Standard molar enthalpies of formation of 2-, 3- and 4-cyanobenzoic acids

The standard (p = 0.1 MPa) molar enthalpies of formation of 2-, 3- and 4-cyanobenzoic acids were derived from their standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpies of sublimation of 2- and 3-cyanobenzoic acids. The standard molar enthalpies of formation of the three compounds, in the gaseous phase, at T = 298.15 K, have been derived from the corresponding standard molar enthalpies of formation in the condensed phase and standard molar enthalpies for phase transition. The results obtained are −(150.7 ± 2.0) kJ · mol⁻¹, −(153.6 ± 1.7) kJ · mol⁻¹ and −(157.1 ± 1.4) kJ · mol⁻¹ for 2-cyano, 3-cyano and 4-cyanobenzoic acids, respectively. Standard molar enthalpies of formation were also estimated by employing two different methodologies: one based on the Cox scheme and the other one based on several different computational approaches. The calculated values show a good agreement with the experimental values obtained in this work.     

Enthalpies of combustion and formation of 2-acetylpyrrole, 2-acetylfuran and 2-acetylthiophene

The combustion energies for 2-acetylpyrrole (cr) and 2-acetylfuran (cr) were determined using a static bomb calorimeter, whereas the combustion energy of 2-acetylthiophene (l) was determined with a rotating bomb calorimeter; both calorimeters have been recently described. The molar combustion energies obtained were: −(3196.1 ± 0.6) kJ mol⁻¹ for 2-acetylpyrrole, −(2933.8 ± 0.7) kJ mol⁻¹ for 2-acetylfuran, and −(3690.4 ± 0.8) kJ mol⁻¹ for 2-acetylthiophene. From these combustion energy values, the standard molar enthalpies of formation in the condensate phase were obtained as: −(163.51 ± 0.97) kJ mol⁻¹, −(283.50 ± 1.06) kJ mol⁻¹ and −(123.93 ± 1.15) kJ mol⁻¹, respectively. The obtained values of combustion and formation enthalpies of 2-acetylthiophene are in concordance with the reported previously. For the two last compounds, polyethene bags were used as an auxiliary material in the combustion experiments. The heat capacities and purities of the compounds were determined using a differential scanning calorimeter.     

Energetics of copper diphosphates – Cu2P2O7 and Cu3(P2O6OH)2

Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂. α-Cu₂P₂O₇ is reversibly transformed to β-Cu₂P₂O₇ at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol⁻¹. Enthalpies of formation from oxides of α-Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂ are −279.0 ± 1.4 kJ mol⁻¹ and −538.8 ± 2.7 kJ mol⁻¹, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol⁻¹ and −4302.7 ± 6.7 kJ mol⁻¹, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu₃(P₂O₆OH)₂, thus decreasing its thermodynamic stability.     

The standard partial molar entropy of the aqueous tetra-n-butylammonium cation

The standard partial molar entropy of the aqueous tetrabutylammonium cation, not known previously, has now been obtained, based on the molar entropy of two of its crystalline salts, the iodide and the tetraphenylborate, recently determined experimentally for this purpose. The calculation required also published molar enthalpies of solution and solubilities of these two salts as well as of the perchlorate. The choice of the anions depended mainly on the limited solubilities of the examined salts in water, facilitating the estimation of the relevant activity coefficients. The result is S^∞(Bu₄N⁺, aq) = (380 ± 20) J · K⁻¹ · mol⁻¹ at T = 298.15 K, on the mol · dm⁻³ scale and based on S^∞(H⁺, aq) = (−22.2 ± 1.2) J · K⁻¹ · mol⁻¹ (yielding the ‘absolute’ value). The molar entropy of this cation in the ideal gas standard state, S(Bu₄N⁺, g) = (798 ± 8) J · K⁻¹ · mol⁻¹ then yielded the molar entropy of hydration Δ_hydS^∞ (Bu₄N⁺) = (−418 ± 23) J · K⁻¹ · mol⁻¹.     

