Degradation of chlorinated phenols in water in the presence of H 2O2 and water-soluble μ-nitrido diiron phthalocyanine

Article abstract of DOI:10.1016/j.cattod.2014.03.016

Efficient disposal of pollutants is a key problem in the environmental context. In particular, chlorinated aromatic compounds are recalcitrant to biodegradation and conventional treatment methods. Iron phthalocyanines were previously shown to be efficient catalysts for the oxidative degradation of chlorinated phenols considered as priority pollutants. We have recently discovered μ-nitrido diiron phthalocyanines as powerful oxidation catalysts. Herein, we evaluate these emerging catalysts in the oxidation of chlorinated phenols in comparison with conventional mononuclear complex. Catalytic performance of iron tetrasulfophthalocyanine (FePcS) and corresponding μ-nitrido dimer [(FePcS)₂N] have been compared in the oxidation of chlorinated phenols by hydrogen peroxide in water. The oxidative degradation of 2,6-dichlorophenol (DCP) and 2,4,6-trichlorophenol (TCP) has been studied. The (FePcS)₂N exhibited better catalytic properties than mononuclear FePcS in terms of conversion and mineralization (transformation of organic chlorine to Cl^- and decrease of total organic carbon due to the formation of CO₂). Kinetics of the DCP oxidation indicated that different reaction mechanisms are involved in the presence of FePcS and (FePcS)₂N. The high catalytic activity of (FePcS)₂N in the degradation and mineralization of chlorinated phenols make μ-nitrido diiron phthalocyanines promising catalyst to apply also in environmental remediation.

Full text of DOI:10.1016/j.cattod.2014.03.016

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Degradation of chlorinated phenols in water in the presence of H O
2
2
and water-soluble ␮-nitrido diiron phthalocyanine
a
a,b
a
a,∗
Cédric Colomban , Evgeny V. Kudrik , Pavel Afanasiev , Alexander B. Sorokin
a
Institut de Recherches sur la Catalyse et l’Environnement de Lyon (IRCELYON), UMR 5256, CNRS-Université Lyon 1, 2, av. A. Einstein, 69626 Villeurbanne
Cedex, France
Institute of Macroheterocyclic Compounds, Ivanovo State University of Chemistry and Technology, 7, av. F. Engels, 153000 Ivanovo, Russia
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Efficient disposal of pollutants is a key problem in the environmental context. In particular, chlori-
nated aromatic compounds are recalcitrant to biodegradation and conventional treatment methods.
Iron phthalocyanines were previously shown to be efficient catalysts for the oxidative degradation of
chlorinated phenols considered as priority pollutants. We have recently discovered ␮-nitrido diiron
phthalocyanines as powerful oxidation catalysts. Herein, we evaluate these emerging catalysts in the
oxidation of chlorinated phenols in comparison with conventional mononuclear complex. Catalytic per-
formance of iron tetrasulfophthalocyanine (FePcS) and corresponding ␮-nitrido dimer [(FePcS)2N] have
been compared in the oxidation of chlorinated phenols by hydrogen peroxide in water. The oxidative
degradation of 2,6-dichlorophenol (DCP) and 2,4,6-trichlorophenol (TCP) has been studied. The (FePcS)2N
exhibited better catalytic properties than mononuclear FePcS in terms of conversion and mineralization
Received 18 November 2013
Received in revised form 30 January 2014
Accepted 5 March 2014
Available online xxx
Keywords:
Chlorinated phenols
Depollution
Oxidation
Catalysis
Phthalocyanine
−
(transformation of organic chlorine to Cl and decrease of total organic carbon due to the formation
␮
-Nitrido dimer
of CO ). Kinetics of the DCP oxidation indicated that different reaction mechanisms are involved in the
2
presence of FePcS and (FePcS)2N. The high catalytic activity of (FePcS)2N in the degradation and miner-
alization of chlorinated phenols make ␮-nitrido diiron phthalocyanines promising catalyst to apply also
in environmental remediation.
©
2014 Elsevier B.V. All rights reserved.
1
. Introduction
pollutants using different metallophthalocyanine complexes
14–23].
