Starch functionalized creatine for stabilization of gold nanoparticles: Efficient heterogeneous catalyst for the reduction of nitroarenes

Article abstract of DOI:10.1016/j.ica.2019.118965

Selective reduction of nitroaromatic pollutants into amines with recoverable and reusable heterogeneous catalysts is highly desirable. Herein, we prepared and characterized an efficient novel catalyst comprising 4 nm size Au nanoparticles supported on creatine modified starch. Using this catalyst, efficient reduction of nitroarenes into amines at room temperature in aqueous media was achieved. The presence of creatine in the structure of the catalyst plays important role in amount of Au loading, efficiency of the catalyst, recycling times, and leaching of Au compared to starch supported Au without creatine.

Full text of DOI:10.1016/j.ica.2019.118965

Accepted Manuscript
Starch Functionalized Creatine for Stabilization of Gold Nanoparticles: Effi-
cient Heterogeneous Catalyst for the Reduction of Nitroarenes
Mohammad Gholinejad, Neda Dasvarz, Mohammad Shojafar, José M. Sansano
PII:
S0020-1693(19)30391-3
https://doi.org/10.1016/j.ica.2019.118965
118965
DOI:
Article Number:
Reference:
ICA 118965
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
25 March 2019
11 June 2019
12 June 2019
Please cite this article as: M. Gholinejad, N. Dasvarz, M. Shojafar, J.M. Sansano, Starch Functionalized Creatine
for Stabilization of Gold Nanoparticles: Efficient Heterogeneous Catalyst for the Reduction of Nitroarenes,
Inorganica Chimica Acta (2019), doi: https://doi.org/10.1016/j.ica.2019.118965
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Starch Functionalized Creatine for Stabilization of Gold Nanoparticles: Efficient
Heterogeneous Catalyst for the Reduction of Nitroarenes
a,b
a
a
c
Mohammad Gholinejad,* Neda Dasvarz, Mohammad Shojafar, José M. Sansano*
a
Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), P. O. Box
4
5195-1159, Gavazang, Zanjan 45137-66731, Iran. E-mail: gholinejad@iasbs.ac.ir
b
Research Center for Basic Sciences & Modern Technologies (RBST), Institute for Advanced
Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
c
Departamento de Química Orgánica, Instituto de Síntesis Orgánica and Centro de Innovación
en Química Avanzada (ORFEO-CINQA). Universidad de Alicante, Apdo. 99, E-03080-Alicante,
Spain. Email: jmsansano@ua.es
Abstract: Selective reduction of nitroaromatic pollutants into amines with recoverable and
reusable heterogeneous catalysts is highly desirable. Herein, we prepared and characterized an
efficient novel catalyst comprising 4 nm size Au nanoparticles supported on creatine modified
starch. Using this catalyst, efficient reduction of nitroarenes into amines at room temperature in
aqueous media was achieved. The presence of creatine in the structure of the catalyst plays
important role in amount of Au loading, efficiency of the catalyst, recycling times, and leaching
of Au compared to starch supported Au without creatine.
Keywords: Starch, Creatine, Gold, Nitro, Reduction, Heterogeneous
1

