Iron nanotube-silica composite (ZVI-S-PCAT modified silica composite) preparation, characterization and application as a recyclable catalytic system for 5-membered ring organic transformations

Article abstract of DOI:10.1039/c5dt02028j

Iron nanotube silica composite have been synthesized and studied through particle-size analysis, FTIR, SEM-EDX, TEM, XRD, UV, VSM, TGA-DTA and XPS techniques. The application of nanoframeworks as sustainable recyclable catalytic systems has been observed

Full text of DOI:10.1039/c5dt02028j

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Iron nanotube-silica composites (ZVI-S-PCAT modified silica composites)-
Preparation, Characterization and Application as a recyclable catalytic system for
5-membered ring organic transformations
5
Gurpreet Koura, Monika Guptaa,*, B.Vishwanathanb, K. Thirunavaskarab
aDepartment of Chemistry, University of Jammu, Jammu-180006
Email- monika.gupta77@rediffmail.com
10 bNational Centre for Catalysis Research, Indian Institute of Technology-Madras,Chennai-600036, India
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
15 Abstract
Iron nanotube silica composite have been synthesized and studied through particle–size analysis,
FTIR, SEM-EDX, TEM, XRD, UV, VSM, TGA-DTA and XPS techniques. Application of nano
frame work has been observed as a sustainable recyclable catalytic system for the synthesis of azole
1
cyclic ring organic transformations. Good yields of reactions and their characterization through H
13
20 NMR, C NMR and mass analysis supports the performance of nanoframework. We also present
here synthesis of two novel compounds. Also the prepared nanoframework has been observed to show
soft magnetism and provides a scope to be used in sensing devices.
25
30
35
1. Introduction
Wonder word “nano” has an amazing relevance in science and technology, from material to
meaning for life, the role is multifaceted. Manually engineered metallic nano-frameworks are
expected to result size-controlled optical, magnetic, electronic and chemical properties serving
as optoelectronic devices, catalysts, chemical and biosensors.1-4 Designing nanoarchitectures
and demanding sustainability are the two important aspects of nanotechnology. An attempt has
been made in the present profile to meet the aforesaid requirements. We here present a
methodology to design sustainable zerovalent iron nanotube silica composites. The prepared
nanomaterial has been designed under controlled pH and temperature conditions to synthesize
iron nanotube framework adhered on chemically modified silica to give transition metal-silica
composite. The prepared nanomaterial has been studied for catalysis as its application aspect in

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this manuscript. The recyclability of the catalyst keeping iron adsorbed strongly without
leaching for 3 runs in the applied synthesis fulfills the criteria of sustainability both
economically and environmentally. Nanostructures of different shapes and sizes do assure a
purpose of activity and so do the nanotubes keeping a maintenance of electron flow to catalyze
the synthetic cause. Iron zero has been explored for few synthetic purposes but is not explored
before for C-X (O, S ,N) bond formations and synthesis of five membered heterocyclic
moieties which allow us to present our work for the practical, educataional and research
objective.
5
Talking zerovalent metals, iron stands a special mention for research in nanotechnology for the
reason being zerovalent iron has been important from environmental perspective as a nature
blessed metal to convert a number of common environmental contaminants like chlorinated
organic solvents, organochlorine pesticides, organic dyes, various inorganic compounds and
metal ions. Nanoscale zero-valent iron (nZVI) is one of the most prevalently used engineered
nanoparticles for groundwater and soil remediation.5 The specific surface area of zero valent
iron increases dramatically and hence the surface reactivity of nanoscaled iron. So this property
of nanoscale zerovalent iron motivated us to see its another variant catalytic property in C-X
organic transformations. In the context of using ZVI as catalyst in organic transformations,
some of the work includes iron (0) nanoparticle-catalyzed hydrogenation in water in flow,6
iron(0) nanoparticles as catalysts for the selective hydrogenation of unsaturated C–C bonds,7
iron-iron oxide core-shell nanoparticles (Fe CSNPs) in the hydrogenation of olefins in ethanol
and in the presence of water,8 graphene-supported iron-based nanoparticles encapsulated in
nitrogen-doped carbon as a catalyst for hydrogen evolution and oxygen reduction reactions, 9
supported iron nanoparticles as catalysts for sustainable production of lower olefins,10
asymmetric transfer hydrogenation of ketones using iron (0).11 From the existing procedures of
preparing and stabilizing zerovalent iron nanoparticles we present here a chemically modified
support material to stabilize Fe (0) nps and the difference observed from the earlier reported
methods have shown the formation of nanotubes of iron and here we present a methodology
wherein chemical modification of support material has brought such structural changes to give
metallic nanotubes formation which is an important feature forming grounds to study their
electrical, thermal and optical properities besides being studied as a catalyst in the present
work. Also the prepared catalyst has been studied to show soft magnetism and can show its
application to be used for preparing sensor devices as well. Moreover, as a catalyst it is a novel
10
15
20
25
30

