Pd(OAc)2-catalyzed oxidative carbonylation of aromatics: Synthesis of naphthalenecarboxylic acids

Article abstract of DOI:10.1016/j.tetlet.2013.07.154

The liquid-phase oxidative carbonylation of aromatics leading to aromatic carboxylic acids is studied to develop new approaches to 2,6- naphthalenedicarboxylic acid (NDA) preparation. It is shown that the catalytic system Pd(OAc)₂/K₂S₂O₈ allows the synthesis of naphthalic anhydride (NAn) by direct oxidative carbonylation of naphthalene under mild conditions (25 C, 2 atm CO). The subsequent alkaline hydrolysis of NAn and isomerization of the obtained 1,8-naphthalenedicarboxylic acid salt is known to lead to NDA.

Full text of DOI:10.1016/j.tetlet.2013.07.154

Tetrahedron Letters 54 (2013) 5527–5531
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Pd(OAc)2-catalyzed oxidative carbonylation of aromatics: synthesis
of naphthalenecarboxylic acids
⇑
Alexander R. Elman
Rostkhim Ltd, 38, Shosse Entuziastov, 111123 Moscow, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 April 2013
Revised 8 July 2013
Accepted 31 July 2013
Available online 7 August 2013
The liquid-phase oxidative carbonylation of aromatics leading to aromatic carboxylic acids is studied to
develop new approaches to 2,6-naphthalenedicarboxylic acid (NDA) preparation. It is shown that the cat-
alytic system Pd(OAc)2/K2S2O8 allows the synthesis of naphthalic anhydride (NAn) by direct oxidative
carbonylation of naphthalene under mild conditions (25 °C, 2 atm CO). The subsequent alkaline hydroly-
sis of NAn and isomerization of the obtained 1,8-naphthalenedicarboxylic acid salt is known to lead to
NDA.
Keywords:
Ó 2013 Elsevier Ltd. All rights reserved.
Oxidative carbonylation
Naphthalenecarboxylic acids
Naphthalic anhydride
1-Naphthoic acid disproportionation
Aromatic carboxylic (including, polycarboxylic) acids are used
widely for the production of medicines, monomers, and dyes.1
2,6-Naphthalenedicarboxylic acid (NDA) is very important among
aromatic acids because it is used in the production of polyethylene
naphthalate polymers, and other polyamides, polyesters, and
polyamides.2 Traditional production of aromatic acids is, as a rule,
multistage, and is based on the oxidation of alkyl aromatics, how-
ever the low selectivity of this process reduces considerably the
economic efficiency. On the other hand, oxidative carbonylation al-
lows aromatic acids to be obtained in one or two steps using cheap
aromatic hydrocarbons, with high selectivity under mild condi-
tions1,3 and therefore is very promising for the production of the
desired products.
2 atm). In turn, naphthalic anhydride can be converted into NDA
through intermediate formation of 1,8-naphthalenedicarboxylic
acid.8
Oxidative carbonylation of benzene
The oxidative carbonylation was carried out as described ear-
lier9 under the following conditions: [Pd(OAc)2] = 1.7 ꢀ 10ꢁ2 M;
[C6H6] = 1.9 M. We added K2S2O8 10 mmol and 10 mL of solvent—
TFA. The temperature was 22 °C and the CO pressure was 2 atm.
The only product of the reaction was benzoic acid, the yield of
which reached 13% with respect to benzene in 20 h. Figure 1 shows
the change of benzoic acid yield versus time.
For the synthesis of aromatic carboxylic acids under mild condi-
tions catalytic systems based on Pd(OAc)2 are used.1 Benzoic acid
was obtained from benzene in 100% yield under mild conditions
(1 atm, 20 °C) in a CO atmosphere when K2S2O8 was used as the
oxidizing agent.4 The selectivity of 2-naphthoic acid formation
from naphthalene reaches 92% in the presence of 1,10-phenanthro-
line (Phen) under the action of a CO/O2-mixture.5 It is known that
2-naphthoic acid potassium salt, at elevated temperature, is
transformed into the salt of 2,6-naphthalenedicarboxylic acid in
high yield (90%).6 Under similar conditions the potassium salt of
1,8-naphthalenedicarboxylic acid isomerizes into the salt of NDA
in a yield of 70%.7 In the present work, the possibility of a one-step
synthesis of naphthalic anhydride is described by the way of naph-
thalene oxidative carbonylation under mild conditions (20 °C,
Thus, benzoic acid can be obtained by the direct oxidative
carbonylation of benzene in a good yield based on the initial
14
12
10
8
6
4
2
0
0
5
10
15
20
Time, h
⇑
Tel.: +7 903 548 7809; fax: +7 495 673 6310.