1
. Introduction
Nowadays green chemistry encourages researchers to develop new chemical process that
eliminate or reduce the production of substances which are harmful for human and environment.
Along this line, eliminating or reducing of the organic pollutants and development of new
sustainable catalysts are two important aims of green chemistry objectives [1,2]. Nitroaromatic
compounds which are potent toxic, carcinogenic and hazardous to human health are among the
largest and most important groups of industrial wastes. In contrast, amines are versatile
precursors in the preparation of various compounds including pharmaceuticals, dyes and
agrochemicals [3,4]. Reduction of nitro compounds is one of the most reliable methods for the
preparation of amines. Traditional methods such as Béchamp reduction in which aromatic nitro
compounds were reduced to the corresponding aromatic amines by iron and ferrous salts
catalysts in aqueous acid, is time consuming method and produce large amount of waste and is
not appropriate for acid sensitive functional groups [5]. To address this issue, in recent years,
catalytic hydrogenation using different transition metals and reducing sources have been
developed for the reduction of nitroarenes [3,4]. For a long time, gold has been considered as an
inactive metal. However, after its well-recognized catalytic activity, gold-catalyzed organic
transformations have attracted a great interest in organic synthesis [6-11]. Along this line,
various gold catalysts in the presence of different reducing agents have been developed
successfully for the selective reduction of nitro groups under homogeneous or heterogeneous
conditions[12-35]. In recent years, using various compounds as support for stabilization of
transition metal and formation of heterogeneous catalysts, which generate new materials of low
human toxicity and environmental impact, attract great attentions [36,37]. For instance, naturally
occurring polysaccharides can be considered as excellent solid for stabilization of transition
2

metals[38-40]. Among different polysaccharides, starch is a polymeric carbohydrate involving
glucose units connected by glycosidic bonds, which is regenerated from carbon dioxide and
water by photosynthesis in plants. Different properties of starch, such as complete
biodegradability, high water-swelling ratio, low cost and renewability make it a promising
support for catalyst design [41-45]. On the other hand, creatine is a nitrogenous organic acid and
naturally occurring substance produced in the pancreas, and liver in vertebrate animals. The main
role of creatine in body is to facilitate recycling of adenosine triphosphate (ATP) via reaction of
creatine with phosphate group of ATP and producing phosphocreatine in muscle and brain tissue
[46].
The main goal of this work is to combine onto a solid phase (starch) a linker bonded to the
natural compound (creatine) and deposit gold nanoparticles. The characterization of this gold
aggregate and its efficiency as catalyst in the reduction of nitroarenes will be also assessed.
2
. Results and discussion
For the preparation of the desired catalyst, commercially available corn starch was reacted with
3-chloropropyl)triethoxysilane in dry toluene giving the resulting starch containing the chloro
(
atom at the end of the linker (starch@Cl). Then, creatine was reacted with starch@Cl in xylene
using Et N as a base. Finally, the creatine-functionalized starch (starch@crt) was treated with
3
NaAuCl . 2H O and reduced with NaBH affording creatine-modified starch supporting Au NPs
4
2
4
(Scheme 1). The obtained new gold composite is referred to as starch-crt@Au throughout the
text. Using atomic absorption spectroscopy (AAS), the content of gold in starch-crt@Au was
found to be 0.0198 mmol/g. This result indicated that 73.3% of Au species was successfully
loaded on starch@crt.
3

OH
Toluene (dry)
O
O Si
O
OH + (EtO) Si
Cl
3
Cl
S t a r c h
OH
S t a r c h
S t a r c h
110 C, 24h
NH
NH
O
O
O
Et N
3
O
O
O
O
O
+
H N
N
Si
Si
N
Si
Cl
2
N
H
Xylene
S t a r c h
S t a r c h
Me OH
Me OH
130 C
NH
NH
O
O
O
NaAuCl4.2H2O
O
O
O
O
O
Si
N
H
N
N
N
H
S t a r c h
NaBH4
S t a r c h
Me OH
Me OH
48h, rt
Scheme 1. Synthesis of starch-crt@Au
Structure of creatine, starch@Cl and starch@crt were studied by Fourier-transform infrared
spectroscopy (FT-IR). As can be seen in Figure 1, FT-IR of starch@crt showed sharp absorption
-1
peak at 1696 cm related to C-O stretching vibrations of carboxylic acid in creatine. Also,
-1
prominent absorption peak related to C-N stretching vibrations of guanidine at 1615 cm and
-1
peak related to NH stretching vibrations centered at 3338 cm were observed in starch@crt
confirming successful grafting of creatine on starch (Figure 1)[47].
4

