Oxidative functional group transformations with hydrogen peroxide catalyzed by a divanadium-substituted phosphotungstate

Article abstract of DOI:10.1016/j.cattod.2011.07.007

A divanadium-substituted phosphotungstate TBA₄[γ-PW ₁₀O₃₈V₂(μ-OH)(μ-O)] (I, TBA = tetra-n-butylammonium) reacts with one equivalent H⁺ to form a bis-μ-hydroxo species [γ-PW₁₀O₃₈V ₂(μ-OH)₂]^3- (I′) in organic media. The strong electrophilic oxidants such as [γ-PW₁₀O ₃₈V₂(μ-OH)(μ-OOH)]^3- (II) and [γ-PW₁₀O₃₈V₂(μ-η²: η²-O₂)]^3- (III) are formed by the reaction of the bis-μ-hydroxo species with H₂O₂. In the presence of I and H⁺, H₂O₂-based oxidations such as (i) epoxidation of alkenes (17 examples including electron-deficient ones), (ii) hydroxylation of alkanes (11 examples), and (iii) oxidative bromination of alkenes, alkynes, and aromatics with Br^- as a bromo source (12 examples including chlorination) chemo-, diastereo-, and regioselectively proceed to give the corresponding oxidized products in moderate to high yields with high efficiencies of H₂O₂ utilization.

Full text of DOI:10.1016/j.cattod.2011.07.007

Catalysis Today 185 (2012) 157–161
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Catalysis Today
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Oxidative functional group transformations with hydrogen peroxide catalyzed
by a divanadium-substituted phosphotungstate
Noritaka Mizuno∗, Keigo Kamata, Kazuya Yamaguchi
Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 May 2011
Received in revised form 7 July 2011
Accepted 11 July 2011
Available online 9 August 2011
A
divanadium-substituted phosphotungstate TBA4[␥-PW10O38V2(␮-OH)(␮-O)] (I, TBA = tetra-
n-butylammonium) reacts with one equivalent H+ to form
a
bis-␮-hydroxo species
[␥-PW10O38V2(␮-OH)2]3− (Iꢀ) in organic media. The strong electrophilic oxidants such as [␥-
PW10O38V2(␮-OH)(␮-OOH)]3− (II) and [␥-PW10O38V2(␮-␩2:␩2-O2)]3− (III) are formed by the reaction
of the bis-␮-hydroxo species with H2O2. In the presence of I and H+, H2O2-based oxidations such as (i)
epoxidation of alkenes (17 examples including electron-deficient ones), (ii) hydroxylation of alkanes
(11 examples), and (iii) oxidative bromination of alkenes, alkynes, and aromatics with Br− as a bromo
source (12 examples including chlorination) chemo-, diastereo-, and regioselectively proceed to give the
corresponding oxidized products in moderate to high yields with high efficiencies of H2O2 utilization.
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Hydrogen peroxide
Oxidation
Polyoxometalate
Vanadium
1. Introduction
of
a
divanadium-substituted phosphotungstate TBA4[␥-
(I, TBA = tetra-n-butylammonium)
PW10O38V2(␮-OH)(␮-O)]
Oxidations of organic substrates are very important reactions,
and the choice of oxidants determines practicability and efficiency
of the systems. H2O2 is regarded as one of the “greenest” oxidants
because of its high content of active oxygen species (47 wt%), high
atom efficiency, and co-production of only water. The key for devel-
opment of efficient H2O2-based oxidation systems is the design of
catalysts that can effectively activate H2O2 and transferring of the
active oxygen species to various substrates with high efficiencies
and selectivities. In order to develop green oxidation systems with
H2O2, our research group has continued to design and synthesize
“molecular catalysts” based on polyoxometalates (POMs) [1].
POMs are thermally and oxidatively stable metal–oxygen
anionic clusters of early transition metals and stimulated many
current research activities in broad fields of science because their
properties can finely be tuned by choosing constituent elements
and counter cations [1–8]. Particularly, the interests in the catal-
ysis of metal-substituted POMs, which can easily be synthesized
by introduction of metal cations into the vacant site(s) of lacunary
POMs as “structural motifs”, have been growing. The rich diver-
sity of lacunary POMs (ranging from monovacant to hexavacant)
can lead to design various metal-substituted POMs with “controlled
active sites” at the molecular level [1–8].