Temperature dependence vapour pressure measurements of Mg(tmhd)2(tmeda) [(tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione, tmeda = N,N,N′,N′-tetramethylethylenediamine]

The reaction between the magnesium β-diketonate complex Mg(tmhd)₂(H₂O)₂ and 1 equiv. of N,N,N′,N′-tetramethylethylenediamine (tmeda = Me₂NCH₂CH₂NMe₂) in hexane at room temperature yielded Mg(tmhd)₂(tmeda). The standard enthalpy of sublimation (83.2 ± 2.3 kJ mol⁻¹) and entropy of sublimation (263 ± 6.3 J mol⁻¹ K⁻¹) of Mg(tmhd)₂(tmeda) were obtained from the temperature dependence vapour pressure, determined by adopting a horizontal dual arm single furnace thermogravimetric analyser as a transpiration apparatus. From the observed melting point depression DTA, the standard enthalpy of fusion (58.3 ± 5.2 kJ mol⁻¹) was evaluated, using the ideal eutectic behaviour of Mg(tmhd)₂(tmeda) as a solvent with bis(2,4-pentanedionato)magnesium(II), Mg(acac)₂ as a non-volatile solute.     

The structure and thermochemistry of 3:4,5:6-dibenzo-2-hydroxymethylene-cyclohepta-3,5-dienenone (1) and some related compounds

Condensed and gas phase enthalpies of formation of 3:4,5:6-dibenzo-2-hydroxymethylene-cyclohepta-3,5-dienenone (1, (−199.1 ± 16.4), (−70.5 ± 20.5) kJ mol⁻¹, respectively) and 3,4,6,7-dibenzobicyclo[3.2.1]nona-3,6-dien-2-one (2, (−79.7 ± 22.9), (20.1 ± 23.1) kJ mol⁻¹) are reported. Sublimation enthalpies at T=298.15 K for these compounds were evaluated by combining the fusion enthalpies at T = 298.15 K (1, (12.5 ± 1.8); 2, (5.3 ± 1.7) kJ mol⁻¹) adjusted from DSC measurements at the melting temperature (1, (T _fus, 357.7 K, 16.9 ± 1.3 kJ mol⁻¹)); 2, (T _fus, 383.3 K, 10.9 ± 0.1) kJ mol⁻¹) with the vaporization enthalpies at T = 298.15 K (1, (116.1 ± 12.1); 2, (94.5 ± 2.2) kJ mol⁻¹) measured by correlation-gas chromatography. The vaporization enthalpies of benzoin ((98.5 ± 12.5) kJ mol⁻¹) and 7-heptadecanone ((94.5 ± 1.8) kJ mol⁻¹) at T = 298.15 K and the fusion enthalpy of phenyl salicylate (T _fus, 312.7 K, 18.4 ± 0.5) kJ mol⁻¹) were also determined for the correlations. The crystal structure of 1 was determined by X-ray crystallography. Compound 1 exists entirely in the enol form and resembles the crystal structure found for benzoylacetone.     

Dinitrogen and carbon monoxide hydrogen bonding in protonic zeolites: Studies from variable-temperature infrared spectroscopy

Adsorption (at a low temperature) of nitrogen on the protonic zeolite H-Y results in hydrogen bonding of the adsorbed N₂ molecules with the zeolite Si(OH)Al Brønsted-acid groups. This hydrogen-bonding interaction leads to activation, in the infrared, of the fundamental N–N stretching mode, which appears at 2334 cm⁻¹. From infrared spectra taken over a temperature range, the standard enthalpy of formation of the OH···N₂ complex was found to be ΔH⁰ = −15.7(±1) kJ mol⁻¹. Similarly, variable-temperature infrared spectroscopy was used to determine the standard enthalpy change involved in formation of H-bonded CO complexes for CO adsorbed on the zeolites H-ZSM-5 and H-FER; the corresponding values of ΔH⁰ were found to be −29.4(±1) and −28.4(±1) kJ mol⁻¹, respectively. The whole set of results was analysed in the context of other relevant data available in the literature.     

