State and reactivity of N-acylimidazolium salts in nonaqueous media

Kinetic investigations are conducted of the intermediate products of nucleophilic catalysis by N-acylimidazolium halides. The authors study the influence of the solvent on the reactivity of a number of 1-acetyl-3-methylimidazolium salts (I), in which X = Cl, Br, ClO4, and B(C6H5)4 in reactions with aromatic amines (p-nitroaniline). It is shown that a sharp fall in the reactivity of N-aclimidazolium salts was observed in the change from weakly polar aprotic media (CH2Cl2) to highly polar aprotic media (CH3CN). The observed reactivity of N-acylimidazolium salts in CH3CN depends considerably on the nature of the ion pair of the salt, diminishing in the order Cl-, Br-, ClO4, B(C6H5)4, which is associated with the low reactivity of acetylimidazolium ions in CH3CN