[9–11]. In this paper, we carefully examine and discuss the acti-
vation of H2O2 with I (in the presence of H+) by means of various
characterizations such as cold-spray ionization mass spectrometry
(CSI-MS) and NMR spectroscopy. In addition, we extend the scope
of the I-catalyzed H2O2-based oxidations such as (i) epoxidation
of alkenes including electron-deficient ones, (ii) hydroxylation of
alkanes, and (iii) oxidative bromination of alkenes, alkynes, and
aromatics with Br− as a bromo source (including chlorination).
2. Experimental
Inorganic salts (precursors of POMs, catalysts, and bromo and
chloro sources), solvents, substrates, and 30% aq. H2O2 were
obtained from Tokyo Kasei, Wako, Kanto, or Aldrich (reagent grade).
Solvents and substrates were purified prior to the use [12]. Com-
pound I was synthesized according to the previously reported
procedures (see Section 3.1) [9].
The catalytic oxidations were carried out with a glass tube reac-
tor containing a magnetic stir bar. Compound I, solvent, substrate,
and acid (70% aq. HClO4 for epoxidation and hydroxylation, AcOH
for halogenation) were charged in the reactor (bromo or chloro
source was also added for halogenation). The reaction was initi-
ated by addition of 30% aq. H2O2. Detailed reaction conditions were
given in the footnotes of Tables and Figures. The reaction progress
was periodically monitored by GC or NMR. The products were con-
firmed by comparison of their GC–MS and NMR (1H and 13C) spectra
with those of authentic data.
Very recently, we found that various H2O2-based oxida-
tions effectively and selectively proceeds in the presence
∗
Corresponding author. Tel.: +81 3 5841 7272; fax: +81 3 5841 7220.
E-mail address: tmizuno@mail.ecc.u-tokyo.ac.jp (N. Mizuno).
0920-5861/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2011.07.007

158
N. Mizuno et al. / Catalysis Today 185 (2012) 157–161
O
A
1
−
without HClO 34% yield, TOF = 300 h
4
−1
with HClO (one equiv.)
83% yield, TOF = 2400 h
A’
4
Fig. 1. Epoxidation of 1-octene. Reaction conditions: I (5 ␮mol), 1-octene (0.1 mmol),
30% aq. H2O2 (0.1 mmol), CH3CN/t-BuOH (1.5/1.5 mL), 60 ◦C, 10 min.
(a)
(b)
3540
3560
3580
3600
3620
3640
m/z
B
A
Fig. 2. (a) Structure of a bis-␮-hydroxo species Iꢀ and (b) activation of H2O2 with Iꢀ
to form strong electrophilic oxidants such as II and III. The {WO6} moieties occupy
the octahedra, and the {PO4} group is shown as the central tetrahedron.
A’
3. Results and discussion
(c)
(d)
3.1. Activation of H2O2 with a bis-ꢀ-hydroxo species
Compound I was synthesized by cation-exchange reaction of the
cesium salt of a deprotonated divanadium-substituted phospho-
tungstate Cs5[␥-PW10O38V2(␮-O)2] [13] with TBABr in an acidic
medium [9]. The divanadium species in I was bridged with one
hydroxo and one oxo ligands ({V2(␮-OH)(␮-O)}). Compound I
showed catalytic activity for epoxidation of terminal alkenes, e.g.,
1-octene, with H2O2 (Fig. 1). In contrast, no reaction proceeded
in the presence of commonly utilized vanadium compounds such
as V2O5, NaVO3, VOSO4, VO(acac)2, and VO(O-t-Bu)3 under the
present conditions. Surprisingly, the rate of the I-catalyzed epox-
idation increased by a factor of 8 in the presence of only one
equivalent HClO4 (H+) with respect to I (Fig. 1). The I-catalyzed
epoxidation was carried out with different amounts of HClO4 (0–1.5
equivalents with respect to I). The yields and the reaction rates lin-
early increased with an increase in the amounts of HClO4 up to 1
equivalent and then did not much change. In addition, no epoxida-
tion with HClO4 proceeded in the absence of I (blank test).