E-mail address: elmanar@yandex.ru
Figure 1. Dependence of benzoic acid yield versus time.
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.07.154

5528
A. R. Elman / Tetrahedron Letters 54 (2013) 5527–5531
hydrocarbon and a very considerable yield (1450%) based on Pd.
Thus the Pd catalyst does not lose activity and the formation of
Pd0 was not observed.
In consideration of the high selectivity and mild conditions, this
method is of practical interest and deserves further study as it
should be extendable to other aromatics, including naphthalene,
for the purpose of obtaining naphthoic acids.
O
O
O
COOH
m CO, [O]
n
+
NAc
NAn
Scheme 1.
Oxidative carbonylation of naphthalene
Preliminary experiments
14
12
10
8
Data on naphthalenecarboxylic acid synthesis by the oxidative
carbonylation of naphthalene in the presence of the Pd(OAc)2/Phen
system have been published.5 However the procedure described
did not provide solubility of naphthalene in the chosen solvent
(acetic acid/cyclohexane) at room temperature; this made the
analysis of the reaction mixture and the taking of samples difficult
during our experiments. So the main task of the preliminary exper-
iments was the choice of a suitable solvent and the concentrations
of the components in the reaction mixture.
(a)
(b)
6
4
2
0
0
10
20
30
40
50
Time, h
60
70
As a result, preliminary experiments were conducted in a
solvent consisting of 6 mL of acetic acid and 5 mL of cyclohexane
30
25
20
15
10
5
at
a temperature of 115 °C; the initial component concen-
trations were: [C10H8] = 1.8 M; [Pd(OAc)2] = 1.9 ꢀ 10ꢁ2 M; [Phen] =
8.3 ꢀ 10ꢁ2 M. This led to full homogeneity of the reaction mixture
both before carrying out the reaction, and after.
a-Naphthol and
b-naphthol were formed as the products and the results are
presented in Table 1 (isomeric naphthols are denoted as and b).
Table 1 shows that - and b-naphthols, with preferential forma-
tion of -naphthol, can be obtained under conditions of oxidative
a
a
a
0
carbonylation of naphthalene; no other products were observed.
b-Naphthol formation requires the presence of oxygen. The ab-
sence of moisture in the solvent has the greatest impact on increas-
ing the catalyst activity. The catalyst is stable and Pd0 formation
does not occur.
Further development of this method is of interest from the
point of view of obtaining naphthols directly from naphthalene un-
der mild conditions, since the traditional method includes applica-
tion of corrosive conditions and is characterized by a large quantity
of acid–base waste.10,11At the same time, unlike the results re-
ported previously,5 naphthalenecarboxylic acids were not found
in the reaction products.
0
10
20
30
40
50
Time, h
60
70
Figure 2. Dependence of (a) the change in 1-naphthoic acid (ꢀ) and 1,8-naphthalic
anhydride (N) concentrations and (b) [NAc]/[NAn] ratio versus time.
[C10H8] = 1.8 M; we added K2S2O8 (10.6 mmol) and trifluoroacetic
acid (10 mL) (solvent); temperature 20 °C and the CO pressure
2 atm.
The main reaction product (Scheme 1) was 1-naphthoic acid
(NAc). Also, for the first time, 1,8-naphthalic anhydride (NAn)
was obtained via the oxidative carbonylation of naphthalene. 2-
Naphthoic acid formation was not observed in this case.4
Figure 2 shows the change in the reaction product concentra-
tion and their ratio versus time.
Figure 2 shows that under the chosen conditions the reaction
products (1-naphthoic acid and 1,8-naphthalic anhydride) were
obtained, probably as a result of consecutive transformations. Thus
their total yield reached 7.8% based on initial naphthalene or
608.7% with respect to Pd.
