Mechanisms of Dioxin Formation from the High-Temperature Oxidation of 2-Bromophenol

摘要

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 deg C.Observed products in ordej 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 contrast to 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 centre dot in the ring-closure reaction.