Synthesis and characterization of polybrominated diphenyl ethers - Unlabelled and radiolabelled tetra-, penta- and hexa-bromodiphenyl ethers

Diphenyl ether, 3-bromodiphenyl ether and 3,3'-dibromodiphenyl ether have been synthesized via coupling of the appropriate phenol and bromobenzene. Each of these compounds was subsequently brominated to (i) 2,2',4,4-tetrabromodiphenyl ether, (ii) 2,2',3,4,4'-pentabromodiphenyl ether and 2,2',4,4',5-pentabromodiphenyl ether and (iii) 2,2',3,3',4,4'-hexabromodiphenyl ether, 2,2',3,4,4',5'-hexabromodiphenyl ether and 2,2',4,4',5,5'-hexabromodiphenyl ether, respectively. The tetrabromodiphenyl ether and two pentabromodiphenyl ethers were also prepared radiolabelled with C-14. The compounds were characterized by H-1 NMR, melting points, mass spectrometry and UV. The structure of 2,2',3,4,4',5'-hexabromodiphenyl ether was unambigously determined by X-ray crystallography. Thereafter, the structure of the two pentabromodiphenyl ethers and remaining two hexabromodiphenyl ethers were assigned by comparison of their H-1 NMR spectra with that of the 2,2',3,4,4',5'-hexabromodiphenyl ether.