Academic literature on the topic 'Enthalpy of solvation'

The structure parameters around the Cu(I) ion in pyridine (PY), 4-methylpyridine (4MPY), 2-methylpyridine (2MPY), 2,6-dimethylpyridine (26DMPY), and acetonitrile (AN) were determined by the extended X-ray absorption fine structure (EXAFS) method. The solvation structures of the Cu(I) ion in PY, 4MPY, and AN are 4-coordinate tetrahedral with Cu-N bond lengths of 205, 205, and 200 pm, respectively. In the case of 2MPY and 26DMPY, the Cu(I) ion has a 3-coordinate triangular structure with a Cu-N bond length of 201 pm. Such a decrease in the coordination number was interpreted in terms of the bulkiness of the solvent molecules. In order to clarify the most stable solvation structure of the Cu(I) ion, we carried out ab initio molecular orbital calculations for the solvation system of [Cu(NCH)n]+ (n = 1 - 6 ) where the steric effect is negligible. The Gibbs free energy of solvation was the smallest in the case of n = 4 and the 4-coordinate tetrahedral solvation of the Cu(I) ion was theoretically evaluated as most stable. The enthalpy of solvation monotonously decreases with increasing n, while the entropy of solvation proportionally increases. Although a larger gain of enthalpy is observed for the octahedral structure rather than the tetrahedral one, the entropic loss for the former overcomes the enthalpic gain.

The process of ion solvation has been studied in the reversible system using the Van't Hoff equilibrium box. It is shown that the Born formula for solvation energy describes a change in enthalpy rather than in Gibbs energy.

The process of interaction between ions of a solute and the molecules of the solvent through relatively weak covalent bonds is called solvation. It involves evening out a concentration gradient and evenly distributing the solute molecules within the solvent. Hydration is a special case of solvation when the solvent molecules are water. Solvation energy, generally, is the energy released when ions in crystal lattices associate with molecules in a solvent, however it can be positive or negative, depending upon the combined effects of lattice and hydration energies in case of aqueous-ionic solid dissolution. Uranous chloride or uranium tetrachloride (UCl4) is a green crystalline solid which sublimes in vacuum at 500°C/10-3 mm. It is a Lewis acid and hence dissolves in solvents which can act as non-protic Lewis bases. Although dissolution of uranium tetrachloride crystals in water is an exothermic process yielding a green solution which is fairly stable in the cold, yet is hydrolyzed to a considerable extent to furnish an acidic reaction. Solvation enthalpies of quadrivalent uranium system have been scantly reported. The present communication deals with the calculation of enthalpy of solution of uranium tetrachloride in aqueous-non-aqueous solvent mixtures, particularly in 10 and 20 weight (wt) % methyl alcohol-water and ethyl alcohol-water systems at 25°C calorimetrically and thereby estimating the solvation enthalpy of UCl4 in the said media.

The application of an extended version of the generalized Born formula including dielectric saturation effects, implemented within the SCF-CNDO/2 approximation, provides a complete set of data concerning the thermodynamics of solvation of some ammonium ions in water. The calculated free energies of solvation are in good agreement with experimental data. An estimation of the entropy and enthalpy of solvation is also given and satisfactory qualitative trends are obtained.

Predictive methods have been employed to characterize chemical separation mediums including solvents and absorbents. These studies included creating Abraham solvation parameter models for room-temperature ionic liquids (RTILs) utilizing novel ion-specific and group contribution methodologies, polydimethyl siloxane (PDMS) utilizing standard methodology, and the micelles cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) utilizing a combined experimental setup methodology with indicator variables. These predictive models allows for the characterization of both standard and new chemicals for use in chemical separations including gas chromatography (GC), solid phase microextraction (SPME), and micellar electrokinetic chromatography (MEKC). Gas-to-RTIL and water-to-RTIL predictive models were created with a standard deviation of 0.112 and 0.139 log units, respectively, for the ion-specific model and with a standard deviation of 0.155 and 0.177 log units, respectively, for the group contribution fragment method. Enthalpy of solvation for solutes dissolved into ionic liquids predictive models were created with ion-specific coefficients to within standard deviations of 1.7 kJ/mol. These models allow for the characterization of studied ionic liquids as well as prediction of solute-solvent properties of previously unstudied ionic liquids. Predictive models were created for the logarithm of solute's gas-to-fiber sorption and water-to-fiber sorption coefficient for polydimethyl siloxane for wet and dry conditions. These models were created to standard deviations of 0.198 and 0.122 logunits for gas-to-PDMS wet and dry, respectively, as well as 0.164 and 0.134 log units for water-to-PDMS wet and dry, respectively. These models are particularly useful in solid phase microextraction separations. Micelles were studied to create predictive models of the measured micelle-water partition coefficient as well as models of measured MEKC chromatographic retention factors for CTAB and SDS. The resultant predictive models were created with standard deviations of 0.190 log units for the logarithm of the mole fraction concentration of water-to-CTAB, 0.171 log units for the combined logarithms of both the mole fraction concentration of water-to-CTAB and measured MEKC chromatographic retention factors for CTAB, and 0.153 log units for the combined logarithms of both the mole fraction concentration of water-to-SDS and measured MEKC chromatographic retention factors for SDS.

