Covalently bonded zwitterionic sulfamic acid onto the SBA-15 (SBA-15/PrEn-NHSO3H) reveals good Bronsted acidity behavior and catalytic activity in N-formylation of amines

Article abstract of DOI:10.1016/j.molcata.2015.11.002

Ethylenediamine-functionalization of SBA-15 with N¹-(3-(trimethoxysilyl)propyl)ethane-1,2-diamine (PrEn) was then underwent covalent sulfonation over secondary and primary amine groups (SBA-15/PrEn-NHSO₃H) on the surface of the mesoporous SBA-15 pore walls. Scanning electron microscope (SEM), transmission electron microscope (TEM), SEM-energy dispersive X-ray (SEM-EDX), BET surface are analysis, thermal gravimetric (TG), FT-IR spectrums and CHNS were recorded for the characterization of SBA-15/PrEn-NHSO₃H. This material was studied as a novel catalyst for N-formylation of amines. Based on the results, SBA-15/PrEn-NHSO₃H acted as zwitterionic IL-type heterogeneous catalyst with simple separation feature from the reaction mixture. Moreover, it exhibited excellent recyclability at least for 12 times, and a higher catalytic activity toward N-formylation.

Full text of DOI:10.1016/j.molcata.2015.11.002

Accepted Manuscript
Title: Covalently bonded zwitterionic sulfamic acid onto the
SBA-15 (SBA-15/PrEn-NHSO H) reveals good Bronsted
3
acidity behavior and catalytic activity in N-formylation of
amines
Author: Sadegh Rostamnia Esmail Doustkhah
PII:
S1381-1169(15)30142-4
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2015.11.002
MOLCAA 9682
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
2-10-2015
31-10-2015
8-11-2015
Please cite this article as: Sadegh Rostamnia, Esmail Doustkhah, Covalently bonded
zwitterionic sulfamic acid onto the SBA-15 (SBA-15/PrEn-NHSO3H) reveals good
Bronsted acidity behavior and catalytic activity in N-formylation of amines, Journal of
Molecular Catalysis A: Chemical http://dx.doi.org/10.1016/j.molcata.2015.11.002
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Covalently bonded zwitterionic sulfamic acid onto the SBA-15
SBA-15/PrEn-NHSO H) reveals good Bronsted acidity behavior
(
3
and catalytic activity in N-formylation of amines
Sadegh Rostamnia,* Esmail Doustkhah
Organic and Nano Group (ONG), Department of Chemistry, University of Maragheh, P.O.
Box. 55181-83111, Maragheh, Iran. Fax: +98 (421) 2276066.E-
mail:srostamnia@gmail.com; rostamnia@maragheh.ac.ir
1

Graphical abstract
2

Research highlights



Preparation of SBA-15/Et-NHSO H
3
An efficient, fast and waste-free green approach for N-formylation reaction
Represents advantages, operational simplicity, higher yield and environment friendly
with easy filterable workup.
3

Abstract
1
Ethylenediamine-functionalization of SBA-15 with N -(3-(trimethoxysilyl)propyl)ethane-1,2-
diamine (PrEn) was then underwent covalent sulfonation over secondary and primary amine
groups (SBA-15/PrEn-NHSO H) on the surface of the mesoporous SBA-15 pore walls.
3
Scanning electron microscope (SEM), transmission electron microscope (TEM), SEM-energy
dispersive X-ray (SEM-EDX), BET surface are analysis, thermal gravimetric (TG), FT-IR
spectrums and CHNS were recorded for the characterization of SBA-15/PrEn-NHSO
material was studied as a novel catalyst for N-formylation of amines. Based on the results, SBA-
5/PrEn-NHSO H acted as zwitterionic IL-type heterogeneous catalyst with simple separation
3
H. This
1
3
feature from the reaction mixture. Moreover, it exhibited excellent recyclability at least for 12
times, and a higher catalytic activity toward N-formylation.
Keywords: SBA-15/PrEn-NHSO H; zwitterionic sulfamic acid; N-formylation; green
3
method.
4

