Highly ordered mesoporous La(III)-substituted 5-oxopyrrolidine-2-carboxylic acid (Glp) immobilized on SBA-15 as a very efficient nanocatalyst for green aerobic oxidative coupling of thiols to disulfides

Article abstract of DOI:10.1002/aoc.5328

Selective aerobic oxidative coupling of thiols that are catalyzed by La(III)-substituted 5-oxopyrrolidine-2-carboxylic acid (Glp) immobilized on SBA-15 (SBA-15@Glp–La; SBA = Santa Barbara amorphous) was studied. Using SBA-15@Glp–La, the complete conversio

Full text of DOI:10.1002/aoc.5328

Received: 12 August 2019
DOI: 10.1002/aoc.5328
Revised: 6 October 2019
Accepted: 14 October 2019
F U L L P A P E R
Highly ordered mesoporous La(III)-substituted 5-
oxopyrrolidine-2-carboxylic acid (Glp) immobilized on SBA-
15 as a very efficient nanocatalyst for green aerobic
oxidative coupling of thiols to disulfides
Somayeh Molaei
| Mohammad Ghadermazi
Department of Chemistry, Faculty of
Science, University of Kurdistan,
Sanandaj, Iran
Selective aerobic oxidative coupling of thiols that are catalyzed by La(III)-
substituted 5-oxopyrrolidine-2-carboxylic acid (Glp) immobilized on SBA-15
(SBA-15@Glp–La; SBA = Santa Barbara amorphous) was studied. Using SBA-
15@Glp–La, the complete conversion was achieved at room temperature in
the presence of air without producing any over-oxidized yields. SBA-15@Glp–
La was prepared by post-grafting technique. 5-Oxopyrrolidine-2-carboxylic acid
(Glp) condensation followed by La(III) impregnation caused this La(III)-
grafted 5-oxopyrrolidine-2-carboxylic acid (Glp) to immobilize on SBA-15. This
SBA-15@Glp–La catalyst shows excellent catalytic activity in the selective aer-
obic oxidative coupling of thiols. Effects of amount of the catalyst, polarity of
the solvent, effects of substrate, and catalyst reusability were investigated. It
has been observed that seven repetitive reaction cycles did not cause any
appreciable loss in the catalytic activity of this catalyst. The catalyst characteri-
zation by scanning electron microscopy, energy-dispersive X-ray spectroscopy,
X-ray diffraction, Fourier-transform infrared spectroscopy, thermal gravimetric
analysis, transmission electron microscopy, inductively coupled plasma, ele-
mental mapping, and N2 adsorption–desorption is reported. The procedure
developed is heterogeneous and environmentally benign.
Correspondence
Mohammad Ghadermazi, Department of
Chemistry, Faculty of Science, University
of Kurdistan, Sanandaj, PO Box,
6617715175 Kurdistan, Iran.
Email: mghadermazi@yahoo.com
Funding information
University of Kurdistan
K E Y W O R D S
aerobic oxidation, La(III) and nanoporous catalyst, thiols
1 | INTRODUCTION
disulfides. Extensive investigations have been performed
to analyze the mechanism underlying the oxidation of
Oxidative coupling of thiols is a significant procedure
from both biological and synthetic viewpoints, owing to
the different features of disulfide bonds, for example, as
an intermediate in organic synthesis; the reaction is also
important in the petroleum industry, as it is useful for
the elimination of thiols by converting them into
thiols to disulfides. However, these catalytic routes suffer
from over-oxidation. The weakness of sulfur–sulfur
bonds leads to over-oxidation of disulfides, which in turn
results in the yield of sulfonates, sulfinates, sulfonic
acids, and sulfoxides. In this regard, selective oxidation
control has attracted attention as it offers some benefits,
Appl Organometal Chem. 2019;e5328.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5328

