Note: Descriptions are shown in the official language in which they were submitted.
BAC~GROUND OF THE INVENTION:
The present invention relates to a process
~or producing 6-hydroxy-2-naphthoic acid which is used
as a monomer for producing aromatic polyesters having
an ability of forming liquid crystals.
Hitherto, as a process for producing 6-hydroxy-
2-naphthoic acid (hereinafter referred to as "BON-6"),
the following processes have been known.
~ 1) A process comprising reacting a potassium salt
of ~-naphthol with gaseous carbon dioxide at a high
temperature and under a high pressure (refer to U.S.
Patents Nos. 1,593,816, 4,287,357, 4,345,095, 4,329,494
and 4,345,094),
(2) A process comprising reacting a potassium salt
of ~-naphthol with gaseous carbon dioxide at a high
temperature and under a high pressure in a medium of
a high boiling point (refer to Japanese Patent Applica-
tions Laid-Open (KOKAI) No. 57-95939 and No. 58-99436),
and
(3) A process comprising reacting 6-bromo-2-
naphthol with carbon monoxide in methanol under a
high pressure (refer to Japanese Patent Application
Laid-Open (ROKAI) No. 57-91955).
However, these processes have the following
defects, and accordingly, are not necessarily favorable
as the industrial process for producing BON-6.
Namely, in the processes (1) and (2),
~-
~2~7~
3-hydroxy-2-naphthoic acid which is an isomer of
sON-6 is inevitably by-produced in addition to BON-6,
and accordingly, the yield of BON-6 is as low as about
26.5 % and 45 ~ in the processes (1) and (2), respec-
tively. In addition, in the processes (1) and (2),
since a large amount of ~-naphthol is by-produced,
complicated steps are necessary for separation thereof.
Moreover, since the process (3) is carried out
under a pressure as high as 70 kg/cm2 by using a
pressure-proof apparatus, the production cost is high,
and the yield of BON-6 is only about 37 ~.
On the other hand, as a process for converting
a compound represented by the formula (I):
IH3
Ar - C - X (I)
CH3
wherein Ar represents an aromatic ring and X represents
a hydroperoxy group or a hydroxyl group, into a
compound represented by the formula of Ar-OH, the
ollowing processes have been known.
(a) In the case where X is a hydroperoxy group, a
process for producing phenol by acid-decomposi-tion
of cumene hydroperoxide in the cumene process, and
(b) In the case where X is a hydroxy group, a
process for converting the compound into a phenol
compound by oxidizing the compound by hydrogen
i7~
peroxide in a solvent in the presence of a strong acid
(refer to Japanese Patent Application Laid-Open (KOKAI)
No. 52-5718, Japanese Patent Publication No. 35-7558,
British Patent No. 910,735, TSUNODA and KATO (Journal
of the chemical Soc. of Japan, 80(7), 689, 1959), and
M.S. Kharasch et al (J. Org. Chem., 15, 748 and 775,
1950)).
However, when a compound represented by the
formula (I) wherein X is a hydroxyl group is subjected
~o a similar reaction as in the process (a) the compound
is not converted into a phenol compound but changed
into a resin-like substance via a compound represented
by the following formula (II):
CH3
Ar - C = CH2 (II)
(refer to Japanese Patent Publication No. 51-29140).
Accordingly, the process (a) is not applicable
in the case where a compound represented by the
formula (I) wherein X is a hydroxyl group or a mixture
of a compound represented by the formula (I) wherein
X is a hydroxyl group and a compound represented by
the formula (I) wherein X is a hydroperoxy group is
subjected to oxidation to convert into Ar-OH.
On the other hand, the process (b) is, from
the reaction disclosed in the above-mentioned references,
a process for converting 2-hydroxy-2-propylbenzene,
~79~
p-di(2-hydroxy-2-propyl)benzene, p-2-hydroxy-2-propyl-
2,2'-dimethylbenzyl-hydroperoxide, etc. into a phenol
or hydroquinone, and there is no disclosure in the
above-mentioned references concerning the process for
converting a compound having the naphthalene ring,
particularly carbinols having the skeletone of naphthoic
acid which is the subject of the present invention, into
BON-6.
In this connection, even in the case of
attempting the reaction according to the present
invention in each of the solvents disclosed in the
above-mentioned references, such a solvent is unsuitable
by the reasons that the starting substance is insoluble
in the solvent, BON-6 is not formed, the solvent
participates in the reaction or the reaction ra-te is
lo~.
The present invention has been attained as a
result of examining the industrially profitable
processes in consideration of the above-mentioned
problems in the production of BON-6.
