Publications

Abstract The present investigation describes the experimental evaluation of relevant physicochemical properties of five organochlorine compounds (OCs), including some that are related to their environmental mobility. The vapor pressures of (2,4′-Dichlorodiphenyl)dichloroethane (2,4′-DDD, CASN:53-19-0), 1,1-Dichloro-2,2-bis(4-chlorophenyl)ethane (4,4′-DDD, CASN:72-54-8) and 2,2-Bis(4-chlorophenyl)acetic acid (4,4′-DDA, CASN:83-05-6), as well as of the bactericide Nitrapyrin (CASN:1929-82-4) and of the rodenticide Crimidine (CASN:535-89-7) were determined at different temperatures. The Knudsen mass-loss effusion technique was employed to determine the sublimation vapor pressures of the referred compounds, apart from Crimidine. For the latter compound, a static method using a capacitance diaphragm manometer enabled the measurement of vapor pressures of both condensed (crystalline and liquid) phases. This technique was also used to measure the vapor pressures of the crystalline phase of Nitrapyrin over a larger temperature range, as well as its vaporization vapor pressures. The results of the standard molar enthalpies, entropies, and Gibbs energies of sublimation for all five compounds and of vaporization for Crimidine and Nitrapyrin, at reference temperatures, were derived. For these two compounds the phase diagram representations of the (p,T) results, in the vicinity of the triple point, were obtained. DSC analysis enabled the determination of the crystalline heat capacities of the five OCs studied and also of their temperatures and enthalpies of fusion. Gas-phase thermodynamic properties were estimated using quantum chemical calculations. The thermodynamic stability of the compounds studied was evaluated and compared in the crystalline and gaseous phases, at 298.15 K, in consideration with estimated results of the standard Gibbs energies of formation. Combined with other physical and chemical properties, the results derived from this study can be used to predict the mobility, and environmental fate of these pollutants. © 2024 Elsevier Ltd

Abstract The need to transition from fossil fuels to renewables arises from factors such as depletion, price fluctuations, and environmental considerations. Lignocellulosic biomass, being abundant, and quickly renewable, and not interfering with food supplies, offers a standout alternative for chemical production. This paper explores the energetic characteristics of two derivatives of furfural-a versatile chemical obtained from biomass with great potential for commercial sustainable chemical and fuel production. The standard (p degrees = 0.1 MPa) molar enthalpies of formation of the liquids furfurylamine and 5-methylfurfurylamine were derived from the standard molar energies of combustion, determined in oxygen and at T = 298.15 K, by static bomb combustion calorimetry. Their standard molar enthalpies of vaporization were also determined at the same temperature using high-temperature Calvet microcalorimetry. By combining these data, the gas-phase enthalpies of formation at T = 298.15 K were calculated as -(43.5 +/- 1.4) kJmol-1 for furfurylamine, and -(81.2 +/- 1.7) kJmol-1 for 5-methylfurfurylamine. Furthermore, a theoretical analysis using G3 level calculations was performed, comparing the calculated enthalpies of formation with the experimental values to validate both results. This method has been successfully applied to similar molecules. The discussion looks into substituent effects in terms of stability and compares them with similar compounds.

Abstract The present work reports an experimental study aiming to determine several thermodynamic properties of fusion and sublimation of the chromophore N,Ndimethyl-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.

Abstract 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.

Abstract 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.

Abstract 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 measure-ments. 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 O-H...O in the crystalline phase of syringaldehyde was estimated.

Abstract 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 the values derived indirectly from the vapor pressure measurements. The thermodynamic results were discussed together with the available literature data for 2,4,6-trichlorophenol. To help rationalize the phase behavior of these substances, the crystallographic structure of 2,4,6-tribromophenol was determined by single crystal X-ray diffraction.

Abstract 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 degrees = 10(5) 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. (C) 2018 Elsevier Ltd.

Abstract 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 (p(0) = 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. (C) 2018 Elsevier Ltd.

Abstract The sublimation vapor pressures of three metallic (group 6) hexacarbonyls, Cr(CO)(6), Mo(CO)(6), and W(CO)(6), were measured using the Knudsen mass-loss effusion method. The standard (p (o) = 0.1 MPa) molar enthalpies, entropies, Gibbs energies, and heat capacity difference between the gas and solid state, at T = 298.15 K, were derived from the experimental results combined with selected literature ones covering a wide range of temperature. The temperatures and molar enthalpies of fusion of those compounds were measured using differential scanning calorimetry. The thermodynamic stability of the hexacarbonyls was evaluated taking into account the standard Gibbs energies of formation in the crystalline and gaseous phases. Gas-phase absolute entropies, heat capacities, and enthalpies of formation of the three compounds studied as well as the bond distances M-C and C-O were calculated.