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MOLAEI AND GHADERMAZI
such as less workup, short reaction time, minimum
waste, and low cost.[1–6] Because of these appealing fea-
tures of selective oxidation procedures, some studies have
focused on the selective oxidation of thiols. Many of the
catalysts used are based on manganese(III) Schiff-base
complex chromium,[3] cobalt–iron magnetic composi-
2 | EXPERIMENTAL
2.1 | Characterization
La loadings in the SBA-15@Glp–La catalyst were deter-
mined by inductively coupled plasma-optical emission
spectrometry (ICP-OES; 730-ES Varian). X-ray powder
diffraction (XRD) data were obtained on an MPD diffrac-
tometer (X’pert) using Cu Kα radiation (45 kV, 40 mA).
The Fourier-transform infrared (FT-IR) spectra were col-
tes,[5]
trichlorooxyvanadium,[6]
benzyltriphenyl-
phosphonium peroxymonosulfate,[7] rhenium,[8] NaI,[9]
Ni-nanoparticles,[10] potassium phosphate,[11] iodine and
CeCl3Á7H2O,[12] metal–organic frameworks,[13] and lead
oxide.[14] These catalytic routes involve high reaction
temperatures, often toxic by-products, expensive cata-
lysts, long reaction times, stoichiometric dosages of cata-
lysts, and use homogeneous catalysts, and thus, have
reusability problems. Some of these catalytic routes also
use strong oxidants such as oxygen with high pressures
and hydrogen peroxides that are dangerous in handling,
storage, and transportation.[2] Therefore, it is favorable to
report a heterogeneous catalytic procedure that is envi-
ronmentally friendly, highly selective, and uses air as an
environmentally benign, sustainable, and green oxidant.
Various elements, such as copper,[15] manganese,[4]
vanadium,[6] bismuth,[16] nickel,[10] have been devel-
oped to catalyze the aerobic oxidative coupling of
thiols into disulfides. Lanthanides have found great
use as Lewis acids in green organic chemistry because
of their availability at a moderate price, stability, and
low toxicity.[17] In recent years, interest in the develop-
ment of heterogeneous catalysts has increased enor-
mously. A variety of approaches have been applied for
the development of heterogeneous catalysts that usu-
ally involve the immobilization of homogeneous cata-
lysts on the surfaces of both organic and inorganic
solids, including mesoporous materials, polymers, and
dendritic systems.[18–20] The ordered mesoporous mate-
rials such as SBA-15 (SBA = Santa Barbara amor-
phous), MCM-41, SBA-16, and MCM-48 have attracted
considerable attention as supports in various catalytic
applications due to their high surface area and pore
volume, uniform pore size distribution, large pore size,
tunable structure, and extraordinarily wide possibilities
for functionalization.[21–26] Among the mesoporous sil-
ica materials, SBA-15 shows interesting textural proper-
ties, such as high hydrothermal stability, thick silica
walls, and high surface-to-volume ratio.[27–32] The aim
of this study was to present an environmentally
benign, economical, heterogeneous catalytic process
using La(III) complexes immobilized on mesoporous
SBA-15 for the oxidation of thiols into the
corresponding disulfides using molecular oxygen for
the first time. Furthermore, air was used as an oxidiz-
ing agent, as it is more economical than pure oxygen
and greener than hydrogen peroxides.
lected with
a spectrometer (VERTEX 80 model;
BRUKER) using the KBr pellet technique. Ther-
mogravimetric analyses (TGAs) were performed for the
catalyst with a thermogravimetric analyzer (Shimadzu
DTG 60). Scanning electron microscopy (SEM) images
were obtained on FESEM-TESCAN MIRA3. Nitrogen
adsorption-desorption isotherm (BET) was recorded on
Volumetric adsorption analyzer Japan, BLlSORP-MINI
II, using a standard gas manifold at 77 K.
2.2 | SBA-15 preparation
The silica SBA-15 catalyst was synthesized according to
the procedure reported previously.[33] A typical synthesis
involves the following steps: pluronic P123 (4.0 g) was
introduced to 30 mL of H2O and 90 mL of HCl (2 M), and
the mixture was stirred at 30 ꢀC for 5 hr. Then, tetraethyl
orthosilicate (9.04 mL, 40.78 mmol) was added dropwise
and stirred for 20 hr. The white precipitate was collected
and washed with distilled water. Then, the powder was
dried. Afterward, the obtained powder was calcined at
823 K (5 hr).
2.3 | Immobilization of 5-oxopyrrolidine-
2-carboxylic acid onto SBA-15
5-Oxopyrrolidine-2-carboxylic acid (Glp) incorporation
into SBA-15 was achieved using the following procedure:
pure SBA-15 (1 g) was introduced to 30 mL deionized
water including 5-oxopyrrolidine-2-carboxylic acid (1.5 g,
11.61 mmol) and then refluxed (48 hr). The precipitate
was collected and washed three times with distilled
water. After that, the powder was dried (SBA-15@Glp).
2.4 | Synthesis of SBA-15@Glp–La
catalyst
The SBA-15@Glp–La catalyst was prepared through the
coordination of La(III) with the Glp ligand grafted on the
SBA-15 support. Approximately 1.0 g of SBA-15@Glp