Naphthalenecarboxylic acid derivatives
Given that benzene, in trifluoroacetic acid under the action of
CO in the presence of Pd(OAc)2 and K2S2O8, is converted into ben-
zoic acid with high selectivity (Fig. 1), these conditions and cata-
lytic system were used in the subsequent experiments to obtain
naphthalenecarboxylic acids by oxidative carbonylation of naph-
thalene. To conduct the reactions the following conditions were
chosen
(similar
to
benzene):
[Pd(OAc)2] = 2.3 ꢀ 10ꢁ2 M;
Table 1
Oxidative carbonylation of naphthalene
Run
Time,(h)
Gas composition (atm)
Solventa
Yieldb of b + ac based on Pd, (%)
[b] ꢀ 102 (M)
Ratio b:a
1
2
3
4
5
25.7
16.0
16.5
19.5
17.0
2 CO + 2 O2
1.4 CO + 0.7 O2
2 CO + 1 O2
10 CO + 1 O2
2 CO
Without dehydration
Water-free
Water-free
Water-free
Water-free
50
0.38
0.80
1.10
0.40
—
1:1.5
1:3.8
1:2.0
1:1.5
—
233
174
51
Traces a
a
b
c
We used acetic acid after threefold fractional crystallization in water-free solvent.
GLC yield.
a
and b denote isomeric a- and b-naphthols.

A. R. Elman / Tetrahedron Letters 54 (2013) 5527–5531
5529
Choice of reaction conditions and composition of the catalytic
system
CO
CO
Naphthalene ⎯⎯→ 1-naphthoic ⎯⎯→1,8-naphthalic
acid
anhydride
The influence of the oxidizing agent (K2S2O8), the solvent com-
position, and temperature on the processes leading to 1-naphthoic
acid and 1,8-naphthalic anhydride was studied (Table 2).
It is apparent from Table 2 that it is necessary to have a certain
molar ratio of an oxidizing agent to Pd(OAc)2 in order to ensure its
stability in solution and to prevent metallic palladium formation
(runs 1–3).
Due to the limited solubility of naphthalene and K2S2O8 in the
reaction mixture when polar acetic acid was added, the formation
of solid particles of naphthalene covered with palladium black was
observed (run 5). However under these experimental conditions
the addition of cyclohexane (2 mL) led to full solubility of naphtha-
lene and the transition of Pd into solution (product formation was
not observed). Thus, potassium persulfate is a re-oxidative agent
for palladium under the conditions of oxidative carbonylation.
The results of runs 2, 5, and 6 show that it was possible to replace
some of the TFA with a less aggressive solvent.
Scheme 2.
was formed as a result of consecutive-parallel transformations
(see Fig. 1). To clarify how 1,8-naphthalic anhydride was obtained,
we carried out several experiments on the oxidative carbonylation
of 1-naphthoic acid (Table 3).
The results shown in Table 3 show that 1,8-naphthalic anhy-
dride can be obtained by direct carbonylation of 1-naphthoic acid.
This confirms the possibility of anhydride formation during the
oxidative carbonylation of naphthalene as a result of consecutive
reactions through the intermediate formation of 1-naphthoic acid.
Hence, the reaction rate, apparently, does not depend on the 1-
naphthoic acid initial concentration (runs 1 and 2).
Run 7 shows that in such a complicated heterophase system,
even simply increasing the rate of stirring leads to a significant in-
crease in the reaction rate and yield of products: the total yield of
products reached 17.5% based on initial naphthalene ([1-naphthoic
acid]:[1,8-naphthalic anhydride] = 5.8:1) or 1312% based on Pd.
Replacing K2S2O8 with Na2O2 or oxygen did not lead to success: so-
dium peroxide decayed considerably with the formation of oxygen
under these experimental conditions; also Pd0 formed, and no
products were observed.
Thus, K2S2O8 plays an important role, as an effective re-oxidant
of palladium which leads to its stability in the reaction mixture,
and also probably is the donor of the oxygen which is necessary
for product formation (Scheme 1).
