Visible-light-driven synthesis of 2-substituted benzothiazoles using CdS nanosphere as heterogenous recyclable catalyst

Article abstract of DOI:10.1016/j.tetlet.2012.12.044

This Letter reports simple, green, and efficient synthesis of mesoporous CdS nanosphere (CdSNS) and its application as heterogeneous catalyst for the synthesis of 2-substituted benzothiazole. We report, for the first time, the synthesis of 2-substituted benzothiazoles from various aryl and alkyl aldehydes under visible light irradiation at room temperature. CdSNS catalyst generated in water demonstrates excellent catalytic activity for both the alkyl and aryl aldehydes, with good recyclability. The reaction yield is high for the electron-donating and electron withdrawing substituents as well as heterocyclic aldehydes with good turn over number (TON) and turnover frequency (TOF).

Full text of DOI:10.1016/j.tetlet.2012.12.044

Accepted Manuscript
Visible-light-driven synthesis of 2-substituted benzothiazoles using CdS nano‐
sphere as heterogenous recyclable catalyst
Sudipto Das, Suvendu Samanta, Swarup Kumar Maji, Partha Kumar Samanta,
Amit Kumar Dutta, Divesh N. Srivastava, Bibhutosh Adhikary, Papu Biswas
PII:
S0040-4039(12)02183-1
DOI:
http://dx.doi.org/10.1016/j.tetlet.2012.12.044
TETL 42289
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
25 September 2012
10 December 2012
12 December 2012
Please cite this article as: Das, S., Samanta, S., Maji, S.K., Samanta, P.K., Dutta, A.K., Srivastava, D.N., Adhikary,
B., Biswas, P., Visible-light-driven synthesis of 2-substituted benzothiazoles using CdS nanosphere as heterogenous
recyclable catalyst, Tetrahedron Letters (2012), doi: http://dx.doi.org/10.1016/j.tetlet.2012.12.044
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Visible-light-driven synthesis of 2-substituted benzothiazoles using
CdS nanosphere as heterogenous recyclable catalyst
Sudipto Das,a Suvendu Samanta,a Swarup Kumar Maji,a Partha Kumar Samanta,a Amit Kumar
Dutta,a Divesh N. Srivastava,b Bibhutosh Adhikary,a and Papu Biswas,*, a
a Department of Chemistry, Bengal Engineering and Science University, Shibpur, Howrah 711
103, West Bengal, India;
b
Department of Analytical Science, Central Salt & Marine Chemicals Research Institute,
Gijubhai, Badheka Marg, Bhavnagar 364002, Gujarat, India
*Corresponding Author. E-mail: papubiswas_besus@ yahoo.com. Tel.: +91-33-2668-4561. Fax:
+91-33-2668 7575.

ABSTRACT
This paper reports simple, green and efficient synthesis of mesoporous CdS nanosphere (CdSNS)
and its application as heterogeneous catalyst for synthesis of 2-substituted benzothiazole. We
report, for the first time, the synthesis of 2-substituted benzothiazoles from various aryl and alkyl
aldehydes under visible light irradiation at room temperature. CdSNS catalyst generated in water
demonstrates excellent catalytic activity for both the alkyl and aryl aldehyde, with good
recyclability. The reaction yield is high for the electron-donating and electron withdrawing
substituents as well as heterocyclic aldehydes with good turn over number (TON) and turnover
frequency (TOF).
Keywords: recyclable nanocatalysis, mesoporous CdS nanosphere, visible light irradiation, 2-
substituted benzothiazole

