Cellulose hydrolysis, partial

Cellulose hydrolysis of 6 and 7. A solution of 6 and 7 (2 mg) in 2 ml 0.1 M HOAc-NaOAc buffer (pH 4.5) was incubated at 40 C with cellulase (1 mg) for 0.5 h. Partially hydrolysed products were identified by comparison with authentic samples on silica gel HPTLC with Et0H-Et0Ac-H20 (20.10 0.1) as developing solvent. 4 h later all glycosides were hydrolyzed and only glucose and aglycone were detected. 

Definition Isolated, colloidal crystalline portion of cellulose fibers partially depolymerized acid hydrolysis prod, of purified wood cellulose... 

Synonyms Cellulose gel MCC Dehnition Isolated, colloidal crystalline portion of cellulose fibers partially depolymerized acid hydrolysis prod, of purified wood cellulose Properties Wh. fine cryst. powd., odorless partly sol. with swelling in dil. alkali insol. in water, dil. acids, and most org. soivs. bulk dens. 18-19 Ib/ft ref. index 1.55 pH 5-7 Toxicology LD50 (oral, rat) > 5 g/kg, no significant hazard irritant by inhalation (dust) may be damaging to lungs TSCA listed... 

This jS-D-glucopyranoside, unlike lactose, is not used in practical feeding, but it is of some interest. The disaccharide is derived from cellulose by partial acid hydrolysis or by the action of cellulase (p. 664). Experimental rats utilize it as completely as glucose (. 7). This indicates that cellobiose is hydrolyzed to D-glucose, but apparently little if anything has been reported on the nature of the enzyme of higher animals that catalyzes the reaction. 

By-product acetic acid is obtained chiefly from partial hydrolysis of cellulose acetate [9004-35-7]. Lesser amounts are obtained through the reaction of acetic anhydride and cellulose. Acetylation of saHcyHc acid [69-72-7] produces one mole of acetic acid per mole of product and the oxidation of allyl alcohol using peracetic acid to yield glycerol furnishes by-product acid, but the net yield is low. 

Many of these reactions are reversible, and for the stronger nucleophiles they usually proceed the fastest. Typical examples are the addition of ammonia, amines, phosphines, and bisulfite. Alkaline conditions permit the addition of mercaptans, sulfides, ketones, nitroalkanes, and alcohols to acrylamide. Good examples of alcohol reactions are those involving polymeric alcohols such as poly(vinyl alcohol), cellulose, and starch. The alkaline conditions employed with these reactions result in partial hydrolysis of the amide, yielding mixed carbamojdethyl and carboxyethyl products. 

Cellulose is the main component of the wood cell wall, typically 40—50% by weight of the dry wood. Pure cellulose is a polymer of glucose residues joined by 1,4-P-glucosidic bonds. The degree of polymerization (DP) is variable and may range from 700 to 10,000 DP or more. Wood cellulose is more resistant to dilute acid hydrolysis than hemiceUulose. X-ray diffraction indicates a partial crystalline stmcture for wood cellulose. The crystalline regions are more difficult to hydrolyze than the amorphous regions because removal of the easily hydrolyzed material has Htde effect on the diffraction pattern. 

Cellulose acetate [9004-35-7] is the most important organic ester because of its broad appHcation in fibers and plastics it is prepared in multi-ton quantities with degrees of substitution (DS) ranging from that of hydrolyzed, water-soluble monoacetates to those of fully substituted triacetate (Table 1). Soluble cellulose acetate was first prepared in 1865 by heating cotton and acetic anhydride at 180°C (1). Using sulfuric acid as a catalyst permitted preparation at lower temperatures (2), and later, partial hydrolysis of the triacetate gave an acetone-soluble cellulose acetate (3). The solubiUty of partially hydrolyzed (secondary) cellulose acetate in less expensive and less toxic solvents such as acetone aided substantially in its subsequent commercial development. 

Solution Process. With the exception of fibrous triacetate, practically all cellulose acetate is manufactured by a solution process using sulfuric acid catalyst with acetic anhydride in an acetic acid solvent. An excellent description of this process is given (85). In the process (Fig. 8), cellulose (ca 400 kg) is treated with ca 1200 kg acetic anhydride in 1600 kg acetic acid solvent and 28—40 kg sulfuric acid (7—10% based on cellulose) as catalyst. During the exothermic reaction, the temperature is controlled at 40—45°C to minimize cellulose degradation. After the reaction solution becomes clear and fiber-free and the desired viscosity has been achieved, sufficient aqueous acetic acid (60—70% acid) is added to destroy the excess anhydride and provide 10—15% free water for hydrolysis. At this point, the sulfuric acid catalyst may be partially neutralized with calcium, magnesium, or sodium salts for better control of product molecular weight. 

The glycosidic bond to an anomeric carbon can be either a or (3. Maltose, the disaccharide obtained by enzyme-catalyzed hydrolysis of starch, consists of two cv-D-glucopyranose units joined by a 1->4-o-glycoside bond. Cellobiose, the disaccharide obtained by partial hydrolysis of cellulose, consists of two /3-o-glucopyranose units joined by a 1—>4-/3-glycoside bond. 

Most of the selective-etherification studies on polysaccharides have been made with cellulose, and nearly all of them have involved quantitative separation of the D-glucose derivatives formed on hydrolysis of the partially substituted celluloses. In view of their stability, ethers of polysaccharides are particularly suited to this approach. 

In further work on nylon [145], this trifunctional reactant was applied simultaneously with various nucleophilic dyes of the aminoalkyl type (Scheme 7.71). As in the case of the Basazol system on cellulose (Scheme 7.60), the intended formation of covalent dye-fibre linkages has to compete with side reactions, such as partial hydrolysis (Scheme 7.70), di- or trimerisation that may lead to less than optimum fastness, or substrate crosslinking that may adversely influence desirable fibre characteristics. 

Partially acetylated cellulose (i.e., cellulose with less than three ester groups per repeat unit) is produced by an indirect route. Direct synthesis yields an inhomogeneous product due to insolubility of cellulose in the reaction mixture. Some chains are completely acetylated while others may be completely unreacted. A partially acetylated product is usually produced by controlled hydrolysis of the triacetate. The triacetate is soluble in the reaction mixture and complete solubility ensures that the final product will be more homogeneous. Hydrolysis of the triacetate is carried out by controlled reversal of the esterification reaction by the addition of water or dilute acetic acid. 

Further, the stabilization boiling of the nitrated cellulose exerts an express influence on the solubility of nitrocellulose. It causes the substance to become more soluble due to partial depolymerization and denitration. (A certain, insignificant decrease of nitrogen value occurs owing to partial hydrolysis). According to Bruley [54] the following relationship exists ... 

Later experiments were carried out with a nitrocellulose stabilization process that consisted in treating a partially purified nitrocotton in an ammonia bath (e.g. Reeves and Giddens [12]). This was based on the supposition that ammonia was capable of neutralizing accurately adds contained in the interior of nitrocellulose fibres. However, this method has not been adopted in practice, since it was feared that the sulpho groups attached to cellulose in the form of mixed esters would undergo only partial hydrolysis in the presence of ammonia and later spontaneous hydrolysis of these substituents in the finished (stabilized) product might reduce its stability. 

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