Electroreductive dechlorination of α-hexachlorocyclohexane catalyzed by iron porphyrins in nonaqueous media

Article abstract of DOI:10.1142/S1088424614500254

Two iron porphyrins, (TPP)FeCl and (OEP)FeCl, where TPP and OEP are the dianions of tetraphenylporphyrin and octaethylporphyrin, respectively, were utilized as catalysts for the electroreductive dechlorination of α-hexachlorocyclohexane (α-HCH) which was monitored by electrochemistry, in situ UV-visible spectroelectrochemistry and controlled potential electrolysis in N,N′-dimethylformamide. GC-MS analysis of the α-HCH degradation products revealed the stepwise formation of pentachlorocyclohexene and tetrachlorocyclohexadiene as intermediates, prior to generation of the final dechlorination products which consisted of an isomeric mixture of trichlorobenzenes. Based on identification of the intermediates and final products in the reaction, an overall dechlorination mechanism of α-hexachlorocyclohexane is proposed.

Full text of DOI:10.1142/S1088424614500254

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2014; 18: 1–9
DOI: 10.1142/S1088424614500254
Published at http://www.worldscinet.com/jpp/
Electroreductive dechlorination of a-hexachlorocyclohexane
catalyzed by iron porphyrins in nonaqueous media
Weihua Zhua◊◊, Cui Nia, Lili Lianga, Junwen Lia, Minzhi Lia, Zhongping Ou*a◊
and Karl M. Kadish*b◊
a School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, P. R. China
b Department of Chemistry, University of Houston, Houston, TX 77204-5003, USA
Received 2 April 2014
Accepted 26 April 2014
ABSTRACT: Two iron porphyrins, (TPP)FeCl and (OEP)FeCl, where TPP and OEP are the
dianions of tetraphenylporphyrin and octaethylporphyrin, respectively, were utilized as catalysts for
the electroreductive dechlorination of a-hexachlorocyclohexane (a-HCH) which was monitored by
electrochemistry, in situ UV-visible spectroelectrochemistry and controlled potential electrolysis in
N,N′-dimethylformamide. GC-MS analysis of the a-HCH degradation products revealed the stepwise
formation of pentachlorocyclohexene and tetrachlorocyclohexadiene as intermediates, prior to generation
of the final dechlorination products which consisted of an isomeric mixture of trichlorobenzenes. Based
on identification of the intermediates and final products in the reaction, an overall dechlorination
mechanism of a-hexachlorocyclohexane is proposed.
KEYWORDS: iron porphyrins, a-hexachlorocyclohexane, reductive dechlorination, electrochemistry,
spectroelectrochemistry, electrocatalysis.
environment and human health. For example, Puc´ko et al.
studied the effect of zooplankton seasonal migrations
on a-HCH bioaccumulation [5] and described the
mechanisms and implications of a-HCH enrichment
in melt ponds formed from ice during the summer in
the Canadian high Arctic [6]. Xu et al. evaluated the
carcinogenic risk of HCHs in the muscles of fish from
Lake Baiyangdian, China [7]. The residue levels of HCH
in sediments from the middle and lower reaches of the
Yellow River, China and its tributaries were investigated
by Wang et al. [8]. Fabre et al. proposed analytical
procedures for determination of the different HCH
isomers present in vegetables, human and animal tissues,
blood and serum [9]. Liu et al. explored the residue status,
factors influencing the distribution patterns, enantiomeric
signature of a-HCH and potential human exposure risks
of HCHs in agricultural soils in China [10]. Xu et al.
propsed the air-water exchange direction of HCHs in the
water phase [11]. Dachs et al. reported the concentrations
of HCHs and other POPs in seawater and phytoplankton
from the Southern Ocean [12].
INTRODUCTION
Technical grade hexachlorocyclohexane (HCH),
which is sold as a mixture of isomers containing 55–80%
of a-HCH, 5–14% of b-HCH, 8–15% of g-HCH, 2–16%
d-HCH, and 3–5% e-HCH [1], was extensively used as
a pesticide during the latter half of the 20th century [2].
Only the g-HCH isomer, known as lindane, has specific
insecticidal activity, but the less expensive technical grade
HCH continued to be used in developing countries for the
economic reasons [1, 3]. However, due to their known
damage to ecosystems and human health, the a, b and g
isomers of HCH were listed in 2009 as persistent organic
pollutants (POPs) by the Stockholm Convention [4].
