Evans Catherine S, Dellinger Barry
Louisiana State University, Department of Chemistry, Baton Rouge, Louisiana 70803, USA.
Environ Sci Technol. 2003 Dec 15;37(24):5574-80. doi: 10.1021/es034387s.
Brominated hydrocarbons are the most commonly used flame retardants. Materials containing brominated hydrocarbons are frequently disposed in municipal and hazardous waste incinerators as well as being subjected to thermal reaction in accidental fires. This results in the potential for formation of brominated dioxins and other hazardous combustion byproducts. In contrast to chlorinated hydrocarbons, the reactions of brominated hydrocarbons have been studied only minimally. As a model brominated hydrocarbon that may form brominated dioxins, we studied the homogeneous, gas-phase pyrolytic thermal degradation of 2-bromophenol in a 1-cm i.d., fused-silica flow reactor at a concentration of 90 ppm, with a reaction time of 2.0 s, and over a temperature range of 300 to 1000 degrees C. Observed products included dibenzo-p-dioxin (DD), 1-monobromodibenzo-p-dioxin (1-MBDD), 4-monobromodibenzofuran (4-MBDF), dibenzofuran (DF), naphthalene, bromonaphthalene, 2,4- and 2,6-dibromophenol, phenol, bromobenzene, and benzene. These results are compared and contrasted with previous results reported for 2-chlorophenol. At temperatures lower than 700 degrees C, formation of 2-bromophenoxyl radical, which decomposes through CO elimination to form a bromocyclopentadienyl radical, forms naphthalene and 2-bromonaphthalene through radical recombination/rearrangement reactions. However, unlike the results for 2-chlorophenol, where naphthalene is the major product, DD becomes the major product for the pyrolysis of 2-bromophenol. The formation of DD and 1-MBDD are attributed to radical-radical reactions involving 2-bromophenoxyl radical with the carbon- (bromine) centered radical and the carbon- (hydrogen) centered radical mesomers of 2-bromophenoxyl radical, respectively. The potential product, 4,6-dibromodibenzofuran (4,6-DBDF) for which the analogous product, 4,6-dichlorodibenzofuran (4,6 DCDF), was observed in the oxidation of 2-chlorophenol, was not detected. This is attributed to the pyrolytic conditions of our experiments (e.g., shorter reaction times and higher temperatures) that favor reaction intermediates that form DD and 1-MBDD.
溴代烃是最常用的阻燃剂。含有溴代烃的材料经常被丢弃在城市和危险废物焚烧炉中，并且在意外火灾中会发生热反应。这导致了形成溴代二恶英和其他有害燃烧副产物的可能性。与氯代烃相比，对溴代烃反应的研究非常少。作为一种可能形成溴代二恶英的模型溴代烃，我们在一个内径为1厘米的熔融石英流动反应器中，研究了2-溴苯酚在90 ppm浓度、2.0秒反应时间以及300至1000摄氏度温度范围内的均相气相热解降解。观察到的产物包括二苯并-p-二恶英（DD）、1-单溴二苯并-p-二恶英（1-MBDD）、4-单溴二苯并呋喃（4-MBDF）、二苯并呋喃（DF）、萘、溴萘、2,4-和2,6-二溴苯酚、苯酚、溴苯和苯。将这些结果与先前报道的2-氯苯酚的结果进行了比较和对比。在低于700摄氏度的温度下，2-溴苯氧基自由基通过消除CO分解形成溴环戊二烯基自由基，通过自由基重组/重排反应形成萘和2-溴萘。然而，与2-氯苯酚的结果不同，在2-氯苯酚热解中萘是主要产物，而在2-溴苯酚热解中DD成为主要产物。DD和1-MBDD的形成分别归因于涉及2-溴苯氧基自由基与以碳-（溴）为中心的自由基以及2-溴苯氧基自由基的以碳-（氢）为中心的自由基异构体的自由基-自由基反应。在2-氯苯酚氧化过程中观察到类似产物4,6-二氯二苯并呋喃（4,6-DCDF）的潜在产物4,6-二溴二苯并呋喃（4,6-DBDF）未被检测到。这归因于我们实验的热解条件（例如，较短的反应时间和较高的温度）有利于形成DD和1-MBDD的反应中间体。