It should be noted that the FePcS–H O2 system was the
[
Contamination of the environment by chlorinated aromatic
2
compounds is a severe problem because of their large-scale appli-
cations as biocides, lubricants, solvents, etc. and their high stability
to bio-degradation. Energy-efficient and low-cost elimination of
toxic organic pollutants from the environment has therefore been
a long-standing challenge. One of the promising approaches is the
application of metal complexes in combination with hydrogen per-
oxide operating at ambient conditions [1]. Metal phthalocyanine
complexes have received a great attention as the catalysts for many
reactions [2] including selective oxidations and bleaching [3]. In
particular, iron 2,9(10),16(17),23(24)-tetrasulfophthalocyanine
most efficient in the presence of an organic solvent (CH CN,
25 vol.%) added to facilitate the dissolution of poorly water-soluble
substrates and phosphate buffer [4–8]. A careful mechanis-
3
tic study disclosed
a non-innocent role of the phosphate
buffer for the degradation of chlorinated phenols, dichloroani-
lines and catechols suggesting the intermediate formation of a
peroxyphosphate–FePcS complex [13]. The involvement of the
organic solvent and phosphate buffer limits a potential for the
practical application of this approach. In this context, the cat-
alytic system operating in pure water would be advantageous from
practical point of view and might provide a deeper insight into reac-
(
FePcS) was shown to be a very active catalyst for the oxidative
degradation of 2,4,6-trichlorophenol (TCP) and other chlorinated
phenols, recalcitrant priority pollutants [4–13]. This topic has been
developed by many researchers toward degradation of different
tivity. For instance, although the formation of CO was evidenced
2
using 14C-TCP substrate [6], the evaluation of mineralization effi-
ciency of the catalytic system by determination of total organic
carbon (TOC) cannot be performed in the presence of the organic
solvent. Hence, the development of the catalytic system capable of
oxidizing chlorinated phenols in water would be of great mecha-
nistic and practical interest.
∗ Corresponding author. Tel.: +33 04 72 44 53 37.
E-mail address: alexander.sorokin@ircelyon.univ-lyon1.fr (A.B. Sorokin).
http://dx.doi.org/10.1016/j.cattod.2014.03.016
0
920-5861/© 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: C. Colomban, et al., Degradation of chlorinated phenols in water in the presence of H O and water-
2
2
soluble ␮-nitrido diiron phthalocyanine, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.016

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2
Recent development of iron phthalocyanine-based catalysts led
to the discovery of the remarkable catalytic properties of ␮-nitrido
diiron phthalocyanines in the oxidation of organic compounds,
formation of C C bonds and oxidative dehalogenation [24–33].
The structure of these bio-inspired catalysts reflects the struc-
tural features of two the most powerful monooxygenase enzymes:
an active site containing two iron ions like in soluble methane
monooxygenase but in the macrocyclic ligand environment sim-
ilarly to iron porphyrin active site in cytochrome P-450. Such a
construction provides better possibilities for stabilization of high
oxidation states of the catalyst developed during catalytic oxi-
dation cycle [2]. The Fe(␮-N)Fe structural unit is also essential
for the improved catalytic properties. Using tetraphenylporphyrin
platform we have shown that a ␮-nitrido high-valent diiron oxo
complex was much stronger oxidant in the oxidation of alkanes
including methane compared to its mononuclear counterpart [34].
Thus, a distinctive feature of ␮-nitrido diiron complexes is their
powerful catalytic properties in oxidation. It is therefore of interest
to evaluate them in the oxidation of difficult-to-oxidize chlori-
nated phenols. On the other hand, the development of ␮-nitrido
diiron complexes via modification of the structure of the macro-
cyclic ligand(s) is a tool which should open new possibilities for
catalytic applications. The complexes with electron-withdrawing
mineralization of the chlorinated phenols. The reaction mixture
was kept at the desired temperature (25 or 60 C) with magnetic
◦
stirring for 3 or 6 h. After cooling to room temperature, the
reaction mixtures were analyzed by HPLC to follow the substrate
conversions and chloride ion concentrations were measured by the
mercury thiocyanate method [39]. Total organic carbon content
was determined using the final reaction mixtures.
