A series of protic acidic ionic liquids have been used as solvents and catalysts for the synthesis of 1,5-benzodiazepines. Success of the condensation appears to lie in the choice of cation–anion combinations and the ionic liquid [HBIm]CF3SO3 was found to be the best. Acidities of five protic acidic ionic liquids have also been investigated using Hammett method in 1,2-dichloromethane solutions. The ionic liquid [HBIm]CF3SO3 can be recovered conveniently and reused for five times without remarkable loss of activity.
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