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one to be used in such organic transformations and the procedure for chemical modification of
the support material using urea and NaOH and the difference observed by a change of solvent
in the modification step is not known earlier..
2. Experimental
5
2.1 Preparation, instrumentation and characterization of ZVI-S-PCAT (zerovalent iron-S-
propylcarbamothioate) modified silica composite
Iron nanoparticles are quite unstable and easily gets oxidized to various species with a shelf-life of few
hours giving a scope to work for its stability. Till now they have been encapsulated in silica directly or
10 supported on MPS (3-mercaptopropylsilane) modified silica. To increase the stability and activity of
iron nanoparticles for a longer shelf-life, we thought of moving a step ahead modifying and elongating
the SH moiety of MPS modified silica to give a species with an N-atom head stabilizing better the
ZVI. Our thought behind the present work was to prepare stable iron nano-material so that to be taken
as recyclable entity for organic transformations. In this direction,
15 Our first attempt (nanomaterial 1) involves modifying activated silica [12] to mercaptopropyl
functionality by adding 5mmole (0.981 g) MPS to 5 g activated silica taken in a 250 mL round bottom
o
flask and stirred in toluene at 110 C for12 h. This MPS modified silica was made alkaline using aq.
o
NaOH sol; pH= 9-10, stirred at 120 C for 5 h and then 5 g urea was added, stirred for 10 h. This
support was neutralized and to this was added Fe nanoparticles sol. The Fe sol. is prepared by taking
20 0.5 g of anhydrous FeCl3 stirred in 30 mL ethanol for 20 min., is chemically reduced using 0.3 M aq.
NaBH4 solution and stirred for 4 h. This catalyst was washed with 20 mL ethanol thrice and dried in
oven at 50 oC. The prepared nanoparticles size has been seen as approx 65nm and the resultant catalyst
is studied using FTIR, XPS, XRD and UV analysis.
Preparation of ZVI-S-PCAT modified silica composite
25 Our next and successful approach involves synthesizing the catalyst in ethanol as the media. For this,
MPS modified 5 g silica was stirred with ethanolic NaOH, pH of alcoholic sol. kept between 9-10 at
o
110 C for 4 h and to this is added 5 g urea and stirred at same temperature for 10 h. This modified
o
support has been neutralized using ethanol washings and dried in oven at 100 C. Finally this amide
modified support is added to simultaneously prepared ZVI nanoparticles prepared as aforementioned
o
[13]
30 methodology and stirred for 4 h at room temperature ( 22 C), washed with 20 mL ethanol thrice

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and dried at vaccum. The yield obtained is 70%. For storage purpose we follow the earlier thought of
storing it in ethanol (Figure 1, Scheme 1) [13].
The first attempt was a failure because urea and dil.aqueous NaOH gave carbonate and ammonia
which means no modification observed (nanomaterial 1) as desired by us. But the change in solvent
from water to alcohol and aqueous NaOH to alcoholic NaOH has given the desired preparation (ZVI-
S-PCAT modified silica composite).
5
Instrumentation
10 SEM has been studied on JEOL Model JSM- 6390LV and EDX has been studied on JEOL Model
JED-2300. TEM has been studied on PHILIPS CM200, TGA-DTA were taken on Perkin Elmer,
Diamond, XRD analysis has been done on Panalyticals‘ X’Pert Pro, FTIR were recorded on Perkin-
Elmer Spectrum-RX-IFTIR and XPS were recorded on a VG microtech ESCA 3000 spectrometer
using Al Kα X-ray at room temperature. ICP-AES was recorded on ARCOS (1.6 KW, 27.12 MHz).
15 Characterization
FTIR analysis
FTIR of nanomaterial 1 and ZVI-S-PCAT modified silica composite show common peaks of silica
which are around 474 cm-1 due to Si-O-Si stretching vibration, 1081 cm-1due to Si-O vibration. In
addition to these peaks, Figure 2 (a) observes a peak at 2341 cm-1 showing presence of some
20 remaining carbonate and thus confirming urea –aqueous NaOH reaction to give carbonate and urea and
also the absence of requisite peaks corresponding to N-H stretchings of amide confirms no desirable
modification. A band at 3466 cm-1 is due to O-H vibration. In Figure 2 (b) amide linkage is confirmed
by peaks at 3466 cm-1, 3289 cm-1 and 1548 cm-1. Also C=O stretching is observed at 1622 cm-1, C-S
stretching to be observed at 701 and 691 cm-1. Fe-O peak is observed at 554 cm-1
25 UV analysis
UV of nanomaterial 1 show a peak at 262 nm which is due to +3 oxidation state of iron but ZVI-S-
PCAT modified silica composite shows an additional peak at 320 nm which shows the presence of

