Thermal behavior of brominated and polybrominated compounds II: Pyroproducts of brominated phenols as mechanistic tools

Abstract

This paper is a continuation of paper I, in which we started to report our research on the thermal behavior of the CBr bond, which has been scantly investigated to date. In the present work, we examine the pyrolytic behavior of brominated phenols. The major findings of this research indicate that the position of the bromine atom in the phenol structure mechanistically controls the pyroproducts distribution. Our work indicates that the first stage in the pyrolysis of these compounds determines the capability of forming dioxins and furans, by cyclic dimerization either in concerted mechanism as for the o-bromophenols or a two-stage cyclization in the case of p-bromophenols. The HBr release is increased when di- and tribromophenols are pyrolyzed in the presence of eicosane (C 20), whereas the production of HBr is less influenced by C 20 for the mono bromophenols. The formation of alkylated phenols probably results from a high-temperature Friedel Crafts secondary reaction. Short-time exposure studies indicate that brominated phenols form brominated dibenzodioxins (DBDs) and some furans. Longer thermal reactions at the same temperature lead to a further release of HBr, leading to the thermally more stable end-products.