Many groups have investigated the chemical and
biological properties of HCH and their effect on the
◊SPP full and ◊◊student member in good standing
*Correspondence to: Zhongping Ou, email: zpou2003@yahoo.
com, tel/fax: +86 511-8879-1800; Karl M. Kadish, email:
kkadish@uh.edu, tel: +1 (713)-743-2740, fax: +1 (713)-743-2745
Copyright © 2014 World Scientific Publishing Company

2
W. ZHU ET AL.
Moreover, with the aim of protecting humans and the
environment from pollution with HCH, several disposal
and remediation techniques have been extensively
studied. Ukisu et al. reported that HCH isomers could be
dechlorinated to give benzene in the presence of alkaline
2-propanolandasupportedpalladiumcatalyst(Pd/C)[13].
Esteruelas et al. used rhodium and ruthenium complexes
to catalyze the dechlorination of HCH to benzene or
cyclohexene [14]. Various final degradation products of
g-HCH, such as benzene, chlorobenzene or cyclohexane,
were reported when the zero-valent iron, Fe-Pd or Pd/
Fe0 nanoparticles were used as catalysts [15–17]. Additi-
onal research has focused on the biodegradation of
HCH isomers and different processes and mechanisms
for dechlorination were also investigated [18–25]. The
electrochemical dechlorination of HCH isomers has also
been proposed [26–29].
present study, two iron porphyrins were utilized as
catalysts for the electrochemical reduction of a-HCH
in DMF. The a-HCH isomer was chosen to study in the
present work because it is the most abundant isomer in the
environment. The utilized porphyrin catalysts were (Por)
FeCl where Por = the dianion of tetraphenylporphyrin
(TPP) or octaethylporphyrin (OEP). The structures of
these macrocycles are shown in Chart 1, along with the
structures of a-HCH and its dechlorination products as
determined in the current study.
RESULTS AND DISCUSSION
Cyclic voltammograms of (Por)FeCl in the absence
and presence of a-HCH
Several porphyrins and phthalocyanines containing
transition metal ions have been applied to catalyze the
reductive dehalogenation of organohalides [30–32]. Our
own group recently reported the use of manganese, cobalt
and iron porphyrins as catalysts for the electroreduction
of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT)
in N,N′-dimethylformamide (DMF) [33–35]. In the
(TPP)FeCl and (OEP)FeCl both undergo three
reversible one-electron reductions in DMF containing
0.1 M TBAP as supporting electrolyte. Examples of
cyclic voltammograms are shown by the solid lines in
Fig. 1. The half-wave potentials corresponding to these
electron transfer processes are located at E1/2 = -0.16,
-1.02 and -1.65 V for (TPP)FeIIICl and E1/2 = -0.29, -1.24
(a) Iron porphyrins
N
N
N
Fe
N
Fe
N
N
N
Cl
Cl
N
(TPP)FeCl
(OEP)FeCl
(b) a-HCH and its final dechlorination products
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
PCCH
Cl
1,3,5-TCB
1,2,3-TCB
Cl
1,2,4-TCB
a-HCH
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
TCDN
Chart 1. Structures of investigated iron porphyrins, as well as a-HCH and its dechlorination products
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 2–9

ELECTROREDUCTIVE DECHLORINATION OF a-HEXACHLOROCYCLOHEXANE CATALYZED BY IRON
3
Fig. 1. Cyclic voltammograms of (a) (TPP)FeCl (5.0 × 10-4 M)
and (b) (OEP)FeCl (5.0 × 10-4 M) in DMF containing 0.1 M
TBAP before (—) and after (- - -) addition 1.0 equivalents
a-HCH to solution. Scan rate = 0.1 V/s
and -1.94 V for (OEP)FeIIICl. Similar electrochemical
behavior has previously been reported for other related
iron porphyrins in nonaqueous media [36, 37].
The first reduction of (Por)FeIIICl generates an Fe(II)
porphyrin and this is followed at more negative potentials
by generation of an Fe(I) porphyrin p-anion radical and
Fe(I) porphyrin dianion as shown in Equation 1 [37].
