THERMOCHEMISTRY OF CHLOROANILINES
Manuel A. V. Ribeiro da Silva, Luísa M. P. F. Amaral, Ana I. M. C. L. Ferreira, José R. B. Gomes
Centro de Investigação em Química da Universidade do Porto
Department of Chemistry, Faculty of Science, University of Porto
Rua do Campo Alegre, 687, P-4169-007 Porto, PORTUGAL
The thermodynamic properties of chlorinated compounds are of major relevance due to their impact on stratosferic ozone deplection and to their role as precursors of air pollutants. The emission of these substances to the atmosphere is associated with practical combustion such as incineration of waste materials.
The combustion method is being or intended to be implementedin the European Union. Being the incineration the recommended method for the disposal of large amounts of chlorinated aromatic compounds, the necessary precautions include the safety of complete combustion.
Nevertheless, thermochemical data are still scarce for the majority of halogenated aromatic compounds, which is even more dramatic for gas-phase reactions involving these compounds.
As a part of a broader research program on the thermochemistry of halogenated aromatic compounds, the results obtained for chloroanilines are presented and discussed.
Teh standard (po = 0.1 MPa) molar enthalpies of formation, in the condensed phase, at T = 298.15 K, of the three isomers of monochloroanilines, the six isomers of dichloroanilines, three isomers of trichloroanilines and one tetrachloroaniline have been measured by rotating bomd combustion calorimetry.
The enthalpies of sublimation of these compounds were measured by high temperature Calvet microcalorimetry, and the standard molar enthalpies of formation in the gaseous phase of all compounds have been calculated.
Ab initio geometry optimizations for all the chloro-substituted anilines were performed using 3-21G* and 6-31+G+ basis sets. Single-point B3LYP/6-31+G*//RHF/6-31+G* energy computations allowed the calculation of the enthalpies of formation for all compounds, including those not studied experimentally.
The experimental and the calculated values of the standard molar enthalpies of formation of the chloroanilines, in the gaseous phase, are compared and interpreted in terms of molecular structure.
Thanks are due to Fundação para a Ciência e a tecnologia (FCT), Lisboa, Portugal, for financial support of Centro de Investigação em Química da Universidade do Porto. L.M.P.F.A. and J.R.B.G., thank FCT for the award of post-doc research grants under PRAXIS XXI (research grants # BPD/16319/98 and # BPD/22098/99, respectively). A.I.M.C.L.Ferreira thanks FCT for the research grant BD/6719/2001.
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