Thermodynamic study of (heptane + amine) mixtures. III: Excess and partial molar volumes in mixtures with secondary, tertiary, and cyclic amines 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 + open chain secondary (diethyl to dibutyl) and tertiary (triethyl to tripentyl) amines} as well as for cyclic imines (C2, C3, C4, C6, and C7) and primary cycloalkylamines (C5, C6, C7, and C12). The VE values were found positive for mixtures involving small size amines, with VE decreasing as the size increases. Negative VE’s were found for tributyl- and tripentylamine, heptamethylenimine, and cyclododecylamine. Mixtures of heptane with cycloheptylamine showed an s-shaped curve.Partial molar volumes V∘V∘ of amines at infinite dilution in heptane were obtained from VE and compared with V∘V∘ of hydrocarbons and other classes of organic compounds taken from literature. An additivity scheme, based on the intrinsic volume approach, was applied to estimate group (CH3, CH2, CH, C, NH2, NH, N, OH, O, CO, and COO) contributions to V∘V∘. These contributions, the effect of cyclization on V∘V∘, and the limiting slope of the apparent excess molar volumes were discussed in terms of solute–solvent and solute–solute interactions.

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► Excess volumes of (sec., tert., or cyclic 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 sec. and tert. than for linear amines in heptane.
► The void volume is much smaller for cyclic than for linear amines in heptane.