Thermodynamics of polymerisation of heterocyclic compounds. Part. III. The heat capacity, entropy, enthalpy, and free energy of tetroxan

A precision, adiabatic vacuum calorimeter and a differential scanning calorimeter have been used to measure the heat capacity of tetroxan over the temperature range 80 to 420°K. An estimate has been made of heat capacity values below 80°K. Values of the heat capacity, entropy, enthalpy, and free energy are listed at 10° intervals. Values of 22.6 ± 0.4 kJ · mole−1 and 385 ± 1°K are obtained for the heat of fusion and melting temperature, respectively. The vapour pressure (P) of tetroxan has been measured over the temperature range 300–375°K. The results are summarized as The results have been used in conjunction with previously published data to evaluate the entropy changes occurring in the system formaldehyde ⇌ trioxan ⇌ tetroxan ⇌ polyoxymethylene.