Standard Enthalpies Of Sublimation Research Articles

Phase transition study of bathophenanthroline and bathocuproine: A multitechnique approach

The thermal behaviour of bathophenanthroline and bathocuproine has been studied using several techniques, namely, differential scanning calorimetry and thermogravimetry. To determine their respective enthalpies of sublimation, vapor pressure measurements were carried out using different methods, such as Knudsen effusion mass loss / mass spectrometry, isothermal thermogravimetry, and a quartz crystal microbalance technique. Furthermore, the enthalpies of sublimation were determined by measuring the heat change of the sublimation process using high-temperature Calvet microcalorimetry.The results obtained in this work allowed the determination of the standard molar enthalpies of sublimation at 298.15 K, for bathophenanthroline and bathocuproine. The values obtained were (183.8 ± 2.2) kJ⋅mol−1 and (206.2 ± 2.8) kJ⋅mol−1, respectively. Additionally, the standard molar enthalpies of fusion were determined to be (30.4 ± 0.4) kJ⋅mol−1 and (26.5 ± 1.6) kJ⋅mol−1 for bathophenanthroline and bathocuproine, respectively. The analysis of the results allows a deeper understanding of the phase transition behavior for these compounds from the condensed phase to the gaseous phase, elucidating molecular decomposition and the inherent intermolecular forces governing the species.

Thermodynamic parameters of L-carnosine dissolution and solvation in binary aqueous-organic mixtures at T = 298.15 K

Isothermal calorimetry was used to measure the enthalpies of L-carnosine digestion in aqueous solutions of acetonitrile (AN) 1,4-dioxane (DO), acetone (AC), dimethyl sulfoxide (DMSO), ethanol EtOH), 1-propanol (1-PrOH), and 2-propanol (2-PrOH). The values of ΔsolH° obtained were combined with the standard enthalpies of L-carnosine sublimation to obtain the corresponding enthalpies of solvation ΔsolvH°. In addition, the enthalpic coefficients of pairwise interactions (hxy) of L-carnosine with organic solvent molecules and the enthalpy of transfer (ΔtrH°) from water in their mixture with the latter were calculated. It is established that the solvation of L-carnosine is weakened in a series of (H2O + EtOH) > (H2O + 1-PrOH) > (H2O + 2-PrOH). This may be due to an increase in the hydrophobicity of alcohols of the same order as well as the presence of CH3-groups within the alcohol molecule. The weakening of the solvation energy of L-carnosine by co-solvent molecules in a series of mixed solvents: (H2O + AN) < (H2O + AC) < (H2O + DO) < (H2O + DMSO) is associated both with an increase in the hydration energy of co-solvents in the same order and with their physicochemical properties. The enthalpic coefficients of water-organic solvent pairwise interactions were discovered to be linearly related to the corresponding coefficients of L-carnosine-organic solvent interactions. An increase in the polarity and acidity of an organic solvent increases the energy of pairwise interactions between L-carnosine and the organic solvent. Increasing the cohesion energy density, molar volume, and basicity of the organic solvent reduces the energy of the pairwise interactions between L-carnosine and the organic solvent.

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.

Phase transitions properties of N,N-dimethyl-4-nitroaniline

The present work reports an experimental study aiming to determine several thermodynamic properties of fusion and sublimation of the chromophore N,N-dimethyl-4-nitroaniline. This compound is commonly used as a reference in studies focused on the non-linear optical (NLO) characteristics of chromophores. Using the Knudsen mass-loss effusion method, the vapor pressures of the crystalline phase of N,N-dimethyl-4-nitroaniline were measured over the temperature range between 341.1 K and 363.5 K. The standard molar enthalpy, entropy, and Gibbs energy of sublimation were calculated from the experimental results, at 298.15 K, and compared with those given in the literature. Differential scanning calorimetry was used to determine the temperature and enthalpy of fusion, as well as the isobaric heat capacities of the crystalline compound under study. Additionally, the enthalpic and entropic contributions to N,N-dimethyl-4-nitroaniline’s volatility were assessed, and it was determined that is greatly conditioned by enthalpic factors.

QSPR models for enthalpy and entropy of organic compounds based on a set of norm indices

In this study, quantitative structure–property relationship (QSPR) models are developed to predict the standard vapourisation enthalpy (ΔvapH°), enthalpy of fusion (ΔfusH), entropy of fusion (ΔfusS), and standard sublimation enthalpy (ΔsubH°) of organic compounds. Molecular size and shape parameters describing the structural information are introduced to improve the accuracy and robustness of the predictive effect. The correlation coefficients (R2) for ΔvapH°, ΔfusH, ΔfusS, and ΔsubH° are 0.981, 0.851, 0.888, and 0.844, respectively, and these results indicate the high accuracy of models. Because some experimental values of the ΔfusH and ΔfusS are less than average absolute error (AAE) of QSPR models, which leads to negative values by linear models, nonlinear models are proposed to mitigate this problem. Additionally, a comparison with previously published results further demonstrates that these QSPR models can achieve high precision for data set comprising numerous chemical substances. From a holistic perspective, the novel QSPR models can be widely used in multiple domains, such as chemical reaction and predesign prediction.

Determination and Analysis of Thermodynamic Properties of Methyl Methylanthranilate Isomers.