The Abraham Solvation Parameter Model (ASPM) is a linear, free-energy relationship that can be used to predict various solute properties based on solute-solvent interactions. The ASPM has been used to predict log (K or Cs,organic/Cs,gas) values, as well as log (P or Cs,organic/Cs,water) values for solute transfer into the following organic solvents: 2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, 2-isopropoxyethanol and 2-butoxyethanol. The derived log (K or Cs,organic/Cs,gas) correlations describe the experimental data to within 0.14 log units (or less). The derived log (P or Cs,organic/Cs,water) correlations describe the experimental data to within 0.16 log units (or less). The ASPM has also been used to predict the enthalpies of solvation of organic solutes dissolved in the following solvents: acetic acid, dimethyl carbonate, diethyl carbonate, 1-butanol, 1-pentanol, 1-hexanol. The derived enthalpy of solvation correlations, using the L solute descriptor, describe the experimental data to within 2.50 log units (or less). The derived enthalpy of solvation correlations, using the V solute descriptor, describe the experimental data to within 3.10 log units (or less). Validation analyses have been performed on several of the correlations; and, as long as the solute descriptors fall within the given ranges as reported, the original correlations show good predictive ability for determining 1) solute transfer into, and 2) enthalpy of solvation for the aforementioned solvents.

Methode microcalorimetrique permettant la mesure des enthalpries de complexation par bf::(3) de molecules organiques en solution, appartenant a des familles modeles (pyridines, composes carbonyles, nitrites) ou communement utilises comme solvants.

Experimental data were obtained for the computation of mole fraction solubilities of three dichloronitrobenzenes in organic solvents at 25oC, and solubility ratios were obtained from this data. Abraham model equations were developed for solutes in tributyl phosphate that describe experimental values to within 0.15 log units, and correlations were made to describe solute partitioning in systems that contain either "wet" or "dry" tributyl phosphate. Abraham model correlations have also been developed for solute transfer into anhydrous diisopropyl ether, and these correlations fit in well with those for other ethers. Abraham correlations for the solvation of enthalpy have been derived from experimental and literature data for mesitylene, p-xylene, chlorobenzene, and 1,2-dichlorobenzene at 298.15 K. In addition, the enthalpy contribution of hydrogen bonding between these solutes and acidic solvents were predicted by these correlations and were in agreement with an established method. Residual plots corresponding to Abraham models developed in all of these studies were analyzed for trends in error between experimental and calculated values.

L'objectif de ce travail est d'étudier et de contribuer à améliorer la capacité des liquides ioniques pour l'absorption sélective de dioxyde de carbone. Pour cela nous avons envisagé la fluorination partielle des cations ou des anions constituant les liquides ioniques. Nous avons sélectionné des liquides ioniques partiellement fluorés à étudier, dont trois ont été synthétisés dans ce travail. Dans un premier temps, nous avons étudié l'impact de la structure des liquides ioniques purs sur leurs propriétés thermophysiques telles que la masse volumique, la viscosité et la stabilité thermique. Dans un deuxième temps, nous avons étudié les propriétés thermodynamiques de mélanges des liquides ioniques avec des gaz ou des liquides. La miscibilité de l'eau a ainsi été étudiée en fonction de la température. Nous avons mesuré la solubilité de cinq gaz (dioxyde de carbone, protoxyde d'azote, éthane, azote, hydrogène) dans les liquides ioniques, pour des températures comprises entre 298 K et 343 K et des pressions proches de la pression atmosphérique. La simulation moléculaire a été utilisée afin d'identifier les sites préférentiels de solvatation de dioxyde de carbone et d'éthane, et de proposer des mécanismes moléculaires de solvatation de ces gaz. Les coefficients de diffusion du dioxyde de carbone et de l'éthane dans les liquides ioniques ont été calculés. Nous avons déterminé l'enthalpie de solution et la limite de solubilité du dioxyde de carbone en fonction de la pression à 313 K utilisant une technique calorimétrique à écoulement.

