A study of halide nucleophilicity in ionic liquids

The relative nucleophilicity of chloride, bromide and iodide anions in [bmim][BF4] ionic liquid has been measured by studying their reaction with methyl p-nitrobenzenesulfonate ([ bmim] = 1-butyl-3-methylimidazolium cation). It has been found that iodide is the most nucleophilic halide, and that chloride and bromide have approximately equal nucleophilicities (Cl- is slightly more nucleophilic than Br-) in [bmim][BF4]. Activation energies for the reaction of chloride and bromide with methyl p-nitrobenzenesulfonate have been calculated. The relative nucleophilicity of the halides has been compared with that observed in molecular solvents and in a tetraalkylammonium tetraalkylboride ionic liquid.