Note: Descriptions are shown in the official language in which they were submitted.
~5~9(~
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28678
PR~CESS FOR THE PRODUCTION OF
6-H~DROXY-2-NAPHTHOIC ACID
The present invention relates to a process for
the preparation of 6-hydroxy-2-naph~hoic a id, more par-
ticularly, by the carboxylation of the potassium salt of
2-hydroxynaphthalene with carbon dioxide. Still more par-
ticularly, the invention relates to an Lmproved process
for the preparation o 6-hydroxy 2-naphthoic acid in which
said potassium salt is reacted with carbon dioxide u~der
~0 specific conditions of temperature, pressure, and ratios
of reactants which results in increased yield o~ the de-
sired product.
The production o~ 6-hydroxy-2-naphthoic acid, an
intermediate useful for the prepartion of synthetic fibers,
and s~ructural plastics, by the reaction of the potassium
salt of 2-hydroxynaphthalene and carbon dioxide at an ele-
vated temperature, is disclos d by Andre in U.S. Patent
1,593,816. Andre, however, does not disclose the criti-
cality of temperature, pressure, or ratios of reactan~s.
Moreover, upon repeating Andre's work, the actual yield of
6-hydroxy-2 naphthoic acid obtained was ound to be only
about one-third of the yield reported by Andre. ~See
Example 6 below).
The carboxylation of alkali metal sal~s o~
phenols with carbon dioxide to foxm acids containing
phenolic substituents, the well-known Rolbe-Schmitt re-
action, is alsa disclosed in U.S. Patents 3,816,521 and
'~'
; ;. . . .
~ 79
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3,405,169.
In the carboxylation of the potassium salt o~ 2-
hydroxynaphthalene, the initial product form is 3-hydroxy-
2-naphthoic acid which subsequently rearranges i~ situ to
form 6-hydroxy-2-naphthoic acid. It has been found tha~ the
conditions which favor the formation of 3-hydroxy-2-naph-
thoic acid in the Kolbe-Schmitt reaction hinder the rear-
rangement reaction.
There is a need, therefore, ~or an improved pro-
cess for the preparation of 6-hydroxy-2-naphthoic acid
which will optimize the yield of 6-hydroxy-2-1~aphthoic acid
in the reaction product.
Summary of the Invention
In accordance wi~h the present invention, there
is provided an improved process for preparing 6-hydroxy-2-
naphthoic acid by reacting essentially anhydrous potassium
2-naphthoxide ~ith carbon dioxide at an elevated tempera-
ture, and recovering 6-hydroxy-2-naphthoic acid therefrom,
the improvement comprising forming a mixture of 2-hydroxy-
naphthalene and a potassium base9 using about 0.8 to 1.45
moles of 2-hydroxynaphthalene per equivalent of potassium
base; dehydrating said mixture, introducing carbon dioxide
into said dehydrated mixture at about 20 to 9() psi at about
255`C to 2~0C, while agitating said mixture in a pressure
reactor; and heating said stirred mixture al: said temper-
ature and under said pressure. PreferabLy the heating
co~tinues until the ratio of 6-hydroxy-2-naphthoic acid to
3-hydroxy-2-naphthoic acid in the reaction mixture is at a
suffieiently high level to increase the yield of the 6-
hydroxy-2-naphthoic acid.
In the preferred embodiment, the reaction mix-
ture of potassium 2-naphthoxide and carbon dioxide also
contains a non-polar organic flux. I~ the especially
preferred embodiment, the flux is a mixture of isopropyl-
naphthalenes. .
The improved process of the present invention
affords the following advan~ages:
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1. A higher yield of 5-hydroxy-2-naphthoic acid
is obtained.
2. The presence oE a ~ioh ratio of 6-~ydroxy-2-
naphthoic acid to 3-hydroxy-2-naphthoic acid abtained will
`5 improve the recovery, yield and purity of the product, but
it is not mandatory.
3. The use of a flux improves heat and mass trans-
fer rates thus reducing time cycles and improving the yield.
