Theoretical Study on Destruction Mechanism of 2,3,7,8-TCDD by O₃ and NO₃

In order to improve the destruction effciency of dioxins and also for developing new dioxin control technology, the destruction mechanisms of 2,3,7,8-tetrachlorodihenzo-p-dioxin (2,3,7,8-TCDD) by O₃ and NO₃, were investigated employing quantum chemical calcula-tions. For involved reactions, the microcosmic reaction processes were analyzed and de-picted in detail based on geometry optimizations made by the B3LYP/6-31G(d) method. At the same time, the reaction activation energies were also calculated at the MP2/6-311G(d,p)//B3LYP/6-31G(d) level. Configuration analysis indicated that 2,3,7,8-TCDD could be destroyed by O₃ and NO₃ in two different ways. The destruction of 2,3,7,8-TCDD by O₃ proceeded via the addition of O₃ and the cleavage of C=C while the destruction of 2,3,7,8-TCDD by NO₃ proceeded via the substitution of chlorine by NO₃. Calculated re-sults show that, the activation energy of the destruction reaction of 2,3,7,8-TCDD by NO₃ (267.48 kJ/mol) is much larger than that of the destruction reaction of 2,3,7,8-TCDD by O₃ (51.20 kJ/mol). This indicated that the destruction of 2,3,7,8-TCDD by O₃ is much more effcient than that of 2,3,7,8-TCDD by NO₃. The reason why the activation energy for the destruction reaction of 2,3,7,8-TCDD by NO₃ is so large, is also discussed.