Nanoporous Cu doped ZnS nanoparticles an efficient photo catalyst for the chemoselective synthesis of 2-substituted azoles via C-N arylation/ CSp3– H oxidation/ cyclization/dehydration sequence in visible light

Article abstract of DOI:10.1016/j.jphotochem.2019.112242

ZnS and Cu:ZnS nanoparticles were prepared by aqueous chemical method and characterized by several analytical tools. Nanoparticles have an average size of about ～ 18 nm and possess highly open mesopores, moderate surface area, and uniform morphology. UV–vis spectra designate that doping of Cu shifted the optical response of the ZnS nanoparticles in to a visible region. These Cu:ZnS nanoparticles were employed as a photocatalyst for chemoselective synthesis of 2-substituted azoles by the reaction of benzyl bromides and 1,2-Diaminobenzene or 2-Mercaptoaniline in visible light. Analogous experiments confirmed that the reaction were proceeds through one pot C–N arylation/ CSp₃– H oxidation/ cyclization/dehydration sequence. The enhanced catalytic activity by doping could be attributed to the presence of trapping level generated by copper doping which augments the relaxation time of electron and holes so that they are easily available for the reaction. The method was also applicable for the synthesis of quinazolin-4(3H)-ones.

Full text of DOI:10.1016/j.jphotochem.2019.112242

Journal Pre-proof
Nanoporous Cu doped ZnS nanoparticles an efficient photo catalyst for
the chemoselective synthesis of 2-substituted azoles via C-N arylation/
CSp3– H oxidation/ cyclization/dehydration sequence in visible light
Anshu Dandia, Sarika Bansal, Ruchi Sharma, Dinesh Kumar
Mahawar, Kuldeep S. Rathore, Mohan Lal Meena, Vijay Parewa
PII:
S1010-6030(19)30900-1
DOI:
https://doi.org/10.1016/j.jphotochem.2019.112242
JPC 112242
Reference:
To appear in:
Journal of Photochemistry & Photobiology, A: Chemistry
Received Date:
Revised Date:
Accepted Date:
1 June 2019
6 November 2019
14 November 2019
Please cite this article as: Dandia A, Bansal S, Sharma R, Kumar Mahawar D, Rathore KS,
Lal Meena M, Parewa V, Nanoporous Cu doped ZnS nanoparticles an efficient photo catalyst
for the chemoselective synthesis of 2-substituted azoles via C-N arylation/ CSp3– H oxidation/
cyclization/dehydration sequence in visible light, Journal of Photochemistry and amp;
Photobiology, A: Chemistry (2019), doi: https://doi.org/10.1016/j.jphotochem.2019.112242
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1
Nanoporous Cu doped ZnS nanoparticles an efficient photo catalyst for the
chemoselective synthesis of 2-substituted azoles via C-N arylation/ CSp3– H
oxidation/ cyclization/dehydration sequence in visible light.
Anshu Dandia,*a Sarika Bansal,a Ruchi Sharma,a Dinesh Kumar Mahawar,a Kuldeep S. Rathore,b Mohan Lal Meena,a,c
Vijay Parewa,*a
aCentre of Advanced Studies, Department of Chemistry,University of Rajasthan, Jaipur, India
bDepartment of Physics, Arya College of Engineering and IT, Jaipur, India.
cDepartment of Chemical Engineering, National Taiwan University, Taipei, Taiwan , ROC
E-maila: dranshudandia@yahoo.co.in
E-maila: parewavijay.parewa@gmail.com
E-mailb: kuldeep_ssr@yahoo.com
Graphical abstract
C u d o p ed Z n S
e -
C B
R 1
N H 2
N
B r
+
h +
Z H
Z
V B
Z = N H , S
Z = N H , S
O n e p o t
R 1
-C -N a ry la tio n
-C S p 3 - H o x id a tio n
-C yc liza tio n
-D e h y d ra tio n
M ild re a ctio n co n d itio n s
V isib le lig h t
C h e m o se lec tive syn th e sis
V isib le lig h t in d u ce d n a n o p h o to ca ta ly sis
Highlights
 Nanoporous Cu doped ZnS nanoparticles as a photo catalyst.
 Visible light driven synthesis.

