Carbonylation of quaternary ammonium salts to tertiary amides using NaCo(CO)4 catalyst

Article abstract of DOI:10.1016/j.molcata.2013.10.014

We reported here the catalytic carbonylation of quaternary ammonium salts under anhydrous condition. Quaternary ammonium salts, a kind of versatile reagents that were widely used in organometallic chemistry, can be carbonylated to tertiary amides by an in situ prepared NaCo(CO)₄ catalyst. It was found that the counterions (Cl^-, Br^-, I^-, OTf^-) in the quaternary ammonium salts played a significant role in the reaction and tetramethylammonium iodide could give high yield (96%) of N,N-dimethylacetamide (DMAc) with only 0.5 mol% cobalt catalyst. Under optimum conditions, several other quaternary ammonium iodides were also carbonylated to corresponding tertiary amides in moderate to excellent yields. Obviously, these results also give us a special apprehension that Me₄NI and other quaternary ammonium salts could be possibly carbonylated to tertiary amides in the carbonylation reaction where they are used as promoters or solvents in most cases. Considering the high activity and moderate to excellent selectivity, this process could be a potential method for the synthesis of certain tertiary amides. Moreover, the cleaving mechanism of CN bonds and the possible catalytic intermediates were discussed in detail.

Full text of DOI:10.1016/j.molcata.2013.10.014

Journal of Molecular Catalysis A: Chemical 381 (2014) 120–125
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Carbonylation of quaternary ammonium salts to tertiary amides using
NaCo(CO) catalyst
4
a
a
a
a
b
a,∗
Yizhu Lei , Rui Zhang , Qing Wu , Hui Mei , Bo Xiao , Guangxing Li
a
School of Chemistry and Chemical Engineering, Hubei Key Laboratory of Material Chemistry and Service Failure, Huazhong University of Science and
Technology, Luoyu Road 1037, Wuhan, Hubei 430074, PR China
College of Environment Science and Engineering, Huazhong University of Science and Technology, Luoyu Road 1037, Wuhan, Hubei 430074, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 June 2013
Received in revised form 12 October 2013
Accepted 20 October 2013
Available online 27 October 2013
We reported here the catalytic carbonylation of quaternary ammonium salts under anhydrous condi-
tion. Quaternary ammonium salts, a kind of versatile reagents that were widely used in organometallic
chemistry, can be carbonylated to tertiary amides by an in situ prepared NaCo(CO)4 catalyst. It was found
that the counterions (Cl , Br , I , OTf ) in the quaternary ammonium salts played a significant role in
the reaction and tetramethylammonium iodide could give high yield (96%) of N,N-dimethylacetamide
−
−
−
−
(
DMAc) with only 0.5 mol% cobalt catalyst. Under optimum conditions, several other quaternary ammo-
Keywords:
Carbonylation
Quaternary ammonium salt
Tertiary amide
NaCo(CO)4 catalyst
nium iodides were also carbonylated to corresponding tertiary amides in moderate to excellent yields.
Obviously, these results also give us a special apprehension that Me4NI and other quaternary ammonium
salts could be possibly carbonylated to tertiary amides in the carbonylation reaction where they are used
as promoters or solvents in most cases. Considering the high activity and moderate to excellent selectiv-
ity, this process could be a potential method for the synthesis of certain tertiary amides. Moreover, the
cleaving mechanism of C N bonds and the possible catalytic intermediates were discussed in detail.
©
2013 Elsevier B.V. All rights reserved.
1
. Introduction
the main products employing benzyltriethylammonium or allyltri-
ethylammonium halides as substrates. Recently, we found that the
tetramethylammonium iodide was in equilibrium with MeI and the
Quaternary ammonium salt, a versatile reagent, is widely used
◦
as phase transfer catalyst, catalyst promoter or ionic liquid sol-
vent in organometallic chemistry and homogeneous carbonylation
reactions [1–4]. Generally, quaternary ammonium salts are con-
sidered to be very stable for their high decomposition temperature
Me N at 220 C [16,17]. It suggests the high possibility that Me NI
3
4
◦
could be carbonylated to DMAc at 220 C. Moreover, quaternary
ammonium salts are widely used as phase-transfer catalysts, cata-
lyst promoters and ionic liquid solvents in many catalytic reactions,
especially in homogeneous carbonylation reactions [1–4]. There-
fore, it is very valuable to investigate the stability and reactivity of
different quaternary ammonium salts under anhydrous carbonyla-
tion reaction conditions.
