Effects of alkali and alkaline earth metals on the Kolbe-Schmitt reaction

Article abstract of DOI:10.1246/bcsj.75.619

It was found that the carboxylations of magnesium, calcium, and barium phenoxides with carbon dioxide at 260 °C produced salicylic acid and dicarboxylic acids (4-hydroxyisophthalic acid and 2-hydroxyisophthalic acid) in very high yields (80-100%), exceeding that of the ordinary Kolbe-Schmitt reaction. The orientation (ortho/para ratio) was controlled not only by chelations of the intermediate with alkaline earth metal (Mg, Ca, Ba) ions, resulting in salicylic acid, but also by the sizes of metal ions (Rb, Cs), giving p-hydroxybenzoic acid in a much higher ratio than the widely used method with potassium or sodium phenoxide. These alkaline earth metals worked to produce 3-hydroxy-2-naphthoic acid by the reaction of 2-naphthoxide with carbon dioxide, but the yield of 6-hydroxy-2-naphthoic acid was comparable to that of 3-hydroxy-2-naphthoic acid when cesium or rubidium 2 naphthoxide was employed. Considerably high yields (～60%) of 6-hydroxy-2-naphthoic acid, a monomer of one of the best liquid-crystal polymers, was attained by the carboxylation of cesium or rubidium 2-naphthoxide in the presence of potassium or sodium carbonate, where the alkali metal ion was supposed to increase the reactivity of the substrate. The formation of "binol" was observed in the preparation of 2-naphthoxides with metal hydroxides, especially with copper(II) ion.

Full text of DOI:10.1246/bcsj.75.619

c. Jpn.
© 2002 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 75, 619–622 (2002)
619
e Chemical
ciety of Ja-
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Effects of Alkali and Alkaline Earth Metals on the Kolbe–Schmitt
Reaction
Effect of Metal Ions on the Kolbe–Schmitt Reaction
M. A. Rahim et al.
Mohammad Abdur Rahim, Yoshihisa Matsui,* and Yoshio Kosugi*,†
02
9
2
Department of Life Science and Biotechnology, Faculty of Life and Environmental Sciences, Shimane University,
Matsue 690-8504
SJA8
09-2673
344
†Advanced Organic Material Chemistry, Faculty of Science and Engineering, Shimane University, Matsue 690-8504
(Received September 25, 2001)
01
It was found that the carboxylations of magnesium, calcium, and barium phenoxides with carbon dioxide at 260 °C
produced salicylic acid and dicarboxylic acids (4-hydroxyisophthalic acid and 2-hydroxyisophthalic acid) in very high
yields (80–100%), exceeding that of the ordinary Kolbe–Schmitt reaction. The orientation (ortho/para ratio) was con-
trolled not only by chelations of the intermediate with alkaline earth metal (Mg, Ca, Ba) ions, resulting in salicylic acid,
but also by the sizes of metal ions (Rb, Cs), giving p-hydroxybenzoic acid in a much higher ratio than the widely used
method with potassium or sodium phenoxide. These alkaline earth metals worked to produce 3-hydroxy-2-naphthoic
acid by the reaction of 2-naphthoxide with carbon dioxide, but the yield of 6-hydroxy-2-naphthoic acid was comparable
to that of 3-hydroxy-2-naphthoic acid when cesium or rubidium 2-naphthoxide was employed. Considerably high yields
(~60%) of 6-hydroxy-2-naphthoic acid, a monomer of one of the best liquid-crystal polymers, was attained by the car-
boxylation of cesium or rubidium 2-naphthoxide in the presence of potassium or sodium carbonate, where the alkali met-
al ion was supposed to increase the reactivity of the substrate. The formation of “binol” was observed in the preparation
of 2-naphthoxides with metal hydroxides, especially with copper(Ⅱ) ion.