The visible light, as the driving force for chemical reactions has attracted much interest of
chemists.1,2 One of the major drawbacks of the classical photochemical reactions is the use of
high-energy UV radiation, which often induces the unselective excitation processes to give
unwanted by-products. The strategy to overcome this disadvantage is the use of photo-sensitizers
or semiconductors for selective activation of reactants. Photoactive semiconducting nanoparticles
have shown potential applications in energy and environmental remediation areas.3–6 But for
useful applications and industrial use, they must be highly porous photocatalysts in order to
provide a large active area and maximum light absorption.7,8 Cadmium sulfide (CdS) is one of
the most important and popular semiconductors, which has a large direct band gap of 2.4 eV at
room temperature and has attracted much attention because of its unique properties and potential
application in light emitting diodes, flat panel displays, solar cells, photocatalysis, and thin-film
transistors.9-11
On the other hand, benzothiazoles have been attracting increasing interest due to their
wide biological activities, such as β-amyloid, anti-parasitics, anti-tuberculosis, chemiluminescent
agents, and as photosensitizers.12-18 Especially, 2-aryl benzothiazoles are highly important in the
realm of organic and medicinal chemistry and have been attracting increasing attention due to
their diverse biological and pharmacological properties, including, antitumor, anti-consultant,
anti-viral, and anti-cancer.19-22 Owing to the wide range of pharmacological and biological
activities, the synthesis of 2-substituted benzothiazoles has become an important goal in recent
time. In the literature, various methods have been reported for the synthesis of 2-
arylbenzothiazoles involving the condensation of 2-aminothiophenols with substituted nitriles,
aldehydes, carboxylic acids, acyl chlorides, or esters.23 Recently, Liu et al. reported the
convenient and general synthesis of aryl-substituted benzothiazoles using aryl boronic acids
through direct arylation reactions catalyzed by a bimetallic system.24 Several catalysts
I2,25TMSCl,26 H2O,27 H2O2/Fe(NO3)3,28 Dowex 50W,29 ionic liquids30 under microwave
irradiation, silica gel,31 Sc(OTf)3,32 CAN,33 PEG 400,34
H2O2/CAN,35
NH4Cl,36
trichloroisocyanuric acid (TCCA)37 and electro-oxidative cyclization of the imines38 have been
exploited to carry out the synthesis of benzothiazoles in high yields from aldehydes.
However, many of these homogeneous catalytic processes suffered from a serious
limitation, namely, the separation and recovery of the catalyst. Therefore, the heterogeneous
alternatives are highly desirable and have already attracted much attention. Furthermore, the

exploitation of heterogeneous catalysts permits the easy separation and reuse of the catalysts.
This methodology constitutes a powerful tool in chemistry, allowing extremely complex
chemical transformations to take place in an one pot, cleaner, and more efficient process.
Recently, nanocatalysts have emerged as viable alternatives to conventional materials in various
fields of chemistry and attracted the interest of chemists. Nanoparticles are promising materials
for heterogeneous catalysts in a variety of organic transformations.
Here in, we report simple and efficient green synthesis of mesoporous CdS nanoshpere
(CdSNS) and demonstrate their potential heterogeneous catalytic activity for synthesis of 2-
substituted benzothiazoles from various alkyl and aryl aldehydes under visible light irradiation.
The reaction yield is high for the electron-donating and electron withdrawing substituents as well
as heterocyclic aldehydes.
Scheme 1
CdSNS, visible light
in methanol at r.t
H2N
HS
N
S
RCHO
+
R
CdSNS were obtained by refluxing the cadmium complex of pyridine-2-carboxamide and
thiourea in aqueous medium at pH 8.5 in presence of excess pyridine-2-carboxamide.39 The
product was separated from the reaction mixture by centrifugation, washed several times with
water and methanol. The XRD pattern of CdSNS (Fig. S1) is attributed to hexagonal CdS phase
(JCPDS card No. 41-1049). No other diffraction peaks were found in the diffraction pattern,
which indicates the purity of the product. Average crystal diameter for CdSNS was calculated
using the Debye-Scherrer equation and is found to be 8.8 nm. The surface morphology of the
catalyst was observed by scanning electron microscopy (SEM) and transmission electron
microscope (TEM). The low-magnification SEM image (Fig. S2) and TEM image (Fig. 1a) show
that CdS NS are composed of spherical or quasi-spherical nanoparticles with average diameter of
25 nm. The selected area diffraction (SAED) pattern (Fig. 1b) shows a set of concentric rings due
to the presence of small crystalline nanomaterials and the diffractions from (100), (110) and
(112) planes can be indexed to the hexagonal phase of CdS (JCPDS No. 41-1049). Fig. 1c is the
HRTEM image of CdS nanospheres, which displays clear image of lattice fringes of the prepared
nanocrystals, indicating the good crystalline nature of CdSNS. The interplanar spacing is about

