Oxido-peroxido W(VI)-histidine–MgAl-layered double hydroxide composite as an efficient catalyst in sulfide oxidation

Article abstract of DOI:10.1002/aoc.4358

Oxido-peroxido W(VI)-histidine–MgAl-layered double hydroxide composite was prepared by using MgAl-layered double hydroxide as a host and oxido-peroxido W(VI)-histidine complex as a guest. The composite was characterized by XRD, IR, EDX,SEM and TEM techniques. This composite is tested for catalytic selective sulfoxidation reactions using hydrogen peroxide as oxidant showing good to moderate conversion along with high selectivity.

Full text of DOI:10.1002/aoc.4358

Received: 27 November 2017
DOI: 10.1002/aoc.4358
Revised: 23 February 2018
Accepted: 25 February 2018
F U L L P A P E R
Oxido‐peroxido W(VI)‐histidine–MgAl‐layered double
hydroxide composite as an efficient catalyst in sulfide
oxidation
Mohammad Nikkhoo1,2 | Mojtaba Amini2
| S. Morteza1 | F. Farnia1 | Arshad Bayrami3 |
Mojtaba Bagherzadeh3
| Sanjeev Gautam4 | Keun Hwa Chae5
1 Department of Chemistry, University of
Tehran, Tehran, Iran
2 Department of Chemistry, Faculty of
Science, University of Maragheh,
Maragheh, Iran
3 Chemistry Department, Sharif University
of Technology, Tehran, P.O. Box 11155‐
3615, Iran
4 Dr. S. S. Bhatnagar University Institute of
Chemical Engineering & Technology, Panjab
University, Chandigarh 160‐014, India
Oxido‐peroxido W(VI)‐histidine–MgAl‐layered double hydroxide composite
was prepared by using MgAl‐layered double hydroxide as a host and oxido‐
peroxido W(VI)‐histidine complex as a guest. The composite was characterized
by XRD, IR, EDX,SEM and TEM techniques. This composite is tested for cata-
lytic selective sulfoxidation reactions using hydrogen peroxide as oxidant show-
ing good to moderate conversion along with high selectivity.
KEYWORDS
LDH, oxidation, oxido‐peroxido, sulfide, tungsten
5 Advanced Analysis Center, Korea
Institute of Science and Technology, Seoul
136‐791, South Korea
Correspondence
Mojtaba Amini, Department of Chemistry,
Faculty of Science, University of
Maragheh, Maragheh, Iran
Email: mamini@maragheh.ac.ir
1 | INTRODUCTION
W(VI)‐histidine–MgAl‐layered double hydroxide (1) was
prepared by using MgAl‐layered double hydroxide as host
and oxido‐peroxido W(VI)‐histidine complex as guest.
The composite was used as a catalyst for sulfide oxidation
with hydrogen peroxide (H2O2) as an oxidant under ambi-
ent conditions (Scheme 1).
Sulfoxides are important intermediates in many industrial
reactions owing to biological and pharmaceutical activi-
ties. Efficient and selective oxidation of sulfides to sulfox-
ides is an essential part of synthetic design in modern
pharmaceutical processes.[1–7] The application of oxido–
peroxido tungsten (VI) complexes are exciting due to
tungsten centers activating peroxido groups for oxidation
of a variety of organic substrates.[8–15]
Layered double hydroxides (LDHs) as a class of
anionic clays with features such as large surface area,
high anion exchange capacity, good thermal stability
and low toxicity have been extensively applied as interca-
lation hosts for metal complexes for recyclable catalysts in
varied organic reactions.[16–20] Herein, an oxido‐peroxido
2 | EXPERIMENTAL
2.1 | Materials
All chemicals and solvents were obtained from Merck and
Fluka Inc. and were used without further purification.
Layered double hydroxide (LDH) with Mg1‐
xAlx(OH)2(Cl)x.zH2O composition and WO3 were synthe-
sized described in previous reported procedures.[21,22]
Appl Organometal Chem. 2018;e4358.
wileyonlinelibrary.com/journal/aoc
Copyright © 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4358