Fig. 2. Plots of Ip’/Ip vs. the ratio of (a) [a-HCH]/[(TPP)FeCl]
and (b) [a-HCH]/[(OEP)FeCl] in DMF, 0.1 M TBAP
III
II
-
(1a)
(1b)
(1c)
ꢀꢀꢁ
ꢂꢀꢀ
(Por)Fe Cl+ e
(Por)Fe + Cl
at a scan rate of 0.1 V/s. The irreversible processes
and increased peak currents in solutions of (TPP)FeCl
or (OEP)FeCl with higher concentrations of a-HCH is
consistent with homogeneous reactions involving a-HCH
(R-Cl) and [(Por)FeI]- or [(Por)FeI]2- to form s-alkyl-
metal porphyrins at the electrode surface [38, 39].
II
I -
ꢀꢀꢁ
ꢂꢀꢀ
(Por)Fe + e
[(Por)Fe ]
I
-
I
2-
ꢀꢀꢁ
ꢂꢀꢀ
[(Por)Fe ] + e
[(Por)Fe ]
The first reduction of (TPP)FeCl and (OEP)FeCl
remains reversible in DMF after 1.0 equivalent a-HCH
has been added to solution. These cyclic voltammograms
are shown by the dashed lines in Figs 1a and 1b. The
second reduction of (TPP)FeCl also remains reversible
in DMF containing 1.0 equivalent a-HCH, although a
higher cathodic current is observed than in the absence
of HCH. In contrast, the second reduction of (OEP)FeCl
is totally irreversible in DMF containing 1.0 equivalent
a-HCH and this process exhibits a much increased peak
current, which increases even further as the concentration
of a-HCH added to the DMF solution is increased above
1.0 equivalent. The electrochemical behavior indicates the
lack of a reaction between a-HCH and the neutral Fe(III)
or singly reduced Fe(II) forms of the two porphyrins. This
is not the case for the electrogenerated Fe(I) porphyrins
which react with the added a-HCH in DMF. The chemical
reaction is slower for [(TPP)FeI]- than for [(OEP)FeI]- as
evidenced by the almost reversible second reduction of
(TPP)FeCl in DMF containing 1.0 equivalent a-HCH
The changes in maximum peak current for the first
two reductions of (Por)FeCl were examined as a function
of increasing a-HCH concentration by constructing plots
of Ip’/Ip vs. the ratio of [a-HCH]/[(Por)FeCl]. Examples
of these plots are shown in Fig. 2, where Ip’ and Ip are
the measured cathodic peak currents obtained from the
cyclic voltammograms for reduction in the presence
and absence of a-HCH, respectively. The Ip’/Ip ratio is
unchanged with increase in the concentration of a-HCH
during the first reduction (FeIII/FeII process) of (TPP)FeCl
(Fig. 2a) or (OEP)FeCl (Fig. 2b), consistent with the fact
that neither the Fe(III) nor the Fe(II) porphyrin reacts
with a-HCH. However, the values of Ip’/Ip for the second
reduction of (TPP)FeCl and (OEP)FeCl both increase as
the ratio of the [a-HCH]/[(Por)FeCl] concentration is
increased, implying that the Fe(I) forms of (TPP)FeCl
or (OEP)FeCl will react with a-HCH under the given
solution conditions. The fastest reaction occurs with
(OEP)FeCl where the ratio of peak currents has increased
more than five times in DMF containing 1.0 equivalent
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W. ZHU ET AL.
a-HCH while in the case of (TPP)FeCl, the peak current
has increased by only a little more than 50% under the
same solution conditions.
Fe(II) does not react with a-HCH under the given solution
conditions. However, the spectral changes obtained
during the second reduction of (TPP)FeCl in the absence
of a-HCH differs from what is seen in the presence of
a-HCH (Fig. 3b). The final spectrum after reduction at
-1.40V in DMF without a-HCH exhibits a split Soret band
at 396 and 427 nm, both of which are characteristic of an
Fe(I) tetraphenylporphyrin [40]. This spectral pattern is
not observed after the second reduction of (TPP)FeCl in
DMF solutions containing a-HCH (Fig. 3b). In this case,
the final UV-visible spectrum displays a singly intense
Soret band at 440 nm (Fig. 3b). A similar spectrum has
been reported for related s-bonded Fe(III) porphyrin with
TPP macrocycle where the Soret band maximum ranges
from 408 to 440 nm [39, 41].
