Structure characterization and thermal stabilities of the isomers of the brominated flame retardant 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane

1,2-Dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH) is used primarily as an additive flame retardant. 1H NMR spectroscopy and an X-ray structure determination have revealed that a technical mixture consists largely of two (of the four possible) diastereomers, rac-(lR,2R)-1,2-dibromo-(4S)-4-((lS)-1,2-dibromoethyl)cyclohexane (a-TBECH) and rac-(lR,2R)-1,2-dibromo-(4S)-4-((lR)-1,2-dibromoethyl)cyclohexane (P-TBECH), in a mole ratio of approximately 1:1. The two other possible isomers, y- and 6-TBECH, were not detected in a technical mixture. The TBECH isomers are thermally sensitive and can easily interconvert at temperatures of 125 oC. A thermal equilibrium mixture of ot-, P-, y- and 8-TBECH consists of approximately 33%, 33%, 17% and 17% of these isomers, respectively. Separation of all four TBECH diastereomers, with minimal thermal interconversion of the isomers, was achieved by careful selection of GC-capillary column length and injector temperature. Although technical TBECH does not contain the y- and 8-isomers, they may still be relevant environmental contaminants since manufacturing processes utilize thermal processes which may induce their formation. (c) 2008 Elsevier Ltd. All rights reserved.