Etude de la solvatation des especes resultant de l'inclusion d'un cation metallique dans la cavite d'un coordinat macrobicyclique, par la mesure des parametres thermodynamiques. Specificite des differents complexes du 222

Les réactions d’oxydation d’hydrocarbures en phase liquide (aussi appelées auto-oxydation) jouent un rôle essentiel dans un grand nombre de procédés de l’industrie pétrochimique car elles assurent la conversion du pétrole en composés chimiques organiques valorisables. Elles régissent également la stabilité à l’oxydation des carburants (vieillissement) et des produits chimiques dérivés du pétrole. Ces réactions d’oxydation en phase liquide relèvent de mécanismes radicalaires en chaîne impliquant des milliers d’espèces et de réactions élémentaires. La modélisation cinétique de tels systèmes reste actuellement un défi car elle nécessite de disposer de données thermodynamiques et cinétiques précises, qui sont rares dans la littérature. Le logiciel EXGAS, développé au LRGP, permet de générer automatiquement des modèles cinétiques détaillés pour des réactions d’oxydation d’hydrocarbures en phase gazeuse. Qu’il s’agisse d’une phase gazeuse ou liquide, les réactions élémentaires mises en jeu sont de même nature et la méthodologie de génération du mécanisme est la même. Pour passer d’un mécanisme en phase gaz à un mécanisme en phase liquide il convient d’adapter les valeurs des constantes d’équilibre et de vitesse (appelées constantes thermocinétiques) des réactions du mécanisme. L’objectif de cette thèse est de proposer une méthode pour corriger les constantes thermocinétiques de la phase gaz pour qu’elles deviennent applicables à la phase liquide. Cette correction fait intervenir une grandeur appelée énergie de GIBBS de solvatation molaire partielle. Une analyse de la définition précise de cette quantité nous a permis de montrer qu’elle s’exprime simplement en fonction d’un coefficient de fugacité et d’une densité molaire. Nous avons ensuite relié cette grandeur à des quantités thermodynamiques mesurables (coefficients d’activité, constantes de HENRY …) et nous nous sommes appuyés sur toutes les données qu’il nous a été possible de trouver dans la littérature pour créer la banque de données expérimentales d’énergies de GIBBS de solvatation molaires partielles la plus complète (intitulée CompSol). Cette banque de données a ensuite servi à valider l’utilisation de l’équation d’état UMR-PRU pour prédire ces énergies. Les bases d’une équation d’état de type SAFT, au paramétrage original, développé dans le cadre de cette thèse, ont été posées. Notre objectif était de simplifier l’estimation des paramètres corps purs de cette équation d’état en proposant une méthode de paramétrage ne nécessitant aucune procédure d’optimisation, claire et reproductible, à partir de données très facilement accessibles dans la littérature. Cette équation a été utilisée pour estimer les énergies de GIBBS de solvatation molaires des corps purs et les énergies de GIBBS de solvatation molaires partielles de systèmes {soluté+solvant}. Enfin, ces méthodes d’estimation des énergies de GIBBS de solvatation molaires partielles ont été combinées au logiciel EXGAS afin de modéliser l’oxydation du n-butane en phase liquide<br>Liquid phase oxidation of hydrocarbons (also called autoxidation) is central to a large number of processes in the petrochemical industry as it plays a key role in the conversion of petroleum feedstock into valuable organic chemicals. This phenomenon is also crucial in oxidation-stability studies of fuels and its derivatives (aging). These liquid-phase oxidation reactions entail radical mechanisms involving more than thousands of compounds and elementary reactions. Kinetic modelling of these kinds of reactions remains a significant challenge because it requires thermodynamic and kinetic parameters, which are not abundant in literature. The EXGAS software, developed at LRGP, is able to generate these kinds of models but only for oxidation reactions taking place in a gaseous phase. It is assumed that the nature of elementary reactions in the liquid and gaseous phases is the same. The unique need to transfer a kinetic mechanism from a gas phase to a liquid phase is to update kinetic rate constant values and equilibrium constant values (called thermokinetic constants) of mechanism reactions. Therefore, in the framework of this PhD thesis, a new method aimed at applying a correction term to thermokinetic constants of gaseous phases is proposed in order to obtain constants usable to describe liquid-phase mechanisms. This correction involves a quantity called partial molar solvation GIBBS energy. An analysis of the precise definition of this property led us to conclude that it can be simply expressed as a function of fugacity coefficients and liquid molar density. As a result, this property could also be expressed with respect to measurable thermodynamic quantities as activity coefficients or HENRY’s law constants. By combining all the experimental data related to these measurable properties that can be found in the literature, it was possible to develop a comprehensive databank of partial molar solvation GIBBS energies (called the CompSol database). This database was used to validate the use of the UMR-PRU equation of state to predict solvation quantities. Moreover, the bases of a new parameterization for SAFT-type equations of state were laid. It consists in estimating pure-component parameters of SAFT-like equation using a very simple, reproducible and transparent path for non-associating pure components. This equation was used to calculate partial molar GIBBS energy of solvation of pure and mixed solutes. Last, equations of state were combined with EXGAS software to model the oxidation of n-butane in the liquid phase

