title: Enantioselective preparative HPLC separation of the HBCD-Stereoisomers from the technical product and their absolute structure elucidation using X-ray crystallography.
abstract: 1,2,5,6,9,10-Hexabromocyclododecane (HBCD) is a widely used flame retardant, which tends to persist in the environment and accumulates in biota. The six stereoisomers (three racemates named alpha-, beta-, and gamma-HBCD) of the technical mixture were isolated with high-performance liquid chromatography (HPLC). Direct separations were performed on a chiral stationary phase containing permethylated beta-cyclodextrin (NUCLEODEX beta-PM column) and the pure enantiomers of alpha-, beta-, and gamma-HBCD were physically characterized for the first time. The absolute configurations of all six isomers were determined by anomalous dispersion using single crystal X-ray crystallography. Optical rotations alphaD in tetrahydrofuran were +4.2/-4.0 (alpha-HBCD), +26.1/-27.5 (beta-HBCD), and +68.0/-66.3 (gamma-HBCD). The sense of rotation could be correlated with the absolute configurations of alpha-, beta-, and gamma-HBCD enantiomers and their order of elution on a chiral permethylated beta-cyclodextrin-bonded stationary phase. The diastereomersalpha-, beta-, and gamma-HBCD displayed distinctly different melting points as well as (1)H-, (13)C NMR, and IR spectra.
authors.affiliation: Department of Analytical Chemistry, Reference Materials, Federal Institute for Materials Research and Testing (BAM), Berlin, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Koeppen
authors.forename: Roland
authors.initials: R
authors.lastname: Becker
authors.forename: Franziska
authors.initials: F
authors.lastname: Emmerling
authors.forename: Christian
authors.initials: C
authors.lastname: Jung
authors.forename: Irene
authors.initials: I
authors.lastname: Nehls