abstract
A combined experimental and computational study was developed with the aim of evaluate and understand the structural, energetic and reactivity properties of phenoxazine and phenothiazine. Experimentally, differential scanning calorimetry, static and rotating bomb combustion calorimetries, Knudsen effusion and Calvet microcalorimetry were employed to determine, respectively, the standard (p degrees = 0.1 MPa) molar enthalpies of fusion, Delta H-1(cr)m degrees, at the temperature of fusion, the standard molar enthalpies of formation, in the crystalline phase, Delta H-f(m)degrees(cr), at T = 298.15 K, the temperature-vapor pressures dependences, and the standard molar enthalpies of sublimation, Delta H-g(cr)m degrees, at T = 298.15 K. These data allowed the derivation the experimental standard molar enthalpies of formation, in the gaseous phase, Delta H-f(m)degrees(g), of phenoxazine, (100.8 +/- 4.3) kJ.mol (1), and of phenothiazine, (273.5 +/- 4.7) kJ.mol (1). Computationally, the composite G3(MP2)//B3LYP approach was used to optimize the structures of these two compounds and to estimate their Delta H-f(m)degrees(g) values, which are found to be in very good agreement with the experimental ones. Calculations were also performed for additional analyses of their natural bond orbitals (NBO) and to obtain other gas-phase thermodynamic properties, namely N-H bond dissociation enthalpies, gas-phase acidities and basicities and proton affinities. (C) 2013 Elsevier Ltd. All rights reserved.
keywords
DIFFERENTIAL SCANNING CALORIMETERS; FLUORESCENT STAIN; THERMOCHEMISTRY; CALIBRATION; ENTHALPIES; HEAT; SUBLIMATION; DERIVATIVES; COMBUSTION; ENERGIES
subject category
Thermodynamics; Chemistry
authors
Freitas, VLS; Gomes, JRB; da Silva, MDMCR
our authors
José R. B. Gomes
Principal Researcheracknowledgements
This work was mainly supported by Fundacao para a Ciencia e a Tecnologia (FCT), Lisbon, Portugal, and European Social Fund through strategic projects PEst-C/QUI/UI0081/2011 and PEst-C/CTM/LA0011/2013 awarded to CIQUP and CICECO, respectively. VLSF thanks FCT for Ph.D. research Grant SFRH/BD/41672/2007 and for the post-doctoral grant SFRH/BPD/78552/2011. JRBG holds an Investigador FCT position.