Cellulose LiCl/DMSO

LiCl/DMAC has been shown to be a facile medium to conduct homogeneous reactions of cellulose (6). Other solvent systems used to conduct homogeneous derivitization of cellulose include LiCl/DMSO and DMSO/SOj/fCHj NH (7). 

Partial dehydration of DMSO/TBAF is possible by vacuum distillation and reactions in the ensuing solvent lead to products comparable to those obtained in reactions of cellulose dissolved in anhydrous DMA/LiCl. In addition to these basic studies, the conversion of cellulose in DMSO/TBAF with more complex carboxylic acids (e.g. furan-2-carboxylic acid) via in situ activation vvith/VA -carbonyldiimidazole (GDI) was studied (see Section 16.2.2.1.3). 

In addition to DMA/LiCl, DMSO/TBAF is an appropriate reaction medium for homogeneous acylation of cellulose applying in situ activation with CDI. Results of reactions of cellulose with acetic-, stearic-, adamantane-1-carboxylic-, and furan-2-carboxylic acid imidazoUdes are summarized in Table 16.7. 

Miyamoto et al. [165] observed a more uniform acetylation among different hydroxyl groups in LiCl dimethylacetamide (DMAC) as compared to heterogeneous reactions (Table 3). Cellulose dissolved in DMSO-PF is known to form methylol derivatives, especially for the 6-OH group. Acetylation of cellulose in this system [174-176] was shown to occur preferentially at the methylol hydroxyl group generated in situ. 

Advances of the past three decades, however, have produced alternatives to the heavy metal-based cellulose solvents. Prominent among them are dimethylacetamide/LiCl (DMAc/LiCl) N,MMN-0 hydrate (NMMO) tetrabutylammonium fluoride/DMSO (TBAF/DMSO) and potassium thiocyanate/DMSO [48]. While many of these solvents have gained significant popularity among laboratory chemists, only the amine oxide solvent, N,MMNO, has achieved industrial practicality. This will be discussed in the section on regenerated cellulose fibers. Several other important physical properties of cellulose are given in O Table 4. 

Esters of cellulose with interesting properties such as bioactivity and thermal and dissolution behavior can be obtained by esterification of cellulose with nitric acid in the presence of sulfuric acid, phosphoric acid, or acetic acid. Commercially important cellulose esters are cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate. Cellulose esters of aliphatic, aromatic, bulky, and functionalized carboxylic acids can be synthesized through the activation of free acids in situ with tosyl chloride, iV,iV -carbonyldiimidazole, and iminium chloride under homogeneous acylation with DMA/LiCl or DMSO/TBAF. A wide range of cellulose esters that vary in their DS, various substituent distributions, and several desirable properties can be obtained through these reactions. Recently, a number of enzymes that degrade cellulose esters have been reported. Some of them are acetyl esterases, carbohydrate esterase (CE) family 1, and esterases of the CE 5 [169-172] family. 

For the direct method special solvent systems are employed without chemical modification of the cellulose chains. Some examples are LiCl/DMAc (lithium chloride/N,N-dimethylacetamide), DMSO/TBAF (dimethyl sulfoxide/tetra-n-butylammonium fluoride). 

Two cellulose solvents, cadoxen (133) and the more recently discovered. A(iV-dimethylacetamide/LiCl system (134), have shown good promise for use in the SEC analysis of cellulose. The use of these two solvents is described here. In addition, the cellulose solvent systems based on iron-sodium tartrate (8) and DMSO-paraformaldehyde (47,110) have had limited use for the SEC analysis of cellulose. 

Figure 16.13 Absolute deviation of the mol fractions of un-, mono-0-, di-0-, and 2,3,6-tri-O-functionalized glucose from the binomial distribution of CMC and methyl cellulose (MC) synthesized via induced phase separation 1 CMC synthesized in DMA/LiCl (DS 2.07) 2 CMC synthesized in DMSO/TBAF (DS 1.89), 3 CMC synthesized in Al-methyhnor-pholine-A-oxide (DS 1.26), 4 CMC synthesized from cellulose acetate, 5 CMC synthesized from trknethylsilyl cellulose,...

Esterification of OH groups in methylol cellulose was studied. Ultimately, we wished to add long graft-like chains to the cellulose, so acid chlorides were the reactants of choice. Acetyl chloride was used as a model reactant. Here, DMSO cannot be used as a solvent because of its reactivity with acid chlorides. Esterifications were carried out by two methods, one involving direct reaction of acetyl chloride with methylol cellulose in DMF/LiCl using pyridine as acid acceptor. The pyridine was probably not necessary, though its equilibrium involvement with the acid chloride caused no apparent problem. 

Cellulose acetate was produced by the room temperature homogeneous acetylation of cellulose with acetic anhydride in the presence of amines in DMSO-H2CO systems Cellusose acetate was also prepared by adding 7ml acetic anhydride to 100ml of a solution of 5 percent cellulose in DMAc-LiCl to which had been added 0.5ml of 71 percent perchloric acid solution. The solution was allowed to stand for one day at room temperature and was then heated at 40°C for 2 hrs. before the ester was precipitated from the solvent by the addition of methanol. Cellulose and chitin have also been esterified and carbanylated at room temperature by the addition of phenyl isocyanate and pyridine to a solution in DMAc-LiCl systems. 

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