Published in
American Chemical Society, The Journal of Physical Chemistry A, 46(118), p. 11026-11032, 2014
DOI: 10.1021/jp507267f
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Enthalpy of Formation of Anisole: Implications for the Controversy on the O–H Bond Dissociation Enthalpy in Phenol
,
Manuel E. Minas da Piedade
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- Must obtain written permission from Editor
- Must not violate ACS ethical Guidelines
Abstract
Significant discrepancies in the literature data for the enthalpy of formation of gaseous anisole, ΔfHº(PhOCH3, g), have fueled an ongoing controversy regarding the most reliable enthalpy of formation of the phenoxy radical and of the gas phase O-H bond dissociation enthalpy, DHº(PhO-H), in phenol. In the present work ΔfHº(PhOCH3, g) was reassessed using a combination of calorimetric determinations and high-level (W2-F12 ) ab initio calculations. Static-bomb combustion calorimetry led to the standard molar enthalpy of formation of liquid anisole at 298.15 K, ΔfHº(PhOCH3, l) = -(117.1±1.4) kJ.mol-1. The corresponding enthalpy of vaporization was obtained as, ΔvapHº(PhOCH3, g)= (46.41±0.26) kJ.mol-1, by Calvet-drop microcalorimetry. These results give ΔfHº(PhOCH3, g)= -(70.7±1.4) kJ.mol-1, in excellent agreement with ΔfHº(PhOCH3, g)= -(70.8±3.2) kJ.mol-1, obtained from the W2-F12 calculations. The ΔfHº(PhOCH3, g) here recommended leads to ΔfHº(PhO•, g) = 55.5±2.4 kJ.mol-1 and DHº(PhO-H) = 368.1±2.6 kJ.mol-1.