Thermodynamic Properties of Some Methylphosphonyl Dihalides From 15 to 335 °K.

Measurements of the heat capacity of methylphosphonyl difluoride (CHPOF), methyl phosphonyl dichloride (CHPOCl), and methylphosphonyl chlorofluoride (CHPOClF) were made from about 15 to 335 °K by means of an adiabatic calorimeter. These highly reactive and toxic substances were purified in a completely closed glass apparatus by combining slow crystallization and fractional melting procedures. The purities determined by the freezing-curve method are shown to be generally in agreement with those values obtained by the calorimetric method.