Thermodynamic study of mixtures containing dibromomethane. II: volumes and enthalpies at 298.15 K

Abstract

Excess molar volumes, VE, of binary mixtures of dibromomethane (DBM) with n-hexane, n-heptane, n-octane, cyclohexane, tetrachloromethane, dipropyl and dibutyl ether, tetrahydrofuran, and 3-pentanone are determined at 298.15 K in the whole composition range by means of a vibrating tube densimeter. For the same DBM mixtures plus with n-pentane and except with dipropyl ether and 3-pentanone, partial molar enthalpies, Hi, and excess molar enthalpies, HE, are obtained through a heat flow calorimeter and a titration method purposely devised. Both excess properties are positive for cyclohexane, tetrachloromethane, and n-alkanes, the latter exhibiting an increase with increasing number of carbon atoms. Dipropyl and dibutyl ether mixtures exhibit negative VE values, while n-hexane, tetrahydrofuran, and 3-pentanone mixtures show an S-shaped VE curve. Negative HEs are observed only for tetrahydrofuran, whereas dibutyl ether exhibits an S-shaped HE curve. HE results are compared with the predictions of the DISQUAC model. The partial molar volumes at infinite dilution, V°, as well as the enthalpies of solvation, ΔsolvH°, of the examined substances in DBM are evaluated and discussed also considering data on other compounds found in the literature. For V° and ΔsolvH°, a group additivity scheme is proposed to enable the estimation of these properties for other molecules and how much structural peculiarities such as chain length, polarity of groups, and cyclic structures influence their values.