探討咪唑類離子液體的黏度與其化學結構之定量關係

離子液體( ionic liquids )具有低熔點、高極性、耐強酸、不可燃性、高熱穩定性、高導電度、電化學性佳以及極低的蒸氣壓和較寬廣的液體溫度範圍等特殊性質，可替代一般所用之揮發性有機溶劑，應用在許多化工製程。離子液體被認為是一種新的綠色溶劑。黏度是離子液體的重要物理性質，離子液體的黏度通常高於一般有機溶劑。低黏度的離子液體可降低輸送成本並增加質傳速度；高黏度離子液體則可應用於潤滑及薄膜用途。離子液體由陰、陽離子組成，其黏度受到分子間氫鍵以及凡得瓦力的影響呈規則性變化。陽離子碳鏈愈長，凡得瓦力愈強，黏度愈高；而陰離子的結構是否形成氫鍵對黏度也有顯著的影響。以近年來文獻中的黏度值，參酌溫度、分子量以及咪唑環上支鏈的碳原子數目，探討黏度性質與陰、陽離子的描述性參數間的定量數學關係式。陰、陽離子以基團貢獻法( group contribution method )分別進行QSPR( Quantitative Structure–Property Relationship )，再以電腦程式找出最佳化的結果。從數學關係式中，可以看出陰、陽離子的參數大小與化學結構的關聯。利用關係式得到的預測值與文獻上的實驗值之間的判定係數R2高達0.9882。預測模型與文獻值的高度吻合性，提供了陰、陽離子陣列式組合設計的可能性。

關鍵字

咪唑；離子液體；黏度

並列摘要

Ionic liquids (IL) have the features such as low melting point, high polarity, resistance to acid, not combustible, high thermal stability, high conductivity, good electrochemical reactivity, low vapor pressure, wide liquid temperature range, and other special natures. IL can replace commonly used volatile organic solvents in many chemical processes. The ionic liquid is considered to be a new green solvent. Viscosity is an important physical property of ionic liquids. The viscosities of ILs are relatively high compared to those of common organic solvents. A low viscosity is generally desired to use IL as a solvent, to minimize pumping costs and increase mass transfer rates while higher viscosities may be favorable for other applications such as lubrication or use in membranes. It is known that the viscosity of ILs vary widely depending on the type of cation and anion. The viscosity of ionic liquids can be affected by intermolecular hydrogen bonds and van der Waals force. The longer the carbon chain in the cations, the stronger van der Waals force causes the higher viscosity of IL. The formation of hydrogen bonds in the anions has a significant impact on the viscosity. This study aimed to develop a prediction model for viscosity of ionic liquids using quantitative structure property relationships (QSPR) coupled with the descriptors of group contribution. Considering the number of the branched-chain carbon atoms in the imidazole ring, temperature, and molecular weight, we formulated a mathematical relationship between the viscosity and the descriptive parameters of anions and cations. The value of R2 for the correlation coefficient between the reported literature values and the predicted values of viscosity is 0.9882. The high correlation between calculated value from QSPR and experimental viscosity offers a prediction possibility of viscosity for the design of new ionic liquids.

並列關鍵字

QSPR ； imidazolium ； viscosity

參考文獻

[1] P. T. Anastas, T. C. Williamson, “Green Chemistry”, ACS symposium series 626, Washington DC, 1996.

[2] P. T. Anastas, J. C. Warner, The 12 Principles of Green Chemistry in “Green Chemistry: Theory and Practice”, Oxford University Press: New York 1998.

[3] B. Arianna, M. Fabio, R. Carmine, S. Luciano, A Preliminary Investigation on the Organic Ionic Liquids as Green Solvents for Acylation and Oxidation Reactions, J. Cleaner Production 18 (2007) 1797-1805.

[6] H. L. Chum, V. R. Koch, L. L. Miller, R. A. Osteryoung, Electrochemical Scrutiny of Organometallic Iron Complexes and Hexamethylbenzene in a Room Temperature Molten Salt, J. Am. Chem. Soc. 97 (1975) 3264-3265.

[7] J. S. Wilks, J. A. Levisky, R. A. Wilson, C. L. Hussey, Dialkylimidazolium Chloroaluminate Melts: A New Class of Room-Temperature Ionic Liquids for Electrochemistry, Spectroscopy, and Synthesis, Inorg. Chem. 21 (1982)

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探討咪唑類離子液體的黏度與其化學結構之定量關係

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