Standard Enthalpies of Formation of Some Methyl Esters of Benzene Carboxylic Acids

Abstract

Enthalpies of combustion of methyl benzoate (I), methyl o-toluate (II), methyl m-toluate (III), methyl p-toluate (IV), monomethyl terephthalate (V), dimethyl phthalate (VI), and trimethyl 1,2,4-benzenetricarboxylate (VII) have been determined using bomb calorimetry. Enthalpies of evaporation of these substances (I−VII), and also of dimethyl terephthalate (VIII) and dimethyl isophthalate (IX), have been measured calorimetrically. Standard molar enthalpies of formation in the gas phase have been calculated (in kJ·mol-1): (I) (−277.7 ± 1.3), (II) (−301.5 ± 1.9), (III) (−309.6 ± 1.6), (IV) (−308.7 ± 1.6), (V) (−648.7 ± 2.3), (VI) (−606.2 ± 2.6), (VII) (−963.3 ± 2.9), (VIII) (−627.4 ± 1.1), and (IX) (−627.1 ± 1.1). Values of additive constants have been obtained to calculate enthalpies of formation of methyl esters of benzene carboxylic acids in the crystal and gas states.