Thermochemistry of 2-methylbenzoxazole and 2,5-dimethylbenzoxazole: an experimental and computational study
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ORIGINAL RESEARCH
Thermochemistry of 2-methylbenzoxazole and 2,5-dimethylbenzoxazole: an experimental and computational study ´ lvaro Cimas • Ana L. R. Silva • A Maria D. M. C. Ribeiro da Silva
Received: 20 February 2013 / Accepted: 23 February 2013 Ó Springer Science+Business Media New York 2013
Abstract The standard (p° = 0.1 MPa) molar energies of combustion of 2-methylbenzoxazole and 2,5-dimethylbenzoxazole were measured by static-bomb combustion calorimetry. The standard molar enthalpies of vapourization, at T = 298.15 K, were obtained from high-temperature Calvet microcalorimetry. The experimental results enable the calculation of the standard molar enthalpies of formation in the gaseous state, at T = 298.15 K, for both compounds, being the results discussed in terms of structural and energetic contributions. The theoretically estimated gas-phase enthalpies of formation were calculated from high-level ab initio molecular orbital calculations at the G3(MP2)//B3LYP level of theory. The computed values compare very well with the experimental results obtained in this work and show that the 2,5-dimethylbenzoxazole is enthalpically the most stable compound. Furthermore, this composite approach was also used to obtain information about the gas-phase basicities, proton and electron affinities and adiabatic ionization enthalpies. Keywords 2-Methylbenzoxazole 2,5-Dimethylbenzoxazole Enthalpy of formation Enthalpy of vapourization Combustion calorimetry
This paper is in honour to Maria Victoria Roux
Electronic supplementary material The online version of this article (doi:10.1007/s11224-013-0245-x) contains supplementary material, which is available to authorized users. ´ . Cimas M. D. M. C. Ribeiro da Silva (&) A. L. R. Silva A Centro de Investigac¸a˜o em Quı´mica, Departamento de Quı´mica e Bioquı´mica, Faculdade de Cieˆncias, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal e-mail: [email protected]
Calvet microcalorimetry Heat capacity G3(MP2)// B3LYP composite method
Introduction Benzoxazole derivatives constitute key structural units present in a wide range of natural products, being appealing targets in drug synthesis [1], due to their recognized biological and therapeutic activities [2–4]. These heterocyclic compounds present good optical properties, as it is evidenced in the literature by many studies describing them as sensing materials, namely as fluorescent and/or colorimetric optical sensors for metals [5], anionic species [6] and pharmaceutical analysis [7]. Complementarily, there is an interest in benzoxazole derivatives for catalytic applications [8–10], as well as for the production of organic light-emitting diodes [11] and high-performance energy storage devices, where they are used in the manufacture of supercapacitors [12]. A better understanding of the chemical behaviour on the possible applications of the benzoxazole derivatives may be provided by the knowledge of its thermodynamic parameters, namely the correspondent enthalpies of formation, in cond
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