Synthesis, Characterization and Catalytic Application of Starch Supported Cuprous Iodide Nanoparticles

Article abstract of DOI:10.1007/s10562-019-02909-1

Abstract: The starch supported cuprous iodide nanoparticles (CuI-NPs@Starch) were synthesized in aqueous medium and characterized by transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, energy-dispersive X-ray spectros

Full text of DOI:10.1007/s10562-019-02909-1

Catalysis Letters
https://doi.org/10.1007/s10562-019-02909-1
Synthesis, Characterization and Catalytic Application of Starch
Supported Cuprous Iodide Nanoparticles
Sadhucharan Mallick1 · Priyabrata Mukhi2 · Poonam Kumari3 · Kumari Reshmi Mahato3 · Suryadev Kumar Verma3 ·
Debjit Das4
Received: 17 February 2019 / Accepted: 19 July 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
The starch supported cuprous iodide nanoparticles (CuI-NPs@Starch) were synthesized in aqueous medium and character-
ized by transmission electron microscopy, scanning electron microscopy, X-ray powder difraction, energy-dispersive X-ray
spectroscopy and atomic absorption spectra analysis. The newly synthesized CuI NPs on starch have been demonstrated frst
time as an efcient catalyst for the regioselective 3-allylation reaction of N-substituted indoles as well as ring-substituted
indoles using various allyl alcohols under moisture and air insensitive conditions.
Graphic Abstract
Keywords Nanocatalysis · CuI NPs · Allylation · Indole · Allylic alcohol
1 Introduction
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-019-02909-1) contains
supplementary material, which is available to authorized users.
In recent years, nanocatalysis has become an emerging feld
of science with the benefts of excellent activity, selectivity
and productivity [1–5]. The nanoscale size, shape and excep-
tionally large surface area to volume ratio of nanocatalysts
impart distinct catalytic properties, which diferentiates them
from the bulk materials [1–10]. Among the various metallic
nanoparticles, copper-based nanoparticles are comparatively
inexpensive, environment-friendly and easily available. As
a consequence, they have received tremendous attention in
the feld of organic transformation and fne chemical syn-
thesis [6–10]. In this regard, cuprous iodide nanoparticles
* Debjit Das
debjitofchem@gmail.com
1
Department of Chemistry, Indira Gandhi National Tribal
University, Amarkantak, India
2
School of Basic Sciences, Indian Institute of Technology,
Bhubaneswar, India
3
Centre for Applied Chemistry, Central University
of Jharkhand, Ranchi, India
4
Department of Chemistry, Triveni Devi Bhalotia College,
Raniganj, India
Vol.:(0123456789)
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S. Mallick et al.
Scheme 1 Schematic representation of the procedure used for the
synthesis of CuI-NPs@starch
(CuI NPs) have been extensively explored recently as highly
selective catalysts in many reactions including synthesis of
phenols, anilines, and thiophenols, carbon-heteroatom bond
forming coupling reactions, multi-component synthesis
and related reactions [7, 11–18]. Hence, the development
of highly selective and efcient strategies for the synthe-
sis of these CuI nanoparticles has captured wide attention.
Recently, several physical methods (such as electrodepos-
iting, pulse laser deposition, vacuum evaporation etc.) as
well as diferent chemical methods (such as the liquid phase
reaction, low temperature solvothermal synthesis, co-pre-
cipitation, and precipitation method) have been reported to
prepare cuprous iodide [19]. Nevertheless, fnding a new
route for green and facile preparation of the cuprous iodide
nanoparticles remains undoubtedly attractive and formidably
challenging. Herein, we presented a new route for the syn-
thesis of starch supported1 CuI NPs in water under ambient
conditions. The starch supported CuI nanoparticles (CuI-
NPs@Starch) have been successfully employed in the regi-
oselective 3-allylation reaction of indoles using allyl alco-
hols. In this context, one may note that a very few transition
metal salts, Lewis acids and Brønsted acids are applicable as
catalysts in these reactions [25–33]. Most of these protocols
are although efcient, a few of them sufer from the draw-
backs of high catalyst loading, requirement of extra additives
etc. It may be emphasized here that, to the best of our knowl-
edge, this is the frst example where this type of reaction has
been studied in presence of CuI NPs only.
Fig. 1 Powder XRD pattern of starch supported CuI nanoparticles
Cu(0) NP was converted to CuI NP. The details of the syn-
thesis are given in the experimental Section.
The XRD pattern of CuI-NPs@starch is shown in
Fig. 1, indicated the occurrence of difraction at 2θ values
of 25.88°, 29.97°, 42.59°, 50.30°, 52.79°, 61.58°, 67.89°,
69.69°, 77.57° and 83.21° which were indexed as due to dif-
fraction from (111), (200), (220), (311), (222), (400), (331),
(420), (422) and (511) planes, respectively, of face centered-
cubic (fcc) crystal planes of CuI. The XRD pattern of the
CuI-NPs@Starch was matched with the standard powder
difraction data fle for CuI (face-centered cubic, JCPDS fle
No. 06-0246). No other difraction peaks were arising from
metallic Cu or cupric oxide (CuO) or cuprous oxide (Cu2O)
in the XRD pattern and indicated the high phase purity of
the as-prepared sample.
In order to obtain the detailed information about the
microstructure, morphology and size of the newly syn-
thesized sample, FESEM observations are carried out and
shown in Fig. 2a, b. FESEM image showed the deposition of
spherical nano-sized CuI crystals with average particle size
of 56.96 7.60 nm on starch. The particle size and distribu-
tion were represented by the histogram shown in Fig. 2c.
The presence of copper and iodine was confrmed during
FESEM analysis by energy dispersive X-ray (EDX) spec-
trum (Fig. 2d).
The morphology and size of CuI NPs were further con-
frmed by transmission electron microscopy (TEM) meas-
urements. TEM images (Fig. 3a, b) clearly indicated the for-
mation of spherical CuI NPs on the starch polymer matrix.
The TEM image (Fig. 3a) also pointed out that most of the
particles were between 45 and 65 nm which is corroborated
to FESEM analysis. HRTEM image of a single particle
(Fig. 3b) as well as selected area electron difraction (SAED)
pattern (Fig. 3c) obviously specifed crystalline nature of
the CuI NPs. Further, EDX analysis (Fig. 3d) was also car-
ried out during TEM analysis confrmed the presence of Cu
and I elements. Copper content in the prepared sample was
estimated by atomic adsorption analysis (AAS) and it was
found to be 11% (w/w).
2 Results and Discussion
The preparation method of CuI-NPs@Starch is straightfor-
ward and can be operated in simple laboratory equipments,
as shown in Scheme 1. Briefy, at frst the alkaline solution
of copper(II) sulphate pentahydrate and starch were treated
with reducing agent hydrazine hydrate to generate in situ
Cu(0) NPs [34]. After that in presence of excess iodide, this
1
Environmental friendly polysaccharides, such as chitosan, cellulose
and agarose are currently being explored as support materials for cat-
alyst systems. Please see the Refs. [20–24].
1 3

