Mechanisms of dioxin formation from the high-temperature oxidation of 2-bromophenol.
The homogeneous, gas-phase oxidative thermal degradation of 2-bromophenol was studied in a 1 cm i.d., fused silica flow reactor at a concentration of 88 ppm, reaction time of 2.0 s, over a temperature range from 300 to 1000 degrees C. Observed products in order of yield were dibenzo-p-dioxin (DD) > 4,6-dibromodibenzofuran (4,6-DBDF) > 4-monobromodibenzofuran (4-MCDF), dibenzofuran (DF), 1-monobromodibenzo-p-dioxin (1-MBDD), naphthalene, bromonaphthalene, 2,4-dibromophenol, 2,6-dibromophenol, phenol, bromobenzene, and benzene. This result is in contrast to the oxidation of 2-chlorophenol, where the major product is 4,6-dichlorodibenzofuran (4,6-DCDF). 4,6-DBDF was observed in high yields in contrastto our previous results for the pyrolysis of 2-bromophenol, where 4,6-DBDF was not detected. The increase in 4,6-DBDF yields is attributed to hydroxyl radical being the major chain carrier under oxidative conditions, which favors hydrogen-abstraction reactions that lead to formation of 4,6-DBDF. However, DD is still the highest yield product under oxidative conditions because of the relative ease of displacement of Br in the ring-closure reaction.
Evans
Catherine S
CS
Louisiana State University, Department of Chemistry, Baton Rouge, Louisiana 70803, USA.
Dellinger
Barry
B
D004147:Dioxins / Q000138:chemical synthesis* / Q000737:chemistry; D008401:Gas Chromatography-Mass Spectrometry; D007700:Kinetics; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry*; D013696:Temperature
D004147:Dioxins; D010636:Phenols; C032038:2-bromophenol