At the same time, in the absence of CO, a small quantity of
anhydride was also formed; it should be noted that the reaction
proceeds only in the presence of the Pd catalyst under chosen con-
ditions (runs 3 and 4). These results indicate the possibility of 1-
naphthoic acid disproportionation with the formation of 1,8-naph-
thalic anhydride and naphthalene derivatives, which form as a re-
sult of C–H bond activation at position 8. They also indicate the
participation of these derivatives in a number of other processes
(alkylation, cyclization, addition, etc.). 1,8-Naphthalic anhydride
formation may occur via consecutive-parallel transformations
according to Scheme 2.
Analyses using GC–MS and HPLC showed that in the absence of
CO (run 3) the main product of 1-naphthoic acid transformation
was 2H-naphtho[1,8-b,c]furan-2-one (I), the product of intermo-
lecular cyclization. Besides, the formation of 1,10-binaphthyl and
other products (II-V) was observed, identified by comparison of
their experimental mass spectra obtained during GC–MS analysis
of the reaction product mixtures with spectra from the library of
Oxidative carbonylation of 1-naphthoic acid
In the previous experiments it was established that during the
oxidative carbonylation of naphthalene, 1,8-naphthalic anhydride
Table 2
Influence of the reaction conditions and catalytic system composition on the results of the oxidative carbonylation of naphthalene
a
a
Run
[Pd(OAc)2]/
[K2S2O8],
Solvent
T (°C)
Yield of Rproduct
Yield of Rproduct
Notes
based on C10H8, (%)
based on K2S2O8, (%)
(mol/mol)
1
2
3
1:47.8
1:20.0
1:10.0
1:19.6
1:21.2
TFA
TFA
TFA
TFA
18
25
30
30
30
7.8
6.9
2.8
5.1
—
12.7
28.6
21.7
20.4
—
Pd0 formation
4
5b
1st stage: 2 mL of TFA, 3 mL of AcOH
2nd stage: 2 mL of cyclohexane added
4 mL of TFA, 1 mL of AcOH
TFA
1st stage: Pd0 formation
2nd stage: Pd dissolved
6
1:21.5
1:18.4
25
25
6.0
17.5
23.0
71.3
7c
a
b
c
GLC yield of [1-naphthoic acid] + [1,8-naphthalic anhydride].
The run was continued after cyclohexane (2 mL) addition under the same conditions (see further).
Rate of stirring was increased twice.
Table 3
Oxidative carbonylation of 1-naphthoic acid
Run
[Pd]0 ꢀ 102 (M)
[K2S2O8]0 (M)
[1-naphthoic acid]0 (M)
Gas
Time (h)
Yield of 1,8-naphthalic anhydridea, (%)
1
2
3
4
2.25
2.31
2.27
0
0.48
0.45
0.46
0.45
1.80
0.59
1.81
0.60
2 atm CO
2 atm CO
2 atm N2
2 atm N2
61.3
19.5
20.3
23.0
12.8
16.9
1.7
—
a
GLC yield based on 1-naphthoic acid.

5530
A. R. Elman / Tetrahedron Letters 54 (2013) 5527–5531
O
O
CO
O
O
O
HOOC
CO, [O]
CO, [O]
-H2O
COOH
-H2O
HOOC
COOH
Scheme 3.
O
O
O
COOK COOK
COOH
430 OC, HCl
2 KOH
2 CO, [O]
HOOC
60 %
90 %
Scheme 4.
COOH COOH
COOH
2 CO, [O], 2 H2O
430°C
HOOC
Scheme 5.
mass spectra.12 Also, structures I–V were confirmed by the analysis
of electron impact fragmentation of these molecules:
acid dehydration. Thus, activation of the C–H bond at position 8 of
1-naphthoic acid and the other C-atoms of naphthalene causes side
O
O
O
O
O
O
II
I
III
IV
V
On the other hand, using HPLC, we detected only a small quan-
tity of naphthofuranone (I) in the products of 1-naphthoic acid car-
bonylation (runs 1 and 2). Also, 1,8-naphthalenedicarboxylic acid
was formed. The main product of the oxidative carbonylation of
1-naphthoic acid was 1,8-naphthalic anhydride.
