Reactions of cellulose

The vulcanization of polychloroprene (Neoprene) is carried out in different ways. Vulcanization by sulfur, even with an accelerator, is not practiced to a large extent. Vulcanizations by metal oxides (without diamine), either alone or in combination with sulfur (sometimes together with an accelerator), give the best physical properties for the crosslinked product. Halogenated butyl rubber is crosslinked in a similar manner. The mechanism for crosslinking by metal oxide alone is not established [Stewart et al., 1985 Vukov, 1984]. 

Cellulosic fibers (cotton, rayon) are crosslinked by reaction of the hydroxyl groups of cellulose with formaldehyde, diepoxides, diisocyanates, and various methylol compounds such as urea-formaldehyde prepolymers, /V, /V -di tnethylol-A(A -dimethy lene urea, and trimethyl-olmelamine [Marsh, 1966]. Crosslinking imparts crease and wrinkle resistance and results in iron-free fabrics. 

Wood contains about 40-50% cellulose with the remaining being lignin and lower-molecular-weight polysaccharides. Treatment of wood pulp with acid and steam followed by basic sodium sulfide yields a product that is 92-98% cellulose. 

The results obtained are discussed in the following Section under the relevant reaction of cellulose. 

Rapid acetylation of cellulose, during which, it is claimed, only about one bond per thousand D-glucose residues is broken, accompanies the use of a mixture of acetic anhydride and trifluoroacetic anhydride as the reaction medium. The preparation of a fibrous triacetate by treating cotton with acetic anhydride containing perchloric acid, as a catalyst, and amyl 

Partial esters of cellulose (degree of substitution, 0.02 to 0.08) have been prepared by causing cellulose to react with either perfluorobutyryl chloride 

The reaction of cotton cellulose with phenyl isocyanate, to give a cellulose phenylurethan, has been investigated further. The extent of the reaction depends on the ability of the solvent to swell the cellulose, methyl sulfoxide being the best medium, followed by i r,f T-dimethylformamide and P3Tidine. The reaction is catalyzed by the addition of di-w-butyltin diacetate, but toluene 2,4-diisocyanate and 1,2,4,5-tetramethylbenzene diisocyanate do not show high reactivity. A survey of the relative behavior of chitin and cellulose toward esterification under comparable conditions, mainly to give arylsulfonate esters, concluded that, of the two, chitin is the less reactive. 

By this means, the distribution of substituents in 0-(2-hydroxyethyl)-cellulose, partially methylated celluloses, 0-ethylcellulose, and a partially 0-(carboxymethyl)ated cellulose has been established. The combined result of the investigation gives a measure of the relative reactivities of the hydroxyl groups at C-2, C-3, and C-6 toward a variety of alkylating agents. These are summarized in Table II. 

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Several cellulose esters (qv) are prepared commercially. Cellulose xanthate [9032-37-5] is made by reaction of cellulose swollen in 8.5—12% sodium hydroxide solution (alkaU cellulose [9081-58-7J) with carbon disulfide and is soluble in the alkaline solution in which it is made. When such a solution, termed viscose, is introduced into an acid bath, the cellulose xanthate decomposes to regenerate cellulose as rayon fibers or cellophane sheets (see Fibers, REGENERATED CELLULOSICS). 

Cellulose acetate [9004-35-7], prepared by reaction of cellulose with acetic anhydride, acetic acid, and sulfuric acid, is spun into acetate rayon fibers by dissolving it in acetone and spinning the solution into a column of warm air that evaporates the acetone. Cellulose acetate is also shaped into a variety of plastic products, and its solutions are used as coating dopes. Cellulose acetate butyrate [9004-36-8], made from cellulose, acetic anhydride, and butyric anhydride in the presence of sulfuric acid, is a shock-resistant plastic. 

