Molybdate and silica sulfuric acids as heterogeneous alternatives for synthesis of gem-bisamides and bisurides from aldehydes and amides, carbamates, nitriles or urea

Article abstract of DOI:10.1016/j.molcata.2012.12.002

Molybdate sulfuric acid (MSA) and silica sulfuric acid (SSA) has been prepared and used as efficient solid catalysts for the synthesis of gem-bisamides and bisurides via the one-pot three-component reaction of two moles of amides, nitriles, carbamates or urea with aldehydes. The catalytic efficiency of SSA, MSA, or H₂SO₄ 98% per H⁺ sites as turnover number (TON), turnover frequency (TOF), and atomic economy (AE) was calculated and compared for quantitative evaluation of catalysts. The AE, TON, and TOF factors show the superiority of the SSA versus MSA and H ₂SO₄. Short reaction times, simple work-up, chemoselectivity, low loading, and reusability of solid acid catalysts are extra advantages than current methods reported in the literature with corrosive acidic catalysts.

Full text of DOI:10.1016/j.molcata.2012.12.002

Journal of Molecular Catalysis A: Chemical 368–369 (2013) 66–71
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Molybdate and silica sulfuric acids as heterogeneous alternatives for synthesis of
gem-bisamides and bisurides from aldehydes and amides, carbamates, nitriles or
urea
Fatemeh Tamaddon∗, Hossein Kargar-Shooroki, Abbas Ali Jafari
Department of Chemistry, Faculty of Science, Yazd University, Yazd 89195-741, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Molybdate sulfuric acid (MSA) and silica sulfuric acid (SSA) has been prepared and used as efficient solid
catalysts for the synthesis of gem-bisamides and bisurides via the one-pot three-component reaction of
two moles of amides, nitriles, carbamates or urea with aldehydes. The catalytic efficiency of SSA, MSA, or
H2SO4 98% per H+ sites as turnover number (TON), turnover frequency (TOF), and atomic economy (AE)
was calculated and compared for quantitative evaluation of catalysts. The AE, TON, and TOF factors show
the superiority of the SSA versus MSA and H2SO4. Short reaction times, simple work-up, chemoselectivity,
low loading, and reusability of solid acid catalysts are extra advantages than current methods reported
in the literature with corrosive acidic catalysts.
Received 27 October 2012
Received in revised form
28 November 2012
Accepted 3 December 2012
Available online 11 December 2012
Keywords:
Gem-bisamides
Bisurides
© 2012 Elsevier B.V. All rights reserved.
N,Nꢀ-alkylidene or arylidene bisamides
Molybdate sulfuric acid
1. Introduction
are among the important amide derivatives and the most stable
protected aldehydes which have been used as versatile inter-
With the advance of green chemistry, heterogeneous solid cata-
lysts have emerged as capable promoters of organic reactions [1–3].
Reusability and non-toxicity of these solids organize them as more
benefit industrial catalysts than homogeneous analogs, and hence
modern processes have turned to the gradual replacing of tradi-
tional catalysts with these advantageous recoverable solids [4].
Silica sulfuric acid (SSA) [5–8] and molybdate sulfuric acid (MSA)
[9,10] are two inexpensive and readily handled solid alternatives
to sulfuric acid which have been used as superior catalysts in var-
ious heterogeneous organic transformations [5–10]. SSA and MSA
could be easily recovered from the reaction mixtures by a simple
filtration and these features make reaction set up cleaner and faster
with higher yielding.
Exceptional properties of amide bond offer many vital roles to
amide derivatives as biochemicals, structural subunit of polymers,
and stable synthetic intermediates in chemistry and materials sci-
ence [11–13]. Impressed by the specificity of the number and
location of the amide linkages, chemical and physical properties
of materials are varied [14]. Gem-bisamides or bisurides [15–26]
mediates in the synthesis of biologically active compounds such
as amidoalkyl phenols [27] and pyrimidinones [26]. As a result,
synthesis of gem-bisamides (N,Nꢀ-alkylidene or N,Nꢀ-arylidene
bisamides) have been developed via the advantageous one-pot
multicomponent reactions (MCR) as ideal eco- and environment-
friendly transformations. Acetic acid is the first catalyst used in
the three-component reaction of aldehydes with two moles of
amides [15] and sulfuric acid 85% is the second catalyst for the
reaction of two moles of nitriles with aldehydes [16]. Although
various acid catalysts have been used in the synthesis of symmet-
rical gem-bisamides via the three-component reactions [17–25], a
similar four-component reaction using acetylene compounds and
solid-supported Lewis acids have been reported for the synthesis
of gem-bisamides in higher yields [28,29]. However, long reac-
tion times, use of phenyl acetylene or toluene as extra organic
compounds, high catalyst loading, and limitation of components
to acetamide or benzamide are the major disadvantages of these
methods. Accordingly, more simple and general methods for the
synthesis of gem-bisamides and bisurides are presently of interest.
Due to the benefits, we have recently reported various het-
erogeneous catalysis organic transformations [30–35]. Following
this area of research, herein a very simple and efficient procedure
is reported for the synthesis of N,Nꢀ-bisamides or bisurides via
the one-pot reaction of various aliphatic and aromatic aldehydes
∗
Corresponding author. Tel.: +98 3518122666; fax: +98 3518210644.
E-mail addresses: ftamaddon@yazduni.ac.ir (F. Tamaddon),
h.kargar1365@yahoo.com (H. Kargar-Shooroki), jafari@yazduni.ac.ir (A.A. Jafari).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.12.002

