Certain compounds exhibit a loss of crystalline structure as a result of kinetic thermal decomposition, known as apparent melting, instead of thermodynamic melting. Apparent melting occurs when the loss of crystalline structure is due to kinetic processes such as chemical reactions, onset of thermal decomposition, denaturation, chemical interactions, dissociations, among others. With an apparent melting point, several limitations arise: determining accurate values of melting temperatures and heats of fusion, measuring impurities depending on the shape of the endothermic peak, distinguishing the polymorphic form of a drug according to the melting temperature, defining the glass transition temperature on a compound after a melt - cool cycle. Thermodynamic melting has been defined as the loss of crystalline structure that occurs at a specific temperature, independent of heating rate, where the system is in equilibrium, therefore the Gibbs free energy is equal to zero, and there is no chemical change (Wunderlich,B. 1990). In this study, several compounds have been tested on a differential scanning calorimetry instrument in order to determine whether their thermodynamic melting point can be detected. Different heating rates have been applied in pursuance of suppressing kinetic processes that correspond to the apparent melting; experiments conducted at multiple heating rates are important to determine whether an endothermic transition is characteristic of melting or decomposition.
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