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 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 to the gaseous phases, elucidating molecular decomposition and the inherent intermolecular forces governing the species. © 2024 The Authors

Abstract The Universidade Junior (U.Jr.) program, initiated by the University of Porto (U.Porto), Portugal, is a comprehensive educational initiative conducted during the summer months, primarily targeting the 10-18 age group. The program aims to promote science, technology, arts, humanities, and sports knowledge among elementary and secondary-level students and to influence their vocational choices and higher education aspirations. The study analyses the relationship between participation in the U.Jr. program and subsequent enrollment in higher education at U.Porto. It utilises data collected from 2006 to 2022, comparing U.Jr. participants with students who enrolled as freshmen at U.Porto. A Pearson correlation coefficient was applied to establish the connection between these datasets. Data analysis reveals a significant positive relationship between participation in U.Jr. and the choice of U.Porto for higher education. The study shows that 22 out of 100 first-year students at U.Porto in 2021 had previously attended U.Jr. Moreover, the geographical provenance of participants and U.Porto first-year students showed a robust correlation. The findings suggest that U.Jr. has a substantial impact on attracting students to U.Porto and influencing their academic choices. The program's diverse activities, coupled with its inclusive approach, have been instrumental in increasing the university's attractiveness and helping mitigate the country's low higher education rates. The study underscores the importance of such initiatives in shaping students' educational trajectories and choices for higher education.

Abstract The present work is focused on determining the enthalpy of formation of several derivatives of amino-1,2,4-triazoles. Experimentally, the enthalpies of formation of the crystalline phase and the enthalpies of sublimation of 3-amino- and 3,5-diamino-1H-1,2,4-triazole were derived, respectively, from static-bomb combustion calorimetry and Calvet microcalorimetry or Knudsen effusion measurements. For 4-amino-4H-1,2,4-triazole, only the enthalpy of sublimation was measured. Gas-phase standard molar enthalpies of formation were also estimated using theoretical calculations performed with the G3(MP2) composite approach. The very good agreement of these estimates with the experimental results, support the extension of this study to the estimate of this property for the remaining compounds not studied experimentally. The results obtained are interpreted in terms of structural contributions.

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 This work reports a combined thermochemical experimental and computational study on 6-hydroxycoumarin. The standard (p degrees = 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 rad-icalar related species, allowing us to further support our experimental measurements and to adequately quantify and rationalize the antioxidant activity of these systems.

Abstract The discrepancy between the calculated (CBS-4M/Jenkins) and experimentally determined enthalpies of formation recently reported for the 2:1 salt TKX-50 raised the important question of whether the enthalpies of formation of other 2:1 C, H, N, O salts calculated using the CBS-4M/Jenkins method are reliable values. The standard (p° = 0.1 MPa) enthalpy of formation of crystalline guanidinium 5,5′-azotetrazolate (GZT) (453.6 ± 3.2 kJ/mol) was determined experimentally using static-bomb combustion calorimetry and was found to be in good agreement with the literature’s values. However, using the CBS-4M/Jenkins method, the calculated enthalpy of formation of GZT was again in poor agreement with the experimentally determined value. The method we used recently to calculate the enthalpy of formation of TKX-50, based on the calculation of the heat of formation of the salt and of the corresponding neutral adduct, was then applied to GZT and provided excellent agreement with the experimentally determined value. Finally, in order to validate the findings, this method was also applied to predict the enthalpy of formation of a range of 1:1 and 2:1 salts (M+X− and (M+)2X2− salts, respectively), and the values obtained were comparable to experimentally determined values. The agreement using this approach was generally very good for both 1:1 and 2:1 salts; therefore, this approach provides a simple and reliable method which can be applied to calculate the enthalpy of formation of energetic C, H, N, O salts with much greater accuracy than the current, commonly used method. © 2023 by the authors.