Carboxylations of alkali metal phenoxides with carbon dioxide

Article abstract of DOI:10.1039/b210793g

The reaction mechanism of the Kolbe-Schmitt reaction of phenol and 2-naphthol has been investigated. An alkali metal phenoxide-CO₂ complex is not an intermediate that can be easily transformed into a carboxylic acid, such as salicylic acid (SA) and p-hydroxybenzoic acid (pHBA). A direct carboxylation of phenoxide with CO₂ takes place even at room temperature, and is competitive with the formation of the CO₂ complex. The resulting complex decomposes thermally (above ca. 100°C) to phenoxide, which then undergoes further competitive reactions. Experiments using a carbon-13 labeled complex support a mechanism of direct carboxylation, and not the mechanism via a CO₂ complex. The reactivity, C-13 NMR and MOPAC/PM3 calculations suggest a new carbonate-like structure for the CO₂ complex.

Full text of DOI:10.1039/b210793g

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Carboxylations of alkali metal phenoxides with carbon dioxide
a,b
b
c
d
Yoshio Kosugi,* Yoshio Imaoka, Fumisato Gotoh, Mohammad A. Rahim,
d
e
Yoshihisa Matsui and Kinya Sakanishi
a
Shimane Institute for Industrial Technology, Research Business Park, Hokuryocho, Matsue,
Shimane, 690-0816, Japan; Fax: ϩ81-852-60-5186; Tel: ϩ81-852-60-5186
Advanced Organic Material Chemistry, Shimane University, Matsue, Shimane, 690-8504,
Japan
Sumitomo Chemical Co. Ltd., Tsukuba Research Laboratory, Tsukuba, 300-3294, Japan
Department of Life Science and Biotechnology, Shimane University, Matsue, Shimane,
b
c
d
6
90-8504, Japan
e
The Institute of Advanced Material Science, Kyushu University, 816-8580, Japan
Received 1st November 2002, Accepted 6th January 2003
First published as an Advance Article on the web 5th February 2003
The reaction mechanism of the Kolbe–Schmitt reaction of phenol and 2-naphthol has been investigated. An alkali
metal phenoxide–CO complex is not an intermediate that can be easily transformed into a carboxylic acid, such as
2
salicylic acid (SA) and p-hydroxybenzoic acid (pHBA). A direct carboxylation of phenoxide with CO takes place
2
even at room temperature, and is competitive with the formation of the CO complex. The resulting complex
2
decomposes thermally (above ca. 100 ЊC) to phenoxide, which then undergoes further competitive reactions.
Experiments using a carbon-13 labeled complex support a mechanism of direct carboxylation, and not the
mechanism via a CO complex. The reactivity, C-13 NMR and MOPAC/PM3 calculations suggest a new
2
carbonate-like structure for the CO complex.
2
1
The Kolbe–Schmitt reaction has been used for more than a
century to produce industrially important aromatic hydroxy
acids, such as salicylic acid (SA), p-hydroxybenzoic acid
hydrogen carbonates originating from potassium hydroxide
used in the preparation of potassium phenoxide.
Phenyl carbonate (A) was originally proposed as an inter-
5
7,8
9
(
pHBA), p-aminosalicylic acid (PAS), 3- and 6-hydroxy-2-naph-
thoic acids (3HNA and 6HNA, respectively). In spite of
various investigations on the reaction, the mechanism of the
carboxylation has not necessarily been clear. Among several
postulations, the most plausible reaction mechanism accepted
today is the formation of an alkali metal phenoxide–CO com-
mediate, and later, structures B and C were suggested based
on IR spectra. Meanwhile the amount of complex formed dur-
ing reactions was estimated by titration, and the substituent
2,3
10
effects on the amount of the complex formed were discussed.
In spite of all the available affirmative evidence this has not
11
been used to suggest the possible structure, however Dewar
2
plex in the first stage of the reaction of phenoxide, followed by
producing SA at elevated temperatures ca. 120 ЊC, and pHBA
described an idea of a π-complex type structure (D).