Les concepts de surfaces de Van der Waals et accessibles au solvant sont définis ainsi que les techniques courantes de calcul, en présentant la nouvelle méthode développée dans ce travail. Des points, appelés sondes, sont placés autour de chaque noyau atomique par des constructions vectorielles spécifiques, qui dépendent de l'hybridation et du nombre de ligands. Des équivalents de surface sont associés aux sondes. Une fonction de la distance permet de calculer un facteur d'occlusion traduisant le degré de recouvrement des surfaces en fonction des sphères atomiques voisines. On montre que le produit des facteurs d'occlusion équivaut à un traitement probabiliste du calcul de la surface exposée d'un atome. Pour chaque étape géométrique et analytique, un paramètre est introduit pour ajuster au mieux le modèle aux surfaces exactes calculées avec un programme de référence, pour une bibliothèque de molécules représentatives. On établit la dérivée première par rapport à chacune des directions de l'espace moléculaire pour toute relation mathématique intervenant dans le modèle. En combinant les surfaces analytiques et des descripteurs structuraux, on propose en modèle pour le calcul des enthalpies libres d'hydratation de la phase gazeuse à une solution aqueuse diluée, de petites molécules organiques. Un autre ajustage des paramètres permet d'adapter ce modèle au calcul des coefficients de partage octanol/eau et des enthalpies libres de solvatation dans l'octanol. Le grand nombre de coefficients de partage expérimentaux permet d'améliorer le modèle, et de rechercher des jeux de paramètres extensifs pour une meilleure modélisation de la solvatation dans des solvants polaires ou non polaires