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NIKKHOO ET AL.
SCHEME 1 Sulfide oxidation in the presence of oxido‐peroxido
oxido‐peroxido W(VI)‐histidine‐ LDH composite
2.2 | Preparation of histidine‐ LDH
LDH (0.3 g) was suspended in a solution of ethanol‐water
(1:1) (20 ml) and L‐histidine (0.39 g) was added to mix.
The pH of the solution was adjusted to 8 by adding
dropwise 0.5 M NaOH solution and stirred for 24 h at
room temperature. The white solid was filtered, washed
with ethanol and deionized water and dried at ambient.
2.3 | Preparation of oxido‐peroxido W(VI)‐
histidine–MgAl‐layered double hydroxide (1)
Freshly prepared WO3·nH2O (0.08 g) was dissolved in
H2O2 (0.3 ml) and stirred until a clear solution is obtained.
Histidine‐ LDH (0.2 g) was suspended in ethanol‐ water
(1:1) (15 ml) and then the tungsten oxide solution was
added to the suspension. Then two drops of
trimethylamine was added to the solution and mixed for
24 h. The resultant precipitate was filtered, washed three
times with ethanol and distilled water and air‐dried.
FIGURE 1 XRD pattern of histidine‐ LDH (A) and oxido‐
peroxidoW‐ histidine‐ LDH (B)
patterns. The interlayer distance of oxido‐peroxido W‐
histidine‐ LDH was at 0.77 nm.
2.4 | Oxidation of sulfides
The SEM images of LDH, histidine‐ LDH and oxido‐
peroxido W‐ histidine‐ LDH are shown in Figure 2. SEM
image shows that LDH crystals in all samples have a
plate‐ like morphology and intermittent plate‐ plate stack-
ing. Histidine‐ LDH and W‐ histidine‐ LDH are similar in
plate as of LDH, and do not break the layers (2c,d and 2e,
f). These demonstrate that histidine and W‐ histidine
complex successfully intercalate into the interlayers of
LDH.[23]
The TEM images for sample oxido‐peroxido W‐ histi-
dine‐ LDH are displayed in Figure 3. oxido‐peroxido W‐
histidine‐ LDH particles showed hexagonal shape with a
length of 60–80 nm.
A round bottom flask containing a mixture of sulfide
(1.0 mmol), oxido‐peroxido W(VI)‐histidine–LDH (1 mg)
and H2O2 (1.5 mmol) in methanol (1 ml) was kept on under
continuous stirring at 65 °C. Then, progress of sulfide oxi-
dation and conversion were determined by GC analysis.
3 | RESULTS AND DISCUSSION
3.1 | Catalyst characterization
The XRD patterns of histidine‐ LDH and oxido‐peroxido
W‐ histidine‐ LDH are shown in Figure 1. The main dif-
fraction peaks of the histidine‐ LDH and oxido‐peroxido
W‐ histidine‐ LDH were in conformance with LDH XRD
EDX analysis shows presence of magnesium, alumi-
num, tungsten and oxygen as elements in the oxido‐

NIKKHOO ET AL.
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FIGURE 2 The SEM images of the (a,b) LDH, (c,d) histidine‐ LDH and (e,f) oxido‐peroxido W‐ histidine‐LDH
peroxido W‐ histidine‐ LDH nanoparticles. The tungsten
in the composite 1 constitute about 4.9% (atomic %).
The FT‐IR spectra of the LDH, histidine‐ LDH sam-
ples and 1 are shown at Figure 4. All three spectra contain
a broad absorption band in the range of 3000–3600 cm−1
corresponding to the O‐H stretching vibrations of the
hydroxide groups in the LDH sheets and interlayer
water.[24] The absorption band around 1620 cm−1 is
attributed to bending vibrations of the interlayer water
molecules and the hydroxide groups in the LDH layers.[25]
The absorption peaks in the low frequency region (400–
1000 cm−1) of the spectra is related to the lattice vibration
modes of M–O and O–M–O in the LDH sheets.
3.2 | Catalytic effects
Catalytic activities of W‐ histidine‐ LDH were studied in
the sulfide oxidation reaction. First the influence of reac-
tion solvent, temperature and time on the conversion
and selectivity of the oxidation reaction of methyl phenyl
sulfide (MPS) as a model reaction were studied (Table 1).
For all oxidation reactions, minimum weighable amount
of catalyst (1 mg) in the presence of H2O2 as oxidant
was used. A control experiment in the absence of catalyst
or in the presence of MgAl‐LDH or histidine‐ LDH
afforded low yields of the sulfoxide without sulfone
(entries 1–3). The MPS oxidation reaction was studied