2
 One pot C-N arylation/ CSp3– H oxidation/ cyclization/dehydration.
 Chemoselective synthesis of 2-substituted azoles.
 Synthesis of medicinally important quinazolin-4(3H)-ones.
Abstract:
ZnS and Cu:ZnS nanoparticles were prepared by aqueous chemical method and characterized by
several analytical tools. Nanoparticles have an average size of about ~ 18 nm and possess highly
open mesopores, moderate surface area, and uniform morphology. UV–vis spectra designate that
doping of Cu shifted the optical response of the ZnS nanoparticles in to a visible region. These
Cu:ZnS nanoparticles were employed as a photocatalyst for chemoselective synthesis of 2-
substituted azoles by the reaction of benzyl bromides and 1,2-Diaminobenzene or 2-
Mercaptoaniline in visible light. Analogous experiments confirmed that the reaction were
proceeds through one pot C-N arylation/ CSp3– H oxidation/ cyclization/dehydration sequence.
The enhanced catalytic activity by doping could be attributed to the presence of trapping level
generated by copper doping which augments the relaxation time of electron and holes so that
they are easily available for the reaction. The method was also applicable for the synthesis of
quinazolin-4(3H)-ones.
Keywords: Nanophotocatalyst, Visible light, CSp3– H oxidation, 2-substituted azoles
1. Introduction
Visible light [1] as an energy source is illustrated by the impressive accelerations produced in
many reactions as a consequence of the photo induced electron-transfer [2] (PET), which cannot
be imitate by conventional routes. In this regards, visible light induced photocatalysis in organic

3
transformations is very gorgeous tool, due to the intrinsic green nature of light, high reactivity,
and good functional group tolerance [3-4]. Numerous visible-light photoredox catalysts i.e.
ruthenium or iridium complexes have been used to resolve the problem of visible light
absorption efficiency [5].
Futhermore, because of the sustainable nature, nanomaterials, would be an appropriate
alternative to these conventional photocatalysts [6]. Nanophotocatalyst have unique optical and
electronic properties and showed intense impact in several areas for example dissociation of
volatile organic pollutants, dyes degradation, water splitting, inactivation of cancer cells and in
organic synthesis [7]. Stability under reaction conditions, tunable band gap, proficient absorption
of visible light, strong adsorption capacity, generation of distinct reactive sites, large surface
area, reusability, non toxicity, and non-hygroscopic properties make nanomaterials much
favoured photocatalysts.
Zinc sulfide (ZnS) at nanoscale, has attracted particular attention to the superior properties such
as high photocatalytic activity in UV light, excellent stability & physical properties, low cost,
semiconductor and chemical inertness [8]. Due to its effective, electrical and optical properties,
ZnS has been widely employed in many fields including light-emitting diodes [9] (LEDs),
sensors [10], photovoltaic cells [11] and photoelectrolysis [12] as well as antibacterial [13],
photochemical water purification [14], and self-cleaning applications [15]. ZnS is only
photocatalytic active to the UV light (λ < 340 nm) [16]. To achieve a better catalytic action in
visible light (λ≥420 nm), the synthesis, structural characterization and the use of ZnS based
nanomaterials as a photocatalysts are also matter of attention.

4
2-substituted azoles are the integral part of the compounds which possess significant biological
activity. 2-substituted benzimidazoles are found to be a potent cannabinoid CB1 receptor [17],
selective COX-2 inhibitors [18], neuropeptide Y5 antagonists [19], cytotoxic agents [20] and
inotropic agents [21]. Furthermore, 2-substituted benzothiazoles also be used as inhibitor for
cancer cell lines [22]. Some other pharmacophores possessing the benzothiazole as the core unit
include the antibacterial compound [23], PPAR agonist [24], H3-receptor ligand [25], and
nicotinic-acetylcholine- receptor ligand [26].
H
O
N
H3C
COCH3
CH3
H
N
S
Cl
COCH3
H
N
N
NH
H3COC
N
S
COOH
N
O
ANTIMICROBIAL
Albendazole
ANTIFLAMMATORY
Benoxaprofen analog
ANTIULCER
Omeprazole
CH3
N
F
F
O
COOH
F
S
Cl
N
NH
F3CO
S
N
O
F
NH2
N
Riluzole
Cl
HO
O
IDD552
(anticonvulsant)
ANTITUMOR
Bendamustine
(oxidoreductase activity)
Fig. 1. Medicinally imperative 2-substituted azoles.
Due to their numerous applications, considerable efforts have been made in the development of
efficient strategies for the construction of 2-substituted benzimidazole and benzothiazole
derivatives using activated acyl components or coupling reagents (Scheme 1a) [27-28]. These
reported procedures involve a two-step process that contains the oxidative cyclo-
dehydrogenation of iminium intermediate (Schiff bases), which requires elevated temperatures or
microwave irradiation with strong acidic conditions [27]. Various oxidative and catalytic
reagents [28] such as (NH4)H2PW12O40, bismuth chloride, solid acid scolecite, Ionic liquids,

