NaY zeolite functionalized by sulfamic acid/Cu(OAc)2 as a new and reusable heterogeneous hybrid catalyst for efficient solvent-free formylation of amines

Article abstract of DOI:10.1016/j.cclet.2017.04.029

NaY zeolite functionalized by sulfamic acid/Cu(OAc)₂ [NaY/SA/Cu(II)] was synthesized and used as a new, efficient and recyclable catalyst for preparation of formamides. This novel organic-inorganic hybrid catalyst was characterized by several techniques such as FT-IR, XRD, SEM, EDX and TG analysis. Chemoselectivity, easy procedure, excellent yields, very short reaction times, solvent-free and mild reaction conditions are some benefits of this new protocol.

Full text of DOI:10.1016/j.cclet.2017.04.029

Accepted Manuscript
Title: NaY zeolite functionalized by sulfamic acid/Cu(OAc)2
as a new and reusable heterogeneous hybrid catalyst for
efficient solvent-free formylation of amines
Authors: Samira Kazemi, Akbar Mobinikhaledi, Mojgan
Zendehdel
PII:
S1001-8417(17)30166-3
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.cclet.2017.04.029
CCLET 4065
To appear in:
Chinese Chemical Letters
Received date:
Revised date:
Accepted date:
13-1-2017
20-4-2017
25-4-2017
Please cite this article as: Samira Kazemi, Akbar Mobinikhaledi, Mojgan Zendehdel,
NaY zeolite functionalized by sulfamic acid/Cu(OAc)2 as a new and reusable
heterogeneous hybrid catalyst for efficient solvent-free formylation of amines, Chinese
Chemical Lettershttp://dx.doi.org/10.1016/j.cclet.2017.04.029
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Original article
NaY zeolite functionalized by sulfamic acid/Cu(OAc)
2
as a new and reusable
heterogeneous hybrid catalyst for efficient solvent-free formylation of amines

Samira Kazemi , Akbar Mobinikhaledi, Mojgan Zendehdel
Faculty of Science, Department of Chemistry, Arak University, Arak 38156-8-8349, Iran
Graphical Abstract
Chemoselective N-formylation of amines with formic acid was achieved using NaY/SA/Cu(II) as a new, recyclable and efficient
hybrid catalyst. Excellent yields, very short reaction times, solvent-free and mild reaction conditions are prominent advantages of
this new protocol.
ARTICLE INFO
ABSTRACT
Article history:
2
NaY zeolite functionalized by sulfamic acid/Cu(OAc) [NaY/SA/Cu(II)] was synthesized and
Received 16 January 2017
Received in revised form 10 April 2017
Accepted 17 April 2017
Available online
used as a new, efficient and recyclable catalyst for preparation of formamides. This novel
organic-inorganic hybrid catalyst was characterized by several techniques such as FT-IR, XRD,
SEM, EDX and TG analysis. Chemoselectivity, easy procedure, excellent yields, very short
reaction times, solvent-free and mild reaction conditions are some benefits of this new protocol.
Keywords:
Heterogeneous catalyst
NaY/SA/Cu(II)
Formylation
Formamides
Zeolite
1
. Introduction
Formamides are important intermediates in organic synthesis [1, 3], and are also precursors for preparation of formamidine,
isocyanides [2] and many pharmaceutically important heterocycles, such as flouroquinolines [3], oxazolidinones [4], 1,2-
dihydroquinolines [5], substituted arylimidazoles [1] and cancer chemotherapeutic compounds [6]. In addition, formyl group has been
—
——

