Isobutoxypentabromocyclododecanes (iBPBCDs): a new class of polybrominated compounds

Isobutoxypentabromocyclododecanes (iBPBCDs) represent a new class of polybrominated compounds found in several flame-proofed polystyrene materials and in a technical mixture of hexabromocyclododecanes (HBCDs). Of the 64 stereoisomers possible, we now have analytical evidence for 16 different stereoisomers. By reversed- and chiral-phase liquid chromatography we distinguished 8 diastereomeric pairs of enantiomers, named alpha-, beta-, gamma-, delta-, epsilon-, xi-, eta-, and theta-iBPBCDs in accordance with their chromatographic retention on a C(18)-RP-column. Crystal structure analysis revealed the stereochemistry of the most prominent theta-iBPBCD stereoisomers, which were determined to be (1R)-1-iso-butoxy-(2R,5R,6S,9S,10R)-2,5,6,9,10-pentabromocyclododecane and its enantiomer. The eight iBPBCD diastereomers were also found in several expanded (EPS) and extruded polystyrene materials (XPS). Stereoisomer pattern varied to a large extent with delta-, eta-, and theta-iBPBCDs dominating in EPS- and alpha-, beta-, epsilon-, and xi-isomers in XPS-materials. The substitution of a bromine atom with an alkoxy group is expected to result in more lipophilic compounds than the parent HBCD compounds. The chromatographic retention on the reversed-phase column supports this assumption. Therefore, we expect that certain iBPBCD stereoisomers may also have the potential to accumulate in biota like e.g. alpha-HBCDs. The presented spectroscopic and chromatographic data allow the identification of 16 different iBPBCD stereoisomers in plastic materials, environmental samples, and biota. With this, the occurrence, fate, and toxicological relevance of this new class of polybrominated compounds can now be studied in more detail.