5
HBF4-SiO2, MoO3/CeO2-ZrO2, Sc(OTf)3, TCCA, ionic liquid, molecular iodine, acetic acid and
silica sulfuric acid etc have been employed.
Reported work
O
R2
NH2
N
Non reusable catalyst
Oxidants, ligands, base
Conventional energy sources
X
R1
R1
(a)
+
ZH
Z
R2
Z= NH, S
Z= NH, S
Our work
R2
NH2
Cu doped ZnS
Visible light
N
Z
Br
R1
R1
+
(b)
ZH
Z= NH, S
Z= NH, S
R2
Scheme 1: Strategies toward the synthesis of 2-substituted azoles.
In spite of the undeniable advances, the reported procedures still endured some downsides in
terms of toxicity, handling, and operational simplicity. Moreover, some of the catalysts are
costly, toxic, and air susceptible. Another alternative is ionic liquid, but these require tedious
preparation and environmental safety is still arguable [29].
Thus, in continuation of our work [30], herein we illustrate the synthesis, characterization and
visible light driven photocatalytic application of nanoporous ZnS and Cu:ZnS nanoparticles for
chemoselective synthesis of 2-substituted azoles through the reaction of benzyl bromides and
1,2-Diaminobenzene or 2-Mercaptoaniline via one pot C-N arylation/ CSp3– H oxidation /
cyclization/dehydration sequence respectively (Scheme 1b).
To the best of our knowledge, there are scanty reports available for the synthesis of 2-substituted
azoles with heterogeneous photocatalysts [31]. In all cases reactions were proceeding through the
iminium intermediate by direct oxidative coupling of 1,2-Diaminobenzene or 2-Mercaptoaniline
and aldehydes. However, in our case we identify that the reaction were accomplished by amide
intermediate via one pot C-N arylation/ CSp3– H oxidation / cyclization/dehydration sequence.

6
This protocol was further expressed for the synthesis of pharmaceutically significant [32]
quinazolin-4(3H)-ones.
2. Results and discussion
These nanoparticles were synthesized by aqueous chemical route [30a] and characterized
through UV-Vis, TEM, SEM, XRD, EDAX, XPS and BET anylysis. In XRD patterns (Fig. 2),
peaks at 2θ values of about 26.55, 44.03 and 52.08 concur to the (111), (220) and (311) planes of
cubic phase of ZnS. No deviation in the XRD profile of ZnS was observed by the introduction of
Cu in the ZnS matrix as no additional peaks of the copper and its associated phase were found.
Due to the replacement of Cu+2 into the Zn+2 sites as the radius of these ions are analogous a
small shift was observed at lower angle. This refined data has further been used to determine the
average crystallite size of these nanoparticles using Debye Scherrer formula [33]. The average
crystallite size of ZnS and ZnS:Cu nanoparticles ~ 8nm and~ 9nm respectively.
Fig.2: XRD patterns of bare ZnS and Cu:ZnS samples
Images obtained by TEM established the spherical nature of particles in 15-20 nm range in size
(Fig. 3a). Fig. 3b shows the typical SEM images of ZnS and ZnS :Cu nanoparticles. It is apparent
that nanoparticles look like agglomerated spherical clusters.

7
Fig.3: (a) TEM images (b) SEM images of ZnS and 4% Cu:ZnS.
The high purity of ZnS NPs (1:1 molar ratio) was established by EDAX analyses (Fig.4a)
Besides this, the EDAX of 4% Cu-doped ZnS nanoparticles illustrated the successful doping of
copper in ZnS NPs matrix (Fig.4b). Additionally, ICP-AES and EDAX analyses showed the
element compositions of all samples were approximately parallel to theoretical values (See ESI:
Table S1, Fig S2).