Introduction
Preparation of both highly active and heterogeneous catalyst with reasonable recyclability could
drastically eliminate harsh work-ups and therefore could minimize the consumption of
unnecessary substances (e.g. VOC compounds), energy and time required. Thus, it can result
in some economic and environmental benefits [1-3]. Among heterogeneous catalysts,
mesoporous silica materials are more famous and popular due to their higher surface area,
intrinsic stability and flexibility in functionalization with a wide range of organic groups (more
particularly with organosiloxane agents) [4-6]. Over such modifications, we can reach out to
various types of hybrid mesopores including supported organocatalysts, metal oxide, and metal
complex supported species of mesoporous silica materials which can be assumed as advanced
catalysts [3, 7]. Silica SBA-15 with rod-like mesochannels and suitable pore size for small
molecules fast diffusion and transfer have brought a wide range of catalytic applications in area
of organic synthesis [8-10]. Moreover, hybrid organic-inorganic mesochannels in catalytic
cases can provide a synergic and cooperative behaviors toward clean, chemoselective, and
favorable products with high yields [11-13].
In organic chemistry, N-formylation [14-16] of amines to give formamide derivatives is a
crucial pathway for synthesis of many pharmaceutical intermediates such as substituted aryl
imidazoles [17], fluoroquinolones [18], and 1,2-dihydroquinolines [19]. In addition, formyl
group can be utilized as an aminoprotecting group for the synthesis of peptides and N-
formylamino acid esters [20] can be regarded as a further useful application.
Herein, we have investigated the potential catalytic activity of hybrid ionic liquid-type
zwitterionic SBA-15/PrEn-NHSO
3
H in the N-formylation condensation under the aerobic and
mild conditions.
Experimental
General procedure for N-formylation
To a mixture of aniline (1 mmol) and ethyl formate (1.5 mmol), 1 mol% of SBA-15/PrEn-
o
NHSO
3
H was added and the mixture was stirred at 50 C under solvent free condition. The
progress of the reaction was monitored by TLC. After completion of the reaction, ethyl acetate
was added to the solidified mixture and the solid catalyst was separated by filtration. The filtrate
was dried over anhydrous Na
2
SO . The solvent was evaporated and the product, obtained, was
4
subjected to column chromatography. The isolated catalyst could be reused by addition of new
portions of substrate. The structure of products obtained had been confirmed by physical
5

1
1
properties such as H NMR. H NMR (300.13 MHz, CHCl
H-Ar), 8.24(d, J 8.7 Hz, H-Ar), 8.49(NH).
3
): 7.40(s, CHO), 7.74(d, J 8.7 Hz,
SBA-15/PrEn-NHSO H
3
The synthesized SBA-15 according to Zhao’s procedure was used after calcination [21, 22].
1
Then the calcined SBA-15 (1 g) reacted with solution of N -(3-(trimethoxysilyl)propyl)ethane-
1
,2-diamine (1 mL) in 50 mL toluene at reflux conditions for 24 h. The solid product was
filtered, and dried under vacuum. As-synthesized SBA-15/PrEn-NH (1 g) reacted with 3 mL
2
of chlorosulfonic acid (Zolfigol’s method) similar to our previous report [21]. Finally, after 5
min sonication and then filtration of the solid was transferred to Soxhlet extractor for 4 hour in
the presence of ethanol to discard other unfavourable produced wastes. The obtained CHNS
analysis for SBA-15/En-NHSO H, the existence of related atoms including S, O, N, H and C is
3
-1
-1
observed. This analysis for loading of nitrogen showed 1.60 mmol.g and 2.6 mmol.g sulfur
content which shows that in addition to amines, some of the hydroxyl of SBA-15 are also
+
sulfonated. pH analysis for measuring total H in SBA-15/PrEn-NHSO
3
H revealed ~2.4
-1
+
mmol.g H which verifies the CHNS analysis.
Results and discussion
Catalyst synthesis and characterization
In this paper, we aimed to design a new hybrid mesoporous silica with ionic nature and
lipophilic feature which has ability to use for organic transformations. Hence, by grafting of the
silica surface of SBA-15 with sulfamic acid, the pore walls of SBA-15 go ionic nature which
through slfamic acid and sulfamate groups. The synthesis of SBA-15/PrEn-NHSO H has been
3
achieved in three main steps: 1) preparation of the SBA-15 which is a known procedure
described by Zhao et al. and our previous report [22, 23]; 2) Post-modification of SBA-15 with
ethylenediamine based organosiloxane agent; and 3) sulfonation of the SBA-15/PrEn-NH
SBA-15/PrEn-NHSO H using chlorosulfonic acid based on Zolfigol’s [24] procedure under
ultrasonic irradiation. General pathway is represented schematically below (Scheme 1).
2
to
3
FT-IR spectra for SBA-15 and SBA-15/PrEn-NHSO
H measured in 400-4000 cm-1 are
3
represented in Figure 2. Generally, some peaks at 2800-2940 can be attributed to the presence
of alkyl chain of propyl ethylenediamine (PrEn). Meanwhile, the presence of N-H bending
-1
-1
vibration around 715 cm and the symmetric -NH bending vibration at 1520 cm further
2
-1
confirmed the existence of amine groups. A peak at 1089 cm is related to stretching of Si-O-
6

