Gibbs Energies Of Sublimation Research Articles

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.

3-formylchromones: Vapor pressures and standard molar enthalpies, entropies and Gibbs energy of sublimation

In present work, the estimation of vapor pressures of 3-formylchromone and 3-formyl-6-methylchromone by the isothermal thermogravimetry method is presented. Briefly, this method consists of measuring the rate of mass loss as a function of temperature in a cylindrical cell and with a flow of nitrogen. To derive the vapor pressure, the Langmuir equation was used, from which the vaporization constant was calculated using anthracene as a calibrating compound. Subsequently, the vapor pressures 3-fromylchromone and 3-formyl-6-methylchromone were estimated. From the vapor pressure, the enthalpy of sublimation was calculated using the Clausius-Clapeyron equation for each compound at its mean sublimation temperature. Finally, the enthalpy of sublimation was calculated at T = 298.15 K. The entropy and Gibbs energy of sublimation at the same temperature were determined. In order to test the validity of the method, the vapor pressures of phenanthrene and pyrene were calculated. The values obtained by isothermal thermogravimetry agree with those reported by other techniques.

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.

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.

Study on the volatility of four benzaldehydes

This work reports the experimental determination of relevant thermodynamic properties of four benzaldehydes. The vapor pressures of both crystalline and liquid phases (including supercooled liquid) of syringaldehyde, 3,4,5-trimethoxybenzaldehyde, 4-(dimethylamino)benzaldehyde and of the liquid phase of veratraldehyde were determined using a static method based on capacitance diaphragm manometers. Additionally, the sublimation vapor pressures of the four compounds were also determined at different temperatures, using the Knudsen mass-loss effusion method. The experimental results allowed accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization for the benzaldehydes studied, at reference temperatures, allowing phase diagram representations of the (p,T) results, in the neighborhood of the triple point of the four compounds. Their temperatures and molar enthalpies of fusion were determined using differential scanning calorimetry and were compared with the ones obtained indirectly through vapor pressure measurements. Using high-precision drop calorimetry, the standard isobaric molar heat capacities of the four crystalline benzaldehydes were determined at 298.15 K. The enthalpy of the intermolecular hydrogen bond OH…O in the crystalline phase of syringaldehyde was estimated.

Formation Thermodynamics of Carbamazepine with Benzamide, Para-Hydroxybenzamide and Isonicotinamide Cocrystals: Experimental and Theoretical Study.

Formation thermodynamic parameters for three cocrystals of carbamazepine (CBZ) with structurally related coformers (benzamide (BZA), para-hydroxybenzamide (4-OH-BZA) and isonicotinamide (INAM)) were determined by experimental (cocrystal solubility and competitive reaction methods) and computational techniques. The experimental solubility values of cocrystal components at eutectic points and solubility product of cocrystals [CBZ + BZA], [CBZ + 4-OH-BZA], and [CBZ + INAM] in acetonitrile at 293.15 K, 298.15 K, 303.15 K, 308.15 K, and 313.15 K were measured. All the thermodynamic functions (Gibbs free energy, enthalpy, and entropy) of cocrystals formation were evaluated from the experimental data. The crystal structure of [CBZ + BZA] (1:1) cocrystal was solved and analyzed by the single crystal X-ray diffractometry. A correlation between the solubility products and pure coformers solubility values has been found for CBZ cocrystals. The relationship between the entropy term and the molecular volume of the cocrystal formation has been revealed. The effectiveness of the estimation of the cocrystal formation thermodynamic parameters, based on the knowledge of the melting temperatures of active pharmaceutical ingredients, coformers, cocrystals, as well as the sublimation Gibbs energies and enthalpies of the individual components, was proven. A new method for the comparative assessment of the cocrystal stability based on the H-bond propensity analysis was proposed. The experimental and theoretical results on the thermodynamic parameters of the cocrystal formation were shown to be in good agreement. According to the thermodynamic stability, the studied cocrystals can be arranged in the following order: [CBZ + 4-OH-BZA] > [CBZ + BZA] > [CBZ + INAM].

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.

Thermodynamic Stability of Fenclorim and Clopyralid.