[
5,6]. The reactivity of quaternary ammonium salt is usually easy
to ignore in transition metal catalyzed reaction. Since Wenkert
et al. documented the first cross coupling of aryltrimethylammo-
nium iodides with aryl and alkyl Grignard reagents in 1988 [7],
transition-metal-catalyzed cross-coupling of quaternary ammo-
nium salts with various nucleophile coupling partners is becoming
an attractive topic [8–10]. And now, transformations of amines
to their salts are also becoming one of the main methods for the
functionalization of unreactive C N bonds [11–13].
Although it was also known in the 1980s [14], the potential for
carbonylation of quaternary ammonium salts has not received a
great deal of attention, and in fact, only a few results have been
reported to date [14,15]. These reactions were usually involved
From the other points of view, amide bond formation, one of the
most important reactions in organic chemistry, is often overlooked
as a contemporary topic due to its widespread occurrence of amide
in chemistry and biology [18–21]. As an important class of amide
compounds, tertiary amides were also frequently used as precur-
sors to unsymmetrical tertiary amines [22,23]. However, traditional
synthesis method of tertiary amides via coupling of carboxylic
acid derivatives and secondary amines is suffering from tedious
processes and poor atom economy. Therefore, there is continuing
interest in the development of new and improved methodolo-
gies for their synthesis [24–37]. As an alternative method for the
synthesis of tertiary amides, efforts have also been made to syn-
thesize tertiary amides by direct carbonylation of tertiary amines
[16,17,38,39]. As the more reactive reagent, however, quaternary
a C H /aqueous NaOH biphasic system and carboxylic acids as
6
6
∗ Corresponding author. Tel.: +86 27 87543632; fax: +86 27 87543632.
E-mail address: ligxabc@163.com (G. Li).
1
381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2013.10.014

Y. Lei et al. / Journal of Molecular Catalysis A: Chemical 381 (2014) 120–125
121
appropriate amount of NaCl solution was added, and then the pre-
cipitate was filtrated, dried and weighed.
2.4. Amine exchange reaction
Me NI (10 mmol), N,N-diethylaniline (10 mmol) and NMP
4
(50 mL) were charged into the autoclave. After purging four times
Scheme 1. Cobalt catalyzed carbonylation of quaternary ammonium salts.
with N2, the autoclave was heated and then kept at the reaction
temperature for 7 h. After the reaction, autoclave was cooled by ice
water and analyzed by GC and GC–MS.
ammonium salts have not yet been employed as the substrates for
the synthesis of tertiary amides.
Based on our previous work on transition metal-catalyzed
carbonylation reactions and continuing focus on the application
of quaternary ammonium salts in homogeneous carbonylation
reactions [16,17,40,41]. Herein, we established the carbonyla-
tion of quaternary ammonium salts under anhydrous condition
3. Results
3.1. Effect of counterion and solvent
Initially, the carbonylation of tetramethylammonium salt bear-
ing different anions (I , Br , Cl and OTf ) was chosen as a model
reaction. [Co(CO) ] , which could be prepared under mild condi-
tions, was used as a catalyst. When the as-prepared NaCo(CO)4
−
−
−
−
(Scheme 1). Due to its high catalytic activity and moderate to excel-
−
lent selectivity, this process can be a promising method for the
synthesis of certain tertiary amides. Moreover, the cleaving mech-
anism of C N bonds was discussed and a plausible mechanism was
also proposed.
4
◦
(5 mol%) was used at 3.0 MPa CO and 200 C, 13.3% yield of DMAc
was observed in the carbonylation of tetramethylammonium chlo-
ride (Table 1, entry 1). Encouraged by this initial result, we tried to
investigate the activity of different tetramethylammonium salts.
Fortunately, tetramethylammonium iodide gave 98.2% yield of
DMAc with MeI as the only byproduct (Table 1, entry 4). Mean-
while, the bromide and triflate gave moderate yields of DMAc
(Table 1, entries 2 and 3). These results suggested that the anion
had a great effect on the activity of tetramethylammonium salts,
and their reactivity increased in the order Cl < OTf < Br < I. Moreover,
as tetramethylammonium iodide is conventionally synthesized by
the quaternization reaction of methyl iodide and trimethylamine.
