Kinetic Study of Mesoionic Compounds

摘要

Mesoionic compounds are heterocyclic betaines with a least one side-chain whose α-atom is also in the ring plane and with dipole moments of the order of 5D. The present work shows the kinetic study of thermal decomposition of following mesoionic: 1,2,3-triphenyl-1,3,4- triazolium-2-thiol chloride (MI-A); 1,3-diphenyl-2(4-chlorophenyl)-1,3,4-triazolium-5-thiol (MIB); 1,2(4-chlorophenyl)-3-phenyl-1,3,4-triazolium-5-thiol (MI-C); 1,3-diphenyl-2(3-nitro-4- chlorophenyl)-1,3,4- triazolium-5-thiol (MI-D); 1(4-fluorphenyl)-2(4-chlorophenyl)-3-phenyl- 1,3,4- triazolium-2-thiol (MI-E); 1,3-diphenyl-2(4-nitrofuranyl)-1,3,4-triazolium-2-thiol (MI-F); 1,3-diphenyl-2-styryl-1,3,4-triazolium-2-thiol (MI-G) and 1,3-diphenyl-2-(4-chlorophenyl)- 1,3,4-triazolium-2-selenolate (MI-H). The non-isothermal termogravimetric curves were obtained in thermobalance Shimadzu TGA-50, under nitrogen atmosphere, flow of 50 mL min~(-1), mass 5 mg, heating rate of 10 °Cmin~(-1) and range 25-1000 °C. Differential scanning calorimetric measurements were performed in Shimadzu Calorimeter DSC 50, under nitrogen atmosphere, flow of 50 mL min~(-1), range of 25-500 °C, heating rate of 10 °Cmin~(-1). The non-isothermal thermogravimetric curves presented three stages of thermal decomposition. The compound MI-F presented smaller stability, starting decomposition at 138 °C and compound MI-E presented greater stability, starting decomposition at 240 °C. The calorimetric curve of compound MI-E had presented two endothermic transitions in following temperatures 282 and 298 °C, with enthalpies 40 and 313 J/g, respectively. In dynamic method, using Coats-Redfern, the kinetic model that better adjusted experimental data was F1. The kinetic parameters reaction order (n), activation energy (E) and pre-exponential factor (A) had presented a good correlation.