Bornanes, polychlorinated

Toxaphene is a complex mixture of compounds prepared by chlorinating camphene, and contains several hundred polychlorinated bornanes. After incubation with Sulfurospirillum (Dehalospirillum) multivorans only the hexa- (B6-923) and the heptachlorinated (B7-1001) remained. The nonachlorinated congener B9-1679 could be transformed by preferential dechlorination of the em-dichloro groups with formation of the heptachlorinated B7-1001 (Ruppe et al. 2003). Further examination showed that this congener could be dechlorinated to penta- and hexachlorinated bornanes (Ruppe et al. 2004). 

It is important to note that some polychlorinated bornanes are very persistent to biodegradation and are bio concentrated in the fatty tissue of fish [227] and other aquatic organisms. In marine fish and other aquatic organisms, such as seals, whales, and penguin 2-endo,3-exo,5-endo,6-exo,8b,8c,10a,10b-octachlorobornane (Parlar No. 26, B8-1413, Tox8) and 2-endo, 3-exo,5-endo,6-exo,8b,8c,9c,10a,10c-nonachlorobornane (Parlar No. 50,B9-1679, Tox9, Toxicant Ac) are dominant [221 -223]. Furthermore, other persistent chlorinated bornanes are 2-exo,3-endo,5-exo,9b,9c,10a,10b-heptachlorobornane (Tox7, B7-1453), 2-... 

Table 13. Chemical name, chemical structure, molecular formula, molecular mass, n-octanol/water partition coefficient (log Kow)> predicted bioconcentration factors (BCFs) of 7 persistent Polychlorinated Bornanes (Toxaphene Components) with high bioconcentration potential, and measured BCFs of Hexachloronorbornadiene, Heptachloronorbornene and of Bromocyclen... 

A recent study by Vetter et al. [225] showed that 11 polychlorinated bornanes were abundant in different seal species. The most important persistent 7 polychlorinated bornanes with their lUPAC name, different abbreviations, chemical structure, molecular formula, n-octanol/water partition coefficient (log Kqw) and predicted bio concentration factors (BCF and BCFl) in fish are compiled in Table 13. The predicted BCFl values of hepta-, octa- and nonachlorobornanes are between 600,000 and 71,000,000, and the predicted BCF values of these congeners in fish with 5 % lipid range from ca. 32,000 to 3,500,000. Furthermore, in Table 13 the BCF and BCFl values of two polychlorinated bornane congeners (Parlar No. 26 and No. 50) are included, which were calculated by the authors from the measured concentrations in zooplankton and different fish species and the water of a Canadian fresh water lake [226]. It is obvious that the BCF values of the chlorinated bornanes calculated from concentrations in aquatic organisms and water from the environment are by a factor between 1 and ca. 70 greater than the BCFs predicted from the log values. This can be explained in part by bio accumulation. 

Pollock and Kilgore found that the amber color of toxaphene arises from the most polar components in the technical product [33], Parlar et al. reported that recrystallization of toxaphene yielded white crystals which mainly consisted (95 %) of polychlorinated bornanes (or dihydrocamphenes) [32], The mother liquid of the recrystallization contained about 25% unsaturated toxaphene components. A fraction enriched in unsaturated toxaphene components can be obtained in this way. 

Higher-chlorinated camphenes are the most plausible side products. They may be formed together with other cyclic carbon skeletons if the Wagner-Meerwein rearrangement (to polychlorinated bornanes) is hindered [38, 39]. The ionic addition of chlorine to the primary olefinic carbon is always in competition with radical chlorination. Although the first mechanism is more likely, the second one may also take place. It was found that a gentle chlorination of... 

In 1993, the number of theoretically possible polychlorinated bornanes was calculated as 32,768 congeners (16,128 pairs of enantiomers and 512 achiral structures) [71]. This surprisingly high number is obtained by the product of the possibility to chlorinate nine positions on secondary or tertiary carbons (29) and three primary carbon positions (C8, C9, and CIO) with a variety of 4 giving... 

