An efficient copper catalyzed formylation of amines utilizing CO2 and hydrogen

Article abstract of DOI:10.1039/c4ra12151a

Trans-Bis-(glycinato)copper(ii) complex was found to be a highly active, economical and efficient heterogeneous catalyst for the formylation of amines utilizing CO₂ and hydrogen under solvent free conditions. This journal is

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An efficient copper catalyzed formylation of amines utilizing CO2 and hydrogen
Subodh Kumar,a Suman L. Jain*a
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
5
characterized by XRD, XPS, FTꢀIR, and TGA. Detailed synthetic
Transꢀbisꢀ(glycinato)copper(II) complex was found to be highly
active, economical and efficient heterogeneous catalyst for the
procedure and characterization of the catalyst is given in
supporting information file. The chemical nature and
formylation of amines utilizing CO2 and hydrogen under solvent 50 functionalities presented in Cu(gly)2 complex were revealed by
less conditions.
FTꢀIR (Fig S1). Two intense peaks at 1604 and 1389 cmꢀ1 in the
spectrum of Cu(gly)2 are attributed to COOꢀ asymmetric and
symmetric stretches, respectively. Furthermore, strong bands at
3334 and 1423 cmꢀ1 are due to NꢀH stretch and bending vibrations
10
Chemical fixation of carbon dioxide (CO2) to high value
chemicals has gained considerable interest in recent years due to 55 of amino functional groups of glycine revealed the formation of
the gowning environmental concerns and its abundant availability
Cu(gly)2 complex.5 Importantly, OꢀH stretching vibration do not
appear in complex in the range (3450 – 3750) cmꢀ1 suggesting the
absence of the lattice and coordinated water. XPS analysis of
Cu(gly)2 complex was carried out to elucidate the chemical
15 at low cost. Replacement of toxic and hazardous C1 building
blocks such as phosgene, carbon monoxide with nonꢀtoxic CO2
represents a green and sustainable approach for the synthesis of
carbonyl group derived industrially important chemicals such as 60 interaction between the CuCl2 and glycine (Fig. 1). The survey
urea, alkyl carbonates, formamides, carbamates and isocynates.1
20 The formylation of amines using CO2 and hydrogen is of great
importance due to versatile applications of formamides such as
solvent, in the manufacture of polyurethane leatherette,
scan XPS spectra explicitly demonstrated the presence of C, N,
O, and Cu elements. The highꢀresolution Cu 2p spectrum
exhibited split bands of Cu 2p peak at 936.1 and 956.8 eV due to
Cu 2p3/2 and Cu 2p1/2, respectively is consistent with Cu(II)
polyacronitrile fiber and pharmaceutical industry.2 In this context 65 oxidation state.6 XRD pattern of the Cu(gly)2 complex (Fig. 1c),
a number of transition metal based catalysts such as iridium oxide
25 cluster dispersed in titania, silica hybrid aerogels containing
exhibits strong peaks and are found to be identical to the pure
Cu(gly)2 (JCPDS card No. 17ꢀ1814).7 TG analysis results of
Cu(gly)2 complex is depicted in (Fig 1d). The TG curve recorded
under N2 atmosphere at 10⁰C/min heating rate shows a single step
bidentate
ruthenium
complexes,
Pd(CO3)[P(C6H5)3]2,
RuCl2[P(CH3)3]4 etc. have been reported.3 However, in most of
the cases the use of expensive metal catalysts, rapid deactivation 70 weight loss at temperatures ranging from 50 ⁰C to 600 ⁰C. It is
of the catalyst and severe reaction conditions make the developed
30 processes less attractive for large scale synthesis. Recently, Feng
Shi et al. have demonstrated the use of Pd/Al2O3ꢀNRs as efficient
heterogeneous catalyst for amine formylation.4 However, the use
observed that there is no weight loss until 250 ⁰C, which further
confirms the absence of lattice water molecules. TGA results are
in good agreement with the results of FTꢀIR. The values of
elemental analyses (found: C, 22.41 %; H, 3.52 %, N, 13.33 %;
of expensive Pd metal, two step process of catalyst synthesis and 75 cal: C, 22.70%, H, 3.81%, N, 13.23 %) suggested the proposed
longer reaction time still leaves
35 development of an efficient and cost effective methodology for
this transformation.
a
scope for the further
formula of complex is Cu(gly)2. These results suggested the
successful formation of the substantive Cu(gly)2 complex.
