Thermochemical Properties of Xanthine and Hypoxanthine Revisited

© 2017 American Chemical Society. The standard molar enthalpies of formation of xanthine and hypoxanthine were measured by using high-precision combustion calorimetry. The standard molar enthalpies of sublimation of these compounds at 298.15 K were derived by the quartz-crystal microbalance technique. Limited thermodynamic data available in the literature are compared with our new experimental data. In addition, we use the G4 method to calculate the molar enthalpies of formation of xanthine and hypoxanthine in the gas phase. There is good agreement between the evaluated experimental data and the quantum-chemical calculations. (Chemical Equation Presented)

Vapor pressures and vaporization enthalpies of 5-nonanone, linalool and 6-methyl-5-hepten-2-one. Data evaluation

© 2014 Elsevier B.V.. Vapor pressures and vaporization enthalpies for 5-nonanone, linalool and 6-methyl-5-hepten-2-one seem to be in disarray. Temperature dependences of vapor pressures for these pure compounds were measured by using the static and the transpiration techniques. Molar standard enthalpies of vaporization at the reference temperature were derived. Available literature data on vapor pressures and vaporization enthalpies were collected and analyzed. The consistent data set for each compound was evaluated. Reliable thermodynamic parameters of vaporization were derived and used to test some commonly used predicting procedures

Structure-property relationships in ionic liquids: Chain length dependence of the vaporization enthalpies of imidazolium-based ionic liquids with fluorinated substituents

© 2015 Elsevier B.V. Molar vaporization enthalpies of fluoroalkyl-substituted imidazolium-based ionic liquids were derived from two concurring quartz crystal microbalance (QCM) and thermogravimetry (TGA) methods. For comparison, enthalpies of vaporization measured at elevated temperatures have been adjusted to the reference temperature 298K and tested for consistency. It was found that vaporization enthalpies of fluorine substituted families are significantly higher compared to the analogous ILs with the alkyl-substituted cation. This is in agreement to molecular solvents, where fluorination typically increases vaporization enthalpy relative to hydrocarbon analogues. A useful group contribution for the incremental CF2 fragment in the alkyl chain was recommended for the quick estimation of vaporization enthalpies of various substituted IL cations (e.g., imidazolium, ammonium, pyridinium, etc.)

Alkyl-imidazolium tetrafluoroborates: Vapor pressure, thermodynamics of vaporization, and enthalpies of formation

© 2017 Elsevier B.V. The absolute vapor pressures for the series of [C n mim][BF 4 ] ionic liquids with (n = 2, 4, 6, 8, and 10) were measured over the temperature range 404–457 K by using the quartz-crystal microbalance. An absence of possible thermal decomposition was monitored by the ATR-IR spectroscopy. The molar enthalpies of vaporization of ionic liquids under study were derived from vapor pressure temperature dependences and adjusted to the reference temperature 298.15 K. The liquid phase molar enthalpy of formation of [C 2 mim][BF 4 ] was derived from the solution calorimetry and combined with its molar vaporization enthalpy to get the first experimental gas-phase molar enthalpy of formation of the [BF 4 ] − containing ionic liquid. A computational approach based on the DLPNO-CCSD(T) method was used to calculate the theoretical gas-phase molar enthalpy of formation of [C 2 mim][BF 4 ]. The theoretical and experimental results were found to be in agreement within the combined uncertainties, providing the mutual validation of experimental and computational procedures used in the current study

Thermodynamic properties of glycerol: Experimental and theoretical study

© 2015 Elsevier B.V. Vapor pressures of highly pure glycerol were measured by the static and the transpiration methods in a broad temperature range. The standard molar enthalpy of vaporization of glycerol was derived from the vapor pressure temperature dependencies. Thermodynamic data on glycerol available in the literature were collected, evaluated, and combined with own experimental results. We recommend the set of vaporization and formation enthalpies for glycerol at 298.15K (in kJmol-1): δfHm° (g)=-(578.8±0.6), δfHm° (l)=-(669.3±0.5), and δlgHm° =(90.5±0.3) as the reliable benchmark properties for further thermochemical calculations. Quantum-chemical calculations of the gas phase molar enthalpy of formation of glycerol have been performed using the G4 method and results were in agreement with the recommended experimental data. The standard molar entropy of formation and the standard molar Gibbs function of formation of glycerol were estimated

