Standard molar Gibbs free energy and enthalpy of solvation of low polar solutes in formamide derivatives at 298 K

Abstract

Novel experimental values of the limiting activity coefficients and standard molar enthalpies of solution in N-methylformamide at 298.15K are reported and used to calculate the thermodynamic functions of solvation. We compare the plots of the standard molar Gibbs free energy against the standard molar enthalpy of solvation of low polar molecules in N-methylformamide, N,N-dimethylformamide, and formamide. The solvophobic effect is responsible for the deviations of the data points from the straight line corresponding to a correlation between thermodynamic functions of solvation in aprotic solvents. It is shown that the solvophobic effects are strong in formamide solutions, significantly weaker in N-methylformamide, and very weak in N,N-dimethylformamide, which coincides with the average number of intermolecular hydrogen bonds per unit volume of these solvents. Behavior of solutions in binary solvents composed of N-methylformamide or formamide mixed with water and ethylene glycol and a possibility to tune the solvophobic effect by changing the solvent composition are also considered.