Studies on thermal decomposition mechanism and kinetics of aspirin

The mechanism of thermal decomposition of aspirin was studied by both thermogravimetry and Mayer bond orders calculated by Cerius2 software. The parameters of thermal decomposition kinetics for aspirin, such as activation energy (E), reaction order (n) and frequency factor (A) were obtained by thermogravimetry. The kinetic equation of thermal decomposition of aspirin is expressed as: dalpha/dt = 4. 74 x 10" [exp( - (100. 34+/-5. 18) x 10(3)/RT)](1 - alpha)(2.8+/-0.3) Melting point, molar enthalpy and entropy of fusion of aspirin were examined to be (409. 19 +/- 0. 22) K, (29. 17 +/- 0. 41) kJ . mol (-1) and (71. 09 +/- 1. 06) J . mol(-1) . K-1, respectively, by means of DSC with a rising temperature program. The results obtained show that theoretical mass-loss derived from Mayer bond orders of aspirin is in very good agreement with that obtained from thermogravimetry experiment.