Corresponding author.
E-mail address: samira.kazemy@gmail.com

widely used as amino protecting group through peptide synthesis [7]. Furthermore, using as reagent in vilsemiere formylation [8] and
as Lewis base catalyst [9], are other applications of formyl group. Numerous formylating methods have been reported in recent years
using acetic formic anhydride [10], chloral [11], activated formic acid using DCC [12] or EDCI [13], activated formic esters [14-16],
ammonium formate [17], solid supported reagents [18], 2,2,2-trifluoroethyl formate [19], aq. 85% formic acid with ZnO [20] and
2 3
sulfonic acid supported hydroxyapatite encapsulated γ-Fe O [21]. However, some limitation factors such as expensiveness and
toxicity of formylating reagents, formation of byproducts, high temperature and prolonged reaction times are besides the usefulness
of these methods. Moreover, due to the environmental considerations, development of environmentally benign chemical reactions has
been emerged as a demanding research area in modern organic chemical research [22]. Recently, application of zeolites as a
heterogeneous catalyst has gained remarkable interest, due to their distinctive chemical and physical properties such as their thermal
stability, their acidic and basic nature or shape selectivity which affects the reaction efficiency, and easy separation from reaction
mixture which facilitates work up and purification of products [23-25]. Furthermore, zeolites are known to catalyze different types of
organic transformations much more effectively and selectively than the Lewis acid catalysts [26]. Recently, Natrolite zeolite has been
reported as a natural catalyst for synthesis of formamides [27]. Also N-formylation of amines using natural HEU zeolite has been
reported [28]. In the other hand, organic-inorganic hybrid materials are of great interest as serve by thermal and mechanical stability
of their inorganic moieties [29]. Therefore, exploiting these unique properties to address the drawbacks of previously reported
procedures and in continuation of our interest toward environmentally benign procedures for organic transformations, herein we have
designed NaY/SA/Cu(II) as a recyclable organic-inorganic hybrid catalyst and used in general procedure for N-formylation of amines
under solvent-free conditions (Scheme 1).
Scheme 1. Chemoselective N-formylation of amines with formic acid and NaY/SA/Cu(II).
2
. Results and discussion
2
.1. Characterization of NaY/SA/Cu(II)
-
1
The FT-IR spectra of all hybrid materials (Fig. 1) indicate an intense band about 1049 cm attributed to the asymmetric stretching of
Al–O–Si chain of zeolite. The symmetric stretching and bending frequency bands of Al–O–Si framework of zeolite appear at 765 and
-
1
-1
4
55 cm , respectively [30]. The out of plane bending and stretching of O-H group appeared at 785 and 3400-3500 cm respectively.
The characteristic peak appears at 1150 assigned to S=O stretching vibrations which confirm the presence of SO H group (Fig. 1,
3
-
1
curves c, d). The symmetric and asymmetric stretching vibration mode of amine group was observed at 3200-3400 cm (Fig. 1, curves
-
1
b-d) The weak band at 2900 cm can be attributed to C-H stretching vibration (Fig. 1, curve d).
2
Fig. 1. The comparative FT-IR spectra of (a) NaY zeolite, (b) NaY zeolite-NH , (c) NaY/SA and (d) NaY/SA/Cu(II).
The microstructure of the catalyst was investigated by scanning electron microscopy (SEM). The SEM image of NaY/SA/Cu(II) in
Fig. 2b shows particles with mean diameter of about 300 nm in a nearly spherical shape which demonstrate structural integrity in the
terms of particle’s size and shape in comparison to NaY/SA in Fig. 2a. The EDX analysis of NaY/SA/Cu(II) that is available in
supporting information file, clearly reveals the presence of Cu as well as other expected main elements including N, Al, Si, O, C, Na
+
and S (Fig. 3b). The lower intensity of Na in compare to that for NaY/SA demonstrated the exchange of Na as a monovalent cation by
2
+
divalent cation Cu in zeolite’s pores without any changes in zeolite’s structure.

