Synthesis of two major toxaphene components and their photostabilities

Article abstract of DOI:10.1021/jf051451b

The synthesis of 2-endo,3-exo,5-endo,6-exo,8,9,10-heptachlorobornane (B7-1001, Hp-Sed) and 2-endo,3-exo,5-endo,6-exo,8,9,9,10-octachlorobornane (B8-1412) is described. Both compounds are components of toxaphene, an insecticide that has been widely used in the past. B7-1001 is an important toxaphene congener, comprising up to 99% of total toxaphene concentrations found in fish and sediment samples from treated lakes. B8-1412 is also a significant component of toxaphene contamination in samples from biota. In synthesizing the compounds, 2-exo,3-endo,6-endo,8,9,10-hexachlorobornane (B6-913) was obtained by reduction of the well-known toxaphene component P 32 (B7-515, 2,2,5-endo,6-exo,8,9,10-heptachlorobornane), which was itself isolated from the chlorination products of (+)-camphene. Chlorination of B6-913 provided B7-1001 in 49.5% yield, and P 32 and four other heptachlorobornanes were also detected in the reaction mixture. Structures of two of the heptachlorobornanes were elucidated by MS and NMR as 2-exo,3-endo,6-endo,8,9,9,10-heptachlorobornane (B7-1461) and 2-exo,3,3,6-encto,8,9,10-heptachlorobornane (B7-1303). B8-1412 was isolated from the product mixture obtained by chlorination of 2-exo,3-endo,6-endo,8,9,9,10-heptachlorobornane. Photolysis experiments at λ = 254 nm revealed that B6-913 is photochemicaly the most stable compound of the seven toxaphene compounds studied, with a t_1/2 of 213 h. B7-1001, having a t_1/2 of 82 h, was the second most stable compound. B8-1412 was degraded more rapidly, with a t_1/2 of 28.8 h, than B7-1001, but was still much more stable than P 50 (B9-1679, 2-endo,3-exo,5-endo,6-exo,8,8,9,10,10-nonachlorobornane), which had a t _1/2 of 9.4 h, despite its reputation as a very persistant compound. Under the same experimental conditions hexachlorobenzene (HLB) and octachlorodibenzodioxine (OCDD) were consumed very quickly with t_1/2 = 0.0025 and 0.0015 h, respectively.

Full text of DOI:10.1021/jf051451b

J. Agric. Food Chem. 2005, 53, 10105−10112 10105
Synthesis of Two Major Toxaphene Components and Their
Photostabilities
§
MEHMET COELHAN*,† AND MARTIN MAURER
Research Center for Brewing and Food Quality, Technical University of Munich, 85350
Freising-Weihenstephan, Germany, and Department of Natural Sciences, University of Kassel,
Heinrich-Plett-Strasse 40, 34132 Kassel, Germany
The synthesis of 2-endo,3-exo,5-endo,6-exo,8,9,10-heptachlorobornane (B7-1001, Hp-Sed) and
2-endo,3-exo,5-endo,6-exo,8,9,9,10-octachlorobornane (B8-1412) is described. Both compounds are
components of toxaphene, an insecticide that has been widely used in the past. B7-1001 is an
important toxaphene congener, comprising up to 99% of total toxaphene concentrations found in
fish and sediment samples from treated lakes. B8-1412 is also a significant component of toxaphene
contamination in samples from biota. In synthesizing the compounds, 2-exo,3-endo,6-endo,8,9,10-
hexachlorobornane (B6-913) was obtained by reduction of the well-known toxaphene component P
32 (B7-515, 2,2,5-endo,6-exo,8,9,10-heptachlorobornane), which was itself isolated from the chlorina-
tion products of (+)-camphene. Chlorination of B6-913 provided B7-1001 in 49.5% yield, and P 32
and four other heptachlorobornanes were also detected in the reaction mixture. Structures of two of
the heptachlorobornanes were elucidated by MS and NMR as 2-exo,3-endo,6-endo,8,9,9,10-
heptachlorobornane (B7-1461) and 2-exo,3,3,6-endo,8,9,10-heptachlorobornane (B7-1303). B8-1412
was isolated from the product mixture obtained by chlorination of 2-exo,3-endo,6-endo,8,9,9,10-
heptachlorobornane. Photolysis experiments at λ ) 254 nm revealed that B6-913 is photochemicaly
the most stable compound of the seven toxaphene compounds studied, with a t1/2 of 213 h. B7-
1001, having a t1/2 of 82 h, was the second most stable compound. B8-1412 was degraded more
rapidly, with a t1/2 of 28.8 h, than B7-1001, but was still much more stable than P 50 (B9-1679,
2-endo,3-exo,5-endo,6-exo,8,8,9,10,10-nonachlorobornane), which had a t1/2 of 9.4 h, despite its
reputation as a very persistant compound. Under the same experimental conditions hexachloroben-
zene (HLB) and octachlorodibenzodioxine (OCDD) were consumed very quickly with t1/2 ) 0.0025
and 0.0015 h, respectively.