2.3. Identification of the reaction products
The oxidation of DCP was performed in water (5 mM, 25 mL
scale) in the presence of (FePcS) N (0.05 mM) and H O (0.1 M)
2
2
2
◦
at 60 C for 3 h. The reaction mixture was saturated with NaCl
and extracted with diethyl ether (3 × 15 mL). The combined ether
extracts were dried with anhydrous sodium sulfate, filtered and the
ether was evaporated under vacuum. The yellow residue was either
dissolved in DMSO-d6 and examined by 1H-NMR or dissolved in
1
acetonitrile and directly analyzed by LC–MS method. The H-NMR
spectrum of the extracted reaction mixture showed the signals
of the vinylic protons of maleic acid (␦ 6.37, 2H), chloromaleic
acid (␦ 6.66, 1H), and fumaric acid (␦ 6.72, 2H). LC–MS analy-
ses confirmed the identification of these products. Chloromaleic
−
−
−
acid: m/z (%) = 151 (40) [(M + 2-H) ], 149 (100) [(M−H) ]. Maleic
[
35] and electron-donating substituents [36] have been prepared.
acid: m/z (%) = 115 (100) [(M−H) ]. The 3,5-dichloro-2-hydroxy-
In this context, the preparation of the first water-soluble ␮-nitrido
diiron tetrasulfophthalocyanine [37] was particularly important
since it provides the possibility to apply these promising catalysts
in water. Up to now, no direct comparison of the catalytic behavior
of mononuclear iron pthalocyanines and their respective ␮-nitrido
dimers has been reported.
1
[
,4-benzoquinone (2) was identified by LC-MS. m/z (%) = 193 (69)
−
−
−
(M + 2-H) ], 191 (100) [(M−H) ], 165 (38.5) [(M + 2-H-CO) ], 163
−
(32) [(M−H-CO) ].
2.4. Instrumentation.
In the present work, we assessed and compared catalytic prop-
HPLC analyses of the oxidation of chlorinated phenols were car-
ried out using an Agilent 1100 liquid chromatograph equipped with
erties of FePcS and (FePcS) N (see Fig. 1 for their structures) in the
2
oxidation of 2,6-dichlorophenol (DCP) and TCP by H O in water.
2
2
a 20 ␮L injection loop and Coregel-87H3 column with detection
The important requirements for the degradation of chlorinated
aromatics are the cleavage of the aromatic cycle and the transfor-
mation of the organic chlorine substituents to inorganic chloride
ions without formation of more dangerous products like chlori-
nated dibenzodioxins and dibenzofurans. To compare conventional
FePcS and its ␮-nitrido dimer and to evaluate the efficiency in the
oxidative degradation of the chlorinated phenols we have deter-
−
1
at 280 nm. Acetonitrile-water mixture (1/1, v/v, 0.8 mL min ) was
used as the eluent. LC–MS analyses were conducted on a Shimadzu
LCMS-2020 instrument equipped with SPD M20A photodiode array
detector using Luna Phenyl-Hexyl column (5 ␮m, 250 × 3.0 mm,
◦
Phenomenex). Conditions: 40 C column oven temperature, 10 ␮L
injection volume, photodiode array (PDA) response at 254 nm,
mobile phase: solvent B (acetonitrile) from 30 to 80% in 30 min
−
mined the conversions, the dechlorination degree (amount of Cl
−
1
and solvent A: water without any additive, flow rate, 0.5 mL min
.
formed per converted substrate) and decrease in the total organic
carbon (TOC) as well as the products of their degradation.
Samples were analyzed using LC–electrospray ionization (ESI)–MS
in the negative ionization mode. Under these conditions, the prod-
−
ucts were identified as their [M−H] ions.
1
2
. Experimental
Liquid-state H NMR spectra were obtained using a AM
2
50 Bruker spectrometer. The UV–vis spectra of solutions were
2
.1. Materials
obtained with Agilent 8453 diode-array spectrophotometer. Total
organic carbon analyses were performed on a Shimadzu TOC-
5050A spectrometer.
