Palladium(II)-catalyzed carboxylation of benzene and other aromatic compounds with carbon monoxide under very mild conditions

Article abstract of DOI:10.1016/S0022-328X(98)01160-7

Aromatic compounds such as benzene, toluene, chlorobenzene, anisole, and naphthalene were carboxylated by palladium(II) acetate catalyst with carbon monoxide in the presence of potassium peroxodisulfate in trifluoroacetic acid (TFA) at room temperature under atmospheric pressure. The aromatic carboxylic acids were formed in good yields; for example, the carboxylation of benzene with carbon monoxide proceeds quantitatively under the optimal conditions.

Full text of DOI:10.1016/S0022-328X(98)01160-7

Journal of Organometallic Chemistry 580 (1999) 290–294
Palladium(II)-catalyzed carboxylation of benzene and other aromatic
compounds with carbon monoxide under very mild conditions
a
b
a
a
b
Wenjun Lu , Yoshinori Yamaoka , Yuki Taniguchi , Tsugio Kitamura , Ken Takaki ,
a,
Yuzo Fujiwara *
a
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu Uni6ersity, Hakozaki, Fukuoka 812-8581, Japan
Department of Applied Chemistry, Faculty of Engineering, Hiroshima Uni6ersity, Kagamiyawa, Higashi-Hiroshima 739-8257, Japan
b
Received 4 November 1998; received in revised form 3 December 1998
Abstract
Aromatic compounds such as benzene, toluene, chlorobenzene, anisole, and naphthalene were carboxylated by palladium(II)
acetate catalyst with carbon monoxide in the presence of potassium peroxodisulfate in trifluoroacetic acid (TFA) at room
temperature under atmospheric pressure. The aromatic carboxylic acids were formed in good yields; for example, the carboxyla-
tion of benzene with carbon monoxide proceeds quantitatively under the optimal conditions. © 1999 Elsevier Science S.A. All
rights reserved.
Keywords: Palladium; Carbon monoxide; Carboxylation; Aromatic compounds
with CO by the Pd(OAc) /Cu(OAc) and Yb(OAc) /
Mn(OAc)2 based catalysts [7,9,10]. However, all of
these reactions require elevated temperature and CO
1
. Introduction
2
2
3
C–H bond activation by transition metal complexes
pressure. Recently, we found that the Pd(OAc) /TFA/
has been of great interest for a few decades [1–3]. In
967, we reported the Pd-catalyzed reaction of olefins
2
K S O system could cause the direct carboxylation of
1
2
2
8
aromatic compounds with CO under very mild condi-
tions such as room temperature and atmospheric pres-
sure to give the acids in high yields as depicted in Eq.
with aromatic compounds to give aromatic-substituted
olefins via thermal activation of both aromatic and
olefinic C–H bonds [4]. This coupling reaction proceeds
via an ArPdL s-complex intermediate derived from
direct activation of an aromatic C–H bond by Pd(II).
It was found that the ArPdL s-complex formed in situ
from the direct aromatic C–H bond activation reacted
with CO, CO [5–7] and O [8] to give carboxylic acids
and phenol in one step, respectively. For example,
various aromatic acids could be prepared from aro-
matic compounds and CO by Pd-based catalysts in the
presence of t-BuOOH at over 75°C [6]. We also suc-
ceeded in the direct carboxylation reaction of alkanes
(
1).
Pd(OAc)
2
Ar−H+ CO
ꢀꢀꢀꢀꢀꢀꢁ Ar−COOH
(1)
Preliminary communication of this work has appeared
11]. Here, we report the details of this reaction of
(
1 atm) K S O8, TFA, r.t.
2 2
[
2
2
aromatic compounds with CO by Pd(OAc) catalyst in
2
TFA solvent.
2. Results and discussion
2.1. Effect of oxidizing agents
*
Corresponding author. Tel.: +81-92-6423548; fax: +81-92-
The Pd(OAc) /trifluoroacetic acid (TFA)/oxidizing
6
423548.
2
E-mail address: yfujitcf@mbox.nc.kyushu-u.ac.jp (Y. Fujiwara)
agent system was selected to study for the carboxyla-
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01160-7