Fig. 2. (a) SEM image of NaY/SA and (b) NaY/SA/Cu(II).
Thermal analysis was used to monitor the decomposition profile of NaY/SA/Cu(II) (Fig. 3). In the first stage, it shows a weight loss
o
of 12% up to 350 C, due to the adsorbed water in catalyst. The second stage weigh loss of 11% was observed at the temperature range
o
o
about 350-430 C due to the organic moiety. The weight loss above 450 C is attributed to the zeolite decomposition.
Fig. 3. TG-DTA image of NaY/SA/Cu(II).
The same peaks are observed in XRD patterns of both NaY/SA and NaY/SA/Cu(II) (Fig. 4) that demonstrates no changes in the
general structure and morphology of NaY zeolite during the immobilization procedures.
Fig. 4. (a) XRD pattern of NaY/SA (b) and NaY/SA/Cu(II).
2
.2.
Catalytic studies
We initiated our investigation to optimize the formylation of aniline as a model reaction by varying reaction parameters including
solvent, catalyst type, catalyst loading and amount of formic acid (Table 1). As the reaction was performed with prolonged reaction
time in the absent of any catalyst, gave dramatic yield (Table 1, entry 19), among different catalyst, NaY/SA/Cu(II) (0.01 g) was found
to provide the best result (Table 1, entry 6). Then, the feasibility of the reaction was probed in various solvent (Table 1, entries 1-5). An
increase in reaction times and a decrease in the yields were observed with using any solvent and the best result was obtained in solvent-
free conditions. Also lowering the amount of formic acid, increased the reaction time in lower yield. The best yield of formamide was
obtained with 5 mmol formic acid and 1 mmol aniline in the presence of 0.01 g NaY/SA/Cu(II), under solvent free conditions at room
temperature without any byproduct (Table 1, entry 6). Then the feasibility of the reaction was probed in various solvent (Table 1,
entries 1-5). An increase in reaction times and a decrease in the yields were observed with using any solvent and the best result was
obtained in solvent-free conditions. Also lowering the amount of formic acid, increased the reaction time in lower yield. The best yield
of formamide was obtained with 5 mmol formic acid and 1 mmol aniline in the presence of 0.01 g NaY/SA/Cu(II), under solvent free
conditions at room temperature without any byproduct (Table 1, entry 6).
Having established the optimized conditions for easy transformation of aniline to N-phenylformamide, formylation of variety of
amines were investigated via this protocol. A series of aromatic, heterocyclic and aliphatic amines were subjected to reaction with
formic acid using NaY/SA/Cu(II) under solvent free conditions at room temperature to obtain the formamide in excellent yields (Table
2
). This methodology showed a wide reaction scope and was found to be effective in formylation of both electron rich and electron

poor anilines in high to excellent yields in short reaction times. This protocol is very valuable from generality point of view and can be
applied successfully to both primary and secondary amines compared to the recent formylation method by use of polyethylene glycol
which is only applicable for aromatic primary amines [31]. However, anilines bearing electron withdrawing groups such as –NO
2
carried out the reaction in longer reaction times than ones bearing electron donating groups such as –Methyl. So, electronic factors play
an important role on yields and reaction times as we observed for 4,6-dimethylpyrimidin-2-amine (Table 2, entry 14) which produced
the product in lower yield and longer reaction time in compare to pyridin-2-amine (Table 2, entry 13). It seems that the presence of two
2
electronegative SP nitrogen atom in heterocyclic ring of 4,6-dimethylpyrimidin-2-amine caused the reaction proceed slightly slower.
Primary amines (Table 2, entries 1-16) easily reacted to give N-formyl product, while secondary amines (Table 2, entries 17-22)
smoothly proceeded to provide the corresponding formamide. We also observed that sterically hindered amines (Table 2, entries 14,
1
7, 21 and 22) took a longer reaction time. It seems that steric factors play an important role on yields and reaction times as well as
electronic factors (Table 2, entry 22). Diphenylamine as a hindered secondary amine which previously has been reported unreactive
13] or provided lower yield [32], was reactive following this reaction protocol (Table 2, entry 21). Interestingly the N-formylation of
,2-phenylendiamine afforded di-formylated product (Table 2, entry 16) in high yield instead of formation benzimidazole which
[
1
previously reported in literature [33]. Unfortunately, acyclic aliphatic amines showed poor activity than cyclic aliphatic amines and
gave a significant lower yield (Table 2, entry 27).
Table 1
a
Screening of reaction parameters for formation of N-phenylformamide.
Formic acid
mmol)
Yield
(%)
85
88
80
65
70
98
95
82
98
95
90
95
86
98
97
90
30
60
10
Entry
Solvent
Catalyst (mg)
Time (min)
(
1
2
3
4
5
6
7
8
9
MeCN
EtOAc
dioxane
5
5
5
5
5
5
5
5
5
5
5
4
3
6
7
5
5
5
5
NaY/SA/Cu(II) (10)
NaY/SA/Cu(II) (10)
NaY/SA/Cu(II) (10)
NaY/SA/Cu(II) (10)
NaY/SA/Cu(II) (10)
NaY/SA/Cu(II) (10)
NaY/SA/Cu(II) (8)
NaY/SA/Cu(II) (5)
NaY/SA/Cu(II) (12)
NaY/SA/Cu(II) (15)
NaY/SA/Cu(II) (20)
NaY/SA/Cu(II) (10)
NaY/SA/Cu(II) (10)
NaY/SA/Cu(II) (10)
NaY/SA/Cu(II) (10)
NaY/SA (10)
10
8
10
20
CHCl
3
H
2
O
15
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
solvent-free
Immediately
5
25
Immediately
Immediately
Immediately
2
1
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
9
10
Immediately
Immediately
15
120
120
120
NaY Zeolite
2
Cu(OAc) (10)
-
a
Conditions: aniline (1 mmol, 0.09 mL), room temperature.
It is noteworthy to mention that the reaction was found to be selective only toward N-formylation. O-Formylation of phenols did not
take place under this protocol, such as, phenol, p-nitrophenol, benzyl alcohol, and (Ph) CHOH. So, any substrate bearing both –OH
and –NH groups, will only be N-formylated which indicate the high chemoselectivity of our method (Table 2, entries 10 and 11). Also
2
2
chemoselectivity was observed in reaction of formic acid with a mixture of primary and secondary amine when only primary amine
was formylated (Scheme 2). Therefore, the primary amines can be formylated in the presence of secondary amines by controlling the
reaction time.
Scheme 2. Chemoselectivity in formylation of primary amine in the presence of secondary amine.
A plausible mechanism is shown in Scheme 3. It probably seems that NaY/SA/Cu(II) has an important role in activation of carbonyl
of formic acid as similar mechanism that has been reported for N-formylation of amines using ZnCl [34]. The catalyst as a Lewis and
2
protic acid coordinates to carbonyl group of formic acid results in enhancement of its electrophilic character to nucleophilic attack by
the amine nitrogen atom.

