Mesalazine (MZ) drug has been used for several
decades as a primary treatment for inflammatory bowel
diseases. The drug was investigated using thermal analysis
(TA) measurements and electron impact mass spectral
fragmentation at 70 and 15 eV of electron energy. The
optimum molecular geometry and the total energy of the
neutral and the positively charged MZ molecules were
calculated by density functional theory method with
6-311??G(d,p) basis sets. Stability of the molecules
arising from hyperconjugative interactions, charge delocalization,
and the natural atomic charges has been analyzed
using natural bond orbital analysis. In electron
ionization mass spectrometry, the primary rupture is due to
successive loss of H2O (OH from carboxyl and H from
phenolic OH of the ring) and CO of the acetyl group.
Thermogravimetric results have revealed two stages of
mass loss at 75.3 and 25.3 % in ranges 225–350 and 350–650 C, respectively. The first one may be due to
successive losses of different groups or molecules with fast
rate of decomposition. A comparison between MS and TA
helped in selection the proper pathway representing the
fragmentation mechanism of this drug.