Heat capacity, enthalpy and entropy of strontium niobate Sr2Nb2O7 and calcium niobate Ca2Nb2O7

The heat capacity and the enthalpy increments of strontium niobate Sr₂Nb₂O₇ and calcium niobate Ca₂Nb₂O₇ were measured by the relaxation time method (2–300 K), DSC (260–360 K) and drop calorimetry (720–1370 K). Temperature dependencies of the molar heat capacity in the form C_pm = 248.0 + 0.04350T − 3.948 × 10⁶/T² J K⁻¹ mol⁻¹ for Sr₂Nb₂O₇ and C_pm = 257.2 + 0.03621T − 4.434 × 10⁶/T² J K⁻¹ mol⁻¹ for Ca₂Nb₂O₇ were derived by the least-square method from the experimental data. The molar entropies at 298.15 K, S_m°(298.15 K) = 238.5 ± 1.3 J K⁻¹ mol⁻¹ for Sr₂Nb₂O₇ and S_m°(298.15 K) = 212.4 ± 1.2 J K⁻¹ mol⁻¹ for Ca₂Nb₂O₇, were evaluated from the low-temperature heat capacity measurements.     

Structural studies of cyclic ureas: 2. Enthalpy of formation of parabanic acid

Thermophysical and thermochemical studies have been carried out for crystalline parabanic acid. The thermophysical study was made by differential scanning calorimetry, DSC, over the temperature interval between T = (263 and 473) K. Two phase transitions were found: at T = (392.3 ± 1.6) K with the enthalpy of transition of (2.1 ± 0.4) kJ · mol⁻¹ and at T = (509.8 ± 1.5) K, when the compound was scanned to its fusion temperature. The standard (p = 0.1 MPa) molar enthalpy of formation, at T = 298.15 K, for crystalline parabanic acid was determined using static-bomb combustion calorimetry as −(590.2 ± 1.0) kJ · mol⁻¹. The standard molar enthalpy of sublimation, at T = 298.15 K, was derived from the variation of their vapour pressures, measured by the Knudsen-effusion method, with the temperature. These two thermochemical parameters yielded the standard molar enthalpy of formation in the gaseous phase, at T = 298.15 K, as −(470.8 ± 1.2) kJ · mol⁻¹.     

An examination of the vaporization enthalpies and vapor pressures of pyrazine, pyrimidine, pyridazine, and 1,3,5-triazine

The vaporization enthalpies and liquid vapor pressures from T = 298.15 K to T = 400 K of 1,3,5-triazine, pyrazine, pyrimidine, and pyridazine using pyridines and pyrazines as standards have been measured by correlation-gas chromatography. The vaporization enthalpies of 1,3,5-triazine (38.8 ± 1.9 kJ mol⁻¹) and pyrazine (40.5 ± 1.7 kJ mol⁻¹) obtained by these correlations are in good agreement with current literature values. The value obtained for pyrimidine (41.0 ± 1.9 kJ mol⁻¹) can be compared with a literature value of 50.0 kJ mol⁻¹. Combined with the condensed phase enthalpy of formation in the literature, this results in a gas-phase enthalpy of formation, Δ_f H _m (g, 298.15 K), of 187.6 ± 2.2 kJ mol⁻¹ for pyrimidine, compared to a value of 195.1 ± 2.1 calculated for pyrazine. Vapor pressures also obtained by correlation are used to predict boiling temperatures (BT). Good agreement with experimental BT (±4.2 K) including results for pyrimidine is observed for most compounds with the exception of the pyridazines. The results suggest that compounds containing one or two nitrogen atoms in the ring are suitable standards for correlating various heterocyclic compounds provided the nitrogen atoms are isolated from each other by carbon. Pyridazines do not appear to be evaluated correctly using pyridines and pyrazines as standards.     

Kinetic and thermodynamic analysis of 10-hydroxy-camptothecin hydrolysis at physiological pH

To derive accurately the thermodynamic parameters governing the hydrolysis of the lactone ring at physiological pH, a derivative spectrophotometric technique was used for the simultaneous estimation of lactone and carboxylate forms of the 10-hydroxy-camptothecin (10-HC). Validation of the analytical method was done with respect to reproducibility, percent recovery, and level of detection. Hydrolysis of the lactone ring of 10-HC followed a 1st order decay with a rate constant equal to (0.0281 ± 0.001) min⁻¹ in PBS at pH 7.4 and at a temperature of 310 K. The activation energy for the hydrolysis reaction as calculated from the Arrhenius equation was (79.41 ± 0.92) kJ · mol⁻¹, whereas the enthalpy and entropy of hydrolysis of 10-hydroxy-camptothecin were on average 12.45 kJ · mol⁻¹ and 52.37 J · K⁻¹ · mol⁻¹, respectively. The positive enthalpy and entropy values of the 10-HC-lactone hydrolysis indicate that the reaction is endothermic and entropically driven.     

