Carbonylation of chlorobiphenyls catalyzed by modified cobalt carbonyl

Article abstract of DOI:10.1134/S1070428007120044

Dichlorobiphenyls having both chlorine atoms in the same benzene ring undergo mild carbonylation in the presence of 1,2-epoxypropane-modified carbonyl cobalt complex to give biphenylcarboxylic acid esters. Monochlorobiphenyls fail to react under analogous conditions. The rate and selectivity of the reaction depend on the position of chlorine atoms. Carbonylation of dichlorobiphenyls having a chlorine atom in the meta position occurs preferentially at that position. 2,4-Dichlorobiphenyl gives rise mainly to the carbonylation product at the 2-position.

Full text of DOI:10.1134/S1070428007120044

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2007, Vol. 43, No. 12, pp. 1760–1764. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © V.P. Boyarskii, T.E. Zhesko, K.E. Tvorogov, 2007, published in Zhurnal Organicheskoi Khimii, 2007, Vol. 43, No. 12, pp. 1759–1764.
Carbonylation of Chlorobiphenyls Catalyzed
by Modified Cobalt Carbonyl
V. P. Boyarskiia, T. E. Zheskoa, and K. E. Tvorogovb
a VNIINeftekhim Public Corporation, Zheleznodorozhnyi pr. 40, St. Petersburg, 193148 Russia
e-mail: vadimpb@yahoo.com
b St. Petersburg State University, Universitetskii pr. 26, St. Petersburg, 198504 Russia
Received June 21, 2006; revised September 12, 2007
Abstract—Dichlorobiphenyls having both chlorine atoms in the same benzene ring undergo mild carbonyla-
tion in the presence of 1,2-epoxypropane-modified carbonyl cobalt complex to give biphenylcarboxylic acid
esters. Monochlorobiphenyls fail to react under analogous conditions. The rate and selectivity of the reaction
depend on the position of chlorine atoms. Carbonylation of dichlorobiphenyls having a chlorine atom in the
meta position occurs preferentially at that position. 2,4-Dichlorobiphenyl gives rise mainly to the carbonylation
product at the 2-position.
DOI: 10.1134/S1070428007120044
Polychlorinated biphenyls possess a number of
unique physical and chemical properties which pre-
determine their wide applications as dielectrics in
transformers and condensers, hydraulic liquids, heat-
transfer materials, and refrigerants. On the other hand,
polychlorobiphenyls are highly toxic substances which
affect immune, endocrine, and nervous systems and
exhibit carcinogenic properties [1]. Therefore, in the
recent time much attention is given to the development
of effective procedures for utilization of polychloro-
biphenyls.
reacted first. Furthermore, at a high substrate conver-
sion it is impossible to obtain monocarbonylation prod-
uct, for methoxycarbonyl group that replaces chlorine
accelerates the carbonylation process [5, 6].
Therefore, it was interesting to perform carbonyla-
tion of polychlorobiphenyls using specially synthe-
sized individual compounds under specific conditions
ensuring a low substrate conversion with a view to
determine the structure of primary carbonylation prod-
ucts. Naturally, the simplest case should be the reaction
with mono- and dichlorobiphenyls. Thus the goal of
the present work was to analyze the structure of prod-
ucts formed in the first stage of carbonylation of low-
chlorinated biphenyls.
We recently described a procedure for utilization of
commercial polychlorobiphenyl mixtures via catalytic
carbonylation [2, 3]. As catalyst we used carbonyl
cobalt complex modified by 1,2-epoxypropane [4].
The mechanism of carbonylation of aryl halides in the
catalytic system Co2(CO)8–epoxide was described in
[5]. It involves reversible opening of the oxirane ring
with formation of intermediate anionic complex which
is the true catalyst of carbonylation of aryl halides.
This complex is strongly nucleophilic, and it activates
aryl halides according to the SRN1 mechanism.
The carbonylation in the presence of modified
carbonyl cobalt complex was carried out under the
conditions described in [2]: carbon(II) oxide pressure
760 mm, 60°C, methanol–potassium carbonate–potas-
sium (tetracarbonyl)cobaltate, 1,2-epoxypropane as ac-
tivator. Short reaction time and low concentrations of
the reactant and catalyst ensured a low substrate con-
version (15–30%). All monochlorobiphenyls, as well
as 4,4′-dichlorobiphenyl, turned out to be inert under
the given conditions. Dichlorobiphenyls having both
chlorine atoms in the same ring underwent carbonyla-
tion to produce the corresponding biphenylcarboxylic
acid esters (Scheme 1). The product structure was
determined on the basis of their NMR and high-
resolution mass spectra and GC–MS data.