W. Lu et al. / Journal of Organometallic Chemistry 580 (1999) 290–294
291
Table 1
Effect of oxidizing agents on carboxylation of benzene with CO
a
Entry
Oxidizing agent
Yield of benzoic acid (%)b
1
2
3
4
None
23
K S O
570
Trace
2
2
8
t-BuOOH
Oxonec
–
d
a
Pd(OAc)2 (0.5 mmol), benzene (5 ml), oxidizing agent (5 mmol),
TFA (5 ml), CO (1 atm), r.t., 20 h.
b
Isolated yield based on Pd.
c
2
KHSO ·KHSO ·K SO .
5 4 2 4
d
Complex reaction occurred.
tion reactions of aromatic compounds with CO (1 atm)
at room temperature.
First, the effect of oxidizing agents was investigated
to make the reaction catalytic with respect to Pd(II)
Fig. 2. Effect of amounts of Pd(OAc)2 on the yield of benzoic acid.
Reaction conditions: benzene, 56 mmol; CO, 1 atm; TFA, 5 ml; r.t.;
2
0 h.
(
Table 1). From the data in Table 1, it is seen that the
and thermal self-decomposition in the first 20 h of the
reaction, and the final yield is dependent of the amount
of oxidizing agent added. The final yields are 3300 and
1800% based on Pd in the presence of 5 mmol and 2.5
mmol K S O , respectively.
yield of benzoic acid was only 23% based on Pd(OAc)2
and palladium black precipitated during the reaction
without any oxidizing agents added (entry 1). However,
when t-BuOOH or Oxone was added in the reaction,
almost no product was obtained (entries 3 and 4). The
good result was obtained with potassium peroxodisul-
fate (K S O ) (entry 2), showing that K S O is an
2
2
8
2.3. Effect of the amounts of Pd(Oac)2
2
2
8
2
2
8
appropriate oxidizing agent which can oxidize Pd(0) to
Pd(II) effectively under very mild conditions such as
room temperature and atmospheric pressure.
Pd(OAc)2 is the catalyst to activate the aromatic
C–H bonds in these reactions. The effect of the
amounts of Pd(OAc) on the product yield was investi-
2
gated (Fig. 2). No product is obtained without
2
.2. Effect of the amounts of K S O
Pd(OAc) in these reactions. With increasing amounts
2
2
8
2
of Pd(OAc) , the product yield increases independent of
2
Then, the effect of the amounts of K S O on the
the amounts of K S O in the first 20 h of these
2
2
8
2
2
8
yield was investigated (Fig. 1). Fig. 1 shows that the
yields of the reactions with 5 mmol K S O and with
reactions as shown in Fig. 2. Then, the time-course of
the reaction was investigated using 0.1, 0.2, and 0.5
2
2
8
2
.5 mmol K S O are not apparently different within
mmol Pd(OAc) , and the results are shown in Fig. 3.
2
2
8
2
the first 20 h of these reactions; however, after 20 h, the
use of 5 mmol K S O gives higher yield than 2.5 mmol
From the figure, one can see that the increase of the
amounts of Pd(OAc) just accelerates the rate of the
2
2
8
2
K S O does. It seems that about 2.5 mmol K S O has
been consumed for both oxidation of Pd(0) to Pd(II)
reactions, and the final product yield is independent of
the amounts of Pd(OAc)2 added. The final yield is
about 3.3 mmol in these cases.
2
2
8
2
2
8
Fig. 1. Effect of amounts of K S O on the yield of benzoic acid
2
2
8
based on Pd. Reaction conditions: Pd(OAc) , 0.1 mmol; benzene, 56
mmol; CO 1 atm; TFA, 5 ml; r.t.
Fig. 3. Time-course of the reaction. Reaction conditions: benzene, 56
mmol; CO, 1 atm; K S O 5 mmol; TFA, 5 ml; r.t.
2
2
2
8

