Direct Synthesis of Cyclic Imides from Carboxylic Anhydrides and Amines by Nb2O5 as a Water-Tolerant Lewis Acid Catalyst

Article abstract of DOI:10.1002/cctc.201501172

In the 20 types of heterogeneous and homogenous catalysts screened, Nb₂O₅ showed the highest activity for the synthesis of N-phenylsuccinimide by dehydrative condensation of succinic anhydride and aniline. Nb₂O₅ was used in the direct imidation of a wide range of carboxylic anhydrides with NH₃ or amines with various functional groups and could be reused. Kinetic studies showed that the Lewis acid Nb₂O₅ catalyst was more water tolerant than both the Lewis acidic oxide TiO₂ and the homogeneous Lewis acid ZrCl₄, which resulted in higher yields of imides through the use of Nb₂O₅. Int-imidation tactics: A general method for the direct synthesis of cyclic imides from cyclic anhydrides with amines (or ammonia) under solvent-free conditions is reported. Kinetic studies indicate that the Lewis acid sites of Nb₂O₅ are highly water tolerant, which results in high catalytic activity for imidation even in the presence of water formed during the reaction. The catalyst can be recovered and reused four times without a marked decrease in yield.

Full text of DOI:10.1002/cctc.201501172

DOI: 10.1002/cctc.201501172
Communications
Direct Synthesis of Cyclic Imides from Carboxylic
Anhydrides and Amines by Nb O as a Water-Tolerant
2
5
Lewis Acid Catalyst
Md. A. Ali, Sondomoyee K. Moromi, Abeda S. Touchy, and Ken-ichi Shimizu*
[a]
[a]
[a]
[a, b]
In the 20 types of heterogeneous and homogenous catalysts
screened, Nb O showed the highest activity for the synthesis
agents. One of the most effective synthesis routes to cyclic
imides by dehydrogenative coupling of diols and amines (or
2
5
[
1a,14]
of N-phenylsuccinimide by dehydrative condensation of suc-
nitriles) catalyzed by a Ru complex
still suffers from limited
cinic anhydride and aniline. Nb O was used in the direct imi-
substrate scope of the diols and amines.
2
5
dation of a wide range of carboxylic anhydrides with NH or
Catalytic synthesis of cyclic imides by condensation of cyclic
anhydrides with amines is one of the most desirable routes. A
3
amines with various functional groups and could be reused. Ki-
netic studies showed that the Lewis acid Nb O catalyst was
few catalytic methods performed with the use of TaCl /
2
5
5
[
15a,b]
[15c]
more water tolerant than both the Lewis acidic oxide TiO and
SiO2
or 1,4-diazabicyclo[2.2.2]octane (DABCO)
are re-
2
the homogeneous Lewis acid ZrCl , which resulted in higher
ported to synthesize cyclic imides from cyclic anhydrides with
4
[
15]
yields of imides through the use of Nb O .
amines. These methods suffer from some drawbacks, includ-
ing a limited substrate scope, no results on catalyst reuse, and
the need for high catalyst loadings and special methods (e.g.,
2
5
[
15a,b]
Cyclic imides and their derivatives are an important class of
microwave heating).
Potentially, the reaction can be cata-
[1,2]
substrates for biological and chemical applications;
they are
lyzed by a Lewis acid, but the co-presence of water as a by-
product can suppress Lewis acidity by hindering coordination.
Inspired by recent reports that several metal oxides, such as
used as intermediates in the industrial production of drugs,
[
1a,b,2]
dyes, and polymers.
However, sustainable methods for the
[
16a]
[16]
synthesis of cyclic imides from readily available starting materi-
als are limited. General methods for the synthesis of cyclic
imides include the dehydrative condensation of dicarboxylic
Nb O ,
act as water-tolerant Lewis acid catalysts, we re-
2
5
cently reported that Nb O acts as a water-tolerant Lewis acid
2
5
catalyst for the direct imidation of dicarboxylic acids with
[
3]
[3f,4,5,6]
[17]
[18]
acids or their anhydrides
conditions (250–3808C, ꢀ33.0 MPa)
heating and the cyclization of an amic acid with the help of
with an amine under harsh
amines and the direct amidation of esters with amines.
