H3PW12O40-[bmim][FeCl4]: A novel and green catalyst-medium system for microwave-promoted selective interconversion of alkoxymethyl ethers into their corresponding nitriles, bromides and iodides

Article abstract of DOI:10.1016/j.crci.2010.03.015

In the present work, the catalytic activity of 12-tungstophosphoric acid immobilized on [bmim][FeCl₄] ionic liquid as a highly efficient and eco-friendly catalytic system for rapid and chemoselective direct conversion of MOM- or EOM-ethers into their corresponding nitriles, bromides and iodides under microwave irradiation is reported. In these reactions, the products are obtained in high yields. The catalyst exhibited remarkable reactivity and was reused several times.

Full text of DOI:10.1016/j.crci.2010.03.015

C. R. Chimie 13 (2010) 1468–1473
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Full paper/Memoire
H3PW12O40–[bmim][FeCl4]: A novel and green catalyst-medium system
for microwave-promoted selective interconversion of alkoxymethyl
ethers into their corresponding nitriles, bromides and iodides
*
**
Iraj Mohammadpoor-Baltork , Majid Moghadam , Shahram Tangestaninejad,
Valiolah Mirkhani, Arsalan Mirjafari
Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746-7344, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
In the present work, the catalytic activity of 12-tungstophosphoric acid immobilized on
[bmim][FeCl4] ionic liquid as a highly efficient and eco-friendly catalytic system for rapid
and chemoselective direct conversion of MOM- or EOM-ethers into their corresponding
nitriles, bromides and iodides under microwave irradiation is reported. In these reactions,
the products are obtained in high yields. The catalyst exhibited remarkable reactivity and
was reused several times.
Received 30 January 2010
Accepted after revision 24 March 2010
Available online 11 May 2010
Keywords:
Methoxymethyl ether
Interconversion
ß 2010 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Microwave irradiation
H3PW12O40@[bmim][FeCl4]
1. Introduction
pharmaceutical and food industries [17]. Heteropoly acids
have many advantages over liquid acid catalysts such as
Catalysts play a great role in organic laboratories and
industries. In comparison with homogeneous catalysts,
heterogeneous catalysts have several advantages, such as
facile recovery from the reaction mixture and possibility of
reusing them. Furthermore, chemical stability and reactiv-
ity of heterogeneous catalysts efficiently increases [1]. One
way for improving the properties of homogeneous
catalysts [2,3] is their immobilization on solid supports
[4–9] and in ionic liquids [10–13].
Heteropoly acids (HPAs) as transition metal oxygen
anion clusters belong to a class of solid acid catalysts
having both redox and acid properties [14–16]. These solid
acids have enormous potential for catalyzing a wide
variety of reactions and also have been developed for the
synthesis of fine chemicals such as flavorings, and in the,
higher acid strength and thermal stability. They are non-
corrosive, environmentally benign, commercially available
and reusable. Among the heteropoly acids, 12-tungstopho-
sphoric acid, H3PW12O40, is the most widely used catalyst
due to its high acid strength, good thermal stability and
low reducibility [16].
Application of ionic liquids (ILs) has increased signifi-
cantly in the chemical research area [18–31].
Dissolving of organometallic complexes in supported
films of ionic liquids (SILP) has recently been introduced as
a strategy for immobilization of molecular catalysts in a
widely tailorable environment [32]. Due to the ionic nature
of ILs, these compounds are good microwave energy
absorbers and therefore, the reaction under MW irradia-
tion can be performed at a temperature higher than normal
heating. On the other hand, ILs are ideal for use in
microwave-promoted synthesis due to their negligible
vapor pressure and high thermal stability [33].
* Corresponding author.
The direct conversion of protected alcohols to other
functional groups is suitable for further chemical elabora-
tion and is a useful tool for synthetic chemists [34]. Nitriles
** Co-corresponding author.
E-mail addresses: imbaltork@sci.ui.ac.ir (I. Mohammadpoor-Baltork),
moghadamm@sci.ui.ac.ir (M. Moghadam).
1631-0748/$ – see front matter ß 2010 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crci.2010.03.015

I. Mohammadpoor-Baltork et al. / C. R. Chimie 13 (2010) 1468–1473
1469
Scheme 1.
are useful intermediates for conversion to various func-
2.3. Preparation of H3PW12O40 immobilized on
[bmim][FeCl4], H3PW12O40@[bmim][FeCl4]
tional groups and construction of N-heterocycles [35].