01
.2
The Kolbe–Schmitt reaction is known to be one of the typi-
cal and efficient methods to use carbon dioxide in organic reac-
tions.1,2 The reaction has been used for over 100 years for pre-
paring aromatic hydroxy acids for pharmaceuticals, pesticides,
pigments, and preservatives of foods, cosmetics etc. Special
demanded productions today for totally aromatic liquid-crystal
polymers are both p-hydroxybenzoic acid, prepared from phe-
nol, and 6-hydroxy-2-naphthoic acid from 2-naphthol.
fewer practical applications to industrial manufacturing. In
this paper, a number of alkali metals and alkaline earth metals
are considered, and the nature of the carboxylating reaction is
discussed.
Experimental
Reagents. Phenol, 2-naphthol, alkali metal hydroxides
(NaOH, KOH, RbOH•H2O, and CsOH•H2O), alkaline earth metal
hydroxides
(Ca(OH)2,
Ba(OH)2•8H2O,
Cu(OH)2,
and
The reaction is carried out with alkali metal phenoxide and
CO2 of high pressure at high temperatures, and is greatly af-
fected by metal ions of phenoxides.3 For example, the carbox-
ylation of sodium phenoxide gives salicylic acid (SA), while
potassium phenoxide yields a mixture of salicylic acid and p-
hydroxybenzoic acid (pHBA) (Scheme 1). Although the
Kolbe–Schmitt reaction is usually limited to potassium and so-
dium phenoxides, various metals would be applicable to the re-
action with CO2. Other metals have not been scrutinized,
probably because of (i) difficulties in preparing their phenox-
ides, (ii) unreactivity of their carbonates in the Marasse meth-
od or a modification of the Kolbe-Schmitt reaction,4 and (iii)
Cu(OH)2•CuCO3•H2O), and Mg turning were of guaranteed grade.
Solvents (diethyl ether, ethyl acetate, hexane, methanol, and tolu-
ene) were purchased and used without further purification. Kero-
sene was distilled, and the fraction at the boiling point (200–215
°C) was collected. Carbon dioxide of more than 99.9% purity and
nitrogen were purchased from Sanin Sanso Ltd. Co.
Preparation of Alkali Metal Phenoxides and 2-Naphthox-
ides. Phenol (5.00 g, 53.2 mmol) or 2-naphthol (5.00 g, 34.7
mmol) was dissolved in 100 mL of an aqueous solution of hydrox-
ides. Water was evaporated on a rotary evaporator at 80 °C and
further dried in vacuo at 180 °C for 3 h. The prepared phenoxides
or 2-naphthoxides were ground to a fine powder in a dry box un-
Scheme 1.

620 Bull. Chem. Soc. Jpn., 75, No. 3 (2002)
Effect of Metal Ions on the Kolbe–Schmitt Reaction
der a dry nitrogen stream.
1H, 5-H); IR (KBr) 3400, 3200-2500, 1700, 1610 cm−1; 4-Hy-
droxyisophthalic acid. 1H NMR (acetone-d6) δ 8.60 (d, J = 2.2
Hz, 1H, 2-H), 8.16 (dd, J = 2.2, 8.79 Hz, 1H, 6-H), 7.06 (d, J =
8.79 Hz, 1H, 5-H); IR (KBr) 3420, 3000-2500, 1660 cm−1; 2-Hy-
droxy-1-naphthoic acid. 1H NMR (D2O/KOH + H2O) δ 7.75 (d,
J = 7.8 Hz, 1H, 8-H), 7.65 (d, J = 9.0 Hz, 1H, 5-H), 7.56 (d, J =
8.5 Hz, 1H, 4-H), 7.42 (t, J = 6.5 Hz, 1H, 7-H), 7.18 (t, J = 7.8
Hz, 1H, 6-H), 7.01 (d, J = 9.0 Hz, 1H, 3-H); 3-Hydroxy-2-naph-
thoic acid. 1H NMR (D2O/KOH + H2O) δ 7.74 (d, J = 8.3 Hz,
1H, 8-H), 7.72 (d, J = 1.4 Hz, 1H, 9-H), 7.59 (d, J = 8.3 Hz, 1H,
5-H), 7.38 (tt J = 0.9, 6.8 Hz, 1H, 6-H), 7.18 (tt, J = 1.2, 7.0 Hz,
1H, 7-H), 6.89 (s, 1H, 4-H); 6-Hydroxy-2-naphthoic acid. 1H
NMR (D2O/KOH + H2O) δ 8.40 (s, 1H, 1-H), 7.94–7.89 (d, 2H,
3,8-H), 7.69 (d, J = 8.7 Hz, 1H, 4-H), 7.18 (dd, J = 2.4, 9.0 Hz,
1H, 7-H), 7.06 (d, J = 2.4 Hz, 1H, 5-H); 1,1ꢀ-Bi-2-naphthol. 1H
NMR (CDCl3) δ 7.98 (d, J = 8.7 Hz, 2H, 3,3 -H), 7.89 (d, J = 7.8
Hz, 2H, 5,5 -H), 7.38 (d, J = 9.0 Hz, 2H, 4,4 -H), 7.28–7.39 (m,
4H, 6,6 ,7,7 -H), 7.15 (d, J = 8.7 Hz, 2H, 8,8 -H); IR (KBr) 3480,
3400, 1620, 1600 cm−1; MS m/z 286 (M+), 257, 239, 226, 119.
