Understanding the Role of Protic Ionic Liquids in Reactive Systems: Rational Selection of PILs for the Design of Green Synthesis Strategies for Allylic Amines and β-amino Esters

BRAVO, M. VIRGINIA; FERNÁNDEZ JOSE LUIS; ADAM CLAUDIA G; CLAUDIA D. DELLA ROSA

CHEMPLUSCHEM

WILEY-VCH Verlag GmbH & Co. KGaA

Lugar: Weinheim; Año: 2019

2192-6506

This work demonstrates that the reactive behaviour of Protic Ionic Liquids (PILs) is governed not only by their chemical structures but also by their global compositions, which include the presence of free acids and bases at equilibrium with the ionic pairs. Six PILs composed by primary, secondary, or tertiary alkyl ammonium cations with two couterions, nitrate or acetate, were tested in model reactions with insaturated substrates. The free species that were naturally present in these liquids were identified by cyclic voltammetry. We show that only tributylammonium nitrate is mostly composed just by the ionic pair, and that the other five PILs also contain variable amounts of free acid and amine. In reactive systems, these free species determine the products of the reaction. In particular, allylic amines and beta-amino esters were obtained with good yields (91 and 75 %, respectively) by reaction of conjugated dienes and acrylates in the presence of PILs. By taking into account the actual composition of each PIL, it was possible to direct the reaction path towards a specific product with good yields, to ensure acid catalysis, to avoid polymerization of the substrate, and to promote phase transference of products. These results establish some useful guidelines for the rational design of new PIL-based one-step synthetic strategies