0.204 nm corresponding to the (101) lattice plane of hexagonal CdS. In addition, the live Fast-
Fourier Transform (FFT) is also consistent with the assigned crystal planes of (101) (Fig. 1d).
Fig. S3 shows the N2 adsorption/desorption isotherm and the pore-size distribution (inset)
of CdS NS. The isotherm belongs to type IV with a hysteresis loop, demonstrating their
mesoporous characteristics. The BET (Brunauer–Emmett–Teller) surface area of the CdSNS was
16.7 m2 gm-1 and the average pore diameter according to the Bopp–Jancso–Heinzinger (BJH)
method of the sample was calculated and found to be 2.98 nm. The band structure of the
semiconductor NS was investigated by the UV-Vis absorption spectrum and shows the
absorption maxima at around 450 nm due to the first excitonic transition (Fig. S4). The band gap
energy (Eg) of 2.47 eV was calculated by the Tauc’s relation, which is blue shifted from the bulk
CdS (Eg = 2.41 eV).
(a)
(b)
(c)
0.204 nm
(d)
(101)
Fig. 1. (a) TEM (b) SAED pattern (c) HRTEM (d) Live FFT images of CdSNS.
It is worth mentioning that CdS, is often used as a photocatalyst in degradation of
halobenzene derivatives, organic dyes and toxic metal ions in aqueous solution, but its
application as a catalyst under visible-light irradiation for synthesis of 2-substituted
benzothiazoles from aldehyde and 2-aminothiophenol has not been reported previously. In a
typical general experiment, a mixture of 2-aminothiophenol (3 mmol) and an aromatic aldehyde

(3 mmol) in 20 ml methanol was irradiated under visible light in presence of 5 mg CdSNS for
30–60 mins.40 A Xenon lamp with a power of 300 W equipped with a cut-off filter (λ > 420 nm)
was used as a visible light source. The reaction was carried out in a 100 ml double walled quartz
beaker flask having water inlet and outlet to maintain the room temperature of the reaction
vessel. The effect of reaction time, solvent and amount of catalyst on the reaction was evaluated
thoroughly (Table 1) and benzaldehyde was chosen as a model substrate for this purpose. The
optimum reaction conditions are 30 mins and in presence of 5 mg catalyst in methanol. Further
prolonging the reaction time or increasing the amount of catalyst did not improve the yield of the
reaction. The solvent has a prominent influence on the yield (Table 1). The experimental results
show that methanol, chloroform and ethanol are good solvents with 96%, 90% and 60% yields
(Table 1, entries 5, 7 and 8), respectively. However, water, dioxane and tetrahydrofuran (THF)
are not suitable for the reaction.
Table 1
Catalytic performance of CdSNS under variuos reaction parametersa.
HS
O
S
CdSNS
+
Solvent, rt
H
N
H2N
visible light
Entry Solvent
Time
[min]
Amount of Yield [%] TONb
catalyst [mg]
1
2
3
4
5
6
7
8
Methanol
60
60
60
45
30
20
1
3
5
5
5
5
5
5
5
5
5
5
40
75
96
96
96
90
90
60
40
0
34.28
64.28
82.28
82.28
82.28
77.17
77.17
51.42
34.28
0
Methanol
Methanol
Methanol
Methanol
Methanol
Chloroform 30
Ethanol
DCM
30
30
30
30
30
9
10
11
12
Water
THF
Dioxane
0
0
0
0
aReaction Condition: benzaldehyde (3 mmol), 2-aminothiophenol
b
(3 mmol). The moles of 2-substitutedbenzothiazole formed per
mol catalyst.

