Standard Enthalpies of Formation of 2,6-Di-tert-butyl4-methylphenol and 3,5-Di-tert-butylphenol and Their Phenoxy Radicals |
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| Authors: | Manuel A V Ribeiro da Silva M Agostinha R Matos Margarida S Miranda M Helena F A Sousa Rui M Borges dos Santos Magda M Bizarro José A Martinho Simões |
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| Institution: | (1) Centro de Investigação em Química, Departamento de Química, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal;(2) Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal;(3) Faculdade de Engenharia dos Recursos Naturais, Universidade do Algarve, Campus de Gambelas, 8000-810 Faro, Portugal |
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| Abstract: | The standard (po = 0.1 MPa) enthalpies of formation of 2,6-di-tert-butyl-4-methylphenol and 3,5-di-tert-butylphenol in the gaseous phase, –315.5 ± 4.4 kJ mol–1 and –312.7 ± 4.6 kJ mol–1, respectively, were derived from the standard enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb combustion calorimetry, and from the standard enthalpies of sublimation, at 298.15 K, measured by Calvet microcalorimetry. The O—H bond dissociation enthalpies in those compounds were determined in benzene by photoacoustic calorimetry, leading to the standard enthalpies of formation of the gaseous phenoxy radicals: –189 ± 8 kJ mol–1 and –154 ± 6 kJ mol–1, respectively. These results were used to calculate enthalpies of substituent redistribution reactions, which are proposed as a method to estimate new data for substituted phenols. |
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| Keywords: | Thermochemistry bond energies phenols combustion calorimetry photoacoustic calorimetry |
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