After the catalytic carbonylation of tetramethylammonium iodide,
the byproduct (MeI) could be easily recovered by a simple process
2
. Experimental
2.1. Reagents
All reagents were analytical grade and used without
further purification. N-methyl pyrrolidone (NMP), N,N-
dimethylformamide (DMF) and toluene were analytical grade
and dried before use by normal procedures. CO with a purity of
9
9.99% was purchased from the local manufacturer. NaCo(CO)4
was prepared as our previous publication [16].
(see supplementary content) and reused again as the raw mate-
2.2. Catalytic experiments
rial for the synthesis of tetramethylammonium iodide. Since a high
recovery of methyl iodide could be achieved, then the poor atom
economy of this process is mitigated and the raw material costs
could be reduced.
It is well-known that solvent is very important in a liquid phase
catalytic reaction, even more so in a two-liquid phase reaction
The catalytic reactions were carried out in a 250 mL stainless
steel autoclave. In a typical experiment, CoCl , Zn, Na SO , quater-
2
2
3
nary ammonium salt and NMP were charged into the autoclave.
After purging four times with CO, the autoclave was pressurized
◦
with CO to 3.0 MPa, heated and kept at 200 C for 7 h. During the
[
4,43]. Therefore, the solvent effect on the reaction was tested.
Similarly, the reaction in DMF solvent gave 93.0% yield of DMAc
Table 1, entry 5). In contrast, only 64.5% yield of the desired prod-
reaction, CO was added to maintain a total pressure of 4.0 MPa.
After the reaction, autoclave was cooled by ice water and slowly
depressurized to atmospheric pressure.
(
uct was achieved in toluene (Table 1, entry 6). To achieve the easy
separation of the catalyst and product, the reaction was also tried
in a biphasic solvent system. When the reaction was carried out
in a toluene-water mixture, very low activity and selectivity were
obtained. Increasing the amount of water in the reaction led to
lower catalytic activity and selectivity of DMAc. Meanwhile, the
yield of acetic acid rapidly increased (Table 1, entries 7 and 8).
The liquid mixture taken from the autoclave after the reac-
tion was analyzed qualitatively by GC–MS. The analyses were
performed in an Agilent 6890/5973 GC–MS apparatus equipped
with a split/splitless injection system and a flame ionization
detector (FID). The capillary column was an Agilent HP-5MS,
3
0 m × 0.25 mm × 0.25 ␮m. He was used as the carrier gas
1.0 mL/min). The quantitative analysis of the reaction mixture was
carried out in an Agilent GC 1790 apparatus equipped with a HP-
(30 m × 0.32 mm × 0.25 ␮m) capillary column, a flame ionization
detector (FID) and using n-butanol as an internal standard.
(
5
3.2. Effect of catalyst and catalyst dosage
Having established the better reactivity of iodide over other
salts, then we explored alternative catalyst to simplify the prepa-
ration procedure of the catalyst and to lower the catalyst dosage.
First, an attempt had been made to use CoCl2 as a catalyst directly,
while only a trace amount of product was observed (Table 2, entry
1). Then, we tried to use CoCl2 as a catalyst precursor for in situ
preparation of NaCo(CO)4 during the catalytic reaction. Notably,
when 5 mol% of CoCl2 and proper amount of reducing agents were
directly added to the reaction, quantitative conversion along with
selectivity (98.8%) was obtained (Table 2, entry 2). The exceptional
reactivity of the tetramethylammonium iodide suggested that the
catalyst dosage could be lowered further; this was indeed possible
2
.3. Quantitative analysis of quaternary ammonium salts
Quantitative analysis of quaternary ammonium salt was made
by a method described in literature with some modification [42].
