Valorization of a halogenated flame retardant: Pathways for the reductive transformation of hexabromocyclododecane (HBCDD)

The valorization of plastics waste is of economic and environmental interest. Being an essential part of plastics formulations, additives must accordingly be considered in recycling processes. Among them, halogenated flame retardants are known for their ecotoxicity and the concerns that they raise for human health. Despite their historical widespread use, the upcycling potential of halogenated flame retardants remains undervalued considering that their complex chemical structure could serve in the production of molecules with higher added values. In this context, the upcycling of hexabromocyclododecane (HBCDD) – a brominated flame retardant – was investigated by applying selected reduction conditions. The resulting products were isolated, characterized, and the mechanistic pathways to their formation carefully investigated. Dibromocyclododecadiene and bromocyclododecatriene were obtained under mild reductive conditions while stronger reducing agents resulted in the formation of fully debrominated cyclododecatriene (CDT). CDT can be converted into laurolactam and polymerized to yield polyamide 12 as an upcycled product. • Reductive transformation of halogenated flame retardants deciphered. • Hexabromocyclododecane converted to valuable cyclododecatriene. • Stereochemistry determines reductive β -elimination of vicinal dibromide and HBr. • Stepwise reduction can be steered through reaction conditions.