Mercerized cellulose fibers have improved luster and do not shrink further. One of the main reasons for mercerizing textiles is to improve their receptivity to dyes. This improvement may result more from the dismption of the crystalline regions rather than the partial conversion to a new crystal stmcture. A good example of the fundamental importance of the particular crystal form is the difference in rate of digestion by bacteria. Bacteria from cattle mmen rapidly digest Cellulose I but degrade Cellulose II very slowly (69). Thus aHomorphic form can be an important factor in biochemical reactions of cellulose as well as in some conventional chemical reactions. 

Cellulose esters of aromatic acids, aUphatic acids containing more than four carbon atoms and aUphatic diacids are difficult and expensive to prepare because of the poor reactivity of the corresponding anhydrides with cellulose Httle commercial interest has been shown in these esters. Of notable exception, however, is the recent interest in the mixed esters of cellulose succinates, prepared by the sodium acetate catalyzed reaction of cellulose with succinic anhydride. The additional expense incurred in manufacturing succinate esters is compensated by the improved film properties observed in waterborne coatings (5). 

The sodium salt of CS [9005-22-5] is prepared by reaction of cellulose with sulfuric acid in alcohol followed by sodium hydroxide neutrali2ation (20). This water-soluble product yields relatively stable, clear, and highly viscous solutions. Introduced as a thickener for aqueous systems and an emulsion stabilizer, it is now of no economic significance. 

CP esters are generally prepared as the ammonium salt [9038-38-4] by the reaction of cellulose with phosphoric acid and urea at elevated temperatures (130—150°C). The effects of temperature and urea/H PO /cellulose composition on product analysis have been investigated (33). One of the first commercially feasible dameproofing procedures for cotton fabric, the Ban-Flame process (34,35), was based on this chemistry. It consists of mixing cellulose with a mixture of 50% urea, 18% H PO, and 32% water. It is then pressed to remove excess solution, heated to 150—175°C for 5—30 minutes, and thoroughly washed (36). 

CP can also be prepared by the reaction of cellulose with phosphoms oxychloride in pyridine (37) or ether in the presence of sodium hydroxide (38). For the most part these methods yield insoluble, cross-linked, CP with a low DS. A newer method based on reaction of cellulose with molten urea—H PO is claimed to give water soluble CP (39). The action of H PO and P2 5 cellulose in an alcohol diluent gives a stable, water-soluble CP with a high DS (>5% P) (40). These esters are dame resistant and have viscosities up to 6000 mPa-s(=cP) in 5 wt % solution. Cellulose dissolved in mixtures of DMF—N2O4 can be treated with PCl to give cellulose phosphite [37264-91-8] (41) containing 11.5% P and only 0.8% Cl. Cellulose phosphinate [67357-37-5] and cellulose phosphonate [37264-91 -8] h.a.ve been prepared (42). 

Fig. 3 Suggested mechanisms for the reaction of cellulose with tosyl chloride in the presence of pyridine (Py) and/or triethylamine (EtsN) base catalyst. Redrawn from [147]...

Figure 3.17 Alkaline chain stabilisation (stopping) reactions of cellulose.

Figure 3.18 Alkaline hydrolysis reactions of cellulose via 1,2-epoxides.

Homogeneous Solution Reactions of Cellulose, Chitin, and Other Polysaccharides... 

In a typical experiment the isocyanate (0.006 moles) was reacted with 1.5 g of the polysaccharide in 150 ml of a 5% LiCl/ N,N-dimethylacetamide solution at 90°C under nitrogen for two hours. The appearance of a strong infrared absorbance at 1705 cm l was an indication of carbamate formation. The derivatized polymer was isolated as a white powder by precipitation of the reaction solution into a nonsolvent such as methanol. Alternatively thin films were cast directly from solution the lithium salt could be removed by rinsing with acetone. Figure 1 illustrates the reaction of cellulose with phenyl isocyanate. 

McCormick, C.L. and D.K. Lichatowich, "Homogeneous Solution Reactions of Cellulose, Chitin, and Other Polysaccharides to Produce Controlled Activity Pesticide Systems," submitted... 

