On the thermally induced isomerisation of hexabromocyclododecane stereoisomers

The interconversion of the stereoisomers contained in technical 1,2,5,6,9,10-hexabromocyclododecane, a major brominated flame retardant increasingly found in the environment and in biota, was investigated at elevated temperatures. The application of pure enantiomers of the three constituents alpha-, beta-, and gamma-HBCD enabled the unambiguous elucidation of the individual isomerisation reactions as well as the quantification of all respective rate constants. At 160 degrees C the rate constants range over two orders of magnitude from 1.50 x 10(-3) to 1.88 X 10(-5) Mol(%) s(-1). A preliminary mechanistic explanation for the differences of the rate constants which govern the composition of HBCD diastereomers at equilibrium is given. (c) 2007 Elsevier Ltd. All rights reserved.