Furthermore, bromides and iodides are important and
versatile intermediates for alkylation reactions and also
for preparation of alkylmetal salts such as Grignard
reagents [36]. There are numerous methods for the
preparation of nitrile, bromide and iodide containing
compounds in the literature; however, to the best of our
knowledge, this is the first report of the synthesis of
nitriles, bromides and iodides by direct conversion of
alkoxymethyl ethers.
Recently, we reported the use of bulk and supported
H3PW12O40 as active catalysts for the protection/deprotec-
tion of alcohols [37,38]. Here, we report the direct
conversion of methoxymethyl (MOM) and ethoxymethyl
(EOM) ethers to their corresponding nitrile, bromides and
iodides using H3PW12O40 (HPW) immobilized on 1-butyl-
3-methylimidazolium tetrachloroferrate, [bmim][FeCl4],
under microwave irradiation (Scheme 1).
In a round bottom flask, H3PW12O40 (5 mol%) was added
slowly to highly pure [bmim][FeCl4] (0.5 mL) and stirred
roughly. To ensure complete homogenisation, the mixture
was left stirring overnight. The catalyst was dried under
reduced pressure and stored under N2.
2.4. General procedure for interconversion of MOM- and
EOM- ethers into their nitriles, bromides and iodides under
MW irradiations
A
mixture of EOM- or MOM-ether (1 mmol),
[Bu4N][X] (X = CN, Br and I) (2 mmol) in H3PW12O40@[b-
mim][FeCl4] (0.5 mL) was exposed to microwave irradi-
ation (170 W, 130–142 8C) for the appropriate time. After
completion of the reaction, indicated by TLC, water
(10 mL) was added and the organic materials were
extracted with diethyl ether (3 Â 10 mL). The organic
layer was dried over anhydrous Na2SO4. Evaporation of
the solvent and purification on a short pad of silica gel
(eluent: n-hexane/ethyl acetate, 5/1) gave the highly
pure products.
2. Experimental
2.1. Materials and methods
All materials were purchased from Merck and Sigma–
Aldrich chemical companies and were used without
further purification. The products were identified by
comparison of their spectral and physical data with those
of authentic samples. All the reactions were monitored by
TLC and all yields refer to the isolated products. 1H NMR
spectra were recorded on a Bruker–AC500P at 500 MHz. IR
spectra were obtained by IR–435 Shimadzu spectropho-
tometer using KBr or sodium chloride pellets.
The microwave system used for these experiments
includes the following items: Micro–SYNTH labstation,
complete with glass door, dual magnetron system with
pyramid–shaped diffuser, 1000 W delivered power, ex-
haust system, magnetic stirrer, ‘‘quality pressure’’ sensor
for flammable organic solvents, ATCFO fiber optic system
for automatic temperature. During experiments, power,
temperature, time and pressure monitored and controlled
with the ‘‘easyCONTROL’’ software.
2.4.1. Selected spectroscopic data
2.4.1.1. Phenylacetonitrile (Table 2, entry 1). Oil, IR (KBr)
(cmÀ1) 3120, 3035, 2921, 2252, 1603, 1588, 1496, 1455,
1416, 1338, 735, 690, 615; 1H-NMR (500 MHz, DMSO):
(ppm) 3.87 (s, 2H), 7.47–7.67 (m, 5H); 13C NMR (125 MHz,
CDCl3): (ppm) 23.8, 118.2, 128.5, 129.1, 130.1.
n
d
d
2.4.1.2. 2-(4-Methoxyphenyl)acetonitrile (Table 2, entry
7). Oil, IR (KBr)
(cmÀ1) 2942, 2903, 2247, 1600, 1566,
1457, 1291, 1089, 1071, 1030, 840, 808, 690, 615; 1H-NMR
(500 MHz, DMSO): (ppm) 3.75 (s, 3H), 3.90 (s, 2H), 6.95
(d, J = 10.32 Hz, 2H), 7.30 (d, J = 9.18 Hz, 2H); 13C-NMR
n
d
(125 MHz, DMSO):
129.4, 159.1.
d (ppm) 22.0, 55.8, 114.9, 119.6, 122, 9,
2.4.1.3. Cinammonitrile (Table 2, entry 16). Oil, IR (KBr)
(cmÀ1) 3028, 2916, 2200, 1618, 1576, 1495, 1448, 1207,
966, 748, 688; 1H-NMR (500 MHz, DMSO):
(ppm) 4.01 (d,
J = 16.65 Hz, 1H), 7.40–7.47 (m, 6H); 13C NMR (125 MHz,
CDCl3): (ppm) 23.4, 96.4, 118.2, 127.5, 129.1, 131.3,
n
d
2.2. Preparation of [bmim][FeCl4]
d
In a round bottom flask equipped with a magnetic
stirrer, anhydrous FeCl3 (16.22 g, 0.1 mol) were slowly
added to 1-butyl-3-methylimidazolium chloride (17.47 g,
0.1 mol). To ensure complete reaction, the reaction
mixture was left stirring overnight. A red-brown liquid
was obtained which was dried under high vacuum and
stored under N2.
