374 J. CHEM. RESEARCH (S), 1997
J. Chem. Research (S),
1997, 374–375†
Effect of Cation Capture by Crown Ether and Polar Solvent
in the Carboxylation with CO2 of Alkali Metal
2-Naphtholates under Ordinary Conditions†
Joseph Baxter and Tatsuaki Yamaguchi*
Department of Industrial Chemistry, Chiba Institute of Technology, 2-17-1 Tsudanuma,
Narashino-shi, Chiba 275, Japan
An efficient method for the carboxylation of sodium 2-naphtholate and potassium 2-naphtholate in benzene with 10 mol%
of crown ether or aprotic polar solvents under 1 atm of carbon dioxide at 60 °C affords 2-hydroxynaphthalene-1-carboxylic
acid in yields ranging from 14.6 to 43.8% and 26.7 to 66.0%, respectively.
A useful process for the carboxylation of alkali metal 2-
naphtholates has been developed based on the principles of
crown ether chemistry. Crown ethers have been exhaustively
studied in the last 25 years.1–3 These macrocyclic ligands are
well known for their superb selectivity towards metal ions.4,5
This modified carboxylation procedure occurs at a reason-
able temperature and carbon dioxide pressure and is practi-
cal for the manufacturing of 2-hydroxynaphthalene-1-car-
boxylic acid (2-H-1-NA), which is useful as a chemical
intermediate for dyes, heat-sensitive dyes, photographic
materials, liquid crystals, chemical feedstock, etc.
taining crown ethers. An increase in the basicity of the crown
ether increases both its solvating and chelating ability.11
To support our proposal that the solvation and/or removal
of the cation is necessary in benzene, polar aprotic solvents
(0.001 mol) were added to the carboxylation reaction without
the use of a crown ether (Table 2).12 A polar solvent aids in
solvating the alkali metal naphtholate, thereby creating a
solvent-separated ion-pair. It acts in a similar way as a crown
ether: increasing the alkali cation and oxygen intranuclear
distance and creating a homogeneous solution.
It is well known that carboxylation of alkali metal naph-
tholates can be carried out under normal temperatures and
pressures because a polar solvent is used.6–9 However, we
found that benzene together with a small amount of crown
ether or polar solvent, which creates a homogeneous solu-
tion, could be used instread. Our reaction in essence is simi-
lar to the alkylation reaction of potassium phenoxide with
butyl bromide using various crown ethers,10 however only a 10
mol% of crown ether is needed. The reaction readily occurs
at atmospheric pressure and at 60 °C for the carboxylation of
potassium 2-naphtholate and sodium 2-naphtholate to give
high selectivity and a relatively high yield of 2-H-1-NA. These
solvation effects were clarified because crown ethers were
used to separate the metal cation from the naphtholate
anion, thereby increasing the charge of the free naphtholate
anion, creating a homogeneous solution, and making a
stronger nucleophilic reagent. Similar results were found
using at trace amount of polar solvents, which solvate the
potassium ion creating a solvent-separated ion-pair.
Table 2 Effects of additive polar aprotic solvents on the
carboxylation of potassium 2-naphtholate (0.01 mol) in benzene
(15 ml)a
Yield of
2-H-1-NA (%)
Additives (0.001 mol)
Time (t/h)
None
6
6
3
3
3
6
3
0.5
66.0
39.4
45.3
26.7
58.5
50.5
DMSO
DMF
Ethylene carbonate
1,2-Dimethoxyethane
1,4-Dioxane
Nitrobenzene
aReaction temperature, 60 °C; atmospheric pressure of CO2.
The yields of 2-H-1-NA in polar aprotic solvents were
greater than the crown ether yields when nitrobenzene,
1,4-dioxane, ethylene carbonate, or DMSO were added. For
all of the solvents, except 1,4-dioxane and DMSO, the reac-
tion time was shortened to 3 h. The greatest yield (66%) after
purification was with DMSO; however, DMF, which is also a
very polar solvent, unexpectedly gave much lower yields. The
reason for this dichotomy is as yet unknown. The yields were
probably lower with crown ethers because a crown ether can
only react once to bind the cation; however, a polar solvent
can make many solvent-separated ion-pairs through the
course of the reaction.
The results are shown in Table 1, and the yields were
calculated after purification. The highest yields were
achieved using the aliphatic crown ethers as compared to the
other crown ethers because the oxygen basicity of the ali-
phatic crown ethers is higher than that of the aromatic-con-
Table 1 Effects of crown ethers on the carboxylation of alkali
metal 2-naphtholates (0.01 mol) in benzene (15 ml)a
In conclusion, the reaction of alkali metal naphtholates
with CO2 has been clarified through the use of crown ethers
and polar solvents in benzene. The yields seem to vary with
the solvating strength of the crown ether or polar solvent.
The crown ether aids in the dissolution of the naphtholate
salt to make a homogeneous solution similar in principle to
polar solutions that solvate the cation-anion pair increasing
their intramolecular distances. The anionic charge is then
more pronounced on the oxygen and naphthalene ring, eas-
ing the electrophilic attack of CO2, as supported by MNDO
and Hu¨ckel calculations. Further experimentation and calcu-
lations are being performed to elucidate the mechanistic
details.
Crown ethers
(0.001 mol)
Alkali
Time
Yield of
metal salt
(t/h)
2-H-1-NA (%)
None
potassium
potassium
sodium
potassium
sodium
potassium
sodium
6
6
6
6
6
5
6
0.5
27.5
21.0
14.6
43.7
43.8
29.8
Dibenzo-18-crown-6
Benzo-15-crown-5
15-Crown-5
18-Crown-6
aReaction temperature, 60 °C; atmospheric pressure of CO2.
*To receive any correspondence.
†This is a Short Paper as defined in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).
Experimental
General Procedure for the Preparation of 2-H-1-NA.sA cylindri-
cal Pyrex reactor was fitted with a Teflon stopper with two holes,