Cellulose homogeneous acylation

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. 

G.T. Ciacco, TF. Liebert, E. Frollini, TJ. Heinze, Application of the solvent dimethyl sulfoxide/tetrabutyl-ammonium flumde trihydrate as reaction medium for the homogeneous acylation of sisal cellulose, Cellulose 10 (2) (2003) 125-132. 

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. 

Homogeneous acylation of cellulose dissolved in dimethyl sulfoxide (DMSO)/tetra-n-butylammonium fluoride (TBAF) with different carboxylic acids, mediated by Af V -carbonyldiimidazole (CDI)... 

In general, by chemical modification reactions of cellulose no equal reactivity of positions 2, 3, and 6 appears. For instance, homogeneous acylation in DMA/LiCl results in products with a preferred functionalization at position 6, while the carboxymethylation in 2-propanol/aqueous NaOH proceeds faster at position 2 compared to 6 and 3. 

Marson GA (1999) Acylation of Cellulose in Homogeneous Mediimi. MSc Thesis, University of Sao Paulo, Brazil... 

Krausz et al. obtained cellulosic plastic films under homogeneous conditions by microwave-induced acylation of commercial or chestnut tree sawdust cellulose by fatty acids (Scheme 14.41) [82]. They studied the effect on the acylation reaction of the amount of N,N-dimethyl-4-aminopyridine (DMAP), which simultaneously... 

Acylation of cellulose by carboxylic acid chlorides can be performed under homogeneous or heterogeneous conditions. During this reaction, the HCl released is captured by a base, most commonly pyridine or A,A-dimethylaminopyridine (DMAP) (Fig. 36). 

The acylation of cellulose with acid chlorides in DMA/LiCl is most suitable for the homogeneous synthesis of readily soluble partially functionalized long-chain aliphatic esters and substituted acetic acid esters (Table 16.3). In contrast to the anhydrides, the fatty acid chlorides are soluble in the reaction mixture and soluble polysaccharide esters may be formed with a very high efficiency. Even in the case of stearoyl chloride, 79 per cent of the reagent is consumed for the esterification of cellulose. 

DMSO/TBAF is highly efficient as a reaction medium for the homogeneous esterification of cellulose by transesterification and after the in situ activation (see below) of complex carboxylic acids. The acylation using acid chlorides and anhydrides is limited because the solution contains a certain amount of water caused by the use of the commercially available TBAF trihydrate and the residual moisture in the air-dried polysaccharides. Nevertheless, this system has shown a remarkable capacity for the esterification of lignocellulosic mataials, for example, sisal fibres, which contain about 14 per cent hemicellulose [28]. The DS values of cellulose acetate prepared from these fibres with acetic anhydride in mixtures of DMSO/TBAF were found to decrease with increasing TBAF concentration from 6 to 11 per cent (Table 16.4), due to the increased rate of hydrolysis both of the anhydride and the ester moieties. 

El Seoud O.A., Marson G.A., Ciacco G.X., FroUini E., An efficient, one-pot acylation of cellulose under homogeneous reaction conditions, Macromol. Chem. Phys., 201, 2000,882-889. 

Zhang Z.B., McCormick C.L., Structopendant unsaturated cellulose esters via acylation in homogeneous Uthium chloride/ A/A/-dimethylacetamide solutions, J. Appl. Polym. Sci., 66, 1997,293-305. 

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