Cellulose acetate and triacetate may be used as plastics or spun into fibers for textiles. They are made by the reaction of cellulose with acetic anhydride. 

Various ether derivatives of cellulose, including some that are water-soluble, are important [Heinz and Liebert, 2001 Just and Majewicz, 1985 Zhang, 2001]. Methyl cellulose and car-boxymethyl cellulose (R = CH3 and CH2COOH, respectively) are synthesized by reaction of cellulose with sodium hydroxide followed by the appropriate alkyl halide ... 

Some mucilages are stained blue, some have the reactions of cellulose (Cydonia) and some are only stained yellow with cellulose-staining reagents. 

Amongst the important chemical conversions of macromolecular substances are the various reactions of cellulose. The three hydroxy groups per CRU can be partially or completely esterified or etherified. The number of hydroxy groups acetylated per CRU are indicated by the names, i.e., cellulose triacetate, cellulose 2-acetate, etc. Another commercially important reaction of cellulose is its conversion to dithiocarboxylic acid derivatives (xanthates). Aqueous solutions of the sodium salt are known as viscose they are spun into baths containing mineral acid, thereby regenerating the cellulose in the form of an insoluble fiber known as viscose rayon. 

Conversion of polymers and biomass to chemical intermediates and monomers by using subcritical and supercritical water as the reaction solvent is probable. Reactions of cellulose in supercritical water are rapid (< 50 ms) and proceed to 100% conversion with no char formation. This shows a remarkable increase in hydrolysis products and lower pyrolysis products when compared with reactions in subcritical water. There is a jump in the reaction rate of cellulose at the critical temperature of water. If the methods used for cellulose are applied to synthetic polymers, such as PET, nylon or others, high liquid yields can be achieved although the reactions require about 10 min for complete conversion. The reason is the heterogeneous nature of the reaction system (Arai, 1998). 

The double dehydrochlorination of 2,6-dichloro-l-oxacyclohexanes to 4//-pyran (5) and its 4-methyl homolog7,9,19,57 has been mentioned in Section III,A. Another double dehydration occurs in the synthesis of 4,4-diphenyl-4//-pyran 280 in 80% yield by the action of tosyl chloride on 2,6-dihydroxytetrahydropyran 279 in pyridine.296 Another diphenyl derivative (mp 56°C) was reported to be isolable from a mixture after the reaction of cellulose with benzene in sulfuric acid.297... 

For discussion of the reaction of cellulose with ethyleneimine see. Refs 1,2 3... 

Sometimes an increase in the viscosity of nitrocellulose is possible, through cross links formed between free hydroxyl groups. This involves the chemical reactions of cellulose, which are discussed later (see p. 303). 

Other characteristics of the reaction of cellulose with nitrogen dioxide solution in carbon tetrachloride in the presence of anhydrous nitric acid, are shown in Table 85. 

The reaction of cellulose with aqueous lithium hydroxide is a continuous function of the hydroxide concentration, and gives no adducts of greatly favored combining ratio. Heuser and Bartunek101 isolated an adduct having a 1 2 ratio of lithium hydroxide to D-glucose residue. At the high concentration of 5 M lithium hydroxide,128 the ratio is 0.75 1. 

Less attention has been paid to the reaction of cellulose with rubidium hydroxide and with cesium hydroxide. Heuser and Bartunek101 isolated adducts of rubidium hydroxide and of cesium hydroxide that had the general formula MOH 3 C Hi0Ot. Their studies showed that the concentration, in weight percent, of alkali metal hydroxide required for forming a stable adduct of the lowest alkali content increases with increase in the atomic weight of the metal Li < Na < K < Rb < Cs. However, on a molar basis, this relationship does not hold. No simple relationship exists between the size of cation and the concentration of hydroxide necessary for the formation of a stable adduct. 

Jones, David M., Structure and Some Reactions of Cellulose, 19, 219-246... 

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