4,5
is produced from dipotassium salicylate at much higher
6
temperatures over 200 ЊC (Scheme 1). The structure of
the CO complex has not been elucidated, probably because of
2
its very hygroscopic nature and the inevitable contamination
of inorganic carbonates such as potassium carbonate and
The formation of a CO complex at low temperatures has
2
10,12
also been examined by thermal analyses (DTA, TGA)
and
13
14
kinetic approaches. In our recent studies, it has been found
that the carboxylation of alkali metal phenoxide with carbon
dioxide takes place and produces not only SA but also pHBA
even at room temperature.
These unexpected results have urged us to investigate the
reaction mechanism and the nature of the CO complex in more
2
detail.
Results and discussion
An introduction of carbon dioxide at room temperature into an
autoclave to react with potassium (or sodium) phenoxide
resulted in the formation of SA and pHBA. The total yield
of the carboxylic acids was ca. 30% at 50 ЊC, and the rest of
Scheme
reaction.
1
Widely accepted mechanisms of the Kolbe–Schmitt
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 8 1 7 – 8 2 1
817

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Table 1 Carboxylations of potassium phenoxide and 2-naphthoxide with carbon dioxide, and reactivities of potassium phenoxide–CO complexes
2
f
Carboxylation
Reaction mixture (%)
a
Run nos.
Phenoxides
CO complex
CO /MPa
Temp/ЊC
Time/min
Phenol
SA
pHBA
2-Naphthol
2H1NA
2
2
1
2
3
4
5
6
7
8
9
PhOK
PhOK
PhOK
PhOK
PhOK
—
—
—
—
—
5.0
5.0
5.0
(5.0
(5.0
5.0
20
50
30
30
30
5
60
60
80
73
80
64
53
100
95
100
—
—
100
87
12.5
17.2
13.2
23.2
30.4
0
3.0
0
—
7.0
9.7
7.4
13.1
16.6
0
1.5
0
—
—
—
—
—
—
—
—
—
53
100
39
41
—
—
—
—
—
—
—
—
47
0
c
60) × 2c
—
60) × 3
60
PhOK–CO2
PhOK–CO2
PhOK–CO2
—
2-NaphOK–CO
PhOK–CO2
50
d
—
—
(N 5.0)
(evacuated)
100
100
50
50
50
60
60
60
60
60
60
2
e
2-NaphOK
—
2-NaphOK
PhOK
5.0
5.0
5.0
5.0
10
11
12
—
0
8
—
0
4.5
2
b
60
58.5
b
2-NaphOK–CO2
50
a
The CO2 complexes were prepared by an introduction of low pressure CO to potassium phenoxide (PhOK) or potassium 2-naphthoxide
2
b
(
2-NaphOK) at room temperature (cf. Experimental). Blend mixtures of the complex and the phenoxide in a molar ratio of 1 : 1 were subjected to
c
reactions in an autoclave. Combination processes of a carboxylation with CO at 3 ЊC and a decomposition under nitrogen at 150 ЊC were repeated
2
d
e
twice or three times. Nitrogen instead of carbon dioxide was applied. Evolved carbon dioxide was removed by suction during the reaction.
f
Products (SA : salicylic acid, pHBA : p-hydroxybenzoic acid, and 2H1NA : 2-hydroxy-1-naphthoic acid) were determined by HPLC.