The present work reports an experimental thermodynamic study of two nitrogen heterocyclic organic compounds, fenclorim and clopyralid, that have been used as herbicides. The sublimation vapor pressures of fenclorim (4,6-dichloro-2-phenylpyrimidine) and of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were measured, at different temperatures, using a Knudsen mass-loss effusion technique. The vapor pressures of both crystalline and liquid (including supercooled liquid) phases of fenclorim were also determined using a static method based on capacitance diaphragm manometers. The experimental results enabled accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation for both compounds and of vaporization for fenclorim, allowing a phase diagram representation of the (p,T) results, in the neighborhood of the triple point of this compound. The temperatures and molar enthalpies of fusion of the two compounds studied were determined using differential scanning calorimetry. The standard isobaric molar heat capacities of the two crystalline compounds were determined at 298.15 K, using drop calorimetry. The gas phase thermodynamic properties of the two compounds were estimated through ab initio calculations, at the G3(MP2)//B3LYP level, and their thermodynamic stability was evaluated in the gaseous and crystalline phases, considering the calculated values of the standard Gibbs energies of formation, at 298.15 K. All these data, together with other physical and chemical properties, will be useful to predict the mobility and environmental distribution of these two compounds.

Predicting aqueous solubility by QSPR modeling

The aqueous solubility is predicted here using quantitative structure property relationship (QSPR) models. In this study, we examine whether descriptors that individually yield favorable models for the prediction of the Gibbs energy of solvation and sublimation can be used in combination with octanol-water partition coefficient to produce QSPR models for the prediction of aqueous solubility. Based on this strategy, applied to seven distinct datasets, all models exhibited an R2 greater than 0.7 and Q2 greater than 0.6 for the estimation of aqueous solubility. We also determined how uncoupling the descriptors used to create QSPR models in the prediction of Gibbs energy of sublimation yielded an improved model. Model refinement using an artificial neural network applying the same descriptors generated significantly better models with improved R2 and standard deviation.

Sublimation thermodynamics of pyrazinoic, dipicolinic and quinolinic acids: Experiment and theoretical prediction

The thermophysical characteristics and decomposition of pyrazinoic (POA), dipicolinic (DPA), and quinolinic (QNA) acids have been studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and mass-spectrometry. The transpiration method has been used to measure the vapour pressures as a function of the POA, DPA or QNA temperature. It has been found that QNA remains thermally stable in the solid form up to the temperature of 367.15 K, and further heating causes its decarboxylation and irreversible conversion to nicotinic acid. The standard molar enthalpies, entropies, and Gibbs energies of sublimation for POA, DPA and QNA have been calculated. A comparative study of five calculation schemes for sublimation enthalpy estimation (periodic Density Functional Theory computations (DFT-D3), Quantum Theory of Atoms in Molecules (QTAIM), Gavezzotti’s Coulomb-London-Pauli model (CLP and PIXEL) and CrystalExplorer CE-B3LYP) has been conducted. The sublimation thermodynamic functions of the compounds studied by the correlation method have been estimated. When applied to the objects of this study, the method proved to be a quick, convenient and inexpensive way to evaluate the sublimation thermodynamic functions of molecular crystals using only the melting temperature of the compound.

Thermodynamic properties of Nalidixic and Oxolinic acids: Experimental and computational study

The thermophysical characteristics of nalidixic (NLD) and oxolinic (OXL) acids have been determined by DSC. The fusion processes of the studied compounds have been analyzed by mass-spectrometry. The transpiration method has been used to measure the vapor pressures as a function of NLD temperature. Based on these results, the standard molar enthalpy, entropy and Gibbs energy of sublimation at T =298.15 K have been calculated. A comparative study of theoretical methods of sublimation enthalpy estimation has been conducted including correlation analysis, periodic DFT computations and additive schemes based on QTAIMC descriptors and Coulomb-London-Pauli model. The thermodynamic parameters of the OXL sublimation have been estimated.

Thermodynamic Properties of Moldy-Musty Contaminants of Wine

This paper reports thermodynamic properties of phase transitions of 2,4,6-trichloro and 2,4,6-tribromo anisoles and of 2,4,6-tribromophenol. The vapor pressures of both crystalline and liquid phases (including supercooled liquid) of the three compounds were measured, respectively, in the temperature ranges T = (297.1 to 368.3) K, T = (330.7 to 391.7) K, and T = (336.5 to 401.7) K, using a static method based on capacitance diaphragm manometers. Moreover, the sublimation vapor pressures of 2,4,6-tribromophenol were also measured in the temperature interval (307.2 to 329.2) K, using a Knudsen mass-loss effusion technique. The standard molar enthalpies, entropies, and Gibbs energies of sublimation and of vaporization, at reference temperatures, were derived from the experimental results as well as the (p,T) values of the triple point of each compound. The temperatures and molar enthalpies of fusion of the three benzene derivatives were determined using differential scanning calorimetry and were compared with...

