Standard Molar Enthalpies Of Sublimation Research Articles

Experimental Determination of the Standard Enthalpy of Formation of Trimellitic Acid and Its Prediction by Supervised Learning.

The standard molar enthalpy of formation for trimellitic acid (TMAc) in the crystalline phase at 298.15 K, ΔfHm°(cr), was calculated experimentally from the enthalpy of combustion through combustion calorimetry experiments. Likewise, the standard molar enthalpy of sublimation was determined from the standard molar enthalpy of fusion and from the standard molar enthalpy of vaporization from differential scanning calorimetry and thermogravimetry, respectively. Subsequently, the standard molar enthalpies of formation in the gas-phase at 298.15 K, ΔfHm°(g), were calculated. The enthalpies of formation for TMAc, hemimellitic, and trimesic acids were predicted using multiple linear regression (MLR) with a nonreplacement evaluation technique. MLR was applied to the data set that allowed estimating these thermochemical properties with an R2 greater than 0.99. This model was used to compare the predicted and experimental results for benzene carboxylic acids.

7-Methoxy-4-methylcoumarin: Standard Molar Enthalpy of Formation Prediction in the Gas Phase Using Machine Learning and Its Comparison to the Experimental Data.

Experimentally, the standard molar enthalpy of formation in the crystalline phase at 298.15 K, ΔfHm°(cr) for 7-methoxy-4-methylcoumarin (7M4MC) was calculated by traditional linear regression, which was obtained by combustion calorimetry. Similarly, the standard molar enthalpy of sublimation was determined through the standard molar enthalpy of fusion and by the standard molar enthalpy of vaporization, from differential scanning calorimetry and thermogravimetry, respectively; lately using these results, the standard molar enthalpy of formation in the gas phase was calculated at 298.15 K, ΔfHm°(g). In addition ML was used to predict the standard molar enthalpy of formation in the gas phase for the 7M4MC, constructing an experimental data set containing three kinds of functional groups: esters, coumarins, and aromatic compounds. The procedure was performed by using multiple linear regression algorithms and stochastic gradient descent with a R2 of 0.99. The obtained models were used to compare those predicted values versus experimental for coumarins, resulting in an average error rate of 9.0%. Likewise, four homodesmic reactions were proposed and predicted with the multiple linear regression algorithm of ML obtaining good results.

On the Enthalpy of Formation and Enthalpy of Sublimation of Dihydroxylammonium 5,5′‐bitetrazole‐1,1′‐dioxide (TKX‐50)

AbstractThe thermodynamic characterization of dihydroxylammonium 5,5′‐bitetrazole‐1,1′‐dioxide (TKX‐50) was reinvestigated. Although TKX‐50 is one of the most promising new‐generation energetic materials, contradictory reports are found in the literature with regard to its solid enthalpy of formation. The standard (po=105 Pa) molar enthalpy of formation of crystalline TKX‐50, (175.3±1.9) kJ ⋅ mol−1, was determined experimentally based on the measured standard massic energy of combustion, determined through static‐bomb combustion calorimetry. Additionally, the standard molar enthalpy of sublimation of TKX‐50, at T=298.15 K, (165.0±2.4) kJ ⋅ mol−1, was derived from vapor pressure measurements determined by a Knudsen mass‐loss effusion technique. Finally, different approaches were used in attempts to calculate the standard enthalpy of formation of TKX‐50 in the solid state. A critical overview and assessment of the data on the enthalpy of formation of TKX‐50 is also presented.

Standard molar enthalpy of sublimation of form I nicotinamide

The standard (p° = 0.1 MPa) molar enthalpy of sublimation of form I nicotinamide (NIC, cr I), at 298.15 K, was determined by drop-sublimation Calvet microcalorimetry. Experiments carried out under isothermal and non-isothermal conditions led to ΔsubHmo(NIC, cr I) = 108.0 ± 0.5 kJ·mol−1. The present study allowed to resolve to a significant extent the large discrepancy observed between published ΔsubHmo(NIC) results obtained by calorimetry and by vapor-pressure measurements, using samples of unspecified crystal form.

Thermochemical study of the antioxidant activity of some hydroxycoumarins

This work reports a combined thermochemical experimental and computational study on 6-hydroxycoumarin. The standard (p° = 0.1 MPa) molar enthalpy of formation in the condensed state of this compound was derived from the standard molar energy of combustion in oxygen at T = 298.15 K, measured by combustion calorimetry. Calvet microcalorimetry was used to derive the standard molar enthalpy of sublimation. By combining these values, the standard molar enthalpy of formation in the gaseous phase, at T = 298.15 K, −(339.8 ± 2.4) kJ⋅mol−1 was derived.Accurate quantum chemical calculations at the composite G3 and at the DLPNO-CCSD(T) levels of theory have also been conducted in order to characterize the energetics of all the hydroxycoumarins studied and their radicalar related species, allowing us to further support our experimental measurements and to adequately quantify and rationalize the antioxidant activity of these systems.

