The standard (pº = 0.1 MPa) molar enthalpies of formation in the condensed state of chromone-3-carboxylic acid and coumarin-3-carboxylic
acid were derived from the standard molar energies of combustion in oxygen at T = 298.15 K, measured by combustion calorimetry. The standard molar enthalpies of sublimation were obtained by Calvet microcalorimetry.
From these values the standard molar enthalpies in the gaseous phase, at T = 298.15 K, were derived. Additionally estimates of the enthalpies of formation, of all the studied compounds in gas-phase,
were performed using DFT and other more accurate correlated calculations (MCCM and G3MP2), together with appropriate isodesmic,
homodesmic or atomization reactions. There is a reasonable agreement between computational and experimental results.
Authors:V. Lukyanova, T. Papina, K. Didenko, and A. Alikhanyan
The standard enthalpy of combustion of crystalline silver pivalate, (CH3)3CC(O)OAg (AgPiv), was determined in an isoperibolic calorimeter with a self-sealing steel bomb, ΔcH0 (AgPiv, cr)= −2786.9±5.6 kJ mol−1. The value of standard enthalpy of formation was derived for crystalline state: ΔfH0(AgPiv,cr)= −466.9±5.6 kJ mol−1. Using the enthalpy of sublimation, measured earlier, the enthalpy of formation of gaseous dimer was obtained: ΔfH0(Ag2Piv2,g)= −787±14 kJ mol−1. The enthalpy of reaction (CH3)3CC(O)OAg(cr)=Ag(cr)+(CH3)3CC(O)O.(g) was estimated, ΔrH0=202 kJ mol−1.
Authors:S. Kurkov, G. Perlovich, and W. Zielenkiewicz
dependences of solubility, saturated vapour pressure and crystal heat capacity
of [4-(Benzyloxy)phenyl]acetic acid were determined. The solubility of this
compound was investigated in n-hexane,
buffered water solutions with pH 2.0 and 7.4 and n-octanol.
The enthalpy of sublimation and vaporization as well as the fusion temperature
were determined. Solvation and solubility processes have been analyzed. The
thermodynamics of transfer processes from one buffer to another (protonation
process), from buffers to 1-octanol (partitioning process), and from n-hexane to the applied solvents (specific interaction)
have been calculated and compared to those of other NSAIDs. The relevant shares
of specific and non-specific interactions in the process of solvation have
been investigated and discussed.
Authors:M. Ribeiro da Silva, C. Santos, M. Monte, and C. Sousa
MPa) molar enthalpies of formation, ΔfHm0, for
crystalline phthalimides: phthalimide, N-ethylphthalimide
and N-propylphthalimide were derived from
the standard molar enthalpies of combustion, in oxygen, at the temperature
298.15 K, measured by static bomb-combustion calorimetry, as, respectively,
– (318.01.7), – (350.12.7) and – (377.32.2)
kJ mol–1. The standard molar enthalpies of
sublimation, ΔcrgHm0, at T=298.15
K were derived by the Clausius-Clapeyron equation, from the temperature dependence
of the vapour pressures for phthalimide, as (106.91.2) kJ mol–1
and from high temperature Calvet microcalorimetry for phthalimide, N-ethylphthalimide and N-propylphthalimide
as, respectively, (106.31.3), (91.01.2) and (98.21.4)
The derived standard molar enthalpies of formation,
in the gaseous state, are analysed in terms of enthalpic increments and interpreted
in terms of molecular structure.
Authors:Joana Cabral, Ricardo Monteiro, Marisa Rocha, Luís Santos, William Acree, and Maria Ribeiro da Silva
The standard (p° = 0.1 MPa) energies of combustion in oxygen, at T = 298.15 K, for the solid compounds 2-methylpyridine-N-oxide (2-MePyNO), 3-methylpyridine-N-oxide (3-MePyNO) and 3,5-dimethylpyridine-N-oxide (3,5-DMePyNO) were measured by static-bomb calorimetry, from which the respective standard molar enthalpies of formation
in the condensed phase were derived. The standard molar enthalpies of sublimation, at the same temperature, were measured
by Calvet microcalorimetry. From the standard molar enthalpy of formation in gaseous phase, the molar dissociation enthalpies
of the N–O bonds were derived, and compared with values of the dissociation enthalpies of other N–O bonds available for other
Authors:Vera Freitas, José Gomes, and Maria Ribeiro da Silva
The present work reports an experimental thermochemical study supported by state of the art calculations of two heterocyclic
compounds containing oxygen in the ring: xanthone and tetrahydro-γ-pyrone. The standard (pº = 0.1 MPa) molar enthalpies of formation in the condensed phase, at T = 298.15 K, were derived from the measurements of the standard molar energies of combustion in oxygen atmosphere, using a
static bomb calorimeter. The standard molar enthalpies of sublimation or vaporization, at T = 298.15 K, of the title compounds were obtained from Calvet microcalorimetry measurements. These values were used to derive
the standard enthalpies of formation of the compounds in the gas-phase at the same temperature, which were compared with estimated
data from G3(MP2)//B3LYP computations.
of polymorphic forms I and II of theophylline in water at 298.15 K using the isoperibol solution calorimeter have been determined
in the range of concentration (0.311–1.547) · 10−3/mol · kg−1. The enthalpies of hydration
at T = 298.15 K, of 2-acetyl-5-nitrothiophene and 5-nitro-2-thiophenecarboxaldehyde as −(48.8 ± 1.6) and (4.4 ± 1.3) kJ mol−1, respectively. These values were derived from experimental thermodynamic parameters, namely, the standard (po = 0.1 MPa) molar enthalpies of formation, in the crystalline phase,
measured by rotating bomb combustion calorimetry, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined from the temperature–vapour pressure dependence, obtained by the Knudsen mass loss effusion method.
The results are interpreted in terms of enthalpic increments and the enthalpic contribution of the nitro group in the substituted
thiophene ring is compared with the same contribution in other structurally similar compounds.