Reactivity of Cellulose

Many physical and chemical methods have been used for determining the accessibility of cellulose, and only examples of recent developments in this field will be given. Earlier work has been reviewed previously. - -  

Infrared absorption can be used in conjunction with deuteration to measure accessibility. The development of this technique has been 

Deuteration has also been used as a gravimetric method for determining accessibility, the results for cotton being in exact agreement with those of Valentine. The linear relationship which exists between moisture sorption and the fraction of material found to be amorphous to infrared has been confirmed for thirteen different t5qies of cellulose, and it is suggested that a difference in the ratio of moisture regain to amorphous content between samples of cellulose I and cellulose II reflect differences in their sorption behavior and, hence, in the structure of their amorphous 

The problem of the existence of so-called acid-sensitive, weak linkages in cotton cellulose has been reviewed. The nature of these linkages remains uncertain. Some investigators favor the view - that, since these linkages can be produced by a wide variety of treatments, it is unlikely that they are formed by any specific chemical reaction and believe that their lability may be attributed to such physical effects as molecular strain or isolated variations in the normal state of hydrogen bonding, whereas others claim that there is no clear evidence of the presence of such links. 

The extent of the recrystallization which is believed to occur during acid 

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Ethylenediamine (70,71), benzyl alcohol and acetone (72), ethylene glycol (73) and C2—C g carboxyUc acids (74) are claimed to increase the reactivity of cellulose toward acetylation. Sodium hydroxide and Hquid ammonia (71) are excellent swelling agents and have been used to activate cellulose before esterification. Ultrasonic treatment of cellulose slurries (75) reportedly swells the fibers and improves reactivity. 

McKelvey etal. (1959) investigated the reaction of epoxides with cellulose in alkaline conditions, reporting that alkaline cellulose reacted readily once the concentration of sodium hydroxide was sufficiently high. However, no evidence was found of reaction between cotton yarn and cellulose with a range of epoxides under a variety of reaction conditions. It was concluded that the apparent reactivity of cellulose with epoxides was primarily due to alkaline swelling of the cellulose, self-polymerization of the epoxide monomers then occurring within the interior structure of the fibres. It was also noted that the reactivity with phenol OH groups was very low (e.g. only 1 % conversion of ethylene oxide with various phenols). 

Cellulose is an unbranched polysaccharide consisting of 1,4-linked 3-D-glucose and can attain lengths of up to 15000 pyranose units. It neither dissolves nor swells in most solvents, but can be hydrolyzed upon prolonged treatment with acids. Cellulose powder was the first type of support to be used (with limited success) for solid-phase peptide synthesis [208]. Limitations were mainly due to the low loading (0.1 mmol/g) attained in these initial experiments, and the high reactivity of cellulose. Despite these... 

Green, J. W. (1963). Wood cellulose. Methods in Carbohydrate Chemistry, Vol. Ill, pp. 9-21. Academic Press, New York Drying and reactivity of cellulose. Methods in Carbohydrate Chemistry, Vol. Ill, pp. 101-103. Academic Press, New York. 

This chapter discusses major factors affecting the reactivity of cellulose, hemicelluloses, and lignin under both acidic and alkaline modifications. 

Different. solubility behaviors were observed in organic solvent systems. Regenerated cellulose did not dissolve in the SOj-amine-DMSO system which, however, readily dissolved the native and mercerized samples [15-17]. Similarly, rayon and mercerized cellulose, unlike native cellulose, were insoluble in the dimethylformamide (DMS)-chloral-pyridine solvent system 114]. Thus, the morphology of the amorphous component in addition to its content plays a significant role in the overall reactivity of cellulose. 

The reactivity of cellulose toward tri(p-toluenesulfonyl)methane chloride was recently examined [89]. The tosyl reagent is more reactive than trityl chloride, and the primary hydroxyl position exhibited 43 times more reactivity than the secondary hydroxyl groups. The products were used as intermediates in the synthesis of selectively modified cellulose derivatives [89]. As mentioned earlier, a high DS, organosol trimethylsilylcellulose has been prepared in DMAc/LiCl [10]. The condensation of polysaccharides with triphenyl-methyl (trityl) chloride proceeds generally with preference for the primary hydroxyl positions. The tritylation of cellulose occurs initially 58 times faster at the hydroxyl group at C6 than at either C2 or C3 [90]. 

We have studied the relative reactivity of cellulose and mixed polysaccharides (III) and (IV) in reactions with aqueous and alcoholic solutions of NaOH. The data on the composition of alkali compounds of polysaccharides are given in Table 6. As seen from the data presented in Table 6, the amount of bound alkali in preparations of alkaline compounds of mixed polysaccharides is le than in alkali cdlulose obtained under the same conditions, the DS with respect to NaOH decreasing with increasing content of altrose units in polysaccharide (III) and of 3,6-anhydroglucose units in polysaccharide (IV). 

Because of consumer demand in the second half of this century for easy care textiles, interest in the reactivity of cellulose from the ever popular cotton and viscose rayon preceded interest in the other products. In fact, it is the alcohol functionality of cotton and viscose cellulose that is responsible for improvements in the aesthetic and functional properties of their fibers and fabrics. 

This article will deal mainly with recent aspects of the determination of the structure and reactivity of cellulose. Some mention is also made of the chemical treatments which are used to modify the physical properties of cellulose, although as yet relatively little is known concerning their exact nature. 

Methods for increasing the accessibility and, hence, the reactivity of cellulose continue to receive attention. These methods are based on the fact that swelling agents can bring about some decrystallization of the structure and this, in turn, increases the extent by which it can be penetrated by chemical reagents. 

An important factor in the esterification reactivity of cellulose is the history of its method of manufacture and pretreatment or activation prior to the reaction. Since cellulose is insoluble in the acGtylation solvent and is in a fibrous form, it is necessary to make the hydroxyl groups as accessible to the acetylating agent as is possible. The pretreatment or activation is designed to accomplish this. Soaking the cellulose in acetic add or aqueous acetic add prior to esterification greatly improves its reactivity. 

In the present study, the role of cellulose physical structure in alkaline reactions was investigated by comparing the alkaline degradation of highly crystalline (cellulose I) fibrous hydrocellulose with that of amorphous (noncrystalline) hydrocellulose. The amorphous substrate was taken as a cellulose model the reactivity of which would most closely approximate that of alkali-soluble cellulose. The availablity of such an approximation to the inherent reactivity of cellulose allowed evaluation of the effects of the more highly ordered structure of the fibrous hydrocellulose. 

Cellulose. — A comprehensive treatise on the modification of cellulose has appeared.The book is sub-divided into five parts a summary of previous work on modified cellulosics, a discussion of cotton and wood cellulose, a review of the accessibility and reactivity of cellulose, a discussion of modification of cellulose by grafting of vinyl monomers, and a description of additional techniques for cellulose modification. 

Schobitz, M.M. RHeinze, T. Unconventional reactivity of cellulose dissolved in ionic liquids. Macromol. 

Many general books develop the structure and reactivity of cellulosic materials and the preparation of their derivatives (112-115). 

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