133.8, 150.5.
2.4.1.4. 1-Bromooctane (Table 2, entry 19). Oil, IR (KBr):
n
(cmÀ1) 2933, 2874, 2839, 1512, 1436, 1379, 1286, 1217,
1039, 908, 740, 642, 561; 1H NMR (500 MHz, CDCl3):
d
(ppm) 0.89 (t, J = 8.37 Hz, 3H), 1.28–1.44 (m, 10H),

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I. Mohammadpoor-Baltork et al. / C. R. Chimie 13 (2010) 1468–1473
1.80–1.89 (m, 2H), 3.38 (t, J = 8.37 Hz, 2H); 13C NMR
[bmim][NTf2] gave a low yield of the product in the model
reaction (Table 2, entries 1–4). Another disadvantage of
[bmim][PF6] is instability of the [PF6]À anion toward
hydrolysis in contact with moisture, forming HF and POF3,
which can dissolve glassware and damage steel autoclaves
and reactors [39].
It is noteworthy that ionic liquids with inherent Lewis
acidity resulted in the formation of the desired product in
high yields (Table 2, entries 5 and 6). Using a room
temperature Lewis acid ionic liquid, [bmim][FeCl4],
(Table 2, entry 6) better result was obtained in comparison
with [bmim][AlCl4] (Table 2, entry 5). The advantage of
iron (III) chloride compared to aluminium (III) chloride is
its hydrolytic stability and higher Lewis acidity strength.
By combining the iron (III) chloride with an organic halide
salt, room temperature ionic liquids with good solvating
ability and negligible vapor pressure can be prepared
which are inherently Lewis acidic and water stable in
contrast to the analogous chloroaluminate system
[40,41].
(125 MHz, CDCl3):
32.6, 35.2.
d (ppm) 14.2, 22.6, 27.8, 28.5, 28.9, 31.7,
2.4.1.5. 1-Iodooctane (Table 2, entry 19). Oil, IR (KBr):
n
(cmÀ1) 2926, 2871, 2732, 1466, 1378, 1349, 1288, 1246,
1204, 1170, 1065, 906, 897, 781, 721, 699, 508; 1H NMR
(300 MHz, CDCl3):
d (ppm) 0.82 (t, J = 6.30 Hz, 3H), 1.21–
1.34 (m, 10H), 1.71–1.80 (m, 2H), 3.11 (t, J = 5.94 Hz, 2H).
13C NMR (75 MHz, CDCl3):
29.1, 30.5, 31.8, 33.6.
d (ppm) 6.6, 14.1, 22.5, 28.5,
3. Results and discussion
3.1. Optimization of reaction conditions
To obtain the optimized reaction conditions, the
reaction of benzylmethoxymethyl ether with tetrabuty-
lammonium cyanide, [Bu4N][CN], in the presence of a
catalytic amount of H3PW12O40@[bmim][FeCl4], was
chosen as a model reaction. The best results obtained
with the 1:2:0.005 molar ratio of benzylmethoxymethyl
ether, [Bu4N][X] (X = CN, Br and I) and H3PW12O40@[b-
mim][FeCl4], respectively, under microwave irradiation
(170 W, 135–140 8C). In this reaction 0.5 mL of ionic liquid
was used as support and medium. The same reaction was
also carried out under thermal conditions (135 8C) but after
48 h, only 34% of the corresponding nitrile was obtained.
Therefore, these interconversions were carried out under
MW irradiation.
In order to show the effect of the ionic liquid on the
catalytic activity, the reaction of benzylmethoxymethyl
ether (1 mmol) with [Bu4N][CN] (2 mmol) in the presence
of different amounts of bulk HPW and HPW@[bmim]
[FeCl4] was carried out under the same reaction conditions
(Table 1). The obtained results showed that the catalytic
activity of HPW increased significantly by immobilization
in the ionic liquid. On the other hand, in the absence of
HPW, the [bmim][FeCl4] was less efficient to catalyze this
interconversion reaction. The results are summarized in
Table 1.
