Thermodynamic study of (heptane + amine) mixtures. II. Excess and partial molar volumes at 298.15 K

Excess molar volumes VE at 298.15 K were determined by means of a vibrating tube densimeter for binary mixtures of heptane + primary n-alkyl (C3 to C10) and branched amines (iso-propyl-, iso-, sec-, and tert-butyl-, iso-, tert-pentyl-, and pentan-3-amine) in the whole composition range. The apparent molar volumes of solid dodecyl- and tetradecylamine in heptane dilute solution were also determined. The VE values were found positive for mixtures involving C3 to C8 linear amines, with VE decreasing with chain lengthening. Heptane + nonyl and decylamine showed s-shaped, markedly asymmetric, curves. Mixtures with branched C3 to C5 amines displayed positive VE’s larger than those observed in the mixtures of the corresponding linear isomers. Partial molar volumes V° at infinite dilution in heptane were evaluated for the examined amines and compared with those of alkanes and alkanols taken from the literature. An additivity scheme, based on the intrinsic volume approach, was applied to estimate group (CH3, CH2, CH, C, NH2, and OH) contributions to V°. The effect of branching on V° and the limiting slope of the apparent excess molar volumes were evaluated and discussed in terms of solute–solvent and solute–solute interactions.

Research highlights
► Excess and partial molar volumes of primary (amines + heptane) mixtures.
► Excess volumes are positive for small size amines and decrease as the size increases.
► Group contributions to predict the partial molar volumes of amines in heptane.
► The void volume is larger for branched than for linear amines in heptane.