Hexabromocyclododecane HBCD

Technical 1,2,5,6,9,10-HBCD is produced industrially by addition of bromine to czs-trfl s-fra 5-l,5,9-cyclododecatriene, with the resulting mixture containing three predominant diastereoisomers a-, p- and y-HBCD. Normally, the y-isomer is the most dominant in the commercial mixtures (ranging between 75 and 89%), followed by a- and / -isomer (10-13% and 1-12%, respectively) [21,22]. 

The dissimilarities in the structure of the a-, p- and y-isomer might raise differences in polarity, dipole moment and in solubility in water for example the solubility of a-, /3- and y-HBCD in water was 48.8, 14.7 and 2.1 pg/1, respectively. These different properties may explain the differences observed in their environmental behaviour [21]. In sediments, the stereoisomeric profile of HBCD is similar to that on commercial HBCD formulations, with y-isomer being the most abundant stereoisomer. In contrast to sediments, the a-isomer is the most prominent stereoisomer in the majority of aquatic invertebrate and fish samples [23,24]. 

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Suggested formulations for various polymers using hexabromocyclododecane (HBCD), a brominated aHphatic a chlorinated paraffin, ie, a chlorinated aHphatic and decabromodiphenyl oxide, a brominated aromatic, are shown in Tables 2—4. These suggested formulations may not be strictiy comparable because of differences in the nature of the base resins. However, the suggestions are specific to a given UL-94 rating. 

Hexabromocyclododecane (HBCD) is prepared by the bromination of lZ,5E,9E-cyclododecatriene (CDT). The term "HBCD" will be used here to denote the commercial product containing various isomer compositions. Bromination of CDT leads to three isomers, HBCD-1 (y), HBCD-2 (P) and HBCD-3(a). All three isomers (Fig. 1) were isolated and fully identified (refs. 1,2). 

BFRs are one of the last classes of halogenated compounds that are still being produced worldwide and used in high quantities in many applications. In order to meet fire safety regulations, flame retardants (FRs) are applied to combustible materials such as polymers, plastics, wood, paper, and textiles. Approximately 25% of all FRs contain bromine as the active ingredient. More than 80 different aliphatic, cyclo-aliphatic, aromatic, and polymeric compounds are used as BFRs. BFRs, such as polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), and tetrabromobisphenol A (TBBPA), have been used in different consumer products in large quantities, and consequently they were detected in the environment, biota, and even in human samples [26, 27]. 

Examples of additives and polymer substrates which could react via [1) would be chlorinated paraffin waxes, hexabromocyclododecane (HBCD) and poly(vinylchloride) or poly(vinylbromide). 

Covaci A, Gerecke AC, Law RJ, Voorspoels S, Kohler M, Heeb NV, Leslie H, Allchin CR, De Boer J (2006) Hexabromocyclododecanes (HBCDs) in the environment and humans a review. Environ Sci Technol 40 3679-3688... 

Roosens L, Abdallah MAE, Harrad S, Neels H, Covaci A (2009) Exposure to hexabromocyclododecanes (HBCDs) via dust ingestion, but not diet, correlates with concentrations in human serum preliminary results. Environ Health Perspect 117 1707-1712... 

Johnson-Restrepo B, Adams DH, Kannan K (2008) Tetrabromobisphenol A (TBBPA) and hexabromocyclododecanes (HBCDs) in tissues of humans, dolphins, and sharks from the United States. Chemosphere 70 1935-1944... 

The term brominated flame retardant (BFR) incorporates more than 175 different types of substances, which form the largest class of flame retardants other classes are phosphorus-containing, nitrogen-containing, and inorganic flame retardants (Bimbaum and Sttaskal 2004). The major BFR substances in use today (depicted in Fig. 4.6) are tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), and mixtures of polybrominated diphenyl ethers (PBDEs) (namely, deca-bromodiphenyl ether (DBDE), octabromodiphenyl ether (OBDE), and pentabro-modiphenyl ether (pentaBDE)). 