The detailed analysis of the products of the transformation of 1-
naphthoic acid indicates that oxidative carbonylation of 1-naph-
thoic acid leads to 1,8-naphthalic anhydride through intermediate
formation of 2H-naphtho[1,8-b,c]furan-2-one. 1,8-Naphthalic
anhydride can also form as a result of 1,8-naphthalenedicarboxylic
reactions to occur, including 1-naphthoic acid disproportionation
with the formation of the same anhydride and other products
(binaphthyl, etc.).
The obtained results allow the following scheme to be proposed
for the product formation during the oxidative carbonylation of
naphthalene (Scheme 3).
In conclusion, we have shown that oxidative carbonylation of
naphthalene leads to naphthalenedicarboxylic acid derivatives
via a one-step process under mild conditions. 1-Naphthoic acid is
the main reaction product under the chosen conditions, its yield

A. R. Elman / Tetrahedron Letters 54 (2013) 5527–5531
5531
reaches 15% based on the initial naphthalene (total yield of prod-
Acknowledgments
ucts is 1312% based on Pd; see Table 2). Also, the yield can be in-
creased significantly by improvement of the process conditions
(solubility of reagents, temperature, pressure, and probably, pre-
vention of CO oxidation into CO2), optimization of the catalytic sys-
tem composition, and other measures.
Funding from the YRD-Center is acknowledged. The author is
thankful to Professor G.A. Korneeva for her promotion in carrying
out this work.
The important task of this work was the development of possi-
ble approaches to 2,6-naphthalenedicarboxylic acid synthesis.
From this point of view, the possibility of obtaining 1,8-naphthalic
anhydride from naphthalene in one step is very attractive. Under
the studied conditions the process proceeds through intermediate
1-naphthoic acid formation; the above-mentioned anhydride,
apparently, is the end product of the process.
In the case of the increased yield of 1,8-naphthalic anhydride, a
new way of obtaining NDA from naphthalene can be postulated
according to Scheme 4, including selective formation of 1,8-naph-
thalic anhydride, its subsequent hydrolysis, and isomerization of
the obtained 1,8-naphthalenedicarboxylic acid salt via a known
procedure.8
References and notes
1. Elman, A. R.; Korneeva, G. A. Ross. Khim. Zhurn. 2006, 50, 115–127.
2. Elman, A. R. Catal. Ind. 2009, 1, 184–189.
3. Temkin, O. N. In Encyclopedia of Catalysis; Horvath, I. T., Ed.; John Wiley & Sons,
2003; Vol. 5, p p 394.
4. Lu, W.; Yamaoka, Y.; Taniguchi, H.; Kitamura, T.; Takaki, K.; Fujiwara, Y. J.
Organomet. Chem. 1999, 580, 290–294.
5. Jintoku, T.; Taniguchi, H.; Fujiwara, Y. Chem. Lett. 1987, 1159–1162.
6. Brownscombe, T. F.; Buechele, J. L.; DuBois, D. A.; King, W. L.; Pfrehm, S. S. WO
0116081 (A2), 2001; Chem. Abstr. 2001, 134, 827.
7. Mitamura, S.; Fujishiro, K; Inoue, H. EP 0217329 (A1), 1987; Chem. Abstr. 1987,
107, 664. .
8. Fieser, L. F.; Fieser, M. Organicheskaya Khimia. Khimia: Moscow 1970, II, 356.
9. Elman, A. R.; Smirnov, V. I. J. Environ. Sci. Eng. 2011, 5, 1006–1012.
10. Karpova, N. B. In Khimicheskaya Enciklopediya; Knunyants, I. L., Ed.; Bolshaya
Rossiiskaya Encikl.: Moscow, 1992; p 198. Vol. 3.
11. G. Booth, Ullmann’s Encyclopedia of Industrial Chemistry, (6th ed.), Wiley-VCH
Verlag GmbH& Co. KGaA, 2002, available online at: http://onlinelibrary.
wiley.com.
Taking into account that 1,8-naphthalenedicarboxylic acid was
found in the reaction products, it could be worth trying to combine
the stages of formation and hydrolysis of 1,8-naphthalic anhydride.
In this case the process becomes simpler (Scheme 5).
12. Agilent NIST05 MS Library and MS Search Program v. 2.0d.