Search Results

You are looking at 1 - 5 of 5 items for

  • Author or Editor: Joana Cabral x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

The present work reports the experimental determination of the standard (p o = 0.1 MPa) molar enthalpies of formation in the condensed and gaseous phases, at T = 298.15 K, of 5- and 6-nitroindazole. These results were derived from the measurements of the standard molar energies of combustion, using a static bomb calorimeter and from the standard molar enthalpies of sublimation derived by the application of Clausius–Clapeyron to the temperature dependence of the vapour pressures measured by the Knudsen effusion technique. The results are interpreted in terms of the energetic contributions of the nitro groups in the different positions of the aromatic ring.

Restricted access

Abstract  

The standard (p 0=0.1 MPa) molar enthalpy of formation of 1-cyanoacetylpiperidine, in the crystalline state, at T=298.15 K, has been derived from measurements of its standard massic energy of combustion, by static bomb combustion calorimetry, as Δf H m 0=−217.1±1.4 kJ mol−1. The standard molar enthalpy of sublimation was measured, at T=298.15 K, by the microcalorimetric sublimation technique as Δcr g H m 0=103.5±1.9 kJ mol−1.

Restricted access

Thermochemical properties of three piperidine derivatives

1-benzyl-4-piperidinol, 4-benzylpiperidine and 4-piperidine-piperidine

Journal of Thermal Analysis and Calorimetry
Authors: M. Ribeiro da Silva and Joana Cabral

Abstract  

The standard (p o=0.1 MPa) molar energies of combustion for the crystalline 1-benzyl-4-piperidinol and 4-piperidine-piperidine, and for the liquid 4-benzylpiperidine, were measured by static bomb calorimetry, in oxygen, at T=298.15 K. The standard molar enthalpies of sublimation or vaporization, at T=298.15 K, of these three compounds were determined by Calvet microcalorimetry. Those values were used to derive the standard molar enthalpies of formation, at T=298.15 K, in their condensed and gaseous phase, respectively.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Maria Ribeiro da Silva, Joana Cabral, Chelsea Givens, Stephanie Keown, and W. Acree

Abstract  

The standard (p 0=0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T-298.15 K, for 2,5-dimethylpyrazine (2,5-DMePz) and for the two dimethylpyrazine-N,N′-dioxide derivatives, 2,3-dimethylpyrazine-1,4-dioxide (2,3-DMePzDO) and 2,5-dimethylpyrazine-1,4-dioxide (2,5-DMePzDO), were derived from the measurements of standard massic energies of combustion, using a static bomb calorimeter, and from the standard molar enthalpies of vaporization or sublimation, measured by Calvet microcalorimetry. The mean values for the molar dissociation enthalpy of the nitrogen-oxygen bonds, 〈DH m 0〉(N-O), were derived for both N,N′-dioxide compounds. These values are discussed in terms of the molecular structure of the two N,N′-dioxide derivatives and compared with 〈DH m 0〉(N-O) values previously obtained for other N-oxide derivatives.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Joana Cabral, Ricardo Monteiro, Marisa Rocha, Luís Santos, William Acree, and Maria Ribeiro da Silva

Abstract  

The standard ( = 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 pyridine-N-oxide derivatives.

Restricted access