The enthalpies of formation in the gaseous phase of methyl 3-methylanthranilate and methyl 5-methylanthranilate were determined from experimental measurements of the corresponding standard energies of combustion, obtained from combustion calorimetry, and the standard enthalpies of vaporization and sublimation, obtained from Calvet microcalorimetry and Knudsen mass-loss effusion. A computational study, using the G3(MP2)//B3LYP composite method, has also been performed for the calculation of the gas-phase standard enthalpies of formation of those two molecules at T = 298.15 K, as well as for the remaining isomers, methyl 4-methylanthranilate and methyl 6-methylanthranilate. The results have been used to evaluate and analyze the energetic effect of the methyl substituent in different positions of the ring.

Thermodynamic analysis of nifedipine sublimation, dissolution and solvation

The saturated vapour pressure of the cardiovascular drug nifedipine is measured within the temperature range (390.15–404.15) K by the inert gas-carrier method. The thermodynamic functions of sublimation of the compounds are calculated at a reference temperature. The standard molar enthalpy of nifedipine sublimation is found to be equal to 144.8 kJ∙mol−1. The drug solubility in solvents modeling various media of the human body is determined in the temperature range (293.15–313.15) K. In the ascending order of solubility values of the studied compound, the solvents can be arranged as follows: buffer pH 7.4, buffer pH 2.0, n-hexane, 1-octanol. The solute–solvent intermolecular interactions are discussed based on the thermodynamic functions of solubility, solvation and transfer.

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.

Phase Transitions Equilibria of Five Dichlorinated Substituted Benzenes

This work reports an experimental study aiming to determine the thermodynamic properties of five chlorinated compounds with environmental impact. The vapor pressures of the crystalline phases of three isomers of dichlorobenzoic acid (2,4-, 2,5-, and 2,6-) and 2,6-dichlorobenzonitrile were measured at several temperatures using the Knudsen effusion technique. Another technique (a static method based on capacitance diaphragm manometers) allowed the measurement of the vapor pressures of both the crystalline and liquid phases of 2,4-dichlorobenzonitrile between 303.0 and 380.0 K. This latter technique also enabled the measurement of sublimation vapor pressures of 2,6-dichlorobenzonitrile over a larger range interval of temperatures, T = 328.7 and 391.8 K. The standard molar enthalpy, entropy, and Gibbs energy of sublimation (for all the compounds studied) and vaporization (for 2,4-dichlorobenzonitrile) were derived, at reference temperatures, from the experimental vapor pressure results. The temperatures and enthalpies of fusion and the isobaric heat capacities of the five crystalline-substituted benzenes were determined using differential scanning calorimetry. The contributions of the three substituents (-COOH, -CN, and -Cl) to the sublimation thermodynamic properties of the compounds studied were discussed.

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.

Sublimation of Drugs from the Site of Application of Topical Products.

The objective of the project was to investigate the plausibility of active pharmaceutical ingredients (APIs) to undergo sublimation from topical application following evaporation of solvent. Topical formulations with different APIs were subjected to a sublimation screening test. The APIs in the selected topical products were found to undergo sublimation to a different extent. The salicylic acid topical product was found to undergo a significant loss due to sublimation. The extent of sublimation of salicylic acid was significantly greater at skin temperature compared to room temperature. When the APIs were subjected to the sublimation screening test in their neat form at 32 ± 1 °C, the natural log of the rate of sublimation decreased linearly with the standard enthalpy of sublimation of compound (R2 = 0.89). The formulation composition was found to have a significant impact on the extent of sublimation of the representative API, salicylic acid. The sublimation of APIs from the topical product was found to affect the mass balance studies in the case of the salicylic acid ointment. Furthermore, the results of the human studies agreed with the in vitro experimental results demonstrating the plausibility of loss of API due to sublimation from the site of application.

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.

Thermodynamic properties of temozolomide in crystalline and gaseous aggregate states

Temozolomide (4-methyl-5-oxo-2,3,4,6,8-pentazabicyclo[4,3,0]nona-2,7,9-triene-9-carboxamide) is an active component of antitumor immunosuppressive alkylating drugs, and it used largely for the treatment of various types of malignant tumors, including malignant gliomas that are difficult to treat by surgery (glioblastoma multiforme and anaplastic astrocytoma). Wide field of temozolomide application dictates the need for its comprehensive thermodynamic study. In this work temperature dependance of the temozolomide heat capacity was obtained using the adiabatic calorimetry method and the standard thermodynamic functions of crystalline temozolomide were calculated in the temperature range 80–370 K. Standard thermodynamic functions of the temozolomide in the ideal gas state were calculated using the statistical thermodynamics approach in the temperature range 0–1000 K. To obtain the standard internal energy and enthalpies of combustion and formation of crystalline temozolomide at T = 298.15 K the combustion bomb calorimetry was used. Standard enthalpy of formation of the gaseous temozolomide was calculated in the framework of the isodesmic reactions method using quantum chemical computing. To calculate standard sublimation enthalpy of temozolomide the electrostatic potential model was applied. The results obtained can find application in solving problems of optimisation of temozolomide production processes and to validate experimentally obtained values of thermodynamic properties of the temozolomide.

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.