Cellulose homogeneous solution reactions

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

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

McCormick, C.L. and Lichatowhich, D.K. (1979) Homogeneous solution reactions of cellulose, chitin and other polysaccharides to produce controlled... 

Several derivatives of cellulose, including cellulose acetate, can be prepared in solution in dimethylacetamide—lithium chloride (65). Reportedly, this combination does not react with the hydroxy groups, thus leaving them free for esterification or etherification reactions. In another homogeneous-solution method, cellulose is treated with dinitrogen tetroxide in DMF to form the soluble cellulose nitrite ester this is then ester-interchanged with acetic anhydride (66). With pyridine as the catalyst, this method yields cellulose acetate with DS < 2.0. 

For the total hydrolysis of polysaccharides, trifluoroacetic acid (TFA) has important advantages over sulfuric acid. The reaction time is short and there is no need for conventional neutralization, as TFA is volatile and can be removed by evaporation. Several methods have been developed, depending on the substance to be hydrolyzed. Soluble saccharides (e.g., polyoses) can be hydrolyzed with diluted TFA, while cellulose, pulp, and wood need treatments with concentrated TFA in homogeneous solution. The presence of lignin impedes the hydrolysis of polysaccharides thus, especially for wood samples, an intensive treatment with TFA is necessary, and correction values have to be considered. Several application examples show that the hydrolysis with TFA enables a rapid quantitative determination of the composition of polysaccharides, pulps, and woods. 

The industrial preparation of cellulose diacetate employs acetic anhydride with sulphuric acid as catalyst. The reaction is conducted at low temperature and cellulose starts to dissolve in the acetylation bath as the reaction progresses. The reaction is conducted until practically full acetylation. The homogeneous solution obtained is then hydrolysed to reduce the DS to 2.4. Precipitation in dilute acetic acid, then washing with water and finally drying produce cellulose acetate flakes. 

Yeast invertase,30 32 33 acid phosphatase,29 32 35 37 39 urease,29 /3-glucosi-dase,29 dCMP-amino hydrolase31 and malic enzyme34 36 have been immobilized in gel form on both flat and capillary membranes. Cellulosic and polyamide polymers have been used as supporting membrane matrices. In all instances, immobilized enzymes behave in a manner almost identical to their behavior in homogenous solution, independent of the nature of the polymer. Neither allosteric nor pseudo-allosteric enzymes, proteins whose kinetic behavior is affected by the presence of particular compounds in the reaction environment (ligands), show different kinetic behavior, as they do when subjected to less gentle immobilization procedures.31 34 36... 

One principal use of cyclohexanol has been in the manufacture of esters for use as plasticizers (qv), ie, cyclohexyl and dicyclohexyl phthalates. In the finishes industry, cyclohexanol is used as a solvent for lacquers, shellacs, and varnishes. Its low volatiUty helps to improve secondary flow and to prevent blushing. It also improves the miscibility of cellulose nitrate and resin solutions and helps maintain homogeneity during drying of lacquers. Reaction of cyclohexanol with ammonia produces cyclohexylamine [108-91-8], a corrosion inhibitor. Cyclohexanol is used as a stabilizer and homogenizer for soaps and synthetic detergent emulsions. It is used also by the textile industry as a dye solvent and kier-boiling assistant (see Dye carriers). 

The kinetics of homogeneous reaction of several reactive dyes of the vinylsulphone type with methyl-a-D-glucoside (7.9), selected as a soluble model for cellulose, were studied in aqueous dioxan solution. The relative reactivities of the various hydroxy groups in the model compound were compared by n.m.r. spectroscopy and the reaction products were separated by a t.l.c. double-scanning method [38]. The only sites of reaction with the vinylsulphone system were the hydroxy groups located at the C4 and C6 positions [39,40]. 

The initial results were interpreted as evidence of catalytic activity by dithiolenes themselves.211,212 However, Kisch et al.m were soon able to demonstrate that the Zn(mnt)2 complex dianion decomposed to ZnS under these conditions and it is now believed that the dithiolene is only the catalyst precursor and that ZnS is the actual catalyst. The sulfide must be extremely finely dispersed, approaching near homogeneous conditions, because filtration of the solution through a cellulose acetate filter of 0.2 /jm pore size did not reduce the rate of reaction. 

An additional example is the preparation of gelatinous IPNs of poly(N,N-dimethylacrylamide) (PDMAm) containing 6-25 wt% cellulose, which were obtained in DMAc-LiCl solution as the homogeneous reaction medium for polymerizing DMAm monomer [75]. It was reported that an IPN of CELL = 25 wt % possessed a sixfold higher modulus than a PDMAm control, when compared to their water-swollen state. 

Table II. Homogeneous Graft Copolymerization of Styrene onto Cellulose Using a SO2-DEA-DMSO Solution as a Reaction Medium...

Thermoplasticization of Wood by Graft Copolymerization in De-crystallized State. We have reported that wood can effectively be decrystallized without a weight-loss by treating with a non-aqueous cellulose solvent, the SO2-DEA-DMSO solution (11). Thus, use of the non-aqueous cellulose solvent as a reaction medium for the graft-copolymerization of monomers to wood was expected to result in products with branch polymers more uniformly distributed. The results obtained by the homogeneous grafting of cellulose (10) were expected to support this idea. 

In another oudine, cellulose was complexed with cuprammonium ions (Nicoll and Conaway, 1943). Lately, laboratory-scale isolation has relied on polar aprotic solvents and solvent systems, e.g., dimethylsulfoxide, pyridine, Af,7V-dimethylacetamide-lithium chloride, and l-methyl-2-pyrrolidinone-lithium chloride (Baker et al., 1978 McCormick and Shen, 1982 Seymour et al., 1982 Arnold et al., 1994). These solvents have enabled such homogeneous17 reactions as O- and N-derivatization of cellulose and chitin (Williamson and McCormick, 1994) and selective site chlorination (Ball et al., 1994). Dimethylsulfoxide was the solvent in a homogeneous reaction of cellulose and paraformaldehyde, prior to isolation of purified cellulose (Johnson et al., 1975). In yet another outline, paraformaldehyde enabled superior quality extracts when the parent tissues were presoaked in this solution (Fasihuddin et al., 1988). 

Only reactions in homogeneous phase, in dilute solution, can be expected to nunimize variations within and between cellulose derivative molecules. 

Cellulose esters are used primarily in structural applications, such as films, fibers, coatings, etc. Since they are processed in solution or in melt state, their resistance to flow (i. e., melt viscosity) represents a distinct handicap. Commercial cellulose esters are all generated by heterogeneous modification reaction [80,81,82,83,84]. However, reactions in homogeneous phase (with various solvents) are increasing in number and variety, and they have recently been reviewed by Heinze et al. [82]. Cellulose esters are usually classified as inorganic and organic esters. 

Dissolution of cellulose has three major purposes. The first is to prepare regenerated and man-made cellulose fibers or films from cellulose solutions at the industrial level. Environmentally friendly and cost-profitable systems to dissolve and regenerate cellulose are now required. The second purpose is to use cellulose solutions as homogeneous reaction media during chemical modifications, which have been investigated at the laboratory level. The last one is to analyze cellulose samples. Molecular mass and molecular mass distribution studies using cellulose solutions are included in this category. Numerous cellulose solvents have, therefore, been developed and studied for these purposes. 

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