Physicochemical properties, Brönsted acidity and ecotoxicity of imidazolium-based organic salts: Non-toxic variants of protic ionic liquids

Abstract

In this study, four new protic ionic liquids (PILs), possessing camphorsulfonate anion with four different cations, 2-methyl-3-(3-sulfopropyl)-imidazolium (7,7-dimethyl-2-oxobicyclo[2.2.1]heptan-1-yl)methanesulfonate [2MeimPS][CS], 2-ethyl-3-(3-sulfopropyl)-imidazolium (7,7-dimethyl-2-oxobicyclo[2.2.1]heptan-1-yl)methanesulfonate [2EteimPS][CS], 2-phenyl-3-(3-sulfopropyl)-imidazolium (7,7-dimethyl-2-oxobicyclo[2.2.1]heptan-1-yl)methanesulfonate [2PhimPS][CS] and 3-(3-sulfopropyl)-benzimidazolium (7,7-dimethyl-2-oxobicyclo[2.2.1]heptan-1-yl)methanesulfonate [BnzimPS][CS] were synthesized and characterized. The effect of alkyl and aromatic substitution on the imidazolium cation was investigated in terms of fluctuations in density, viscosity and thermal degradation of ILs. The density and viscosity were determined within a broad temperature range and measured values of density were used to calculate molar volume, standard molar entropy, lattice energy and thermal expansion coefficients. The refractive indices were measured with an ATAGO refractrometer (RX-5000a) within the temperature range of 288.15–333.15 K. The studied ILs exhibited strong Brönsted acidities as determined by Hammett method. Three human pathogenic bacteria i.e. Escherichia coli E149 (EC), Staphlylococcus aureus S244 (SA) and Aeromonas hydrophilla A97 (AH), were deployed to investigate the toxicity behaviour of studied ILs and their 50% effective concentrations (EC50) were found in comparison with the least toxic imidazolium-based ILs. COSMO-RS was used to determine δ-surface, δ-potential and δ-profile of the investigated ILs.