The increase in current at potentials for the second
and third reductions of (Por)FeCl is not due to the direct
reduction of a-HCH, since no reductions are seen for this
compound in DMF containing 0.1 M TBAP between 0.0
and -2.0 V vs. SCE. An electroreduction of g-HCH has
been reported at -2.16 V vs. SCE in DMF containing 0.1
M TBABF4 [27, 28], but this potential is beyond that for
the catalytic reductions illustrated in Fig. 1. Therefore,
the increased peak currents observed during the last two
reductions of (Por)FeCl in DMF containing a-HCH
are generated from a catalytic reduction which occurs
between the Fe(I) porphyrins and a-HCH.
The spectroelectrochemical data in Fig. 3 is thus
consistent with the cyclic voltammetric data in Fig. 1
in that a catalytic reaction involving a-HCH and the
electrogenerated Fe(I) porphyrin occurs after the second
reduction in DMF containing added a-HCH.
Spectroelectrochemical monitoring of (Por)FeCl
reductions in DMF with and without added a-HCH
In a previous study, in situ UV-visible spectroelectro-
chemistry was utilized to monitor the products of a
chemical reaction involving a-HCH and electrogenerated
cobalt, manganese or iron metalloporphyrins [33–35].
Spectroelectrochemistry is also used in the current study
to monitor the reductions of (Por)FeCl in DMF with
and without added a-HCH. Examples of the spectral
changes which occur during the first two reductions of
(TPP)FeCl in the absence and presence of a-HCH are
shown in Fig. 3.
Controlled-potential bulk-electrolysis
To determine the dechlorination products of a-HCH,
controlled-potential bulk electrolysis was carried out in
DMF solutions containing 2.0 × 10-4 M (Por)FeCl and
2.0 × 10-3 M a-HCH. The potentials applied for bulk
electrolysis were set at -1.40V for (TPP)FeCl and -1.50V
for (OEP)FeCl. Both potentials are sufficiently negative
to generate the Fe(I) form of the porphyrin and also to
reduce any homogeneously generated s-bonded Fe(III)
porphyrin products [36]. Figure 4 illustrates GC analysis
Identical spectral changes are observed during the first
one-electron reduction of (TPP)FeCl in DMF with and
without added a-HCH (Fig. 3a). This result confirms that
Fig. 3. Thin-layer UV-visible spectral changes of (TPP)FeCl during (a) the first and (b) second one-electron reductions in DMF
containing 0.1 M TBAP with and without added 5 equivalents a-HCH
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 4–9

ELECTROREDUCTIVE DECHLORINATION OF a-HEXACHLOROCYCLOHEXANE CATALYZED BY IRON
5
Fig. 5. The distribution of a-HCH and its products obtained in
DMF at different electrolysis times during controlled-potential
reduction of (a) (TPP)FeCl at -1.40V and (b) (OEP)FeCl at -1.50V
Fig. 4. GC analysis of a-HCH and its dechlorinated products in
DMF at different controlled-potential electrolysis times
and tetrachlorocyclohexadiene (TCDN), but it should be
noted that authentic samples of PCCH and TCDN are not
commercially available. Other less dechlorinated products
like di- or monochlorobenzene or benzene were not detected
even after longer electrolysis time in these experiments.
The data in Table 1 indicates that the dechlorination
efficiency of a-HCH is affected by the structure of the
catalysts, either (TPP)FeCl or (OEP)FeCl. When (TPP)
FeCl is used as the catalyst, a-HCH was 100% mono-
dechlorinated after 6h of controlled-potential electrolysis
while only 4 h are needed to totally convert a a-HCH
to the less dechlorinated products using (OEP)FeCl. In
addition, 8 h are needed for a-HCH to be completely
degraded to form TCB when using (TPP)FeCl as the
catalyst as compared to 6 h in the case of (OEP)FeCl.
Thus, (OEP)FeCl is a better electrocatalyst for the
reductive dechlorination of a-HCH as compared to
(TPP)FeCl under the same solution conditions.
of a-HCH and its dechlorinated products in DMF for
controlled-potential electrolysis times of 1–8 h. As seen
in this figure, five main a-HCH dechlorinated products
(PCCH, TCDN, 1,2,4-TCB, 1,2,3-TCB and 1,3,5-TCB)
are detected after 3–5 h of electrolysis when using (TPP)
FeCl as the catalyst and 2–4 h of electrolysis when
(OEP)FeCl was used as catalyst. However, only three
TCB isomers (1,2,4-TCB, 1,2,3-TCB and 1,3,5-TCB,
see Chart 1) are seen after 6–8 h of bulk electrolysis for
(OEP)FeCl and (TPP)FeCl, respectively. The calculated
distribution (mol%) of a-HCH and its dechlorinated
products which as a function of electrolysis time are
summarized in Table 1 and plotted in Fig. 5.