Thermodynamic properties of phase transitions of phenyl derivatives of maleic anhydride and oxazole

An experimental study of the vapour pressures and related thermodynamic properties of three phenyl derivatives of maleic anhydride and oxazole is reported. The vapour pressures of the crystalline phase of these compounds were measured at different temperatures using the Knudsen mass-loss effusion method, enabling the determination of the standard (p° = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation. The enthalpies and temperatures of fusion were determined from DSC experiments. Quantum chemical calculations were used to calculate gas-phase isobaric heat capacities and absolute entropies.

Vapour pressures and thermodynamic stability of the three aminophenol isomers

The Knudsen mass-loss effusion method was used to determine the sublimation vapour pressures, at different temperatures, of ortho and para aminophenols in the temperature intervals T = (321.1 to 343.3) K and T = (337.2 to 359.2) K, respectively. The vapour pressures of crystalline meta-aminophenol were measured using the referred to above technique, between (321.4 and 343.3) K, and a static method, based on capacitance diaphragm manometers, between (354.4 and 391.8) K. The latter technique was also used to measure the liquid vapour pressures of this isomer over the temperature range T = (370.0 to 423.3) K. The experimental results enabled the determination of the standard (po = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, of the three compounds, and of vaporization of the meta isomer. The standard enthalpies of formation in the gaseous phase were calculated using quantum chemical calculations and also by combining literature results of enthalpies of formation in the crystalline phase with the sublimation enthalpies results determined in this work. Gas-phase absolute entropies and heat capacities of the three compounds studied were also calculated using theoretical methods. The standard Gibbs energies of formation in crystalline and gaseous phases were determined and used to evaluate the thermodynamic stability of the three isomers in standard conditions. DSC analysis enabled the determination of the temperature and molar enthalpies of fusion of the compounds studied.

Volatility and thermodynamic stability of vanillin

Vanillin is a naturally occurring phenolic aldehyde that is world-wide known for its flavouring properties. This work reports an extensive experimental and computational study of its thermodynamic properties. The vapour pressures of crystalline and liquid phases of vanillin were measured in the following temperature ranges T = (321.0–350.7) K and (324.9–382.3) K respectively, using a static method based on diaphragm capacitance gauge. Additionally, the crystalline vapour pressures were also measured in the temperature interval T = (303.1–325.2) K, using a Knudsen mass-loss effusion technique. The standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization, at selected reference temperatures, were derived from the vapour pressure measurements. The enthalpies of vaporization and of sublimation, at T = 298.15 K, were also determined using Calvet microcalorimetry and the standard (p° = 105 Pa) molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, was derived from its standard massic energy of combustion measured by static-bomb combustion calorimetry. From the experimental results, the standard molar enthalpy of formation in the gaseous phase, at T = 298.15 K, was calculated and compared with the values estimated by employing quantum chemical calculations. To analyse the thermodynamic stability of vanillin, the standard Gibbs energies of formation in crystalline and gaseous phases were calculated. The molar enthalpy of fusion determined using DSC is compared with indirect results determined using Calvet microcalorimetry and vapour pressure measurements.

Predicting the Enthalpy and Gibbs Energy of Sublimation by QSPR Modeling

The enthalpy and Gibbs energy of sublimation are predicted using quantitative structure property relationship (QSPR) models. In this study, we compare several approaches previously reported in the literature for predicting the enthalpy of sublimation. These models, which were reproduced successfully, exhibit high correlation coefficients, in the range 0.82 to 0.97. There are significantly fewer examples of QSPR models currently described in the literature that predict the Gibbs energy of sublimation; here we describe several models that build upon the previous models for predicting the enthalpy of sublimation. The most robust and predictive model constructed using multiple linear regression, with the fewest number of descriptors for estimating this property, was obtained with an R2 of the training set of 0.71, an R2 of the test set of 0.62, and a standard deviation of 9.1 kJ mol−1. This model could be improved by training using a neural network, yielding an R2 of the training and test sets of 0.80 and 0.63, respectively, and a standard deviation of 8.9 kJ mol−1.

