GREEN SYNTHESIS OF ALKANE BRIDGED BISIMIDAZOLIUM SALTS UNDER SOLVENT-FREE CONDITIONS

A series of N-aryl or N-methyl substituted bisimidazolium dichloride or dibromide salts with different alkyl bridge lengths (n = 1-4) have been synthesized starting from N-arylimidazoles or N-methylimidazoles with dialkyl bromides or the less expensive but less reactive dialkyl chlorides under solvent-free conditions. This green protocol provided most bisimidazolium chloride and bromide salts in good yields, and the reaction time was shortened to a few hours. In two examples, we showed either bisimidazolium dichloride (1a) or dibromide salt (3c) can be easily converted to the corresponding dihexafluorophosphate salt (1a' or 3c') in near quantitative yield.