In the present we disclose for the first time an efficient, easily
accessible and inexpensive bisꢀ(glycinato)copper(II) i.e. Cu(gly)2
complex as a recyclable catalyst for the formylation of various
40 secondary amines including aliphatic and aromatic using CO2 and
H2 under solvent less conditions (Scheme 1).
O
H
N
Cu(Gly)2
C
R1
H2O
CO2
H2
R1
R2
H
N
R2
Scheme 1 Cu(gly)2 catalysed formylation of amines
The Cu(gly)2 complex was easily obtained from the reaction of
45 copper chloride and glycine in ethanol under refluxing condition
in almost quantitative yields. The synthesized catalyst was
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transꢀCu(gly)2 both the axial positions are free to interact with
hydrogen and therefore gave higher rate of the reaction. Besides
these experiments, we also investigated the effect of temperature,
35 molar ratio of CO2 and H2, and reaction time on the formylation
of diethyl amine under described reaction conditions. At ambient
⁰
temperature (25 C), the reaction rate was found to be slow and
depended on the CO2 pressure applied (Fig. 2a). Among the
⁰
various conditions 85 C temperature and 50 bar CO2 pressure
40 was found to be optimum for maximum conversion of
diethylamine to corresponding formamide. Further increase in
⁰
temperature (120 C) was found to be unsuitable and exhibited
significant decrease in the formylation of diethyl amine. This may
be due to the formation of undesired Nꢀmethylated byꢀproducts.
45 In addition, the reaction was found to be increased with
increasing the molar ratio of CO2 and H2 up to 1.25 (Fig. 2b).
Further increase in CO2/H2 molar ratio did not affect the reaction
to any significant extent (Fig 2b). Next, we studied the effect of
the reaction time on the yield of the formylated product (Fig 2c).
50 The yield of the desired product was found to be increased with
time up to 4h, however further increase in reaction time did not
influence the reaction to any considerable level.
Fig 1: a) Broad scan XPS spectra of Cu(gly)2; b) High resolution XPS
spectra of Cu2p; c) XRD of Cu(gly)2; d) TGA of Cu(gly)2
The catalytic activity of the synthesized heterogeneous catalyst
i.e. Cu(gly)2 was tested for the formylation of various primary
and secondary amines including aliphatic and aromatic to the
corresponding formamides by using CO2 and hydrogen. At first,
diethyl amine was chosen as a model substrate to optimize the
reaction conditions. The experiments were carried out in a
10 stainless steel 15 ml autoclave under stirring at 85 ⁰C and 50 bar
pressure for 4h. The maximum formylation of diethyl amine
under the optimized reaction condition was found to be 95 % as
shown in Table 1, entry 4.
5
(a)
(b)
100
90
80
70
60
50
40
30
100
80
60
40
20
0
Yield
Conversion
Pressure = 50 bar
20
40
60
80
100
120
0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00
CO /H molar ratio
Temperature (oC)
2
2
In the absence of any catalyst, no reaction was taken place
15 under identical experimental conditions (Table 1, entry 1). In
order to compare the catalytic activity of the developed
heterogeneous catalyst with its homogeneous analogue, we also
carried out the formylation of diethyl amine from hydrogen and
CO2 using homogeneous copper CuCl2 and mix of CuCl2/glycine
20 as catalyst under described experimental conditions. The results
are summarized in Table 1 (entry 2ꢀ3).
100
80
60
40
20
0
100
90
80
70
60
50
40
30
(c)
(d)
1
2
3
4
5
6
7
1
2
3
4
5
Time (h)
Run
Table 1 Catalytic activity of Cu(gly)2 over its analogue
Fig. 2 a) Effect of temperature on the yield of product at 50 bar ; b) effect
55 of molar ratio of CO2/H2 on the yield of product keeping reaction pressure
50 bar at 85⁰C; c) effect of time on the yield of product at 85⁰C and 50
bar CO2 pressure; d) recyclability of the catalyst
Entry Catalyst (mol %)
Yield (%)
Selectivity (%)
1.
2.
3.
4.
5.
