A green recyclable poly(4-vinylpyridine)-supported copper iodide nanoparticle catalyst for the chemoselective synthesis of pentaerythritol diacetals from aromatic aldehydes

Article abstract of DOI:10.3184/174751912X13460806564901

Poly(4-vinylpyridine)-supported copper(I) iodide nanoparticles have been used as an efficient, green recyclable catalyst for the chemoselective synthesis of pentaerythritol diacetals from aromatic aldehydes and pentaerythritol under solvent-free conditions. This catalyst was reused six times without any loss of its activity.

Full text of DOI:10.3184/174751912X13460806564901

610 RESEARCH PAPER
OCTOBER, 610–611
JOURNAL OF CHEMICAL RESEARCH 2012
A green recyclable poly(4-vinylpyridine)-supported copper iodide
nanoparticle catalyst for the chemoselective synthesis of pentaerythritol
diacetals from aromatic aldehydes
Jalal Albadia*, Nasir Iravanib, Farhad Shirinic and Farzaneh Dehghanb
aCollege of Science, Behbahan Khatam Alanbia University ofTechnologhy, Behbahan, Iran
bDepartment of Chemistry, Gachsaran branch, Islamic Azad University, Gachsaran, Iran
cDepartment of Chemistry, College of Science, University of Guilan, Rasht, Iran
Poly(4-vinylpyridine)-supported copper(I) iodide nanoparticles have been used as an efficient, green recyclable cata-
lyst for the chemoselective synthesis of pentaerythritol diacetals from aromatic aldehydes and pentaerythritol under
solvent-free conditions. This catalyst was reused six times without any loss of its activity.
Keywords: poly(4-vinylpyridine)-supported, nanoparticles, copper(I) catalysis, pentaerythritol diacetals, synthetic carbohydrates,
steroid chemistry
Acetals are important in synthetic carbohydrate and steroid
chemistry. In the phytopharmaceutical, fragrance and lacquer
industries acetals are used both as intermediates and as end
products. Pentaerythritol diacetals are also used as plasticisers
and vulcanisers, physiologically active substances and as pro-
tecting groups for aldehydes and ketones.1–3 Strong protic acids
and various Lewis acids have been employed as catalysts for
the synthesis of pentaerythritol diacetals.4–11 However, many
of these procedures suffer from one or more of the following
disadvantages: toxic solvents, tedious work-up procedure, long
reaction times, low yields, corrosive reagents, effluent pollu-
tion and non-recyclable catalysts. Therefore, there is scope to
develop an alternative method for the synthesis of pentaeryth-
ritol diacetals. In recent years, nano-catalysis has emerged as a
sustainable and competitive alternative to conventional cataly-
sis since the nanoparticles possess a high surface-to-volume
ratio, which enhances their activity and selectivity.12 Nano-
materials with their large surface area and high density of
active sites, are used as heterogeneous catalysts in organic
synthesis. In particular, the immobilisation of copper(I) salts
on nanoparticles with high-surface-area supports affords a
higher stability and dispersion of the particles as well as a
further exploitation of the special activity and recycling prop-
erties of the catalyst. Recently CuI has emerged as an effective
Lewis acid catalyst for various organic transformations.13–18
However, in spite of its potential application, CuI has some
limitations such as thermodynamic instability, long reaction
times, non-recyclable, toxicity and difficulty in separation of
the product from the reaction medium. Such drawbacks could
be obviated by a supported catalyst. Nitrogen-based polymer
have been shown to protect the metal centre from oxidation
and disproportionation, while enhancing its catalytic activity.19
To improve the recovery and reuse, copper species have
been immobilised on various supports such as carbon,20 amine-
functionalised polymers,21 zeolites,22 amine-functionalised
silica and aluminum oxide/hydroxide fibre.23–24 Poly(4-vinyl-
pyridine)-supported reagents are active in various organic
reactions including oxidations, reductions and halogenations.
Simple recovery from reaction mixtures, their reusability,
compatibility with a wide range of solvents, physical stability,
and their toleration of a great number of reaction conditions
bodes well for the future of P4VPy-supported reagents where
their properties can be fine-tuned for specific chemical trans-
formations.25 Recently, we have reported the preparation of
copper iodide nanoparticles supported on poly(4-vinylpyri-
dine) (P4VPy–CuI) and their application for the click synthesis
of triazole derivatives.26–27 In continuation of these studies,
we now report the application of this reagent to the chemose-
lective synthesis of pentaerythritol diacetals from aromatic
aldehydes under solvent-free conditions (Scheme 1).
Results and discussion
The copper(I) iodide catalyst immobilised on poly(4-vinyl-
pyridine), was readily prepared in a one-step procedure. Poly(4-
vinylpyridine) was refluxed with a solution of CuI under a N2
atmosphere in EtOH for the synthesis of polymer-supported
CuI nanoparticles. This method was developed for the effec-
tive synthesis of copper nanoparticles incorporated heteroge-
neously as a catalyst in some organic reactions. 28 Optimisation
of the reaction conditions showed that the best results were
obtained under solvent-free conditions, in the presence of
0.1 g of P4VPy–CuI at 100 °C when the relative ratio of the
substrate to pentaerythritol was 2:1, respectively. A wide range
of various aromatic aldehydes were then successfully reacted
to afford the desired products. Among the various substrates
which were studied, compounds containing electron-with-
drawing groups were found to be the most reactive and were
converted to the corresponding products in shorter reaction
times. (Table 1, entries 4, 8 and 9). Because ketones were
unreactive under these conditions (Table 1, entries 16 and 17),
the reported method can be used for the chemoselective
acetalisation of aldehydes in the presence of ketones (Table 1,
entry 18).
The activity of the recovered catalyst was also examined
under the optimised conditions and the desired product was
obtained in high yields after 1–6 runs (Table 2) using the
reaction of benzaldehyde with pentaerythritol as the model
(Table 2). After the reaction was completed the P4VPy–CuI
was washed with ethylacetate, dried and stored for another
reaction. This process was repeated for six runs and no appre-
ciable decrease in the yield was observed. Next we checked the
leaching of CuI into the reaction mixture from the poly(4-
vinylpyridine) support using ICP-AES. The difference between
the copper content of the fresh and reused catalyst (sixth run)
Scheme 1 Synthesis of pentaerythritol diacetals catalysed by P4VPy–CuI.
* Correspondent. E-mail: Chemalbadi@gmail.com