8
Fig.4: EDX spectrum of (a) ZnS and (b) 4% Cu: ZnS.
UV-Visible study of bare ZnS and Cu:ZnS (0−6%) were demonstrated in Fig.5a. A minor red
shift is noticed with Cu doping. The calculated band gap using Tauc’s relation [34] of bare ZnS
diminishing from 3.03 to 2.86 eV by rising the amount of copper from 0 to 6% (Fig. 5b), which
showed that Cu: ZnS can be employ as a visible light induced catalyst.

9
Fig.5 : (a) UV−Vis absorption spectra and (b) band gap value of ZnS and Cu:ZnS.
As compared to the XPS spectra of bare ZnS (Fig. 6), a peak of Cu was observed in XPS spectra
of Cu: ZnS. However in both the XPS spectra, peak of Zn and S can also be observed. The peaks
of Zn2p3/2 and Zn2p1/2 was recognized at 1022.1 eV and 1045.1 eV. Peak position at 162.5 eV
and 160.9 eV were assigned for S2p3/2 and S2p1/2. Furthermore, for the dopant copper, the
binding energies at 932.4 eV and 952.5 eV with spin orbit separation 20.1 eV were allocated for
Cu2p3/2 and Cu2p1/2. Peaks of zinc and copper in XPS spectra confirmed their Zn+2 and Cu+2
oxidation state [35]. Furthermore, due to the presence of dopant and interaction between ZnS
slight shift of binding energies of Zn and S towards the higher side was observed.

10
Fig.6 : (a) Survey spectrum of bare ZnS and 4% Cu:ZnS and (b) Zn (2p) (c) S(2p) (d) Cu(2p)
XPS spectra of ZnS and 4% Cu:ZnS
The peaks at 1120 and 672 cm−1 in FT-IR spectrum could be assigned for bare ZnS (Fig. 7). In
FT-IR spectrum of Cu:ZnS, the peaks are nearly comparable as compared to ZnS additionally
two new peaks at 1130 and 997 cm−1 was observed because of the distinction in vibrational mode
of Zn and Cu ions [36]. Due to the water absorption on the surface of nanoparticles a wide band
at 3000−3600 cm−1 (OH stretching frequency) was observed. Additionally the band around 1548
and 1432 cm−1 was owing to the asymmetric and symmetric stretching of C=O (occurrence of
environmental CO2 on the face of the nanoparticles) [37]. The peak at 1626-1652 cm-1 is
attributed due to the H-O-H bending vibration of H2O [38]. Sulphur-oxygen interactions and
some microstructure formation bands of ZnS Nps also present in this area [39].

11
Fig. 7 : FT-IR spectra of ZnS and 4% Cu:ZnS
The specific surface area was inferred by standard multipoint Brunaur-Emmett-Teller (BET)
method [40]. The sample followed a typical type IV isotherm and accounts for the relatively
ordered mesopores material. The pore size distribution (PSD) and pore volume of the sample
were evaluated by Barrett-Joyner-Halenda (BJH) method using the desorption branch [41] and
shown in fig. 8, which suggests that ZnS and Cu doped ZnS nanoparticles fall in the meso range
(2-50nm) throughout the sample with average pore diameter of 5.62 and 5.12 nm respectively.
Obtained total pore volume of ZnS and Cu doped ZnS for pores smaller than 20.16 nm
(diameter) at P/Po = 0.89687 was measured 0.1024, 0.1011 cc/g respectively. The surface area of
the ZnS and Cu doped ZnS catalyst was found to be 82.30 and 78.88 m2/g correspondingly. The
addition of Cu2+ ion in the catalyst slightly decreased the average pore size, total pore volume,
specific surface area. However, almost similar pore size distribution curve was obtained for ZnS
and Cu doped ZnS due to the nearly equal ionic radii of Cu2+ (0.073 nm) and Zn2+ (0.074 nm).

