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Differential Hydration of Phenol and Phenoxy Radical and the Energetics of the Phenol O−H Bond in Solution

R. C. Guedes,^†^‡ K. Coutinho,^§ B. J. Costa Cabral,*^†^‡ and S. Canuto

Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, 1749-016 Lisboa, Portugal, Grupo de Física Matemática da Universidade de Lisboa, Av. Professor Gama Pinto 2, 1649-003 Lisboa, Portugal, Universidade de Mogi das Cruzes, CP 411, 08701-970 Mogi das Cruzes, SP, Brazil, and Instituto de Física, Universidade de São Paulo, CP 66318, 05315-970 São Paulo, SP, Brazil

J. Phys. Chem. B, 2003, 107 (18), pp 4304–4310

DOI: 10.1021/jp0219449

Publication Date (Web): April 10, 2003

†

Faculdade de Ciências da Universidade de Lisboa.

‡

Grupo de Física Matemática da Universidade de Lisboa.

Universidade de Mogi das Cruzes.

To whom correspondence should be addressed at the Grupo de Física Matemática da Universidade de Lisboa.

‖

Universidade de São Paulo.

Abstract

Monte Carlo simulations and thermodynamic perturbation theory calculations have been carried out to analyze the differential hydration of phenol (PhOH) and phenoxy radical (PhO^•). The hydration enthalpy of phenol predicted by different phenol−water interaction models is in good agreement with experimental data. On the basis of the difference in the hydration enthalpy of phenol and phenoxy radical, we find that the O−H bond dissociation enthalpy in water is above the recommended experimental value for the gas phase by ca. 7 kcal/mol. This result is in agreement with photoacoustic calorimetry measurements for phenol in other polar solvents. Thermodynamic perturbation theory results for the relative hydration Gibbs energy of phenol and phenoxy radical are also reported. The structure of the solutions suggests that the differential solvation of phenol and phenoxy radical can be related to the strong character of phenol as a hydrogen bond donor in comparison with the role played by phenoxy radical as a hydrogen bond acceptor.

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