Figure 1. FT-IR spectra of creatine, starch@Cl and starch@crt
5

The scanning electron microscopy (SEM) images of starch-crt@Au in different magnification
showed amorphous starch sheets and also the presence of Au nanoparticles (bright dots) (Figure
2
).
Figure 2. SEM images of starch-crt@Au
Energy dispersive spectroscopy (EDS) confirmed the existence of different elements such as
Au, O, N, Si, and C into the structure of starch-crt@Au (Figure 3).
6

Figure 3. EDS spectra of starch-crt@Au
Furthermore, SEM-Map images of elements (Figure 4) and overlay mapping image (Figure 5)
showed uniform dispersion of Au, C, N, and Si in starch-crt@Au structure.
Figure 4. EDS mapping images of starch-crt@Au
7

Figure 5. Overlay mapping image of starch-crt@Au
X-ray photoelectron spectroscopy (XPS) of starch-crt@Au in Au, N, C and Si regions were
studied (Figure 6). The XPS spectrum in the Au 4f region showed an intense doublet at 83.6 and
8
7.4 eV confirming complete reduction of Au(III) to Au(0) (Figure 6a) [48]. Also, XPS analysis
for the N 1s region confirmed the presence of nitrogen in the structure by appearing a peak
centered at 400 eV (Figure 6b) [49, 50]. In addition, peaks located at 284.6, 286.5 and 288.2 eV
were related to C 1s orbital in C–C/C–H, C–O and O–C–O forms, respectively (Figure 6c)
[51,52]. Finally, Si 2p region XPS spectrum showed two binding energies at 101.9 eV and 102.8
eV, which are related to Si-O bonds (Figure 6d) [53,54].
8

Figure 6. XPS spectra of starch-crt@Au in a) Au b) N c) C d) Si
Transmission electron microscopy (TEM) images of starch-crt@Au at different magnification
levels showed presence of small size Au nanoparticles (Figure 7). The average size of Au
∑
푑 푛
푖 푖 ∑푛 , was found to be 4.3 nm, where, n
nanoparticles using the following equation: 퐷 =
푖
i
was the number of particles whose diameter was d (Figure 8).
i
Figure 7. TEM images of starch-crt@Au
9

Figure 8. Distribution diagram of Au nanoparticles in starch-crt@Au
X-ray diffraction (XRD) analysis of the starch-crt@Au showed Bragg's reflections at 2θ=17°,
2
3° corresponding to the (200) and (211) planes of starch [55,56] and Bragg's reflections for
Au(0) at 2θ=38°, 44.2°, 65° and 78° (Figure 9)[48,57].
Figure 9. X-Ray diffraction analysis of starch-crt@Au
1
0

Next, the catalytic activity of starch-crt@Au was assessed in the reduction of nitroarenes to the
corresponding amines. The reduction of 4-nitrotoluene was selected as benchmark reaction and
the effect of different factors such as catalyst mol%, type of reductant, solvent and reaction time
were studied. Initially reaction was performed using 0.01 mol% of catalyst in the presence of
NaBH (5 equiv) in water during 4 h. In this reaction, the formation of 4-aminotoluene took
4
place in poor yield (Table 1, entry 1). With increasing the catalyst loading to 0.03-0.1 mol%,
yields were improved (Table 1, entries 2-5) and 89% was obtained using 0.1 mol% catalyst
(Table 1, entry 5). Then, we tried the efficiency of other reducing agents in water using 0.1
mol% of the catalyst. However, the formation of amines took place in lower yields than the
reactions employing NaBH (Table 1, entries 6-9). Other organic solvents tested, such as THF,
4
DMF, 1,4-dioxane and EtOH gave also poor yields (Table 1, entries 10-13). While, using
EtOH:H O (1:1) mixture as reaction medium, gave quantitative yield of the desired product in 4
2
h (entry 14). Shorter reaction times and lower amounts of NaBH produced a decrement of yields
4
(Table 1, entries 15-18). Therefore, we selected, aqueous ethanol as solvent, 0.1 mol% catalyst,
NaBH as reducing agent at room temperature as the most efficient reaction conditions (Table 1,
4
entry 14). It should be noted that the study of reaction in the absence of this catalyst and using
NaBH (5 equiv) gave only 3% conversion (GC) to the product (Table 1, entry 19).
4
Table 1. Optimization of the reaction conditions for the reduction of 4-nitrotoluene
NH2
NO2
Catalyst (X mol%)
Solvent, r.t.
+
Reductant
Me
Me
1
1