SELECTIVE AEROBIC S-S COUPLING
3 of 14
was added into 30 mL of ethanol containing 2.5 mmol of
La(NO3)3 (1.08 g) and then refluxed for 16 hr. The resul-
tant solid was collected and extensively washed with eth-
anol. After that, the powder was dried at 60 ꢀC.
Schematic presentation of these catalysts is displayed in
Scheme 1.
of the reaction was observed with thin-layer chroma-
tography. Then, the catalyst was collected by centrifu-
gation. The filtrate was separated and washed several
times with water. The filtrate was then separated with
ethyl acetate and finally dried by evaporating of sol-
vent to obtain a solid product.
2.5 | General procedure for aerobic
oxidative coupling of thiols over SBA-
15@Glp–La
2.6 | Selected spectral data
1
Dibenzyl disulfide (Table 5, Entry 3) – H (400 MHz,
To the SBA-15@Glp–La (5 mg) complex in ethanol
(5 mL), the thiol (1 mmol) was introduced and molec-
ular oxygen/air was simply bubbled. At room tempera-
ture, the reaction mixture was stirred and the progress
CDCl3, ppm): δ 3.65 (s, 4H), 7.30–7.38 (m, 10H).
1,2-Bis(4-methyl phenyl) disulfane (Table 5, Entry 9)
– H NMR (400 MHz, CDCl3): δ 2.48 (s, 6H), 4.11–4.16
1
(m, 4H), 7.81–7.83(m, 4H) ppm.
SCHEME 1 Schematic depiction of
the preparation of the catalysts

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MOLAEI AND GHADERMAZI
3 | RESULTS AND DISCUSSION
3.1 | Low-angle XRD pattern studies
As shown in Figure 1, the low-angle XRD patterns dem-
onstrated that the SBA-15 sample exhibited an intense
(100) reflection and two weak diffraction corresponding
to the (110) and (200) reflections attributable to the hex-
agonal mesostructure (p6mm).
A comparison of the XRD patterns of SBA-15, SBA-
15@Glp–La shows that the intensity of the peak charac-
teristic of the (100) diffraction has been decreased and
the two peaks corresponding to the (110) and (200) reflec-
tions have disappeared after metal complex formation in
SBA-15.
This result could be attributed to the lowering of local
order, such as variations in the wall thickness, or might
be due to the reduction of scattering contrast between the
channel wall of the silicate framework and the La com-
plex present in SBA-15@Glp–La.[34–36]
FIGURE 2 N2 adsorption–desorption of SBA-15 (labeled a)
and SBA-15@Glp–La (labeled b). STP, standard temperature and
pressure
(Vp) of 0.554 cm3 g−1. The average pore diameter was cal-
culated to be 2.4 nm for SBA-15 using the Barrett–
Joyner–Halenda (BJH) method. All the calculated values
were in agreement with those reported for good-quality
mesoporous silica. By contrast, the SBA-15@Glp–La cata-
lyst shows smaller N2 uptake (BET surface area
3.2 | N2 adsorption–desorption studies
N2 adsorption–desorption isotherms demonstrate that
both the pristine SBA-15 and the SBA-15@Glp–La sam-
ples (Figure 2) present the typical IV type isotherms
(according to the IUPAC nomenclature) with hysteresis
loops, indicating that the mesoporous structure has been
preserved. With immobilization of the La(III) Glp com-
plex, hysteresis occurs at lower P/P0 values.
Some structural parameters were calculated, on the
basis of the N2 adsorption–desorption isotherms, and are
listed in Table 1. The SBA-15 has a BET surface area
(AsBET) of 555 m2 g−1 and a primary mesopore volume
TABLE 1 Surface exclusivity of SBA-15 and metal-grafted
SBA-15
BET surface Pore diameter
Pore
area
(cm2/g)
by the BJH
method (nm)
volume
(cm3/g)
Sample
SBA-15
555.2
2.4
1.2
0.554
0.396
SBA-15@Glp– 321.5
La
aBET, Brunauer–Emmett–Teller; BJH, Barrett–Joyner–Halenda.
FIGURE 1 X-ray diffraction analysis of SBA-15@Glp–La
(labeled a) and SBA-15 (labeled b)
FIGURE 3 Thermogravimetric analysis curves of SBA-15,
SBA-15@Glp, SBA-15@Glp–La, and recovered SBA-15@Glp–La

