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Reactions of Diphenyl Ether with Chlorine and Bromine Atoms Around 750 K – Relevance for Gas‐Phase “Dioxin” Formation
Author(s) -
Wiater Izabela,
Louw Robert
Publication year - 1999
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199901)1999:1<261::aid-ejoc261>3.0.co;2-i
Subject(s) - chemistry , chlorobenzene , radical , bromobenzene , bromine , halogen , benzene , hydrogen atom abstraction , ether , chlorine , diphenyl ether , medicinal chemistry , photochemistry , organic chemistry , alkyl , catalysis
The title reactions have been studied to scrutinize rate data recently inferred for the two reverse steps – reaction of phenoxy radicals with chlorobenzene and bromobenzene – which were at variance with commonly accepted model values. Both with chlorine and bromine atoms, splitting to halobenzene and phenoxy radical was found to occur in competition with abstraction of o ‐, m ‐, p ‐hydrogen atoms. On this basis, the displacements of Cl and Br from the benzene ring by phenoxy radicals must have activation energies above 20 kcal/mol, and are therefore slow. As a consequence, formation of “dioxins” from halogenated phenols, in (slow) combustion, should proceed by combination of two (halo)phenoxy radicals rather than by displacement of ( ortho ‐)halogen in a halophenol molecule.