[3a,b]
or under microwave
We reported our preliminary results on the synthesis of cyclic
[
5,6]
[17]
imides from cyclic anhydrides, but detailed catalytic proper-
acidic reagents or in the presence of an excess amount of
a promoter (e.g., Lewis acid, base, dehydrating agent). These
methods suffer from drawbacks such as low atom efficiency,
limited substrate scope, production of stoichiometric amounts
of byproducts, and the need for special procedures (e.g., mi-
ties such as substrate scope and kinetic studies were not re-
ported. Herein, we report a general catalytic method for the
direct synthesis of cyclic imides from cyclic anhydrides with
amines (or ammonia) under solvent-free conditions.
2
À1
Nb O (surface area=54 m g ) was prepared by calcination
2
5
[7]
[8]
crowave heating). New synthetic routs from nitriles, halides,
of niobic acid (supplied by CBMM) at 5008C for 3 h; the Lewis
[
9]
[10]
[11]
alkynes, arylboronic acids,
aromatic amides,
aliphatic
acid characteristics of Nb O are reported in our previous
2
5
[
12]
[13]
[17–19]
amides,
and cyclic amines
have been developed, but
studies.
these homogeneous catalytic methods have drawbacks such
as low atom efficiency, narrow substrate scope, the use of
toxic reagents or additives, and difficulties in catalyst/product
separation and catalyst reuse. For example, a reusable hetero-
As listed in Table 1, 20 types of heterogeneous and homoge-
neous catalysts were screened for the model imidation of equi-
molar amounts of succinic anhydride and aniline under sol-
vent-free conditions at 1408C for 15 h (Table 1). Note that the
reaction hardly proceeded under catalyst-free conditions
(Table 1, entry 1). Thus, Table 1 shows the results of catalytic
imidation. First, we screened 12 types of simple metal oxides
[8d]
geneous catalytic system of Pd/C suffers from the need for
the use of halides and CO as less environmentally benign re-
(
Table 1, entries 2–13). Among the metal oxides tested, Nb O5
2
[
a] M. A. Ali, S. K. Moromi, Dr. A. S. Touchy, Prof. Dr. K.-i. Shimizu
Institute for Catalysis
Hokkaido University
showed the highest yield (90%) of the corresponding imide, N-
phenylsuccinimide. The hydrate of Nb O , called niobic acid
2
5
N-21, W-10, Sapporo (Japan)
E-mail: kshimizu@cat.hokudai.ac.jp
(Table 1, entry 3), gave a lower yield (22%) than Nb O . Two of
2
5
[
19,20]
the oxides having Lewis acidity (ZrO and TiO )
showed
2
2
[
b] Prof. Dr. K.-i. Shimizu
moderate yields of 59–65% (Table 1, entries 4 and 5). Other
Elements Strategy Initiative for Catalysis and Batteries
Kyoto University
Katsura, Kyoto 615-8520 (Japan)
oxides such as SnO , g-Al O , SiO , and CaO showed low yields
2
2
3
2
of 8–45%. Next, we tested conventional solid acids such as
3
+
a Lewis acidic clay, Fe -mont (Table 1, entry 14), HBEA zeolite
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201501172.
(Table 1, entry 16), and water-tolerant Brønsted acid catalysts
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Table 1. Catalyst screening for the synthesis of cyclic imides from
anhydrides.
[a]
Entry
Catalyst
blank
Yield [%]
1
2
3
4
5
6
7
8
9
<1
90
22
65
59
45
42
38
17
16
15
15
8
31
60
40
31
46
44
33
18
Nb
niobic acid
ZrO
TiO
SnO
Ta
ZnO
g-Al
2 5
O
2
Figure 1. Initial rate for imidation of succinic anhydride (1 mmol) with aniline
2
(1 mmol) in the presence of H
2
O (0, 1, 3, and 5 mmol) catalyzed by 50 mg of
2
Nb , TiO , or ZrCl as a function of the initial concentration of water.