There are some published data on the structure of
polychlorobiphenyl carbonylation products obtained
under conditions ensuring complete substrate conver-
sion [3]. However, these data provide no information
on the positional selectivity of carbonylation: the prod-
ucts contained on the average two carboxy groups per
molecule, and it remained unclear which chlorine atom
1760

CARBONYLATION OF CHLOROBIPHENYLS
1761
Scheme 1.
O
O
O
COOMe
Cl
Cl
MeO
Cl
MeO
Me
+
+
I
II
III
IV
I:II :III = 1:0.12:<0.01
O
O
Cl
OMe
Me
O
+
Cl
Cl
MeO
V
VI
VII
VI:VII = 1:0.08
O
O
Cl
Cl
Me
OMe
+
+
Cl
MeO
Cl
MeO
O
O
VIII
IX
X
XI
IX :X:XI = 0.8:0.2:1
O
Cl
MeO
Cl
Cl
O
+
Cl
MeO
XII
XIII
XIV
O
MeO
O
+
+
MeO
XV
XVI
XIII :XIV :XV :XVI = 1:0.08:0.1:0.1
carbon atom and 6-H, while no couplings between the
same carbon atom and other protons were observed.
These data indicate interaction through three bonds,
which should occur in 2-chlorobiphenyl-3-carboxylic
acid but not in isomeric 3-chlorobiphenyl-2-carboxylic
acid.
Another carbonylation product derived from 2,3-di-
chlorobiphenyl (I) was diester III. It was isolated from
the second fraction after separation of the product mix-
ture by column chromatography. In the 1H NMR spec-
trum of III we observed two signals at δ ~3.9 and
~3.6 ppm, corresponding to protons of the methoxy
The major carbonylation product obtained from
2,3-dichlorobiphenyl (I) was methyl 2-chlorobiphenyl-
3-carboxylate (II). Its structure was determined by
alkaline hydrolysis which resulted in the formation of
known carboxylic acid XVII [7]. The latter was also
identified by NMR spectroscopy. Acid XVII displayed
1
in the H NMR spectrum a doublet of doublets at
δ 7.78 ppm, which is likely to belong to proton in the
6-position; the 13C NMR spectrum contained a signal
at δC 167.6 ppm corresponding to the carbonyl carbon
1
atom. The two-dimensional H–13C NMR spectrum
revealed an appreciable coupling between the C=O
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 12 2007

BOYARSKII et al.
1762
groups. The first of these is likely to belong to the ester
group in the meta position, and the second, to that in
the ortho position.
According to the GC–MS data, the product mixture
(after isolation and methylation) contained a small
amount (~0.5%) of ester IV ([M]+ 212) resulting from
hydrodechlorination of II or III (we failed to deter-
mine the position of the ester group in the benzene ring
of compound IV).
those found for diester XI: about 3.9 and 3.6 ppm. The
upfield signal in the spectrum of IX/X belonged to the
minor product. Analogous signals were observed in
the spectra of isomeric esters II and III (see above).
Therefore, we assigned the signal at δ 3.6 ppm to
the ester group in the ortho positions, and that at
δ 3.9 ppm, to the ester group in the meta position (C5).
This means that the major monocarbonylation product
of 2,5-dichlorobiphenyl (VIII) is methyl 2-chlorobi-
phenyl-5-carboxylate (IX) rather than methyl 5-chloro-
biphenyl-2-carboxylate (X).