The 31P NMR spectrum (in CD3CN) showed a single line at
−13.8 ppm, showing that the polyanion exists as a single species
in the solution. The 51V NMR spectrum of I with HClO4 (one
equivalent) gave a single line at −578 ppm, showing that the two
vanadium species are equivalent. The 1H NMR spectrum gave a
broad line at 7.0 ppm (two H+ per one anion) assignable to protons
of the bis-␮-hydroxo groups [14,15]. These results show that pro-
tonation of the oxo species in I takes place to form a bis-␮-hydroxo
species [␥-PW10O38V2(␮-OH)2]3− (Iꢀ, Fig. 2(a)). Taking the above-
mentioned results into account, the formation of the bis-␮-hydroxo
species is very important to activate H2O2 effectively (Fig. 1), and
the role of HClO4 is a proton source to generate the active Iꢀ species
from I.
3540
3560
3580
3600
3620
3640
m/z
Fig. 3. CSI-MS (cation mode) of (a) Iꢀ and (c) Iꢀ treated with H2O2: Iꢀ (0.56 mM),
1,2-dichloroethane, 95% H2O2 (430 equivalents with respect to Iꢀ), −20 ◦C, 5 min.
The lines in (b) are the pattern calculated for a mixture of {TBA4[PW10O38V2(␮-
+
+
O)]} (35%) and {TBA4[PW10O38V2(␮-OH)2]} (65%). The lines in (d) are the pattern
+
calculated for a mixture of {TBA4[PW10
O
38V2(␮-O)]} (35%), {TBA4[PW10O38V2(␮-
+
+
OH)2]} (40%), and {TBA4[PW10O38V2(␮-OH)(␮-OOH)]} (II, 25%).
appeared (Fig. 3(c)). The set of signals is likely assignable to the
calculated pattern of a hydroperoxo species {TBA4[PW10O38V2(␮-
OH)(␮-OOH)]} (Fig. 3(d)). In addition, in the 1H NMR spectrum of Iꢀ
+
treated with H2O2 (in 1,2-dichloroethane-d4), protons assignable to
hydroperoxo (at 9.49 ppm) and hydroxo (at 5.31 ppm) species were
observed [14,15]. These CSI-MS and NMR data strongly suggest
the formation of a hydroperoxo species [␥-PW10O38V2(␮-OH)(␮-
OOH)]3− (II) by the reaction of the bis-␮-hydroxo core in Iꢀ with
H2O2.
In the 51V NMR spectrum of Iꢀ treated with H2O2 (in CD3CN/t-
BuOH), three signals were observed (Fig. 4), and these species are
in equilibrium. Signals at −582 and −561 ppm were assignable to
the bis-␮-hydroxo (Iꢀ) and the hydroperoxo species (II) [9–11],
respectively. In addition to these signals, a signal at −630 ppm
was observed (III). The concentration ratio of [II]/[Iꢀ] in equilib-
rium was proportional to [H2O2]/[H2O] (Fig. 5(a)), supporting the
reversible formation of II. The ratio of [III]/[Iꢀ] was proportional to
[H2O2]/[H2O]2 (Fig. 5(b)). Therefore, it is likely that III is the ␮-
␩2:␩2-peroxo species [␥-PW10O38V2(␮-␩2:␩2-O2)]3− formed by
the successive dehydration of II [14,15].
Next, the reaction of Iꢀ with H2O2 was investigated. The CSI-MS
(cation mode) spectrum of Iꢀ in 1,2-dichloroethane showed two set
of signals (Fig. 3(a)). The set of signals A (centred at m/z = 3583) had
an isotopic distribution that agrees with the calculated pattern of
On the basis of the above-mentioned experimental results, we
summarize a possible path for the formation of electrophilic oxi-
dants II and III by the reaction of I (in the presence of H+) with H2O2
(Fig. 2(b)). Upon addition of organic substrates, e.g., 1-octene, to a
CH3CN/t-BuOH (v/v = 1/1) solution containing Iꢀ, II, and III, the 51
V
+
a bis-␮-hydroxo species {TBA4[PW10O38V2(␮-OH)2]} (Fig. 3(b)).
The set of signals Aꢀ (centred at m/z = 3565 (3583 − 18)) was due
NMR signal of II was weakened and that of III almost disappeared,
suggesting that III is the (main) active species for the oxidation.
