Selective N-alkylation of amines with alcohols via hydrogen transfer catalyzed by copper complex in an ionic liquid media

Abstract

A catalytic system containing a copper-Schiff base complex in ethyl methyl imidazolium hexafluoro phosphate [(EMIM)PF₆] ionic liquid, where the ionic liquid was used as a solvent, was found to be very effective to catalyze the synthesis of benzazoles [i.e. imidazoles (C–N), thiazoles (C–S) and oxazoles (C–O)]. Substituted amines and alcohols reacted with each other in the given reaction conditions to give benzazoles. The reaction proceeded via a hydrogen transfer mechanism, which was proved by conducting series of reactions involving the conversion of aldehydes/ketones to corresponding primary and secondary alcohols. The reaction conditions were optimized with respect to catalyst concentration, best choice of the solvent, effect of different bases and the optimized chosen ones. It was found that the reaction required as low as 0.1 mol% of the catalyst and potassium carbonate as the base. Most interestingly the quantity of the products yielded the same when an equal ration of water: [EMIM]PF₆ mixture was used as the solvent, same as when the ionic liquid alone was used as the solvent. A wide range of substituted alcohols and amines were tested and the products were formed within a short reaction time and comparatively good yields.