Chemistry and characterization of binary organic eutectics and molecular complexes. The urea-m-nitrobenzoic acid system

Abstract

Solid-liquid equilibrium data on a binary organic system involving urea and m-nitrobenzoic acid show the formation of a 1:1 molecular complex surrounded by two eutectics. Growth data studied by measuring the growth velocity (v) at different undercoolings (ΔT) by following the rate of movement of the interface suggest that they obey the Hillig-Turnbull equation, v = u(ΔT)n, where u and n are constants depending on the nature of the materials involved. From the heat of the fusion values, determined by the D.S.C. method, the heat of mixing, entropy of fusion, roughness parameter, interracial energy, radius of the critical nucleus and the excess thermodynamic functions were calculated. While the X-ray diffraction data show that the eutectics are not a mechanical mixture of the components under investigation, the microstructural investigations give their characteristic features. The spectral studies suggest intermolecular hydrogen bonding between the components forming the molecular complex. © 1998 Elsevier Science B.V.