Namely, the present inventors have found a
process for profitably producing BON-6, which is
useful as a monomer for aromatic polyesters having an
ability of forming liquid crystals (liquid crystal
polymer), by oxidizing 2-(2-hydroxy-2-propyl)naphthalene-
6-carboxylic acid represented by the formula (III):
9L2~
= C - OH
HOOC CH3 (III)
which is derived from 2,6-diisopropylnaphthalene
easily available industrially, or a mixture of 2-(2-
hydroxy-2-propyl)naphthalene-6-carboxylic acid and
2-(2-hydroperoxy-2-propyl)naphthalene-6-carboxylic
acid represented by the formula (IV):
CH3
~ C - OOH
HOOC CH3 (IV)
under the specified conditions, and based on the
finding, the present inventors have attained the pre-
sent invention.
SU~ARY OF THE INVENTION
In an aspect of the present invention, there
is provided a process for producing 6-hydroxy-2-
n~phthoic acid comprising oxidizing 2-(2-hydroxy-2-
~ropyl)naphthalene-6-carboxylic acid or a mixture of
2-(2-hydroxy-2-propyl)naphthalene-6-carboxylic acld
and 2-(2-hydroperoxy-2-propyl)naphthalene-6-carboxylic
acid by hydrogen peroxide in acetonitrile and/or
dioxane in the presence of an inorganic acid.
DETAILED DESCRIPTION OF THE INVENTION
The characteristic of the present invention
lies in the production of 6-hydroxy-2-naphthoic acid
~'~167g~
(BON-6) by oxidizing 2-(2-hydroxy-2-propyl)naphthalene-
6-carboxylic acid or a mixture of 2-(2-hydroxy-2-
propyl)naphthalene-6-carboxyllc acid and 2-(2-hydro-
peroxy-2-propyl)naphthalene-6-carboxylic acid by
hydrogen peroxide in acetonitrile and/or dioxane in
the presence of an inorganic acid.
Particularly in the present invention, it is
important to use acetonitrile, dioxane or a mixture
thereof as a solvent for the reaction, and by the use
of the above-mentioned solvents, it has become possible
to produce BON-6 not only from 2 (2-hydroxy-2-propyl)-
naphthalene-6-carboxylic acid but also from a mixture
of 2-(2-hydroxy-2-propyl)naphthalene-6-carboxylic acid
and 2-(2-hydroperoxy-2-propyl)naphthalene-6-carboxylic
acid.
Namely, in the production of BON-6 from these
starting substances, the selectivity largely depends
on the solvents used in the reaction. When the reac-
tion is carried out in the solvent disclosed in the
aforementioned references, for instance in acetone,
it participates in the reaction and although BON-6 is
partially formed, a large amount of by-products
derived ~rom acetone is formed. When the reaction is
carried out in ethanol, the reaction rate and yield
of BON-6 are low. In acetic acid, although the
starting substance is consumed, BON-6 i5 scarcely
~L267~
formed and the side reaction occurs preferentially.
Further, since the starting substance does not dissolve
in hydrocarbons, hydrocarbons are unsuitable as the
solvent of the present invention.
Tl~e starting substance according to the
present invention, 2-(2-hydroxy-2-propy])naphthalene-
6-carboxylic acid or a mixture of 2-(2-hydroxy-2-
propyl)naphthalene-6-carboxylic acid and 2-(2-hydro-
peroxy-2-propyl)naphthalene-6-carboxylic acid, are
produced by a process for producing 6-substituted
naphthalene-2-carboxylic acids represented by the
formula (V):
X - C ~ COOH (V)
CH3
wherein X represents a hydroperoxy group or a hydroxy
~roup, comprising the step of reacting 6-isopropyl-
naphthalene-2-carboxylic acid with molecular oxygen at
a temperature in the range of from 50 to 90C in the
presence of a salt of persulfuric acid as a catalyst in
an aqueous alkaline solution.
~`
~26~
The weight ratio of 2-(2-hydroxy-2-propyl)-
naphthalene-6-carboxylic acid (hereinafter referred
to as "NCC") to 2-(2-hydroperoxy-2-propyl)naphthalene-
6-carboxylic acid (hereinafter referred to as "NMCA-
HPO") in the mixture is not particularly limited,
however, the mixture of the weight ratio of 40 - 60 :
5 - 10 (NMCA-HPO : NCC) is inexpensive and is easily
available.
The solvent comprising acetonitrile and/or
dioxane is used in an amount of from 3 to 30 ml per
1 g of the starting substance.
The commercialized aqueous 30 ~ solution
of hydrogen peroxide may be used as the hydrogen
peroxide in the present invention in an amount of
from one to ten times by mol of the amount of NCC in
the starting substance.
In the case where the amount of hydrogen
peroxide to the amount of NCC is less than the amolmt
set forth above, the rate of conversion of the
starting substance is low. On the other hand, in
the case of more than the amount set forth above, the
remarkably colored reaction product is produced,
and accordingly, the both cases are not favorable.