La production de bio-huiles par conversion thermochimique de la biomasse estun procédé prometteur pour le bio-raffinage. Alors que la cinétique en phase gazeuse de la conversion de la bio-huile est bien avancée, sa réactivité en phase liquide reste mal connue.L’objectif de cette thèse est de comprendre le mécanisme cinétique détaillé de la décomposition thermochimique de la biomasse à basse température en phase liquide. Comme indiqué par Basu et al. (June 2010) et Nakamura et al. (2007a,b)et Kawamoto (2017), une phase liquide est observée pendant la première étape de la pyrolyse de la biomasse. Dans cette étude, nous tenterons de modéliser le premier stade de la pyrolyse de la biomasse. A notre connaissance, aucune étude de modélisation de la réactivité en phase liquide n’a été proposée pour la pyrolyse de la biomasse. L’étude des réactions en phase liquide de ces systèmes complexes nécessite une bonne connaissance de l’influence du solvant sur la cinétique. Nous avons en premier temps comparé la prédiction des modèles COSMO-SAC avec celles du modèle de solvatation Abraham, en considérant la base de données COMPSOL de Moine et al. (2017) comme données de référence. Nous avons ensuite proposé une re-paramétrisation de ces modèles COSMO-SAC qui conduit à de bien meilleures prédictions et nous permets d’étendre ces modèles à l’utilisation des cavités CPCM (Nait Saidi et al. (2020)). Les méthodes prédictives basées sur des calculs ab initio peuvent être très précises pour prédire les propriétés thermochimiques en phase gazeuse et sont généralement plus polyvalentes que les méthodes de contribution de groupe. Une extension de la méthode ab initio de prédiction des enthalpies de formation de Paulechka et Kazakov (2017) a été proposée dans ce travail (Mielczarek et al. (2019)) et utilisée pour les composés de la biomasse. En troisième partie de cette étude, nous avons prédit les différents chemins réactionnels possibles de la décomposition des composés représentatifs de la partie lignine de la biomasse à l’aide du générateur de mécanismes réactionnels (RMG). Les composés choisis sont le créosol, le gaïacol et le méthoxy vinylphénol. Ce travail peut être considéré comme une extension du mécanisme en phase gazeuse de la pyrolyse proposé par Ranzi et al.(2017a,b) en considérant la recombinaison radicalaire et la polymérisation qui se produit à basse température entre100°C et 300°C. Pour modéliser la cinétique des réactions clés, nous les avons étudiés par l’approche des états de transition à l’aide de Gaussian09 et d’ORCA. L’estimation des paramètres cinétiques est ensuite déterminé par la théorie des états de transition à l'aide du Kisthelp tool (Canneaux et al. (2014)) pour la cinétique en phase gazeuse et cinétique en phase liquide à partir de l’approche Green (Jalan et al. July 2013)<br>Production of bio-oils through thermochemical biomass conversion is a promising process for biorefining. While gas phase kinetics of bio-oil conversion has been improving, its liquid phase reactivity is currently poorly understood. The aim work of my thesis is about the understanding of detailed kinetics mechanism of biomass thermochemical decomposition at low temperature range in the liquid phase. As mentionned by Basu (June 2010); Nakamura et al. (2007a,b); Kawamoto (2017) a liquid phase is observed during the initial stage of biomass pyrolysis. In this study, we will try to model the initial stage of biomass pyrolysis. To our knowledge, no modelling study of the rate of reactions in the liquid phase has been proposed for biomass pyrolysis. The investigation of liquid phase reactions of such complex systems requires a good knowledge of solvent effects. We compared the prediction capabilities of COSMO-SAC with those of the Abraham solvation model, by considering the COMPSOL database of Moine (2017) as the reference data. We then proposed a re-parametrization of these COSMO-SAC models that leads to much better predictions, and extended these models to CPCM cavities(Nait Saidi et al. (2020)). Predictive methods based on ab initio calculations can be very accurate for predicting gas phase thermochemical properties and are usually more versatile than group contribution methods. An extension of Paulechka and Kazakov (2017) ab initio prediction method of enthalpies of formation was proposed in this study (Mielczarek et al. (2019)) and used for biomass compounds. We then used Reaction Mechanism Generator (RMG) to investigate the possible reaction mechanism of different Tar surrogate compounds of biomass decomposition. The surrogate compounds that we chose are Creosol, guaiacol and methoxy vinylphenol to model the lignin. This work can be considered as an extension of the gas phase reaction mechanism of pyrolysis proposed by Ranzi(2017a,b) taking in consideration the primary tar recombination/polymerisation reaction that occur in the temperature range 100°C to 300°C.To model the kinetics of the key reaction, we investigated the transitional state using Gaussian 09 and ORCA. We then estimated the kinetics parameters using Transitional State Theory with Kisthelp tool (Canneauxet al. (2014)) and liquid phase kinetics approach based on the gas phase kinetics and solvation free energies correction (Jalan et al. July 2013)