292
W. Lu et al. / Journal of Organometallic Chemistry 580 (1999) 290–294
Table 2
Effect of amounts of TFA and benzene on carboxylation of benzene with CO
a
Entry
Benzene (mmol)
K S O (mmol)
TFA (ml)
Benzene conversion (%)
Yield of benzoic acid (%)b
2
2
8
1
2
3
4
5
6
56
28
10
1
1
1
5
5
5
2.5
2.5
2.5
5
5
5
5
2.5
1
2.5
5.6
17
48
89
1400
1571
1700
480
890
1000
100
a
Pd(OAc)2 (0.1 mmol), CO (1 atm), r.t., 20 h.
Isolated yield based on Pd.
b
2.4. Effect of the amounts of TFA and benzene
in the Pd(OAc) /t-BuOOH/allyl halides system at ele-
2
vated temperature and CO pressure [6]. This result
Then, the effect of the amounts of TFA and benzene
indicates that the Pd(OAc) /TFA/K S O system is
2
2
2
8
on the product yield was investigated (Table 2). From
the results in the table, one can see that the benzene
conversion always increases with decreasing amounts of
benzene (entries 1–4). Also, the conversion increases
with decreasing amounts of TFA (entries 4–6). The
carboxylation of benzene proceeds quantitatively when
much effective to activate the aromatic C–H bonds in
the carboxylation reactions of aromatic compounds
with CO under very mild conditions.
2.6. Mechanism
1
mmol of benzene, 2.5 mmol of K S O , and 1 ml of
2 2 8
That the reaction proceeds with ortho–para orienta-
TFA were employed in the presence of 10 mol% of
Pd(OAc) catalyst (entry 6).
tion when an electron releasing group is attached to the
benzene ring and that naphthalene gives a-naphthoic
acid as a main product suggest that the reaction pro-
ceeds via electrophilic attack of cationic Pd(II) [6].
Competitive reaction of benzene and chlorobenzene
with CO gave benzoic and chlorobenzoic acids in 580
and 60% yields, respectively. Similarly, the reactivities
of other aromatic compounds were investigated by
competitive reactions. From the result, the relative reac-
tivity was found to be in the order of anisole\
toluene\benzene\chlorobenzene. This result also
indicates that the reaction is electrophilic.
2
2
.5. Carboxylations of arenes with CO
The results of carboxylation of various arenes with
CO by using Pd(OAc) at room temperature and under
2
atmospheric pressure are listed in Table 3. It is found
that the reaction proceeds with ortho–para orientation
if an electron-releasing group is attached to the benzene
ring (entries 2 and 4) and that naphthalene gives a-
naphthoic acid as a main product. The yields of these
products (800ꢀ3300% based on Pd(II)) are much
higher than those obtained (48–1240% based on Pd(II))
Isotope effect for this carboxylation reaction was also
studied by using d -benzene. The competitive reaction
6
of C H and C D with CO afforded the mixture of
6
6
6
6
benzoic acid and d -benzoic acid. The k /k ratio was
5
H
D
Table 3
a
found to be 6.1 by GC-MS analysis of the products.
This result indicates that the C–H bond activation of
arenes is the rate-determining step of this reaction.
Carboxylation of arenes with CO by Pd(OAc)2
Entry Substrate
Product
Yield (%)b
Ratio
The possible reaction mechanism is shown in Scheme
1
2
3
benzene
toluene
benzoic acid
toluic acids
1420
800
–
+
c
d
1. First, Pd (OCOCF ) is formed by the reaction of
3
26:6:67
19:27:54
e
Pd(OAc) and TFA. Then, electrophilic attack of an
chlorobenzene chlorobenzoic 1700
acids
anisole
2
+
electropositive Pd (OCOCF ) species on the benzene
3
d
4
5
anisic acids
naphthoic
acids
1200
3300
33:0:67
ring produces an arylpalladium species which under-
goes insertion of CO to give an aroylpalladium(II). The
subsequent reductive eliminations give Pd(0) and the
acid anhydride which reacts with TFA to form Ar-
COOH and (CF CO) O. Pd(0) is reoxidized by K S O
naphthalene
66:34f
a
Pd(OAc)2 (0.1 mmol), arene (56 mmol), CO (1 atm), K S O (5
2
2
8
mmol), TFA (5 ml), r.t., 20 h.
3
2
2
2
8
b
Isolated yield based on Pd.
Bitolyl type coupling products formed in considerable amounts.
o:m:p, isomer ratio determined by C-NMR.
o:m:p, isomer ratio determined by GLC analysis of the methyl
to Pd(II) and thus the catalytic cycle is completed. The
reason why the present reaction proceeds under milder
c
d
e
13
conditions than those of the usual Pd(OAc) /AcOH
2
system [6] could be attributed to the formation of more
esters.
f
+
a:b isomer ratio determined by GLC analysis.
electropositive Pd (OCOCF ) species by use of TFA
3

