Design of greener cycloaddition reactions. Selection of ionic liquids (ILs) from their actual microstructural composition

ADAM, C.; FERNÁNDEZ, JOSÉ L.; DELLA ROSA, CLAUDIA; BRAVO, MA VIRGINIA; MA. BELEN MARTINI

Buenos Aires

Simposio; GS03-Global Symposium on Ionic Liquids (JE-II CIBIQ) ?A WCCE11 Joint Event; 2023

Predicting the physicochemical behaviours of ILs requires to have a deep knowledge of their actual compositions, which define their unique microstructures, a sort of “fingerprint” of each IL. Besides, knowing the “real” structure of ILs allows to find sense for many reported unexpected behaviours of these materials that led to so-called “surprising” results, recognising the factors that actually affect these behaviours for extrapolating them to other ILs from the same family and for defining their further applications.The cyclic voltammetry is suitable to determine the actual compositions of alkyl ammonic and imidazolic ILs combined with varied anions [1], and of task specific ILs (TSILs) whose imidazolic bases were modified by introducing a sulfonic functional group 2,3. In many of these cases it was verified that the ionic pairs coexisted in equilibrium with their precursors or neutral species, so the actual or “natural” compositions of these ILs depended on the equilibrium constant of the reaction between the parent neutral species that led to the ionic pair. On this context, the goal of this work is to use this knowledge about the actual microstructures of these two ILs families for designing greener synthetic strategies in order to direct the reactions toward the product of the Diels-Alder (DA) cycloaddition.The conditions for the reaction of 1-nitronaphthalene and 2-nitrofuran with isoprene were optimized in 60°C/12 hours. The alkyl ammonium IL tributylammonium nitrate (TBAN) and the TSILs (1-(4-sulfonic acid)-butyl-3-methylimidazolium) that were selectively selected based on their previously determined microstructures were added to the reacting system in a 10 wt.% ratio. It was verified that only the Diels-Alder and the hetero Diels-Alder products were transferred to a different phase respect to the aqueous phase, with 50 and 55 % yields, respectively. The insightful knowledge of the ILs microstructures allowed us to apply chemical criteria for selecting the best ILs for these reactions and for developing more environmentally friendly reaction conditions, and with very good yields respect to the same reactions carried out in molecular solvents.References1. Bravo, Ma V., Fernández, J.L., Adam, C.G., Della Rosa, C. D. (2020). 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. ChemPlusChem, 84, 919–926.2. a) Martini Ma B, Fernández, J.L., Adam, C.G. (2021) Insights on the catalytic behaviour of sulfonic acid-functionalized ionic liquids (ILs) in transesterification reactions – Voltammetric characterization of sulfonic task-specific ILs with bisulfate anions. Physical Chemistry Chemical Physics, 4; 23(4): 2731-2741 b) Martini Ma B, Adam, C.G, Fernández, J.L. (2021) Significant effects of the anion on the catalytic behaviour of sulfonic acid-functionalized ionic liquids in transesterification reactions – A combined electrochemical/catalytic study. Molecular Catalysis, 51, 111821