12
[42] The detailed studies showed that the ordered mesoporous arrangement are produced by the
self-assembly of zinc-blende ZnS nanoparticales. [43]
0.008
ZnS
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0.0070
Cu-ZnS
0.006
0.005
0.004
0.003
0.002
0.001
0.000
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18
Dp (nm)
Fig. 8: Pore size distribution of ZnS and 4% Cu-doped ZnS
The photocatalytic performance of ZnS and Cu:ZnS NPs were tested for selective synthesis of
benzimidazoles under visible light (table 1). At first, for optimization of the reaction conditions,
the reaction of 4-chloro benzyl bromide (1 mmol) with 1-2-Diaminobenzene (1 mmol) in
CH3CN as a solvent in the presence of a catalytic amount of ZnS nanoparticles under visible
light was studied. The reaction did not proceed under these circumstances and starting materials
remained intact. Due its large band gap (3.03ev) ZnS nanoparticles was non responsive to the
visible light. However the corresponding product 3a was observed in 34% yield with excellent
selectivity using 2% Cu:ZnS NPs as a photocatalyst. It is revealed from table-1 that when we
increase the amount of copper in ZnS matrix consequent enhancement in the photocatalytic
activity was observed.

13
Table 1. Screening of the reaction conditions a
S.
No.
Catalyst
Solvent Time Yield
(%)b
TOF c
1.
2.
3.
4.
5.
6.
7.
8.
-
CH3CN 4 h
CH3CN 4 h
CH3CN 2 h
CH3CN 1 h
CH3CN 2 h
CH3CN 1 h
CH3CN 1 h
-
n.c.
n.c.
ZnS NPs ((10 mol %)
-
2% ZnS:Cu NPs (10 mol %)
4% ZnS:Cu NPs (10 mol %)
4% ZnS:Cu NPs (5 mol %)
4% ZnS:Cu NPs (20 mol %)
6% ZnS:Cu NPs (10 mol %)
4% ZnS:Cu NPs (10 mol %)d, f CH3CN 1 h
4% ZnS:Cu NPs (10 mol %)e, f CH3CN 1 h
34
84
43
84
73
-
81.3
401.9
217.2
178.7
349.3
n.c.
9.
-
n.c.
10.
4% ZnS:Cu NPs (10 mol %)
4% ZnS:Cu NPs (10 mol %)
H2O
1 h
29
138.7
11.
12.
13.
14.
15.
16.
MeOH 1 h
DMSO 1 h
41
44
196.2
210.5
177.0
n.c.
4% ZnS:Cu NPs (10 mol %)
4% ZnS :Cu NPs (10 mol %)
4% ZnS:Cu NPs (10 mol %)
4% ZnS:Cu NPs (10 mol %)
CuO NPs (10 mol %) f
THF
1 h
37
DCM 1 h
CHCl3 1 h
CH3CN 4 h
Trace
Trace
-
n.c.
n.c.
[a] Reactions were performed with 4-chloro benzyl bromide (1 mmol) and 1,2-Diaminobenzene (1 mmol) in various solvent under visible light.
[b] Isolated yield. [c] TOF (number of moles of product produced per mole of catalyst used per min.) [d] Under dark. [e] under nitrogen
atmosphere. [f]In all these cases only intermediate 3a' was formed.
The excellent result of the reaction was observed using 4% Cu :ZnS NPs (10 mol%) with high
turnover frequency (TOF). This outcome is in accordance with our functioning assumption that
doping of Cu+2 ions into ZnS matrix shifts its absorption band into visible area.
Fig. S3 (See ESI) has showed the fluorescence spectra of ZnS and 4% Cu doped ZnS samples.
For ZnS a band at 427nm has been found due to the recombination between the sulfur-vacancy-
related donorand the valence band [44]. The doping of Cu in to the ZnS matrix particular shifted

14
the emission maximum toward longer wavelengths (474nm), and also increases emission
intensity. That was observed due to the the recombination between the shallow donor level
(sulfur vacancy) and the acceptor t2 level of Cu2+ [44c,45]. Doping of copper in ZnS lattice alter
forbidden band and create a new energy level or trapping pool for excited electrons among the
valence and conduction band of ZnS and make the photocatalysts respond to visible region as
shown in Fig. 9.The study established the formation of the medium band (formed from Cu
dopant) between conduction band and Valance band of the ZnS matrix effectively decreasing
electron-hole recombination rate via trapping electrons or holes, which endorsed the charge
separation vital for the photocatalytic reaction [46].
Fig. 9: Band gap diagram of (a) ZnS (b) and 4% Cu-doped ZnS
However, further increasing in the dopant concentration, decrease the photo catalytic activity of
the catalyst. It is probably due to the charge carrier transportation and deviation from the phase
structure and redox potential on excess doping [47]. The reaction was also examined in different
solvents with all the other parameters kept constant. CH3CN were found to be most suitable
solvent for above transformation due to its high dielectric constant [48]. The model reaction was
also performed under nitrogen atmosphere and the reaction proceeded rather tediously and only
intermediate 3a' was formed. However, the best result was found in the presence of ambient

