Formation of bromochlorodibenzo-p-dioxins and furans from the high-temperature pyrolysis of a 2-chlorophenol/2-bromophenol mixture.
The homogeneous, gas-phase pyrolytic thermal degradation of a 50:50 mixture of 2-bromophenol and 2-chlorophenol was studied in a 1 cm i.d., fused silica flow reactor at a total concentration of 88 ppm, reaction time of 2.0 s, and temperatures from 300 to 1000 degrees C. Observed products included (in decreasing yield) naphthalene, dibenzo-p-dioxin (DD), phenol, dibenzofuran (DF), bromobenzene, chloronaphthalene, 4-bromo-6-chlorodibenzofuran (4-B,6-CDF), bromonaphthalene, benzene, 4,6-dichlorodibenzofuran (4,6-DCDF), chlorobenzene, 4-monobromodibenzofuran (4-MBDF), 4-monochlorodibenzofuran (4-MCDF), 1-mono-bromodibenzo-p-dioxin (1-MBDD), 2-chloro,4-bromophenol, 2,4-dibromophenol, and 2-bromo-4-chlorophenol. Unlike the case for the pyrolysis of pure 2-chlorophenol, 4,6-DCDF was observed, but the analogous 4,6-DBDF remained undetected similar to the individual results with 2-MBP. This indicates that the presence of bromine increases the concentration of chlorine atoms available for the formation of 4,6-DCDF. Due to bromine atoms acting as better leaving groups than chlorine atoms, the yield of DD was increased over that observed for the pyrolysis of 2-chlorophenol. The addition of bromine to a chlorinated hydrocarbon system results in an increase in the total yield of PCDD/Fs as well as PBDD/Fs and mixed PBCDD/Fs due to the ease of bromine elimination reactions as well as an increase of the chlorine atom concentration.
Evans
Catherine S
CS
Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
Dellinger
Barry
B
D001572:Benzofurans / Q000138:chemical synthesis*; D002733:Chlorophenols / Q000737:chemistry*; D004147:Dioxins / Q000138:chemical synthesis* / Q000737:chemistry; D006358:Hot Temperature; D006842:Hydrocarbons, Brominated / Q000138:chemical synthesis* / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D010636:Phenols / Q000737:chemistry*
D001572:Benzofurans; D002733:Chlorophenols; D004147:Dioxins; D006842:Hydrocarbons, Brominated; D010636:Phenols; C032038:2-bromophenol; C030683:2-chlorophenol