SELECTIVE AEROBIC S-S COUPLING
5 of 14
321 m2 g−1) as well as smaller pore volume (0.396 cm3 g−1
)
mesoporous materials. The weight loss from 150 to
365 ꢀC was assigned to the decomposition of the structure
of organic groups. The weight loss from 365 to 650 C
and pore diameter (1.2 nm). The decrease in the BET sur-
face area and Vp value of SBA-15@Glp–La in comparison
with those of SBA-15 clearly demonstrates that the
immobilization of Glp–La onto the mesoporous silica has
a significant effect on pore structure of the catalyst. One
of the possible reasons for this difference in the BET sur-
face area, Vp, and pore diameter values between SBA-15
and SBA-15@Glp–La might be the immobilization of
metal complex onto the nanosized pores of the meso-
porous material.[35,37]
ꢀ
3.3 | Thermogravimetric studies
The TGA curves of SBA-15, SBA-15@Glp, SBA-15@Glp–
La, and recovered SBA-15@Glp–La are depicted in
Figure 3. In all samples the weight loss from 35 to 150 ꢀC
was assigned to the removal of adsorbed water in the
FIGURE 5 Energy-dispersive X-ray spectroscopy pattern of
SBA-15@Glp–La
FIGURE 4 Scanning
electron microscopy images of
SBA-15 (top) and SBA-15@Glp–
La (bottom)

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MOLAEI AND GHADERMAZI
was attributed to the decomposition of organic residues
with high molecular weight, whereas the weight loss
between 600 and 800 ꢀC resulted from the decomposition
of silanol groups.[38,39]
3.4 | SEM photographs, energy-
dispersive X-ray analysis, and elemental
mapping
Therefore, in order to obtain more information about
the SBA-15@Glp–La catalyst, both the support (SBA-
15@Glp) and the catalyst (SBA-15@Glp–La) were treated
in an N2 atmosphere. As a result, the final decomposition
temperatures for the SBA-15@Glp–La catalyst compare
with SBA–15@Glp increased. This phenomenon can also
be explained by the strong interaction of La(III) with
organic groups that enhanced the catalyst stability, as
observed for the delayed starting decomposition tempera-
ture. The TG results of the as-prepared SBA-15@Glp–La
also confirmed that La(III) had a strong interaction with
the Glp group. TGA analysis of reused SBA-15@Glp–La
Figure 4 shows the SEM of the SBA-15 and SBA-
15@Glp–La at different magnetization. It can be observed
that SBA-15@Glp–La has a pipe-like domain morphol-
ogy. Furthermore, the SEM measurements indicate that a
similar morphology can be seen in the SBA-
15-functionalized sample. Energy-dispersive X-ray analy-
sis of SBA-15@Glp–La shows the existence of silicon,
oxygen, carbon, nitrogen, and La in the catalyst and the
spectrum is depicted in Figure 5. As shown in Figure 6,
the elemental mapping confirmed a homogeneous distri-
bution of silicon, oxygen, carbon, nitrogen, and La in the
SBA-15@Glp–La catalyst. Finally, the amount of La(III)
in the catalyst was estimated using ICP-OES to be
0.32 mmol g–1.
ꢀ
showed a mass loss between 200 and 600 C, which cor-
responds to the removal of organic moieties.
FIGURE 6 Elemental mapping images of
SBA-15@Glp–La

