Radical/radical vs radical/molecule reactions in the formation of PCDD/Fs from (chloro)phenols in incinerators.
Pathways from chlorinated phenols as precursors to PCDD/Fs are discussed with focus on the effect of (poly)chlorination on thermochemistry and rate in the displacement of chlorine from a chlorophenol molecule by a (chloro)phenoxy radical (reaction (A) as a key example). Through measurements on the respective methylethers (anisoles) the O-H bond of 2,4,6-TCP turns out to be 5 kcal/ mol, and that in PCP 4 kcal/mol, less strong than O-H in phenol itself. On this basis it is concluded that-in contrast with earlier proposals--displacements such as in reaction (A) are at least as slow as reaction (B) of phenoxy radical with chlorobenzene. PhO. + PhCl -->PhOPh + Cl. reaction B Compared with condensation of two (chloro)phenoxy radicals, such radical/molecule reactions are therefore an insignificant pathway to dioxins in incinerators.
Louw
Robert
R
Center for Chemistry and the Environment, Leiden Institute of Chemistry Gorlaeus Labs, Leiden University, Netherlands. r.louw@chem.leidenuniv.nl
Ahonkhai
Samuel I
SI
D001572:Benzofurans / Q000032:analysis / Q000737:chemistry*; D000072338:Dibenzofurans, Polychlorinated; D004784:Environmental Monitoring; D017745:Incineration; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry*; D012037:Refuse Disposal; D012989:Soil Pollutants / Q000032:analysis*; D013696:Temperature
D001572:Benzofurans; D000072338:Dibenzofurans, Polychlorinated; D000072317:Polychlorinated Dibenzodioxins; D012989:Soil Pollutants