Bromobenzene pyrolysis

Pyrolysis of FireMaster BP-6 in the temperature range of 600 900 °C in the absence of oxygen produced bromobenzenes and brominated biphenyls as key products, but no brominated dioxins and dibenzofurans (Thoma and Hutzinger 1987 Thoma et al. 1987). Thermolysis of Hi re Mast a- BP-6 between 400 and 600 °C in the presence of air produced 23,7,8-tetrabromodibenzofuran in the percent ( 1 %10 g/kg) range (Rappe and Buser 1980). Pyrolysis of FireMaster BP-6 in an open quartz tube at 800 °C produced 0.48 1.49 gZkg2,3,7,8-TCDD equivalent levels of polybrominated dibenzofurans (Zacharewski et al. 

However, bromobenzene and chloroaromatics (chlorobenzene, 1,2-dichlorobenzene, 1,2,4-trichlorobenzene) are inert enough to be used routinely,131 181 222-223 except when the aryl cation generated during dediazoniation is stable enough to arylate the aromatic solvents.137 The advantage of pyrolysis in chlorobenzene over dry decomposition has been illustrated in the synthesis of mono- and difluorobenzo[c]phenanthrenes.230... 

Kominar and coworkers115 used the toluene carrier technique for the pyrolysis of bromobenzene. The elimination process was found to be homogeneous and of first order. The Arrhenius expression for equation 26 is log kx (s-1) = (14.6 0.3) - [(317.000 5.4550)/19.157]. The result of this pyrolysis was discussed in terms of the following mechanism (equations 26-31) ... 

Z)(G-H) in benzene has not been determined directly, but has been inserted here for purposes of comparison. It may be derived from the activation energy of the pyrolysis of bromobenzene, which has been shown by Szwarc and Williams to produce phenyl radicals and bromine atoms when the reaction is carried out using the toluene carrier gas technique. Z)(C6H5 -Br) is deduced to be 70 9 kcal, whence Z)(G6H5 -H) = 101 8 kcal, if the heat of formation of bromobenzene quoted by Szwarc and Williams is known to the required accuracy. 

Some PBBs are considered possible precursors of toxic poly-brominated dibenzo-p-dioxins (12-138) and dibenzofurans (12-139), which are formed during combustion. The formation of degradation products of PBBs depends generally on the temperature, the amount of oxygen present and certain other factors. A study of the pyrolysis of the commercial mixture FireMaster BP-6 in the absence of oxygen at 600-900 °C showed the formation of bromobenzenes and lower brominated biphenyls, but polybromi-nated furans did not result. Pyrolysis in the presence of oxygen at 700-900 °C, however, yielded di- to heptabromodibenzofurans. 

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