SELECTIVE AEROBIC S-S COUPLING
7 of 14
3.5 | FT-IR spectra
FT-IR spectrum of the reused SBA-15@Glp–La sample
(Figure 7, d) shows that the structure of the catalyst
has remained unchanged even after seven runs. The
FT-IR spectrum of reused catalyst indicated that it can
be recycled seven times without significant change in
the structure of silicate.
The FT-IR spectra of SBA-15, SBA-15@Glp, SBA-
15@Glp–La, and reused SBA-15@Glp–La are shown in
Figure 7. The FT-IR spectra of siliceous materials, con-
taining asymmetric Si–O–Si stretching at 1082 cm−1
,
symmetric Si–O–Si stretching at 806 cm−1, and bend-
ing Si–O–Si vibration at 463 cm−1 were seen in the
FT-IR spectra of all samples, indicating that the silica
framework remains unaffected upon modification. The
FT-IR spectrum of the SBA-15@Glp sample shows
bands around 1639 and 1383 cm−1, which can be
assigned to the C=O stretching vibration and the C–N
stretching vibration, respectively, indicating the suc-
cessful attachment of the Glp groups onto the solid
surface SBA-15 support. The FT-IR spectrum of the
SBA-15@Glp–La sample (Figure 7, c) shows the band
for the C=O stretching vibration at 1635 cm−1, which
has been shifted to a lower wavenumber, showing that
C=O groups are coordinated to La(III) species. The
3.6 | TEM images
The TEM image of SBA-15@Glp–La (Figure 8) shows the
presence of ordered mesostructures in this sample. The
TEM micrograph of SBA-15@Glp–La viewed along the
pore axis reveals a hexagonal array. The TEM image pro-
vides strong evidence that the long-range ordering of the
support framework is retained even after the immobiliza-
tion of the La(III)–Glp complex in the mesoporous silica
matrix. These data indicate that the immobilization of
the La(III)–Glp complex has taken place substantially
inside the pore channels of SBA-15.
FIGURE 7 Fourier-transform infrared
spectra of SBA-15 (labeled a), SBA-15@Glp
(labeled b), SBA-15@Glp–La (labeled c), and
recovered SBA-15@Glp–La (labeled d)

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MOLAEI AND GHADERMAZI
15@Glp–La originates from the immobilized La sites
(Table 2). 4-methylthiophenol was chosen as a substrate
to perform this control test. We have performed the oxi-
dation of 4-methylthiophenol using SBA-15 and SBA-
15@Glp as catalysts in ethanol at room temperature, but
in these cases, no reaction occurs after 2 hr. Then, the
aerobic oxidation of thiol was performed using
homogeneous-phase La(NO3)3 as the catalyst (Table 2,
Entry 3). The conversion of 4-methylthiophenol was 80%.
It is evident that the presence of La is essential for this
transformation. However, it cannot be reused due to the
homogenous nature of the La(NO3)3. After that, the
TABLE 3 Effect of various solvents on the oxidative coupling
of thiol using 4-methylthiophenol with molecular oxygen/air as
oxidant and SBA-15@Glp–La as catalysta
Entry
Solvent
Time (min)
Yield (%)b
1
2
3
4
5
n-Hexane
45
35
30
25
20
72
78
84
88
92
Dichloromethane
Ethyl acetate
Acetonitrile
EtOH
FIGURE 8 Transmission electron microscopy images of SBA-
15@Glp–La
aReaction conditions: thiol (1 mmol), catalyst (6 mg), and solvent (3 mL) at
3.7 | Catalytic studies
room temperature (r.t.).
bIsolated yield.
The SBA-15@Glp–La catalyst has been used for the aero-
bic oxidation of thiols to disulfides. We performed a test
to confirm that the catalytic performance of SBA-
TABLE 4 Effect of catalyst dosage on the oxidative coupling of
thiol using 4-methylthiophenol with molecular oxygen/air as
oxidant and SBA-15@Glp–La as catalysta
TABLE 2 Testing of various catalysts for oxidation of
4-methylthiophenola
Entry
Catalyst (mg)
Time
Yield (%)b
1
2
3
4
5
6
7
0
2
10 hr
Trace
80
Entry
Catalyst
Time
2 hr
Yield (%)b
45 min
30 min
20 min
15 min
12 min
10 min
1
2
3
4
5
SBA-15
0
0
4
87
SBA-15@Glp
La(NO3)3
2 hr
2 hr
6
92
80
85
91
8
93
La supported over SBA-15
SBA-15@Glp–La
2 hr
10
12
94
15 min
94
aReaction conditions: 4-methylthiophenol (1 mmol), catalyst (6 mg), r.t.
(room temperature).
bIsolated yield of product.
aReaction conditions: thiol (1 mmol), catalyst, and EtOH (3 mL) at room
temperature (r.t.).
bIsolated yield.