15
oxygen (air) in terms of TOF, yield and reaction time. These results demonstrate that as an
economical concern, air would constitute more sustainable green oxidant and the oxygen
molecules in air were further activated by photocatalyst as absence of photo catalyst no desired
product was formed. In the absence of visible light, only N-arylated intermediate 3a' was formed
as a main product. Analogous result was found when the reaction was tried with CuO Nps.
To find out the accurate mechanism of this photo catalytic transformation some control
experiments were carried out. We isolate the N-aryleted product in the control optimize
condition, which ruled out the formation of acyl surrogate (benzyl alcohol, benzaldehyde, and
benzoic) or acyl radical (Scheme 2a). We assumed the reaction were proceeds by two possible
pathway: path a (Scheme 2b, via amide intermediate A) or path b (Scheme 2b, via iminium
intermediate B). Path b has been commonly reported in the literature [27-28]. The involvement
of an amide intermediate was observed during the reaction process which was further confirmed
by NMR spectroscopy and ruled out the path b (see ESI). Moreover, amide intermediate A was
synthesized and exposed to optimize conditions to formed desired product in good yield with
excellent selectivity (Scheme 2c). With TEMPO (radical scavenger), the reaction (Scheme 2d)
was entirely hampered which confirmed the radical nature of the reaction. No acyl radical was
trapped in our case. However, we have already highlighted the significant role of oxygen in the
reaction. Desired product was formed in good yield when we subjected the intermediate 3a' in
optimized conditions (Scheme 2e).

16
Cu doped ZnS,
CH3CN
NH2
NH2
N
NH2
Br
+
+
N
Visible light, 10min
H
N
H
(a)
3a, 41%
NH2
3a', 28%
path b
N
NH2
B
+
Br
N
NH2
NH2
N
(b)
path a
O
H
N
H
A
NH2
Optimized
conditions
O
N
N
H
N
(c)
(d)
H
A
Optimized
conditions
NH2
N
Br
+
N
TEMPO
NH2
H
Not Observed
NH2
Optimized
conditions
N
N
H
N
H
(e)
3a'
Scheme 2: Control Experiments
From the above speculations a reasonable mechanistic pathway for synthesis of compound 3 was
outlined in Scheme 3. Firstly, the acidic sites of nanocatalyst facilitate the N-arylation of o-
phenylenediamine by benzyl bromide and formed the N-arylated intermediate (3a’). Now
photocatalyst absorb the visible light which excite electron and generate the hole. This excite
electron produce the radical intermediate (Y) from N-arylated intermediate (3a’).
-.
Simultaneously, hole convert O2 into O2 which subsequently convert radical intermediate (Y)
into amide intermediate A via CSp3– H oxidation [49]. The subsequent intramolecular
cyclization of amide intermediate A followed by dehydration gave the desired product and the
catalyst go in the catalytic cycle. Generation of holes and electron by visible light absorption is
recognized to be a decisive step in the reaction. In this case, creation of radicals appears to be
easier because of the occurrence of acceptor trapping level generated by copper doping. It’s also

17
increases the relaxation time of electron and holes so that they are easily available for the
reaction.
N
(i) Cyclization
(ii) Dehydration
NH2
O
N
H
N
H
A
O2
e-
CB
VB
or
O2
-
CSp3- H oxidation
O2
NH2
h+
+
N
H
NH2
Y
N
H
3a'
NH2
NH2
C-N arylation
NH2
+
Br
N
H
Scheme 3: Proposed catalytic mechanism
Next we examined the scope of the reaction with respect to various benzyl bromides under the
optimized conditions and the results are summarized in Table 2. Good to admirable product
yields (3a-m) were gained virtually independent of electronic properties of substituents; electron-
withdrawing and electron-donating on benzyl bromide almost did not affect on the reaction
course. We have also explored the constriction of 2-substituted benzothiazoles via the reaction of
2-Mercaptoaniline with various benzyl bromides (Table 2, entry 5a-l). All the reactions were
proceeds smoothly give the target product in good to excellent yield. However, ortho substitute
benzyl bromide gave lower yield as compared to the meta and para substitute benzyl bromide
due to the the steric hindrance.