KEYWORDS: Toxaphene; single compounds; B6-923; B7-1001; B8-1412; photostability
INTRODUCTION
growing regions in the southern United States has been
considered as the major contamination source to these areas
(10-13). Toxaphene was the contaminant responsible, at least
in part, for the issuance of a total of six fish consumption
advisories by four states of the United States (Arizona, Georgia,
Oklahoma, and Texas) in 1998 (1).
Toxaphene belongs to a class of widespread organochlorine
contaminants that give rise to general concerns due to their
ability to accumulate in the food chain and, thereby, pose
potential risks even to humans (1-3). It is a complex mixture
consisting of more than 1000 polychlorobornanes and poly-
chlorocamphenes (4). In the United States, Canada, and western
European countries, it has been banned since the early 1980s
because of its toxicity, its environmental persistence, and its
high potential for bioaccumulation (5). However, due to its
relatively long half-life, it persists in the environment. The
presence of these compounds is of great concern in the Canadian
Arctic food web, in Great Lakes fish, and on the Canadian east
coast (6-9). Atmospheric transport of toxaphene from cotton-
An examination of sediment cores from two toxaphene-treated
lakes in Canada showed that toxaphene peak pattern and
concentration differed depending on sediment depth (14). The
peak patterns of sediments from the years of treatment were
similar to that of the technical toxaphene standard, whereas the
peak patterns of the near-surface sediments were very different
due to the absence of octa- and nonachlorobornane peaks in
the chromatograms. Rainbow trout samples from both lakes
showed a similar altered peak pattern. The most abundant
hexachlorobornane is labeled Hx-Sed (B6-923, 2-exo,3-endo,6-
exo,8,9,10-hexachlorobornane) and the most abundant hep-
tachlorobornane, Hp-Sed (B7-1001) (15). B7-1001 constituted
up to 99% of the total toxaphene concentration in sediment and
* Author to whom correspondence should be addressed (telephone ++49
8161 714280; fax ++49 8161 714418; e-mail coelhan@wzw.tum.de.
† Technical University of Munich.
§ University of Kassel.
10.1021/jf051451b CCC: $30.25
© 2005 American Chemical Society
Published on Web 11/22/2005

10106 J. Agric. Food Chem., Vol. 53, No. 26, 2005
Coelhan and Maurer
solution of 35 g of (+)-camphene in 300 mL of CCl4 was chlorinated
at 0 °C. The chlorination was first performed in the dark. After the
camphene peak was observed to disappear by gas chromatography, the
reaction was continued under a sun lamp and monitored by GC-MS.
When a maximum concentration for P 32 was reached, the reaction
was ceased. A 25 g portion of the product obtained, which contained
P 32 at ∼10%, was separated by column chromatography. The column
(150 cm × 5.6 cm) was packed with silica gel (0.063-0.2 mm) and
eluted with n-pentane. Elution of P 32 began after ∼33 L of n-pentane
had been eluted and was essentially complete after an additional 8 L
of n-pentane. This procedure was repeated for a further three portions,
each of 25 g. From the cyrstals obtained by concentration of the
fractions, 1100 mg of P 32 was isolated in a purity of 99% after
recrystallization from n-hexane. The yield was 1.1%.
Step 2: Dechlorination of P 32 by Reduced Hematin To Obtain
B6-913. The reaction was performed as described by Saleh and Casida
with little modifications (26). Briefly, 1050 mg of P 32 was treated
with reduced hematin. From nearly 840 mg of crude product, which
was purified with n-pentane on a silica gel column (100 cm × 3.0
cm), 90 mg of B6-913 was obtained in pure form, in addition to 440
mg of B6-923, 152 mg of 2,5-endo,8,9,10-pentachlorotricyclene, and
47 mg of 2,5-endo,6-exo,8,9,10-hexachlorobornene-2.