Following receipt of data the Commission drew up priority lists of substances that, on the basis of that data, were thought to have the potential to pose a risk of harm to human health or the environment. By the publication of the EU White Paper in 2001, four lists, containing a total of 141 substances, had been adopted by the relevant technical committee (CEC, 2001). The progress of these risk assessments was very slow. Risk assessment of hexabromocyclododecane (HBCD), for example, commenced in 1997 but was still not completed nine years later (ENDS, 2006). In 2006 around 16,700 tonnes of HBCD were produced every year for use as a flame retardant. It may have neurotoxic effects and interfere with the metabolism of thyroid hormone, but because risk assessment of it had not reached a conclusion there were no restrictions on its use. By 2006 final risk assessment reports were available for only about 70 substances (European Commission, 2006b) — less than 0.5 per cent of the 30,000 or so existing substances on the European market at quantities of above 1 tonne per annum. 

Table 11.7 Concentrations of selected polybrominated diphenyl ethers (PBDE) and hexabromocyclododecane (HBCD) in house dust (mgkg1).

Other flame-retardants selected as priority chemicals for the EU Risk Assessment process included tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), tris(2-chloroethyl) phosphate (TCEP), tris (2-chloropropyl) phosphate (TCPP), tris(2-chloro-l-(chloromethyl)ethyl) phosphate (TDCP), and 2,2-bis(chloromethyl) trimethylene bis (bis(2-chloroethyl)phosphate) (V6). The flame-retardant synergist, antimony trioxide (Sb ), was also identified as a priority substance. Table 22.1 contains information on the EU Risk Assessments on the nine flame-retardants and one synergist. 

Inspection of Table 1.1 reveals that while all those listed under the original test of the Convention are organochlorines, those under consideration for inclusion include one organofluorine and a number of organobromine chemicals. Hence while this book addresses, to at least some degree, most or all of the chemicals listed in Table 1.1, it focuses particularly on polychlorinated biphenyls (PCBs), hexabromocyclododecane (HBCD), perfluorinated chemicals (PFCs), and polybrominated diphenyl ethers (PBDEs). These are selected on the basis that they either ... 

Admon, S., Davis, J. W., Gonsior, S. J., Friederich, U., Hunziker, R. W., Ariano, J. M., Weiss, M. (2007) Environmental fate of hexabromocyclododecane (HBCD), the degradation pathway. In Proceedings of the 4th International Workshop on Brominated Flame Retardants, Amsterdam, The Netherlands, 24-27 April 2007 (unpaginated). 

Reled, M. Scharia, R. Sondack, D., Thermal rearrangement of hexabromocyclododecane (HBCD) In Advances in Organobromine Chemistry II, J.R. Desmurs B. Gerard M.J. Goldstein, editors Elsevier Amsterdam, 1995, p. 92-99. 

Heeb, N.V. Schweizer, W.B. Mattrel, R Haag, R. Gerecke, A.C. Schmid, R Zennegg, M. Vonmont, H., Regio- and stereoselective isomerization of hexabromocyclododecanes (HBCDs) Kinetics and mechanism of y- to a-HBCD isomerization Chemosphere 2008, 73, 1201-1210. 

The most frequently used BFRs are polybrominated diphenylethers (PBDEs), tetrabromobisphenol A (TBBPA), and hexabromocyclododecane (HBCD). The use of FRs has been growing rapidly in recent years. BFRs are the most often used FRs, and their market is still growing. However, the estimated annual use of OPFRs in Western Europe was almost twice that of all BFRs combined. Many FRs have been banned for use because of their potential toxicity, environmental occurrence, and accumulation in human tissue. FRs taken off the market are likely to be replaced by others. Although the REACH (registration, evaluation, authorization and restriction of chemicals) regulatory system has been introduced in Europe to improve protection of human health and the environment, it is still necessary to monitor FRs in environmental samples [84, 88]. 

Another approach to durable flame retardant finishes for polyester is the use of highly brominated chemicals as topical finishes. One particularly useful material is hexabromocyclododecane (HBCD, Fig. 8.19). To achieve durable flame retardancy, fabric padded with 8 % of a dispersion of this water insoluble material must be heated above 190 °C or 375 °F to form a film of the flame retardant on the fibre surface."... 

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