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ZVI nano particles as also been observed by Li et al. in the U V studies at zero air exposure of their
4
freshly prepared zerovalent iron nanoparticles. The presence of Fe +3 species cannot be ignored as
peak at 260 nm is also observed in the spectrum (Figure 3a, 3b).
XPS analysis
5
The XPS provides informative details regarding the surface composition as it can be seen from Figure
4 that in nanomaterial 1formation of Fe (0), FeO and Fe2O3 is observed with B.E. at 706.8, 708.8 and
710.3 ev, C1s B.E. at 284.8 ev suggests C-C linkage, Si 2s and 2p B.E. observed at 154 ev and 103 ev,
Sulphur B.E. at 162 ev with a noise in 390-410 ev B.E. region showing no modification ahead
mercapto functionality. O1s B.E. is seen at 532 ev which comprises both Si-O and metallic oxide
10 binding energy. XPS study obtained for ZVI-S-PCAT modified silica composite clearly shows surface
modified morphology. C1s peaks at 285.5 ev due to C-C is taken as a reference and 288.8 envelopes
diff peaks of C-S, C-N, C=O of carbamothioate functionality. Something weird in the XPS analysis
have been seen with respect to Fe, O, Si and S values. Fe 2p3/2 peak is observed at 715.5 ev, O1s
binding energy is at 535.5 ev Si 2p at 105.5 ev, N1s at 402.3 ev and S 2p at 166.6 ev. We propose here
15 that irregular shift in binding energies of Si, O, N and Fe is due to complex arrangement of atoms
within the catalytic framework creating a complex structural environment around these elements to
show irregular trends in their binding energy values in comparison to that known in literature. Also, we
can say so because C1s which is taken as standard is showing normal value of binding energy as
reported in literature (Figure 5).
20 XRD analysis
XRD of nanomaterial 1(Figure 6 a) shows crystallanity to the prepared material and iron to be in +3
oxidation state as two peaks at 29 o and 35 o are observed which are typical of Fe2O3. However, XRD
of ZVI-S-PCAT (Figure 6 b) shows the amorphous nature of nanoframework and shows a peak
around 44.5 o which is due to Fe (0). This infers that in ZVI-S-PCAT modified silica composite, iron is
25 present in zero oxidation state in bulk whereas the nanomterial 1 contains iron in +3 oxidation state in
bulk.
SEM analysis
SEM micrographs of the desired modified nanomaterial i.e. ZVI-S-PCAT modified silica composite,
at different magnifications show a topography image of the prepared nanomaterial and observes the
30 presence of metallic nanoparticles as hexagonal surface moieties (Figure 7). EDX analysis of the ZVI-

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S-PCAT modified silica composite shows its surface atomic composition to have 3.48 % Fe, 5.68 % C,
36.01 % O, 51.47 % Si and 3.35 % S as shown in Figure 7.
TEM analysis
TEM micrographs of ZVI-S-PCAT modified silica composite (Figure 8) show the formation of iron
nanotubes of length 75 nm and diameter of 5.7 nm. Also there are seen spherical particles of diameter
11-14 nm which can be thought of either the modification part of silica or some of the oxide particles
formed.
5
ICP-AES
The weight percentage of iron in the catalyst as determined by inductively coupled plasma atomic
10 emission spectroscopy was 6.85 wt%.
TGA analysis
Thermal gravimetric analysis of ZVI-S-PCAT modified silica composite reports a loss of around 3%
o
o
o
at 100 C, which gears upto 4.9 % at 300 C along with a continuous loss of 11.34 % upto 717 C
(Figure 9). TGA analysis confirms the stability of ZVI nanotubes supported on S-PCAT modified
15 silica composite for its application part as a catalyst in the observed synthetic transformations.
VSM analysis
Figure 10 shows the magnetization curves and nanomaterial 1 shows 0.63 esu/ g and ZVI-S-PCAT
modified silica composite shows 0.49 esu/ g. It is observed that extent of magnetization in ZVI-S-
PCAT modified silica composite is quite less than nanomaterial 1 but as a hysteric loop is observed in
20 ZVI-S-PCAT modified silica composite VSM plot concludes it to be ferromagnetic in nature and acts
as a soft magnet that provides a scope to be used in sensor devices.
,

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oxide shell
e-
e-
e- e-
Feo core
Feo
Feo
Feo
NH2
O
NH2
O
NH2
NH2
O
NH2
O
NH2
O
O
S
S
S
S
S
S
O
O
O
O
O
O
Silica
Feo
Feo
Feo
Feo
Feo
NH2
O
S
NH2
O
S
NH2
O
S
NH2
O
S
NH2
O
S
NH2
S
O
O
O
O
O
O
O
Silica
Figure1. ZVI-S-PCAT modified silica composite