2
O
5
2
4
2
O
5
2
O
3
reaction order with respect to water. The reaction orders are
1
0
SiO
2
1
1
CeO
2
À0.11, À0.34, and À0.50 for Nb O , TiO , and ZrCl , respective-
2
5
2
4
1
1
1
1
1
1
1
1
2
2
2
3
4
5
6
7
8
9
0
1
MgO
CaO
ly, which clearly indicates that the negative impact of water in-
creases in the order Nb O <TiO <ZrCl . Figure 2 compares
3
+
2
5
2
4
Fe -mont
HZSM5 zeolite
HBEA zeolite
Amberlyst-15
Nafion–SiO
ZrCl
Sc(OTf)
HfCl
2
4
3
4
[
a] Determined by GC.
including HZSM5 zeolite with a SiO /Al O ratio of 300 (Table 1,
2
2
3
entry 15) and commercial acidic resins (Table 1, entries 17 and
[21]
1
8). These solid acids gave low to moderate yields (31–60%)
of N-phenylsuccinimide. Finally, we tested homogeneous Lewis
[
22]
acids
Lewis
Sc(OTf) ; Table 1, entry 20]. These homogeneous catalysts
(Table 1, entries 19–21) including the water-tolerant
Figure 2. Time–yield profiles for the imidation of succinic anhydride
4
(1 mmol) with aniline (1 mmol) catalyzed by 50 mg of Nb , TiO , or ZrCl .
[
22c,d]
2
O
5
2
acid
scandium(III)
trifluoromethanesulfonate
[
3
gave low yields of the product (18–44%).
the time–yield profiles for the imidation reaction in the ab-
sence of water. The initial slopes for Nb O , TiO , and ZrCl do
With the most effective catalyst (i.e., Nb O ), we tested the
2
5
2
5
2
4
model reaction in the absence and in the presence of different
solvents (Table S1, Supporting Information). We found that if
the reaction was performed under solvent-free conditions, the
product was obtained in a higher yield than if the reaction was
performed in a solvent such as toluene or o-xylene.
not markedly depend on the catalyst, but the final yield after
15 h depends strongly on the catalyst. The yield for the Nb O -
2
5
catalyzed reaction monotonically increased with time, whereas
the yields for the TiO - and ZrCl -catalyzed reactions leveled
2
4
off. Considering that water is produced during the dehydrative
condensation reaction, combined with the result that the neg-
ative impact of water increases in the order Nb O <TiO <
To discuss a possible reason why Nb O showed high catalyt-
2
5
ic activity for the model reaction of succinic anhydride with
aniline, we studied kinetic experiments. First, we measured ini-
tial rates of imide formation in the absence and in the pres-
2
5
2
ZrCl (Figure 1), the result in Figure 2 indicates that the water
4
molecules formed during the reaction inhibit the Lewis acid
catalysis of TiO and ZrCl , whereas the water molecules do not
ence of H O (1, 3, and 5 mmol) by using 50 mg of the catalysts.
2
2
4
Two heterogeneous Lewis acid catalysts (i.e., Nb O and TiO )
markedly inhibit the Lewis acid catalysis of Nb O . Thus, Nb O
2 5 2 5
2
5
22a]
2
[
and a homogeneous Lewis acid catalyst (i.e., ZrCl4)
were se-
is a more water-tolerance Lewis acid catalyst than TiO and
2
lected for comparative purposes. Note that the rates were
measured under conditions for which the conversions were
below 40%. Figure 1a plots the reaction rates as a function of
the initial concentration of water. For all catalysts, the addition
of water decreased the reaction rate, and the rate was lower at
a higher concentration of water. Figure 1b shows double loga-
rithmic plots for the results in the presence of water in the ini-
tial mixture, in which the slope of the line corresponds to the
ZrCl4.