Found: C, 82.25; H, 5.27%. Calcd for C20H14O2: C, 83.91; H,
4.89%.
Preparation of Alkaline Earth Metal Phenoxides and 2-
Naphthoxides. Calcium and barium phenoxides or 2-naphthox-
ides were prepared in a similar manner as described above. Mag-
nesium phenoxide was prepared as follows: a mixture of phenol
(5.00 g, 53.2 mmol) and magnesium turning (0.62 g, 25.6 mmol)
was refluxed in 80 mL of toluene with stirring for 24 h. The mix-
ture was cooled to room temperature and the solid portion was
dried in a vacuo for 2 h at 110 °C. The same method did not work
for the preparing magnesium 2-naphthoxide.
General Reactions and Analyses. The prepared metal phen-
oxide (1.0 g) or 2-naphthoxide (1.0 g) was placed in an autoclave
(200 mL), and CO2 was introduced after flushing with N2. The
vessel was heated quickly to the reaction temperatures and kept
for a certain reaction time. The reaction mixture in the autoclave
was cooled in an ice bath, and then washed out with a small
amount of aqueous methanol. The solution was neutralized with
dilute HCl and analyzed using a high-performance liquid chro-
matograph (HPLC) with a Shimadzu LC-10AD chromatograph
and a column (ODS column 150 × 4.6 φmm); the peak areas were
obtained with a Shimadzu chromatopack C-R3A.
Spectral Identifications. The products were isolated by ex-
traction with ether from the aqueous reaction mixture after adjust-
ing the pH value. The isomeric isophthalic acids were separated
from each other by column chromatography (Wakogel C-300) and
eluted with hexane/ethyl acetate (2/1). Binol was also isolated
from 2-naphthol on the same column and eluted with hexane/ethyl
acetate (1/1). 1H NMR and IR spectra were obtained on a JNM-
GX-270, FT-NMR spectrometer (JEOL) and a FT/IR-620 (JAS-
CO), respectively. 2-Hydroxyisophthalic acid. 1H NMR (ace-
tone-d6) δ 8.09 (d, J = 7.5 Hz, 2H, 4,6-H), 6.98 (t, J = 7.5 Hz,
Results and Discussion
The Carboxylation of Phenoxides. Three kinds of alka-
line earth metal phenoxides were subjected to carboxylation
with carbon dioxide (Table 1, run nos. 1–10). It is a surprised
to see that the Kolbe–Schmitt reaction using metals other than
potassium and sodium gives carboxylic acids in high yields. In
most cases, a yield of more than 80% was attained in 1 h when
the reaction temperature was 260 °C; further carboxylation
Table 1. Carboxylation of Various Alkali and Alkaline Earth Metal Phenoxides with Carbon Dioxide
Reaction condition
Recovered
phenol
Yield/ %a)
Run no. Metal
CO2
MPa
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
Temp.