phenoxide changed into an alkali metal phenoxide–CO com-
competitive reactions between carboxylations and a reform-
ation of the complex. After the second carboxylation at 30 ЊC,
the total yield of the carboxylic acids was double the amount
(36.3%), and was 47.0%, almost equivalent to the expected
value (50%) with another repetition of a combination process
of decomposition–carboxylation (Table 1). Since the amount of
alkali metal ion for restoring phenoxide decreased with the
accumulation of both inorganic carbonates and dipotassium
(or disodium) carboxylates, the repetitive reactions at room
temperature did not give yields higher than ca. 70%. It is known
2
plex. The carboxylation occurred in a few minutes at temper-
atures lower than 30 ЊC, but the yield did not change with a
prolonged reaction time. These facts indicate that the carboxyl-
ation is very fast even at room temperature and is competing
with the formation of the CO complex. A gradual introduction
2
of carbon dioxide of pressure less than 1.0 MPa onto potas-
sium (or sodium) phenoxide produced preferentially the CO2
complex at 30 ЊC. Thus ‘pure CO complex’ free of the carb-
2
oxylation products was prepared with carbon dioxide at the
pressure of 0.1–1.0 MPa. The prepared complex was exposed to
carbon dioxide at high pressure (5.0 MPa) for a longer time
that a CO molecule is involved in a complex composed of
2
transition metals or heavy metals which coordinate to an anti-
15,16
(
60 min) at 50 ЊC, phenol was recovered in 100% yield after
bonding π-orbital of CO2.
Among various possible struc-
work-up. This fact means the complex is not an intermediate of
the carboxylation reaction. Contrary to the mechanism widely
tures, MOPAC/PM3 calculations have suggested E as the most
appropriate structure for potassium phenoxide CO complex.
2
accepted for a long time, once the CO complex forms, the reac-
This is energetically much more stable than a π-complex, D
2
Ϫ1
Ϫ1
tion does not proceed further to give carboxylic acids. The CO2
complex starts decomposing to phenoxide at ca. 90 ЊC, and
decomposes easily at 150 ЊC, while carboxylated products such
as SA, pHBA are stable at higher temperature such as 180 ЊC, at
least.
(ϩ209 kJ mol ), and more stable by 60.9 kJ mol than the
17
transition states or the intermediates which control products
Ϫ1
(ϩ3.9 and ϩ2.9 kJ mol for ortho and para carboxylates,
respectively). Therefore, the formation of the complex is pre-
dominant (four times more) over the direct reaction of CO on
2
When the CO complex was heated at ca. 100 ЊC in an auto-
the benzene ring.
2
clave filled with nitrogen instead of carbon dioxide, formations
of SA and pHBA were in yields of only a few percent . This is
ascribable to a reaction scheme where the CO2 complex
decomposes to phenoxide, and a part of the liberated carbon
dioxide reacts with regenerated phenoxide to give carboxylic
acids (Table 1 and Scheme 2).
A carboxylation of potassium 2-naphthoxide gave 2-hydroxy-
1-naphthoic acid (2H1NA) of rather high yields (ca. 50%) at
50 ЊC. The CO complex of potassium 2-naphthoxide was pre-
2
pared in a similar manner to that of the phenoxide, and was
allowed to react with carbon dioxide of high pressure (5 MPa).
Essentially, any carboxylations did not take place. This result
proves again that the CO complex is inert to carbon dioxide. In
2
order to scrutinize the reactivity of the complex further, carb-
oxylations of phenoxide or 2-naphthoxide were carried out in
the presence of the complex. These two kinds of powder were
blended in a dry-box using a mortar prior to the reaction with
5
MPa CO at 50 ЊC for 60 min. The CO complex of potassium
2
2
phenoxide blended with potassium 2-naphthoxide did not pro-
duce SA or pHBA as expected, but 2H1NA was obtained in a
yield exceeding 50%. On the other hand, a reaction of the CO2
complex of potassium 2-naphthoxide in the presence of potas-
sium phenoxide suppressed formations of SA and pHBA, but
unexpected 2H1NA was produced in a yield of 58%. These
results suggest that the carbon dioxide molecule in the CO2
complex presumably binds to potassium phenoxide more
strongly than potassium 2-naphthoxide, and therefore, the CO2
molecule in the 2-naphthoxide complex shifts to the phenoxide
Scheme
2
Carboxylation of potassium phenoxide with carbon
dioxide.