Estimations of the thermodynamic properties of halogenated benzenes as they relate to their environment mobility

In this work, several simple new equations for predicting important environmental mobility properties, at T = 298.15 K, were derived for halogenated benzenes: standard Gibbs energy of hydration, aqueous solubility, octanol-water partition coefficients, and Henry's law constants. A discussion on our previous estimates of other related properties (standard Gibbs energy and vapor pressure of sublimation and of vaporization) and their relation with entropy of fusion is also presented. As we aimed to estimate these properties for any of the ca. 1500 halogenated benzenes that may exist theoretically, an equation for estimating the temperature of fusion was also derived, since some of the proposed predictive equations (solubility of solids and Gibbs energy of sublimation) require its knowledge. For the other estimated properties just the number of each halogen that replaces hydrogen atoms in the halogenated benzene is needed. It was found that the coefficients that multiply the number of halogen atoms in the predictive equations vary linearly with the volume of the halogen atom.

Prediction of Sublimation Functions of Molecular Crystals Based on Melting Points: Cocrystal Formation Thermodynamics Application

On the basis of the values contained in the literature published in 1900–2016, we have developed an experimental database including sublimation Gibbs energies, enthalpies, and melting temperatures of 1515 compounds. We have also suggested an algorithm of database fragmentation which includes groups/clusters with structurally similar compounds. For this aim we used Tanimoto similarity coefficients. Clusterization was carried out for each substance of the test set. All the points within a cluster were smoothed by a linear function in the coordinates of Gibbs energy vs melting temperature. Using the training and test sets, it has been shown that the algorithm suggested by us describes experimental data well (rms = 3.89 kJ·mol–1). We have developed quantitative structure–property relationship models based on HYBOT physicochemical descriptors and melting points in order to predict sublimation Gibbs energies and enthalpies of molecular crystals. The developed approach was applied to determine cocrystal formatio...

Vapour pressures, enthalpies and Gibbs energies of formation and sublimation of fluorene-2-carboxaldehyde

This work presents a comprehensive experimental and computational study of the thermodynamic properties of fluorene-2-carboxaldehyde. The crystal vapour pressures of this compound were measured between (335.16 and 355.09)K, using the Knudsen mass-loss effusion method. From these results the standard molar enthalpies, entropies and Gibbs energies of sublimation were derived. The standard molar enthalpy of formation in the crystalline phase at the temperature 298.15K was derived from the standard molar energy of combustion, determined from combustion calorimetry measurements. This result was combined with the enthalpy of sublimation yielding the standard molar enthalpy of formation in the gaseous phase at T=298.15K, that was also derived from a computational study at the G3 and G4 levels. Theoretical calculations were also used to calculate heat capacity and entropy results in the gaseous phase. The enthalpy and temperature of fusion were determined from DSC experiments. From the thermodynamic properties of fusion and sublimation, those of vaporization were derived.The thermodynamic stability of fluorene-2-carboxaldehyde in the crystalline and gaseous phases was evaluated determining the standard Gibbs energies of formation, at the temperature 298.15K, and compared with the ones reported in the literature for fluorene.

Vapour pressures and phase transition properties of four substituted acetophenones

This paper reports experimental vapour pressures at different temperatures of four substituted acetophenones. Using the diaphragm manometer static method, the vapour pressures of both (crystalline and liquid) condensed phases of ortho and para acetoxyacetophenones and also of para-methoxyacetophenone were measured in the following temperatures ranges T=(313.0–398.0)K, (315.0–378.3)K and (296.2–355.7)K, respectively. This experimental technique was also used to measure the vapour pressures of the liquid phase of meta-acetoxyacetophenone through the temperature interval T=(305.1–368.5)K. The vapour pressures of the crystalline phase of meta-acetoxyacetophenone were measured using the Knudsen effusion technique over the temperature ranges, T=(297.7–307.3)K. This technique was also used for complementing the range of the vapour pressure measurements of the ortho and para acetoxyacetophenone isomers between T=(298.0–321.3)K and (298.1–309.3)K, respectively. The standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization, at references temperatures, were derived from the experimental results. Differential scanning calorimetry was used to determine the temperatures and molar enthalpies of fusion and of the observed crystalline transitions. The contributions of the acetoxy and acetyl groups to the sublimation properties of the compounds studied were calculated.