F. Tamaddon et al. / Journal of Molecular Catalysis A: Chemical 368–369 (2013) 66–71
67
According to the KBr disk FT-IR spectrum of MSA, the char-
acteristic bands of OH and OSO3 group are evidently distinct.
Broadening of the absorbance band positioned at 3600–2400 cm−1
is due to the acidic hydrogens of HOSO3, the well defined bands
at 3501 and 1659 cm−1 are related to OH stretching and H
O H
bending mode of the lattice water, the bands at 1300–1100 cm−1
show the asymmetric and symmetric stretching modes of S O,
while strong band at 871 cm−1 is assigned to the stretching mode of
Mo O (Fig. 2). Additionally, comparison between FT-IR spectrum
of sodium molybdate and MSA confirms formation of MSA (Fig. 3).
Scheme 1. SSA and MSA-catalyzed synthesis of gem-bisamides.
with amides, nitriles, carbamates or urea using MSA and SSA as
readily handled and reusable solid Brönsted acids and proficient
alternatives to sulfuric acid (Scheme 1).
2.3. Reusability of catalysts
2. Experimental
The recovered MSA and SSA from the reaction of two moles of
benzamide with benzaldehyde were regenerated by washing with
acetone/EtOH mixture and drying at 120 ◦C for 1 h. Both recycled
SSA and MSA were reusable for four times.
2.1. Preparation and characterization of SSA [5]
A 500 mL suction flask was equipped with a constant pressure
dropping funnel containing chlorosulfonic acid (23.3 g, 0.2 mol) and
a gas inlet tube for conducting HCl gas over H2O. Then 60.0 g of silica
gel was charged in to the flask and chlorosulfonic acid was added
drop wise over a period of 30 min at room temperature. HCl gas
evolved from the reaction vessel immediately. After end of the addi-
tion, the mixture was shaken for extra 30 min. SSA was obtained
(76 g) as a white solid [5,10]. The acid strength and number of
H+ site of prepared SSA was determined by acid-base titration as
2.50 0.05 mmol g−1 [10] which shows that several surface OH of
silica are in the sulfonated form [5]. The surface area of the prepared
SSA was evaluated by nitrogen adsorption desorption following the
Brunauer Emmett Teller method (BET) and was found 225.5 m2/g.
2.4. General procedure for the synthesis of gem-bisamides
To a mixture of aldehyde (2 mmol) and amide or urea (4 mmol)
in EtOAc (1 mL) was added 10 mol% MSA or 0.1 g of SSA. The
resulting mixture was stirred at 80–90 ◦C for the given times
(Tables 1 and 2). After completion of the reaction (TLC monitoring),
hot acetone (10 mL) was added and the catalyst was separated by
filtration. Evaporation of acetone under reduced pressure or addi-
tion of cold water gave the product.
2.5. Selected spectral data
2.2. Preparation and characterization of MSA
2.5.1. N,Nꢀ-benzylidene bisbenzamide (Tables 3 and 4, entries 1
and 2)
To a suspension of anhydrous sodium molybdate (20 mmol,
4.118 g) and dry n-hexane (25 mL) in a two-necked 100 mL round
bottom flask equipped with ice bath and overhead stirrer was
added drop wise chlorosulfonic acid (0.266 mL, 40 mmol) during
30 min with stirring for extra 1.5 h. The reaction mixture was grad-
ually poured into 25 mL of chilled distilled water with agitation. The
molybdate sulfuric acid was separated as a bluish solid by filtration,
washed with cold distilled water five times until the negative test
of Cl− for filtrate, and dried at 120 ◦C for 5 h. The catalyst structure
was verified by checking the decomposition point (∼354 ◦C), acid
capacity (2 mmol H+ per 1 mmol of acid [32]), XRD pattern, and
FT-IR spectrum of the prepared catalyst (Figs. 1 and 2).
The commercial Na2MoO4 presents the main diffraction peaks
at 16.88, 27.78, 32.68, 48.98, 52.18 and 57.18 of 2 a.u, referred to
the 111, 220, 311, 422, 511 and 440 diffraction plans, respectively
[36] (JCPDS file No. 01-070-1710). The XRD pattern of the prepared
(SO3H)2MoO4 (Fig. 1) shows a series of new peaks, randomly dis-
tributed crystallites by planes, and a large shift in the original peaks
of Na2MoO4. These can be attributed to the formation of MSA as
a new phase system, whereas broadening of all peaks shows less
crystallization structure and more amorphous shape of MSA.
White solid, mp = 235–237 ◦C (Lit = 237–238 ◦C [23]). FT-IR:
ꢀmax (KBr) ␯max = 3272 (NH stretching), 1644 (C O), 1535, 1270,
1142, 1051, 802, and 694 cm−1 1H NMR (DMSO-d6, 500 MHz)
.
ı: 7.00 (t, J = 7.3 Hz, 1H), 7.44–7.50 (m, 11H, Haromatic), 7.92 (d,
J = 7.4 Hz, 4H), 9.1 (d, J = 7.2 Hz, 2H, 2 × NH).
2.5.2. N,Nꢀ-(4-methylphenylmethylene) bisacetamide (Table 4,
entries 13 and 14)
White solid, mp = 260–264 ◦C. FT-IR: ꢀmax (KBr) ␯max = 3269 (NH
stretching), 1667 (C O), 1510, 1363, 1276, 1182, 1090, 1021, 788,
and 628 cm−1. 1H NMR (DMSO-d6, 500 MHz) ␦: 1.85 (s, 6H, 2 × CH3),
2.28 (s, 3H, CH3), 6.47 (t, J = 7.3 Hz, 1H, CH), 7.16–7.18 (m, 4H,
Haromatic), 8.46 (d, J = 7.3 Hz, 2H, 2 × NH).
3. Results and discussion
The reaction conditions were optimized using benzamide and
benzaldehyde as model substrates. An initial screening of the
solvents and catalysts revealed that reaction of two moles of benza-
mide with benzaldehyde in the absence of catalyst gave no product,
while the yield of N,N’-phenylidene bisamide was much higher
with solid protic acids SSA or MSA than sulfuric acid at 80–90 ◦C
in EtOAc. No amidation of EtOAc was observed in the presence of
these acids under current conditions. However, lower yield of the
phenylidene bisbenzamide was obtained when reaction was run in
ethanol or under solvent-free conditions at room temperature. Due
to the simplicity and higher yield, optimization of catalyst loading
was investigated for both SSA and MSA (Table 1).
As illustrated in Table 1, the best yield of N,Nꢀ-benzylidene bis-
benzamide was obtained with either 10 mol% of MSA or 0.05 g of
SSA (equal to 0.2 mmol H+ and 0.125 mmol H+ [10], respectively)
in EtOAc at 80–90 ◦C (Table 1, entries 12 and 17). The superiority of
these solid analogs of sulfuric acids than commercial sulfuric acid is
Fig. 1. The powder X-ray diffraction pattern of the MSA.