We hereafter mention the applicability of the I/H+/H2O2 system to
various H2O2-based oxidations.
+
to the fragment of Iꢀ (possibly {TBA4[PW10O38V2(␮-O)]} ) [16].
Upon addition of H2O2 (430 equivalents with respect to I) to the
solution, a new set of signals (B) centred at m/z = 3599 (3583 + 16)

N. Mizuno et al. / Catalysis Today 185 (2012) 157–161
159
Table 1
Epoxidation of various alkenes.a
Substrate
Product
Time (min)
Yield (%)
O
10b
10
90
90
O
n-C H
n-C H
4
9
4
9
O
n-C H
n-C H
5
11
5
11
10
5
88
74
O
–520
–540
–560
–580
–600
–620
–640
–660
O
chemical shift (ppm)
10
95
Fig. 4. 51V NMR spectrum of
a bis-␮-hydroxo species [␥-PW10O38V2(␮-
OH)2]3−treated with H2O2: I (3.3 mM), HClO4 (3.3 mM), CD3CN/t-BuOH (1/2 mL),
87c
81d
H2O2 (72 mM), H2O (106 mM).
O
10
10
O
3.2. Epoxidation of alkenes
The development of efficient catalysts for the H2O2-based epox-
idation of alkenes is one of the most important challenging subjects.
We found that epoxidation chemo-, diastereo-, and regioselectively
proceeds, giving the corresponding epoxides in high yields with
high efficiencies of H2O2 utilization in the presence of I. The scope
of the I-catalyzed epoxidation is summarized in Table 1. Epoxida-
tion of common terminal (including propylene) as well as cyclic
alkenes efficiently proceeded to give the corresponding epoxides
in high yields within only 10 min using one equivalent H2O2. As
O
10
60
60
85d
84
O
AcO
AcO
O
Cl
O
Cl
O
73
O
O
O
60
87
O
O
O
n-C H
n-C H
4
9
4
9
60
60
68
70
O
Ph
O
Ph
O
O
O
O
O
O
60
60
74
O
94e
O
HO
HO
94e
86e
O
O
60
60
O
NC
NC
a
Reaction conditions: I (5 ␮mol), HClO4 (5 ␮mol), substrate (0.3 mmol), 30% aq.
H2O2 (0.3 mmol), CH3CN/t-BuOH (1.5/1.5 mL), 60 ◦C.
b
Propylene (6 atm).
Trans/cis = 94/6.
c
d
[Terminal epoxide]/[Total epoxides] ≥ 0.99.
e
Substrate (3 mmol).
mentioned in Fig. 1, the turnover frequency (TOF) for the I-
catalyzed epoxidation of 1-octene reached up to 2400 h−1, and the
value was the largest among those reported for the metal-catalyzed
H2O2-based epoxidations of terminal alkenes (∼700 h−1) [17–20].
For the epoxidation of cis-2-octene, the configuration around
the double bond was completely retained in the corresponding
epoxide, showing that the present epoxidation proceeds via a non-
radicalic way. The high trans diastereoselectivity (trans/cis = 94/6)
for the epoxidation of 3-methyl-1-cyclohexene was observed. In
the case of non-conjugated dienes such as trans-1,4-hexadiene and
d-limonene, the more accessible terminal double bonds (not more
reactive electron-rich internal ones) were epoxidized with a com-
pletely regioselective manner. These unprecedented diastereo- and
regioselectivities are likely due to the steric hindrance of the active
oxygen species formed on the rigid polyanion framework.
Fig. 5. Plots of (a) [II]/[Iꢀ] against [H2O2]/[H2O] and (b) [III]/[Iꢀ] against
[H2O2]/[H2O]2. The concentrations of Iꢀ, II, and III were estimated by 51V NMR.