A similar reaction was repeated and the evolved gas was
evacuated continually by a low-power pump (ca. 100 mmHg).
None of carboxylic acids were obtained after 1 h heating. Upon
heating at 150 ЊC under a nitrogen atmosphere, the complex
decomposed to phenoxide, and a subsequent introduction of
carbon dioxide at high pressure to the cooled mixture led to
in a structure like F. Successive shifts of CO from inactive
2
2-naphthoxide complex resulted in production of higher yields
of 2H1NA. When the 2-naphthoxide complex and phenoxide
were placed separately using aluminium foil in an autoclave,
8
18
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 8 1 7 – 8 2 1

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Table 2 Mass spectral data of esters of products
Esters (C H O )
m/z 152
m/z 153
8
8
3
Methyl salicylate
Methyl p-hydroxybenzoate
Observed (average)
If path a (Intramolecular migration)
If path b (Decompositon of the complex followed by carboxylation)
89.86 (%)
91.11
90.49
0
10.14 (%)
8.89
9.51
100
9.72
a
90.28
a
13
13
This figure is based on the following calculations: CO = 0.93 (%) and unlabeled CO = 99.07 (%) were used. The latter included C of natural
2
2
1
3
13
abundance ( = 1.10%). Theoretical amounts of C in the carboxyl carbon would be 0.93(%) ϩ 99.07(%) × 0.0110 = 2.02 (%) and C in the other 7
carbons : 1.10(%) × 7 = 7.70 (%). Therefore, the total amount of C in the esters should be: 2.02 ϩ 7.70 = 9.72 (%)
1
3
Scheme 3 Incorporation of carbon-13 in the reaction of potassium phenoxide–carbon dioxide complex
and warmed at 50 ЊC for 60 min, followed by an introduction of
carbon dioxide of 5 MPa, 2H1NA was not produced at all, and
SA and pHBA were obtained in 28% yield, as much as normal.
(Scheme 3 and Table 2). These labeled experiments have
furnished unambiguous support for the direct reaction between
carbon dioxide and benzene ring, but not for the mechanism of
carboxylations via a CO2 complex. It is rather natural for
chemists in a laboratory to be reluctant to open the lid of an
autoclave where very hygroscopic materials are kept dry. Any
consideration to the competitive formation of carboxylic acids
Calculations by MOPAC/PM3 method support a coordination
Ϫ1
structure E, and prove 2-NaphOK–CO (Ϫ48.3 kJ mol ) is less
2
Ϫ1
stable than PhOK–CO (Ϫ57.5 kJ mol ). These energy differ-
2
ences may be enough for the CO in the complex to shift from
2
2
-NaphOK to PhOK in a sandwich form like structure F during
with the formation of a CO complex even at the initial stage of
2
the blending process under nitrogen atmosphere at room
temperature.
the reaction has not been given in the past experimental work
8,13
6,12
elaborated on the mechanism using kinetics,
reactivity,
10,12
and thermal analysis.