Iron 2,9(10),16(17),23(24)-tetrasulfophthalocyanine was syn-
thesized by Weber-Busch method [38]. ␮-Nitrido diiron tetra-
sulfophthalocyanine was prepared according to the published
protocol [37]. 2,6-dichlorophenol (99%) and 2,4,6-trichlorophenol
3. Results and discussion
(
99%) were purchased from Sigma-Aldrich and used without addi-
3
.1. Oxidative degradation of 2,6-dichlorophenol
tional purification. All other reactants were obtained commercially
and used as received. Hydrogen peroxide (35% aqueous solution)
was obtained from Sigma–Aldrich.
Two complexes were first examined in the oxidative degra-
dation of DCP using 0.5 mol% and 1 mol% catalyst loadings. Both
complexes exhibited a good catalytic activity toward this pollut-
ant, but their oxidation kinetics were very different. In course of
2
.2. Catalytic tests and product analyses
the reaction with (FePcS) N, a rapid disappearance of DCP was
2
Reaction vessel was charged with 4 mL H O containing 2,6-
observed and the blue color of the reaction mixture was retained
during all reaction time indicating the high stability of the complex.
This conclusion was supported by UV–vis study of the evolution of
the reaction mixture during the reaction (Fig. 2). After 1 h reac-
tion only ∼6% decrease of the catalyst concentration was observed.
2
dichlorophenol (5 mM) or 2,4,6-trichlorophenol (1 mM), H O2
2
(
typically 0.1 M in the case of DCP and 0.02 M in the case of TCP)
and catalyst (0.05 mM or 0.025 mM in the case of DCP and 0.01 mM
in the case of TCP). The large excess of H O was intentionally
2
2
used to avoid the lack of the oxidant for complete degradation and
More than 80% of the (FePcS) N catalyst was still present in the
2
Please cite this article in press as: C. Colomban, et al., Degradation of chlorinated phenols in water in the presence of H O2 and water-
2
soluble ␮-nitrido diiron phthalocyanine, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.016

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SO3Na
3
SO3Na
N
SO3Na
SO3Na
N
N
N
SO3Na
IV N
N
N
III
Fe
N
Fe
N
N
SO Na
3
N
N
N
N
NaO3S
N
N
III
N
N
N
_
N
Cl
Fe
NaO3S
N
N
NaO3S
N
N
NaO3S
N
SO3Na
FePcS
(FePcS)
2
N
SO3Na
Fig. 1. Structures of iron 2,9(10),16(17),23(24)-tetrasulfophthalocyanine (FePcS) and ␮-nitrido diiron 2,9(10),16(17),23(24)-tetrasulfophthalocyanine [(FePcS)2N] complexes.
Only one of possible position isomers is depicted for monomeric and dimeric structures.
Table 1
◦
Comparison of the catalytic activity of (FePcS)2N and FePcS in the oxidative degradation of 2,6-dichlorophenol in water at 60 C.
Catalyst
Reaction time (h)
Conversion (%)
mol% catalyst
Dechlorination degree
1 mol% catalyst
Total organic carbon removal (%)
1
0.5 mol% catalyst
0.5 mol% catalyst
1 mol% catalyst
0.5 mol% catalyst
(
FePcS)2N
1
2
3
80
94
94
70
81
92
0.81
0.92
1.00
0.36
0.7
0.91
–
–
43
–
–
33
FePcS
1
2
3
0
61
86
0
49
81
0
1.16
1.04
0
0.57
0.81
–
–
31
–
–
27
reaction mixture after the reaction (3 h). With 1 mol% catalyst load-
ing the DCP conversion was 80% after 1 h (Table 1). After 3 h of
the reaction the conversion reached 94% and one of two chlo-
rine substituents was converted to chloride anion. In contrast to
The reactions were allowed to react for 15 h to achieve 65–75%
conversion and 0.9–0.95 dechlorination degree.
The efficiency of degradation was further evaluated by the mea-
surements of total organic carbon (TOC) after 3 h reactions. In the
(
FePcS) N, a blue color of FePcS disappeared within 1 h owing to
presence of 1 and 0.5 mol% of (FePcS) N the TOC removal was 43%
2
2
its degradation. UV–vis study indicated that the Q band of FePcS
core almost disappeared after 15 min reaction (Fig. 3). Noteworthy,
no DCP conversion was detected during first hour of the reaction.