160
N. Mizuno et al. / Catalysis Today 185 (2012) 157–161
Table 2
Next, we turn our attention to epoxidation of electron-deficient
Hydroxylation of various alkanes.a
alkenes with acetate, chloro, ether, carbonyl, and cyano groups at
the allylic positions. Orbital energies of ␲(C C) HOMO of these
alkenes (ranging from −10.15 to −10.95 eV) are significantly lower
than those of common alkenes (ca. −9 eV). Therefore, nucleophilic
oxidants, e.g., OOH− generated from H2O2 under strong alkaline
conditions, rather than electrophilic oxidants are generally use-
ful for these alkenes [21–25]. However, many functional groups
are not intact because of the strong alkaline conditions and the
strong nucleophilic nature of oxidants. Thus, the applicability of
nucleophilic oxidants is very limited. In the presence of I, alkenes
with various electron-withdrawing functional groups at the allylic
positions, e.g., acetate, chloro, ether, carbonyl, and cyano groups,
selectively oxidized to the corresponding epoxides in moderate to
high yields (Table 1). These results suggest that the electrophilic
oxidants formed on I are strong enough to oxidize such electron-
deficient alkenes. In particular, it is notable that the epoxidation
of methacrylonitrile chemoselectively proceeded to give the cor-
responding epoxynitrile without formation of the corresponding
epoxyamide. On the other hand, in the epoxidation with OOH−, the
formation of epoxyamide is intrinsically inevitable [21–25].
Substrate
Product
Time (min)
Yield (%)
OH
60
60
92
84
OH
OH
60
79
Adamantanols
120
120
98b
80
OH
Dimethylcyclohexanols
60
59c
H
H
H
OH
3.3. Hydroxylation of alkanes
H
60
300
300
51
Selective oxygenation of alkanes under mild conditions remains
to be a major challenge in industrial as well as synthetic chem-
istry [26–29]. We found that I can act as an efficient homogeneous
catalyst for H2O2-based hydroxylation of various alkanes. The
results are summarized in Table 2. Oxidation of cyclic alkanes
such as cyclohexane, cyclooctane, cyclododecane, adamantane, and
norbornane proceeded selectively (≥98% selectivity), giving the
corresponding secondary alcohols without significant formation of
the corresponding ketones and C–C bond cleaved products. Previ-
ously, we reported that secondary alcohols hardly react with the
bis-␮-hydroxo in [␥-SiW10O38V2(␮-OH)2]4− because of the steric
crowding between secondary alcohols and the polyanion frame-
work [30]. Therefore, the present high selectivity to secondary
alcohols for cyclic alkanes would cause the suppression of succes-
sive alcohols oxidations. Acyclic alkanes such as propane, butane,
2-methylpropane, and n-hexane were also oxidized to the corre-
sponding alcohols as major products.
OH
17d
21e
OH
OH
300
240
29f
52g
Hexanols
a
Reaction conditions: I (1.3 mM), HClO4 (1.3 mM), substrate (4.7 M for cyclohex-
ane, 0.3 M for adamantine, 7.5 M for n-hexane, 2.5 M for others), 30% aq. H2O2
(50 mM), CH3CN/t-BuOH (0.67/1.33 mL), 60 ◦C (69 ◦C for n-hexane).
b
1-ol:2-ol:1,3-diol = 82:15:3.
3,4-Dimethyl:1,2-dimethyl:2,3-dimethyl = 86:10:4.
Propane (6 atm). Acetone (17% yield).
Butane (2.2 atm). 2-Butanone (3% yield).
2-Methlpropane (2.2 atm).
2-ol:3-ol:1-ol = 70:27:3. 2-Hexanone (4% yield).
c
d
e
f
g
The regioselectivity for the hydroxylation of substituted
cycloalkanes such as 1,2-dimethylcyclohexane and trans-decalin
with both secondary and tertiary C–H bonds was next examined.
For both substrates, the stereospecific hydroxylations took place
(Table 2): The oxidation of 1,2-dimethylcyclohexane and trans-
decalin gave trans-3,4-dimethylcyclohexanol and trans-2-decalinol
in 86% and 93% selectivities, respectively. In contrast, the mixtures
of various alcohols and the corresponding ketones are obtained in
the previously reported iron- and osmium-based systems [31–33].
Such high regioselectivities of I to the only one secondary alco-
hols even in the presence of the more reactive electron-rich tertiary
C–H bonds have never been reported so far. This is also due to the
steric hindrance of the active oxygen species formed on the rigid
polyanion framework.
ciently oxidize Br− to Br+ and/or Br2 species (active species for
bromination).