SELECTIVE AEROBIC S-S COUPLING
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MOLAEI AND GHADERMAZI

SELECTIVE AEROBIC S-S COUPLING
11 of 14
aerobic oxidation of 4-methylthiophenol was carried out
by La-immobilized SBA-15, after which the conversion
increased a little. By contrast, when the aerobic oxidation
of 4-methylthiophenol was performed in the presence of
SBA-15@Glp–La as the catalyst, the yield increased
remarkably. Large surface area enables organic molecules
to diffuse into the channel of SBA-15 and helps them
interact with La(NO3)3. This explains why the rate of aer-
obic oxidation of 4-methylthiophenol in the presence of
SBA-15@Glp–La is quite higher than other conventional
catalysts.
In the second part of the study, thiols were oxidized
to disulfides in different solvents under aerobic
condition using SBA-15@Glp–La as the catalyst. 4-
Methylthiophenol was selected as the model substrate.
The results are presented in Table 3. n-Hexane, dic-
hloromethane, ethyl acetate, acetonitrile, and ethanol
were tested as solvents in the reaction. The non-polar sol-
vent n-hexane provided the lowest conversion, whereas
polar aprotic solvents such as dichloromethane, EtOAc,
and CH3CN gave 78%, 84%, and 88% conversion, respec-
tively. When the polar protic solvent EtOH was utilized,
92% conversion was achieved. In polar aprotic acetoni-
trile, with low basicity, 4-methylthiophenol reacted
slowly (Table 3, Run 4). In ethanol, with high basicity,
4-methylthiophenol proceeded to react easily.
The influence of catalyst dosage on the oxidative
coupling of 4-methylthiophenol was investigated. Cata-
lyst dosage was changed from 0 to 15 mg, with the
increase in catalyst dosage increasing the conversion
(Table 4). The reaction, however, did not proceed in
the absence of any catalyst. In fact, more amount of
catalyst could offer more reactive sites for the same
amount of substrate.
Next, selective aerobic oxidative coupling of various
thiols catalyzed by SBA-15@Glp–La was investigated
FIGURE 9 Effect of recycling of SBA-15@Glp–La on catalytic
oxidative coupling of mercaptosuccinic acid (labeled a, red line)
and benzo[d]oxazole-2-thiol (labeled b, green line)
FIGURE 11 Transmission electron microscopy images of
reused SBA-15@Glp–La
FIGURE 10 Scanning
electron microscopy images of
recovered SBA-15@Glp–La