Thermochemistry of ammonium based ionic liquids: Thiocyanates - Experiments and computations

© Springer Science+Business Media New York 2015. Abstract Molar enthalpies of solution of tetra-n-butylammonium thiocyanate [N(Bu)4][SCN] and tetra-n-pentylammonium thiocyanate [N(Pe)4][SCN] in water were measured by using solution calorimetry. The enthalpy of combustion of [N(Bu)4][SCN] was measured by using rotation bomb combustion calorimetry and the enthalpy of formation of this ionic liquids was derived. The thermal behavior of [N(Bu)4][SCN] was studied using differential scanning calorimetry. Quantum-chemical calculations of the molar enthalpy of formation in the gaseous phase have been performed for the series [N(R)4][SCN] with RA =(Me, Et, n-Bu, and n-Pe) using the G3MP2 level of theory. Experimental and calculated values of the enthalpies of formation are in agreement within the boundaries of the experimental uncertainties

Prediction of the enthalpies of vaporization for roomerature ionic liquids: Correlations and a substitution-based additive scheme

© 2015 Elsevier B.V. All rights reserved. The literature data on the enthalpies of vaporization for aprotic ionic liquids (ILs) published by the end of May 2014 were analyzed and the most reliable ΔlgHm values were derived for 68 ILs. The selected enthalpies of vaporization were correlated with density and surface tension using symbolic regression and a number of effective correlation equations were proposed. The substitution-based incremental scheme for prediction of the enthalpies of vaporization of imidazolium, pyridinium and pyrrolidinium ILs was developed. The standard error of the regression for the developed scheme is significantly lower than that for the atom-based group-contribution schemes proposed earlier

Thermochemistry of Pyridinium Based Ionic Liquids with Tetrafluoroborate Anion

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimEnthalpies of vaporization of five pyridinium based ionic liquids (ILs): 1-R-pyridinium (with R = ethyl, butyl-, and hexyl), 1-butyl-3-methyl-pyridinium, and 1-butyl-4-methyl-pyridinium with tetrafluoroborate anion were studied using Quartz Crystal Microbalance (QCM). Enthalpies of solution of these ionic liquids were measured by high-precision solution calorimetry. Gas-phase enthalpies of formation of ILs were calculated by using the high-level quantum-chemical method G3MP2. From combination of experimental and theoretical results, enthalpies of formation of aqueous pyridinium based cations were derived for the first time

Benzoic acid derivatives: Evaluation of thermochemical properties with complementary experimental and computational methods

© 2015 Elsevier B.V. Molar sublimation enthalpies of the methyl- and methoxybenzoic acids were derived from the transpiration method, static method, and TGA. Thermochemical data available in the literature were collected, evaluated, and combined with own experimental results. This collection together with the new experimental results reported here has helped to resolve contradictions in the available enthalpy data and to recommend sets of sublimation and formation enthalpies for the benzoic acid derivatives. Gas-phase enthalpies of formation calculated with the G4 quantum-chemical method were in agreement with the experiment. Pairwise interactions of the methyl, methoxy, and carboxyl substituents on the benzene ring were derived and used for the development of simple group-additivity procedures for estimation of the vaporization enthalpies, gas-phase, and liquid-phase enthalpies of formation of substituted benzenes

Thermochemical Properties of Tunable Aryl Alkyl Ionic Liquids (TAAILs) based on Phenyl-1H-imidazoles

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimVaporization enthalpies of five different imidazolium based Tunable Aryl Alkyl Ionic Liquids (TAAILs) with a common bis(trifluoromethylsulfonyl)imide ([NTf2]) anion were measured using a Quartz Crystalline Microbalance (QCM) and by Thermogravimetric Analysis (TGA). The counter anion and the alkyl chain of these imidazolium-based ionic liquids with one N-aryl and one N-alkyl substituent were kept constant to study the influence of the ortho- and para-substituted aryl moieties on the vaporization enthalpies of these ionic liquids. For comparison, enthalpies of vaporization measured at elevated temperatures were adjusted to the reference temperature 298 K. Structure-property relations between TAAILs and similarly shaped corresponding 1-(R-phenyl)-imidazoles were analyzed. An incremental approach to predict vaporization enthalpies of ionic liquids by group contributions was suggested. The procedure is based on vaporization enthalpy of a starting IL and group contributions well established from molecular compounds