In order to identify carbonylation products of
2,4-dichlorobiphenyl (V), the reaction mixture was
subjected to hydrolysis. The 1H NMR spectrum of car-
boxylic acid mixture thus obtained contained a signal
at δ 7.73 ppm, which was assigned to 3-H in the major
product. This signal is displaced appreciably downfield
relative to the corresponding signal of initial 2,4-di-
chlorobiphenyl (δ 7.53 ppm), indicating that the car-
boxy group is attached to C2. Otherwise (replacement
of the 4-Cl atom), signals from protons in positions 3
and 5 should be displaced approximately equally. The
signal at δ 7.52 ppm (d.d) was assigned to 5-H (para
position with respect to the carboxy group); it was
displaced only slightly (Δδ < 0.15 ppm) relative to the
5-H signal in the spectrum of V. This spectral pattern
corresponds to 4-chlorobiphenyl-2-carboxylic acid
(XVIII). The downfield region of the spectrum con-
tained signals from the minor product: broadened sin-
glet and doublet were attributed to protons in positions
3 and 5 of biphenyl-2,4-dicarboxylic acid (XIX). We
can conclude that the carbonylation of 2,4-dichloro-
biphenyl (V) yields mainly ester VI and that diester
VII is formed as minor product.
Gas chromatographic–mass spectrometric analysis
of the reaction mixture obtained by carbonylation of
2,5-dichlorobiphenyl (VIII) showed the presence of
three products, two of which were isomeric methyl
chlorobiphenylcarboxylates IX and X ([M]+ 246) and
the third was diester XI ([M]+ 270). Compound XI and
one of the monoesters predominated in the product
mixture. Our attempts to avoid formation of the dicar-
bonylation product were unsuccessful; taking into
account low reactivity of 2,5-dichlorobiphenyl (VIII),
the reaction rate considerably increases after replace-
ment of the first chlorine atom. The product ratio in
the carbonylation of VIII was determined from the
GC–MS data. The ester mixture was separated by
column chromatography. We isolated two fractions, the
first of which contained esters IX and X, and the
second, diester XI.
1
The H NMR spectrum of mixture IX/X also con-
tained doublets at δ 7.62 and 7.76 ppm corresponding
to 3-H in the major and minor products, respectively.
The downfield signal is likely to belong to a proton
neighboring to the carboxy group, i.e., 3-H in X, while
the 3-H proton neighboring to chlorine atom (isomer
IX) resonates in a stronger field. These findings pro-
vide further support to the above conclusion.
GLC analysis of the product mixture obtained by
carbonylation of 3,4-dichlorobiphenyl (XII) showed
that the major product is a chlorobiphenylcarboxylic
acid ester. Its structure was determined by comparing
1
the H NMR spectrum of the isolated substance with
that of initial 3,4-dichlorobiphenyl (XII). The 2-H
signal in the spectrum of the former (δ 8.01 ppm) was
displaced by 0.26 ppm downfield relative to the cor-
responding signal of initial 3,4-dichlorobiphenyl (XII)
(δ 7.75 ppm). The isolated product also displayed
a broadened doublet at δ 7.76 ppm, which was as-
signed to 6-H; this signal also appears in a weaker field
relative to the corresponding signal of XII. The 2-H
and 6-H protons in molecule XII occupy, respectively,
the ortho and para positions with respect to the chlo-
rine atom in position 3. The observed changes in their
chemical shifts indicate that the ester group is located
in the 3-position, i.e., the major carbonylation product
is ester XIII rather than XIV. The product composition
was determined from the GC–MS data.
The reaction mixtures obtained by carbonylation of
2,3-dichlorobiphenyl (I) and 3,4-dichlorobiphenyl
(XII) also contained reductive hydrodechlorination
products (compounds IV, XV, and XVI). The absence
of monochlorobiphenyls, as well as their inertness in
the carbonylation process, indicates that carbonylation
of dichlorobiphenyls precedes hydrodechlorination.
This means in turn that initial dichlorobiphenyls do not
undergo hydrodechlorination, i.e. hydrodechlorination
is not a concurrent pathway of transformation of inter-
mediate dichlorobiphenyl radical anions. It should be
noted that hydrodechlorination occurs when chlorine
The chemical shifts of methoxy protons in the
1H NMR spectrum of mixture IX/X were similar to
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CARBONYLATION OF CHLOROBIPHENYLS
1763
atoms in initial dichlorobiphenyl are located in the
ortho position with respect to each other, i.e., only
chlorine atom in the ortho position with respect to the
carboxy group undergoes reductive substitution. Anal-
ogous pattern was observed previously in the Co-
catalyzed carbonylation of polyhalogenated benzenes
and o-halobenzoic acids under UV irradiation [8] and
in the carbonylation of o-halobenzoic acids catalyzed
by cobalt carbonyl–methyl iodide [9].
