Thermal decomposition and kinetic analyses of sulfonamide Schiff's bases in oxygen atmosphere - A comparative study

Two sulfonamide Schiff's bases namely, 4-(benzylideneamino)benzenesulfonamide (BABS) and 4-((4-methylbenzylidene)amino)benzenesulfonamide (4-MBABS) have been synthesized from benzaldehyde or 4-methylbenzaldehyde and 4-aminobenzenesulfonamide by condensation method and characterized by micro analysis, Fourier Transform Infrared and NMR (1H and 13C) techniques. The thermal decomposition of these compounds was studied by thermogravimetry/derivative thermogravimetry analysis (TG/DTG) under dynamic oxygen atmosphere at different heating rates of 10, 15 and 20 K min−1. The decomposition process of BABS is single step, whereas 4-MBABS followed two steps as evidenced from the data. The kinetic parameters were estimated using model-free (Friedman, Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO)) and model-fitting methods (Coats-Redfern (CR)). Invariant kinetic parameters are consistent with the average values obtained by Friedman and KAS isoconversional methods of these compounds. Each step decomposed in different kinetic models. The calculated thermodynamic parameters values show that the decomposition process is endothermic and non-spontaneous nature.