-1
Si of silica walls. 1633 cm can be assigned to vibration frequency of absorbed water in silica
-1
structure. 1445 cm can probably be attributed to presence of quaternary amine [25]. SiO-H
-1
band is appeared around 3400 cm .
Scanning electron microscope images exhibits morphology of SBA-15/En-NHSO H which has
3
been functionalized by sulfamic acids. SEM images show rod-like morphology as revealed in
Figure 3a. The transmission electron microscope image shows a maintained array for
mesoscopic channels after functionalization through IL-type sulfamic acids (Figure 3b).
Figure 4a shows the N
distribution curve of SBA-15/En-NHSO
with a H1 hysteresis loop, characteristic of mesoporous materials with uniform cylindrical pore
26]. The pore-size distribution has its maximum at 6.6 nm, as shown in the Fig. 4b. The BET
surface area, average pore diameter and total pore volume of SBA-15/En-NHSO H are 430
2
adsorption-desorption isotherm and the corresponding BJH pore-size
3
H. The material showed the typical type IV isotherms
[
3
2
-1
3 -1
m g , 5.9 nm and 1.076 cm g respectively.
Thermal gravimetery analysis (TGA) indicates the successful functionalization of SBA-15
o
surface over organic residue, sulfamic acid. A significant weight loss below 100 C can be
attributed to elimination of the adsorbed water and other physically adsorbed solvents such as
o
methanol. A weight loss between 150-400 C could be assigned to removal of organic motif
(
ethylenediamine and sulfamic acid) from the structure of SBA-15/En-NHSO H (Figure 5).
3
Catalyst test
Due to the fact that the N-formylation reaction is industrially important, several precursors are
developed for this reaction [27-30]. Hence, we selected ethyl formate for N-formylation of
amines. The advantage of ethyl formate compared to other precursors is that it is safer
compound and its handling is relatively easier than the others. In this manner, SBA-15/PrEn-
NHSO H as a catalyst was tested in the N-formylation reaction of aniline and ethyl formate as
3
model reaction under different conditions.
The effect of catalyst amount, solvent, and reaction time were carefully monitored in the
reaction under the comparable conditions. Accordingly, 1 mol% of the catalyst (based on the
+
mols of H in the catalyst) was acquired as an optimum amount and also under solvent-free
o
conditions at 50 C during 4 h reached out the yield to maximum amount (Table 1).
7

To investigate the catalytic behavior of SBA-15/PrEn-NHSO H, we compared it with various
3
types of catalysts and the results exhibited an excellent catalytic behavior compared to other
types of SBA-15 supported acidic catalysts. This can be attributed to both acidic and ionic liquid
type behavior of SBA-15/PrEn-NHSO
3
H which other traditional sulfonated heterogeneous
H, this catalyst has more acidic and efficient
catalysts. Also, compared to SBA-15/Pr-NHSO
3
ionic liquid feature in every single site of SBA-15 pore walls. To find out the active catalytic
sites, we separately studied the catalytic activity of SBA-15. We also tested the catalytic activity
of SBA-15-PrEn and found that it has low catalytic activity (Fig. 6).
Following to obtained results, we explored the scope of our method. So, we used the
optimized conditions for N-formylation of the various amines (Table 2). There was a partial
difference in the yield of products between electron-rich and un-substituted aromatic and hetero
aromatic amines. Based on the results, electro-rich and aliphatic amines were relatively more
active than the other amines which can definitely be attributed to higher nucleophilic activity
of electron-riches.
To investigate the chemoselectivity of the SBA-15/PrEn-NHSO H, the N-formylation
3
condensation reaction was performed using an equimolecular mixture of the aniline (1 mmol)
and diphenylamine (1 mmol) in the optimized reaction conditions. After 4 h, the yield of 1 was
7
9%, whereas 2 and 3 were ~0% and 10%, respectively (Scheme 2).
As mentioned, one of the advantages of heterogeneous catalysts could be their recyclability
in the reaction. To understand the recyclability of SBA-15/PrEn-NHSO
consecutive runs under the optimum conditions. Based on this test, the catalyst was recycled at
least for 12 consecutive runs. The SEM image of recycled SBA-15/PrEn-NHSO H reveals well-
3
H, we tested in
3
ordered arrays when viewed perpendicular to the channel axis even after 12 run (Figure 7b).
TON of the reaction after 12 runs was 1128.
A plausible mechanism is proposed for explanation the reaction achievement (Scheme 3).
Although this mechanism is not demonstrated based on the experimental, a rational mechanism
can be speculated for the mechanism based on the logic organic chemistry and previous reports
[
33, 34].
Conclusion
8