Step 3: Chlorination of B6-913 and Isolation of B7-1001. A solution
of 90 mg of B6-913 in 100 mL of CCl4 was chlorinated at 0 °C under
a sun lamp. The reaction was monitored by GC-MS. To avoid
overchlorination, the reaction was terminated after consumption of
approximately half of B6-913. The chlorination product was chromato-
graphed on a silica gel column (100 cm × 1.4 cm) to isolate the
remaining B6-913, which was chlorinated again as described above to
increase the B7-1001 yield. The purification of B7-1001 was performed
by using a silica gel column (100 cm × 1.4 cm). n-Pentane was used
as the elution solvent. Twenty-seven milligrams of B7-1001 could be
obtained this way, in a purity of ∼93%. Fourteen milligrams of 2-exo,3-
endo,6-endo,8,9,9,10-heptachlorobornane (4, purity ∼70%) and 2 mg
of 2-exo,3,3,6-endo,8,9,10-heptachlorobornane (5, purity ∼65%) were
isolated as byproducts.
Step 4: Formation of B8-1412. This compound was obtained starting
from 4 according to the same procedure used to obtain B7-1001.
Thirteen milligrams of 4 was used for the chlorination. B8-1412 (2.4
mg) was isolated in a purity of 91% after silica gel chromatography
using a column of 100 cm × 1.4 cm and pentane as elution solvent.
Photolysis. An oxygen-free solution containing 10 mg of toxaphene
in 80 mL of n-hexane was irradiated with a high-pressure mercury lamp
(HPK 125 W, Philips) jacketed with a water-cooled quartz filter (λ g
230 nm) for 48 h. Samples were analyzed in 4 h intervals using GC-
ECD. Photolysis of single compounds dissolved in cyclohexane was
carried out in triplicate in quartz tubes (i.d. ) 5 mm, length ) 35 cm).
Initial concentrations of individual compounds were 400 pg/µL. The
solutions (5 mL) were purged of oxygen by passage through a gentle
stream of nitrogen for 10 min before irradiation. Tubes were placed
circularly at a distance of 2 cm around the light source (mercury low-
pressure lamp, type Vycor 250 mA; Gra¨ntzel, Germany) and irradiated
at λmax ) 254 nm for up to 250 h. Sampling intervals varied widely
and depended on degradation rates.
fish samples from the treated lakes (16). B6-923 and B7-1001
were the most abundant toxaphene components in the sediment
and biota samples from an estuarine salt marsh near a former
toxaphene plant in Georgia (17). In air samples, which were
found to contain transformed toxaphene residues, both B7-1001
and B8-1412 were detected (18, 19).
In well-aerated soils, toxaphene is extremely persistent due
to its highly oxidized nature. However, rapid degradation can
take place in anaerobic soil environments (20). The main
reaction under these conditions is reductive dechlorination,
resulting in the formation of B6-923 and B7-1001 as major
products (21). Studies on the degradation of single toxaphene
components under anaerobic conditions confirmed the depen-
dence of microbial dechlorination rates on the chlorine substitu-
tion pattern of the six-membered ring (21-23). B7-1001 has
been identified as the main metabolite during anaerobic
degradation of the toxaphene components having only a single
chlorine atom at each secondary ring carbon atom in alternating
orientation and chlorine atoms at carbon positions 8, 9, and 10.
On the other hand, P 32 and five analogous compounds
possessing 2,2,5-endo,6-exo chlorine substitution at the six-
membered ring formed B6-923 and B6-913 upon degradation,
which were stable metabolites (24). There is no information
about the photostability of B7-1001 and B8-1412, whereas some
data are available for several other toxaphene components (21-
23, 25-28).
Only stable components can be bioaccumulated and are
therefore of toxicological relevance at the subacute or chronic
level of exposure. Although some data exist on the toxicity of
B6-923 (29), to our knowledge, there have been no toxicological
studies on B7-1001 and B8-1412, primarily due to the lack of
availability of these compounds in sufficient amounts. For the
same reason, there is only very litle information about the
environmental occurrence of B7-1001 and B8-1412. B7-1001
has been isolated in very small amounts from a toxaphene-like
mixture and is available only in microgram amounts for
analytical purposes (30). One aim of this study is therefore to
develop a synthesis pathway for both compounds from P 32,
which can be isolated in gram quantities from the technical
mixture (26). Additionally, the photostabilities of toxaphene and
seven single toxaphene congeners were studied in the presence
of UV light and compared with those of hexachlorobenzene
and octachlorodibenzodioxine.
EXPERIMENTAL PROCEDURES
General Procedures. All chemicals were purchased from com-
mercial sources and used without additional purification. If known,
Parlar names (31) or AV codes (32) were used as trivial names for the
chlorobornanes. The GC-MS measurements were performed with a
mass selective detector (MSD, Hewlett-Packard 5970). The capillary
column used was a 30 m × 0.25 mm × 0.25 µm DB-5MS column.
