期刊
CELLULOSE
卷 21, 期 3, 页码 1193-1204出版社
SPRINGER
DOI: 10.1007/s10570-014-0184-8
关键词
Kinetics of Cellulose acetylation; Ionic liquids; Mixtures of ionic liquids with molecular solvents; 1-Allyl-3-methylimidazolium chloride; N,N-dimethylacetamide; Acetonitrile; Molecular dynamics simulation of cellulose dissolution
资金
- TWAS (The Academy of Sciences for the Developing World)
- CNPq (National Council for Scientific and Technological Research)
- FAPESP (Sao Paulo research Foundation)
Rate constants for the acetylation of microcrystalline cellulose (MCC), by ethanoic anhydride in the presence of increasing concentrations of the ionic liquid (IL), 1-allyl-3-methylimidazolium chloride in dipolar aprotic solvents (DAS), N,N-dimethylacetamide (DMAC), and acetonitrile (MeCN), have been calculated from conductivity data. The third order rate constants showed a linear dependence on [IL]. We explain this result by assuming that the reacting cellulose is hydrogen-bonded to the IL. This is corroborated by kinetic data of the acetylation of cyclohexylmethanol, FTIR of the latter compound and of cellobiose in mixtures of IL/DAS, and conductivity of the binary solvent mixtures in absence, and presence of MCC. Cellulose acetylation is faster in IL/DMAC than in IL/MeCN; this difference is explained based on solvatochromic data (empirical polarity and basicity) and molecular dynamics simulations. Results of the latter indicate hydrogen-bond formation between the hydroxyl groups of the anhydroglucose unit of MCC, (Cl-) of the IL, and the dipole of the DMAC. Under identical experimental conditions, acetylation in IL/DMAC is faster than that in LiCl/DMAC (2.7-8 times), due to differences in the enthalpies and entropies of activation.
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