In order to get an insight into the effect of starting materials on the yield 2-substituted
benzothiazole, various aldehydes were used as the starting materials and the results are listed in
Table 2. Most of the aldehydes gave excellent yields over 90%. The highest yield > 98% was
obtained in the case of salicyldehyde as a starting material (entry 2), while the relatively lower
yield of 50% was obtained in the case of anthracene-9-carbaldehyde (entry 14). The reaction was
also investigated for both the electron-donating or electron-withdrawing substituents in the
aromatic ring. The experimental results show that reaction yield is excellent (> 90%) for both the
electron-donating and electron withdrawing substituents. The heterocyclic aldehydes such as 2-
pyridine-, 2-thiophene-carboxaldehydes, furfural and 3H-imidazole-4-carbaldehyde (entries 10–
13) also furnish the corresponding benzothiazoles without any difficulty. The catalytic TONs and
1
TOFs obtained in the synthesis of different benzothiazoles were found to be moderate. H and
13C NMR spectra of all compounds are given in Supplementary Data.
Another interesting aspect of our synthesis is the selective formation of mono- or di-
benzothiazole in case of terephthalic aldehyde. The 4- benzothiazole-yl-benzaldehyde (entry 15)
is selectively formed when reaction was carried out in methanol medium irrespective of ratio of
aldehyde and 2-amino thiophenol. On the other hand, when the reaction was carried out in
chloroform medium, exclusively phenyl-1, 4-dibenzothiazole (entry 16)41 was formed. Scheme 2
shows the formation mono- or di-benzothiazole.
We have also investigated the catalytic activity of bulk CdS, common cadmium salt such
as CdCl2 and Cd(OAc)2 to compare (Table 3) using benzaldehyde as substrate. As expected, bulk
CdS shows low catalytic activity (Table 3, entry 1). On the other hand, CdCl2 and Cd(OAc)2
show no catalytic activity at all for this reaction (Table 3, entries 2, 3). To investigate the role of
visible light, same reaction was also carried out in the absence of visible light. CdSNS shows no
catalytic activity (Table 3, entry 5), which clearly demonstrates the role of visible light in this
reaction. A control experiment showed that no reaction took place without CdSNS (Table 3,
entry 9).

Table 2
Synthesis of 2-substituted benzothiazole with CdSNSa, b

Entry
1
Aldehyde
Product
Time [min] Yield [%] TONb TOFc [h-1]
S
30
96
82.28
164.57
CHO
N
OH
S
OH
2
3
4
20
98
84
252.25
CHO
N
MeO
MeO
OH
S
MeO
OH
25
25
96
95
82.28
81.42
197.47
CHO
N
S
MeO
HO
195.408
CHO
CHO
CHO
HO
N
S
5
6
30
30
92
90
78.85
77.14
157.7
Cl
F
Cl
N
S
154.28
F
N
S
7
8
20
20
95
95
81.42
81.42
244.285
244.285
O2N
CHO
CHO
O2N
N
S
Me2N
Me2N
N
OH
CHO
OH
9
30
95
81.42
162.84
S
N
Br
Br
N
N
S
10
11
12
13
30
45
40
90
92
95
95
60
78.85
81.42
81.42
51.42
157.71
108.56
122.13
34.28
CHO
CHO
CHO
CHO
N
S
S
N
S
S
O
N
O
S
N
N
N
N
N
H
H
CHO
14
90
70
60
40
S
N

S
N
15
16d
17
20
30
30
95
96
92
81.42
82.28
78.85
244.26
164.56
157.7
OHC
OHC
CHO
CHO
CHO
OHC
N
S
N
S
S
Me
HO
Me
N
HO
OH
CHO
OH
18
20
95
81.42
244.285
S
N
S
N
19
20
60
60
80
84
68.57
72.00
68.57
72.00
H-CHO
H
S
Me-CHO
Me
N
aReaction Condition: aldehyde (3 mmol), 2-aminothiophenol (3 mmol), 5 mg CdSNS, methanol
b
c
20–30 ml. The moles of 2-substitutedbenzothiazole formed per mol catalyst. Rate of the
d
formation of 2-substituted benzothiazoles per mol catalyst per unit time. Solvent: chloroform, 2-
aminothiophenol (6 mmol).
Recent studies show that molecular species leached from the nanoparticles can be
responsible for the catalytic activity of nanoparticles.42-44 In order to study this possibility, a
filtration test was done. The above reaction using benzaldehyde as substrate was stopped after 15
minutes at a conversion of 60%, the nanoparticles were removed by centrifugation. Then, the
corresponding filtrate was placed under visible light. The reaction does not proceed further after
the filtration of the CdSNS from the reaction vessel, indicating that the CdSNS and no leached
metal, if any, were responsible for the catalytic activity.

