New aspects of relationship between the enthalpies of fusion of aromatic compounds at the melting temperatures and the enthalpies of solution in benzene at 298.15 K. Part I

Abstract

In the present work the relationship between the enthalpies of fusion at the melting temperatures and the enthalpies of solution in benzene at 298.15K of aromatic compounds is discussed in details. The difference between the fusion enthalpy at the melting temperature and the solution enthalpy at 298.15K is determined by the temperature dependence of the fusion enthalpy, the solution enthalpy of the compound in the hypothetical liquid state at 298.15K and the enthalpies of solid–solid phase transitions occurring between 298.15K and the melting temperature. The latter contribution into the difference can be measured directly. The first two contributions were analyzed in a series of 17 aromatic compounds which do not exhibit solid-solid phase transitions between 298.15K and the melting temperature. We calculated the fusion enthalpies at 298.15K of these compounds in two different ways. On the one hand, they were derived from the fusion enthalpies at the melting temperature according to Kirchhoff’s law using experimental data on solid and liquid heat capacities. It was assumed that the linear temperature dependence of melt heat capacity can be extrapolated down to 298.15K. On the other hand, the fusion enthalpies at 298.15K were calculated from the solution enthalpies in benzene at 298.15K of the compounds in solid and hypothetical liquid states. Good agreement between the fusion enthalpies at 298.15K calculated in different ways was demonstrated.The solution enthalpies of eight solid and six liquid aromatic compounds in benzene at 298.15K and the fusion enthalpies of two aromatic compounds were measured.