As seen in this table and Figs 4 and 5, the conversion
of a-HCH to the less-chlorinated compounds depends on
the time. For example, pentachlorocyclohexene (PCCH)
increases in abundance at the start of electrolysis, but
declines as the electrolysis proceeds. Identification of
the final dechlorinated products of a-HCH are the three
trichlorobenzene isomers (1,2,3-TCB, 1,2,4-TCB and
1,3,5-TCB) are based on an real sample and GC-mass
spectrum. Two intermediates are proposed to be PCCH
Proposed mechanism for dechlorination of a-HCH
A proposed catalytic cycle for the reductive dechlori-
nation of a-HCH is illustrated in Scheme 1 based on the
Copyright © 2014 World Scientific Publishing Company
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W. ZHU ET AL.
Table 1. Analysis data of a-HCH and its dechlorinated products at different reaction time during the controlled-potential electrolysis
at -1.40 V for (TPP)FeCl and -1.50 V for (OEP)FeCl in DMF
Catalyst
Electrolysis
time, h
Distribution, mol%a
a-HCH
PCCH
TCDN
1,2,4-TCB
1,2,3-TCB
1,3,5-TCB
(TPP)FeCl
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
100
83.3
60.8
35.2
20.4
8.1
0.0
10.2
16.4
21.5
25.7
24. 9
13.3
6.2
0.0
6.4
0.0
0.0
0.0
0.0
0.0
0.0
10.1
15.3
11.2
5.2
6.8
4.6
1.4
15.3
23.7
34.2
45.6
49.8
51.9
0.0
9.2
3.6
12.4
17.4
26.8
28.5
29.3
0.0
6.6
10.3
13.3
15.6
18.8
0.0
0.0
1.1
0.0
0.0
0.0
0.0
0.0
(OEP)FeCl
100
56.9
29.0
10.3
0.0
0.0
0.0
16.7
20.4
23.0
12.9
5.7
5.4
11.5
18.6
30.1
45.4
48.2
50.8
6.4
3.1
14.8
8.4
11.5
18.7
23.4
27.4
28.5
5.7
9.6
3.7
14.5
18.7
20.7
0.0
0.0
0.0
0.0
0.0
a Distribution (%) = [(moles of a specific compound)/(moles of all compounds)] × 100%.
electrochemistry, spectroelectrochemistry and GC-MS
EXPERIMENTAL
analysis. Neutral (Por)FeIIICl initially undergoes two
stepwiseone-electronreductionstoyieldthecorresponding
Chemicals
Fe(I) porphyrin which then reacts with a-HCH to generate
the organometallic intermediate having an Fe–C s-bond,
(Por)Fe–(R). This Fe(III) intermediate is further reduced
and undergoes a cleavage of the Fe–C bond leading to the
Fe(II) porphyrin with the subsequent stepwise generation
of PCCH, TCDN and then TCB.
Tetra-n-butylammonium perchlorate (TBAP) was
purchased from Fluka Chemical Company and recry-
stallized prior to use. N,N′-dimethylformamide (DMF)
was purchased from Shanghai Sinopharm Chemical
Reagent Co. (SCRC) and freshly distilled before use. The
iron porphyrins (TPP)FeCl and (OEP)FeCl were purchased
from Sigma-Aldrich, a-hexachlorocyclohexane (a-HCH)
was purchased from Shanghai Anpel Scientific Instrument
Co. and the TCBs (1,2,3-TCB, 1,2,4-TCB, 1,3,5-TCB)
were purchased from SCRC. All the iron porphyrins,
a-HCH, TCBs and other chemicals were of high-purity
grade and were used without further purification.
The formation of (Por)Fe–(R) is a nucleophilic
substitution process with the tendency of the reaction
depending on the R–Cl bond energy and the nucleo-
philicity of [(Por)FeI]-. The nucleophilicity [(OEP)FeI]-
is stronger anionic nucleophile than [(TPP)FeI]- due
to different substituents [36]. Thus, (OEP)FeCl has a
higher catalytic efficiency than (TPP)FeCl in the process
involving dechlorination of a-HCH. However, this does
not mean that any iron porphyrin with a higher electron
density on the macrocycle can be a better catalyst for
the dechlorination of a-HCH. This is because higher
electron density on the macrocycle will result in the
porphyrin being more difficult to be reduced to form the
reactive Fe(I) species. In the extreme case, if the potential
for generating the Fe(I) porphyrin becomes too negative
then, a-HCH would be directly electroreduced at the
same time for a formation of an Fe(I) porphyrin and there
could be no need for a catalyst.
