Standard molar enthalpy of the orthorhombic to monoclinic polymorphic phase transition in 4′-hydroxyacetophenone from enthalpy of solution measurements

Abstract

The standard molar enthalpy of transition between the two known polymorphs of 4′-hydroxyacetophenone (HAP), at 298.15 K, was determined from measurements of their standard molar enthalpies of solution in dimethyl sulfoxide (DMSO). The obtained result ΔtrsHmo(cr II→cr I) = (0.48 ± 0.10) kJ.mol−1 is in excellent agreement with a previously reported value measured in ethanol with an isoperibol calorimeter, using ~ 7 times larger amounts of sample and solvent. The fact that the two polymorphs are easily prepared, and such good agreement was observed between results from two considerably different calorimetric techniques and solvents, suggests that HAP may be a convenient benchmark system for the validation of solution calorimetry measurements or force field predictions on the relative enthalpic stability of organic polymorphs.