When FePcS was completely bleached, the consumption of the DCP
started (Table 1) to reach a 86% DCP conversion and dechlorination
and 33%, respectively, indicating that up to 2.74 carbon atoms of
substrate from six were mineralized. When FePcS was used as
the catalyst, the TOC removal was lower: 31% and 27% for 1 and
0.5 mol% catalyst loading, respectively (Table 1). In principle, a
degradation of the catalysts could contribute to observed TOC val-
degree of 1.04 after 3 h. Similarly, (FePcS) N was more efficient than
ues. The UV–vis study showed that more than 80% of (FePcS) N
2
2
FePcS with 0.5 mol% catalyst loading providing conversion of 92%
vs. 81% and dechlorination degree of 0.91 vs. 0.81, respectively. The
reaction can also be performed at 25 C, though the rate of oxida-
was unchanged after the reaction. Thus, a maximal possible con-
tribution to TOC values due to the degradation of the catalyst can
be estimated as 2% and 1% with 1 mol% and 0.5 mol% catalyst load-
ings, respectively. These maximal values could be obtained if all
◦
tion of DCP was slower. After 5 h of the reaction, 6% and 27% DCP
conversions were obtained with FePcS and (FePcS) N, respectively.
2
Fig. 3. Evolution of UV–vis spectrum of FePcS (0.05 mM) in water in the presence
of 2,6-DCP (5 mM) and H O (0.1 M) at 60 ◦C: before H O addition (1, solid line)
and after 15 min (2, solid line), 45 min (3, dashed line), and 1 h (4, dotted line) of
Fig. 2. Evolution of UV–vis spectrum of (FePcS)2N (0.05 mM) in water in the pres-
ence of 2,6-DCP (5 mM) and H2O2 (0.1 M) at 60 C: before H2O2 addition (1, solid
line), after 1 h (2, dashed line), 2 h (3, solid line) and 3 h (4, dotted line) of reaction.
2
2
2
2
◦
reaction.
Please cite this article in press as: C. Colomban, et al., Degradation of chlorinated phenols in water in the presence of H O and water-
2
2
soluble ␮-nitrido diiron phthalocyanine, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.016

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OH
NO
O
N
N
N
N
N
N
N
N
N
N
Fe IV
+
. N
Fe III
N
N
N
N
N
H
N
N
Fe
N
H
NN
N
N
N
(OH)
N
FeIV
O
N
N
N
N
N
N
N
N
N
Fe IV
N
N
N
N
iron complex with
tridentate ligand
N
di _i ron oxo complex
diiron peroxo complex
Fig. 4. Proposed iron and diiron active species involved in the oxidation of chlorinated phenols in the presence of FePcS and (FePcS)2N, respectively. The structure of iron
complex with tridentate ligand was proposed by N. d’Alessandro et al. (Ref. [42]). SO3Na substutuents are omitted for clarity.
degraded catalyst molecules would be mineralized to CO2 that
is certainly not the case. d’Alessandro and co-workers showed
that major degradation products of phthalocyanine core were
sulfonated isoindole and tridentate sulfoindole ligand [40–42].
Consequently, the contribution to TOC values due to degradation
of (FePcS) N should be negligible. The same considerations should
2
be valid for FePcS case.
Fig. 5. Proposed first step of the oxidation of chlorinated phenols: formation of the
quinone.
The products of DCP mineralization in the presence of (FePcS) N
were identified by microGC-MS analysis of gas phase. To this aim
the reaction was performed under argon. Importantly, the DCP con-
2
2
mol%. After 6 h reaction, a 46% conversion of TCP and 11% TOC
removal were obtained. Noteworthy, no TCP conversion (<1.5%)
was detected when (FePcS) N was replaced with FePcS, other con-
versions and TOC losses obtained under air and under argon were
the same with (FePcS) N suggesting that O was not involved in the
2
2
reaction. After 3 h reaction the gas phase contained 4.7% CO2 and
.5% of CO. This result corroborates with the TOC analysis and con-
firms the significant mineralization of DCP mediated by (FePcS) N.
2
ditions being the same. Thus, (FePcS) N showed a higher catalytic
0
2
activity and stability compared with FePcS.