°C
Time
h
1.0
1.0
1.0
1.0
5.0
1.0
1.0
1.0
1.0
5.0
%
SA
4.0
pHBA
0
4HIPA
0
0
0
0
0
0
trace
0.6
3.0
5.5
2HIPA
0
0
1.0
4.4
8.0
0
trace
0
Total yieldb)
4.0
1
2
3
4
5
Mg
Mg
Mg
Mg
Mg
Ca
150
200
230
260
260
150
200
150
260
260
96.0
83.0
56.5
21.0
14.7
70.0
54.4
20.0
8.4
16.0
40.5
72.0
74.0
26.7
42.7
76.0
77.0
64.8
0.5
1.8
2.5
3.0
2.8
2.8
3.0
2.0
2.0
16.5
44.3
83.3
93.0
29.5
45.5
80.2
104.0
99.8
6
7
Ca
8
Ba
9
Ba
9.5
11
10
Ba
16.0
11
12
13
14
15
16
17
18
Rb
Rb
Rb
Rb
Cs
Cs
Cs
Cs
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
150
150
150
200
150
150
200
260
0.25
1.0
1.0
1.0
1.0
5.0
1.0
1.0
29.3
6.5
19.6
1.4
29.5
7.5
17.0
6.0
30.6
39.8
36.1
37.0
20.7
29.0
26.0
26.5
39.0
51.5
42.8
51.6
48.0
57.0
35.0
19.0
0.9
1.8
1.3
7.8
1.6
5.5
16.0
35.0
0
0
0
1.8
0
0
71.4
94.9
81.5
107.8
71.9
97.0
4.5
12.5
102.0
140.5
a) Determined by HPLC. An unidentified peak was observed in run nos. 17 (ca. 1.0%) and 18 (ca. 3.9%) of retention time at
8.5 min. SA, pHBA, 4HIPA, and 2HIPA denote salicylic acid, 4-hydroxybenzoic acid, 4-hydroxyisophthalic acid, and 2-
hydroxyisophthalic acid, respectively.
b) Total yield of the carboxylation based on the amount of phenol used.

M. A. Rahim et al.
Bull. Chem. Soc. Jpn., 75, No. 3 (2002) 621
proceeded with an increase in the reaction time to give dicar-
boxylic acids, such as 4-hydroxyisophthalic acid (4HIPA) and
2-hydroxyisophthalic acid (2HIPA). There is a single report
on the carboxylation of barium and calcium phenoxides in
DMF, but the yields were less than 50%.5 The mechanism of
the Kolbe-Schmitt reaction has recently been checked in this
laboratory:6 the [PhOM•CO2] complex2,3,7 is not an intermedi-
ate of the reaction, but a direct carboxylation on the benzene
ring by carbon dioxide; that is, an electrophilic substitution re-
action takes place. Thus, the reaction would be affected by not
only the electron density on the benzene ring, but also by the
stabilization energy of the intermediate to produce final prod-
ucts. The present results well reflect the stability of the inter-
mediate forming a chelate8 between SA and the bivalent metal
ion. Thus, the ratio of SA to pHBA is 10–40, which is very
different from the ratio of 2–7 in the case of potassium or sodi-
um phenoxides.
On the other hand, for rubidium and cesium in the series of
alkali metals, the ratio of SA to pHBA was less than 1.0 (Table
1, run nos. 11–18). The remarkable increase of dicarboxylic
acid 4HIPA may be due to the carboxylation of pHBA at 260
°C (no. 18). The prominent selectivity of para-carboxylation
is ascribable to their larger ionic radii (147 and 167 pm of Rb+
and Cs+, respectively), which interfere with a direct attack of
carbon dioxide at the ortho position. The order of Li < Na <
K < Rb < Cs agrees with the observed ratio (o/p) as 1.0/0,9
6/1, 3/2, 4/5, 3/5, respectively. Alternatively, the size is impor-
tant to stabilize the transition states of the chelation at the
ortho position in a similar way of bivalent metal ions, as de-
scribed above.