Carbon-13 NMR spectra
Phenyl carbonate (PhOCO M, where M was K or Na) was
2
5
originally proposed for the complex, but the IR absorption
7
Ϫ1
spectra showed a band at 1684 cm which was not in agree-
ment with those of structurally similar carbonates such as
Experiments of CO complex labeled with carbon-13
2
Ϫ1
methyl phenyl carbonate (1754 cm ) and dimethyl carbonate
(1748 cm ). Therefore a structure D was proposed based on a
13
13
Ϫ1
The CO complex was prepared using CO . The PhOK– CO
2
2
2
7,11
complex was heated in the presence of a large excess of
normal CO2 at 120 ЊC for 1 h. The produced carboxylic
acids were subjected to esterification with methyl iodide in
DMF, followed by GC/MS analyses. If an internal migration
plausible interaction between the π-electrons and CO2. But
the IR spectrum itself is not sufficient for providing persuasive
evidence, because the adulteration of inorganic carbonates in
the sample is more or less inevitable in the preparation of phen-
13
18
of the CO in PhOK– CO would be involved in the reaction
oxides. Their strong absorption bands (e.g. both potassium
2
2
(
1
path a), the relative intensity of the molecular peak of m/z
53 should be 100%. However, a found value, 9.51% relative
to m/z 152 (90.49%) agrees with the calculated figures based
carbonate and potassium hydrogen carbonate show very broad
Ϫ1
and strong absorptions at ca. 1650 cm ) mar the characteristic
Ϫ1
absorption around 1600–1700 cm . This contamination also
13
on the assumption of a thorough mixing of CO with CO ,
which is containing CO2 by natural abundance (1.1%)
makes X-ray analysis of the structure difficult. The complex
was slightly soluble in dimethylformamide (DMF), but most
2
2
13
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 8 1 7 – 8 2 1
819

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Table 3 Carbon-13 chemical shifts of CO2 of an alkali metal
Experimental
phenoxide–CO complex and related compounds
2
All chemical reagents of extra pure grade were purchased from
Tokyo Kasei Chemical Co.Ltd. Carbon dioxide of purity more
than 99.95% was supplied by Sanin Sanso Co.Ltd. Carbon-13
Compounds
δC/ppm
Notes
a
b
c
c
c
d
CO in C H OK–CO
154
169
168
162
160
124
more than 99% enriched CO was supplied by ISOTEC INC
2
6
5
2
2
COOK of potassium salicylate
(
Miamisburg, Ohio).
K CO in D O–acetone-d
2
3
2
6
Potassium (or sodium) phenoxide and 2-naphthoxide were
prepared with potassium (or sodium) hydroxide and the corre-
KHCO in D O–acetone-d
6
3
2
(
NH ) CO in D O–acetone-d
4 2 3 2 6
sponding phenols. Phenoxide–CO complexes were prepared by
CO in DMF
2
2
introducing carbon dioxide of 0.1 MPa onto fine powdered
phenoxide for 24 h. The potassium 2-naphthoxide–CO2
a
The complex was prepared with potassium phenoxide and carbon-13
enriched carbon dioxide of 0.1 MPa at room temperature. A CP-MAS
was applied. The carbon-13 enriched complex prepared as in footnote
a was heated with CO at 130 ЊC. A CP-MAS was applied. A mixture
of deuterium oxide and acetone-d in a ratio of 3 : 1 was used. Carbon
b
complex was prepared in a similar manner to the phenoxide
13
c
complex, but CO of 1.0 MPa was used in an autoclave for
2
2
d
6
1.5 h. Phenoxides or these complexes of ca. 0.5 g were placed in
an autoclave (SUS-316) with a volume of 200 ml (Taiatsu
Techno Co. Osaka). An autoclave was flashed with nitrogen
and warmed to the reaction temperature prior to the intro-
duction of carbon dioxide. Carbon dioxide was released after
the reaction, and the reaction mixture was washed out with
H O–CH OH, and was analyzed by HPLC (Shimadzu LC-
dioxide was saturated in DMF at room temperature.
decomposed to phenol or phenoxide, disturbing measure-
ments of proton NMR spectra of the complex. A CP-MAS
NMR spectrum of the CO complex of potassium phenoxide
enriched with carbon-13 showed a peak at 154 ppm (Fig. 1).
Chemical shifts of several kinds of carbonates were 168–
2
2
3
1
0AD) using a silica gel column of 10 cm with an eluent
of aqueous phosphate buffer solution–CH OH (70:30 v/v%)
3
1
60 ppm, and potassium salicylate showed a peak at 169 ppm
Ϫ1
at a flow rate of 1.0 ml min . Carbon-13 enriched CO com-
2
for the carboxyl carbon of less electron density (Table 3).
