose content and to endow the wood pulp with a shape conducive to easy nitration. This is the last operation prior to nitration. It consists in removing hemicelluloses, pentosans, and hexosans, which are undesirable ingredients of wood pulp. An insufficiently purified wood pulp may contain 5-6% of pentosans, straw cellulose even as much as 20%, whereas cotton does not contain more than 0.5-0.6%. 

Experiments on the nitration of hemicelluloses composed mainly of pentosans were carried out by Will and Lenze [1]. These authors treated hemicelluloses with strong nitric acid, and isolated the nitration product by precipitation with water or sulphuric acid. The product obtained was insoluble in ether-alcohol. 

Rassow and Dorr [2] nitrated hemicelluloses using the mixed acids applied for nitrating cellulose. Thus, making use of a mixture composed of... 

As a result of nitrating hemicelluloses by means of more dilute acids, including 16.5-21.0% of water, at 20°C, a product containing even less nitrogen (5.8-7.2%) was obtained. It was scarcely soluble in mixtures of ether and alcohol. 

CanP 198328(1920) CA 13,2763(1919) 14, 1609(1920) (A chge of nitrated hemicellulose together with TNT, PA LA and a MF-KCI03 mixt or other primary chge is suitable for detong dynamite)... 

The result of nitrating hemicellulose (after Rassow and DOrr [2])... 

Hemicelluloses and pentosan nitrates Pectin nitrates ( Niiropcctinc )... 

The method of characterization by high-performance liquid chromatography [HPLC] is as follows 25 mg of hemicellulose was put into 50 mL volumetric flask and pure water was added to the mark. The mixture was shaken and then filtered [first few milliliters of filtrate was discarded]. The solution was then filtered through a membrane filter of 0.2 pm cellulose nitrate. Then about 100 mL solution was injected into the HPLC system via a loop injector with a 20 mL, using an isocratic elution system with distilled water with a mobile phase, flow rate 0.8 mL/min. The detection was made using a UV detector at a wavelength of 280 nm [34]. 

After removal of lignin, the nitrated cellulosic products can be separated into three fractions, which are designated A, B, and C, of which Fraction A is insoluble in acetone Fraction B is soluble in acetone, but insoluble in water and Fraction C is soluble in both acetone and water. Analysis shows the acetone-soluble fractions B and C to consist of nitrated a-cellulose of DP about 4450, and nitrated hemicellulose, respectively. Both these products are also found in the acetone-insoluble fraction, A. 

This pattern of behavior is considered by Lewin and Epstein to indicate the presence of chemical linkages between a-cellulose and the hemicelluloses in jute that hold these components together in Fraction A and render the complex insoluble in acetone. The release of increasing amounts of acetone-soluble nitrated a-cellulose in Fraction B then arises from breakage of the links by the nitrating adds, with more breakages occurring as the time of nitration is increased. 

---