Cellulose dissolution, mechanism

A comment on these structures is relevant to understanding the mechanism of cellulose dissolution by these solvent systems. Support for association... 

Remsing, R.C., Swatloski, R.P., Rogers, R.D., and Moyna, G., Mechanism of cellulose dissolution in the ionic liquid l-n-butyl-3-methylimidazolium chloride a and 35/37(21 NMR relaxation study on model systems, Chem. Commun., 1271-1273, 2006. 

Dissolution of wood using [C mimHCl] has also been reported [127-129], Based on the same mechanism of cellulose dissolution, the dissolution of wood also requires the virtual absence of water, which necessitates extensive drying of the wood, small particle size, drying of the ionic liquid, and reaction under an inert atmosphere. Long dissolution times are usually required unless microwave heating is used. 

Figure 1. Dissolution mechanism of cellulose in S02-amine-DMS0 systems.

Striegel AM (2003) Advances in the understanding of the dissolution mechanism of cellulose in DMAc/LiCl. J Chil Chem Soc 48 73-77... 

Petrus L., Gray D.G., BeMiUer J.N., Homogeneous alkylation of cellulose in Uthium chloride/dimethyl sulfoxide solvent with dimsyl sodium activation. A proposal for the mechanism of cellulose dissolution in Uthium chloride/DMSO, Carbohyd. Res., 268, 1995, 319-323. 

Zhang, J., Zhang, H., Wu, J., Zhang, J., He, J. and Xiang, J., NMR spectroscopic studies of cellobiose solvation in EmimAc aimed to understand the dissolution mechanism of cellulose in ionic liquids, Phys. Chem. Chem. Phys. 12,1941-1947 (2010). 

Both the cations and anions of ILs contribute to the dissolution of cellulose. The mechanism of the dissolution is that the anion of the IL acts as H-bond acceptor that interacts with the hydroxyl group of cellulose in a stoichiometric manner to generate an electron donor-electron acceptor (EDA) complex [4]. The cation, on the other hand, with its electron-rich aromatic 7t system acts as an electron acceptor center and prevents the cross linking of the cellulose. When the anion and the cation are in close proximity to each other, the formation of the EDA complexes between cellulose and ILs become feasible and the network of hydrogen bonds between the glycosidic monomers are disrupted, resulting in dissolution of the cellulose. 

FIGURE 13.9 Dissolution mechanism of cellulose by ionic liquids (Feng and Chen, 2008). 

These dyes have affinity for one or, usually, more types of hydrophobic fibre and they are normally applied by exhaustion from fine aqueous dispersion. Although pure disperse dyes have extremely low solubility in cold water, such dyes nevertheless do dissolve to a limited extent in aqueous surfactant solutions at typical dyeing temperatures. The fibre is believed to sorb dye from this dilute aqueous solution phase, which is continuously replenished by rapid dissolution of particles from suspension. Alternatively, hydrophobic fibres can absorb disperse dyes from the vapour phase. This mechanism is the basis of many continuous dyeing and printing methods of application of these dyes. The requirements and limitations of disperse dyes on cellulose acetate, triacetate, polyester, nylon and other synthetic fibres will be discussed more fully in Chapter 3. Similar products have been employed in the surface coloration of certain thermoplastics, including cellulose acetate, poly(methyl methacrylate) and polystyrene. 

In the fourth chapter, Thomas Rosenau, Antje Potthast, and Paul Kosma describe current investigations on reactive intermediates and reaction mechanisms in cellulose chemistry. The chemical modification and regeneration of cellulose requires its activation and/or dissolution in media like sodium lye, N-mclhybnorpholine-N-oxide (NMMO), N, N-dimethylacetamide (DMAc), or in carbanilation mixtures containing dimethylsulfoxide (DMSO). In these media - very important for research and large-scale processes - the trapping and characterization of the intermediates has been carried out. 

Equation (6.94) illustrates that zero-order release kinetics are obtained if drug dissolution controls the release kinetics. However, as soon as the last particle in the matrix dissolves, the controlling mechanism of drug release shifts to Fickian diffusion. Figure 6.19 shows the dissolution-controlled release of KC1 at the early stage of release and the diffusion-controlled release at the later stage of release from an ethyl cellulose tablet. 

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