Study of the self-association of ε-caprolactam in non-polar solvents by linear and nonlinear dielectric effects

Abstract

Abstract The results of linear and nonlinear dielectric polarizibility for e−caprolactam in solutions of benzene, cyclohexans and dioxane over the temperature range 10 – 40δC and in all available concentration ranges are presented. It was established that the best model for association of e-caprolactam in these solvents is as follows: monomer + cyclic dimer + open dimer + solvent complexes with monomers and dimers. The participation of longer chain multimers was small and below 2%. The calculations performed for different association models did not confirm the well-known literature hypothesis that a high effective dipole moment for dimer μ d =_2.7 D is caused by the non-planarity of the dimer, the high atomic polarization or the presence of higher multimers. This problem was explained by the presence of relatively small, but significant amounts (about 10%) of open polar dimers in the neighbourhood of large amounts of cyclic dimers with a completely compensated dipole moment. The differences in association in different solvents can be explained by the assumption that dimerization constants are independent of the solvent, whereas concurrent complexation processes also occur. The values of the equilibrium constants, free energy, enthalpy and entropy were determined for all considered association processes.