Entry
Cat (mol%)
0.01
Solvent
t(h)
4
reductant
NaBH4
NaBH4
NaBH4
NaBH4
NaBH4
Glycerol
NH NH
Yield(%)
1
2
3
4
5
6
7
8
9
H O
2
13
44
52
65
89
0
0.03
H O
2
4
0.05
H O
2
4
0.07
H O
2
4
0.10
H O
2
4
0.10
H O
2
4
0.10
H O
2
4
4
2
2
0.10
H O
2
4
HCO H
0
2
0.10
H O
2
4
NH₄HCO₂
NaBH4
NaBH4
NaBH4
NaBH4
NaBH4
0
1
1
1
1
1
0
1
2
3
4
0.10
THF
1,4-Dioxane
EtOH
4
1
0.10
4
0
0.10
4
1
0.10
DMF
4
1
0.10
H O:EtOH
2
4
100
1
1
1
1
1
5
6
7
8
9
0.10
0.10
0.10
0.10
-
H O:EtOH
3
2
4
4
4
NaBH4
NaBH4
NaBH4
NaBH4
NaBH4
75
32
2
H O:EtOH
2
H O:EtOH
2
46c
78d
3e
H O:EtOH
2
H O:EtOH
2
a
Reaction conditions: 4-nitrotoluene (0.5 mmol), reductant agent (5 equiv), solvent (2 mL).
Yield determined by GC.
b
1
2

c
d
e
Reaction run in the presence of 3 equivalents of NaBH4.
Reaction run in the presence of 4 equivalents of NaBH4.
Reaction run in the absence of the catalyst.
Having optimized reaction conditions, the reduction of a variety of nitroaromatic compounds
were assessed. Results indicated that reduction of nitroarenes having electron withdrawing
groups such as -Cl, -Br, -F, -COR proceeded very efficiently and desired amines were obtained
in excellent yields. Reduction of nitroarenes possessing electron donating groups such as -Me, -
OMe, -OH, -CH OH, -NH as well as 1-nitronaphthalene and 4-nitrobiphenyl were performed
2
2
and the expected products were obtained in high to excellent yields (Table 2, entries 1-20).
Generally, results showed that electron rich nitroarenes reacted much more slowly than the
substrates with electron deficient ones. Furthermore, reduction of 2-nitropyridine proceed well
affording 2-aminopyridine in 90% yield (Table 2, entry 21). While in the case of nitroarenes
having ketone or amido functional groups, selective reduction of nitro group were achieved
under optimized reaction condition (Table 2, entries 22-24). In the cases of high molecular
weight nitro compounds, 2wt % of TPGS-750-M as surfactant was added to the reaction mixture
affording 85-89% isolated yields (Table 1, entries 25-26). In order to show how important was
the effect of the creatine in the stabilization of Au-NPs, we prepared starch supported Au-NPs in
the absence of ligand and studied its catalytic activity. Results indicated that, in the absence of
creatine, 42% of Au was loaded on starch and also reduction of nitroarenes using starch@Au
gave lower yields than starch-crt@Au (Table 2, entries 6, 8, 10 and 16).
1
3