After the reaction, the reaction mixture was filtrated to remove
solid residues. The filtrate obtained was vacuum distilled to remove
the liquid substances. Then the residual solid was dissolved in
water, and after that, an excess amount of aqueous sodium
tetraphenylborate solution was added dropwise into the solution
and the white precipitate was formed immediately. To insure the
fully precipitation of quaternary ammonium tetraphenylborate,

1
22
Y. Lei et al. / Journal of Molecular Catalysis A: Chemical 381 (2014) 120–125
Table 1
Effect of counterion and solvent.a
Entry
Solventb
Counterion
Time (h)
Conversion (mol%)
Selectivity (mol%)
YieldDMAc (mol%)d
Acetic acid (mol%)d
−
1
2
3
NMP
NMP
NMP
NMP
Cl
14
14
14
7
7
7
13.6
65.7
55.0
99.7
95.6
65.4
55.8
32.1
97.5
98.1
97.2
98.5
97.2
98.7
63.0
12.7
13.3
64.5
53.5
98.2
93.0
64.5
35.2
4.1
–
–
–
–
–
–
19.4
11.0
−
Br
−
OTf
c
−
4
I
−
5
6
7
8
DMF
Toluene
Toluene/water (9:1)
Toluene/water (1:1)
I
−
−
I
I
7
7
−
I
a
◦
Reaction conditions: NaCo(CO)4 (0.75 mmol); tetramethylammonium salt (15 mmol); solvent (50 mL); CO (3 MPa); 200 C; stirring speed, 500 rpm.
Toluene/water (weight ratio).
b
c
Yield of MeI 98.0 mol%.
d
nx
n0
Yield =
× 100% (nx, the molar number of the product; n0, the molar number of the initially added ammonium salt).
Table 2
Effect of catalyst and catalyst dosage.a
Entry
Catalyst
Substrate:catalyst molar ratio
Conversion (mol%)
Selectivity (mol%)
Yield (mol%)
TONb
1
2
3
4
5
6
7
CoCl2
20
20
50
100
200
400
400
6.3
99.6
99.8
99.5
97.4
83.3
84.9
99.0
98.8
98.7
98.7
98.9
98.7
98.5
6.2
98.4
98.5
98.2
96.3
82.2
83.6
1.2
19.7
49.3
CoCl2/Zn/Na2SO3
CoCl2/Zn/Na2SO3
CoCl2/Zn/Na2SO3
CoCl2/Zn/Na2SO3
CoCl2/Zn/Na2SO3
NaCo(CO)4
98.2
192.6
328.8
334.4
a
◦
Reaction conditions: CoCl2:Zn:Na2SO3 = 1:1.33:1 (mole ratio); Me4NI (15 mmol); NMP (50 mL); CO (3 MPa); 200 C; reaction time, 7 h; stirring speed, 500 rpm.
TON (mol converted Me4NI/mol cat.).
b
and the reaction proceeded almost equally as fast with 0.5 mol% cat-
gave excellent conversion with moderate selectivity. Alicyclic
quaternary ammonium salts, such as N,N-dimethylpyrrolidinium
iodide and N,N-dimethylpiperidinium iodide, reacted with CO
to afford the corresponding amides in moderate to excellent
yields (Table 4, entries 2 and 3). N,N-dimethylmorpholinium
iodide, as a representative example of heterocyclic quaternary
ammonium salt, resulted in 72.3% yield of N-acetylmorpholine
(Table 4, entry 4). Aryltrimethylammonium iodide, one of the
most common substrates in cross coupling reaction [7,10], gave
N-methyl-N-phenyl-acetamide in 93.7% yield (Table 4, entry
5). Aryltriethylammonium iodide and benzyltrimethylammonium
iodide gave the corresponding products in 49.7% and 41.7% yield,
respectively (Table 4, entries 6 and 7). These results demonstrated
that the carbonylation of quaternary ammonium salts was a com-
mon phenomenon under these carbonylation reaction conditions.
Obviously, it gives us a special alarm that Me4NI and other qua-
ternary ammonium salts could be possibly carbonylated to tertiary
amides in the carbonylation reaction where they are used as pro-
moters or solvents in most cases, more or less, which would be
interfere the main carbonylation reaction.
alyst (Table 2, entry 5). Next experiments revealed that this in situ
synthesis of NaCo(CO)4 showed almost the same catalytic activity
as the as-prepared NaCo(CO)4 (Table 2, entries 6 and 7). It must be
noted that the catalytic activity of this process is much higher than
those reported for the carbonylation of trimethylamine [16,17].
