Theoretical study of the dechlorination reaction pathways of octachlorodibenzo- p-dioxin

• Published in: Chemosphere (Oxford) 2002-09, Vol.48 (8), p.771-778
• Main Authors: Fueno, Hiroyuki, Tanaka, Kazuyoshi, Sugawa, Seiichi
• Format: Article
• Language: English
• Subjects: Applied sciences; Chlorine - chemistry; Density-functional theory; Dioxin; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Pollutants; Exact sciences and technology; Global environmental pollution; Hydrodechlorination; Incineration; PCDD; Pollution; Pollution, environment geology; Polychlorinated Dibenzodioxins - analogs & derivatives; Polychlorinated Dibenzodioxins - chemistry; Refuse Disposal; Temperature
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/S0045-6535(02)00141-8

The dechlorination reaction pathways of 1,2,3,4,6,7,8,9-octachlorodibenzo- p-dioxin (OCDD) by the hydrogen atom are investigated by the density-functional theory B3PW91 method. The dechlorination reactions have large exothermicity and small activation energies. The activation energies (≈5 kcal/mol) of the σ-complex formation due to the hydrogen addition are lower than those (≈9 kcal/mol) of the direct chlorine abstraction. It is suggested that the σ-complex plays an important role in the reactions, although it has scarcely been shown in previous studies of the dechlorination of dioxins. The σ-complex formation is favored at low temperatures and the chlorine abstraction is favored at high temperatures. Furthermore, it is found that the lateral positions have a marginal preference over the longitudinal positions. The dechlorination of OCDD by the hydrogen atom is thus not likely to result in a dominant formation of the laterally substituted toxic congeners.