The complex composition of toxaphene also creates nomenclature problems. Initially, toxaphene was the trademark of the product manufactured by the Hercules Inc. However, due to the non-restricted use of the trademark, toxaphene has become a general term for this pesticide. Further frequently applied terms were camphechlor , polychlorinated bornanes , camphenes , and ter-penes , as well as chlorobornanes . The expression toxaphene is not the same as the trademark Toxaphene , since residues in the environment may also originate from other technical products (see Table 2). Toxaphene is the reaction product of the chlorination of technical camphene is a suitable definition of the expression used in the scientific language [27]. Owing to the problems with abbreviations as described below, toxaphene will be used in the following chapters as a synonym for the compounds of technical toxaphene. 

As mentioned before, most toxaphene components are chiral. Polychlorinated bornanes contain a plane of symmetry. The structures of enantiomers are generated by reflection of the substituents at C2, C3, and C9 with those at C6, C5, and C8, respectively (see Fig. 4). Consequently, enantiomers of chlorinated bornanes have a different nomenclature which causes additional troubles with naming [71,83]. 

The following year, Andrews and Vetter introduced a system which allowed a conversion of the structure into a code with a computer program [88]. These so-called AV-codes (Andrews and Vetter codes) start with a number and a letter representing the C-backbone and the degree of chlorination which are connected to a one to four-digit number by a hyphen. The latter is the isomer-specific assignment. So far, this system is restricted to polychlorinated bornanes since the IUPAC nomenclature for camphenes and dihydrocamphenes is still not completely clarified (see Sect. 1.2). 

To facilitate comparison and conversion, a list of 39 polychlorinated bornane structure is given in Table 4 which includes the coding according to all systems discussed above. 

Compounds with a sufficient volatility and thermal stability can be ionized in the vapor phase by bombardment with high-energy electrons which removes electrons from occupied orbitals [107]. According to our search of the literature, the first mass spectrometric analysis of toxaphene was reported in 1966 [108], and the first GC/EI-MS of a single toxaphene was published in 1974 [62]. Nowadays, numerous references are available containing many mass spectra and detailed descriptions of the EI-MS-fragmentations of polychlorinated bornanes [109-116]. Here, only the basic approach is given for the interpretation of El-MS. Most El-MS of polychlorinated bornanes lack the molecular ion in contrast to toxaphene components with one or two double bonds where it is clearly visible [109]. 

Fig. 7. Postulated EI-MS fragment ions of polychlorinated bornanes according to Parlar [119]...

Table 5. Typical H-NMR chemical shifts and coupling constants (in CDC13) of polychlorinated bornanes [3,83,94]...

Non-polar stationary phases were also found to show a structure-dependent elution order of toxaphene congeners [147]. For example, the substitution pattern at the bridge can be deducted. 8,8-substituted polychlorinated bornanes eluted much earlier than 8,9-substituted ones [147,149,150], The less polar the stationary phase, the more this rule comes to fruition. However, such structure-dependent selectivities do not necessarily improve the separation performance. For 8,8,9- or 8,9,9-substituted chlorobornanes having otherwise the same substitution pattern (e.g., B8-806 (P-42a) and B8-809 (P-42b)), the difference in retention decreases with decreasing polarity of the stationary phase. These components can only be separated on more polar stationary columns. Resolution of B8-806 (P-42a) and B8-809 (P-42b) was obtained on Optima 17 and Optima 3 stationary phases [151,152]. When using ECD it has to ensured in addition that no other organochlorine compounds interfere with the toxaphene compounds. 

The bulk of the toxaphene components detected in environmental samples are polychlorinated bornanes and a few camphenes or bornenes. Since reductive dechlorination of polychlorinated bornanes leads to bornanes with one less chlorine atom, at present it is not possible to distinguish unequivocally between components originating from technical toxaphene and dechlorinated metabolites. This question can only be solved with fate studies of single components in the laboratory [122,165],... 

Structure elucidation of polychlorinated bornanes has become a routine method. 

It should be also noted that considerable attention has been directed to the highly toxic polychlorinated bornanes (toxaphene) and derivatives of hexachlorocyclopentadiene (chlordane) that were used as pesticides. Chlor-dane has been recovered from biota (Buser et al. 1992), and toxaphene components from sediments (Stem et al. 1996), so that these are highly persistent contaminants. For both, the commercial products contained a large number of congeners, and the analysis of chlordane is complicated additionally by the occurrence of enantiomers, some of which have undergone degradation and transformation after discharge. Nevertheless, only limited attention appears to have been directed to waste from locations at which these products were manufactured. 

---