Scheme 3. The suggested mechanism for synthesis of N-phenylformamide.
Table 2
a
NaY/SA/Cu(II) catalyzed N-formylation of primary and secondary amines.
Entry
R
1
R
2
Product
Mp
b
Time (min)
Yield (%)
Found
Reported
46-48 [32]
51-55 [32]
57-61 [32]
114-118 [27]
78-80 [21]
193-195 [32]
115-119 [32]
99-101 [32]
-
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
Phenyl
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
-
immediately
immediately
4
5
immediately
7
immediately
immediately
1
2
3
4
5
6
7
8
98
96
92
95
98
94
97
98
98
93
91
95
98
85
92
96
90
47-49
52-54
56-58
112-114
81-83
194-196
117-119
100-103
154-157
Oil
4-Methylphenyl
2-Methylphenyl
2,4-dimethylphenyl
4-Methoxyphenyl
4-Nitrophenyl
4-Bromophenyl
4-Chlorophenyl
2,4-dichlorophenyl
3-Hydroxyphenyl
2-Hydroxyphenyl
Benzyl
2-Pyridyl
4,6-dimethylpyrimidyl
1-naphthyl
1,2-phenylendiaamine
Benzyl
immediately
12
7
9
0
1
2
3
4
5
6
7
8
10
11
12
13
14
15
16
17
18
Oil [27]
130-132
58-60
129-131 [21]
60-62 [21]
-
5
10
15
5
5
25
130-132
145-148
140-142
180-182
50-52
-
141-143 [27]
-
51-52 [27]
Benzyl
-
-
5
5
93
95
Liquid
Oil
Liquid [27]
Oil [21]
1
2
9
0
19
20
-
5
87
91
83-85
68-70
82-84 [27]
67-71 [32]
2
2
1
2
Phenyl
Phenyl
30
21
22
-
60
30
Liquid
Liquid [27]
Oil [32]
2
3
1-Butyl
H
60
23
40
Oil
a
Conditions: amine (1 mmol), formic acid (5 mmol, 0.19 mL), catalyst (0.01 g), room temperature.
Isolated yields.
b
To evaluate the recyclability of NaY/SA/Cu(II), the reaction of aniline and formic acid was studied under the optimal reaction
conditions using recycled catalyst from the previous run. The catalyst was separated by simple filtration, adequately washed with
o
3
CHCl , dried at 60 C and reused for further reactions. The recovered catalyst could be reused up to 6 cycles for N-formylation without
any significant loss of activity (Fig. 5) as its FT-IR spectrum showed no distinct change in its structure in compare to FT-IR spectrum
of fresh catalyst (Fig. 6).