Synthesis, Characterization and Catalytic Application of Starch Supported Cuprous Iodide…
Fig. 2 a FESEM image of starch supported CuI NPs. b High resolution FESEM image of starch supported CuI NPs. c Size distribution of starch
supported CuI NPs from FESEM images. d FESEM-EDX spectrum of CuI-NPs@Starch
Indoles are imperative structural motifs of numerous bio-
logically and pharmaceutically active compounds [35–37].
Regioselective allylic alkylation at the 3-position of indoles
by the nucleophilic substitution of π-activated electrophiles
(RY, such as alcohols, acetates and carbonates) is a direct
approach for the synthesis of many naturally occurring
indole alkaloids and potent HIV inhibitors (Scheme 2) [27,
29, 31].
catalytic efciency of 10 mol% CuI-NP@Starch in acetoni-
trile as the solvent giving a yield of 74% only C-3 allylated
product 3-(1,3-diphenyl-allyl)-1H-indole (3a) at 90 °C after
2 h (Table 1, entry 2). For comparison, the catalytic ef-
ciency of bulk CuI (15 mol%) in acetonitrile solvent is stud-
ied and no product as formed. Based on the catalytic activity
of CuI-Np@Starch in various solvents, acetonitrile is judged
as the best solvent over tetrahydrofuran, trichloromethane or
toluene (Table 1). The obtained results were also compared
with diferent available commercial bulk copper catalysts
with 15 mol% loading (Table 1, entries 8–12) and it was
observed that starch supported CuI NPs catalyst exhibited
superior activities. The optimum catalyst loading was found
to be 10 mol%. Reduction of catalyst loading from 10 to
5 mol% drastically reduced the yield of the reaction (entry
3, Table 1).
Notably, the electrophiles like acetates and carbonates
used in these reactions are normally derived from the cor-
responding alcohols. Therefore, direct coupling of indole
with allyl alcohols would be synthetically attractive and
environmentally benign due to readily availability and lower
toxicity of alcohols (compared to other alkylating agents
like acetates etc.). Moreover only stoichiometric amounts
of water are generated as the by-product. But the major dif-
fculty in the direct allylation reaction is the inertness of the
OH group. In view of the importance of alcohol activation
[27] and encouraged by the catalytic efcacy of the copper-
based nanoparticles, [6–10] we became interested to study
the activation of alcohols across CuI-NPs@Starch system.
For model studies, we have chosen the reaction between
1, 3-diphenyl-prop-2-en-1-ol (1a) and indole (2a). The
Attracted by the direct allylation of indole (2a), we
extended the coupling of various allylic alcohols with a
variety of N-substituted (alkyl-, benzyl-, allyl-, propargyl-)
indoles and ring-substituted indoles, which led to efcient
carbon–carbon bond formation at 90 °C in MeCN (Fig. 4).
Signifcantly, with free indoles, the reactions were com-
pletely C3-selective, with no N-alkyl product being formed.
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S. Mallick et al.
Fig. 3 a TEM micrograph of CuI-Np@Starch. b HRTEM micrograph of CuI-NPs@Starch. c Selected area difraction (SAED) pattern of CuI-
NPs@Starch. d TEM–EDX spectrum of CuI-NPs@Starch
studies using a representative alcohol PhCH=CCH(Ph)OH
(1a). The spectrum of 1a was recorded in CD3CN solvent in
presence as well as in absence of catalyst CuI-NPs@Starch.
In the absence of catalyst, alcohol 1a showed a triplet at
5.30 ppm (J=4.8, 5.6 Hz) for allylic proton and a doublet
Scheme 2 Nucleophilic substitution of π-activated electrophiles (RY)
at 3.56 ppm (J=4.0 Hz) for –OH proton. After addition of
with indole
the catalyst and heating at 85 °C for 30 min, the initial tri-
plet of the allylic –CH proton of 1a was converted to a well
resolved doublet (J=6.4 Hz) at 5.30 ppm, while the –OH
proton became a broad singlet (see supplementary material).
From these observations we believe that in the initial stage
of the cycle, the alcohol could be activated by the catalyst
[38].
It was also observed that allylation of indole proceeded best
with electron-rich alcohols, whereas electron-defcient allyl
alcohols were less efective. However, the catalyst was not
very active after the frst reaction and was not recyclable.
Copper content of the recovered catalyst showed 1.6% (w/w)
from the AAS analysis which indicates substantial amount
of leaching of catalyst in solution.2
Although detailed mechanistic studies must be awaited,
on the basis of the above results, we propose that an electro-
philic mechanism may be operating in the present allylation
of indole (Fig. 5). The proposal invokes prior activation of
allyl alcohol via coordination with the CuI NPs, followed by
the nucleophilic attack of indole and a subsequent aromati-
zation by deprotonation to furnish corresponding 3-allylated
indole [38, 39].
To gain preliminary insight into the initial activation of
1
allyl alcohol by CuI NPs, we undertook in situ H NMR
2
The non-reusability of catalyst may also be caused by the degra-
dation of the starch polymer. We thank one of the reviewers for this
insightful suggestion.
1 3

