CALORIMETRIC STUDY OF NITRO-GROUP INTERACTIONS IN ALKANE SOLUTIONS - COMPARISON WITH DISQUAC PREDICTIONS

A flow microcalorimeter, Model 2277-LKB, has been used to determine the excess enthalpies, H(E), as a function of concentration at atmospheric pressure and 298.15 K for binary liquid mixtures containing 1-nitropropane, 1-nitrobutane or 1-nitropentane with heptane or cyclohexane. These H(E) data, along with literature data on vapor-liquid equilibrium, H(E) liquid-liquid equilibrium, activity coefficients and partial molar excess enthalpies at infinite dilution for 1- or 2-nitroalkanes and excess heat capacities with n-alkanes or cycloalkanes, are examined on the basis of the DISQUAC group contribution model. The interaction parameters for the nitro group / n-alkane and nitro group / cycloalkane contacts are reported. The quasichemical parameters decrease with the chain length of 1-nitroalkanes and are smaller for 2-nitroalkanes (steric effect) but are the same for n-alkanes and cycloalkanes. The dispersive parameters are the same for all the nitroalkanes. The model provides a fairly consistent description of phase equilibria and related excess functions, using a unique set of parameters. The deviations between experimental and calculated quantities are typical for mixtures containing a very polar compound.