Fig. 5. Catalytic efficiency of the recycled catalyst.
Fig. 6. FT-IR spectra of fresh catalyst and the six times reused catalyst.
Finally, to establish the efficiency of this methodology, it was compared with some reported methods. As Table 3 shows this method
clearly improved yields and reaction times. Also, the reusability of the catalyst makes this method less contaminate and nearly green.
In addition, since the catalyst is heterogeneous, the work-up procedure is easy and chromatography or other complex purification
methods are not necessary. According to the obtained results, it seems that NaY zeolite also helps the catalytic effect of sulfonic acid
group and accelerates the reaction.
Table 3
Comparing this method with some reported methodologies for synthesis of N-phenylformamide.
Entry Catalyst
Temp
Time (min)
Yields (%)
Ref.
1
2
3
4
5
6
7
8
NaY/SA/Cu(II)
ZnO
r.t.
70 C
70 C
r.t.
< 1
10
60
20
60
5
98
99
86
89
97
99
97
91
This work
o
21
32
27
33
35
22
31
o
FSG-Hf(NPf
2
)
4
Natrolite zeolite
IL
HIL
o
70 C
r.t.
r.t.
r.t.
2 3
γ-Fe O @HAp-SO
3
H
20
240
PEG-400
3
. Conclusion
We have developed an efficient method for chemoselective N-formylation of various amines by use of NaY/SA/Cu(II) as a reusable
heterogeneous organic-inorganic hybrid catalyst to give access formamides at room temperature under solvent-free conditions.
Prominent advantages of this protocol include short reaction times, easy work up, high to excellent product yields and the
recoverability of the catalyst. Also this rapid synthesis of formamides make this protocol, practical and energy efficient and it can be
considered as “green procedure” as no volatile solvent is released into the environment.
4
. Experimental
4
.1. Materials
All used chemicals were purchased from Merck and Fluka chemical companies. Melting points were determined on an electro
thermal digital melting point apparatus. The catalyst was characterized by atomic absorption instrument (Varian SpectrAA 200), X-
Ray diffract meter (Philips 8440) with radiation at room temperature Cu Ka, FT-IR (Galaxy series FT-IR 5000 spectrometer), and
TGA-DSC (Rheometric scientific STA-1500 thermo gravimetric analyser). NMR spectra were recorded on a Bruker (300 MHz)
spectrometer. Chemical shifts (ppm) were referenced to the internal standards tetramethylsilane (TMS). Microanalyses were performed
by the Elemental Analyzer (Elemental, Vario EL III) at Arak University. The microanalyses results were agreed favorably with the
calculated values. Reactions were monitored by thin layer chromatography using silica gel F254 aluminium sheets (Merck).