Helium was the carrier gas with a flow of ∼0.8 mL/min. A gas
chromatograph equipped with an electron capture detector (ECD) was
also used in some analyses. For GC-ECD analyses a DB-5 column
was used, with a length of 60 m, i.d. of 0.25 mm, and film thickness
of 0.25 µm. Nitrogen was used as the carrier gas with a flow of ∼0.6
mL/min.
RESULTS AND DISCUSSION
To obtain B7-1001 from B6-913 it was assumed that the
introduction of the new chlorine should take place preferentially
at the exo-position of the C-5 atom. The presence of an endo-
chlorine at the neighboring C-atom should favor this reaction
because of reduced steric hindrance. Product analysis confirmed
this assumption; however, the yield was hampered by the
formation of other heptachlorobornanes and further chlorination
reactions (Figures 1 and 2).
Under the assumption that position 4 will not be chlorinated
(33), eight different heptachlorobornanes are possible by
substitution of a proton in B6-913. There can be only three
different heptachlorobornanes, if the CH2Cl (C8, C9, and C10)
groups of B6-913 are chlorinated. The other five heptachlo-
1H and 13C NMR Spectroscopy. A Bruker AC-400 spectrometer
was employed with tetramethylsilane (TMS) as a standard and
deuterated chloroform (CDCl3) as the solvent, but B7-1001 was
measured in deuterated benzene (C6D6). An additional 13C NMR
spectrum of B7-1001 was recorded in CDCl3 with a 250 MHz
instrument from Bruker. All chemical shifts were referenced to the
solvent peak and recalculated with respect to TMS, δ (1H) 7.24 ppm
for CHCl3.
Synthesis. Step 1: Isolation of P 32. P 32 was synthesized after
modifying a previously published procedure (26). A magnetically stirred

Synthesis of Toxaphene Components
J. Agric. Food Chem., Vol. 53, No. 26, 2005 10107
Figure 1. Formation of B7-1001 (3) and other heptachlorobornanes (4−8) from B6-913. The asterisks indicate unconfirmed structures.
robornanes can be formed by replacing one of the H atoms with
chlorine at the 2-endo, 3-exo, 5-endo, 5-exo, and 6-exo positions.
At least six different heptachlorobornanes were formed from
B6-913 (Figure 1). The presence of the remaining two hep-
tachlorobornanes in the reaction mixture cannot be excluded.
However, no other heptachlorobornanes could be discerned with
the DB 5 column used in this study. B7-1001 is by far the main
product among the heptachlorobornanes, followed by compound
4 (Figure 1).
Compounds 7 and 8 could not be isolated. Fortunately,
compound 8 showed the same relative retention time as 2-exo,3-
endo,6-endo,8,9,10,10-heptachlorobornane (34). In that study,
the retention order of chlorobornanes was given in dependence
of chlorine substitution as 8,8,9,10 or 8,9,9,10 < 8,9,10,10,
which was in agreement for compound 8.
Structure Elucidation by MS and NMR. The number of
CH2Cl and CHCl2 groups in a chlorobornane molecule can be
determined by studying the ratio of ion intensities of m/z 49
(CH2Cl+) to m/z 83 (CHCl2+) in an EI mass spectrum (33). If
the ratio is >1, then there is no CHCl2 group. The molecule
possesses a CHCl2 group if the ratio lies between 0.5 and 1.
The ratios were 2.09, 2.10, and 2.32 for compounds 3, 5, and
6, respectively. Compounds 4, 7, and 8 exhibited ratios of 0.74,
1.09, and 0.89, respectively. This indicates that compounds 4,
7, and 8 possess a dichloromethyl group, and the heptachlo-
robornanes 3, 5, and 6 should have four chlorines on the six-
membered ring. Mass spectrometrical discrimination of these
three compounds is rather complicated by the fact that the
spectra are very similar. The number of chlorines at positions
8 and 9 cannot be determined by conventional EIMS (33).
However, the mass spectrum of compound 8 differs from those
of 4 and 7 by the presence of a significant peak group starting
at m/z 327, which derives from the elimination of a CH2Cl group
from M+. Another ion in the mass spectrum of 8, which does
not exist in the spectra of 4 and 7, is [M - HCl - CH2Cl]+,
which is also present in the spectra of compounds 3, 5, and 6.