2
In contrast to (FePcS) N, the oxidation of DCP in the presence of
2
1
mol% FePcS was less efficient under Ar. Only 39% DCP conversion
3.3. Mechanistic considerations
was observed after 3 h compared with 86% conversion obtained
under air. The TOC removal dropped from 31% (under air) to 12%
Different kinetics of DCP conversion found for FePcS and
(FePcS)2N imply that different reaction pathways should be
involved. In the case of FePcS, the oxidation of DCP started only
after bleaching of the complex. This observation can be explained
by the involvement of free-radical Fenton chemistry initiated by
iron ions liberated during degradation of FePcS. Strong dependence
of the efficiency of the oxidation on the presence of O2 in this
case is in agreement with this suggestion. However, efficient Fen-
ton reaction needs a significant iron loading and operates in the
narrow acidic pH range (typically pH 2.5–3.5). Alternatively, the
products of degradation of metallophthalocyanines can also show
some catalytic activity [40,41]. This catalytic activity was associated
with the formation of meso-nitrogen oxide derivatives and metal-
biliverdin-like compounds formed from RuPcS and FePcS in the
presence of H O or KHSO5 [42]. These compounds were identified
(
under Ar). This strong influence of O2 on the reaction in the pres-
ence of FePcS suggests the possible involvement of free radical
chemistry.
3.2. Oxidative degradation of 2,4,6-trichlorophenol
The solubility of TCP in pure water is significantly lower than
solubility of DCP. For this reason the experiments were performed
with 0.001 M TCP solution compared with 0.005 M in the DCP
case. In these conditions, the oxidation of TCP in water was less
efficient compared with DCP. Using 1 mol% (FePcS) N loading, a
2
1
2% TCP conversion was observed after 4 h. In the next set of the
experiments the initial 0.001 M TCP solution was adjusted to pH
with NaOH and loading of (FePcS) N catalyst was increased to
2
2
7
by ESI-MS and NMR techniques at short reaction times. Although
2
-
HCl
1
2
+
2
H O
-
2
H O
Fig. 6. Proposed second step of the oxidation of chlorinated phenols: epoxidation of 2,6-dichlorobenzoquinone.
Please cite this article in press as: C. Colomban, et al., Degradation of chlorinated phenols in water in the presence of H O2 and water-
2
soluble ␮-nitrido diiron phthalocyanine, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.016

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5
FeNFe
FeNFeOO-
4
3
[
O]
2
H O
-
CO
x
-CO
2
Fig. 7. Proposed mechanism of the cleavage of the aromatic cycle of chlorinated phenols.
some involvement of Fenton chemistry cannot be excluded, the lat-
ter mechanism involving an iron complex with a tridentant ligand
could also be responsible for the DCP degradation.
In the presence of (FePcS) N the oxidation of DCP shows no
2
induction period and not sensitive to the presence of O . Both obser-
2
vations are more compatible with the involvement of oxo- and
hydroperoxo diiron-centered species rather than with free-radical
Fenton chemistry. The (FePcS) N is also quite stable under reac-
2
tion conditions (Fig. 2). The preparation and characterization of
both high-valent iron [43] and diiron [29] oxo species supported
by phthalocyanine ligand in organic solvents have previously been
published. The results of this study suggest that with mononuclear
FePcS in aqueous medium the oxo pathway is probably less favored
than in organic solvents. In contrast, ␮-nitrido diiron construction
is more suitable for obtaining oxo and peroxo diiron species and
their involvement in the oxidation which is in accordance with pre-
vious results [24,26,29,34]. The structures of the proposed iron and
diiron active species are depicted in Figure 4. Iron complex with tri-
dentate ligand proposed by N. d’Alessandro et al. [42] might activate
H O and form active species capable of oxidizing DCP. Recently,
Fig. 8. 1H-NMR spectrum of the products of DCP oxidation isolated as described in
Section 2 showing the presence of vinylic protons of maleic, fumaric and chloroma-
lein acids. Solvent: DMSO-d6.
2
2
transition state. Decarboxylation and decarbonylation of differ-
ent intermediates formed after the cleavage of the aromatic cycle
should provide CO2 and CO detected by microGC–MS method as
iron complexes with modified phthalocyanine core were shown to
catalyze the oxidation of alkanes [44] and epoxidation of olefins
[
45] with H O .