Table 2. Reduction of structurally different nitroarenes in the presence of starch-crt@Aua,b
NO2
starch-crt@Au(0.1 mol%)
NH2
X
X
H O:EtOH (1:1)
2
NaBH4
NH2
NH2
NH2
NH2
F
2
Cl
Br
1
. 4h <99%c
4. 4h 90%
NH2
. 2h 100%c
3. 4h 92%
NH2
NH2
NH2
I
Me
6.
MeO
H N
2
h 100%c
91%)c,e
5. 6h 91%
8.
4
(
4h 90%
(40%)e
7
. 7h 90%
H N
2
NH2
NH2
NH2
NH2
HO
HO
HO
NH2
0. 4h 80%
32%)e
1
2. 4h 89%
9
. 2h 95%
11. 4h 94%
1
(
NH2
OH
3. 6h 87%
NH2
NH2
NH2
Cl
NO2
4. 4h 90%
H N
2
1
5. 4h 90%
16. 4h 87%d
61%)e
1
1
(
NH2 HO
NH2
NH2
OH
NH2
18. 3h 90%
19. 7h 86%
17. 4h 85%
20. 4h 85%
1
4

O
O
O
N
N
N
NH2
H N
2
H N
2
H N
2
21. 7h 90%
22. 4h 93%
23. 4h 98%
24. 4h 87%
NH2
Cl
H
H
N
N
N
N
O
2
5. 6h, 85%f
NH2
Cl
2
6. 6h, 89%f
a
Nitroarene (0.5 mmol), starch-crt@Au (0.1 mol%), NaBH (5 equiv), H O:EtOH (1:1, 2 mL),
4
2
at room temperature.
b
Isolated products.
c
GC yield.
d
Using 10 equivalent of NaBH4.
e
Nitroarene (0.5 mmol), starch@Au (0.1 mol%), NaBH (5 mmol), H O:EtOH (1:1, 2 mL), at
4
2
room temperature.
f
Reaction performed using 2wt % of TPGS-750-M as a surfactant
It should be noted that in the case of nitroarenes having a formyl group such as m and p-
nitrobenzaldehydes carbonyl group was reduced to alcohol selectively whilst the nitro group
remained intact under optimized reaction conditions. However, using 10 equivalents of NaBH4
both aldehyde and nitro functional groups were conveniently reduced (Table 3).
Table 3. Reduction of m and p-benzaldehydes using starch-crt@Au
H
starch-crt@Au (0.1 mol%)
C
O
Product
H O:EtOH (1:1, 2 mL), r.t.
2
O N
2
NaBH , 4 h
4
1
5

Substrate
Product
Yield(%)a
90b
O
OH
H
O N
2
O N
2
H
O
OH
7
0b
O N
2
O N
2
O
OH
91c
H
O N
2
H N
2
H
O
OH
8
9c
O N
2
H N
2
a
b
c
GC yield.
Using 5 equivalents of NaBH4
Using 10 equivalents of NaBH4
The rates of the reduction for the three isomers of nitroaniline were also studied under
optimized reaction conditions and the following rate order was: 3-nitroaniline > 4-nitroaniline >
2
-nitroaniline (Figure 10). This result may be explained by the conjugation effect caused by
electron donating groups. Both para- and ortho-isomer can delocalize electrons onto the nitro
group and the reduction reaction rate can diminish. The ortho-isomer exhibited the lowest
reactivity because of its steric effect.
1
6

Figure 10. Reduction rates for nitroaniline isomers.
The recovery and reusing of heterogeneous catalysts are highly important since the
environmental and economical points of view. Here, the recycling of starch-crt@Au in the
reduction of 4-nitrotoluene under optimized reaction conditions is evaluated. Result showed that
catalyst was recycled for 12 consecutive runs with negligible loss of activity (Figure 11).
However, from run 13 to 16, the yield of desired product decreased to 87%. For highlighting
essential rule of creatine ligand on stabilization of Au NPs and reactivity of the catalyst, we also
studied recycling of starch@Au on the same reaction. The results of this study revealed that the
th
yield of the reaction decreased to 40% in the 6 catalytic cycle (Figure 12). Furthermore,
leaching of Au from starch-crt@Au and starch@Au in run 6 was investigated by AAS. Results
indicated that 20% and 97% leaching occurred from starch-crt@Au and starch@Au,
respectively. These facts confirmed the crucial role of creatine in the stabilization of Au
nanoparticles.
NO2
NH2
starch-crt@Au (0.1 mol%)
Me
H O:EtOH, NaBH
Me
2
4
r.t.
1
7

