Melting, volatilisation and crystal lattice enthalpies of acridin-9(10H)-ones

The enthalpies and temperatures of melting and sublimation of acridin-9(10H)-one, 10-methylacridin-9(10H)-one, 2,10-dimethylacridin-9(10H)-one, 10-methyl-2-nitroacridin-9(10H)-one, 10-ethylacridin-9(10H)-one and 10-phenylacridin-9(10H)-one were measured by DSC. Enthalpies and temperatures of volatilisation were also obtained by fitting TG curves to the Clausius-Clapeyron relationship. Complementary investigations for anthracene showed the extent to which the thermodynamic characteristics thus obtained compare with those determined by means of other techniques. For compounds whose crystal structures are known, experimental enthalpies of sublimation correspond reasonably well to crystal lattice enthalpies predicted theoretically as the sum of electrostatic, dispersive and repulsive interactions. Analysis of crystal lattice enthalpy contributions indicates that dispersive interactions always predominate. Interactions are enhanced in acridin-9(10H)-one where intermolecular hydrogen bonds occur: this is reflected in the relatively high enthalpy of sublimation.