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

Highlights: • The general scheme for the analysis of the relationship between solution and fusion enthalpies was proposed. • The solution enthalpies of fourteen aromatic compounds in benzene were determined. • The fusion enthalpies of two aromatic compounds were measured. - Abstract: In the present work the relationship between the enthalpies of fusion at the melting temperatures and the enthalpies of solution in benzene at 298.15 K of aromatic compounds is discussed in details. The difference between the fusion enthalpy at the melting temperature and the solution enthalpy at 298.15 K is determined by the temperature dependence of the fusion enthalpy, the solution enthalpy of the compound in the hypothetical liquid state at 298.15 K and the enthalpies of solid–solid phase transitions occurring between 298.15 K 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 298.15 K and the melting temperature. We calculated the fusion enthalpies at 298.15 K 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 298.15 K. On the other hand, the fusion enthalpies at 298.15 K were calculated from the solution enthalpies in benzene at 298.15 K of the compounds in solid and hypothetical liquid states. Good agreement between the fusion enthalpies at 298.15 K calculated in different ways was demonstrated. The solution enthalpies of eight solid and six liquid aromatic compounds in benzene at 298.15 K and the fusion enthalpies of two aromatic compounds were measured.