Neutral Ionic Liquids as Catalysts

Neutral ionic liquids such as [AMIM]BF4 and [AMIMJPF function as catalysts for a limited number of reported reactions. The purities of such ionic liquids have been a concern. Because unknown impurities could give misleading results, care needs to be taken in the preparations 153). 

In the presence of [BMIM]Br, aryl oxiranes are cleaved by a variety of amines, giving exclusively a regioselective product from benzylic attack. Other epoxides (including glycidyl aryl ethers, glycidyl alkyl ethers, and esters), alkyl oxiranes, and cycloalkyl epoxides are also converted. Remarkably, all the reactions were found to proceed efficiently at ambient temperature with high regioselectivity. The product yields reached 80-90% in a few hours. 

The products were weakly soluble in the ionic phase. They were separated by extraction with ether. The viscous ionic liquid could be reused in five runs without any loss of activity after thorough washing with ether and drying at 80°C after each run. In contrast, the reaction did not proceed in the polar organic solvents DMF and 7V-methylpyrrolidine, even at higher temperatures (75-80°C). The ionic liquids [Bu4N]C1 and [BMIM]C1 were also found to be ineffective. 

The ionic liquid [BMIM]BF4 was found to efficiently catalyze the three-component coupling reactions of aldehydes, amines, and homophthalic anhydride under ambient conditions to give the corresponding c/ -isoquinolonic acids in excellent yields with 

Tetraalkylammonium bromide was found to be a good catalyst for the conjugate addition of thiols to a,p-unsaturated nitriles, carboxylic esters, ketones, aldehydes, and nitro alkenes. The reactions proceeded rapidly and gave high yields of products (typically, 90%) (160). 

---