W. Lu et al. / Journal of Organometallic Chemistry 580 (1999) 290–294
293
equipped with a 1 m×3.2 mm i.d. glass column of
OV-17 (2%) on 60 mesh Chromosorb W.
4.2. General procedure for carboxylation of arenes with
CO
In a 50-ml round-bottomed flask equipped with a
magnetic stirring bar, arene (56 mmol), Pd(OAc) (0.1
2
mmol), K S O (5 mmol) and TFA (5 ml) were placed.
2
2
8
The mixture was stirred at room temperature for 20 h
under atmospheric pressure of CO (balloon). After
addition of ether (50 ml), the mixture was treated with
2
M KOH solution (50 ml×3). To the aqueous layer
was added concentrated HCI (30 ml) and the products
were extracted with ether (50 ml×3). The combined
ethereal layer was dried over MgSO and filtered. After
4
evaporation of the solvent, the products were isolated
by SiO (1 g) short column chromatography.
2
Scheme 1. The possible mechanism of Pd(II)-catalyzed carboxylation
of aromatic compound with CO.
4.3. Analysis of isomer ratio of substituted benzoic
acids and naphthoic acids
+
compared with Pd (OCOCH ) which is formed under
3
the usual conditions.
The product mixture (200 mg) was dissolved in ether
(
20 ml) and esterified by diazomethane evolved from
p-toluenesulfonyl-N-methyl-N-nitrosoamide until the
solution turned yellow. The resulting ester was analyzed
by GLC or NMR. Isomer ratios of chlorobenzoic acids
and naphthoic acids were determined by GLC and
others were analyzed by NMR. Results are listed in
Table 3.
3
. Conclusions
Benzene and other aromatic compounds can react
with CO to produce aromatic acids by using Pd(OAc)2
catalysts in the presence of TFA and K S O at room
temperature under atmospheric pressure. The reaction
2
2
8
is electrophilic and proceeds with ortho–para orienta-
4
.3.1. o-Toulic acid
tion when an electron-donating group such as CH or
3
l
H-NMR (CDC1 , 270.05 MHz) l 2.65 (3H, s, CH ),
3
3
CH O is attached to the benzene ring. This method is
3
13
7
.00–8.00 (4H, m, Ph), 11.79 (1H, s, COOH); C-
convenient and useful to synthesize the aromatic acids
in a single step via direct C–H bond activation under
mild conditions such as room temperature and atmo-
spheric pressure.
NMR (CDCl , 67.80 MHz) l 22.7, 128.6, 131.6, 131.9,
3
1
32.9, 134.3, 144.3, 172.8.
4.3.2. m-Toulic acid
l
H-NMR (CDCl , 270.05 MHz) l 2.42 (3H, s, CH ),
3
3
1
3
7
.32–7.94 (4H, m, Ph), 11.10 (1H, s, COOH); C-
4. Experimental
NMR (CDC1 , 67.80 MHz) l 21.1, 127.3, 128.3, 128.7,
3
1
30.7, 134.6, 138.2, 173.7.
4.1. Materials and methods
4
.3.3. p-Toulic acid
Pd(OAc) was prepared by the procedure of Wilkin-
2
l
H-NMR (CDCl , 270.05 MHz) l 2.43 (3H, s, CH3),
3
son and coworkers [12]. All the other starting materials
and solvents were reagent grade and purified before
use.
NMR spectra were obtained on a JOEL JNM-270
spectrometer; chemical shifts were expressed in parts
per million downfield from tetramethylsilane. GC
analyses were performed on a Shimadzu GC-14A sys-
tem with a 3 m×3.2 mm i.d. glass column of OV-17
7
.30 (2H, d, J=7.9 Hz, Ar), 7.98 (2H, d, J=7.9 Hz,
13
Ar), 11.10 (1H, s, COOH); C-NMR (CDCl , 67.80
MHz) l 21.7, 126.5, 129.2, 130.2, 144.6, 172.7.
3
4.3.4. m-Anisic acid
l
H-NMR (CDCl , 270.05 MHz) l 4.05 (3H, s,
3
OCH ), 7.03–8.53 (4H, m, Ar), 12.00 (1H, s, COOH);
3
13
(
2%) on 60 mesh Chromosorb W. Mass spectra were
C-NMR (CDCl , 67.80 MHz) l 56.4, 112.9, 116.2,
3
obtained on a Shimadzu GC-MS QP1000 spectrometer
121.5, 132.7, 134.7, 161.4, 172.6.

294
W. Lu et al. / Journal of Organometallic Chemistry 580 (1999) 290–294
4
.3.5. p-Anisic acid
Pd(OAc) (0.1 mmol), K S O (5 mmol) and TFA (5
2 2 2 8
ml). The ratio of products was determined by GC-MS
analysis.
1
H-NMR (CDCl , 270.05 MHz) l 3.82 (3H, s, CH ),
3
3
6
.97 (2H, d, J=8.5 Hz, Ar), 7.94 (2H, d, J=8.5 Hz,
13
Ar), 12.00 (1H, s, COOH); C-NMR (CDCl , 67.80
3
MHz) l 55.5, 114.2, 123.3, 132.1, 164.1, 172.6.
References
4.4. Competiti6e reactions
[
1] C.L. Hill, Activation and Functionalization of Alkenes, Wiley
Interscience, New York, 1989.
The competitive reaction of benzene and chloroben-
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0 h under 1 atm CO (balloon), charging benzene,
[
[
[
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2
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2
[5] H. Sugimoto, I. Kawata, H. Taniguchi, Y. Fujiwara, J.
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[
K S O (5 mmol) and TFA (5 ml) in a 50-ml round-
2
2
8
6] T. Jintoku, Y. Fujiwara, I. Kawata, T. Kawauchi, H. Taniguchi,
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[
[
silica gel, 60°C; eluent, MeOH:H O=65:35, 0.5 ml
2
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−
1
min ) by using absorbance at 254 nm. Similarly,
competitive reactions of other aromatic compounds
with CO were performed.
[
[
[
The isotope experiment was performed similarly at
room temperature under 1 atm of CO (balloon) for 20
12] T.A. Stephenson, S.M. Morehouse, A.R. Powell, J.P. Heffer, G.
Wilkinson, J. Chem. Soc. (1965) 3632.
h, charging benzene, d -benzene (28 mmol, each),
6
.