The Carboxylation of 2-Naphthoxides. 2-Naphthol is
another interesting phenol in the Kolbe–Schmitt reaction, be-
cause the reactivity at the 1-, 3-, and 6-positions is competitive
with each other. Although sodium and potassium 2-naphthox-
ides easily produce 2-hydroxy-1-naphthoic acid (2H1NA) at
room temperature, the corresponding 3- and 6-naphthoic acids
(abbreviated as 2H3NA and 2H6NA, respectively) were ob-
tained above 200 °C. The CO2 complex of 2-naphthoxide is
unreactive to produce 2H1NA, and is decomposed to naph-
thoxide at higher temperatures.
When the rubidium and cesium 2-naphthoxides were sub-
jected to carboxylation with 2.0–5.0 MPa CO2, 2H3NA and
2H6NA were produced in almost equal amounts, but smaller
amounts of 2H1NA remained at 200–230 °C (Table 2). On the
other hand, when alkaline earth metals (Ca and Ba) were used,
2H6NA was not obtained, but 2H3NA was the single major
product, which was ascribed to the chelate formation as ob-
served in the case of phenoxides. Similar chelations at 1-
COOH, especially with barium ion, increased the stability
against the thermal decomposition, even at 260 °C. During
studies on the carboxylation of 2-naphthoxides, the formation
of 1,1 -bi-2-naphthol “binol” was observed. The preparation
of copper 2-naphthoxide by the addition of copper(Ⅱ) hydrox-
ide to 2-naphthoxide was in vain. The oxidative dimerization
of 2-naphthol catalyzed by copper(Ⅱ) or iron(ꢀ) has been well
studied.10–13 The present results may be explained by the pro-
cess of the homolytic bond fission of 2-naphthoxy-metal, espe-
cially alkaline earth metal, at high temperatures, followed by
Table 2. Carboxylation of Various Kinds of Alkali and Alkaline Earth Metal 2-Naphthoxides with Carbon Dioxide.
Reaction condition
Recovered
2-naphthol
Yield/%a)
Run no. Metal
CO2
MPa
5.0
5.0
5.0
5.0
2.0
5.0
5.0
5.0
2.0
2.0
5.0
5.0
5.0
5.0
5.0
5.0
Temp.
°C
Time
h
1.0
0.5
%
2H1NA
52.0
22.3
4.0
2.0
3.0
14.5
trace
10.0
3.0
2H3NA
2H6NA
0
Binol
0
1.7
0
0
0
0
0
0
0
1
2
K
K
20
47.0
27.5
24.0
10.0
5.0
11.0
13.0
53.0
55.0
49.0
36.8
33.4
55.7
48.5
43.7
36.8
0
230
230
250
230
230
250
230
230
260
230
230
230
230
230
230
33.2
72.0
87.0
86.5
71.5
84.5
24.6
21.0
22.4
16.4
16.1
15.0
19.0
24.0
21.2
9.0
0
0
4.5
2.5
2.0
3
K
10
4
K
10
15
10
10
5
K
6
7
8
9
10
11
12
13
14
15
16
Na
Na
Rb
Rb
Rb
Cs
Cs
Cs
Cs
Cs
Cs
1.0
11.8
20.6
22.0
18.7
19.3
19.7
28.0
28.0
37.2
5.0
5.0
0.5
0.5
1.0
5.0
5.0
6.4
0
14.8
12.3
9.4
4.0
3.8
1.0
1.6
0
0
0
10
3.4
1.0
17
18
19
20
21
Ca
Ca
Ba
Ba
Ba
5.0
5.0
5.0
5.0
5.0
230
230
230
230
260
3.0
10
3.0
5.0
3.0
37.9
65.0
52.0
38.0
32.5
7.8
2.5
21.0
33.0
52.5
28.0
15.5
10.0
14.0
8.5
0
0
0
0
0
25.9
16.5
16.7
14.0
6.0
a) Determined by HPLC. 2H1NA, 2H3NA, 2H6NA, and Binol denote 2-hydroxy-1-naphthoic acid, 3-hydroxy-2-naph-
thoic acid, 6-hydroxy-2-naphthoic acid, and 1,1 -bi-2-naphthol, respectively.

