Cation–Anionic Interactions of Dyes in Aqueous Solutions: Bromocresol Purple in the Processes of Dissimilar Association

The interaction between single- or double-charged anions of bromocresol purple (BP) and cyanine cations (quinaldine blue, QB, or quinaldine red, QR) at concentrations of dyes 5.0·10−7–4.0·10−5 mol/L has been investigated by vis-spectroscopy. The thermodynamic constants of dissimilar associations (Kas) have been studied. Comparison of the values of lg Kas shows that QB− associates of BP− are more stable (6.61 ± 0.07) than QR associates (4.84 ± 0.06); a similar phenomenon is observed for associates of the BP2− anion. Semi-empirical calculations (PM3 method) are in agreement with the vis-spectroscopy data and indicate that the association of dye into an associate is possible. The standard enthalpies of formation of associates (ΔfHo) and energy diagrams have been determined. The ΔfHo data indicate that the formation of an associate between dye ions is an energetically favourable process. The gain in energy significantly exceeds the systematic error of semi-empirical calculations and increases from 157 kJ/mol (associate ”BP− + QB+”) to 729 kJ/mol (associate “BP2− + QR+”). The most probable structures of dissimilar associates are presented. The study of the dissimilar association develops the concept of intermolecular interactions in solutions.

Thermodynamic Description of Dilution and Dissolution Processes in the MgCl2−CsCl−H2O Ternary System

Thermodynamic data on the properties of the water-based electrolyte systems are very valuable for fundamental physical chemistry and for industrial applications. The missing data both on the dilution and dissolution enthalpies for the ternary CsCl−MgCl2−H2O mixed electrolyte system were investigated by means of the calorimetry method. The dilution calorimetry was performed at 298 K for the set of solutions from diluted to concentrated at constant ratio Cs+/Mg2+=1.8. The relative partial molar enthalpies, ideal, total, and excess ones were calculated. By means of the dissolution calorimetry, the standard enthalpies of formation, the enthalpies, and entropies for the double salt formation from simple salts were evaluated. The results obtained indicate that entropy as the major factor affecting the formation of the joint compound, both in the liquid and solid phases. These data can be implemented in thermodynamic databases and allow for accurate thermodynamic calculations for the salts extraction from natural water sources and for its possible application as thermochemical energy storage.

CALCULATE THE STANDARD ENTHALPIES OF COMBUSTION, FORMATION AND MELTING OF THE COMPLEX ROSEOFUNGIN WITH α-, β- and γ-CYCLODEXTRIN

One of the most important quantities in chemical thermodynamics and thermochemistry is the enthalpy of combustion. Of the currently existing methods for calculating the heat of combustion of natural and synthetic organic compounds, the most acceptable and correct in our case was the Karash method. In this study, the standard enthalpy of combustion, the standard enthalpy of formation, and the melting enthalpy of the antibiotic roseofungin and its cyclodextrin derivatives were calculated. As a result of the study, the thermodynamic constants of the standard enthalpies of combustion, standard enthalpies of formation, and the enthalpies of melting of the above compounds were calculated, which are of interest for physicochemical modeling of processes with their participation, serve as initial information arrays for loading into fundamental thermodynamic data banks and reference books, and is also important for standardization and certification of these complexes. It should be noted that the presence of a large number of hydroxyl groups in the structures of the studied complexes allows them to be attributed to polar compounds.

THE VALUES OF ΔfHo298.15 AND So298.15 OF THE RADICALS, FORMED BY THE ABSTRACTION OF H ATOM FROM THE p-BENZYLPHENOL AND DIMETHYL PHTHALATE

In the present work, the standard thermochemical properties of the most thermochemically stable radicals (p-Benzylenephenol and 1-Methyl-2-methylene phthalate), formed by abstraction of the hydrogen atom from the p-Benzylphenol and Dimethyl phthalate are determined using the results of B3LYP/6-311++G(d,p), M06-2X/6-311++G(d,p) and RO/CBS-4M calculations. The consistent values of the standard enthalpies of formation of these structures are determined using the corrected thermochemistry of the homodesmotic and atomization reactions. The values of the standard entropies of these compounds and the temperature dependencies of their thermochemical properties are also calculated in the present work. It is found that the H-transfer reaction of HO2 with p-Benzylenephenol is thermochemically favorable and can lead to the chain oxidation of p-Benzylenephenol at relatively low temperatures.

Thermochemistry, Bond Energies and Internal Rotor Potentials of Acetic Acid Hydrazide, Acetamide, N-Methyl Acetamide (NMA) and Radicals

Structures, thermochemical properties, bond energies, and internal rotation potentials of acetic acid hydrazide (CH3CONHNH2), acetamide (CH3CONH2), and N-methyl acetamide (CH3CONHCH3), and their radicals corresponding to the loss of hydrogen atom, have been studied. Gas-phase standard enthalpies of formation and bond energies were calculated using the DFT methods B3LYP/6-31G(d,p), B3LYP/6-31G(2d,2p) and the composite CBS-QB3 methods employing a series of work reactions further to improve the accuracy of the ΔHf°(298 K). Molecular structures, vibration frequencies, and internal rotor potentials were calculated at the DFT level. The parent molecules’ standard formation enthalpies of CH3–C=ONHNH2, CH3–C=ONH2, and CH3–C=ONHCH3 were evaluated as −27.08, −57.40, and −56.48 kcal mol−1, respectively, from the CBS–QB3 calculations. Structures, internal rotor potentials, and C–H and N–H bond dissociation energies are reported. The DFT and the CBS-QB3 enthalpy values show close agreement, and this accord is attributed to the use of isodesmic work reactions for the analysis. The agreement also suggests this combination of the B3LYP/work reaction approach is acceptable for larger molecules. Internal rotor potentials for the amides are high, ranging from 16 to 22 kcal mol−1.