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NIKKHOO ET AL.
FIGURE 3 TEM image of oxido‐peroxido W‐ histidine‐ LDH
FIGURE 4 IR spectra of (a) LDH, (b) histidine‐ LDH and (c) oxido‐peroxido W‐ histidine‐ LDH
using various solvents to carry out the reaction at room
temperature. The results listed in Table 1 show that the
reaction results depends on the nature of solvent
(entries 4–8). Yields of 63% and 59% were obtained using
methanol and dichloromethane (entries 6 and 8) but poor
conversion was obtained in other solvents such as water,
acetonitrile and ethylactate (entries 4, 5 and 7). Reactions
in methanol had the best conversion rate and all other
reactions were carried out in this solvent. To obtain a
complete transformation of MPS, reaction temperature
was increased to 65 °C, and result showed that the oxida-
tion of MPS is highly selective (89%) to sulfoxide with
100% conversion of the substrate at a reaction time of
105 min (entry 13). It is noteworthy that the oxidation of
MPS using H2O as a solvent under identical reaction con-
ditions, afforded the almost complete conversion (97%),
but with low selectivity (64%) to the sulfoxide (entry 14).
It can be observed that the conversion of MPS increased
to 100% with the reaction time of 105 min (entry 13).
The selectivity to sulfoxide was excellent (higher than
89%). A control experiment without W‐ histidine‐ LDH
afforded the sulfoxide in only 11% yields without sulfone.
To study the scope of reaction, the oxidation of a vari-
ety of aromatic and aliphatic substrates was studied
(Table 2). A series of substrates, aryl‐alkyl (entry 1), diaryl
(entry 2), benzyl–aryl (entry 3), dibenzyl (entry 4) and

NIKKHOO ET AL.
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TABLE 1 The results for various conditions on the oxidation of sulfidesa
Entry
catalyst
Solvent (1 ml)
Temperature (°C)
Time (min)
Conversion (%)b
Selectivity (%)c
1
‐
CH3OH
CH3OH
CH3OH
H2O
65
65
65
r.t.
r.t.
r.t.
r.t.
r.t.
65
65
65
65
65
65
120
120
120
120
120
120
120
120
120
30
11
14
13
48
42
59
40
63
100
65
89
98
100
97
100
100
100
56
2
MgAl‐ LDH
3
Histidine‐LDH
4
1
1
1
1
1
1
1
1
1
1
1
5
EtOAc
CH2Cl2
CH3CN
CH3OH
CH3OH
CH3OH
CH3OH
CH3OH
CH3OH
H2O
68
6
82
7
78
8
89
9
87
10
11
12
13
14
92
60
90
90
88
105
105
89
64
aReaction conditions: 1 ml of solvent; 1 mmol of methylphenylsulfide; 1.5 mmol H2O2.
bDetermined by GC on the crude reaction mixture. c Selectivity to sulfoxide = (sulfoxide%/ (sulfoxide% + sulfone%)) × 100.
TABLE 2 Oxidation of various sulfides in the presence of 1
Conversion Selectivity
Entry Substrate
(%)
(%)
1
100
89
2
3
4
83
94
92
86
90
85
FIGURE 5 Recycling studies of 1 in the oxidation reaction
5
6
7
69
99
58
100
100
100
aReaction conditions: 1 mmol of sulfide; 1.5 mmol H2O2; 1 mg of 1; 1 ml of
MeOH. bDetermined by GC. cSelectivity to sulfoxide
(sulfoxide% + sulfone%)) × 100.
= (sulfoxide%/
dialkyl sulfides (entries 5–7), are selectively oxidized to
the corresponding sulfoxides in high yields and purity.
The reactivity and conversion were dependent on the
nature of the substituents. Dialkyl sulfides, diethyl sulfide
and dioctyl sulfide, were mildly reactive affording the cor-
responding sulfoxide without over oxidation to the sul-
fone (entries 5, 7). In the case of diallyl sulfide, no
oxidation was observed at the carbon–carbon double bond
(entry 6).
SCHEME 2 Mechanism of sulfide oxidation in the presence of 1

