Heat capacities of ionic liquids based on tetrahydrothiophenium cation and NTf2 anion

Abstract

The isobaric heat capacities of seven ionic liquids (ILs) based on the S-alkyl-tetrahydrothiophenium cation [CnTHT] with alkyl chain lengths of Cn = 4,5,6,7,8,9,10 and the bis[(trifluoromethyl)sulfonyl]imide, [NTf2] anion were measured in a differential scanning calorimeter in the temperature range 310−376 K. Measurements have been performed for the first time. Experimental results were extrapolated to the reference temperature of 298 K. A linear trend of the Cp,mo(liq, 298 K) -values for [CnTHT][NTf2] with the growing alkyl chain length was observed and compared with trends available for the other ILs with 5-membered (imidazolium and pyrrolidinium) and 6-membered (pyridinium) ring cations as [NTf2] salts. The new Cp,mo(liq, 298 K) -values for for [CnTHT][NTf2] were used for mutual validation of experimental and theoretical results by a group-additivity method available in the literature. The agreement observed between experimental and additive calculations, together with the reasonable chain-length dependence demonstrated for the [CnTHT][NTf2] series was considered as evidence of internal consistency of the heat capacities measured in this work.