In carrying out the Lmproved process of the pre-
sent invention, 2-hydroxynaphthalene and a potassium base
are mixed in amounts sufficient to provide a ratio of about
0.8 to 1.45 moles of 2-hydroxy-naphthalene per equivalent of
potassium base, and the reaction mixture is dehydrated by
distillation, or by passing it through a dehydration ~ppa-
ratus.
. Suitable potassium bases inciude potassium
hydroxide, potassium carbonate, potassium hydride, potas-
sium amide, and the like, as well as mixt~re~s thereof. The
preerred potassium base is potassium hydxoxide with or
without potassium c~ konate.
. Pre~erably, the potassium base and 2-hydroxy~
naphthalene are mixed in ~he presence of a non-polar organic
flux to form the potassium 2-naphth~xide and the reaction
mixture is dehydra~ed by distillation under nitrogen until
essentially all of the water is removed.
Preferably~ tn foxming the reaction mixture about
1.0 to 1.1 moles of 2-hydroxynaph~halene, and m~st prefer-
ably, about 1.02 to 1.04 moles, are used per mole of yotas
sium base. A large excess of 2-hydroxynaphthalene, for
example, a~out 1.5 moles per mole of potassium hydroxide,
has ~een found to produce a large decrease in the yield of
the final product.
It has been found that higher yields may be Ob-
tained when a fIux is used. As used herein, th~ term '7flux"
defined as any non-polar organic material which is not a
.
~ '7
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solvent for the reactants and which is a liquid under the
reaction conditions employed. Suitable materials which may
be used as a flux include the following:
l-isopropylnaphthalene,
2-isopropylnaphthalene,
naphthalene,
kerosene, and the like
T~e preferred ~lux is a mixture of i-, and 2-
isopropylnaphthalene. Preferably, the dehydrated mixture
contains about one part by weight of potassium 2-naphthoxide
per part by weight of the mixed isopropylnaphthalenes.
The dehydrated mixture is charged to a pressure
xeactor, preferably with additional flux and purged with
carbon dioxide~ The reactor is then se~led and heated at
akout 255C to 285~C, preferably about 260C to 280C, more
preferably abaut 260C to 270JC, under a carbon dioxide
pressure of about 20 psi to 90 psi, preferabl~ about 30 psi
to 80 psi, more preferably about 40 psi to 60 p9i, while
stirring the reaction mixture vigorously, until analysis of
an aliquot of the reaction mixture shows a molecular ratio
o 6-hydroxy-2-naphthoic acid ~o 3-hydroxy-2-naphthoic acid
of the desired level, preferably more than ~, more preferably
more than 3, and most preferably more than 6. The agitation
must be sufficient to ensure the uniform mixing of the carbon
dioxide into the reaction mixture~ otherwise the carboxylation
~eaction stops.
At temperatures belo~ 255C, the reaction product is
found to bè mainly 3-hydroxy-2-naphthoic acid. Only about a
20% yield of the desired 6-hydroxy-2-~aphthoic acid was ob-
tained below ~55C.
At pressures below 40 psi, the yield of 6-hydroxy-
2-naphthoic acid decreases. At pressures above 60 psi, the
ratio of 6-hydroxy-2-naphthoic acid to 3-hydroxy-2-naphthoic
.. . . . . .
acid decreases.
At temperatures of 280C, or higher, ~he reaction
time can be critical because of ~he formation of tars. In
carrying out the reaction at 2~0C and 60 psi, the reac~ion
~ 7
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time should be limited to maximize the produc~ion of the
desired product.
When the ratio of 6-hydroxy-2-naphthoic acid to 3-
hydroxy-2-naphthoic acid reaches the desired level, with
the higher ratio being better, the reactor is vented to the
atmosphPre and the reaction mixture is cooled under a nitro-
gen atmosphere to about 120C. The reaction mixture is then
either diluted with water and/or discharged into water
containing enough sulfuric acid to bring the pH of ~he re-
sulting mixture to 7, or above, preferably about 7.1 + 0.2.
