New biobased tetrabutylphosphonium ionic liquids: synthesis, characterization and use as a solvent or co-solvent for mild and greener Pd-catalyzed hydrogenation processes

Abstract

Phosphonium-based Ionic Liquids (PhosILs) with natural organic derived anions (L-lactate, L-tartrate, malonate, succinate, L-malate, pyruvate, D-glucuronate, D-galacturonate, ferulate, p-coumarate) were easily prepared by acid–base method from tetrabutylphosphonium hydroxide and an excess of the corresponding acid with good yields. Their characterization was realized through classical NMR, IR and elemental analysis techniques; their viscosity and ATG parameters were also determined. These ionic liquids showed good performance and recyclability in the selective Pd-catalyzed hydrogenation of alkenes, polyenes like linoleic acid and enantioselective hydrogenation of unsaturated ketones such as isophorone at room temperature under atmospheric H₂ pressure. Furthermore, NMR studies leading to computational calculations were performed to establish easily the composition of the resulting mixture obtained through the hydrogenation of linoleic acid.