with 2 g (14 mmol) of potassium carbonate, 10 ml of
methanol, and 0.5 g (2 mmol) of dichlorobiphenyl I,
V, VIII, or XII, and carbon(II) oxide preliminarily
passed through methanol was bubbled through the
mixture over a period of 0.5 h under stirring using
a magnetic stirrer. A solution of 29 mg (0.133 mmol)
of KCo(CO)4 in 0.7 ml of methanol was then added
with a syringe, the mixture was heated to 60°C, and
0.35 g (6 mmol) of 1,2-epoxypropane was added with
a syringe. The needle was withdrawn from the septum
to prevent gas exhaust from the reactor. The reaction
was carried out until a conversion of 15–30% was
reached, the conversion being monitored by the con-
sumption of carbon(II) oxide. Gas supply was then
terminated, 1 g of potassium hydroxide was added (to
hydrolyze esters), and the mixture was stirred at 60°C
or was left overnight at room temperature. When the
hydrolysis was complete, the mixture was diluted with
diethyl ether and extracted with water. The aqueous
phase was acidified with concentrated hydrochloric
acid and was left to stand for product crystallization.
The precipitate was filtered off and dried.
EXPERIMENTAL
1
The H and 13C NMR spectra were recorded on
a Bruker DPX-300 spectrometer at 300.130 and
75.03 MHz, respectively, using CCl4–DMSO-d6 (2:1
by volume) as solvent and on a Bruker Avance DRX-
500 instrument at 500 and 125 MHz, respectively,
using acetone-d6 as solvent. The mass spectra (electron
impact, 70 eV) were obtained on an MKh-1321 instru-
ment with direct sample admission into the ion source
(ion source temperature 200°C) or on a TOF Micro-
mass LCT mass spectrometer (electrospray ionization,
ESI-TOF MS). Gas chromatographic–mass spectro-
metric analysis was performed using an Agilent 5973
instrument (electron impact, 70 eV; ion source tem-
perature 200°C; HP-5-MS capillary column, 0.25 mm×
30 m; injector temperature 260°C, detector tempera-
ture 250°C, oven temperature programming) or
a Shimadzu QO-5000 instrument (SE-54 capillary col-
umn, 0.25 mm×60 m; injector temperature 260°C,
detector temperature 250°C, oven temperature prog-
ramming). Gas–liquid chromatography was performed
on a Chrom-5 chromatograph equipped with a flame
ionization detector [glass column, 3 mm×2.5 m, sta-
tionary phase 10% of SE-30 on Chromaton N-Super
(80–100 mesh); carrier gas argon, flow rate 20–30 ml×
min–1; injector temperature 200°C, oven temperature
200°C]. The elemental compositions were determined
on a Hewlett–Packard 185B analyzer.
Carbonylation of 2,3-dichlorobiphenyl (I). The
mixture of acids obtained at a conversion of 30% was
dissolved in 10 ml of methanol, the solution was
cooled, and 0.6 g (5 mmol) of thionyl chloride was
added with care. The mixture was left overnight,
excess thionyl chloride and the solvent were removed
under reduced pressure, and the residue (a mixture of
methyl esters) was analyzed by GC–MS and separated
by column chromatography using ethyl acetate–hexane
(1:5) as eluent to isolate 80 mg (89%) of methyl
2-chlorobiphenyl-3-carboxylate (II) as an oily sub-
1
stance, Rf 0.38. H NMR spectrum, δ, ppm: 3.91 s
(3H), 7.37–7.50 m (7H), 7.67 d.d (1H). Found, %:
C 68.17; H 4.50. C14H11ClO2. Calculated, %: C 68.16;
H 4.50.
A mixture of 80 mg of compound II and 0.4 g of
potassium hydroxide in 10 ml of methanol was heated
for 5 h under reflux. The solvent was removed, 10 ml
of water was added to the residue, the mixture was
acidified with hydrochloric acid to pH <1, and the
precipitate was filtered off. Yield of 2-chlorobiphenyl-
3-carboxylic acid (XVII) 60 mg (79%), mp 154°C;
published data [7]: mp 156–158°C. 1H NMR spectrum,
δ, ppm: 7.37–7.53 m (7H, Harom), 7.78 d.d (1H, 4-H).
