Phase transitions in resorcinal

Abstract

Optically clear crystals of resorcinal [C6H4(OH)2] were grown and employed in the Raman and calorimetric studies of the phase transitions. The enthalpy and entropy change for the solid–solid (α–β) phase transition at 369±6 K are 1.370±0.007 kJ mol−1 and 3.71±0.05 J K−1 mol−1, respectively. The slope (dp/dT) of the α–β phase boundary at 1 atm is negative (−16.7 atm K−1). The characteristic Raman features of the α–β transition are the disappearance of the librational mode at 102 cm−1 and one of the O–H stretching modes at 3060 cm−1 (298 K and 1 atm), while other vibrations remain continuous in both phases. The pressure induced α–β phase transition at room temperature was observed in a diamond anvil cell at 5 kbar. The enthalpy of fusion of β-resorcinal at 382.8 K is 20.89±0.07 kJ mol−1 and the entropy change is 54.59±0.18 J K−1 mol−1.