ENTHALPIES OF FORMATION OF METHYL BENZENECARBOXYLATES

The relative stabilities of the isomeric dimethyl benzenedicarboxylate s have been studied by a thermochemical investigation of dimethyl phth alate, dimethyl isophthalate and dimethyl terephthalate. The enthalpie s of formation in the condensed state for dimethyl phthalate and dimet hyl isophthalate, determined from combustion calorimetry measurements, are -683.8 +/- 2.7 and -730.1 +/- 2.0 kJ mol(-1), respectively. The e nthalpies of sublimation for dimethyl isophthalate and dimethyl tereph thalate, determined by the Knudsen effusion technique are 100.9 +/- 0. 2 and 104.6 +/- 0.3 kJ mol(-1), respectively. From the above results a nd the value of the enthalpy of formation in the condensed state of di methyl terephthalate, previously determined in our laboratory, and the value of the enthalpy of vaporization of dimethyl phthalate taken fro m the literature, the enthalpies of formation in the gaseous state at 298.15 K for the ortho-, meta- and para-isomers of dimethyl benzenedic arboxylates are found to be -606.1, -629.2 +/- 2.0 and -628.0 +/- 1.0 kJ mol(-1), respectively. The relative stabilities of the isomeric dim ethyl benzenedicarboxylates, isomeric dicyanobenzenes and dinitrobenze nes are compared.