3.3. Effect of temperature and CO pressure
Quaternary ammonium salts are widely used as phase-transfer
catalysts, catalyst promoters and ionic liquid solvents in catalytic
carbonylation reaction [4]. However, the reactivity of quaternary
ammonium salts in catalytic carbonylation reactions is seldom
documented. Alper and Caubere have reported that benzyltri-
ethylammonium and allyltriethylammonium halides could be
carbonylated to corresponding acids in a C H /aqueous NaOH
6
6
solution [14,15]. Unfortunately, substrates in these reports were
only limited to aryl or benzyl quaternary ammonium halides
and the reactions took place under specific conditions, that is, in
C H /aqueous NaOH solution. To investigate the reactivity of qua-
6
6
ternary ammonium salts in anhydrous organic solvent, the effect of
reaction temperature and CO pressure on the carbonylation in NMP
4. Discussion
solvent was examined (in Table 3). It was found that Me NI could
4
◦
react with CO in a very low rate at 140 C (Table 3, entry 2). With
4.1. C N bond cleavage of quaternary ammonium salts
◦
◦
the increase of reaction temperature from 140 C to 180 C, Me NI
4
conversion increased significantly and a consistent selectivity of
DMAc was preserved (Table 3, entries 2–4). Further increasing the
temperature to 200 C, much higher yield of DMAc was obtained
The cleavage of C N bonds to form useful N-containing fine
chemicals is of significant interest because such bonds are very
common in organic chemistry [44,45]. However, C N bonds are
generally very strong and usually difficult to cleave. For the func-
tionalization of the unactivated C N bonds, the bonds are usually
activated by conversion to their salts [7–13]. Therefore, investiga-
tion about the cleaving mechanism of C N bonds in ammonium
salts could be informative for such kinds of reactions. We orig-
inally assumed that C N bonds in quaternary ammonium salts
could be cleaved either by the thermal decomposition or by the
◦
(Table 3, entry 5). The influence of pressure on the carbonylation
of Me NI was presented in Table 3 (entries 5–8). It is obvious that
4
there is a significant relationship between the conversion and the
CO pressure. The conversion increased notably from 12.1% to 97.4%
when the pressure varied from 0.5 to 3.0 MPa.
3.4. Carbonylation of quaternary ammonium iodides
−
nucleophilic attack of [Co(CO)4] on the electropositive nitrogen
The results of carbonylation of several quaternary ammonium
atom. However, Me NI and other ammonium salts were reported
4
iodides were given in Table 4. Ethyltrimethylammonium iodide
to be thermally quite stable even at much higher temperature

Y. Lei et al. / Journal of Molecular Catalysis A: Chemical 381 (2014) 120–125
123
Table 3
Effect of temperature and CO pressure.a
◦
TONb
Entry
T ( C)
Pressure (MPa)
Conversion (mol%)
Selectivity (mol%)
YieldDMAc (mol%)
1
2
3
4
5
6
7
8
120
140
160
180
200
200
200
200
3
3
3
3
3
2
1
0.5
–
7.2
–
–
7.1
–
14.2
53.6
181.6
192.6
180.4
111.6
23.8
98.8
98.6
98.9
98.9
98.4
98.1
98.5
27.2
91.8
97.4
91.7
56.9
12.1
26.8
90.8
96.3
90.2
55.8
11.9
a
Reaction conditions: CoCl2 (0.075 mmol); Zn (0.1 mmol); Na2SO3 (0.075 mmol); Me4NI (15 mmol); NMP (50 mL); reaction time, 7 h; stirring speed, 500 rpm.
TON (mol converted Me4NI/mol cat.).
b
Table 4
Cobalt catalyzed carbonylation of quaternary ammonium iodides.a
Entry
Quaternary ammonium salts
Products
Conversion (mol%)
98.1
Selectivity (mol%)
78.7
Yield (mol%)
77.2
1
2
99.5
95.4
94.9
3
4
98.6
97.4
83.0
74.2
81.8
72.3
5
97.8
88.6
95.8
56.1
93.7
49.7
6b
7b
92.4
45.2
41.7
a
◦
Reaction conditions: CoCl2 (0.075 mmol); Zn (0.1 mmol); Na2SO3 (0.075 mmol); quaternary ammonium salt (15 mmol); NMP (50 mL); CO (3 MPa); 200 C; reaction time,
h; stirring speed, 500 rpm.
Reaction temperature: 180 C, 12 h.