68
F. Tamaddon et al. / Journal of Molecular Catalysis A: Chemical 368–369 (2013) 66–71
Table 1
Screening conditions for the model reaction.
O
O
NHCOPh
Conditions
+
Ph
2
Ph
NH2
H
Ph
NHCOPh
H
Entry
Solvent
Catalyst loading/Temp. (–)/◦C
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
None
None
None
None
EtOAc
None
EtOH
EtOH
H2O
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
None
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
H2O
None/70–80
600
60
60
60
60
30
100
100
100
60
30
60
30
30
30
60
60
60
30
60
30
30
60
40
60
–
84
75
66
74
80
35
42
40
85
82b
84
91
87b
83b
27
59
85
90
85
80b
80b
50
60
51
ZnCl2/SiO2 (10 mol%)/80–90
ZnCl2 (10 mol%)/90–100
H2SO4 (10 mol%)/80–90
H2SO4 (10 mol%)/80–90
MSA (5 mol%)/80–90
MSA (5 mol%)/70–80
MSA (10 mol%)/70–80
MSA (10 mol%)/80–90
MSA (5 mol%)/80–90
MSA (5 mol%)/90–100
MSA (10 mol%)/70–80
MSA (10 mol%)/80–90
MSA (10 mol%)/90–100
MSA (15 mol%)/80–90
SiO2 (0.1 g)/80–90
SSA (0.05 g)/80–90
SSA (0.05 g)/70–80
SSA (0.05 g)/80–90
SSA (0.025 g)/80–90
SSA (0.1 g)/80–90
SSA (0.05 g)/90–100
SSA (0.05 g)/90–100
SSA (0.05 g)/80
EtOH
CH3CN
SSA (0.05 g)/80
a
Isolated yield.
Due to deprotection of the produced bisamide.
b
Table 2
The catalytic performances of MSA, SSA, and sulfuric acid 98%.
Entry
Catalyst loading for
higher yield
Acid capacity
Molecular
weight
Time (min)
Isolated yield (%)
Atom economy
(reaction/method)
TON
TOF
1
2
3
H2SO4 (10 mol%)
MSA (10 mol%)
SSA (0.05 g)
0.2 mmolH+ per 0.02 g
0.2 mmolH+ per 0.029 g
0.125 mmol H+ per 0.05 g
98
291.9
-
60
30
30
66
91
90
94.83/62.59
94.83/86.30
94.83/84.35
330
455
720
5.5
15.2
24
Table 3
Influence of R group of amide on the reaction.
R
NHC
X
X
MSA (10 mol%) or SSA (0.05 g)
2
PhCHO
Ph
+
H2N
R
NHC
R
X
EtOAc, 80-90 ºC
Entry
R
X
Catalyst
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Ph
Ph
Me
Me
Me and Ph
Me and Ph
OMe
OMe
OMe
NH2
NH2
NH2c
NH2
4-MeC6H5
4-MeC6H5
4-ClC6H5
4-ClC6H5
4-O2NC6H5
4-O2NC6H5
O
O
O
O
O
O
O
S
MSA
SSA
MSA
SSA
MSA
SSA
SSA
MSA
SSA
MSA
SSA
MSA
SSA
MSA
SSA
30
25
60
60
30
91
90
87
86
91b
90b
89
–
25
30
600
600
600
600
25
20
30
30
30
S
S
S
–
–
–
O
O
O
O
O
O
O
O
91
91
90
90
91
90
83
81
MSA
SSA
MSA
SSA
30
60
60
a
Isolated yield.
b
N,Nꢀ-benzylidene bisbenzamide was isolated as the only product.