It was observed that changing the anion in the structure
of the ionic liquid led to different results (Table 2). These
observations may be due to the ability of the anion for
stabilization of charged intermediate. By increasing the
coordination ability of anion, the feasibility of ion pair
formation between anion and charged intermediate
(protonated ether) decreased which in turn decreases
the product yield [30].
3.2. Direct conversion of MOM- and EOM-ethers into
corresponding nitriles, bromides and iodides under
microwave irradiation
Under the optimized conditions, direct conversion of
structurally different primary aromatic, aliphatic and
allylic MOM- and EOM-ethers to their corresponding
nitriles, bromides and iodides was carried out and these
useful products were obtained in good to excellent yields
and short reaction times (Table 3). In the case of
alkoxymethyl ethers bearing substituted aromatic rings,
the nature of substituent has no significant effect on the
reactivity of the alkoxymethyl ethers toward interconver-
sion reactions.
It was observed that the other imidazolium-based ionic
liquids such as [bmim][Cl], [bmim][PF6], [bmim][BF4] and
Table 1
Direct conversion of benzylmethoxymethyl ether into its corresponding nitrile by different amounts of catalyst after 10 minutes.a
Entry
Catalyst amount
(mol%)
Catalyst
Yield (%)b
HPW
HPW@[bmim][FeCl4]
1
2
3
4
5
0.2
0.3
0.4
0.5
0.6
0
11
20
24
31
15
40
83
95
95
a
Reaction conditions: benzylmethoxymethyl ether (1 mmol), [Bu4N][CN] (2 mmol) and [bmim][FeCl4] (0.5 mL).
Isolated yields.
b

I. Mohammadpoor-Baltork et al. / C. R. Chimie 13 (2010) 1468–1473
1471
Table 2
Direct conversion of benzylmethoxymethyl ether into its corresponding nitrile by various imidazolium-based ionic liquids.a
Entry
Ionic liquids
Yield (%)b
1
2
3
4
5
6
[bmim][Cl]
69
73
78
65
81
95
[bmim][PF6]
[bmim][BF4]
[bmim][NTf2]
[bmim][AlCl3]
[bmim][FeCl4]
a
Reaction conditions: benzylmethoxymethyl ether (1 mmol), [Bu4N][CN] (2 mmol), HPW (0.5 mol%) and ionic liquids (0.5 mL).
Isolated yields.
b
Table 3
Direct conversion of MOM- and EOM-ethers into their nitriles, bromide and iodides by HPW@[bmim][FeCl4] and MW irradiation.a
Entry
R
EOM-ethers
MOM-ethers
Yield, % (time, min)b
Yield, % (time, min)b
X = CN
X = Br
X = I
X = CN
X = Br
X = I
1
C6H5CH2
95 (2)
90 (2)
93 (2)
95 (2)
91 (2)
94 (2)
2
4-(CH3)3C6H4CH2
4-(CH2)C6H4CH2
2-HOC6H4CH2
3-CH3O-4-(OH)C6H3CH2
3-CH3OC6H4CH2
4-CH3OC6H4CH2
4-PhCH2OC6H4CH2
2-ClC6H4CH2
91 (2.5)
93 (2)
88 (2.5)
91 (2)
91 (2.5)
92 (2)
92 (2.5)
92 (2)
87 (2.5)
90 (2)
91 (2.5)
92 (2)
3c
4
87 (3)
84 (3)
86 (3)
88 (3)
85 (3)
88 (3)
5
89 (2.5)
92 (1.5)
86 (3)
86 (2.5)
89 (1.5)
84 (3)
87 (2.5)
92 (1.5)
86 (3)
91 (2.5)
93 (1.5)
88 (3)
87 (2.5)
88 (1.5)
85 (3)
90 (2.5)
93 (1.5)
87 (3)
6
7
8
92 (1.5)
88 (2.5)
90 (2.5)
88 (3)
90 (1.5)
85 (2.5)
87 (2.5)
87 (3)
92 (1.5)
89 (2.5)
89 (2.5)
87 (3)
94 (1.5)
89 (2.5)
90 (2.5)
89 (3)
89 (1.5)
85 (2.5)
88 (2.5)
88 (3)
93 (1.5)
88 (2.5)
91 (2.5)
88 (3)
9
10
11
12
13
14
15
16
17
18
19
4-ClC6H4CH2
2,4-Cl2C6H3CH2
2-BrC6H4CH2
86 (3)
84 (3)
83 (3)
88 (3)
85 (3)
83 (3)
4-BrC6H4CH2
91 (2.5)
96 (1)
87 (2.5)
94 (1)
91 (2.5)
96 (1)
92 (2.5)
97 (1)
88 (2.5)
95 (1)
93 (2.5)
95 (1)
3-NO2C6H4CH2
4-NO2C6H4CH2
C6H5CH = CHCH2
C6H5CH2CH2
97 (0.5)
97 (0.5)
92 (2)
94 (0.5)
95 (0.5)
89 (2)
97 (0.5)
97 (0.5)
91 (2)
97 (0.5)
97 (0.5)
93 (2)
96 (0.5)
95 (0.5)
90 (2)
97 (0.5)
97 (0.5)
93 (2)
CH3(CH2)5CH2
CH3(CH2)6CH2
94 (2)
88 (2)
92 (2)
94 (2)
90 (2)
93 (2)
94 (2)
89 (2)
93 (2)
94 (2)
91 (2)
93 (2)
a
Reaction conditions: alkoxymethyl ether (1 mmol), [Bu4N][X] (2 mmol), HPW (0.5 mol%) and [bmim][FeCl4] (0.5 mL).