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HCl:H2O
1:1
120 oC
MPS
MPS modified silica
Silica
Activated Silica
Toluene
110 oC
12 h
Activation
alc. NaOH
pH 9-10
Ethanol
4 h
90-100 oC
12 h
O
Si
S-Na+
Silica
Urea 12 h
O
O
ZVI Np Sol.
Si
S
NH2
Silica
Si
S
NH2
Silica
RT
4 h
Scheme1. Preparation of ZVI-S-PCAT modified silica composite
Size Distribution by Intensity
5
(a)
10

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(b)
Figure 2. IR analysis of (a) nanomaterial 1, (b) ZVI-S-PCAT modified silica composite
5
(a)
(b)
Figure 3. UV analysis of (a) nanomaterial 1 and (b) ZVI-S-PCAT modified silica composite
10

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2200
2150
2100
2050
2000
1950
1900
1850
1800
1200
1100
1000
900
Fe O
2
3
C-C
FeO
Fe(0)
C-S
800
700
600
500
700
705
710
715
720
725
730
275
280
285
290
295
300
B.E.(ev)
B.E. (ev)
5
(a)
(b)
Si-O
6000
5000
4000
3000
2000
1000
Fe-O
700
Noise
690
680
670
660
650
640
630
620
524
526
528
530
532
534
536
538
540
392 394 396 398 400 402 404 406 408 410 412
B.E.(ev)
B.E. (ev)
(c)
(d)

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750
700
650
600
550
500
C-S
900
800
700
600
500
400
300
200
S-S
450
160
162
164
166
168
170
94
96
98
100
102
104
106
108
110
B.E. (ev)
B.E.(ev)
(e)
(f)
5
6000
O 1s
5000
4000
3000
2000
1000
0
Fe 2p
C 1s
Si 2p
Si 2s
0
200
400
600
800
1000
B.E.(ev)
(g)
Figure 4. XPS of nanomaterial 1 (a) Fe 2p, (b) C 1s, (c) N 1s, (d) O 1s, (e) Si 2p, (f) S 2p, (g) Overall
10 survey

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44000
43000
42000
41000
40000
39000
22000
20000
18000
16000
14000
12000
10000
8000
715.19
728.70
2p
2p
1/2
3/2
6000
4000
700
710
720
730
740
90
95
100
105
110
115
B.E (ev)
B.E.(ev)
(a)
(b)
30000
25000
20000
15000
10000
C 1s
13200
13000
12800
12600
12400
12200
O=C-N
C-C, C-H
C-S
275
280
285
290
295
300
385
390
395
400
405
410
415
Binding energy (ev)
B.E.(ev)
5
(c)
(d)

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35000
30000
25000
20000
15000
10000
5000
9000
8800
8600
8400
8200
8000
7800
7600
7400
Si-O
Fe-O
O=C-N
520
525
530
535
540
545
550
160
162
164
166
168
170
Binding energy (ev)
B.E.(ev)
(e)
(f)
5
140000
120000
100000
80000
60000
40000
20000
0
1s
O
Fe 2p
S 2p
Si 2s
Si 2p
1s
C
N 1s
S 2s
0
200
400
600
800
1000
1200
B.E.(ev)
(g)
Figure 5. XPS of ZVI-S-PCAT modified silica composite (a) Fe 2p, (b) Si 2p, (c) O 1s, (d) N 1s, (e)
C1s (f) S 2p, (g) Overall survey

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(a)
(b)
Figure 6. XRD of (a) nanomaterial 1, (b) ZVI-S-PCAT modified silica
5

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Element (keV) Mass% Atom%
K
C K
O K
Si K
S K
Fe K
Total
0.277
0.525
1.739
2.307
6.398
2.85
24.09
60.44
4.5
5.68
36.01
51.47
3.35
3.48
100
3.4242
1.3028
1
5
1.2265
3.0674
8.12
100
10
Figure 7. SEM images and EDS of ZVI-S-PCAT modified silica composite at a
15
magnification of 1500 X and 10,000 X

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Figure 8. TEM images of ZVI-S-PCAT modified silica composite showing nanotubes
formation
5
Figure 9. Thermogravimetric analysis of ZVI-S-PCAT modified silica composite

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Figure 10. Magnetisation curves for nanomaterial 1 and ZVI-S-PCAT modified silica composite
5
Figure 11. Photos of (a) Nanomaterial 1 (b) ZVI-S-PCAT modified silica composite -dried (left)
and stored in ethanol (right)
3. Application of ZVI-S-PCAT modified silica composite as a recyclable catalyst
The prepared nanomaterial has been seen for its application in catalysis technology for
synthesizing 5-membered heterocyclic derivatives.
10
3.1.1. Synthesis of tri-substitued imidazoles
Imidazole has been seen as a wide utility heterocyclic moiety in serving as a pharmacophore
[14] in many drugs (such as trifenagrel, eprosartan etc.) [15], as a therapeutic agent [16], P38
MAP kinase inhibitor [17], modular of glucagon receptors [18], anti-thrombotic agent,
herbicidal, fungicidal [19], green solvent and catalyst source as an ionic liquid precursor [20],
core unit of many natural products, present in a natural amino acid ( histidine), [21] and in
photography as photosensitive compounds [22]. Earlier work comprises synthesis of imidazole
15