Next, we studied the effectiveness of the Nb O -catalyzed
2
5
imidation of carboxylic anhydrides with amines. The results of
a gram-scale reaction are shown in Scheme 1. The reaction of
succinic anhydride (10 mmol) with n-octylamine (10 mmol) in
the presence of Nb O (50 mg) for 67 h gave the correspond-
2
5
ing imide in 79% yield. Previously, we reported the number of
surface Lewis acid sites on the Nb O catalyst by pyridine ad-
2
5
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Scheme 1. A gram-scale reaction of succinic anhydride with n-octylamine in
the presence of Nb
2
5
O .
[17,19]
sorption IR spectroscopy at 2008C.
The turnover number
(
(
TON) with respect to the Lewis acid sites of Nb O5
2
À1
0.056 mmolg ) was calculated to be 2820.
Figure 3 shows the reusability of the Nb O catalyst for the
2
5
imidation of succinic anhydride (1 mmol) with n-octylamine
Scheme 2. Substrate scope for imidation of succinic anhydride with different
amines.
Figure 3. Reuse of Nb
2 5
O for the imidation of succinic anhydride with
n-octylamine under the conditions shown in Scheme 2.
(
1 mmol) over 15 h. After the reaction, 2-propanol (4 mL) was
added to the mixture, and the catalyst was separated from the
mixture by centrifugation, followed by washing with acetone
and drying at 908C for 3 h. The recovered catalyst was reused
over four cycles without a marked decrease in the yield of the
product. Analysis of the solution by inductively coupled
plasma atomic emission spectroscopy (ICP-AES) confirmed that
the content of Nb in the solution was below the detection
limit. From the results, we can conclude that Nb O is as a reus-
Scheme 3. Synthesis of phthalimides from phthalic anhydride and various
primary amines.
2
5
able heterogeneous catalyst for the title reaction.
groups, cyclohexylamine, phenylethylamine, and n-octylamine
were all converted into the corresponding N-substituted
phthalimides in moderate to high yields (55–92%).
Finally, we studied the substrate scope for the present cata-
lytic system. Scheme 2 shows the results of the imidation of
succinic anhydride (1 mmol) with different amines (1 mmol).
Under the standard solvent-free conditions with the use of
a small amount of Nb O (0.29 mol% based on the number of
Scheme 4 shows the reactions of n-octylamine with various
cyclic anhydrides. Gluteric anhydride, 1,8-naphthalic anhydride,
and 4-nitrophthalic anhydride were all transformed into the
corresponding N-substituted cyclic imides in moderate to high
yields (65–88%).
2
5
[17,19]
Lewis acid sites on Nb O ),
the mixture was heated at
2
5
1
408C for 15 h. Anilines with different functional groups (e.g.,
H-, MeO-, Cl-) in the para position, benzylamines, heteroaro-
matic amines with pyridyl and furanyl groups, linear and cyclic
aliphatic amines, and amines with phenyl and hydroxy groups
were all converted into the corresponding N-aryl imides in
good to high yields (65–98%).
Notably, unsubstituted cyclic imides were also synthesized
from cyclic anhydrides and ammonia under azeotropic reflux
conditions in n-octane (Scheme 5). The reactions of succinic
anhydride and phthalic anhydride in a closed stainless reactor
under NH pressure (0.3 MPa) at 1408C resulted in succinimide
3
The method was also effective for the direct synthesis of
phthalimides from readily available phthalic anhydride and
equimolar amounts of amines (Scheme 3). Benzyl amine, heter-
oaromatic amine, anilines with electron-rich and electron-poor
in 78% yield and phthalimide in 81% yield, respectively.
Summarizing the above results, we can conclude that the
present method involving the use of a catalytic amount of
Nb O is widely applicable to the direct imidation of various
2
5
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Published online on February 4, 2016
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