Synthesis, Characterization and Catalytic Application of Starch Supported Cuprous Iodide…
Table 1 Catalysts screening
Entry
Catalyst (mol%)
Solvent
Yield of 3a (%)
1
–
MeCN
MeCN
MeCN
Toluene
CHCl3
THF
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
Nil
74
18
Trace
67
Nil
Nil
18
11
10
Trace
32
2
CuI-NPs@Starch (10 mol%)
CuI-NPs@Starch (5 mol%)
CuI-NPs@Starch (10 mol%)
CuI-NPs@Starch (10 mol%)
CuI-NPs@Starch (10 mol%)
Bulk CuI (15 mol%)
CuBr (15 mol%)
CuO (15 mol%)
Cu2O (15 mol%)
Cu(OAc)2 (15 mol%)
CuSO4·5H2O (15 mol%)
3a
4
5
6
7
8
9
10
11
12
A mixture of 1a (0.3 mmol), 2a (0. 25 mmol), and catalyst in 2 mL of MeCN was stirred at 90 °C for 2 h. Only starting materials were obtained
after 2 h when the model reaction was performed with starch (30 mg) as catalyst
aThe reaction was carried out for 12 h
difractometer using Cu Kα radiation (λ=1.5406 Å). Field-
emission scanning electron microscopy (FESEM) measure-
ments were made in a Zeiss Merlin compact instrument.
Transmission electron microscopy (TEM) was performed
using a JEM 2100 instrument at an accelerating voltage of
200 keV. The chemical composition of the prepared nano
structures was measured by energy dispersive X-ray spec-
troscopy (EDS) performed in SEM and TEM.
3 Conclusion
In conclusion, we have reported the preparation, charac-
terisation as well as use of starch supported CuI nanopar-
ticles (CuI-NPs@Starch) as a new catalyst in regioselec-
tive 3-allylation reaction of indoles with allyl alcohols.
While the exact nature of the active catalyst remains to
be established, preliminary spectroscopic investigations
suggested the activation of alcohol by the catalyst. Fur-
ther work is now underway in our laboratory to broaden
the scope of this new catalyst and to better understand its
mechanism.
4.2 Preparation of CuI‑NPs@starch
Starch stabilized CuI NPs were synthesized under normal
atmospheric conditions. For this, 400 mg of starch and
160 mg of copper(II) sulphate pentahydrate were added
to 50 mL Milli-Q grade water in a 100 mL round bottom
fask placed in an oil bath with vigorous stirring at 85 °C
for 20 min, resulting in a light blue coloured solution. To
this solution 0.8 mL of 50 mM NaOH was added and stirred
for 30 min, followed by the addition of 0.4 mL hydrazine
hydrate. The solution became reddish brown indicating the
formation of Cu(0) NPs. After 15 min, 7 mL of an aqueous
4 Experimental
4.1 Materials and Methods
Copper(II) sulphate pentahydrate, starch and other reagents
were purchased from common commercial sources and were
used without further purifcation. X-ray powder difraction
(XRD) data were collected on Bruker D8 advance powder
1 3