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NIKKHOO ET AL.
TABLE 3 Comparison of the catalytic activity of 1 with some oxido‐peroxido W/ Mo catalysts
Entry Catalyst
Reaction Condition
Conversion (selectivity to sulfoxide) % References
1
2
3
4
5
1
H2O2/PhSCH3/CH3OH/65 °C/ 105 min 100 (89)
H2O2/CH3SCH3/CH2Cl2/ 40 °C/60 min 100 (6%)
Present work
[28]
[WO(O2)(CPHA)2]
[29]
[30]
[2]
[PPh4][MoO(O2)2(QO)]
H2O2/CH3SCH3/CH2Cl2/ 40 °C/60 min
18 (82)
PPh4[WO(O2)2(HPEOH)] H2O2/CH3SCH3/CH3CN/reflux/ 60 min 100 (4%)
[MoO(O2)(phox)2] TBHP/CH3CN/rt/ 30 min 99 (100)
The recoverability and reusability of the oxido‐
cycles in oxidation reaction with no significant loss in cat-
alytic activity.
peroxido W‐ histidine‐ LDH was investigated in the con-
secutive reaction of MPS oxidation (Figure 5). At the
end of each run the catalyst was filtered and removed
from reaction and after washing with ethanol and ace-
tone, dried and then reused. The results of these studies
showed that the oxido‐peroxido W‐histidine‐ LDH com-
posite preserved its activity after three runs without any
significant loss of catalytic activity. The reduction of the
catalytic efficiency after three cycles is mainly due to loss
of catalyst during the filtration and separation processes.
The mechanism of sulfide oxidation to sulfoxide is
well studied using oxido‐peroxido molybdenum (VI) or
tungsten (VI)‐ containing catalyst.[26,27] In this mecha-
nism, the oxidation reaction starts with nucleophilic
attack of sulfide on one of the oxygen atoms of
the peroxido ligand, providing sulfoxide and generating
the related dioxido tungsten (VI)‐ LDH complex. Then
the primary catalyst, oxido‐peroxido W‐ histidine‐ LDH,
is obtained with reaction of dioxido intermediate and
H2O2 oxidant, which restarts the cycle (Scheme 2). Partic-
ularly, Calhadro et al. have shown by using DFT studies
that this transformation by oxido‐peroxido Mo(VI) com-
plex takes place with the same mechanism.[3]
ACKNOWLEDGEMENTS
Partial funding support was provided by the Research
Council of University of Maragheh (M.A.) and Tehran
University (S.M.F.).
ORCID
Mojtaba Amini http://orcid.org/0000-0001-6509-5942
Mojtaba Bagherzadeh
http://orcid.org/0000-0003-3009-
3693
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How to cite this article: Nikkhoo M, Amini M,
Morteza S, et al. Oxido‐peroxido W(VI)‐histidine–
MgAl‐layered double hydroxide composite as an
efficient catalyst in sulfide oxidation. Appl
Organometal Chem. 2018;e4358. https://doi.org/
10.1002/aoc.4358
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