A combined experimental and computational thermodynamic study of fluoronitrophenol isomers

Combustion energies of the 5-fluoro-2-nitrophenol, 4-fluoro-2-nitrophenol, 3-fluoro-4-nitrophenol and 2-fluoro-4-nitrophenol isomers were obtained by means of a rotating-bomb combustion calorimeter. From these determinations, standard molar combustion enthalpies and standard molar formation enthalpies, at T = 298.15 K, in the crystalline state, were derived. The Knudsen mass-loss effusion technique was used to determine the standard molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, of the studied compounds. The standard molar enthalpies of sublimation of the four isomers were also measured by Calvet microcalorimetry. The gas-phase standard molar enthalpies of formation were derived from the experimental measurements, at T = 298.15 K, for the fluoronitrophenols studied.Additionally, the standard molar enthalpies of formation were estimated by means of computational methodology at the G3(MP2)//B3LYP level. The estimated values are in very good agreement with experimental data, giving us support to estimate the gas-phase enthalpies of formation of the remaining isomers whose values have not been determined experimentally.A simple group additivity scheme was successfully applied for prediction of molar enthalpies of formation.The computational study was also extended to the determination of OH bond dissociation enthalpies for all the isomers.

Abraham Solvation Parameter Model: Calculation of L Solute Descriptors for Large C11 to C42 Methylated Alkanes from Measured Gas–Liquid Chromatographic Retention Data

Abraham model L solute descriptors have been determined for 149 additional C11 to C42 monomethylated and polymethylated alkanes based on published Kovat’s retention indices based upon gas–liquid chromatographic measurements. The calculated solute descriptors, in combination with previously published Abraham model correlations, can be used to predict a number of very important chemical and thermodynamic properties including partition coefficients, molar solubility ratios, gas–liquid chromatographic and HPLC retention data, infinite dilution activity coefficients, molar enthalpies of solvation, standard molar vaporization and sublimation at 298 K, vapor pressures, and limiting diffusion coefficients. The predictive computations are illustrated by estimating both the standard molar enthalpies of sublimation and the enthalpies of solvation in benzene for the monomethylated and polymethylated alkanes considered in the current study.

Metal–ligand binding energies in copper (II) and nickel (II) complexes with tetradentate N2O2 Schiff base ligands

This work constitutes a new contribution for understanding the relationship between the metal–ligand bonding and, indirectly, the inherent reactivity of metallic complexes with tetradentate N2O2 Schiff base ligands, being reported the energetic characterization of two transition metal complexes – (N,N'́-bis(salicylaldehydo)tetramethylenediiminate)nickel(II) and (N,N'-bis(salicylaldehydo)propylenediiminate)copper(II). The standard molar enthalpies of formation of these complexes were determined by solution-reaction calorimetry measurements. Their standard molar enthalpies of sublimation, at T = 298.15 K, were obtained by an effusion method. From these studies, the gas-phase enthalpies of formation of Ni(II) and Cu(II) complexes, at T = 298.15 K, were derived. Differences between the metal–ligand and mean hydrogen-ligand bond dissociation enthalpies were derived and discussed in structural terms, in comparison with identical parameters for complexes of the same metals with analogous tetradentate Schiff bases. High-level quantum chemical calculations have also been conducted, complementing the results obtained experimentally.

Experimental and Theoretical Investigation on the Thermochemistry of 3-Methyl-2-benzoxazolinone and 6-Nitro-2-benzoxazolinone.

The determination of the reliable thermodynamic properties of 2-benzoxazolinone derivatives is the main goal of this work. Some correlations are established between the energetic properties determined and the structural characteristics of the title compounds, and the reactivity of this class of compounds is also evaluated. Static-bomb combustion calorimetry and high-temperature Calvet microcalorimetry were used to determine, respectively, the standard molar enthalpies of formation in the solid state and the standard molar enthalpies of sublimation, both at T = 298.15 K. Using the results obtained for each compound, the respective gas-phase standard molar enthalpy of formation was derived. High-level quantum chemical calculations were performed to estimate the same property and the results evidence good accordance. Moreover, the gas-phase relative thermodynamic stability of 2-benzoxazolinone derivatives was also evaluated using the respective gas-phase standard molar Gibbs energy of formation. In addition, the relationship between the energetic and structural characteristics of the benzoxazolinones is presented, evidencing the enthalpic increments associated with the presence of a methyl and a nitro groups in the molecule, and this effect is compared with similar ones in other structurally related compounds.

