The thermal properties of three para-halotoluenes (Cl, Br-,I-); Formation of glassy crystals

The heat capacities of three para-halotoluenes, p-chlorotoluene, p-bromotoluene and p-iodotoluene, were measured with an adiabatic calorimeter. All three compounds showed the formation of glassy crystals. The glass transition temperatures are 220, 242 and 250 K respectively. The temperature and enthalpies of fusion are: for p-chlorotoluene, 280.69±0.01 K and 13554 J mol-1; for p-bromotoluene, 299.94±0.01 K and 15127 J mol-1; and for p-iodotoluene, 306.70±0.05 K and 14963 J mol-1. The heat capacity of p-iodotoluene was measured from 5 K; the derived thermodynamic properties are given. Those of the other compounds were measured from 80 K.