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-(1R,2R)-1,2-dibromo-(4S)-4-((1S)-1,2-dibromoethyl)cyclohexane (α-TBECH) and rac-(1R,2R)-1,2-dibromo-(4S)-4-((1R)-1,2-dibromoethyl)cyclohexane (β-TBECH), in a mole ratio of approximately 1:1. The two other possible isomers, γ- and δ-TBECH, were not detected in a technical mixture.The TBECH isomers are thermally sensitive and can easily interconvert at temperatures of 125 °C. A thermal equilibrium mixture of α-, β-, γ- and δ-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 γ- and δ-isomers, they may still be relevant environmental contaminants since manufacturing processes utilize thermal processes which may induce their formation.