Enthalpies of solution at infinite dilution for linear and branched aliphatic aldehydes in heptane. Calorimetric measurements compared with DISQUAC predictions

The molar enthalpies of solution at infinite dilution of 16 linear and branched alkanals in heptane were determined calorimetrically at 298.15 K. These data and the literature data for the molar excess Gibbs energies, molar excess enthalpies, and activity coefficients at infinite dilution of alkanal + n-alkane mixtures were examined on the basis of the DISQUAC group contribution model. The quasi-chemical and dispersive interaction parameters were compared with those of alkanones. There is clear evidence for both a steric and an inductive effect exerted by the alkyl groups adjacent to the carbonyl group. The steric effect results in a regular decrease of the quasi-chemical parameters; the inductive effect increases the dispersive parameters. DISQUAC offers a consistent description of the thermodynamic properties of alkanal + n-alkane mixtures, even at infinite dilution.