18
Table 2. Substrate scope for the synthesis of 2-substituted benzimidazoles and benzothiazolesa
N
N
N
N
N
NO2
Me
N
H
N
H
Cl
N
H
N
H
Cl
N
H
3c, 54%
3b, 73%
3a, 71%
N
3e, 84%
3d, 70%
Me
N
N
N
N
F
OMe
Br
Cl
N
H
N
H
N
H
N
H
N
H
Cl
3h 63%
N
3j, 67%
3f, 76%
3i, 52%
3g, 82%
N
N
N
S
N
S
Cl
OMe
N
H
N
H
N
H
Cl
3l, 72%
3m, 63%
3k, 71%
5a, 74%
5b, 76%
HO
OMe
N
N
S
N
S
N
S
N
Br
NO2
Me
S
S
5d, 78%
5c, 61%
N
5e, 62%
5g, 71%
5f, 57%
N
S
N
S
Cl
N
S
N
S
CF3
OH
OH
S
NO2
5h, 81%
5i, 73%
5j, 60%
5k, 47%
5l, 52%
[a] Reactions are performed with various benzyl bromide (1 mmol) and 1,2-Diaminobenzene or 2-Mercaptoaniline (1 mmol) in CH3CN using
4%Cu: ZnS NPs under visible light.
In most of the cases the synthesis of the desired 2-aryl-1H- benzimidazoles is competes with the
formation 1-benzylated 2-arylbenzimidazoles as by-products [50], and occasionally these
disubstituted compounds have been formed as the major product [51]. While in the synthesis of 2-
substituted benzothiazoles, other side reaction was also observed [52]. The current procedure gives
selective formation of 2-substituted benzimidazole and benzothiazoles. The structure of the
products and intermediates were established by 1H/13C NMR and mass spectrometric studies.
This protocol was further apply for the synthesis of quinazolin-4(3H)-ones. We used our
optimized conditions on the model substrates, that is, o-aminobenzamides, and benzyl bromides.

19
It was found that our optimized photocatalytic protocol gave quantitative amounts of the
quinazolin-4(3H)-one derivatives. As mentioned in
Table 3, the reaction proceeded smoothly with electron-withdrawing, and electron-releasing
benzyl bromides. All the reactions were accomplished by amide intermediate via one pot C-N
arylation/ CSp3– H oxidation / cyclization/dehydration sequence.
Table 3. Synthetic application of protocol for the synthesis of quinazolin-4(3H)-one derivativesa
O
O
Cu doped ZnS NPs
Visible light
NH2
NH
Br
+
NH2
N
R
R
O
N
O
N
O
N
NH
NH
NH
7b, 77%
7c, 76%
O
7a, 73%
O
O
NH
NH
N
NH
N
N
Me
Br
F
7d, 75%
7e, 78%
O
7f, 61%
O
O
NH
N
NH
NH
N
N
OMe
7g, 71%
O
7h, 82%
Cl
NO2
7i, 61%
O
O
NH
N
NH Me
NH
Cl
Me
N
N
7k, 70%
7l, 74%
7j, 68%
O
NH Cl
N
7j, 70%
[a] Reactions are performed with various benzyl bromides (1 mmol) and o-aminobenzamide (1 mmol) in CH3CN using 4%Cu doped ZnS NPs
under visible light.
After the completion of the photochemical reaction, the Cu:ZnS NPs were separated from
reaction mixture by mild centrifugation and reused for the identical reaction. Optimum activity