Figure 11. Recycling study of the catalyst starch-crt@Au during the reduction of 4-
nitrotoluene.
NO2
NH2
Starch@Au (0.1 mol%)
Me
H O:EtOH, NaBH
2
4
Me
r.t.
Figure 12. Recycling study of the starch@Au during the reduction of 4-nitrotoluene.
th
XPS spectra of the reused catalyst (starch-crt@Au) after 6 runs showed the preservation of
Au(0) oxidation state and also the presence of N, C and Si species similar to fresh catalyst
th
(
Figure 13). Also, TEM images of reused catalyst after 6 runs showed the presence of almost
uniform Au-NPs with average particle-size of 3.8 nm (Figure 14 and 15).
1
8

Figure 13. XPS spectra of reused catalyst starch-crt@Au a)Au b) N c) C d) Si.
th
Figure 14. TEM images of reused catalyst after 6 catalytic cycle.
1
9

th
Figure 15. Distribution diagram of Au nanoparticles in reused catalysis after 6 catalytic
cycle.
Conclusion
In summary, we have developed a highly active, resistant, chemoselective and recoverable
creatine modified starch supported gold catalyst for the reductions of nitroaromatic compounds.
Using this green catalyst, a wide range of substrates was successfully reduced to the
corresponding amines under mild conditions. In particular, the performance of the catalyst was
fully retained during its employment in several catalytic batches, and it is possible to recover it
up to twelve times without decreasing its catalytic activity. This catalyst is much more
appropriate than creatine-free starch@Au catalyst and starch-crt@Au, in terms of Au loading
during its preparation, activity and recyclability with lower Au leaching during the recycling
process.
3
. Experimental
3
.1.General remarks.
2
0

All materials were purchased from Sigma-Aldrich, Across and Merck Millipore. Reactions
1
13
were monitored by GC in a Varian CP-3800 apparatus. H NMR and C NMR spectra were
recorded at 400 MHz and 100 MHz, respectively on a Bruker Avance HD apparatus in DMSO-d6
and CDCl FT-IR studies of samples were performed using a FT-IR spectrophotometer Bruker
3
.
-1
vector 22, by preparing their KBr pellets from 400 to 4000 cm . The TEM and SEM mapping
images were captured with EOL JEM-2010 and Hitachi S3000N respectively. XPS analyses
were performed using a K-Alpha spectrometer. The weight loss of samples was measured using
-1
a thermogravimeter NETZSCH STA 409 under an O flow rate of 20 ml.min with a heating
2
-1
rate of 10 °C·min from 30 to 800 °C. Digital images of the samples were acquired with Hitachi
S4160 FE-SEM apparatus operating at 20 kV. X-Ray diffraction (XRD) was recorded using
Philips X’Pert Pro instrument.
3
.2.
Procedure for the preparation of starch@Cl
Starch (3.6 g) was sonicated in dry toluene (30 mL) for 20 minutes and then (3-
chloropropyl)triethoxysilane (10.4 mmol, 2.5 mL) was added. The resulting mixture was
refluxed at 110 C under argon atmosphere for 24 h. Then, the white suspension was separated
by centrifugation, washed with ethyl acetate (3×10 mL) and dried in an oven at 60 C.
3
.3.
Procedure for the preparation of functional starch@crt
The starch@Cl (2.5 g) was added to a flask containing xylene (15 mL) and the mixture was
sonicated for 10 min. Then, creatine (11.4 mmol, 1.5 g) and Et N (23 mmol, 3.2 mL) were added
3
and the mixture was stirred at 130 C for 24 h. Next, white solid was separated by centrifugation
washed with water (3×10 mL) and ethyl acetate (3×10 mL) and dried in the oven at 60 C.
3
.4.
Procedure for the preparation of starch-crt@Au
2
1

