Hydrogen bond promoted thermal stability enhancement of acetate based ionic liquid

doi:10.1016/j.cjche.2020.02.019

Abstract

Abstract: Acetate-based imidazolium ionic liquids (ILs) are of great importance and widely applied in biomass processing and engineering but under stability issue due to the structure self-rearrangement induced by C₂-H deprotonation, by which the IL based biomass processing will be challenging. Herein, we demonstrated that the thermal stability of normal acetate-based imidazolim[C₈C₁Im] [OAc] could be significantly improved by changing its cation and anion environment with the presence of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide IL ([C₄C₁Im] [NTf₂]). When the molar fraction of[C₈C₁Im] [OAc] was 0.3, the thermal stability of[C₈C₁Im] [OAc] could be significantly improved (ΔT_5%dec=+43℃). Detailed information obtained from thermal gravimetric analysis (TGA) and nuclear magnetic resonance (NMR) revealed that the addition of[C₄C₁Im] [NTf₂] played a significant role in enhancing the thermal stability of[C₈C₁Im] [OAc]. It was proposed that the formation of an anion-π⁺ structure network between[C₈C₁Im] [OAc] and[C₄C₁Im] [NTf₂] via strong hydrogen bond interactions greatly affects the environment of hydrogen atom in the imidazolium ring of each IL.

Key words: Imidazolium salt, Binary ionic liquids, Thermal stability, Hydrogen bond interactions

摘要： Acetate-based imidazolium ionic liquids (ILs) are of great importance and widely applied in biomass processing and engineering but under stability issue due to the structure self-rearrangement induced by C₂-H deprotonation, by which the IL based biomass processing will be challenging. Herein, we demonstrated that the thermal stability of normal acetate-based imidazolim[C₈C₁Im] [OAc] could be significantly improved by changing its cation and anion environment with the presence of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide IL ([C₄C₁Im] [NTf₂]). When the molar fraction of[C₈C₁Im] [OAc] was 0.3, the thermal stability of[C₈C₁Im] [OAc] could be significantly improved (ΔT_5%dec=+43℃). Detailed information obtained from thermal gravimetric analysis (TGA) and nuclear magnetic resonance (NMR) revealed that the addition of[C₄C₁Im] [NTf₂] played a significant role in enhancing the thermal stability of[C₈C₁Im] [OAc]. It was proposed that the formation of an anion-π⁺ structure network between[C₈C₁Im] [OAc] and[C₄C₁Im] [NTf₂] via strong hydrogen bond interactions greatly affects the environment of hydrogen atom in the imidazolium ring of each IL.

关键词: Imidazolium salt, Binary ionic liquids, Thermal stability, Hydrogen bond interactions

Ling Zhang, Ligang Wei, Shangru Zhai, Dingwei Zhao, Jian Sun, Qingda An. Hydrogen bond promoted thermal stability enhancement of acetate based ionic liquid[J]. Chinese Journal of Chemical Engineering, 2020, 28(5): 1293-1301.

Ling Zhang, Ligang Wei, Shangru Zhai, Dingwei Zhao, Jian Sun, Qingda An. Hydrogen bond promoted thermal stability enhancement of acetate based ionic liquid[J]. 中国化学工程学报, 2020, 28(5): 1293-1301.

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