In summary, sulfamic-based catalyst was used as a Bronsted solid acid for the catalysis of N-
formylation condensation of various amines for green synthesis of biologically and industrially
interesting formamides. Double-sulfonation of ethylenediamine on SBA-15 led to formation of
a cooperative system for the catalysis of the reaction. This heterogeneous catalyst is more
advantageous such in viewpoint of easy handling, easy recovery and high recyclability, low
amount catalyst and bifunctional role of the catalyst, both catalyst and reaction media over ionic
liquid type behavior of sulfamic acid. Thus, a mild and green approach for N-formylation
reaction through catalysis of SBA-15/PrEn-NHSO H was developed in this paper.
3
9

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3

Fig. 1. A glimpse at N-formylation reaction under the catalysis of SBA-15/PrEn-NHSO H.
3
1
4

Fig. 2. FT-IR pattern a) SBA-15 and b) SBA-15/En-NHSO H.
3
1
5

Fig. 3. SEM a) and b) TEM images of SBA-15/En-NHSO H.
3
1
6

Fig. 4. a) N
2
adsorption–desorption isotherms and b) BJH pore size distributions for SBA-
H.
1
5/En-NHSO
3
1
7

Fig. 5. TGA of SBA-15/En-NHSO H.
3
1
8

Fig. 6. Comparison of various catalysts with SBA-15/PrEn-NHSO H. Reaction scale (2.2
3
mmol/based on aniline).
a
Details for Fe
3
O
4
@Si-OSO
The catalyst detail is in literature [32]
Details for SBA-15/Pr-NHSO H is in literature [21]
3
H is in literature [31]
b
c
3
1
9

Fig. 7. Recyclability on the N-formylation condensation: a) the resulted yields over each run,
b) TEM image of the catalyst after 12 runs.
2
0

Scheme 1. Schematic representation of preparation of SBA-15/PrEn-NHSO H.
3
2
1

Scheme 2. Chemoselectivity of the SBA-15/PrEn-NHSO H.
3
2
2

Scheme 3. Plausible mechanisms for the N-formylation condensation by SBA-15/PrEn-
NHSO H.
3
2
3

Table 1. Study of model reaction in different conditions. a
Entry Solvent b
Mol%
cat.
t (h)
T (˚C)
Yield c
(%)
1
2
3
4
5
6
7
8
9
1
1
1
PhMe
PhMe
MeOH
EtOH
2
2
1
2
2
1
0.5
1
2
8
6
6
4
8
5
4
4
4
6
2
4
r.t.
40
40
50
r.t.
50
50
50
50
50
50
r.t.
73
65
42
67
34
68
82
97
94
82
65
76
H
H
2
O
O
2
S-F
S-F
S-F
S-F
S-F
S-F
0
1
2
3
1
1
a
b
c
Reaction conditions: 2 mmol aniline, 3 mmol ethyl formate.
mL for each solvent and S-F is abbreviation of solvent-free
Isolated yields.
3
2
4

Table 2. SBA-15/PrEn-NHSO
H catalyzed green N-formylation condensation. a
3
Entry
1
Amine
Product
Yield (%) b
97
98
2
3
95
56c
85
87
4
5
6
7
8
88
82
9
90
98
1
0
2
5

1
1
97
a
b
c
Reaction conditions: scale was based on 3 mmol of amine.
Isolated yields.
o
The reaction temperature of this amine was 55 C
2
6