The aqueous phase of the resulting two pbase liq-
uid mixture is split off from the organic phase at a
temperature of about 85-98C, preferably about 95C, and
back-extracted twice with an equal volume of an organic flux
(even if the flux was not present during the reaction) at
the same temperature as the aqueous phase. A buffer,
preferably about 0.1 gram of acetic acid per gram of 6-
hydroxy-2-naphthoic acid expected, is added to the ex-
tracted aqueous phase, and then enough dilute sulfuric acid
is added to adjust the pH to about 4.8 to 5.2 to precipitate
the 6-hydroxy-2-naphthoic acid. The precipitate may then
be recovered by conventional means and dried to obtain the
desired 6-hydroxy-2-naphthoic acid in a yield of about 40-
60% of theoretical.
The mother liquor obtained on recovery of the
product may be treated with additional sulfuric acid to
adjust the pH to about 2-4 and precipitate 3-hydroxy-2-
naphthoic acid, which may be recovered by filtration.
In the examples which follow, all parts are by
3~ weight unless otherwise indicated. All yields are based on
potassium base charged. A theoretical yield is defined as
one mole of 6-hydroxy-2-naphthoic acid produced for every 2
moles of potassium 2-naphthoxide.
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Exam~le 1
A mixture of 2-hydroxynaphthalene (84 grams; 0.58
mole), 45% potassium hydroxide (70O5 grams; 0.56 mole), and
100 mls of a mixture of 1-, and 2-isopropylnaphthalenes is
stirred and heated under a nitrogen abmosphere until 100
mLs total of water and isopropylnaphthalane are distilled
off, At that point, 100 mls of isopropylnaphthalene is
added and the mixture is fur~her heated to distil off an
addi~ional 50 mls of isopropylnaphthalene, and obtain a
dehydrated mixture.
The dehydrated reaction mixture is cooled to
265C, charged to a pressure reactor, and purged with car-
bon dioxide. The reactor is then sealed and pressurized
with carbon dioxide to 40 psi while stirring slowly. The
rate of stirring is then increased to 1500 rpm and the mix-
ture is stirred at 265C under 40 psi of carbon dioxide for
16 hours. The reaction mixture is then cooled to 260C,
vented to atmospheric pressure, and cooled under a nitrogen
atmosphere to 120C. Water is then added to dilute the re-
action mixture~
The diluted reaction mixture ls discharged into
a flask containing 7.5 grams of sulfuric acid in 100 mls of
water. The pH of the resulting mixture is then adjusted to
7.0 ~ 1 with sulfuric acid, and the two--phase liquid mix-
ture is heated to 95C while stirring. The mixtur~ is
allowed to set~le, the layers are split apart, and the
aqueous phase is washed twice with 100-rnl portions of
isopropylnaphthalene. The isopropylnaphthalene-wash~d
aqueous phase is then stirred at 65-75t and 20 grams of a
3~ 15~ by weight solution o acetic acid in water is added
thereto. Sulfuric acid (15 grlms of sulfuric acid per 100
mls of solution) is then added over a period of 15 to 30
minutes until the pH of the resulting sl~rry is 4.8 to 5.2.
The slurry is then cooled to 25-35C and filtered. The re~
- sulting filter cake is then washed with water and dried to
obtain 27.4 grams ~54% of theoretical) of 6-hydroxy-2-
naphthoic acid.
~ 3~
The aqueous mother liquor is adjusted to pH 2.5
with dilute sulfuric acid and the resulting precipitate is
collected by filtration, washed, and dried to afford a mix-
ture containing 1.6 grams of 6-hydro~y-2-naphthoic acid and
2.9 grams of 3-hydroxy-2-naphthoic acid.
The com~ined organic phases contain 50.2 grams of
2--hydroxynaphthalene, which can be recovered and recycled.
In the manner described above, carrying out the
reaction at 80 psi, and 100 psi, the yields of 6-hydroxy~2-
naphthoic acid obtained are 49.7~, and 26.8%, respectively.
The above example illustrates the present inven-
tion as well as the effect of increased pressure on the
yield of 6-hydroxy-2-naphthoic acid.