As we expected, I showed the high catalytic performance for the
H2O2-based oxidative bromination of various alkenes, alkynes, and
aromatics under ambient conditions (Table 3). When the bromi-
nation of 1-octene was carried out with I using stoichiometric
amounts of H2O2 (one equivalent) and NaBr (two equivalents), 90%
yield of 1,2-dibromooctane was obtained within only 10 min. In
this case, TOF reached up to 10,800 h−1 and much larger than those
of previously reported H2O2-based oxidative bromination systems
(∼315 h−1) [35–38]. The bromination of cis- and trans-2-octenes
diastereoselectively proceeded to afford threo- and erythro-2,3-
bromooctanes, respectively. Cyclohexene also diastereoselectively
gave trans-1,2-dibromocyclohexane. For 1,5-cyclooctadiene, the
corresponding trans-dibromoalkene was selectively obtained as a
major product.
3.4. Oxidative bromination of alkanes, alkynes, and aromatics
Bromination of organic substrates is one of the most important
transformations. Br2 has still widely been utilized for bromination
even at present despite their disadvantages. An alternative environ-
mental friendly and economical approach is oxidative bromination
using inorganic bromide (Br−) salts as bromo sources and oxidants
(H2O2 or O2 is the oxidant of choice from the standpoint of green
chemistry) [34]. As mentioned in Section 3.1, strong electrophilic
oxidants are formed by the reaction of Iꢀ with H2O2, would effi-
Notably, the I-catalyzed bromination of terminal as well
as internal alkynes exclusively gave the corresponding
E-dibromoalkenes without formation of Z-isomers, tetrabro-
moalkane, ketones, and bromoketones. As above-mentioned, the
strong electrophilic oxidants formed on I likely oxidize Br− species.
The reaction of an alkyne with the oxidized bromide species (Br+
and/or Br2 species) gave a cyclic bromonium cation intermediate
on which unoxidized Br− readily reacts from the reverse side

N. Mizuno et al. / Catalysis Today 185 (2012) 157–161
161
Table 3
Bromination of various alkenes, alkynes, and aromatics with NaBr.a
4. Conclusions
In summary, compound I could act as an efficient homogeneous
catalyst for H2O2-based epoxidation, hydroxylation, and bromina-
tion. The strong and rigid electrophilic oxidants such as II and III
were formed by the reaction of I (in the presence of H+) with H2O2,
which would be the active species for the present oxidations (in
particular III).
Substrate
Product
Time (min)
Yield (%)
90
Br
Br
Br
Br
n-C6H13
n-C5H11
n-C6H13
n-C5H11
10
10
10
76b
87c
Acknowledgment
Br
n-C5H11
This work was supported in part by the Japan Society for
the Promotion of Science (JSPS) through its Funding Program for
World-Leading Innovative R&D on Science and Technology (FIRST
Program), the Global COE Program (Chemistry Innovation through
Cooperation of Science and Engineering) and Grants-in-Aid for
Scientific Researches from Ministry of Education, Culture, Sports,
Science and Technology.
n-C5H11
Br
Br
Br
10
10
82
84
Br
Br
Br
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30
10
10
96
NH2
OH
NH2
OH
81d
50e
Br
MeO
OMe
MeO
OMe
Cl
88f
OMe
OMe
120
a
Reaction conditions: I (0.5 ␮mol), substrate (1 mmol), 30% aq. H2O2 (1 mmol),
NaBr (2 mmol for alkenes and alkynes, 1 mmol for aromatics), AcOH/1,2-
dichloroethane (2/1 mL), 20 ◦C.
b
Threo isomer.
Erythro isomer.
Para:ortho = 82:18.
Para:ortho = 59:41.
c
d
e
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f
Reaction conditions: I (0.5 ␮mol), substrate (1 mmol), 30% aq. H2O2 (2 mmol),
LiCl (5 mmol), AcOH/1,2-dichloroethane (2/1 mL), 60 ◦C.
[39], resulting in the exclusive formation of the correspond-
ing E-dibromoalkene. The above-mentioned diastereoselective
bromination of internal alkenes also supports this mechanism.
Bromination of aromatics such as anisole, aniline, and phenol
efficiently proceeded using stoichiometric amounts of H2O2 (one
equivalent) and NaBr (one equivalent), affording the corresponding
monobromobenzene derivatives. In addition, the present system
was applicable to oxidative chlorination using LiCl as a chloro
source, giving the corresponding monochlorobenzene in high yield.
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