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using HBF4–SiO2 and LiBF4 [23], Lipase [24], PEG1000-based functional dicationic acidic
ionic liquid and propylene glycol monomethyl ether [25], Fe3O4–PEG–Cu [26], SbCl3/SiO2
[27] etc. as catalysts.
The prepared nanomaterial (ZVI-S-PCAT modified silica composite) has been
5
10
15
20
25
30
studied as a catalytic system for the synthesis of imidazole ring derivatives. Also an
experimental comparison is made with different parallels and blank (catalyst-free, silica, Fe-
silica, MPS-Fe) and the results obtained as: without ZVI-S-PCAT, no reaction initiation is seen
for 24 h; silica catalyzed synthesis initiated the reaction in 12 h but never moved to completion
even after more than 12 h run; Fe-silica showed a good reaction in 5 h with 75% yield which
may be due to oxidized nature of iron as iron is in direct contact with available oxygen sites of
silica; Fe-MPS gave 62% yield in 6 h and ZVI-S-PCAT yielded 92% in 1 h. These obtained
yields discussed here are with 0.2 g of ZVI-S-PCAT for 1mmol reaction and the rates are
slower with 0.1g of ZVI-S-PCAT. For optimizing the reaction parameters, control experiments
are conducted with three different solvent conditions- solvent-free, ethanol, water and the
reaction moved quite well in ethanol. Had water given the best yields,was not a choice as there
are chances of oxidation of ZVI much faster leaving ZVI-S-PCAT non-recyclable.
Temperature effects has been observed too at RT, 60 oC and 80 oC, wherein 60 oC temperature
showed the optimized yields and moreover served milder condition (Scheme 2). The reaction
has been carried out with variable aldehydes (1mmol), benzil (1mmol) and ammonium acetate
(4mmol) as reactants (Table 1).
For each synthetic transformation, appropriate amounts of aldehyde (1mmol), benzil (1mmol),
ammonium acetate (4 mmol), 4 mL ethanol and 0.2 g of ZVI-S-PCAT are taken in a round
bottom flask (100 mL) fitted with a condenser and stirred on a magnetic stirrer in an oil bath at
o
80 C for appropriate times (Table 1). Working up the reaction involves addition of ethyl
acetate (15-20 mL) to the reaction mixture, heat and filter using sintered glass crucible to
separate ZVI-S-PCAT catalyst. The filtrate is given brine solution washings and dried over
sodium sulphate for 4 h. The filterate is then reduced in amount to give the crude product
which is recrystallized using ethanol. The products have been confirmed using 1H NMR, 13C
NMR and mass analysis. Also their melting points have been determined and matched to the
earlier reported in literature. Also, two new compounds (2l, 2m, Table 1) in this series of
reactions have been reported here.

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Scheme2. Comparision of ZVI-S-PCAT with different parallels and optimization of chosen
conditions for the synthesis of trisubstituted imidazoles using the three components in
equimolar ratios
without ZVI-S-PCAT
24 h, no reaction
solvent-free
Ethanol
silica
12 h, Reaction initiated
no product obtained
70%
O
O
Fe-silica
5 h, 75%
2 h, 62%
1 h, 92%
2 h
2 h
Fe-MPS
NH4OAc
RCHO
92%
67%
ZVI-S-PCAT
Ethanol
ZVI-S-PCAT
Water
ZVI-S-PCAT
60 oC
2 h
Ethanol
RT
80 oC
92%
No reaction
92%
5
Table 1. Application of ZVI-S-PCAT modified silca composite for the synthesis of 2,4,5-
trisubstituted imidazoles
H
N
ZVI-S-PCAT
60 o
R
2
C
N
O
O
Ethanol
NH4OAc
R-CHO
1
4a-4m
3
10
S.No
1
R
Product Time (min) %yield
M.pt/ Lit. M.pt (oC)
272/ 272-27428
4a
60
92
NO2
2
3
4b
4c
85
45
87
90
232 / 230-23131
314/ > 300 30
O2N