The agreement of the mass spectra of 4 and 7 indicates that
both compounds should be structurally similar. Because of the
lack of other useful fragment ions to identify 4, 7, and 8, the
mass spectra cannot be used to establish without a doubt which
compound has two chlorines at C10. Hence, the structure of 8
(B7-1462) is based on its relative retention time (34).
focus our discussion on compound 5. The structure of this
substance cannot be deduced from its mass spectrum, but it can
be assumed that the new chlorine is not added to the methylene
group to produce 2-endo,3-endo,5-endo,6-exo,8,9,10-heptachlo-
robornane. The evidence for this assumption is that all hep-
tachlorobornanes formed possess two peak groups starting at
m/z 278 and 243, with the exception of B7-1001 and P 32, which
have two chlorine atoms at each side of the six-membered ring.
The first ion group corresponds to [M - HCl - C2H3Cl]+,
which is formed by a retro-Diels-Alder reaction after the
cleavage of a HCl from the side of a six-membered ring with
at least two chlorines at two adjacent carbons. This ion group
is one of the major peaks. The latter ion group is probably
formed from the first group at m/z 278 by cleavage of chlorine.
HCl elimination is obviously favored from the side of the six-
membered ring with two alternating chlorines. For instance,
dehydrochlorination of P 32 in the presence of base yields
3,6,6,8,9,10-hexachlororobornene-2 and 2,5-endo,6-exo,8,9,10-
hexachlorobornene-2 in a ratio of 2.4:1 (35). This behavior was
explained by the greater acidity of the 5-exo-hydrogen compared
with the 3-exo-hydrogen in P 32. From these considerations it
may be deduced that compound 5 is either 2,2,3-endo,6-endo-
or 2-exo,3,3,6-endo,8,9,10-heptachlorobornane.
Final confirmation of compound 3 as B7-1001 was made by
1
comparison to known H NMR data (15) (Tables 1 and 2).
Additionally, we recorded a 13C NMR spectrum, which is in
agreement with the structure of B7-1001 (Table 3). The two
quaternary carbon signals at δ 58.89 and 62.82 belonging to
C1 and C7 cannot be assigned distinctly on the basis of our
measurements (Table 3). This might be possible with hetero-
nuclear multiple bond correlation (HMBC) experiments, but with
bicyclic and similar compounds coupling constants do not follow
the order 2J > 3J > 4J > 5J and are very strongly dependent
on angle. Hence, HMBC is not very helpful. However, the
proximal environment of the C1 atom is equivalent in B7-1001,
4, and 5, whereas that of C7 is equivalent only in B7-1001 and
5. Chemical shifts of 62.3, 61.1, and 61.3 ppm are close and
therefore designated to C1 atoms of B7-1001, 4, and 5,
respectively. On the other hand, the chemical shift of 64.3 ppm
differs significantly from the other two values of 58.6 and 59.9
ppm, and consequently it can be assigned only to C7 of
compound 4 (Table 3).
The mass spectrum of compound 3 is identical to that of B7-
1001 (15), and no further comment is necessary. Instead, we
The 1H NMR spectrum of 4 differs from that of B7-1001 by
the presence of a CH2 group at 2.43 and 2.70 ppm on the carbon

10108 J. Agric. Food Chem., Vol. 53, No. 26, 2005
Coelhan and Maurer
Figure 2. HRGC-ECD chromatograms of technical toxaphene (A), toxaphene irradiated for 12 h (B) and 48 h (C), and heptachlorobornanes (3
−8)
formed by chlorination of B6-913 (D).
Table 1. Proton Chemical Shift Data for 3 (B7-1001), 4, and 5a
compd
H2
H3
H4
H5
-
H5
-endo
H6
H8a
H8b
H8c
H9a
H9b
H9c
H10b
H10c
exo
3 in C6D6
4
5
4.80 d
4.93 d
5.35 s
4.58 d
4.60 o
2.28 d
2.99 t
3.1 d
3.82 t
2.70 m
2.75 o
4.38 d
5.01 q
4.99 q
3.70 q
3.87 q
3.64 q
3.48 d
3.98 q
6.88 d
4.9 q
4.39 d
3.97 d
4.08 d
4.33 d
3.12 d
3.57 d
3.58 d
2.43 q
2.70 o
4.66 d
4.57 d
4.08 d
a Lettering of the positions at C8, C9, and C10 was made according to method of Hainzl et al., whereby 8a, 9a, and 10a mean downwards; 8b, 8c, in front of; and 8c,
9c behind the paper sheet; and 10a,10b, 10c counterclockwise (33). s singlet, d doublet, t triplet, q quartet, o octet.