ꢀ
ꢀ
ꢀ
CuCl2
21
39
95
71
70
75
71
98
95
92
Furthermore, we checked the recycling ability of the recovered
catalyst. The results of the recycling experiments are summarized
60 in Fig 2d. The recovered catalyst exhibited almost similar activity
under identical conditions at least for five runs. Moreover, to
ascertain the leaching of metal, we analyzed the reaction mixture
after separating catalyst by ICPꢀAES analysis. No detectable
leaching of copper could be observed during the course of
65 reaction which further proved that the developed catalyst is truly
heterogeneous in nature.
CuCl2/Glycine
TransꢀCuꢀ(Gly)2
Cis-Cu(Gly)2.H2O
6. Trans-Cu(Gly)2.H2O
a Reaction conditions: diethyl amine (5 ml); catalyst (0.1g); molar ratio of
CO2/H2 (1.25); Total pressure of reaction (50 bar); reaction time 4h.
25
Furthermore, the reaction was extended to a variety of secondary
amines including aliphatic and aromatic under the optimized
reaction conditions. The results of these experiments are
70 summarized in Table 2. The reaction proceeded successfully and
afforded 81ꢀ95 % yield of the desired product in all cases (Table
2, entry 1,2,4ꢀ8) except in Nꢀmethyl aniline (Table 1, entry 3).
The lower reactivity of Nꢀmethyl aniline might be due to the
In the present study, we observed that transꢀCu(gly)2 complex
exhibited higher catalytic activity as compared to its hydrated cisꢀ
and transꢀanalogues (Table 1, entry 4ꢀ6). The lower catalytic
activity of the hydrated complexes might be due to the presence
30 of water molecules on the axial position8 which hindered the
copper to interact with hydrogen from one side. While in case of
2
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presence of aromatic ring and steric hindrance.
reacts with CO2 to give HCOOH. Formic acid subsequently
reacts with amine in the dehydration step to give corresponding
15 formamides. It is also clear from the mechanism that high
pressure of CO2 is favourable to shift the equilibrium towards
forward direction.
In summary, we have developed an easily accessible, cost
effective copper (II) glycinato to be used as highly efficient,
20 recyclable and selective catalyst for the formylation of secondary
amines directly from the reaction of CO2 and H2 without using
any solvent.
Table 2 Cu(Gly)2 catalyzed formylation of amines
Entry
Substrate
Product
Yield
(%)
Select.
(%)
O
H
N
CH3
1.
91
95
96
98
H
N
H3C
CH3
CH3
O
H
C2H5
N
2.
3.
4.
H
N
Notes and references
C2H5
C2H5
H
C2H5
aChemical Sciences Division, CSIR-Indian Institute of Petroleum,
25 Mohkampur, Dehradun-248005, India. Fax: +91-135-2525788; Tel:
+91-135-2660202; E-mail: suman@iip.res.in
† Electronic Supplementary Information (ESI) available: [Experimental,
FTꢀIR, XRD, TGA and Proton NMR data of products]. See
DOI: 10.1039/b000000x/
H3C
N
O
41
95
85
97
H
N
CH3
30
35
40
45
50
55
1
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O
H
N
H
O
N
H
N
H
N
5.
6.
91
90
97
96
2
3
CH3
CH3
NH
O
H
N
O
H
N
4
5
H
N
7.
8.
81
92
91
N
H
N
H
6
7
O
O
O
8
9
95
H
N
N
H
O
a Reaction conditions: amine (5 mL); catalyst (0.1 g); molar ratio of
5
CO2/H2 =1.25; Total pressure of reaction 50 bar; 85 ⁰C; 4 h
Although, the exact mechanism of the reaction is not clear at this
stage, based on the existing literature reports,9 a plausible
mechanism for the reaction is shown in Scheme 2. In analogy to
10 the previous reports, we presumed that Cu activates the H2 which
H
H2
Cu
Cu
H
H
ꢀCO2
CO2
Cu
N
R1
R2
O
R1
N
C
R2
ꢀH2O
H
HCOOH
Scheme 2 Possible Reaction Mechanism
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An efficient copper catalyzed formylation of amines utilizing
CO2 and hydrogen
Cu(gly)2
CO2
O
R1
T=85oC, P=50 bar
H2
H
N
H
N
R2
R1
R2
4
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