Characterization and purification of the ionic liquid Cyphos IL 101 by non-aqueous solvent extraction

Abstract

The chemical composition of the quaternary phosphonium ionic liquid Cyphos IL 101 was characterized by 31P NMR spectroscopy and LC–MS analysis, revealing the presence of at least 22 distinct phosphorus-containing species in the commercial product. Anomalous results observed when using deuterated chloroform as a solvent for NMR analysis of Cyphos IL 101 were addressed, demonstrating that protic solvents are essential for accurate quantitative NMR measurements. Different batches of Cyphos IL 101 showed significant variations in the concentrations of trialkylphosphonium chlorides and trialkylphosphane oxides. Aging and storage conditions were identified as key factors influencing the overall composition of the ionic liquid. A purification strategy for Cyphos IL 101 based on non-aqueous solvent extraction using ethylene glycol with NaCl was developed. A purity of 99% was obtained by a process with 10 steps. Quantitative removal of the protonated phosphanes was achieved, but the overall purity remained dependent on the initial composition, particularly due to the poor extractability of the phosphane oxides. Process kinetics and settling behavior were investigated, and the method was successfully demonstrated on a liter scale in continuous countercurrent mode in a Kühni column with rotary agitation, achieving the same 99% purity as in batch operations. The variation in Cyphos IL 101’s composition across batches and within batches over time might have some serious implications for the usefulness of this ionic liquid as an extractant for metal ions.