)
)
)
)
)
atom with 29.8 ppm, and a proton (6.88 ppm) exhibiting a long-
range coupling of 1.9 Hz from a dichloromethyl group indicates
that the introduction of chlorine must have occurred in either
the C8 or C9 position. NOESY experiments lead to the
conclusion that the dichloromethyl group is over C2-C3 and
that compound 4 must be 2-exo,3-endo,6-endo,8b,9b,9c,10a-

Synthesis of Toxaphene Components
J. Agric. Food Chem., Vol. 53, No. 26, 2005 10109
Table 2. 1H NMR Coupling Constant Data for 3 (B7-1001), 4, and 5
compd
J23
J34
4.5
J35
J45
J5
-
J5
-
J5
-
J5
-exo/6-exo
J8ab
J8ac
J8a9a
J9ab
J9ac
J10bc
-
exo
-
exo
endo
/
5
-
ex0
endo
/
6-exo
exo
/
6
-endo
3
4
5
4.8
4.8
4.4
4.7
4.4
4.8
12.2
2.1
1.9
2.5
12.1
12.6
12.8
12.5
2.1
15.3
15.8
4.8
4.3
11.2
10.5
13.7
12.3
12.6
gives only dechlorination or dehydrochlorination products, with
reaction rates depending on the structure and chlorine number
of parent compounds (23, 25-28). Generally, during irradiation
in solvents, the bornane structure is preserved (39).
The photolysis rate of studied compounds fits a first-order
reaction kinetic profile with a half-life of
Table 3. Carbon Chemical Shift Data for 3 (B7-1001), 4, and 5
compd
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
3 in C6D6
62.8 69.0 60.7 57.6 65.7 66.8 58.9 44.6 44.0 41.3
3 in CDCl3 62.3 68.4 60.0 57.3 65.1 66.2 58.6 43.8 43.4 40.8
4
5
61.1 67.5 65.7 51.5 29.8 59
61.3 73.6 92.5 62.0 34.9 57.5 59.9 44.8 44.7 41.2
64.3 41.2 73
40.8
ln(Ct/C0) ) -kt
t1/2 ) ln 2/k
heptachlorobornane. This finding leads to the conjecture that
compound 7 should be 2-exo,3-endo,6-endo,8,8,9,10-heptachlo-
robornane (B7-1458) because the positions of the other two
dichloromethyl groups are already known. Compound 4 is
identical to B7-1461, which was found as one of three primary
degradation products of 2,2,5-endo,6-exo,8,8,9,10-octachlo-
robornane (B8-806) under anaerobic conditions (36).
where C0 and Ct are the concentrations at times 0 and t,
respectively, and k is the photolysis rate constant. The slope of
a linear plot of ln(Ct/Co) versus time gives the photolysis rate
constant. Photolysis rate constants and half-lives are listed in
Table 4.
It is apparent from the H NMR, 13C NMR, and H COSY
spectra of compound 5 that there are three chloromethyl groups,
one methylene group, and two chloromethylene groups. This
means that there is a geminal dichloro group at the six-
membered ring in either the C2 or C3 position. It is also evident
from the 1H,1H COSY spectrum that the protons at δ 4.99 (C6)
and 3.1 (C4) are in the next neighborhood to the methylene
protons at δ 2.75 and 2.70 (C5). According to NOESY and
HMQC spectra, the proton at 5.35 ppm does not couple with
the C4 proton at 3.1 ppm and also does not show any interactions
with the proton at the C9a position, but with the C10c proton at
3.58 ppm. Consequently, the seventh chlorine must be located
on the C3 atom, and compound 5 must have the structure
2-exo,3,3,6-endo,8b,9c,10a-heptachlorobornane (B7-1303).
