Rates in ionic liquids

Although cycloadditions and rearrangements often proceed without catalysts, the selectivity of the reaction and the reactivity of very reluctant molecules can be enhanced by a Lewis acid. The Diels-Alder reaction can be performed at enhanced reaction rate in ionic liquids with the addition of ZnCl2 (eq. (4)) [42]. The Claisen rearrangement was also reported to be superior if catalyzed by Sc(OTf)3 in ionic liquids [43]. 

More recently, Eastman Chemical Company published three patents involving the use of ionic liquids containing carboxylate anions for cellulose acetylation [163-165], Ionic liquids with carboxylate anions resulted in faster acetylation of cellulose at lower temperatures relative to the rate in ionic liquids with the same cation and a chloride anion. Transition metals such as zinc were found to be good catalysts for the acetylation of cellulose in ionic liquids [164],... 

An easily accessible neutral ionic liquid, 1 -methyl-3-pentylimidazolium bromide ([pmim][Br]) is prepared by Ranu et al. and used for the promotion of the one-pot three-component condensation of an amine, carbon disulfide, and an activated alk-ene/dichloromethane/epoxide to produce the corresponding dithiocarbamates in high yields at room temperature (Fig. 12.58) [37]. The reactions proceed at faster rate in ionic liquid relative to their rates in other reaction media. These reactions do not require any additional catalyst or solvent. The ionic liquid can be recovered and recycled for subsequent reactions. 

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