An experimental thermochemical study of arylguanidines

In the present work some thermochemical properties of 1,3-diphenylguanidine and 1,3-di-o-tolylguanidine were determined experimentally. To achieve this goal, differential scanning calorimetry was used to obtain purities, temperatures of fusion, enthalpies of fusion, entropies of fusion and heat capacities of the crystal phase as a function of temperature. Using thermogravimetry, the loss rate mass was measured for the crystal phase, and by applying the Langmuir equation the vapor pressure was estimated as a function of temperature, the enthalpy of sublimation was calculated by means of the Clausius-Clapeyron equation. Additionally, the entropy of sublimation and the Gibbs energy of sublimation were derived. With combustion calorimetry in a static bomb, the massic combustion energy was obtained and the standard molar enthalpy of formation in the crystal phase was determined. By combining the enthalpy of formation in the crystal phase and the enthalpy of sublimation, the standard molar enthalpy of formation in the gaseous phase was obtained for two arylguanidines. With the experimental data, the energetic effect due to the presence of two methyl groups in 1,3-di-o-diphenylguanidine was analyzed.