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O2N
4
5
4d
4e
40
60
84
240/ 239-24229
82
91
227/ 227-22932
230/ 228-23128
H3CO
6
7
8
4f
75
45
70
H3CO
HO
4g
4h
87
170 / 168 33
H3CO
H3CO
5
84
218/ 216-218 34
262/ 262-264 28
212/ 213-214 35
Cl
9
4i
60
70
90
92
O
10
4j
N
H
11
4l
90
90
88
170172
H
N
12
4m
120
200-203
a
10
Reaction conditions: 0.2g catalyst (0.38 mol% iron), aldehyde (1mmol), benzil (1mmol), ammonium acetate (4
mmol), solvent-ethanol, 60 oC
15
20

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Scheme3. Plausible mechanism for the role of ZVI-S-PCAT-modified silica composite in
the organic transformation of aldehyde, benzil and ammonium acetate into
2,4,5-trisubstituted imidazoles
Ph
H
N
R
N
Ph
NH2
Fe
H2N
H2N
NH2
H2N
H2N
NH2
NH3
NH4OAC
N
H2
Fe
NH
N
H2
H
2
H
R
N
NH2
NH2
Ph
N
NH3
Ph
H2N
Fe
N
H2
O
O
Ph
NH
2
-H2O
Ph
NH2
NH2
NH2
H
N
Ph
Ph
H2N
Fe
N
H2
H
NH2
NH2
C
H
N
Ph
H2N
Fe
R
N
N
H2
OH
NH
2
O
Ph
R
HN
C
H
RCHO
NH3
5

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3.1.2 Synthesis of benzothiazoles
Another application of ZVI-S-PCAT modified silica composite has been studied for the
synthesis of bioactive, natural products swaddled benzothiazole moiety. These have served as
anti-tuberculotic [36], anti-hypoxic, anti-inflammatory [37], anti-convulsant, anti-diabetic and
anti-cancer activities [38]. Benzothiazoles have been used as tracing agents for β-amyloid in
Alzheimers’, invitro activities against human colon, breast and renal cell-lines [39], an
iminocoumarin based zinc sensor and as a bioluminogenic substrate. Previous work has
included synthesis using microwave conditions having longer time [40], CuCl as catalyst [41],
glycerol [36], PEG-400 [42], TsOH [43], nano acid catalysts [44].
5
10
15
20
25
30
For synthesizing substituted benzothiazoles, a similar trend of comparison with parallels and
optimization of reaction parameters has been checked before, as has been performed during the
synthesis of imidazole derivatives (described earlier). The results of the optimization and
parallel comparison can be identified in Scheme 4. For each experiment, aldehyde and 2-
aminothiophenol are taken in a 1:1 molar ratio. To these, are added 0.2 g of ZVI-S-PCAT, 4
mL ethanol and the round bottom flask is fitted to a condenser. The mixture is stirred well on a
magnetic stirrer in an oil bath with temperature at 80 oC for variable times as given in Table 2.
Working up the reactions have the same methodology as stated before in the manuscript. Good
results have been recorded and the products obtained have been confirmed using 1H NMR,
13C NMR, mass analysis and also their melting points have been observed and compared well
to the literature reported. One new compound, 3k, has also been synthesized in satisfactory
yield.

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Scheme 4. Comparision of ZVI-S-PCAT with different parallels and optimization of
chosen conditions for the synthesis of benzothiazoles
without ZVI-S-PCAT
24 h, no reaction
solvent-free
silica
12 h, No reaction
3 h, 60%
63%
CHO
Fe-silica
H2N
2 h
2 h
Ethanol
Water
Fe-MPS
90%
52%
3.30 h, 70%
2 h, 90%
ZVI-S-PCAT
Ethanol
HS
ZVI-S-PCAT
ZVI-S-PCAT
2 h
Ethanol
60 oC
RT
80 oC
90%
50%
No Reaction
5
Table 2. Application of ZVI-S-PCAT modified silca composite for the synthesis of 2-
substituted benzothiazoles
SH
S
ZVI-S-PCAT
R
R-CHO
80 o
C
Ethanol
N
NH2
2
1
3a-k
10
S.No
1
R
Product
Time(h)
2
%yield
90
M.pt/ Lit. M.pt
111/ 113-114 38
3a
NO2
2
3
3b
3c
1.45
1.20
85
82
210-213
O2N
181/ 181-18341

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229/ 229-23038
85/ 86-87 38
O2N
4
5
3d
3d
1.40
2
90
87
120/119-12038
118/ 117-118 38
H3CO
6
7
3e
3f
2.30
2.10
89
Cl
89
O
5
8
3g
3h
3
82
102/ 102-10338
130/131-13238
Br
9
2.25
86
a
Reaction conditions: 0.2g catalyst (0.38 mol% iron), aldehyde (1mmol), 2-aminothiophenol (1 mmol), solvent-
ethanol, 80 oC
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15
20
25