622 Bull. Chem. Soc. Jpn., 75, No. 3 (2002)
Effect of Metal Ions on the Kolbe–Schmitt Reaction
Table 3. Carboxylation of Cesium 2-Naphthoxide with Carbon Dioxide in the Presence of Alkali and Alkaline Earth Metal Car-
bonates
Carbonate
Reaction condition
Recovered
2-naphthol
Yield/%a)
Run no.
CO2
Temp.
°C
Time
(mole ratio)
MPa
0.3
0.3
5.0
5.0
5.0
5.0
5.0
5.0
5.0
h
6
6
6
%
80.0
50.0
30.0
14.6
11.3
16.5
6.5
2H1NA
1.0
2.0
4.2
2.1
trace
6.5
2.4
5.3
6.5
2H3NA
5.0
9.0
22.0
13.7
29.3
15.0
7.8
2H6NA
13.0
38.8
36.5
58.3
33.9
37.0
55.0
23.6
38.3
1b)
2b)
3
4
5
6
7
8
9
kerosene
Cs2CO3/kerosene
Cs2CO3
—
265
265
230
230
230
230
230
230
230
0.1
0.1
1.0
3.0
1.0
1.0
1.0
1.0
K2CO3
K2CO3
Na2CO3
Na2CO3
CaCO3
24
6
6
24
6
28.4
13.4
20.5
22.5
BaCO3
6
a) Determined by HPLC.
b) The reactions were carried out as Ref. 14.
the formation of carbon radicals, which were stabilized by res-
onating forms, giving a coupling product, binol.
of the carbonate and the reaction time increase, even at a tem-
perature (200–260 °C) lower than the melting or decomposing
points of these carbonates (egs. 981 °C for K2CO3, 851 °C for
Na2CO3).
Production of 6-Hydroxy-2-naphthoic Acid (abbreviated
as 2H6NA for convenience). A copolymerization of 2H6NA
and pHBA gives an engineering plastic of high quality, and an
efficient supply of 2H6NA has recently been expected to con-
tribute to “information technology”. The carboxylation of ce-
sium 2-naphthoxide gave 2H6NA in 37% yield, which was
much better than those (20–30%) with potassium 2-naphthox-
ide. A US patent14 also claims 35–39% yield from cesium 2-
naphthoxide with the addition of cesium carbonate in a sol-
vent, such as isopropylnaphthalenes, trimetylphenylindanes,
tetradecanes, and hexadecanes at 265 °C. In the present exper-
iments, not only some modifications of the US patent, but also
novel methods, were conducted (Table 3). Nearly a 40% yield
of 2H6NA was obtained from the carboxylation of cesium 2-
naphthoxide in kerosene, which could be recycled, if neces-
sary, thus avoiding decomposition of the solvent at high tem-
perature. When the reaction was carried out under a higher
pressure of CO2 with the addition of potassium carbonate, but
without solvents, the yield was almost 60%, and the formation
of 2H3NA was surpressed to 14–18%. Generally, the solvent
has a role to homogenize the heat distribution in the reactor,
but, at the same time, decreases the contact between the solid
substrate and the reagent gas and slows down the reaction rate.
The large size of cesium ion blocks the attack neighbor (ortho)
position, and favors para carboxylation of phenoxide, as dis-
cussed in Table 1. However, their reactivity to carbon dioxide
is inferior to those of potassium and sodium 2-naphthoxides.
Since the bonding between cesium and oxygen of 2-naphthox-
ide is less polarized, the potassium ion of the carbonate would
approach and coordinate weakly to the oxygen atom, resulting
in an increased reactivity of the substrate. Sodium carbonate
showed a similar effect to give 2H6NA in high yields. Calci-
um and barium carbonates behaved so as to increase the car-
boxylation, but might have replaced cesium during the reac-
tion, resulting in the high yield of 2H3NA. The exchange be-
tween metal ions would occur in any case as the concentration
A scholarship given to M. A. R. in the program for Foreign
Research Student by the Ministry of Education, Science,
Sports and Culture is gratefully acknowledged.
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