Further Chlorination Reactions. Chlorination of 4 and B7-
1001 led to the formation of the octachlorobornane B8-1412 as
the main product in nearly identical yields ( ∼50%). MS and
NMR data of B8-1412 from these reactions conform with those
given in the literature (37). However, 4 was used as starting
compound to prevent wasting B7-1001. Besides B8-1412, 2,2,5-
endo,6-exo,8,8,9,10-octachlorobornane (P 42a, B8-806) was a
major product, which has been considered in commercial
analytical quantification standards together with 2,2,5-endo,6-
exo,8,9,9,10-octachlorobornane (P 42b, B8-809) as one com-
pound by suppliers, because up to now they could not be
separated from each other (38). A third major product’s structure
was deduced from its mass spectrum as 2-exo,3-endo,6-
endo,8,9,9,10,10-octachlorobornane (B8-1957). From B7-1001
five octachlorobornanes were formed. Apart from B8-1412, two
of them were identified by comparison of retention times as
2,2,3-exo,5-endo,6-exo,8,9,10-octachlorobornane (P 39, B8-531)
and 2-endo,3-exo,5-endo,6-exo,8,9,10,10-octachlorobornane (P
40, B8-1414). This last compound was also the major chlorina-
tion product of a fraction containing compound 8 formed from
B6-913. Chlorination of Hx-Sed yielded P 32 as the main
product (>50%). 2-endo,3-exo,5-endo,6-exo,8,8,9,10,10-Oc-
tachlorobornane (P 50, B9-1679) was formed via chlorination
from B8-1412 in high yield (>50%). These chlorination
experiments revealed that suitable chlorobornanes can be used
to obtain analytical standards of environmentally important
toxaphene components.
1
1
In addition to the seven chlorobornanes, HCB and OCDD
were irradiated for a comparison of degradation rates. Photo-
stabilities of the studied compounds varied widely. From the
chlorobornanes, P 32 was consumed most quickly, resulting in
a t1/2 of 3.9 h. B6-913 was the most stable chlorobornane, with
a t1/2 of 112 h, followed by B7-1001 and B6-923 with t1/2 values
of 82.0 and 76.5 h, respectively. 4 and B8-1412 were degraded
more rapidly, having half-lives of 32.5 and 28.8 h, respectively,
but these values were still significantly higher than that of P
50, with a half-life of 9.4 h. This is in agreement with previous
studies, which counted P 50 as one of most stable toxaphene
components (22, 23). However, compounds B6-913, B6-923,
B7-1001, 4, and B8-1412 were not available at the time of those
studies. B6-913’s half-life was 74500 times longer than that of
OCDD, which was degraded within a few seconds. HCB
displayed a degradation rate comparable to that of OCDD. The
extraordinary reactivity of HCB and OCDD is due to their high
degree of chlorination and, unlike the chlorobornanes, their
strong absorption of light at 254 nm because of their aromatic
structures. It is to be noted that the half-lives given in this work
are not relevant to environmental fate in water or the atmosphere
except in a relative way.
Structure and Photostability. Some relationships are ap-
parent between the photostability and structure of chlorobor-
nanes (22, 23, 25). Introduction of a chlorine atom leading to a
geminal group resulted in a higher degradation rate as a
comparison of the half-lives of B6-913 (or B6-923) and P 32
shows. The position of the geminal group is also very important
for photochemical degradation. For instance, P 32 has a geminal
group at C-2 and was degraded 8.3 times more quickly than 4,
which has a dichloromethyl group at position 9. The presence
of a second dichloromethyl group causes stability to drop
noticably. P 50 and B8-1412 both have four chlorine atoms in
alternating positions on the six-membered ring, which has been
considered to be an important factor for stability (22, 23).
However, the t1/2 of B8-1412 is 3 times longer than that of P
50, which has a second dichloromethyl group contrary to B8-
1412, and this characteristic resulted in a much lower photo-
stability. The number of chlorines also influences the degrada-
tion rate. For example, B7-1001 differs from B6-913 only by
the presence of a fourth chlorine atom on the six-membered
ring, and yet its half-life is 26.7% lower. In the same manner,
Photostability of Single Toxaphene Congeners. Previous
studies exhibit that photolysis of single toxaphene components

10110 J. Agric. Food Chem., Vol. 53, No. 26, 2005
Coelhan and Maurer
Table 4. Rate Constants and Half-Lives for the Decomposition of Studied Compounds in the Presence of UV Light (λ ) 254 nm)
compd
B6-913
8
B6-923
B7-1001
82 12
4
B8-1412
P 50
P 32
3.9
0.18
28.7
HCB
0.5)
OCDD
0.4)
-3
-3
half-life t1 2 (h)
112
(6.13
1
±
76.5
9.05
1.5
±
×
7
10
±
32.5
2.12
3.5
±
×
4
10
28.8
2.40
3.9
±
×
3
10
9.4
±
2
±
0.5 (2.5
±
277.2
45000
×
10
(1.5
462
±
×
10
/
-1
-3
-3
-3
-2
-
2
-2
rate const k (h
)
±
4.5)
×
10
8.45
1.4
×
10
7.37
11.9
× 10
rel rate consta
74500
a Values are rounded.