F. Tamaddon et al. / Journal of Molecular Catalysis A: Chemical 368–369 (2013) 66–71
69
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber cm-1
Fig. 2. FT-IR spectrum of MSA.
4000
3500
3000
2500
2000
1500
1000
Wavenumber cm-1
Fig. 3. FT-IR spectrum of Na2MoO4.
attributed to their top hydrophilic porosity, higher capacities, and
large surface areas.
The practical reusability of MSA and SSA were examined by reac-
tion of benzaldehyde with benzamide using the recycled catalysts
and N,Nꢀ-benzylidene bisbenzamide was isolated without signifi-
cant decreasing in the yield (Fig. 4).
Nitriles can be also reacted with aldehydes to give N,Nꢀ-
bisamides via a Ritter-type reaction. To check the feasibility of
the synthesis of N,N’-benzylidene bisbenzamide from benzoni-
trile, the reaction of benzaldehyde and 2 moles of benzonitrile was
As Fig. 4 shows, despite of the authority of SSA than MSA, using
the both recycled acids for four consecutive times in the model reac-
tion gave the gem-bisamide product with only a little decreasing in
the reaction yield. In the fifth and sixth reaction runs with SSA and
MSA 80 and 75 percentage of product was isolated.
The catalytic performances as atom economies (AE), turnover
numbers (TON), and turnover frequencies (TOF) of these reusable
analogs of sulfuric acid were compared with commercial available
98% sulfuric acid for the synthesis of N,Nꢀ-benzylidene bisbenza-
mide via the reaction of 2 moles of benzamide with benzaldehyde
under optimized conditions (Table 2).
The results of AE, TON, and TOF show much superiority of the
SSA versus MSA and H2SO4 which is due to the higher hydrophilic
porosity, capacity, and surface area.
Fig. 4. Comparison of the reusability of SSA and MSA.