JOURNAL OF CHEMICAL RESEARCH 2012 611
Table 1 P4VPy–CuI catalysed synthesis of pentaerythritol
In conclusion, we have descibed a new, green and efficient
procedure for the chemoselective synthesis of pentaerythritol
diacetals catalysed by P4VPy–CuI under solvent-free condi-
tions. This catalytic system is stable and can promote the
yields and reaction times over six runs without loss of activity.
Moreover, the heterogeneous reaction conditions, high yields
of products, short reaction times, ease of work-up and clean
procedure, could make this procedure a useful addition to the
available methods.
diacetals
Entry
Substrate
Time Yield
M.p./°Cb
/min
/%a
Found Reported7–11
1
2
PhCHO
25
20
25
20
25
30
25
25
15
60
60
50
25
45
60
95
93
92
92
91
92
94
93
93
86
85
86
89
85
87
153–154
140–141
120–122
198–200
189–191
209–211
163–165
183–185
226–228
180–182
109–111
160–162
221–223
157–159
223–224
155–156
141–142
121–122
196–197
190–191
211–212
162–164
185–186
226–227
180–182
108–110
160–161
222–224
157–159
223–224
2-ClPhCHO
3
3-ClPhCHO
4-ClPhCHO
4
5
3-MePhCHO
4-MePhCHO
2-NO2PhCHO
3-NO2PhCHO
4-NO2PhCHO
4-MeOPhCHO
4-HOPhCHO
2-HOPhCHO
4-BrPhCHO
2-Furaldehyde
4-Me2NPhCHO
6
Experimental
7
Chemicals were purchased from the Fluka, Merck and Aldrich Chem-
ical Companies .All the products were characterised by comparison of
their spectroscopic data (1H NMR and IR) and physical, properties
with those reported in the literature. The IR spectra were recorded on
a Perkin-Elmer 781 Spectrophotometer. All the NMR spectra were
recorded on a Bruker Avance 400 MHz. Melting points were recorded
on a Bransted Electro thermal 9100BZ melting point apparatus.Yields
refer to isolated pure products.
8
9
10
11
12
13
14
15
General procedure
16
45
0c
–
111–113
A mixture of the aldehyde (2 mmol), pentaerythritol (1 mmol) P4VPy–
CuI (0.1 g) was heated in an oil bath (100 °C) for the appropriate time
(Table 1). After completion of the reaction, as shown by TLC, the
reaction mixture was cooled to room temperature and ethyl acetate
(5 mL) was added to the mixture which was filtered. The catalyst was
washed with ethyl acetate, dried and stored for another reaction run.
Evaporation of the solvent from the filtrate and recrystallisation of the
solid residue from hot ethanol afforded the pure products in high
yields.
17
18
Ph2CO
PhCHO
+
60
30
0c
100d
+
–
163–164
155–156
153–154
Ph2CO
0d
a Isolated yield. b Products were characterised by comparison of
their spectroscopic data (NMR and IR) and melting points with
those reported in the literature7–11. c Starting material recovered
intact. d Conversion.
We thank the Behbahan Khatam Alanbia University of
Technology for partial support of this work.
Table 2 Re-use of P4VPy–CuI
Received 12 July 2012; accepted 11 August 2012
Paper 1201410 doi: 10.3184/174751912X13460806564901
Published online: 28 September 2012
Run
Time/min 25
Yield/%a
95
1
2
25
95
3
28
93
4
30
93
5
40
90
6
45
90
a Isolated yield
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Entry
Reagent
Conditions
Toluene/reflux
100 °C
Time Yield Ref.
/min
/%a
92
1
2
H3PW12O4
120
9
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3
4
NH2SO3H
H3PW12O4 suported Toluene/reflux
on MCM-41
Toluene/110 °C 240
96
92
7
120
10
5
6
FeSO4
P4VPy–CuI
Benzene/reflux
Solvent-free
/100 °C
90
25
97
8
95 This
work
a Isolated yield

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