2 2
1
well as chloromaleic acid identified by LC–MS and H-NMR anal-
Based on the results obtained in this study and our previous
studies on TCP oxidation [4–7] we propose the following mech-
anism. The first step includes the oxidation of both DCP and TCP
yses (Fig. 8). The proposed intermediate 1 undergoes the second
dechlorination according to the same reaction sequence to provide
maleic and fumaric (isomerization product) acids which were also
to 2,6-dichlorobenzoquinone which involve the cleavages of C
and C Cl bonds in the para-position to phenolic group, respectively
Fig. 5). A diiron oxo species should be competent to perform this
H
1
detected by LC–MS and H-NMR analyses (see Section 2 for details).
(
oxidation. The higher reactivity of DCP compared with TCP can
be explained by an easier cleavage of the para-C H bond of DCP
with respect to para-C Cl bond of TCP. The further key step of the
reaction is the epoxidation of the electron-deficient double bond
of 2,6-dichlorobenzoquinone (Fig. 5). This step can be performed
either by nucleophilic diiron peroxo complex or electrophilic diiron
oxo species. Hydrolysis of the epoxide to diol followed by HCl
4. Conclusions
We have shown that water-soluble ␮-nitrido diiron phthalo-
cyanine is an efficient catalyst for the oxidative degradation of
chlorinated phenols in water with hydrogen peroxide, cheap
and clean industrial oxidant. Almost complete conversion of
2,6-dichlorophenol has been achieved using 0.5–1 mol% catalyst
amounts with the total organic carbon removal up to 43% to form
CO and CO in ∼10:1 ratio. The (FePcS) N–H O catalytic system is
or H O elimination gives violet quinones 1 and 2, respectively
2
(Fig. 6). These quinones were isolated and characterized in our pre-
2
2
2
2
vious work [5]. A violet color of the reaction mixture observed
at short reaction times in the present work suggests that these
intermediates are also formed during the oxidation of DCP [5].
This suggestion was confirmed by identification of 3,5-dichloro-
more efficient than mononuclear FePcS–H O system in terms of
2 2
conversion and mineralization of chlorinated phenols. In addition,
mechanistic studies indicate that (FePcS) N–H O system operates
via diiron-centered oxo and peroxo species while FePcS itself was
not active in the oxidation of chlorinated phenols in pure water. The
mononuclear FePcS complex was not stable under reaction con-
ditions giving rise to iron ions and iron complex with tridentate
sulfoisoindole ligand, previously proposed by d’Alessandro et al.
[42]. These species are responsible for the oxidation of DCP occur-
ring after degradation of FePcS.
2
2
2
2
-hydroxy-1,4-benzoquinone (2) using LC–MS technique. Second
epoxidation step provides intermediate 3 via 4 (Fig. 7). Another key
step is the cleavage of the aromatic cycle according to the mecha-
nism proposed in Fig. 7. A nucleophilic attack of peroxo complex on
the quinone carbonyl group of 3 having Cl and OH substituents in
the orto-position leads to the C-C bond cleavage via six-membered
Please cite this article in press as: C. Colomban, et al., Degradation of chlorinated phenols in water in the presence of H O and water-
2
2
soluble ␮-nitrido diiron phthalocyanine, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.016

G Model
CATTOD-8963; No. of Pages6
ARTICLE IN PRESS
C. Colomban et al. / Catalysis Today xxx (2014) xxx–xxx
6
N-Bridged diiron phthalocyanine complex is non-expensive and
non-toxic, and can be readily available on a large scale. The hydro-
gen peroxide is green and cheap industrial oxidant. The catalytic
system operates in water with no need for organic co-solvent
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2
readily immobilized onto different supports via covalent anchor-
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This work was supported by the grant ANR-08-BLANC-0183-01
from Agence Nationale de Recherche (ANR, France). C.C. is grate-
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Please cite this article in press as: C. Colomban, et al., Degradation of chlorinated phenols in water in the presence of H O2 and water-
2
soluble ␮-nitrido diiron phthalocyanine, Catal. Today (2014), http://dx.doi.org/10.1016/j.cattod.2014.03.016