Instrumentation
Cyclic voltammetry was performed in a three-
electrode cell using a CHI-730D electrochemistry
station. A glassy carbon disk electrode was utilized as the
working electrode while a platinum wire and a saturated
calomel electrode (SCE) were employed as the counter
and reference electrodes, respectively. An “H” type cell
with a fritted glass layer to separate the cathodic and
anodic sections of the cell was used for bulk electrolysis.
Copyright © 2014 World Scientific Publishing Company
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ELECTROREDUCTIVE DECHLORINATION OF a-HEXACHLOROCYCLOHEXANE CATALYZED BY IRON
7
+
e
e
FeIII
FeI
Fe = (Por)Fe
FeII
(1)
(2)
(3)
Cl
Cl
Cl
Cl
Cl
Cl
III
FeI
Cl
+
Cl
Cl
Fe
Cl
Cl
Cl-
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
+e
III
Fe
Cl
Cl
H+
(Por)FeII
Cl
Cl
Cl
Cl
Cl
PCCH
Cl
Cl
III
Fe
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
III
Cl
Cl
Fe
Cl
Cl
Cl
Cl
+
Cl
Cl
Cl
+e, -H+
(Por)FeII
Cl
Cl
FeI
Cl or
Cl
(4)
Cl
Cl
Cl-
III
Cl
PCCH
Cl
Cl
Cl
Fe
Cl
Cl
Cl
Cl
Cl
Cl
Cl
or
III
Fe
Cl
Cl
Cl
TCDN
Cl
Cl
Cl
Cl
Cl
Cl
Cl
+e, -H+
(Por)FeII
FeIII (TCB)
(5)
FeI
+ TCDN
Cl
Cl
Cl-
Cl
Cl
TCB
Scheme 1. Proposed mechanism of electroreductive dechlorination of a-HCH to give PCCH, TCDN and TCB when catalyzed by
iron porphyrins
The working and counter electrodes were made from
platinum mesh and the reference electrode was an SCE.
Both the working and reference electrodes were placed
in one compartment while the counter electrode was in
other compartment of the cell.
UV-visible spectroelectrochemical measurements
were performed with a home-made optically transparent
thin-layer cell with a Pt mesh as the working electrode.
The potential was applied using
a
CHI-730D
electrochemistry station. Time-resolved UV-visible
spectra were recorded with an Agilent 8453A diode
array spectrophotometer. All electrochemical and
spectroelectrochemical measurements were carried out
under a nitrogen atmosphere.
The electrolysis products were identified with the aid
of gas chromatography-mass spectrometry (GC-MS); an
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W. ZHU ET AL.
Agilent 6890 gas chromatograph fitted with a 30 m × 0.25
mm DB-5MS capillary column (Agilent Corporation)
in tandem with an Agilent 5975 inert mass-selective
detector was employed for these measurements. After
each hour of electrolysis, 1.0 mL of solution was taken
from the H-cell and the supporting electrolyte removed
prior to the GC-MS analysis which was carried out as
described in the literature [34].
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CONCLUSION
In summary, the doubly reduced (TPP)FeIIICl and
(OEP)FeIIICl, which are represented as [(Por)FeI]-, can
catalyze the dechlorination of a-hexachlorocyclohexane
(a-HCH) to stepwise generate pentachlorocyclohexene
(PCCH) and tetrachlorocyclohexadiene (TCDN) as
intermediates, prior to generation of the final dechlorination
products which consisted of an isomeric mixture of
trichlorobenzenes (TCB). The experimental data indicate
that (OEP)FeCl is a better catalyst for the reductive
dechlorination of a-HCH as compared to (TPP)FeCl under
the given experimental conditions.
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Acknowledgements
The Natural Science Foundation of China (No.
21171076), the Robert A. Welch Foundation (KMK,
Grant E-680) and the Foundation of Jiangsu University
(No. 11JDG124) are gratefully acknowledged.
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