Starch@crt (1 g) was added to flask containing H O (10 mL) and the resulting mixture was
2
sonicated for 10 min. Then, aqueous NaAuCl .2H O solution (0.027 mmol, 11 mg in 2 mL H O)
4
2
2
was added slowly. Afterwards, aqueous NaBH (1 mmol, 37 mg in 1 mL H O) were added
4
2
slowly during 5 min and the resulting mixture was stirred for 24 h at room temperature. Then,
the solid was separated by centrifugation, washed with H O (10 mL) and ethyl acetate (3×5 mL)
2
and dried in an oven at 70 C. The loading of Au was determined using atomic absorption
spectroscopy (AAS) to be 0.0198 mmol/g indicating that a 73.3% of Au was successfully loaded.
3
.5.
General procedure for the reduction of nitro aromatic using starch-crt@Au
To a flask containing nitroarene (0.5 mmol), starch-crt@Au (0.1 mol%, 25 mg) and NaBH4
(
2.5 mmol, 45 mg), 2 mL of H O:EtOH (1:1) was added. Reaction mixture was stirred at room
2
temperature for the appropriate reaction times (see Tables 2 and 3). Progress of the reactions
1
were monitored by GC, TLC and or H NMR. After completion of the reaction, the crude
product was extracted with ethyl acetate (3×5 mL). The solvent was evaporated and the residue
was purified using column or plate chromatography.
3
.6.
Procedure for the preparation of starch@Au
A solution of starch (1 g) in H O (10 mL) was sonicated for 10 min. Then, a solution of
2
NaAuCl .2H O (0.027 mmol, 11 mg in 2 mL H O) was added slowly. Then, NaBH (1 mmol, 37
4
2
2
4
mg in 1 mL H O) were added slowly during the 5 min and resulting mixture was stirred for 24 h
2
at room temperature. Afterwards, the solid was separated by centrifugation, washed with H O (5
2
mL) and ethyl acetate and dried in the oven at 70 C. The loading of Au was found to be 0.011
mmol/g (using AAS) indicating that a 42% of Au was successfully loaded.
3
.7.
General procedure for the reduction of nitro aromatic using starch@Au
2
2

A solution of H O:EtOH (1:1) (2 mL) was added to a flask containing nitroarene (0.5 mmol),
2
starch-crt@Au (0.1 mol%, 45 mg) and NaBH (2.5 mmol, 94 mg). The reaction mixture was
4
stirred at room temperature for appropriate reaction times and the progress of the reactions were
1
monitored by GC, TLC and or H NMR. After completion of the reaction, the crude product was
extracted with ethyl acetate (3×5 mL). The solvent was evaporated and the residue purified using
column or plate chromatography.
Acknowledgements
The authors are grateful to Institute for Advanced Studies in Basic Sciences (IASBS) Research
Council and Iran National Science Foundation (INSF-Grant number of 97021804) for support of
this work. We also gratefully acknowledge financial support from the Spanish Ministerio de
Economía y Competitividad (MINECO) (projects CTQ2013-43446-P and CTQ2014-51912-
REDC), the Spanish Ministerio de Economía, Industria y Competitividad, Agencia Estatal de
Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER, EU) (projects
CTQ2016-76782-P
and
CTQ2016-81797-REDC),
the
Generalitat
Valenciana
(PROMETEOII/2014/017) and the University of Alicante.
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Graphical Abstract
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Research Highlights
A novel and green gold catalyst was prepared by simple method.
This material showed high catalytic activity for selective reduction of nitroarenes.
The catalyst recycled for several runs.
Fresh and reused catalysts were fully characterized.
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