Insights into Cellulose Dissolving in Ionic Liquids By Molecular Simulation

Insights into Cellulose Dissolving in Ionic Liquids by Molecular Simulation

Xiaomin Liu,^a Yao Li, ^a Yuling Zhao,^b Jianji Wang,^b and Suojiang Zhang^a,*

a State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, China.

b Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, School of Chemistry and Environmental Science, Henan Normal University, Xinxiang, Henan 453007, China.

Abstract

Ionic liquids (ILs) have been used in an enormous number of chemical and biological processes. In recent years, great progress has been made in the dissolution of cellulose with ILs. However, the mechanism of cellulose dissolution has not been clearly understood. ^[1,2]

Molecular simulations were performed to investigate the effects of cation and anion structures on cellulose dissolution in ILs. It was found that the presence of electron-withdrawing group in alkyl chain of the cation enhanced the interaction between the cation and cellulose by comparing the interaction energy between [Amim]⁺ and [C₃mim]⁺ with cellulose.^[3] Effects of anionic structure on the dissolution of cellulose in ILs revealed that hydrogen bonds (HBs) were formed between anions of the ILs and hydroxyl protons of cellulose. we also investigated the effects of electronegativity of HB acceptor atoms, steric effect of alkyl chain length and electron-withdrawing group of the anions on their HB acceptor ability. ^[4] Furthermore, molecular simulations were performed to depict the cosolvent effect of cellulose dissolution in imidazolium-based ILs. DMSO partially breaks down the ionic association of [C₄mim][CH₃COO] by solvation of the cation and anion, but no preferential solvation was observed. The dissociated anions would readily interact with cellulose to improve the dissolution of cellulose. ^[5] Besides, the spontaneous dissolution process was investigated through all-atom molecular dynamics simulations of cellulose bunche in EmimAc and EmimCl within 0.5~2µs. Synergistic effect of cations and anions was revealed by analysing the whole dissolving process in EmimAc. Initially, cations bind to the side face of cellulose bunch and anions insert into the cellulose strands to form HBs with hydroxyl groups. Then cations start to intercalate into cellulose chains due to their strong electrostatic interaction with the anions.

Figure 1. The spontaneous dissolution snapshot of cellulose in EmimAc.

References

1. S. Zhang, J. Sun, X. Zhang, et al, Chem. Soc. rev., 2014, 43, 7838-7869.

2. K. Dong, Q. Wang, S. Zhang, Sci. China Chem., 2015, 58,495-500.

3. Y. Zhao, X. Liu, J. Wang, S. Zhang. ChemPhysChem, 2012, 13, 3126-3133.

4. Y. Zhao, X. Liu, J. Wang, S. Zhang. Carbohydr. Polym., 2013, 94: 723-730.

5. Y. Zhao, X. Liu, J. Wang, S. Zhang. J. Phys. Chem. B, 2013, 117, 9042-9049.