Scheme 2
Selective synthesis of 4-benzothiazole-yl-benzaldehyde and phenyl-1, 4-dibenzothiazole
OHC
CHO
Methanol,CdSNS,
visible light
2-aminothiophenol
Chloroform,CdSNS,
visible light
2-aminothiophenol
N
S
N
S
S
CHO
N
Table 3
Synthesis of 2-Substitutedbenzothiazole with Variuos Catalystsa, b
HS
O
S
Catalyst
+
Solvent, rt
H
N
H2N
entry catalystc
yield [%]
BET surface area TONd
[m2 gm-1]
1
2
3
4
5
6
7
8
9
bulk CdSe
CdCl2
Cd(OAc)2
CdSNSe
CdSNSf
10
0
0
96
0
85
0
3.0
8.57
e
e
16.7
16.7
13.8
13.8
82.28
0
72.85
recycled CdSNSe,g
recycled CdSNSf,g
without any catalyste
without any catalystf
0
0
aReaction Condition: benzaldehyde (3 mmol), 2-aminothiophenol (3
b
c
mmol), methanol (20 ml). Reaction Time: 30 minutes. Amount of
catalyst for entry 1–9: 5 mg. dThe moles of 2-substitutedbenzothiazole
e
formed per mol catalyst. Reaction in presence of visible light.
fReaction in absense of visible light. Yield for fourth cycle in
g
methanol.

A significant industrial viability of heterogeneous catalysis is in the ability to easily
remove the catalyst from the reaction mixture and reuse it for subsequent reactions until the
catalyst is sufficiently deactivated. The recyclability of the CdSNS nanocatalyst was examined
using the reaction of benzaldehyde with 2-aminothiophenol at room temperature under visible
light irradiation and the reaction was completed after 30 minutes. After each run, catalyst was
separated by simple centrifugation followed by washing with methanol and chloroform to
remove the remaining organic compounds and reused in subsequent four runs of 30 minutes for
the same reaction (Table 3, entry 6). The experimental results demonstrate that the performance
of CdSNS shows some minor degradation after four times reuse, such as the yield of 2-
substitutedbenzothiazole and specific surface area of CdSNS which decreases to 85% and 13.8
m2 gm-1 (Fig. S5), respectively. To understand the deactivation mechanism of the CdSNS
catalyst, low magnification SEM image of catalyst was obtained after the 4th run of catalyst as
shown in Fig. S6. It is clear that the CdSNS catalyst shows significant agglomeration after the 4th
run. This is consistent with lower specific surface area (13.8 m2 gm-1) and average pore diameter
(2.31 nm). This result indicates that the mechanism of deactivation is likely to involve the
formation of agglomerated CdSNS which leads to the decrease of the surface area.
To obtain more insight into the reaction process, we move toward the mechanism of the
CdSNS catalysed synthesis of 2-substitutedbenzothiazole. Primarily, we investigated whether the
imine intermediate is formed prior to formation of benzothiazole. For that we have carried out
the reaction with preformed imine compound under same condition and found that the efficiency
of the catalyst remains the same. It can also be seen that for those aldehydes which formed imine
readily, reaction time is low and yield is relatively much higher (Table 2). On the other hand,
aldehydes which do not form imine easily, ie. 1H-pyrazole-4-carbaldehyde, anthracene-9-
carbaldehyde, formaldehyde and acetaldehyde (Table 2, entries 13, 14, 19 and 20), reaction time
is relatively longer and yield is moderately poor. Now, visible light can excite electrons (e−) from
the valence band of the CdSNS, leaving behind a hole (h+) in the conduction band. The active
radical species R1, which was formed by the photogenerated electron-induced reduction of imine
intermediate during light irradiation. This radical species R1, instantaneously converted to
radical species R2. Finally, radical-radical recombination takes place followed by oxidation in
presence of air producing the final product. To prove the formation radicals, this reaction was

also followed in the presence of a radical scavenger, TEMPO (TEMPO = 2,2,6,6-
tetramethylpiperidinoxyl). Addition of TEMPO to the reaction mixture, did not yield any 2-
substituted benzothiazole. Scheme 3 illustrates a plausible reaction pathway for this reaction.
Scheme 3
A plausible reaction mechanism for the catalytic cycle of the CdSNS during synthesis of 2-
substituted benzothiazole
R
N
NH2
SH
O
H
H
R
SH
CB
VB
R
H
N
C
-
e
Visible
Light
N
S
R
C
SH
CdSNS
R1
h+
R
H
H
N
air
N
C
R
C
e-
SH
H+
+
H
S
H
R
H
R
N
C
N
C
H
S
S
R2
In conclusion, a simple and effective method for the synthesis of 2-substituted
benzothiazoles from aldehyde and 2-aminothiophenol has been developed using mesoporous
CdS nanosphere as a catalyst under visible light irradiation. The heterogeneous catalyst CdSNS
with high surface area and fine mesoporous structure shows excellent catalytic performance for
various aryl and alkyl aldehydes and also is easy to separate from the reaction mixture to be
reused, has been reported first time. The most significant advantage of this method is to use
visible light as energy source. The CdSNS catalyst is a good candidate to substitute metal salts or
other heterogeneous catalysts and has potential value for industrial applications. Furthermore, the

