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.

Standard molar enthalpies of formation of 3-methylglutaric and 3,3-dimethylglutaric anhydrides

In this research, both the standard molar enthalpy of formation in the crystalline phase and in the gas phase of 3-methylglutaric anhydride was calculated from experimental data. The temperature and enthalpy of fusion, as well as the molar heat capacity in solid phase was calculated by differential scanning calorimetry; the molar enthalpy of sublimation at 298.15 K by the Knudsen effusion method, the molar enthalpy of vaporization at 298.15 K by thermogravimetric analysis, and the standard massic combustion energy by combustion adiabatic calorimetry. Since 3,3-dimethylglutaric anhydride presented crystal transitions (with endothermic points at 352.76 K, 356.98 K and 397.15 K), some of its thermochemical properties were estimated from the functional group-contribution methods proposed by Benson, Gani and Naef and from application of Machine Learning based models.

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.

Standard enthalpies of formation of 3-hydroxyphthalic anhydride

In this investigation thermochemical properties of 3-hydroxyphthalic anhydride were determined. Fusion enthalpy, fusion temperature and molar heat capacity in solid phase were obtained by differential scanning calorimetry. By the Knudsen effusion method, the molar enthalpy of sublimation at 298.15 K was obtained. By thermogravimetric data, it was possible to determine the molar enthalpy of sublimation and the molar enthalpy of vaporization. On the other hand, the molar enthalpy of formation in solid phase at 298.15 K was determined by combustion calorimetry. The molar enthalpy of formation in gas phase at 298.15 K was calculated from molar enthalpy of sublimation at 298.15 K and molar enthalpy of formation in solid phase at 298.15 K. This experimental value was compared both theoretical enthalpy of formation in gas phase by using Gaussian methods at the G3 and G4 levels and with an estimated value in relation to phthalic anhydride.

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.

Sublimation Study of Six 5-Substituted-1,10-Phenanthrolines by Knudsen Effusion Mass Loss and Solution Calorimetry.

The vapor pressures of six solid 5-X-1,10-phenanthrolines (where X = Cl, CH3, CN, OCH3, NH2, NO2) were determined in suitable temperature ranges by Knudsen Effusion Mass Loss (KEML). From the temperature dependencies of vapor pressure, the molar sublimation enthalpies, ΔcrgHm0(⟨T⟩), were calculated at the corresponding average ⟨T⟩ of the explored temperature ranges. Since to the best of our knowledge no thermochemical data seem to be available in the literature regarding these compounds, the ΔcrgHm0(⟨T⟩) values obtained by KEML experiments were adjusted to 298.15 K using a well known empirical procedure reported in the literature. The standard (p0 = 0.1 MPa) molar sublimation enthalpies, ΔcrgHm0(298.15 K), were compared with those determined using a recently proposed solution calorimetry approach, which was validated using a remarkable amount of thermochemical data of molecular compounds. For this purpose, solution enthalpies at infinite dilution of the studied 5-chloro and 5-methylphenantrolines in benzene were measured at 298.15 K. Good agreement was found between the values derived by the two different approaches, and final mean values of ΔcrgHm0(298.15 K) were recommended. Finally, the standard molar entropies and Gibbs energies of sublimation were also derived at T = 298.15 K. The volatilities of the six compounds were found to vary over a range of three orders of magnitude in the explored temperature range. The large difference in volatility was analyzed in the light of enthalpies and entropies of sublimation. The latter was tentatively put in relation to the rotational contribution of the substituent group on the phenanthroline unit.

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.

JPCRD: 50 Years of Providing the Scientific Community with Critically Evaluated Thermodynamic Data, Predictive Methods, and Large Thermodynamic Data Compilations

A brief overview is provided on articles published in the Journal of Physical and Chemical Reference Data containing experimental thermodynamic data as well as group contribution methods used to predict thermodynamic quantities of organic compounds. Published papers have contained large compilations of experimental and calculated condensed-phase and gas-phase standard molar enthalpies of formation, isobaric molar heat capacities, molar enthalpies of fusion, molar enthalpies of sublimation, and molar enthalpies of vaporization.

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.