70
F. Tamaddon et al. / Journal of Molecular Catalysis A: Chemical 368–369 (2013) 66–71
Table 4
MSA- and SSA-catalyzed condensation of amides and aldehydes.
O
O
NHCOR
O
MSA (10 mol%) or SSA (0.05 g)
EtOAc, 80-90 ºC
+
NH2
+
R1
R1
NH2
R
R
H
NHCO
R
H
Entry
R
R1
Catalyst
Time (min)
Yield (%)a,b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH2 = CH
CH2 = CH
CH2 = CH
CH2 = CH
OCH3
Ph
Ph
MSA
SSA
MSA
SSA
MSA
SSA
MSA
SSA
MSA
SSA
MSA
SSA
MSA
SSA
MSA
SSA
MSA
SSA
MSA
SSA
MSA
SSA
MSA
SSA
30
25
25
25
40
35
35
45
50
55
45
50
60
70
45
45
50
55
45
50
20
25
15c
20c
25
20
91
90
89
88
86
85
85
86
84
80
86
84
80
75c
82
74c
86
85
86
86
70c
68
75c
73c
93
94
4-O2NC6H4
4-O2NC6H4
4-H3CC6H4
4-H3CC6H4
4-ClC6H4
4-ClC6H4
Ph
Ph
4-O2NC6H4
4-O2NC6H4
4-H3CC6H4
4-H3CC6H4
4-ClC6H4
4-ClC6H4
Ph
Ph
4-O2NC6H4
4-O2NC6H4
Ph
OCH3
OCH3
OCH3
NH2
Ph
4-O2NC6H4
4-O2NC6H4
Ph
MSA
SSA
NH2
Ph
a
Isolated yield.
b
c
All products were fully characterized by FT-IR, 1H NMR and 13C NMR spectroscopy.
At longer reaction times the yield was not changed.
attempted in the presence of MSA and SSA under optimized con-
ditions. The desired product was isolated in 78% and 73% yields
from SSA and MSA, respectively. The lower yield of bisamide prod-
uct from benzonitrile is certified the lower nucleophilicity of PhCN
than PhCONH2.
With the optimized conditions in hand, the influence of R
of amide was compared for parallel reactions of benzamide,
acetamide, urea, and thiourea with benzaldehyde (Table 3).
Although acetamide and benzamide were individually reacted
with benzaldehyde (entries 1–4), reaction with a 1:1 mixture of
benzamide and acetamide gave exclusively N,Nꢀ-benzylidene bis-
benzamide in the presence of both solid acids (entries 5 and 6).
This fact confirms chemoselectivity of the reaction; however, ben-
zamide gave higher yield of the corresponding product in a very
short reaction time (entries 1–6). Similarly, urea furnished the
gem-bisuride product in excellent yield, while thiourea remained
un-reactive under such conditions (entries 10–13). This difference
is in agreed with the higher nucleophilic power of nitrogen of urea
than thiourea due to the difference in electronegativity and softness
of sulfur and oxygen.
Scheme 2. Plausible mechanism for SSA and MSA-catalyzed reaction.
4. Conclusion
In summary, we have demonstrated herein the superiority of
SSA and MSA with the reactivity order of SSA > MSA for the syn-
thesis of gem-bisamides and bisurides via the three-component
reaction of various aldehydes with two moles of amides, carba-
mates, nitriles, or urea. The reusability of solid acid catalysts, short
reaction times, high yields, and easily handling of process are
advantages of the MSA and SSA catalyzed procedures which provide
better practical alternatives to the current catalysts.
Next, the reaction scope was investigated by examining various
amide and aldehyde substrates under optimized reaction condi-
tions for MSA and SSA (Table 4).
Both electron-rich and electron-deficient aldehydes and amides,
urea, and carbamates gave the N,Nꢀ-arylidene and alkylidene
bisamides in good to excellent yields. According to these results,
a pleasurable mechanistic pathway for the probable sequence of
events is given in Scheme 2. It seems that initially H+ activates
the carbonyl group of aldehyde for reaction with amide to form
a hemiamidal intermediate. Subsequently hemiamidal dehydrates
to an acyliminium intermediate and finally condenses with another
molecule of amide to produce the gem-bisamide (Scheme 2).
Acknowledgment
We gratefully thank the Yazd University Research Council for
financial supports.

F. Tamaddon et al. / Journal of Molecular Catalysis A: Chemical 368–369 (2013) 66–71
71
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