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  • 1 College of Pharmacy and Department of Chemistry, The University of Toledo, 43606 Toledo, OH USA
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Ibuprofen has been subjected to a TG/DTA study over the temperature range of 30 to 350°C in a flowing atmosphere of nitrogen. The heating rate and the flow rate were varied. The DTA shows a melting at around 80°C and boiling point range from 212 to 251°C depending upon the heating rate. The mass loss in the TG data confirms the evaporation of Ibuprofen between them.p. and the normalb.p. Evaporation is limited to the surface area, which is a constant in the crucible holding the sample. The DTG plot shows clearly a zero order process which is consistent with the process of evaporation. The enthalpy of vaporization (ΔvapH) calculated by Trouton's rule is found to be in the range of 42.7–46.1 kJ mol−1. TheEact for the zero order reaction is in the range of 81.8–87.0 kJ mol−1 and is calculated by use of the derivative method. The value ofEact is about twice that for ΔHvap in Ibuprofen and differs from other compounds, whereEact≈Δ Hvap. It is suggested that the Ibuprofen molecule is existing as a dimer in the liquid state and dissociates to a monomer in the vapor state.