resumo
In the present work, the standard (p degrees = 0.1 MPa) molar enthalpies of formation of xanthydrol, 9-xanthenecarboxylic acid and 9-xanthenecarboxamide, in the gaseous state, at T = 298.15 K, were determined by experimental and computational studies. The experimental techniques used were the static-bomb combustion calorimetry, which enabled the determination of the standard molar enthalpy of formation, in the crystalline state, and the vacuum drop microcalorimetric and the Knudsen effusion techniques used to derive the enthalpy of sublimation. For comparison purposes, we performed standard ab initio molecular orbital calculations, using the G3(MP2)//B3LYP composite procedure, of the enthalpies of several homodesmotic reactions, allowing to extract the standard molar enthalpies of formation, in the gaseous state, of the three xanthene derivatives considered in this work. The calculated results are in good agreement with the experimental data. (C) 2012 Elsevier Ltd. All rights reserved.
palavras-chave
XANTHONE DERIVATIVES; ENTHALPIES; DENSITY; DESIGN; CALORIMETRY; SUBLIMATION; ENERGETICS; ACID; BOND
categoria
Thermodynamics; Chemistry
autores
Freitas, VLS; Gomes, JRB; da Silva, MDMCR
nossos autores
José R. B. Gomes
Investigador Principalagradecimentos
Thanks are due to Fundacao para a Ciencia e Tecnologia (FCT), Lisbon, Portugal, for Programa Ciencia 2007, for financial support to Centro de Investigacao em Quimica - UP and for strategic project Pest-C/CTM/LA0011/2011 granted to CICECO. V. L. S. Freitas thanks FCT and European Social Fund for the award of a Ph. D. Research Grant (SFRH/BD/41672/2007).