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Scheme 5. Plausible mechanism for the role of ZVI-S-PCAT-modified silica composite in
the organic transformation of aldehyde and 2-aminothiophenol into substituted
benzothiazoles
5
N
R
S
NH2
NH2
H2N
H2N
Fe
H
N
N
H2
H
SH
NH
2
R
NH2
H2N
H2N
S
Fe
N
H2
NH2
H2N
H2N
H2N
NH
2
Fe
N
H2
R
N
C
NH
2
HS
R
H
NH2
H2N
H2N
HS
Fe
O
N
H2
NH
H
2
-H2O
3.2. Recyclability of ZVI-S-PCAT
10
Recyclability of ZVI-S-PCAT modified silica composite as a catalyst has been observed in
both the worked heterocyclic organic transformations for three consecutive runs. The results
obtained have been shown in Figure10, which suggests sustainable rates of reactions without
much loss in activity as catalyst. Also, to check the metal leaching ICP-AES analysis of the
used catalyst was carried out which showed a metallic weight loss of 0.02% which is almost
negligible. Further, we come up with a thought that as the core shell iron gets consumed for
each run to maintain the zero valency of surface iron, after three runs the catalyst will be more
of an oxidized framework and thus results may be in increase of rate of reaction but not as a
zerovalent species but more of as an oxidized form. For recyclability purpose, catalyst is
15

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washed with 20 mL ethanol thrice after each run and is vacuum dried. Loss of amount of
catalyst after each run has occurred due to manual error but for recyclability check each time
the reactants amount is adjusted. Transformations using benzaldehyde as the variant substrate
is used in the test reactions.
5
Figure 12. Recyclability of ZVI-S-PCAT modified silica composite as a supported
catalytic- metallic nanotube framework
4. Spectral Data of some compounds
2,4,5-Triphenyl-1H-imidazole (4a):
10
1H NMR (DMSO-d6 δ): 11.8 (bs, 1H, NH), 8.1 (d, 2H, J = 8.4 Hz,), 7.2-7.7 (m, 13H, Ar-H);
13C NMR (DMSO-d6 δ): d 145.9, 135.6, 131.5, 130.7, 128.6, 128.3, 128.2, 128, 127.6, 127.4,
126.4, 125.2. HRMS (ESI) m/z: [M + H]+ calcd for C21H16N2, 297; found, 297.
2-(3-Nitrophenyl)4,5-diphenyl-1H-imidazole (4c):
1H NMR (CDCl3 -DMSO-d6 δ): 12.7 (bs, 1H, NH), 9.0 (s, 1H, Ar-H), 8.4 (d, 1H, J= 8Hz, Ar-
H), 8.0 (d, 1H, J=8Hz, Ar-H), 7.4 (m, 4H, Ar-H), 7.2 (m, 4H, Ar-H), 7.1(m, 2H, Ar-H); 13C
NMR (CDCl3 -DMSO-d6 δ): d 148.6, 143.9, 132.4, 131.4, 129.7, 128.5, 128.2, 127.9, 127.5,
126.8, 122.3, 120.0. HRMS (ESI) m/z: [M + H]+ calcd for C21H15N3O2, 342; found, 342.
2-(furan-2-yl)-4,5-diphenyl-1H-imidazole (4j):
15
1H NMR (CDCl3 -DMSO-d6 δ): 12.4 (bs, 1H, NH), 7.6 (d, 1H, J=8.4Hz, Ar-H), 7.1-7.5 (m,
10H, Ar-H), 6.9(d, 1H, J=12Hz, Ar-H), 6.4 (d, 1H, J= 16Hz, Ar-H); 13C NMR (CDCl3 -
DMSO-d6 δ ): 145.8, 142.2, 139.1, 137.5, 128.5, 128.1, 127.7, 127.6, 126.7, 126.6, 111.6,
107.4. HRMS (ESI) m/z: [M + H]+ calcd for C19H14N2O, 287; found, 287.
3-(4,5-diphenyl-1H-imidazol-2-yl)-1H-indole (4l):
20