7
b
◦
[
5,6]. But considering the differences of reaction conditions, the
4.2. The acyl complex intermediates
thermal behavior of Me NI in the solution might be quite differ-
4
ent. Taking this matter into account, an amine exchange reaction
Based on the results above, we assumed that the intermediates
should be the acylcobalt tetracarbonyl and acyl halide. Just like the
mechanism of cobalt carbonyl catalyzed carbonylation of methanol
to acetic acid [46], acylcobalt tetracarbonyl could be generated
between Me NI and N,N-diethylaniline was conducted (Table 5).
4
The results indicated that Me NI could be thermally decomposed
4
◦
at 200 C and Me NI would be in equilibrium with MeI and Me N
4
3
−
under the reaction conditions. However, when the exchange reac-
from alkyl iodide and Co(CO)4 , and then acylcobalt tetracarbonyl
◦
tion was conducted at 150 C, no Me N was detected (Table 5, entry
reacted with iodide ion to produce acyl halide. The presence of
acetic acid as byproduct (Table 1, entries 7 and 8) could be indi-
rect evidence for the existence of acyl complex intermediate [46].
To gain additional insight into the catalytic intermediates and to
confirm the presence of acyl complex in this reaction, additional
experiments about catalytic carbonylation of quaternary ammo-
nium iodide were carried out in the presence of tertiary amine
3
3
). These results suggested that Me NI did not thermally decom-
4
◦
pose at 150 C. It is concluded that the cleavage of C N bonds in the
catalytic carbonylation of Me NI below 150 C should be attributed
to catalytic transformation of Me NI by [Co(CO) ] (Table 3,
◦
4
−
4
4
entry 2).
(Table 6). If the acylcobalt tetracarbonyl existed, the generated acyl
halide should react with both the added tertiary amine as well as
the one produced, thus resulted in different tertiary amides [47]. As
we expected, when tetramethylammonium iodide was carbony-
lated in the presence of other tertiary amines (Table 6, entries 1
and 2), different tertiary amides bearing the same acetyl group
were obtained. Likewise, when aryltriethylammonium iodide was
mixed with trimethylamine, two kinds of tertiary amides bearing
the same propionyl group were obtained (Table 6, entry 3). These
results in Table 6 give us a positive reply and a further evidence of
the existence of the acyl complex.
Table 5
a
Amine exchange reaction between Me4NI and N,N-diethylaniline.
◦
Yield of Me3N (%)b
Entry
T ( C)
1
2
3
200
180
150
27.3
6.4
0
a
Reaction conditions: Me4NI (10 mmol); N,N-diethylaniline (10 mmol); NMP
(
50 mL); reaction time, 7 h; stirring speed, 500 rpm.

1
24
Y. Lei et al. / Journal of Molecular Catalysis A: Chemical 381 (2014) 120–125
Table 6
Cobalt catalyzed carbonylation of quaternary ammonium iodide in the presence of tertiary amine.
a
Entry
Ammonium salt
Tertiary amine
Yield (%)b
A
B
1
2
Me4NI
Me4NI
(C2H5)3N
PhNEt2
(
55.3)
(20.7)
(
59.0)
(12.6)
3
Me3N
(
32.1)
(
10.6)
a
Reaction conditions: CoCl2 (0.075 mmol); Zn (0.1 mmol); Na2SO3 (0.075 mmol); quaternary ammonium iodide (15 mmol); tertiary amine (15 mmol); NMP (50 mL); CO
◦
(
3 MPa); 200 C; reaction time, 3 h; stirring speed, 500 rpm.
b
Yield of A: based on the amount of the added ammonium iodides; Yield of B: based on the amount of the added tertiary amine.
in carbonylation reaction where they are used as promoters or
solvents in most cases. Due to the high catalytic activity and recy-
clability of alkyl iodide, this process can be a potential procedure for
the preparation of certain tertiary amides. Moreover, the cleaving
mechanism of C N bonds and the possible catalytic intermediates
were discussed in detail; these could be also informative for other
reactions which involved the cleaving C N bond of ammonium
salts or tertiary amines.
Acknowledgements
This work is partly supported financially by the 863 Program
of Ministry of Science and Technology of China (NC2010MA0137).
Thankfulness is expressed for the spectroscopic analysis to the
Analytical and Testing Center, Huazhong University of Science and
Technology, Wuhan, China.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.molcata.
013.10.014.
Scheme 2. Proposed mechanism for carbonylation of quaternary ammonium salts.
2
4.3. Mechanistic considerations
References
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1
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