Electrochemical measurements have been playing an increasingly important role in the thermodynamic study of reactions in solution, not only because they provide data that are difficult (or even impossible) to obtain by other methods but also because these data can often be compared with the values determined for the analogous gas-phase reactions, thus yielding information on solvation energetics. Figure 16.1 was adapted from a scheme proposed by Griller et al. It summarizes the thermochemical information on the R–X bond that can be probed by electrochemical methods. The vertical arrows represent homolytic cleavages, and the horizontal arrows depict reduction or oxidation potentials. The authors have appropriately called the scheme in figure 16.1 a “mnemonic,” rather than a “thermochemical cycle,” because not all arrow combinations define thermochemical cycles. This can be made more clear by inspecting figure 16.2, where true thermochemical cycles are defined. For example, the enthalpy of reaction 7 is not the sum of the enthalpies of reactions 1 and 4 (as might be suggested by figure 16.1) but their sum minus the enthalpy of reaction 12. In fact, true thermochemical cycles in figure 16.1 can only be defined by considering parallelograms confined either to the upper or the lower part of the mnemonic. For instance, the enthalpy of reaction 7 is given by the enthalpy of reaction 4 plus the enthalpy of reaction 9 minus the enthalpy of reaction 3, but it is not equal to the enthalpy of reaction 6 minus the enthalpy of reaction 11 plus the enthalpy of reaction 10. Also, the enthalpy of reaction 1 (the homolytic dissociation of the R–X bond in the neutral molecule RX) can be given by the sum of the enthalpies or reaction 5 and 11 minus the enthalpy of reaction 3 or, for example, by the sum of the enthalpies of reactions 7 and 12 minus the enthalpy of reaction 4. The attractive feature of the mnemonic in figure 16.1 (or the thermochemical cycles in figure 16.2) is that it depicts the seven possible R–X cleavage reactions of RX, RX−, and RX+, as well as their relationships.

In any reversible reaction such as . . . vA A + vB B ↔ vR R + vS S [2.1] . . . the system inevitably moves toward a state of equilibrium, or maximum probability. This equilibrium state is very important in analyzing chemical reactions because it defines the limit to which any reaction can proceed. Organic reactions, particularly those constituting a synthetic scheme for a fine chemical, usually involve molecules reacting in the liquid phase. The effects of reactant structure and of the solvent (medium) in which the reaction occurs (the solvation effects) are not included in the conventional macroscopic approach to thermodynamics. Therefore, the treatment of liquid-phase reactions tends to be less exact than that of gas-phase reactions involving simpler molecules without these influences. A convenient way of approaching this problem is to start with the conventional macroscopic or thermodynamic approach and add enough microscopic detail to allow for the effects of solute (reactant) structure and the medium. This approach is called the extrathermodynamic approach and may be regarded as bridging the gap between the two rather disparate fields of rates and equilibria represented by kinetics and thermodynamics, respectively. Such an approach is particularly useful in organic synthesis and forms the subject matter of this chapter. An important consideration in process calculations is the change that results in the basic thermodynamic properties, internal energy (U), enthalpy (H), Helmholtz work function (A), and Gibbs free energy (G) when a closed system of constant mass moves from one macroscopic state to another. For a homogeneous fluid, these change equations can be expressed in terms of four differential equations, which then can be written in difference form by employing the operator Δ to represent the change from state 1 to state 2: Of these, the enthalpy and free energy change equations are the most frequently used in the analysis of reactions.

In this work, molecular dynamics simulation (MD) was used to study the encapsulation of fat-soluble vitamins D3 (vD3) and E (a-TOC) into cucubit[7]uril (CB[7]) in an aqueous solution. Cucurbiturils is a class of macrocyclic molecules largely used as carrier and controlled release agent in order to improve the solubility and chemoprotective of drugs. Along 50 ns of MD trajectory, the vitamins formed a stable complex with CB[7] without significantly altering its structure. Moreover, the second solvation shell of the CB[7] was not disrupted by the inclusion of the vitamins. The solvation enthalpy was ~ –173.0 kcal/mol for both complexes and –177.6 kcal/mol for the isolated CB[7], suggesting that the vitamin@CB[7] complexes are soluble in water. The binding free energy indicates that CB[7] can act as carrier agent for these vitamins, with values of –17.54 and –23.76 kcal/mol for vD3@CB[7] and a-TOC@CB[7], respectively. Finally, herein we highlight that CB[7] can be a new host to be used for vitamin delivery in biological systems.