Isavuconazole: Thermodynamic Evaluation of Processes Sublimation, Dissolution and Partition in Pharmaceutically Relevant Media.

A temperature dependence of saturated vapor pressure of isavuconazole (IVZ), an antimycotic drug, was found by using the method of inert gas-carrier transfer and the thermodynamic functions of sublimation were calculated at a temperature of 298.15 K. The value of the compound standard molar enthalpy of sublimation was found to be 138.1 ± 0.5 kJ·mol−1. The IVZ thermophysical properties—melting point and enthalpy—equaled 302.7 K and 29.9 kJ mol−1, respectively. The isothermal saturation method was used to determine the drug solubility in seven pharmaceutically relevant solvents within the temperature range from 293.15 to 313.15 K. The IVZ solubility in the studied solvents increased in the following order: buffer pH 7.4, buffer pH 2.0, buffer pH 1.2, hexane, 1-octanol, 1-propanol, ethanol. Depending on the solvent chemical nature, the compound solubility varied from 6.7 × 10−6 to 0.3 mol·L−1. The Hansen s approach was used for evaluating and analyzing the solubility data of drug. The results show that this model well-described intermolecular interactions in the solutions studied. It was established that in comparison with the van’t Hoff model, the modified Apelblat one ensured the best correlation with the experimental solubility data of the studied drug. The activity coefficients at infinite dilution and dissolution excess thermodynamic functions of IVZ were calculated in each of the solvents. Temperature dependences of the compound partition coefficients were obtained in a binary 1-octanol/buffer pH 7.4 system and the transfer thermodynamic functions were calculated. The drug distribution from the aqueous solution to the organic medium was found to be spontaneous and entropy-driven.

Sublimation thermodynamics of antifungal drugs: Tioconazole, miconazole and climbazole

The temperature dependence of the saturated vapour pressure of the antifungal drugs – tioconazole (TCZ), miconazole (MCZ) and climbazole (CLZ) – was determined by the inert gas carrier transfer method. The standard molar enthalpies of sublimation at T = 298.15 K calculated from these data were 117.2 ± 0.5 kJ·mol-1 for TCZ ± 0.9, 106.2 ± 1.0 kJ·mol-1 for MCZ and 113.3 kJ·mol-1for CLZ. The vaporization and sublimation enthalpies of the compounds were found by the Langmuir and Clausius-Clapeyron equations without determining the vapour pressures of the drugs. Sublimation enthalpies derived by both these methods were in good agreement. It was shown that it was possible to estimate the thermodynamic sublimation functions by applying the space clusterization approach to the studied and structurally related compounds. In addition, the temperature and enthalpy of fusion of the compounds were measured by differential scanning calorimetry.

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.

Experimental and computational thermochemical study of dimethoxyacetophenones

The standard (po = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, for 2′,4′-, 2′,5′-, 2′,6′- and 3′,4′-dimethoxyacetophenones, in the condensed phase, were derived from measurements of the standard massic energies of combustion using a static bomb combustion calorimeter. The standard molar enthalpies of sublimation or vaporization, at T = 298.15 K, were determined by high temperature Calvet microcalorimetry. Combining the results measured by these two techniques, the standard molar enthalpies of formation in the gaseous phase, at T = 298.15 K, were derived.Computational studies for the experimentally studied compounds were also performed, as a complement to the experimental work, being also extended to the 2′,3′- and 3′,5′-dimethoxyacetophenone isomers. The gas-phase enthalpies of formation were estimated from high level ab initio molecular orbital calculations, at the G3 level.Group additivity values and corrections for functional group interactions in the benzene ring were derived and used for predicting enthalpies of formation for dimethoxyacetophenones. The applicability of simple group-additivity procedures to tri-substituted benzenes was discussed.

Influence of the functional groups −NH2, −OCH3, and −OH on the thermochemistry of indanes

This work is a contribution to the thermochemical characterization of bicyclic hydrocarbons, reporting the study of six indane derivatives: 4-aminoindane, 5-aminoindane, 5-methoxyindane, 1-indanol, 2-indanol, and 5-indanol. The combustion calorimetry technique was used to measure the massic energy of combustion of each compound in the condensed state, which has been used to derive the corresponding standard (p° = 0.1 MPa) molar enthalpy of formation, at 298.15 K. The standard molar enthalpies of sublimation or vaporization of the compounds were determined by high-temperature Calvet microcalorimetry. For each indane derivative, the results obtained for those two properties, allowed to derive the respective value of standard molar enthalpy of formation, in the gaseous phase. Additionally, a theoretical study at the G3(MP2)//B3LYP level has been carried out, and the calculated enthalpies of formation have been compared with the experimental values. The values of the enthalpy of formation, in the gaseous phase, were analysed in terms of correlations between the structural (different substituents in the indane core) and energetics characteristics.