Diffusion of Sr and Zr in BaTiO3 single crystals

The diffusion of strontium and zirconium in single crystal BaTiO₃ was investigated in air at temperatures between 1000 °C and 1250 °C. Thin films of SrTiO₃, deposited by spin coating a precursor solution and thin films of zirconium, deposited onto the sample surfaces by sputtering, were used as diffusion sources. The diffusion profiles were measured by SIMS depth profiling on a time-of-flight secondary ion mass spectrometer (ToF-SIMS). The diffusion coefficients of strontium and zirconium were given by D_Sr = 3.6 × 10^2.0±4.4 exp[−(543 ± 117) kJ mol⁻¹/(RT)] cm² s⁻¹ and D_Zr = 1.1 × 10^1.0±2.1 exp[−(489 ± 56) kJ mol⁻¹/(RT)] cm² s⁻¹. The results are discussed in terms of different diffusion mechanisms in the perovskite structure of BaTiO₃.     

Thermodynamic characteristics of thermal dissociation of platinum tetrachloride

The pressure of thermal dissociation of platinum tetrachloride by the first step PtCl₄(s) = PtCl₃(s) + 0.5 Cl₂(g) was measured by the static method with a quartz membrane-gauge zero-pressure manometer. An approximating equation for the dissociation pressure vs. temperature was found. The enthalpy (52160±880 J mol⁻¹) and entropy (72.1±1.6 J mol⁻¹ K⁻¹) of dissociation were calculated. The heat of formation found for platinum tetrachloride (−246.3±1.3 kJ mol⁻¹) at 298.15 K agrees well with the value obtained by the calorimetric method (−245.6±1.9 kJ mol⁻¹).__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2028–2031, October, 2004.     

Thermodynamic characteristics of thermal dissociation of platinum dichloride

The dissociation pressure for the process PtCl₂(s) → Pt(s) + Cl₂(g) was measured by the static method with diaphragm zero-pressure gauges. The approximating equation for the temperature dependence on the dissociation pressure for the above reaction was found. The enthalpy (137.7±0.3 kJ mol⁻¹) and entropy (163.6±0.4 J mol⁻¹ K⁻¹) of PtCl₂(s) dissociation and enthalpies of formation and absolute entropies of platinum di- and trichlorides at 298.15 K were calculated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1345–1348, June, 2005.     

Vapor pressure, kinetics and enthalpy of sublimation of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II)

The kinetics of sublimation of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II), [Cu(tmhd)₂] was studied by non-isothermal and isothermal thermogravimetric (TG) methods. The non-isothermal sublimation activation energy values determined following the procedures of Friedman, Kissinger, and Flynn–Wall methods yielded 93 ± 5, 67 ± 2, and 73 ± 4 kJ mol⁻¹, respectively and the isothermal sublimation activation energy was found to be 97 ± 3 kJ mol⁻¹ over the temperature range of 375–435 K. The dynamic TG run proved the complex to be completely volatile and the equilibrium vapor pressure (p_e)_T of the complex over the temperature range of 375–435 K determined by a TG-based transpiration technique, yielded a value of 96 ± 2 kJ mol⁻¹ for its standard enthalpy of sublimation (Δ_subH°).     

Equilibrium constant for the reaction Xe + 2Ar XeAr + Ar in the temperature range 150–300 k and the dissociation energy of XeAr

The equilibrium Xe + 2Ar has been investigated in the temperature range 150–300 K using a selected ion flow tube appratus. From the temperature variation of the equilibrium constant the standrad enthalpy change for the reaction is determined to be −25 ± 5 kj mol⁻¹ and the dissociation energy of XeAr⁺ is estimated to be 24 ±5 kj mol⁻¹ (0.25 ± 0.05 eV). At ≈ 150 K the approach to equilibrium is consistent with a rate coefficent of (5 ± 3) × 10⁻²¹ cm ⁶ s⁻¹ for the forward three-body association reaction.     