13C NMR spectrum, δC, ppm: 127.85, 128.83, 129.15,
129.26, 129.51, 130.38, 131.05, 134.56, 140.25, 143.23,
167.60. Found: [M – H]– 231.0219. C13H9ClO2. Cal-
culated: [M – H]– 231.0291.
Commercial inorganic reagents of chemically pure
grade were used without preliminary purification.
Potassium carbonate of analytical grade was calcined
for 6 h at 150°C. Cobalt carbonyl was commercial
product (from Merck). The solvents used were purified
and dehydrated (if necessary) according to standard
procedures. Commercial 4,4′-dichlorobiphenyl and
1,2-epoxypropane (analytical grade) were used without
additional purification. Mono- and dichlorobiphenyls
were synthesized by the Cadogan reaction according to
the procedures described in [10, 11].
The second fraction isolated by column chromatog-
raphy contained dimethyl biphenyl-2,3-dicarboxylate
General procedure for carbonylation of di-
chlorobiphenyls. A glass jacketed reactor was charged
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 12 2007

BOYARSKII et al.
1764
(III). Yield 10 mg (11%), oily substance, Rf 0.22.
1H NMR spectrum, δ, ppm: 3.09 s (3H, CH3), 3.36 s
(3H, CH3), 7.31–7.41 m (5H), 7.58–7.69 m (2H),
7.96 d.d (1H). Found, %: C 71.11; H 5.23. C16H14O4.
Calculated, %: C 71.10; H 5.22.
Methyl 3-chlorobiphenyl-4-carboxylate (XIV)
(6.4%). Mass spectrum, m/z (Irel, %): 248 (19.9)
[M + 2]+, 246 (53.8) [M]+, 217 (36.8), 215(100), 186
(2.7), 152 (56.0), 107 (7.4), 76 (12.8), 51 (2.0).
Methyl biphenyl-3-carboxylate (XV) and methyl
biphenyl-4-carboxylate (XVI) (7.8% each). Mass
spectrum, m/z (Irel, %): one isomer: 212 (100) [M]+,
181 (88.6), 152 (50.9), 127 (3.5), 76 (13.2), 51 (1.8);
another isomer: 212 (76.5) [M]+, 181 (100), 152 (61.2),
127 (4.1), 76 (26.5).
Carbonylation of 2,4-dichlorobiphenyl (V) (con-
version 30%) gave 140 mg (97%) of a mixture of
4-chlorobiphenyl-2-carboxylic acid (XVIII) and bi-
phenyl-2,4-dicarboxylic acid (XIX) at a ratio of
1
1:0.08. H NMR spectrum, δ, ppm: XVIII: 7.29–
7.47 m (6.5H), 7.52 d.d (1H), 7.73 d (1H); XIX: 7.94 d
(0.08H), 8.04 s (0.08H).
Pure ester XIII was isolated by column chromatog-
raphy using ethyl acetate–hexane (1:5) as eluent. Yield
1
102 mg, Rf 0.45, colorless oily substance. H NMR
Carbonylation of 2,5-dichlorobiphenyl (VIII).
The mixture of acids obtained at a conversion of 15%
was esterified with methanol as described above to
obtain compounds IX–XI (GC–MS data).
spectrum, δ, ppm: 8.01 d (1H), 7.76 d.d (1H), 7.56–
7.63 m (3H), 7.37–7.40 m (3H). Found, %: C 68.18;
H 4.50. C14H11ClO2. Calculated, %: C 68.16; H 4.50.
Methyl 2-chlorobiphenyl-5-carboxylate (IX)
(40%). Mass spectrum, m/z (Irel, %): 248 (27.8) [M +
2]+, 246 (78.1) [M]+, 217 (36.1), 215 (100), 152 (92.1),
107 (9.65), 76 (23.7), 44 (7.89).
REFERENCES
1. Zanaveskin, L.N. and Aver’yanov, V.A., Usp. Khim.,
1998, vol. 67, p. 788.
2. Zhesko, T.E., Boyarskii, V.P., Lanina, S.A., and Niki-
forov, V.A., Russian Patent no. 2215729, 2002; Byull.
Izobret., 2003, no. 31.