b
c
Isolated yields.
1 mol% of catalyst and 4 mmol of [Bu4N][X] were used.
In order to explore the general applicability of this
to nitriles, bromides and iodides in the presence of other
hydroxyl protecting groups such as benzyl or methyl
ethers (Table 3, entries 5–8).
method, several competitive interconversion reactions
were designed. As shown in Table 4, these reactions, using
this catalytic system, were found to be highly chemose-
lective for primary MOM- and EOM-ethers in the presence
of secondary, tertiary and phenolic ethers. In other words,
in an equimolar binary mixture of primary and secondary
MOM-ethers, the primary ether was converted quantita-
tively to its corresponding nitrile, bromide and iodide;
while in the case of secondary ether the amounts of
corresponding products were less than 48% (Table 4, entry
1). Also, excellent chemoselectivity was also observed for
the transformation of primary ethers in the presence of
tertiary and phenolic ethers which tertiary and phenolic
ethers remained intact in the reaction mixture (Table 4,
entries 2 and 3). In addition, this method can be selectively
applied for the conversion of these MOM- and EOM- ethers
3.3. Recyclability and reusability of catalyst
The reusability of the catalyst was examined in the
conversion reaction of benzylmethoxymethyl ether to its
corresponding nitrile. After completion of reaction, the
heteropoly acid and IL were recovered by addition of Et2O.
The diethyl ether was further washed with water and the
aqueous layer was evaporated under reduced pressure to
obtain the catalyst. The combined organic layer was dried
over anhydrous sodium sulfate and evaporated under
reduced pressure to isolate the product. The results
showed that after third run, the yield of the product was
83% (Table 5).

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I. Mohammadpoor-Baltork et al. / C. R. Chimie 13 (2010) 1468–1473
Table 4
Competitive interconversion reactions of various MOM-ethers to nitriles, bromides and iodides catalyzed by HPW@[bmim][FeCl4] under MW irradiation.a
Entry
1
MOM-ethers
Products
X = CN
Yield (%)b
95
X = Br
Yield (%)b
91
X = I
Time (min)
Time (min)
Yield (%)b
94
Time (min)
2
4.5
2
48
95
41
91
43
94
2
2
4.5
2
–
–
–
3
95
91
94
2
4.5
2
–
–
–
a
Reaction conditions: MOM-ethers (1 mmol), [n-Bu4N][X] (2 mmol), HPW (0.5 mol%) and [bmim][FeCl4] (0.5 mL).
b
Isolated yields.
Table 5
Investigation of reusability of catalyst in conversion reaction of benzylmethoxymethyl ether into its corresponding nitrile.
Cycle
Time (min)
Yield (%)a
1
2
3
2
2
2
95
89
83
a
Isolated yields.
4. Conclusion
Cell) and also Research Council of the University of Isfahan
for financial support of this work.
In conclusion, we demonstrated a convenient, efficient
and chemoselective catalytic method for the direct
transformation of MOM- and EOM-ethers into the other
important functional groups such as nitriles, bromides and
iodides under MW irradiation. The use of HPW@[bmim][-
FeCl4] as a novel, green and reusable catalyst makes this
procedure environmentally friendly and economically
acceptable. Furthermore, easy workup, short reaction
times and high yields of products are other noteworthy
advantages of this catalytic system.
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