Hydration of alkynes using Br枚nsted acidic ionic liquids in the absence of Nobel metal catalyst/H₂SO₄

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• 作者：Rajkumar Kore ; T.J. Dhilip Kumar ; Rajendra Srivastava ; ^{rajendra@iitrpr.ac.in}
• 关键词：Brö ; nsted acidic ionic liquids ; Hydration reaction ; Acid catalyst ; Hammett acidity ; Acid value ; DFT calculations
• 刊名：Journal of Molecular Catalysis A ; Chemical
• 出版年：2012
• 期刊代码：57_13811169
• 类别：ch
• 出版时间：August, 2012
• 卷：360
• 期：Complete
• 页码：61-70
• 文件大小：1412 K

摘要

In this study, a variety of imidazole based sulfonic acid group functionalized Br枚nsted acidic ionic liquids (BAILs) were synthesized. BAILs have been successfully developed as task specific ionic liquids for hydration of alkynes under mild conditions to give high yields of ketones as a selective product. Acidity of BAILs was determined using volumetric titration and UV-visible spectroscopic methods. The Hammett acidity order and acid value of BAILs correlate well with the activity order observed for most of the BAILs in the hydration reaction of phenylacetylene. Theoretical studies demonstrate that hydrogen bonding plays a key role in tuning the acidity of BAILs. Density function theory calculations are also able to explain the difference in activity observed in these BAILs. The activity of ionic liquids was theoretically studied by computing the activation energy for the hydration reaction. Recycling experiments suggest that these novel BAILs can be reused without significant loss in activity. BAILs are simple and easy to prepare and exhibit excellent activity toward the hydration of a variety of alkynes to ketones. Moreover, the reaction involving BAILs does not involve heavy metal catalysts or H₂SO₄. Novel BAILs offer several attractive features such as sustainable synthetic route, low cost, moisture stability, high yields, and recyclability.