12 of 14
MOLAEI AND GHADERMAZI
(Table 5). Thiophenols having electron-donating groups,
such as 4-methylthiophenol, showed oxidation at high
rates. The reaction of thiols with electron-withdrawing
groups showed oxidation at low rates. Many nucleophilic
compounds are more active to attack La(III) species. All
these reactions gave corresponding disulfides in excellent
yields under mild conditions.
small decrease of the yield was noted after seven runs.
The SEM images of the recovered SBA-15@Glp–La
(Figure 10) are identical to those of fresh SBA-
15@Glp–La, which indicated that the novel catalysts
have excellent mechanical property. The TEM image of
reused SBA-15@Glp–La (Figure 11) indicates that the
catalyst can be reused for seven runs without any sig-
nificant change in the mesoporosity.
3.8 | Recyclability of the catalyst
3.9 | Hot filtration study
To investigate the recyclability of the SBA-15@Glp–La
catalyst, aerobic oxidation of mercaptosuccinic acid
and benzo[d]oxazole-2-thiol to their corresponding dis-
ulfides was studied (Figure 9). The catalyst was iso-
lated by centrifugation after the reaction. The
recovered catalyst was then washed with acetone and
dried in an oven. For the SBA-15@Glp–La catalyst, a
A hot filtration test was performed with mercap-
tosuccinic acid as the model substrate under optimized
condition. In the half time of the reaction, only 55%
conversion was achieved. Then the aerobic oxidation
of benzo[d]oxazole-2-thiol was repeated under similar
reaction conditions and in half time of the reaction
TABLE 6 Comparison of SBA-15@Glp–La catalysts for the oxidative coupling of 4-methylthiophenol and thiophenol with some
recently reported catalysts
Temperature
(ꢀC)
Yield
(%)
Entry Substrate
Catalyst
Solvent
Time
30 min
9 min
90 min
20 hr
1
2
3
4
5
6
7
8
4-Methylthiophenol
K-OMS-2
Acetonitrile
Acetonitrile
EtOAc
100
r.t.a
r.t.
r.t.
70
100[2]
98[10]
97[44]
96[6]
<99[15]
83[4]
4-Methylthiophenol
4-Methylthiophenol
4-Methylthiophenol
4-Methylthiophenol
4-Methylthiophenol
4-Methylthiophenol
4-Methylthiophenol
Nickel nanoparticles
CoTSPc/SiO2
VOCl3
EtOAc
Cu/DH
Ethanol
2.5 hr
Mn–ZSM-5 (MZ-1RC)
Diaryl telluride
Ethanol
70
6 hr
15 min
1 hr
CH2Cl2
0
99[1]
100[5]
Cobalt–iron magnetic
Dimethylformamide
25
composites
9
4-Methylthiophenol
Manganese(III)
CH3OH
25
17 min
97[3]
Schiff-base complex
10
11
12
13
14
15
16
17
18
4-Methylthiophenol SBA-15@Glp–La
Ethanol
r.t.
100
r.t.
r.t.
r.t.
70
20 min
30 min
6 min
90 min
52 hr
92 (this work)
61[2]
Thiophenol
Thiophenol
Thiophenol
Thiophenol
Thiophenol
Thiophenol
Thiophenol
Thiophenol
K-OMS-2
Acetonitrile
Acetonitrile
EtOAc
Nickel nanoparticles
CoTSPc/SiO2
VOCl3
98[10]
98[44]
93[6]
<99[15]
84[4]
EtOAc
Cu/DH
Ethanol
4 hr
Mn–ZSM-5 (MZ-1RC)
Diaryl telluride
Ethanol
70
6 min
15 min
3 hr
CH2Cl2
r.t.
25
Quant[1]
100[5]
Cobalt–iron magnetic
Dimethylformamide
composites
19
Thiophenol
Manganese(III)
CH3OH
25
18 min
98[3]
Schiff-base complex
20
Thiophenol
SBA-15@Glp–La
Ethanol
r.t.
30 min
92 (this work)
Note: the entries of 10 and 20 were bold because these are our work compare with other works.
aRoom temperature.

SELECTIVE AEROBIC S-S COUPLING
13 of 14
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In summary, we present a very active and environmen-
tally benign process for the selective aerobic oxidative
coupling of thiols under mild reaction conditions. In the
presence of SBA-15@Glp–La as heterogeneous catalyst,
100% selectivity and complete conversion at room tem-
perature were achieved. The catalyst could be recycled
after the reaction without notable reduction in catalytic
performance. The non-caustic waste by-product and sim-
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process.
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ACKNOWLEDGEMENTS
We are grateful to Erfan Ghadermazi and the University
of Kurdistan for support of this work.
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ORCID
Somayeh Molaei https://orcid.org/0000-0001-6040-4830
Mohammad Ghadermazi https://orcid.org/0000-0001-
8631-6361
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How to cite this article: Molaei S,
Ghadermazi M. Highly ordered mesoporous
La(III)-substituted 5-oxopyrrolidine-2-carboxylic
acid (Glp) immobilized on SBA-15 as a very
efficient nanocatalyst for green aerobic oxidative
coupling of thiols to disulfides. Appl Organometal
Chem. 2019;e5328. https://doi.org/10.1002/
aoc.5328
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