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

• Published in: Chemical engineering journal advances Vol. 17; p. 100585
• Main Authors: Asharani, N., Shakeel Nawaz, S., Ranganatha, S., Supriya, S., Ramakrishna, Dileep
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.03.2024; Elsevier
• Subjects: Benzazoles; Copper complexes; Immobilization; Ionic liquids; Schiff base; Schiff base; Ionic liquids; Immobilization; Benzazoles; Copper complexes
• ISSN: 2666-8211; 2666-8211
• DOI: 10.1016/j.ceja.2024.100585

•Ethyl methyl imidazolium hexafluorophosphate, [EMIM] PF6, ionic liquids mediated synthesis catalyzed by a copper complex.•Excellent catalytic efficiency in C‒N, C‒O, and C‒S coupling reactions forming benzazoles.•The catalyst followed a hydrogen transfer mechanism.•In the ionic liquid‒water mixture as solvent, the competence of the catalyst was accelerated, in just two hours and achieving up to 96 % yield.•The catalyst in the ionic liquid: water mixture was recyclable and was reused up to 5 times effectively. 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. [Display omitted]