STANDARD ENTHALPIES OF FORMATION OF SOME METHYL-ESTERS OF BENZENE CARBOXYLIC-ACIDS

Enthalpies of combustion of methyl benzoate (I), methyl o-toluate (II) , methyl m-toluate(III), methyl p-toluate (IV), monomethyl terephthala te (V), dimethyl phthalate (VI), and trimethyl 1,2,4-benzenetricarboxy late (VII) have been determined using bomb calorimetry. Enthalpies of evaporation of these substances (I-VII), and also of dimethyl terephth alate (VIII) and dimethyl isophthalate (IX), have been measured calori metrically. Standard molar enthalpies of formation in the gas phase ha ve been calculated tin 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 ha ve been obtained to calculate enthalpies of formation of methyl esters of benzene carboxylic acids in the crystal and gas states.