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1H NMR (400 MHz, DMSO-d6 δ): 12.2 (s, 1H, NH), 11.3 (s, 1H, NH), 8.47 (d, J= 8 Hz, 1H,
Ar-H), 7.9 (s, 1H) 7.5-7.7 (m, 5H, Ar-H), 7.3-7.4(m, 6H, Ar-H), 7.14(dd, J= 8Hz, Ar-H); 13C
NMR (100 MHz, DMSO-d6 δ): 144.1 (C2, C4), 136.7 (C1, C7, C20, C22), 129.0 (C6, C10,
C14, C15), 122.2 (C9, C11, C16), 121.9 (C19), 120.12 (C24, C25), 112.0 (C23), 107.2 (C26),
107.02 (C5). HRMS (ESI) m/z: [M + H]+ calcd for C23H17N3, 336; found, 336.
4,5-diphenyl-2-(1H-pyrrol-2-yl)-1H-imidazole (4m):
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1H NMR (400 MHz, DMSO-d6 δ): 12.3 (s, 1H, NH), 11.3 (s, 1H, NH), 8.1-7.3 (m,11H), 6.7 (d,
J =5.2Hz, 2H) 6.15 (d, 1H); 13C NMR (100 MHz, DMSO-d6 δ): 141.8, 136.0, 130.1, 130.0,
129.7, 129.4, 129.2, 128.1, 126.9, 126.6, 123.3, 119.9, 109.1, 106.7. HRMS (ESI) m/z: [M +
H]+ calcd for C19H15N3, 286; found, 286.
2-Phenylbenzothiazole 3(a):
1H NMR (400 MHz, DMSO-d6, δ): 8.06 (m, 4H, Ar H), 7.55 (m, 4H; Ar H), 7.46 (t, J = 8 Hz,
1H, Ar H); 13C NMR (100 MHz, DMSO-d6, δ): 167.8, 153.9, 134.8, 133.27, 131.9, 129.9,
127.6, 127.1, 126.0, 123.3, 122.8; HRMS (ESI) m/z: [M + H]+ calcd for C13H9NS, 212; found,
212.
2-(2-Nitrophenyl)-benzothiazole 3(b):
1H NMR (400 MHz, DMSO-d6, δ): 9.0 (s, 1H, Ar H), 8.4(d, J = 4.4 Hz, 1H, Ar-H), 8.1 (d, J =
8 Hz, 2H; Ar-H), 7.7 (t, 2H, J= 8 Hz, Ar-H), 7.1 (m, 9H, Ar-H) ; 13C NMR (100 MHz, CDCl3,
δ): 156.1, 155.5, 148.9, 147.7, 133.8, 132.4, 131.5, 130.9, 130.2, 127.9, 126.2, 124.5, 117.6;
HRMS (ESI) m/z: [M + H]+ calcd for C13H8N2O2S, 257 found, 257.
2-(4-Methoxyphenyl)benzothiazole (3e):
1H NMR (400 MHz, DMSO-d6, δ): 8.6 (s, 1H, Ar H), 7.96 (d, J = 8 Hz, 2H, Ar H), 7.51 (d, J =
8 Hz, 1H, Ar H) 7.2 (d, 2H, Ar H), 3.86 (s, 3H; OCH3); 13C NMR (100 MHz, CDCl3, δ): 162.5,
160.5, 149.0, 131.3, 129.2, 127.8, 127.1, 125.4, 118.2,115.23, 114.8, 55.89; HRMS (ESI) m/z:
[M + H]+ calcd for C14H11NOS, 242; found, 242.
2-(4-Chlorophenyl)-benzothiazole (3f):
1H NMR (400 MHz, DMSO-d6, δ): 7.6-8.0 (m, 4H, Ar H), 7.2-7.6 (m, 4H; Ar-H); 13C NMR
(100 MHz, CDCl3, δ): 162.4, 154.2, 138.0, 135.1, 130.3, 129.4, 128.6, 126.7, 125.2, 123.8,
120.9; HRMS (ESI) m/z: [M + H]+ and [M + 2 + H]calcd for C13H8NSCl, 246 and 248; found,
246, 248.
5. Conclusion
We conclude the work with a satisfaction of achievement in the sysnthesis of a sustainable
ZVI-S-PCAT modified silica composite which can be used as a soft magnet in future sensor

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devices too besides being studied as a catalyst. The sustainability has been seen as a nano-
recyclable catalytic performer for synthesizing 5-membered heterocyclic rings but the iron (0)
core shell model continues to serve the explaination. Also the synthesized nanomaterial for its
tube framework leaves a scope for different future studies in different fields besides only acting
as a catalytic framework. We have come up with findings that aqueous NaOH/ urea treatment
does not gives a modified material but gives crystallanity to support as can be observed from
the nature of XRD patterns which has not been observed in case of alcoholic NaOH/urea
treatment which though gives modification into thiocarbamate moiety but unables to change
the amorphous nature. So, one more outcome is that aqueous NaOH/ urea treatment also acts as
a swelling agent to supports also like that as observed in case of cellulose fibres in textiles and
may be this water imbibtion has lead iron to change completely from zerovalent state to +3
oxidation state.
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Acknowledgements
We are thankful to NCCR, Chennai and CSIR, NCL, Pune for conducting XPS analysis; SAIF,
Kochi for SEM-EDS, XRD, TGA-DTA analysis; SAIF, Mumbai for TEM and ICP-AES
analysis; SAIF, Chandigarh for FTIR, XRD analysis and Department of Chemistry for Particle
1
13
size analysis and H NMR and C NMR analysis. We would like to thank IIT Guwahati for
carrying out VSM studies. Also we are thankful to IIIM, Jammu for mass analysis.
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