Thermophysical Properties of Amino Acid-Based Ionic Liquids

Abstract

Ionic liquids (ILs) having either cations or anions derived from naturally occurring amino acids have been synthesized and characterized as amino acid-based ionic liquids (AAILs). In this work, the experimental measurements of the temperature dependence of density, viscosity, heat capacity, and thermal conductivity of several AAILs, namely, tributylmethylammonium serinate ([N4441][Ser]), tributylmethylammonium taurinate ([N4441][Tau]), tributylmethylammonium lysinate ([N4441][Lys]), tributylmethylammonium threonate ([N4441][Thr]), tetrabutylphosphonium serinate ([P4444][Ser]), tetrabutylphosphonium taurinate ([P4444][Tau]), tetrabutylphosphonium lysinate ([P4444][Lys]), tetrabutylphosphonium threonate ([P4444][Thr]), tetrabutylphosphonium prolinate ([P4444][Pro]), tetrabutylphosphonium valinate ([P4444][Val]), and tetrabutylphosphonium cysteinate ([P4444][Cys]), are presented. The influence of cations and anions on studied properties is discussed. On the basis of experimental data, the QSPR (quantitative structure−property relationship) correlations and group contribution methods for thermophysical properties of AAILs have been developed, which form the basis for the development of the computer-aided molecular design (CAMD) of AAILs. It has also been demonstrated that that the predictive data obtained by correlation methods are in good agreement with the experimental data. The correlations developed, herein, can thus be used to evaluate the studied thermophysical properties of AAILs for use in process design or in the CAMD of new AAILs.