Substance Identity

For the purposes of this document, this substance will be referred to as HBCD, which has been derived from the chemical name hexabromocyclododecane.

The chemical structures of HBCD are shown in Table 1. HBCD is a cyclo-aliphatic bromide produced by the bromination of cyclododecatriene (CAS RN 27070-59-3: Mack 2004). The resulting technical product is primarily a mixture of three diastereomers (stereoisomers), designated alpha (α), beta (ß) and gamma (γ) and defined according to their order of elution from a reverse-phase high-performance liquid chromatography column. Trace amounts of two other diastereomers--delta (δ) and epsilon (ε)--have also been reported, and in principle up to 16 stereoisomers, including 6 diastereomeric pairs of enantomers and 4 meso forms, are possible based on the structural characteristics of the substance (Heeb et al. 2004; Law et al. 2005). The α-, ß- and γ-isomers have been observed in chiral pairs, while no optical rotation was detected for the δ- and ε-stereoisomers; therefore, these have been tentatively assigned as meso forms (Law et al 2005).

Commercial HBCD is typically composed of approximately 80-85% γ-isomer, 8-9% α -isomer and 6% ß-isomer (ACCBFRIP 2005). Four commercial grades are available--low melt, medium range, high melt and thermally stabilized--with each containing different proportions of the three stereoisomers (Tomy et al. 2004a). Final use determines the grade of HBCD selected.