Kinetic Study of Mesoionic Compounds

摘要

Mesoionic compounds are heterocyclic betaines with a least one side-chain whose α-atomrnis also in the ring plane and with dipole moments of the order of 5D. The present workrnshows the kinetic study of thermal decomposition of following mesoionic: 1,2,3-triphenyl-1,3,4-rntriazolium-2-thiol chloride (MI-A); 1,3-diphenyl-2(4-chlorophenyl)-1,3,4-triazolium-5-thiol (MIB);rn1,2(4-chlorophenyl)-3-phenyl-1,3,4-triazolium-5-thiol (MI-C); 1,3-diphenyl-2(3-nitro-4-rnchlorophenyl)-1,3,4- triazolium-5-thiol (MI-D); 1(4-fluorphenyl)-2(4-chlorophenyl)-3-phenyl-rn1,3,4- triazolium-2-thiol (MI-E); 1,3-diphenyl-2(4-nitrofuranyl)-1,3,4-triazolium-2-thiol (MI-F);rn1,3-diphenyl-2-styryl-1,3,4-triazolium-2-thiol (MI-G) and 1,3-diphenyl-2-(4-chlorophenyl)-rn1,3,4-triazolium-2-selenolate (MI-H). The non-isothermal termogravimetric curves werernobtained in thermobalance Shimadzu TGA-50, under nitrogen atmosphere, flow of 50 mL min~(-1),rnmass 5 mg, heating rate of 10 ℃min~(-1) and range 25-1000 ℃. Differential scanning calorimetricrnmeasurements were performed in Shimadzu Calorimeter DSC 50, under nitrogen atmosphere,rnflow of 50 mL min~(-1), range of 25-500 ℃, heating rate of 10 ℃min~(-1). The non-isothermalrnthermogravimetric curves presented three stages of thermal decomposition. The compound MI-Frnpresented smaller stability, starting decomposition at 138 ℃ and compound MI-E presentedrngreater stability, starting decomposition at 240 ℃. The calorimetric curve of compound MI-Ernhad presented two endothermic transitions in following temperatures 282 and 298 ℃, withrnenthalpies 40 and 313 J/g, respectively. In dynamic method, using Coats-Redfern, the kineticrnmodel that better adjusted experimental data was F1. The kinetic parameters reaction order (n),rnactivation energy (E) and pre-exponential factor (A) had presented a good correlation.