These data indicate that the complex is not a carbonate, but a
more polarized molecule than carbon dioxide (124 ppm). A
broad IR absorption band at ca. 1650 cm of the complex
indicates a bent CO molecule (most stable at 130–140Њ), and is
different from an absorption at 2349 cm of carbon dioxide
in a linear sp configuration. Unlike alkali alkyl carbonate,
O-alkylation which would give phenyl carbonate such as
PhOCO K, did not occur under conditions employed for the
plex was heated in an autoclave at 120 ЊC for 1 h. An aqueous
solution of the reaction mixture was neutralized and was
extracted with diethyl ether to remove phenol. Diluted hydro-
chloric acid was added to the aqueous layer, adjusting the
pH value to 2–3 before extraction of the carboxylic acids
with diethyl ether. The products were esterified with methyl
iodide and sodium hydrogen carbonate in dimethylformamide
Ϫ1
2
Ϫ1
19
21
at 50 ЊC for 3 h. These methyl esters were obtained with con-
2
versions of 100%. A Shimadzu GC17A/QP5000 MS spectro-
meter was used for isotopic analyses. Semiempirical calcu-
lations using a program of MOPAC6 with Hamiltonian PM3
were carried out for unimolecular models. While distances of
present carboxylations.
PhO-K and CO -K were fixed to be 3.0 Å and 3.2 Å, respect-
2
ively, the distance (R) between the phenoxide and CO was
2
variable to minimize the energy. A CP-MAS sample, potassium
1
3
phenoxide– CO , was prepared using C-13 enriched carbon
2
Φ
dioxide. The sample was sealed in a glass tube of 5 × 5 mm,
and was set in a NMR rotor. Spectra were obtained on a
1
13
Varian XL-400 spectrometer ( H: 400 MHz, C: 100 MHz).
CP-MAS conditions applied were as follows: MAS rate: 6 KHz,
CP contact time: 3 ms, relaxation delay: 5 sec, 90 degree pulse
width: 6.5 µsec, number of repetition: 384, spectrum width:
4
0000 Hz.
Conclusion
The Kolbe–Schmitt reaction is the reaction of alkali metal
phenoxide with carbon dioxide, and has been a useful method
over more than a century to obtain aromatic hydroxy carb-
oxylic acids. An alkali metal phenoxide–CO complex had been
2
widely accepted for a long time as an intermediate of the reac-
tion, but it has been proved, in this paper, that the CO complex
2
is not an intermediate to give carboxylic acids, such as salicylic
acid (SA) and p-hydroxybenzoic acid (pHBA). A direct carb-
Fig. 1 A CP-MAS (6 K) carbon-13 NMR spectrum of the potassium
13
phenoxide– CO complex in a sealed ampoule.
2
oxylation of phenoxide with CO takes place even at room
2
temperature, and is competitive with formation of the CO2
complex. The resulting complex decomposes thermally (above
ca. 90 ЊC) to phenoxide, which then undergoes further competi-
tive reactions. Thus the increment of yields of the carboxylic
acids is directly dependent on the repetition number of
carboxylations at room temperature in combination with
decompositions at 150 ЊC under nitrogen atmosphere. The new
mechanism is also supported by labeling experiments: the CO2
complex prepared with carbon dioxide enriched with carbon-13
does not give carboxylic acids with labeled by carbon-13, but
completely scrambled with normal carbon dioxide.
In the NMR spectra, the chemical shifts of o-, m- and p-car-
bons of the potassium complex were 121.4, 130.4 and 115.0
ppm, respectively. Differences of chemical shifts (∆δ ) from
C
those of potassium phenoxide were 0, Ϫ2.4 and ϩ1.0 ppm,
respectively. Such small changes in the carbon-13 NMR spec-
trum would not be expected for the formation of a π-complex
20
on the benzene ring. On the other hand, the ipso- carbon
shifted significantly upfield (Ϫ6.5 ppm), which was similar to
the chemical shift of undissociated phenol, but not of phenoxy
species.