4
.2. Procedure for synthesis of NaY/SA/Cu(II)
To a mixture of NaY zeolite in toluene (20 mL), trimethoxysilyl propylamine (2 mL) was added and stirred for 24 h under reflux
o
conditions. Then zeolite was separated by filtration and dried at 60 C. For sulfonation, chlorosulfonic acid (2 mL) and triethylamine
(
0.2 mL) was added to a mixture of functionalized zeolite (1 g) in toluene (20 mL) and stirred at reflux conditions for 24 h. Finally, the
o
participated solid was filtrated, washed with water and dried over 60 C to obtain the NaY-SA compound. A pH analysis of NaY-SA
showed 1.5 mmol/g loading of SO H. In the next step, NaY-SA (1 g) was reacted with 100 mL of a 0.001 mol/L solution of Cu(OAc)
in toluene for 24 h at room temperature. After sonication (2 × 3 min) the NaY/SA/Cu(II) product was filtered, and dried at 60 C
Scheme 4). Then the loading of copper in NaY/SA/Cu(II) was determined to be 2% by atomic absorption spectroscopy.
3
2
o
(
Scheme 4. Step by step synthesis of NaY/SA/Cu(II).
4
.3. General procedure for formylation of amines
To a mixture of amine (1 mmol) and NaY/SA/Cu(II) (0.01 g), formic acid (5 mmol, 0.19 mL) was added and stirred for appropriate
time at room temperature. After completion of the reaction as monitored by TLC (n-hexane/ EtOAc = 8/2), NaY/SA/Cu(II) catalyst
was filtered and organic layer evaporated under reduced pressure to give pure product. The structure of the products was established
1
13
from their physical properties and spectral ( H NMR, C NMR and IR) analysis and were compared with the data reported in the
literature and are available as the Supporting information.
Physical and spectroscopic characterization data of selected new compounds (9, 13, 14 and 16) are shown below, and others were
given in Supporting information.
o
-1
N-(2,4-Dichlorophenyl) formamide (9): Mp: 154-157 C. IR (KBr pellet, cm ): νmax 3244, 3090, 3034, 2986, 2899, 1695, 1664,
1
1
585, 1529, 1398, 1298, 1103, 1049, 817, 752, 700, 381. H NMR (DMSO-d
6
, 300 MHz): δ 9.74 (s, 1H, CHO). 7.37-8.14 (m, 3H, Ar-
, 75 MHz): δ 161.03, 133.88, 129.29, 128.79, 128.14, 124.73, 124.43. Elemental analysis for
2
NO, Calcd. C, 44.25; H, 2.65; N, 7.37. Found: C, 44.00; H, 2.80; N, 7.37.
1
3
H), 7.15 (s, 1H, NH), C NMR (DMSO-d
Cl
N-(Pyridin-2-yl)formamide (13): Mp: 130-132 C. IR (KBr pellet, cm ): νmax 3319, 3157, 2876, 1668, 1624, 1589, 1454, 1369, 1327,
6
C
7
H
5
o
-1
1
, 300 MHz): δ 7.67-7.94 (m, 1H, CHO), 6.01-7.15 (m, 4H, Ar-H), 5.78 (s, 1H, NH). 13
O calcd. C, 59.01; H,
1
248, 1134, 765, 387. H NMR (DMSO-d
NMR (DMSO-d , 75 MHz): δ 160.08, 155.91, 149.63, 136.91, 120.72, 105.79. Elemental analysis for C
.95; N, 22.94. Found: C: 59.20, H: 5.15, N: 23.00.
N-(4,6-Dimethylpyrimidin-2-yl)formamide (14): Mp: 145-148 C. IR (KBr pellet, cm ): νmax 3325, 3182, 3094, 2930, 2858, 2735,
6
C
6
6 6 2
H N
4
o
-1
1
1
682, 1662, 1635, 1574, 1589, 1373, 1323, 1136, 935, 553, 387. H NMR (DMSO-d
6
, 300 MHz): δ 7.90 (s, 1H, CHO), 6.11 (m, 2H,
1
3
NH and Ar-H), 1.92 (s, 6H, CH
3
). C NMR (DMSO-d
6
, 75 MHz): δ 164.06, 159.63, 156.81, 137.39, 18.21. Elemental analysis for
7 9 3
C H N O: calcd. C, 55.62; H, 6.00; N, 27.80. Found: C: 56.00, H: 5.86, N: 27.81.
o
-1
N,N'-(1,2-Phenylene)diformamide (16): Mp: 180-182 C. IR (KBr pellet, cm ): νmax 3101, 2922, 2856, 2808, 2696, 1682, 1620,
1
1
(
560, 1485, 1452, 1398, 1249, 1120, 1035, 802, 605, 624, 426. H NMR (DMSO-d
6
, 300 MHz): δ 8.22-8.34 (m, CHO, 2 H), 7.62-7.65
m, Ar-H, 2 H), 7.20-7.23 (m, Ar-H, 2 H), 6.89 (NH, 2 H). C NMR (75 MHz, DMSOd ): δ 163.62, 130.12, 124.64, 122.58. Elemental
analysis for C : Calcd. C, 58.53; H, 4.91; N, 17.06. Found: C: 59.19, H: 5.00, N: 17.39.
1
3
6
8
8 2 2
H N O
Acknowledgment
We thank Arak University for financial support for this work.
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