Synthesis and characterization of highly polybrominated diphenyl ethers

Abstract: Polybrominated diphenyl ethers (PBDEs) make up an important class of brominated flame retardants. The present production is mainly concentrated to DecaBDE but until recently also a significant production of PentaBDE and OctaBDE took place, leaving us with a large number of different PBDE congeners. The PBDEs have become widespread pollutants abiotically and in biota, particularly in high trophic level wildlife and in humans. Accordingly, pure authentic reference standards have been required to promote high quality exposure assessments of wildlife and humans and analysis of abiotic matrices, to study both chemical and physical properties of the PBDEs and to allow toxicological studies. The objective of this thesis was to develop methods for synthesis of polybrominated diphenyl ether (PBDE) congeners and to characterize them. Further, some octabrominated DEs were determined with x-ray crystallography. Main focus has been to prepare highly brominated PBDE congeners, i.e. PBDEs substituted with six to nine bromine atoms.A total number of twenty-three PBDE congeners were synthesized via reduction of decabromodiphenyl ether receiving nonaBDEs; perbromination and bromination of mono- and diaminodiphenyl ethers followed by diazotization of the amino group(s) and reduction of the diazonium ion(s) receiving octaBDEs and nonaBDEs; selective bromination of diaminodiphenyl ethers followed by diazotization of the amino groups and insertion of bromine receiving hexaBDEs and heptaBDEs; bromination of the latter PBDEs giving octaBDEs; and an improved coupling of symmetrical diphenyliodonium salts with bromophenols yielding tetraBDEs to octaBDEs. To enable these compounds to be synthesized three hexabromodiphenyl iodonium salts were prepared: 2,2’,3,3’,4,4’-, 2,2’,4,4’,5,5’- and 2,2’,4,4’,6,6’ - hexabromodiphenyliodonium salts. These iodonium salts are described for the first time which made it possible to synthesize PBDE congeners with 2,3,4-, 2,4,5- and 2,4,6-tribromo substitution in the phenyl rings originating from the diphenyliodonium salts. Among the PBDE congeners 18 are synthesized for the first time. The thesis includes an improved methodology for synthesis of polybromodiphenyl iodonium salts which is based on improved solubilization of both one of the reactants and the product formed. The present work on PBDE synthesis adds useful methods for synthesis of the most highly brominated diphenyl ether congeners.