Probing Cellulose Acetylation In Binary Mixtures Of An Ionic Liquid With Dimethylsulfoxide And Sulfolane By Chemical Kinetics, Viscometry, Spectroscopy, And Molecular Dynamics Simulations

Acetylation of microcrystalline cellulose (MCC) by ethanoic anhydride (Ac2O) in mixtures of the ionic liquid (IL) 1-allyl-3-methylimidazolium chloride and the (structurally related) molecular solvents (MSs), dimethylsulfoxide (DMSO) and sulfolane (Sulfn), is studied. Values of the reaction third-order rate constants, k(3), are calculated from conductivity data; they are linearly dependent on c(IL), due to (cellulose-solvent) complex formation, as corroborated by Fourier Transform Infrared (FTIR) spectroscopy. The observed order of reactivity (IL/DMSO > IL/Sulfn) is explained by examining differences in the following properties of the MCC-IL/MS solutions: macroscopic (viscosity); microscopic (empirical polarity and basicity), and from the results of molecular dynamics simulations. The latter indicate faster reactant diffusion in IL/DMSO and more interaction between the biopolymer hydroxyl groups and the ions of the IL.