Methyl 5-chlorobiphenyl-2-carboxylate (X)
(10%). Mass spectrum, m/z (Irel, %): 248 (19.4) [M +
2]+, 246 (54.8) [M]+, 217 (37.6), 215 (100), 180 (3.2),
152 (69.9), 126 (5.4), 76 (12.9), 44 (19.4).
3. Boyarsky, V.P., Zhesko, T.E., Lanina, S.A., and Nikifo-
rov, V.A., Organohal. Compd., 2001, vol. 54, p. 226;
Nikiforov, V.A., Boyarsky, V.P., Zhesko, T.E., Lani-
na, S.A., Kolehmainen, E., and Virtanen, E., Organohal.
Compd., 2002, vol. 56, p. 409; Lanina, S.A., Boyar-
sky, V.P., Zhesko, T.E., Nikiforov, V.A., Kolehmai-
nen, E., and Virtanen, E., Organohal. Compd., 2003,
vol. 63, p. 268.
4. Zhesko, T.E. and Boyarskii, V.P., Kinet. Katal., 1994,
vol. 35, p. 320.
5. Boyarskii, V.P., Larionov, E.V., Polyakova, S.M., Boyar-
skaya, I.A., and Zhesko, T.E., Russ. J. Gen. Chem.,
2007, vol. 77, p. 915.
6. Boyarskii, V.P., Zhesko, T.E., and Lanina, S.A., Russ. J.
Appl. Chem., 2005, vol. 78, p. 1844.
7. Kikuchi, K., Yagi, M., and Takadaet, K., Bull. Chem.
Soc. Jpn., 1968, vol. 41, p. 424.
8. Kashimura, T., Kudo, K., Mori, S., and Sugita, N.,
Chem. Lett., 1986, vol. 15, p. 299; Kashimura, T.,
Kudo, K., Mori, S., and Sugita, N., Chem. Lett., 1986,
vol. 15, p. 483.
Dimethyl biphenyl-2,5-dicarboxylate (XI) (50%).
Mass spectrum, m/z (Irel, %): 270 (75.0) [M]+, 239
(100), 207 (13.4), 180 (9.8), 152 (32.1), 112 (3.8), 76
(7.1), 44 (21.4).
Ester mixture IX–XI was subjected to column
chromatography using ethyl acetate–hexane (1:5) as
eluent. The first fraction contained mixture of esters
1
IX and X. Yield 23 mg (4%), Rf 0.45. H NMR spec-
trum, δ, ppm: IX: 3.88 m (3.0H), 7.61 d (1H); X:
3.59 s (0.6H), 7.76 d (0.2H); IX/X: 7.36–7.47 m
(6.2H), 7.91–7.94 m (2.2H). The second fraction was
pure diester XI. Yield 27 mg (5%), Rf 0.27, colorless
oily substance. 1H NMR spectrum, δ, ppm: 3.62 s (3H),
3.91 s (3H), 7.30 d (2H), 7.35–7.49 m (3H), 7.82 d
(1H), 7.97 s (1H), 8.03 d (1H). Found, %: C 71.11;
H 5.23. C16H14O4. Calculated, %: C 71.10; H 5.22.
Carbonylation of 3,4-dichlorobiphenyl (XII). The
mixture of acids obtained at a conversion of 30% was
esterified with methanol as described above for the
carbonylation products of I. According to the GC–MS
data, the resulting ester mixture contained compounds
XIII–XVI.
9. Miura, M., Itoh, K., and Nomura, M., J. Mol. Catal.,
1990, vol. 59, p. 11.
10. Mullin, M.D., Pochini, C.M., McCrindle, S.,
Romkes, M., Safe, S.H., and Safe, L.M., Environ. Sci.
Technol., 1984, vol. 18, p. 468.
Methyl 4-chlorobiphenyl-3-carboxylate (XIII)
(78%). Mass spectrum, m/z (Irel, %): 248 (34.1)
[M + 2]+, 246 (91.8) [M]+, 217 (36.9), 215 (100), 182
(1.6), 152 (94.5), 107 (3.6), 76 (6.5), 51 (1.0).
11. Bolgar, M., Cunningham, J., Cooper, R., Kozloski, R.,
Hubball, J., Miller, D.P., Crone, T., Kimball, H.,
Janooby, A., Miller, B, and Fairless, B., Chemosphere,
1995, vol. 31, p. 2687.
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