Example 2
The procedure of Example 1 is followed in every
detail except that a mixture of 2 hydroxynaphthalene (83
grams; 0.576 mole), 45% potassium hydroxide (69.7 grams;
0.559 mole), and potassium carbonate (20 grams; 0.145 mole)
is employed initially, the dehydrated reaction mixture is
~0 heated under 60 psi of carbon dioxide fox 10 hours, and the
aqueous phase is washed twice with 100-ml portions of iso-
propylnaphthalene at 85-95C. There is obtained 25.5 grams
of 6-hydroxy-2-naphthoic acid (48.1~ of theoretical), and
4.6 grams of 3-hydroxy-2-naphthoic acid.
~5 Example 3
The procedure of Example 2 is followed in every
detail except that no potassium carbonate is used. There
is obtained 23.? grams (44.5~ of theoretical) of 6-hydroxy-
2-naphthoic acid, and 4.8 grams of 3-hydroxy-2-naphthoic
acid.
Example 4
The procedure of Example 1 is followed in every
detail except that the reaction mixture is heated at 265C
in a pressure reactor for 16 hours under a pressure of 60 psi.
There is obtained 36.6 grams t49.5~ of the~retical) of
6-hydroxy-2-naphthoic acid. The yield of 3-hydroxy-2-naph-
thoic acid is 7.5%. The ratio of 6-hydroxy-2-naphthoic acid
to 3-hydroxy-2-naph~hoic acid is 6.6 to 1.
Carrying Out the reaction described above, at
250C for 16 hours under a pressure of 60 psi, af~ords only
ll.S grams ~15.5~ of theoretical) of 6-hydroxy-2-naphthoic
acid. The yield of 3-hydroxy-2-naphthoic acid is 53.6~.
The above example illustrates the decreases in
the yield of 6-hydroxy-2-naphthoic acid of 6-hydroxy-2-
naphthoic acid to 3-hydroxy-2-naphthoic acid obtained when
the temperature is reduced helow 255C.
Examp_e 5
A mixture of 2-hydroxynaphthalene (116 gxams;
0.80 mole), and 45% potassium hydroxide (97.8 grams; 0.78
mole), is stirred and heated under nitrogen until distil-
lation stops and the temperature rises to 275~C. The mix-
ture is then cooled to 270C and held under a fast stream
of nitrogen for 30 minutes. The mixture is then further
cooled to 265C and purged with carbon dioxide while stirring
rapidly.
The reaction mixture is placed in a pressure
reactor, and the reactor is sealed and pressurized with
carbon dioxide ~o 60 psi. The reaction mixture is then
stirred at 600 rpm and 265C for 11 hours under a pres~ure
of 60 psi. The reactor is then vented to atmospheric
pressure, and cooled under a nitrogen atmosphere to 120C.
The reaction mixture is then processed as described in
Example 2. There is obtained 29.0 grams (39.3% of theo-
retical) of 6-hydroxy-2-naphthoic acid and 6.0 grams (8.2%
of theoretical) of 3-hydroxy-2-naphthoic acid.
The above example illustrates the process of
the present invention carried out without a flux.
Example 6
The procedure o~ Example 5 is followed in every
detail except that the reaction mixture is heated at 230C
t 5C for 18 . 5 hours . The yield of 6-hydroxy 2-naphthoic
acid obtained is only 19.5~ of theoretical, whereas the
~ 79~
yield of 3-hydroxy-2~naphthoic acid is 37.6~ of theoretical.
The above example represents the process of Andre
carxied out under conditions which should have maximized
the yield of 6-hydroxy-2-naphthoic acid. It is obvious
from these results that the process of Andre neither af~ords
a high yield of 6-hydroxy-2-naphthoic acid, nor a high ratio
of 6-hydroxy-2-naphthoic acid to 3-hydroxy-2-naphthoic acid.
A comparison of Example 5 with Example 6 again
illustrates the beneficial effect of tempexatures above
255C on the yield of 6 hydroxy-2-naphthoic acid.
.