8
20
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 8 1 7 – 8 2 1

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A carbonate-like structure has been proposed for the
8 T. Kwan, H. Yamamoto, H. Mori and H. Samejima, Kagaku Kogyo
Chemical Industry, in Japanese), 1972(No.12), 618.
(
CO complex suitable for the data of the reactivity, C-13 NMR
2
9
E. A. Shilov, I. V. Smirov-Zamkov and K. I. Matkovskii, Ukr. Khim.
Zh., 1955, 21, 484.
and MOPAC/PM3 calculations. Spectral and thermoanalytical
data in past studies may have been required to consider the
instant and competitive formation of carboxylic acids, though
relatively small amounts, at any stage of the reaction.
1
1
0 T. Kito and I. Hirao, Bull. Chem. Soc. Jpn., 1973, 46, 3470.
1 M. S. J. Dewar, The Electronic Theory of Organic Chemistry, Oxford
University Press, London, 1949, pp. 168–171.
1
2 M. Kunert, E. Dinjus, M. Nauck and J. Sieler, Chem. Ber./Recueil,
1
997, 130, 1461.
1
3 T. Imoto, Y. Harano, M. Yano and R. Komota, Kogyou Kagaku
Zasshi (J. Industrial Chemistry, in Japanese), 1966, 69, 73.
Acknowledgements
The endowment of carbon-13 enriched CO2 by Professor
Takeshi Kobayashi (Department of Bio-Engineering, Nagoya
Univ.) is very much appreciated. Preliminary measurements of
CP-MAS NMR of very hygroscopic samples were conducted
by Dr Hisayuki Tsuno (JEOL Ltd.). Financial support by
San-In Kensetsu Kougyou Co., Ltd. is acknowledged.
14 (a) Y. Kosugi, Md. A. Rahim, K. Takahashi, Y. Imaoka and
T. Kitayama, Appl. Organomet. Chem., 2000, 14, 841; (b) Y. Kosugi,
K. Takahashi and Y. Imaoka, J. Chem. Res., 1999, 114; (c) Y. Kosugi,
R. Ueno and M. Kitayama, Japanese patent Hei 11–171819 (1999);
(
(
d ) Y. Kosugi, R. Ueno and M. Kitayama, patent 2000–72709
2000); (e) N. Morinaga, M. Uchigashima, Md. A. Rahim,
K. Onishi, K. Takahashi and Y. Kosugi, Nippon Kagaku Kaishi
(
J. Chem. Soc. Jpn, Chem. And Industrial Chem. in Japanese), 2002,
4
67.
1
5 (a) M. E. Vol’pin and I. S. Kolomnikov, Pure Appl.Chem., 1973, 33,
67; (b) Y. Iwashita and A. Hayata, J. Am. Chem. Soc., 1969, 91,
2525.
16 (a) D. H. Gibsson, Chem. Rev., 1996, 96, 2063; (b) X.-Z. Sun,
M. W. George, S. G. Kazarian, S. M. Nikiforov and M. Poliakoff,
J. Am. Chem. Soc., 1996, 118, 10525.
17 Md. A. Rahim, Y. Matsui and Y. Kosugi, Bull. Chem. Soc. Jpn.,
2002, 75, 619.
18 Y. Kosugi, and K. Takahashi, Advances in Chemical Conversions for
Mitigating Carbon Dioxide, Elsevier, Oxford, 1998, pp. 487–489.
19 T. Kito and I. Hirao, Bull. Chem. Soc. Jpn., 1971, 44, 3123.
20 J. B. Stothers, Carbon-13 NMR Spectroscopy, Academic Press,
New York, 1972, Chapter 6, pp. 208–238.
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4
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6
E. Baumann, Ber., 1907, 11, 1878.
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3
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O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 8 1 7 – 8 2 1
821