Ionic liquids alkyl-imidazolium thiocyanates: Comprehensive thermochemical study

Abstract

Ionic liquids containing imidazolium cation and thiocyanate anion are attracting considerable attention for industrial applications due to low viscosities, low melting points and good conductivity. A comprehensive thermodynamic study of [Cnmim][SCN] series with (n = 2, 4, and 6) was performed in this paper. Vapor pressures were measured by using the quartz-crystal microbalance (QCM). Vaporization enthalpies have been derived by using thermogravimetry and QCM and adjusted to the reference temperature 298.15 K. An absence of possible thermal decomposition during vapor pressure measurements was monitored by the ATR-IR spectroscopy. The liquid phase standard molar enthalpy of formation of [C4mim][SCN] was measured by using combustion calorimetry, combined with the evaluated vaporization enthalpy to get gas-phase standard molar enthalpy of formation. The latter experimental value was in close agreement with theoretical gas-phase molar enthalpy of formation of [C4mim][SCN], calculated by the high-level quantum chemical method G3MP2. These experimental and theoretical results were applied for estimation of aqueous standard molar enthalpies of formation of [Cnmim] cations, as well as for calculation of solubilities of practically relevant solutes in of [Cnmim][SCN] series of ionic liquids