S. Mallick et al.
Fig. 4 Substrate scope of the
direct allylation of indoles
solution of KI + I2 (prepared by dissolving 2 g of KI and
635 mg of I2 in 10 mL of water) was added to this red col-
oured solution over a period of 60 min and the solution stirred
for overnight at 85 °C. The red coloured solution gradually
faded to of white colour which indicated the grown of CuI
NPs. These of white particles were washed several times
with deionized water followed by centrifugation. Then it was
recovered and dried at 60 °C in hot air oven for 12 h.
4.3 General Procedure for the Catalytic Allylation
of Indole
A mixture of allylic alcohol (0.3 mmol), indole (0.25 mmol),
and CuI-NPs@Starch (10 mol%) in 2 mL of acetonitrile was
stirred at 90 °C. Following completion (vide TLC), the reac-
tion mixture was fltered and the solvent was evaporated
under reduced pressure. The residue was subjected to col-
umn chromatography (eluting with 2–10% EtOAc/petroleum
ether) to give rise to the allylated indole.
1 3

Synthesis, Characterization and Catalytic Application of Starch Supported Cuprous Iodide…
Fig. 5 Plausible mechanism of
allylation of indoles
16. Safaei-Ghomi J, Akbarzadeh Z (2015) Ultrason Sonochem 22:365
Acknowledgements D.D. acknowledges the fnancial support (project
ref. No. YSS/2015/001425) from Science & Engineering Research
Board (SERB), New Delhi. Also, D.D. is highly grateful to Dr. Asish
Kumar Dey (Principal, TDB College, Raniganj) for support and
encouragement.
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