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

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.

Enthalpies of sublimation of l-methionine and dl-methionine: Knudsen’s effusion mass spectrometric study

We report sublimation enthalpies of sulfur-containing amino acids, l- and dl-methionine, investigated by Knudsen’s effusion method with mass spectrometric vapor composition control. The fragmentation of molecules under electron ionization (EI) was discussed. For these compounds, the molar sublimation enthalpies were derived from the Clausius-Clapeyron equation. Using the isobaric heat capacities in the crystal phases of the compounds the standard molar enthalpies of sublimation at T = 298.15 K, were obtained. In addition, conformational analysis of methionine (Met) was performed by hybrid DFT and MP2 calculations. Analysis of natural bond orbitals (NBO) carried out for the three low-energetic conformers of Met revealed intramolecular hydrogen bonds in one of these. The average interaction energies between a lone electron pair (donor) of nitrogen and “antibonding” orbital of O–H bond (acceptor) were obtained and used in the interpretation of the structure.

Phenyl substituted ureas: Evaluation of thermochemical data with complementary experimental and computational methods

Standard molar enthalpies of formation of 1-phenyl-3-isopropyl-urea and 1-phenyl-3-tert-butyl-urea were derived from results of high-precision combustion calorimetry. Standard molar enthalpies of sublimation of these compounds and of phenyl-urea were derived from their vapour pressure – temperature dependences measured by the transpiration method. Thermal behaviour of phenyl substituted ureas was studied by DSC. Thermochemical data on phenyl-substituted ureas available in the literature were collected, evaluated, and combined with our own experimental results. We have evaluated and recommended for further thermochemical calculations a set of sublimation, vaporization, fusion and formation enthalpies for the phenyl-substituted ureas at 298.15 K. A computational procedure was developed to support the experimental gas-phase enthalpies of formation. The theoretical gas phase molar enthalpies of formation of the phenyl-substituted ureas calculated by the high-level quantum-chemical G3MP2 method were in a good agreement with the recommended experimental data. General regularities in energetics due to introduction of phenyl substituent in the alkyl-substituted ureas have been revealed and used for validation of the experimental and theoretical data. Additivity methods were developed to estimate the thermochemical properties of organic compounds containing the carbamide moiety.

Thermodynamic Properties of Trimethylene Urethane (1,3-Oxazinan-2-one)

The standard molar enthalpy of formation of trimethylene urethane (1,3-oxazinan-2-one) in the crystalline state at 298.15 K was derived using combustion calorimetry. Standard molar enthalpies of sublimation and vaporization of this compound at 298.15 K were derived by the transpiration method. The enthalpies of fusion were measured using differential scanning calorimetry technique. Thermodynamic data on trimethylene urethane available in the literature were collected, evaluated, and combined with our experimental results. Quantum-chemical calculations of the molar enthalpies of formation of the compound in the gaseous state were performed using the G4 method, and the results are in excellent agreement with the recommended experimental data. Thermodynamic properties of trimethylene urethane in the ideal gas state were calculated from molecular and spectral data in the temperature range from 298.15 to 1500 K. The strain energy values (Estr) of different six-member cyclic compounds were estimated.

Experimental and computational thermochemical studies of acridone and N-methylacridone

Abstract This paper reports the standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of acridone and N-methylacridone as (50.0 ± 5.0) kJ·mol−1 and (60.6 ± 4.3) kJ·mol−1, respectively. These data were obtained from experimental thermodynamic parameters, namely the standard molar enthalpies of formation, in the crystalline phase, at T = 298.15 K, derived from the standard molar enthalpies of combustion measured by static-bomb combustion calorimetry, and the standard molar enthalpies of sublimation, at T = 298.15 K, determined by Calvet microcalorimetry or the Knudsen effusion techniques. Additionally, the gas-phase enthalpies of formation were estimated by G3(MP2)//B3LYP calculations, using several hypothetical gas-phase reactions, and were compared with the corresponding ones determined experimentally. The gas-phase keto-enol tautomerization chemical equilibrium of acridone ↔ 9-acridinol was analysed using the Boltzmann’s distribution, being confirmed that the equilibrium favours the formation of the keto form. The bond dissociation enthalpies (N-H) and (C-H) and the gas-phase acidities were also determined. The electrostatic potential surfaces and the frontier molecular orbitals were determined for both compounds, allowing us to infer about their reactivity properties. Other properties studied include the HOMO-LUMO energy gap and the ionization potential.

Thermochemical Properties of Xanthine and Hypoxanthine Revisited

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.