Study on the interaction between antibacterial drug and bovine serum albumin: A spectroscopic approach

The binding of sulfamethoxazole (SMZ) to bovine serum albumin (BSA) was investigated by spectroscopic methods viz., fluorescence, FT-IR and UV–vis absorption techniques. The binding parameters have been evaluated by fluorescence quenching method. The thermodynamic parameters, ΔH°, ΔS°and ΔG° were observed to be −58.0 kJ mol⁻¹, −111 J K⁻¹ mol⁻¹ and −24 kJ mol⁻¹, respectively. These indicated that the hydrogen bonding and weak van der Waals forces played a major role in the interaction. Based on the Forster's theory of non-radiation energy transfer, the binding average distance, r, between the donor (BSA) and acceptor (SMZ) was evaluated and found to be 4.12 nm. Spectral results showed the binding of SMZ to BSA induced conformational changes in BSA. The effect of common ions and some of the polymers used in drug delivery for control release was also tested on the binding of SMZ to BSA. The effect of common ions revealed that there is adverse effect on the binding of SMZ to BSA.     

The enthalpies of formation of two dibenzocyclooctadienones

The standard molar enthalpies of formation (Δ_fH_m⁰(s)/kJmol⁻¹) for 2,3:6,7-dibenzocycloocta-2,6-dien-1-one and 2,3:7,8-dibenzocycloocta-2,7-dien-1-one [6H-11,12-dihydro-dibenzo[a,e]cycloocten-5-one (ketone 1) and 10H-11,12-dihydrodibenzo[a,d]-cycloocten-5-one (ketone 2), respectively] were derived from enthalpies of combustion, measured by means of a microbomb calorimeter. The fusion and vaporization enthalpies of these compounds were obtained from DSC and correlation gas chromatography measurements. The standard molar enthalpies of formation in the gas phase were calculated by combining the condensed phase standard molar enthalpies of formation with the fusion and vaporization enthalpies adjusted to 298.15 K. Values for Δ_fH_m⁰(g) of (−39.9±5.5) and (−14.8±5.3) kJ mol⁻¹ were obtained for 2,3:6,7-dibenzocycloocta-2,6-dien-1-one and 2,3:7,8-dibenzocycloocta-2,7-dien-1-one, respectively. Quantum chemical calculations are reported for the compounds investigated experimentally and an additional four isomers. Isomerization enthalpies are derived from computed energies. The enthalpies of formation are also calculated by group additivity, compared with the experimental values and then correlated with the structure of the molecules investigated. The X-ray analysis of ketone 1 is also reported.     

NMR study of the dynamic behaviour of the system 2-ethylhexylsodium-2-ethylhexyllithium in heptane

Mixtures of 2-ethylhexylsodium and 2-ethylhexyllithium are studied by ¹H- and ¹³C-NMR spectroscopy in the temperature range from 20 to −50°C in hydrocarbon solutions. Characteristic temperature-dependent spectra obtained are indicative of dynamic exchange processes taking place in the system. The following activation parameters are found: ΔH^≠=31.7±2.7 kJ mol⁻¹; ΔG^≠₃₁₃=58.7±0.6 kJ mol⁻¹; ΔS^≠=−86.37±10.8 J mol⁻¹ K⁻¹. The negative value of the activation entropy indicates that the exchange proceeds through the associative mechanism. The participation in exchange reactions of aggregates, containing both sodium and lithium derivatives, is suggested.     

The Plausible Aromaticity of 1,8-Naphthalimides: The Enthalpy of Formation of N-Methyl-1,8-Naphthalimide

In order to understand the aromaticity of 1,8-naphthalimides, the enthalpies of combustion and sublimation of N-methyl-1,8-naphthalimide were determined. The numerical values are –6095.8 ± 3.5 and 109.7 ± 0.8 kJ · mol^–1. The enthalpies of formation of condensed and gas phase N-methyl-1,8-naphthalimide are accordingly –306.1 ± 3.9 and –196.4 ± 4.0 kJ · mol^–1. It is deduced that naphthalimides enjoy some 40 kJ · mol^–1 of aromatic stabilization over that of the maleimides, shown to be nominally destabilized and modestly antiaromatic in our recently published thermochemical study.