Ionic Liquids

Ionic liquids are generic terms for the organic salts that are liquid at relatively low temperatures. Recently, application of ionic liquids as organic reaction solvents are being vigorously explored for various reactions. One example is the Heck reaction that utilizes 1. In this reaction, the product cinnamate can be extracted with cyclohexane after the reaction, and the byproduct triethylammonium halides can be washed away with water. The catalyst retained in 1 can be reused.¹⁾ In the Diels-Alder reaction shown below the catalyst is retained in 2, and the recovered ionic liquid phase containing the catalyst can be reused for several times. There is no loss of any activity even after eleventh use.²⁾ Ionic liquids are receiving much attention as they are environmentally friendly. They are recyclable as solvents and often can be reused with the catalyst.