Pyrrolidinium salt based binary and ternary deep eutectic solvents: green preparations and physiochemical property characterizations

Ionic liquids (ILs) are considered to be green solvents for various applications. However, their synthesis via chemical reaction with by-products or waste produced is contradictory to the concept of green chemistry, and the purity problem and economic feasibility limit their applications in some large-scale industrial applications. 1-Butyl-1-methylpyrrolidinium bromide ([bmpy][Br]), which is a molten salt with melting point above 100 degrees C is a precursor of pyrrolidinium ILs, but hardly can be put under the category of IL because of its high melting point. In this study, [bmpy][Br] based binary deep eutectic solvent (BDES) and ternary deep eutectic solvent (TDES) were synthesized to prepare [bmpy][Br] in liquid form. During the preparation process, no reaction media was employed, no by-product was generated, and no further purification was required, thereby making it a completely green process. The prepared TDES has better thermal stability and larger free volume than BDES, which is potentially useful for sorption applications with high temperature requirement. It is also because of the green preparation process that the TDES is also expected to be capable for the large-scale industrial applications. This work is opening up new avenues for the study of binary and ternary IL-DES system and their applications.