Enthalpy of formation of methyl benzoate: calorimetry and consequences

Abstract

Methyl benzoate is a particularly simple and important organic compound. We are thus not prepared for the “discovery” that there are three relatively recent literature determinations of its enthalpy of formation that span a 15 kJ mol⁻¹ range. The current study provides yet another, more reliable, measurement of the energy of combustion of this species, −3956.7 ± 3.1 kJ mol⁻¹. Joined with one obtained from the literature a weighted average value for the enthalpy of formation in liquid phase for methyl benzoate can be given as Δ_fH_m°(l) = −332.8 ± 4.0 kJ mol⁻¹ Combined with a literature suggested value for the enthalpy of vaporization we obtain the standard molar enthalpy of formation of methyl benzoate in gaseous state, Δ_fH_m°(g) = −276.1 ± 4.0 kJ mol⁻¹. Confident of this new value, we reconcile a disconcerting disparity in the energetics of other methyl benzenecarboxylates discussed in the recent literature.