Figure 3. Chlorination products of 2-exo,3-endo,8,9,10-pentachlorobornane.
the t1/2 values of 4 and B8-1412 differ, but only by 11.5% from
each other. The reason for this relatively small difference is
probably the presence of a dichloromethyl group in both
compounds, which has a greater effect on the photostability than
a fourth chlorine atom on the six-membered ring.
prevalent in samples of aquatic biota in the northern hemisphere
(42). Despite the degradation of several nona- and decachlo-
robornanes, the composition of this mixture was still very
complex. A number of new compounds were detected in the
retention time range of the hexa- to octachlorobornanes.
Nevertheless, after 48 h of irradiation, the degree of degradation
was 99.8%, and the GC-ECD chromatogram became very
simplified, containing B7-1001 as the main compound. Other
major components were B6-923, B6-913, 2-exo,3-endo,8,9,10-
pentachlorobornane (compound 1, B5-483), and two unknown
hexachlorobornanes. The pentachlorobornane 1 was also re-
ported as an anaerobic transformation product of B6-923 and
B7-1001 (43). It should be noted that the irradiation times
employed in this work are much longer than those of previous
studies. It has been shown that all toxaphene components were
degraded and that there were great differences in the degradation
rates of individual compounds.
From the discussion so far one might expect that the two
new apparently highly photostable hexachlorobornanes possess
no geminal chlorine groups and that chlorines at adjacent carbon
atoms are in alternating positions. Consequently, altogether there
can be six different hexachlorobornanes besides B6-913 or B6-
923, making the assumption that there are three chloromethyl
groups. One supposition is that these hexachlorobornanes have
structures similar to B6-913 or B6-923, by the dissimilarity that
the third chlorine atom on the six-membered ring is located on
the C5 atom with endo or exo stereochemistry, resulting in
2-exo,3-endo,5-exo,8,9,10- or 2-exo,3-endo,5-endo,8,9,10-hexa-
chlorobornane. Another supposition is that the positions of
chlorine atoms at C2 and C3, for example, 2-endo,3-exo instead
of 2-exo,3-endo, are exchanged. In this case, there are four
possibilities for the third chlorine atom, namely, the 5-endo,
5-exo, 6-endo, and 6-exo positions. To ascertain the structures
of two new hexachlorobornanes, 2-exo,3-endo,8,9,10-pentachlo-
robornane (1, B5-483) was chlorinated (Figure 3). B6-923 and
Photoproducts. When P 32 was photolyzed, 2,5-endo,6-
exo,8,9,10-hexachlorobornene-2 was initially formed as the main
product with B6-913 forming in similar concentrations and B6-
923 forming in much lower amounts. However, further irradia-
tion led to decomposition of 2,5-endo,6-exo,8,9,10-hexachlo-
robornene-2. In former studies of P 32 this bornene was not
detected as a product (26). In our experiments, as long as P 32
was not completely degraded this compound was present in the
reaction solution. From P 50 five compounds were formed but
in very small amounts, together comprising ∼4-6% of the
starting concentration of P 50. Two of them could be identified
as B6-913 and P 40 by matching their retention times to those
of standards. No products could be detected by GC-ECD after
photolysis of all other chlorobornanes, even if the compounds
were photolyzed until total degradation.
Photolysis of Toxaphene. It has been shown that irradiation
of toxaphene solutions causes slight degradation at wavelengths
above 290 nm, but significant decomposition at wavelengths
below 290 nm (39). On the other hand, irradiation of toxaphene
adsorbed to silica gel at wavelengths above 290 nm resulted in
mineralization to HCl and CO2 (27, 28, 40). In previous work,
toxaphene was photolyzed at 254 nm for 2 h, resulting in a
mixture having a peak pattern which resembled that of tox-
aphene residues in many fish and cod liver oil samples (41).
Photolysis of toxaphene with UV light (λ g 230 nm) initially
led to rapid degradation of particularly highly chlorinated
bornanes, which was in agreement with previous results (41)
(Figure 2). After 12 h of irradiation, this mixture contained
compounds such as B7-1001, P 26 (B8-1413), B8-1412, and P
40 as major components. These compounds are also especially

Synthesis of Toxaphene Components
J. Agric. Food Chem., Vol. 53, No. 26, 2005 10111
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ACKNOWLEDGMENT
We are grateful to Prof. Dr. H. Parlar for valuable suggestions.
Supporting Information Available: Mass spectra of 3, 4, 5,
7, and 8; 13C NMR spectra of 3, 4, and 5; H NMR spectra of
1
4 and 5. This material is available free of charge via the Internet
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Received for review June 21, 2005. Revised manuscript received
October 11, 2005. Accepted October 13, 2005.
JF051451B