A thermal analysis study of ibuprofen

Ibuprofen has been subjected to a TG/DTA study over the temperature range of 30 to 350 degrees C in a flowing atmosphere of nitrogen. The heating rate and the flow rate were varied. The DTA shows a melting at around 80 degrees C and boiling point range from 212 to 251 degrees C depending upon the heating rate. The mass loss in the TG data confirms the evaporation of Ibuprofen between the m.p. and the normal b.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 (Delta H-vap) calculated by Trouton's rule is found to be in the range of 42.7-46.1 kj mol(-1). The E-act 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 of E-act is about twice that for Delta H-vap in Ibuprofen and differs from other compounds, where E(act)approximate to Delta H-vap. It is suggested that the Ibuprofen molecole is existing as a dimer in the liquid state and dissociates to a monamer in the vapor state.