20
of the catalyst was observed for fifth cycle (see ESI, Fig. S1). Further there was no leaching of
the catalyst was observed in final product the as confirmed by ICP-AES.
3. Experimental
3.1 General
Chemicals and the solvents were purchase from commercially and used without further
purification. XRD patterns was carried out using (PW3040/60) using Cu Kα source (k = 1.5406
Å). X-ray photoelectron spectroscopic analysis was taken on SPECS spectrometer (Germany)
with Al-Kα X-ray source (1486.5eV). USB 2000 spectrophotometer was used for the optical
study. The textural properties pore volume (VP), average pore diameter (DP) and BET surface
area of Cu doped ZnS were examined by nitrogen(N2) adsorption desorption isotherm at liquid
nitrogen temperature i.e -196oC using a Autosorb iQ2 gas sorption equipment (Quantachrome
Instruments, USA). Approximately 99.99% pure N2 was used for this analysis. Before adsorption
measurement, catalyst sample was degassed at 170oC for 4 h under vacuum. The FT-IR
spectrum were obtained with KBr using Shimadzu- 8400S. Transmission electron microscope
(TEM) observation was performed on JEOL 1011 instrument. Ultrasonic experiment was
13
conducted on Processor SONOPROS PR-1000MP, OSCAR ULTRASONICS. C NMR and 1H
spectra were recorded on JEOL NMR spectrometer at 400 and 100 MHz. Waters-Xeevo G2S Q-
T instrument was used for the detection of the mass spectrum of compounds. FEI Quanta 200F
was used for the SEM and EDX analysis.
3.2 Preparation of photocatalyst
For the preparation of the ZnS NPs, a 100 ml of 1M solution of Zn(CH3COO)2·2H2O and 100 ml
of 1M solution of Na2S was added drop-wise into 500 ml of deionized water containing 100 ml
of 0.1M solution of EDTA. The resulting solution was kept under constant stirring for 2 h. Then,
the flask was sonicated for 30 min with the probe (diameter =12 mm) at 4s pulse mode using

21
50% power. After the sonication the precipitate was separated, dried and crushed to fine powder.
Copper doping has been done by adding Cu(CH3COO)2·H2O (0 to 6%) to Zn(CH3COO)2·2H2O
(at the beginning of the reaction).
3.3 Synthesis of 2-substituted benzimidazoles and benzothiazoles (3&5)
A mixture of 1,2-Diaminobenzene 1 or 2-Mercaptoaniline 4 (1 mmol), benzyl bromides (1
mmol) 2 and 4% Cu:ZnS NPs (10 mol %) in 10 ml of CH3CN were irradiated in visible light
(100 W OSRAM Tungsten Lamp, EFP 64627 HLX) with continuous stirring for the appropriate
time. Catalyst was separated by centrifugation after the completion of reaction. Evaporation of
the above solution gave the crude product which was purified using crystallization.
3.4 Synthesis of quinazolin-4(3H)-ones (7)
A mixture of o-aminobenzamide 6 (1 mmol), benzyl bromides (1 mmol) 2 and 4% Cu:ZnS NPs
(10 mol %) in 10 ml of CH3CN were irradiated in visible light (100 W OSRAM Tungsten Lamp,
EFP 64627 HLX) with continuous stirring for the appropriate time. Catalyst was separated by
centrifugation after the completion of reaction. Evaporation of the above solution gave the crude
product which was purified using crystallization.
3.5 Recyclability of the catalyst
Recycling trial was carrying out by the reaction of 4-chloro benzyl bromide (1 mmol) with 1-2-
Diaminobenzene (1 mmol) in CH3CN as a solvent. The reaction was performed by using 4%
Cu:ZnS NPs (10 mol %). After the completion of the reaction, the catalyst was separated by
centrifugation (10000 rpm for 15 min). Washed the recovered catalyst from water and ethanol,
dried in oven and kept in desiccator for further use.
Conclusion
In conclusion, we have developed a vastly competent visible light driven photocatalytic protocol
for chemoselective synthesis of 2-substituted azoles in Cu doped ZnS NPs. Doped NPs acted as
active photocatalyst for the reaction as compared to bare ZnS. The doping procedure augmented

22
the activity to a degree proportional to the dopant amount up to 4%. This protocol tailored the
selectivity of the doped nanoparticles and commences the reaction in to a visible region. The
reaction proceeded to give the desired product via one pot C-N arylation/ CSp3– H oxidation/
cyclization/dehydration sequence. Further, the Cu doped ZnS NPs were reused for five rounds of
reactions. The working ease of this process and the purity of the products make it applicable not
only for the synthesis of 2-substituted azoles, but also for construction of biologically active
quinazolin-4(3H)-one library.
Conflict of Interest
The authors declare no conflict of interest.
Acknowledgements
The authors gratefully acknowledge financial support by, DST-SERB, U.G.C. and C.S.I.R., New
Delhi. MNIT, Jaipur is also acknowledged for their precision instrument support for
measurement facilities.
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