title: Structure elucidation of hexabromocyclododecanes--a class of compounds with a complex stereochemistry.
abstract: Hexabromocyclododecanes (HBCDs) are high production volume chemicals (16700 t worldwide in 2001) used as flame-retardants for plastics and textiles. HBCDs exhibit typical properties of persistent organic pollutants (POPs). They are highly lipophilic and accumulate in biota. Increasing environmental concentrations of HBCDs, mostly reported as sum values, have been observed. As such, HBCDs have to be considered as potential emerging POPs, but their occurrence and environmental fate have not yet been addressed at the level of individual HBCD stereoisomers. Considering the six stereogenic centers of HBCDs, 16 stereoisomers, six diastereomeric pairs of enantiomers as well as four meso forms, can be deduced. Herein, we report spectroscopic and chromatographic data for eight out of 16 possible HBCD stereoisomers, which were isolated from a technical product. Six stereoisomers were identified as three pairs of enantiomers ((+/-) alpha-, beta-, and gamma-HBCDs), differing in optical rotation and chromatographic retention on a chiral phase. The crystal structures of these pairs of enantiomers were determined. Another two of these eight HBCD stereoisomers, not yet described in the literature, showed no optical rotation and are tentatively assigned as meso forms (delta- and epsilon-HBCD). The given spectroscopic and chromatographic information allows the unambiguous identification of eight HBCD stereoisomers and the occurrence, fate, and toxicology of these individual stereoisomers can now be studied.
authors.affiliation: Swiss Federal Institute for Materials Science and Technology (Empa), Laboratory of Organic Chemistry, Uberlandstrasse 129, 8600 Dübendorf, Switzerland. norbert.heeb@empa.ch
authors.forename: Norbert V
authors.initials: NV
authors.lastname: Heeb
authors.forename: W Bernd
authors.initials: WB
authors.lastname: Schweizer
authors.forename: Martin
authors.initials: M
authors.lastname: Kohler
authors.forename: Andreas C
authors.initials: AC
authors.lastname: Gerecke
mesh_terms: D002845:Chromatography; D003460:Crystallization; D004785:Environmental Pollutants; D005411:Flame Retardants; D006842:Hydrocarbons, Brominated / Q000737:chemistry*; D013057:Spectrum Analysis; D013237:Stereoisomerism
chemical_list: D004785:Environmental Pollutants; D005411:Flame Retardants; D006842:Hydrocarbons, Brominated; C089796:hexabromocyclododecane