Morpholinium and piperidinium based ionic liquids: Vaporization thermodynamics

Ionic liquids (ILs) have gained increasing attention in a wide range of material synthesis related applications. For the first time, vapor pressures and vaporization enthalpies of four morpholinim based ILs with a common bis(trifluoromethylsulfonyl)imide ([NTf2]−) or trifluorotris(perfluoroethyl)phosphate ([FAP]−) anions were measured using a Quartz Crystal Microbalance (QCM). The enthalpies of vaporization measured at elevated temperatures have been adjusted to the reference temperature 298 K. The experimental vaporization enthalpies were compared with theoretical values available in the literature, as well as with empirical values derived from a gas-liquid-chromatographic method based on activity coefficients at infinite dilution. New experimental vaporization enthalpies were tested for consistency with help of structure property-relationships

Vapour pressures of methoxy substituted benzaldehydes

Absolute vapour pressures of 4‑hydroxy‑3-methoxybenzaldehyde (vanillin), 2‑hydroxy‑3-methoxybenzaldehyde (ortho-vanillin), 2‑hydroxy‑5-methoxybenzaldehyde, and 3,5-dimethoxy-benzaldehyde were measured by using transpiration method. Standard molar enthalpies of sublimation and vaporization were derived from vapour pressures temperature dependences. Available primary experimental results on vapour pressures were collected from the literature and evaluated. The consistent set of thermodynamic data can be recommended to optimize the lignin valorisation technologies

Vaporization Thermodynamics of Morpholinium Based Ionic Liquids

Ionic liquids (ILs) have gained increasing attention in a wide range of material synthesis related applications. For the first time, vapor pressures and vaporization enthalpies of four morpholinim based ILs with a common bis(trifluoromethylsulfonyl)imide ([NTf2]) anion were measured using Langmuir-Quartz Crystal Microbalance (QCM). The enthalpies of vaporization measured at elevated temperatures have been adjusted to the reference temperature 298 K. The experimental vaporization enthalpies were compared with theoretical values available in the literature, as well as with empirical values derived from a gas-chromatographic method based on activity coefficients at infinite dilution. New experimental vaporization enthalpies were tested for consistency with help of structure property-relationships

Thermochemistry of di-substituted benzenes: Ortho-, meta-, and para-hydroxyacetophenones

© 2019 Elsevier Ltd Standard molar enthalpy of vapourisation of 2′-hydroxyacetophenone and standard molar enthalpies of sublimation of 3′-hydroxyacetophenone and 4′-hydroxyacetophenone were obtained from the temperature dependence of vapour pressure measured by the transpiration method. Enthalpy of fusion of 3′-hydroxyacetophenone was measured by using DSC. Available from literature primary experimental results on temperature dependences of vapour pressures have been collected and they have been treated uniformly in order to derive vapourisation/sublimation enthalpies at the reference temperature 298.15 K. The available data were successfully checked for internal correlation. Gas phase molar enthalpies of formation of hydroxyacetophenones calculated by the high-level quantum-chemical methods G3MP2 and G4 were in good agreement with the experimental results. A set of thermodynamic properties of hydroxyacetophenones was recommended as reliable reference properties for thermochemical calculations. Simple group-additivity procedures were developed for estimation of vaporisation enthalpies, gas-phase, and liquid-phase enthalpies of formation of substituted benzenes

Symmetry vs. asymmetry – Enthalpic differences in imidazolium-based ionic liquids

© 2020 Elsevier B.V. Enthalpies of ionic liquids [CnCnIm][X] synthesis reactions were measured with help of differential scanning calorimetry. These results in combination with quantum-chemical calculations were used for estimation of vaporization enthalpies of symmetric imidazolium based ionic liquids with X = Cl, Br, and I. Vaporization enthalpies of the symmetric ([CnCnIm][X]) series were found to be systematically lower (of 5–8 kJ mol−1) in comparison with the corresponding asymmetric imidazolium-based ILs ([CnC1Im][X]). This energetic difference was attributed to the intensity of dispersion interactions

Thermochemistry of phthalic acids: Evaluation of thermochemical data with complementary experimental and computational methods

© 2020 Elsevier B.V. Available from literature primary experimental results on temperature dependences of vapour pressures of phthalic, isophthalic, and terephthalic acids have been collected and they have been treated uniformly in order to derive sublimation enthalpies at the reference temperature 298.15 K. In order to evaluate the available experimental data, enthalpies of sublimation of isophthalic and terephthalic acid were obtained from the temperature dependence of vapour pressure measured by the transpiration method. Enthalpies of formation of crystalline isophthalic acid and 4-methylphthalic acid were derived by using combustion calorimetry. Gas phase enthalpies of formation of phthalic acids were calculated by the composite quantum-chemical methods G4 and G3MP2. These values were used for evaluation of experimental results and recommendation of reliable benchmark properties for thermochemical calculations. Mutual interactions of carboxylic substituents in the benzene ring were derived and discussed

Ionic liquids alkyl-imidazolium thiocyanates: Comprehensive thermochemical study

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

Heat capacities of ionic liquids based on tetrahydrothiophenium cation and NTf<inf>2</inf> anion

© 2020 Elsevier B.V. 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