strategy of using semiconductor nanoparticles that absorb visible light can be expanded to the
utilization of solar energy in various organic reactions.
Acknowledgements
S.D. and S.S. are indebted to CSIR, India for their JRF [08/003(0072)/2010-EMR-I] and
[08/003(0083)/2011-EMR-1], respectively. P.B. acknowledges DST-India for the Fast Track
Project (No.SR/FT/CS-022/2009). The authors also acknowledge the facility developed in the
Department of Chemistry, BESUS through MHRD, India and UGC-SAP
Supplementary data
Supplementary data associated (synthetic details, materials characterization, Fig. S1-S6, 1H, and
13NMR spectra of 2-substituted benzothiazoles) with this article can be found, in the online
version.
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39. Preparation of CdS nanosphere (CdSNS): Complex [CdL2(H2O)2]Cl2 (10 mmol, 3.91 g) was
dissolved in 50 ml water. Then 1.52 g (20 mmol) thiourea solution in 20 ml water was added
dropwise by stirring and pH of the solution was adjusted to 8.5 by slow addition of dilute
ammonium solution. Another 1.22 g (10 mmol) ligand pyridine 2-carboximidine was added to
this resulting solution. Solution was then refluxed for 4 h. A yellow precipitation of CdS
nanosphere was obtained. It was separated from the reaction mixture by centrifugation and
washed with methanol and water for several times. The product was then dried in a vacuum oven
at 110 °C for 2 h and kept for further characterization.
40. Catalytic procedure: In the experimental procedure for catalytic reaction, a mixture of
aldehyde (3 mmol), 2-amino thiophenol (3 mmol) and CdS nanosphere (5 mg) was taken in a
100 ml double walled quartz beaker flask having water inlet and outlet to maintain the
temperature of the reaction vessel at room temperature in methanol (20 ml). The beaker was
exposed to visible light under stirring condition for the required time period (Table 3). After
completion of the reaction (monitored by TLC and GC), methanol was evaporated by rotary and
the product was dissolved in dichloromethane. The catalyst was separated from the reaction
mixture by centrifugation. Dichloromethane was then evaporated to dryness and the product was
purified by column chromatography using silica gel G60.
41. Synthesis of phenyl-1, 4-dibenzothiazole (entry 16): In the experimental procedure for
catalytic reaction, a mixture of aldehyde (3 mmol), 2-amino thiophenol (6 mmol) and CdS
nanoshere (5 mg) was taken in a 100 ml beaker in chloroform (20 ml). The insoluble product was
collected through filtration and washed thoroughly with methanol and chloroform. The solubility
of the isolated 1, 4-dibenzothiazole is poor in almost all common solvents, so it was
characterized by its C, H, N and S analysis, IR spectrum and melting point. Off white solid. FT-
IR (KBr, ν/cm-1) 1482 w, 1432 w, 1387 s, 1310w, 1230 w, 970 m, 842 w, 762 m, 724 w, 686 w,

624 w. Found: C, 69.80; H, 3.48; N, 8.15; S, 18.60. C20H12N2S2 requires: C, 69.74; H, 3.51; N,
8.13; S, 18.62. LC-MS (ESI+): m/z = 345.50, [100%, MH+]. Calcd. for C20H12N2S2: 345.47. mp
(ºC): 265.
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Graphical Abstract
Visible-light-driven synthesis of 2-substituted benzothiazoles using
CdS nanosphere as heterogenous recyclable catalyst
Sudipto Das, Suvendu Samanta, Swarup Kumar Maji, Partha Kumar Samanta, Amit Kumar Dutta, Divesh
N. Srivastava, Bibhutosh Adhikary, and Papu Biswas
Visible light
H2N
CdSNS
N
RCHO
+
R
Methanol, room temperature
S
HS
R = alkyl or aryl
Recyclable mesoporous CdS nanospheres is a novel heterogeneous catalyst for synthesis of 2-
sustitutedbenzothiazole from various aryl and alkyl aldehyde under visible light irradiation with excellent
catalytic performance