As the inorganic acid, sulfuric acid or
perchloric acid is preferably used, and sulfuric acid
may be a concentrated sulfuric acid or a sulfuric
~6~
acid containing up to 30 ~ of water. ~s perchloric
acid, commercialized 70, 60 or 40 ~ perchloric acid
may be preferably used.
The amount of the above-mentioned inorganic acid is
preferaDly from 0.1 to 4, more preferably 0.5 to 3 times by
~eight of the starting substance. In the case where the
amount of the inorganic acid used in the reaction is less
than the amount set forth above, the reaction is not
completed, and on the other hand, in the case of more
than the amount set forth above, the selectivity is
lowered, thereby resulting the coloration of the
reaction product.
The inorganic acid is added to the starting
substance by means of dropping, etc., simultaneously
with hydrogen peroxide or after the addition of hydrogen
peroxide. Namely, it is necessary that the inorganic
acid is added so as to coexist wi~h hydrogen peroxide.
In addition, the reaction temperature according
to the present invention may be selected from the range
of from room temperature to 80C, preferably from the
range o~ from 30 to 60C.
The reaction time depends on the composition
of the reaction mixture and the reaction temperature,
however, the reaction completes within from 10 min to
3 hours ordinarily.
-- 10 --
~2~i7~
After finishing the reaction, the reaction
mi~ture is adjusted to pH 2.5 - 3.5 by the addition
of caustic alkali, sodium carbonate, sodium hydro-
gencarbonate, etc., and after separating the precipi-
tated salt by filtration, the solvent is distilled
off from the filtrate to obtain the raw BON-6. By
recrystallizing the thus obtained raw BON-6 from a
suitable solvent, for instance, acetonitrile and
acetic acid, the purified BON-6 can be obtained.
According to the present invention, 6-hydroxy-
2-naphthoic acid (BON-5) which is useful as a monomer
or liquid crystalline polymer can be profitably
produced in a high yield as will be shown in the
following Examples by using NCC or a mixture of NCC
and NMCA-HPO derived from 2,6-diisopropylnaphthalene
which is easily available industrially via 2-isopropyl-
6-naphthoic acid.
The present invention will be explained more
in detail while referring to the following non-
limitative Examples.
E~AMPLE 1:
After dissolving 0.5 g of NCC in 10 ml of
acetonitrile, 1 g of an aqueous 30 % solution of hydrogen
peroxide and 1 g of an aqueous 70 ~ solution of perchlo-
ric acid were successively added to the solution, and
the thus prepared mixture was stirred at 50C for 30 min.
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~26~
After the reaction was over, the reaction
mixture was examined by a high-speed liquid chromato-
graphy (HPLC), thereby confirming that BON 6 was
produced in an almost quantitative yield. After adjusting
the reaction mixture to p~ 3 by an aqueous 20 % solution
of sodium carbonate and removing the precipitated salts
by filtration, acetonitrile was distilled of
therefxom under a reduced pressure and the precipita~ed
BON-6 was collected by filtration, washed with water
and dried to obtain 0.4 g of crude BON-6.
The yield was nearly quantitative.
E~AMPLE 2:
In 6 litre of acetonitrile, 300 g of a mixture
comprising 20 % by weight of NCC and 80 % by weight
of NMCA-HPO was dissolved and a mixture of 120 g of
an aqueous 30 % solution of hydrogen peroxide and
8~0 g of an aqueous 70 % solution of sulfuric acid
was added to the thus prepared solution and the mixture
was stirred at 50C for one hour.
After the reaction was over, the reaction
mixture was examined by HPLC, thereby confirming that
BON-6 was produced in an almost quantitative yield.
~ter adjusting the reaction mixture to pH 3 by
addition of an aqueous 20 % solution of sodium carbonate
and removing the precipitated salts by filtration,
acetonitrile was distilled off therefrom
under a reduced pressure and the precipitated BON-6
was collected by filtration, washed with water and
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î~67~
dried to obtain 225 g of crude BON-6.
By recrystallizing the thus obtained crude
BON-6 from acetonitrile, the purified BON-6 of a
purity of higher than 99 % was obtained.
EX~PLE 3:
Into 20 g of dioxane, 5 g of the same mixture
of NCC and NMCA-HPO as in Example 2 was dissolved, and
after adding successively 1 g of an aqueous 30 %
solution of hydrogen peroxide and 2.5 g of an aqueous
90 % solution of sulfuric acid to the thus prepared
solution, the mixture was stirred at 50C for one hour.
After the reaction was over, the reaction mixture was
examined by HPLC, thereby confirming that BON-6 was
produced in an almost quantitative yield. After
adjusting the reaction mixture to pH 3 with an aqueous
20 ~ solution of sodium carbonate and removing the
precipitated salts by filtration, dioxane was distilled
off therefrom under a reduced pressure. The precipitated
BON-6 was collected by filtration, washed with water
and dried to obtain 3.75 g of crude BON-6 .
E~AMPLE 4:
In the same procedures as in Example 3 except
for using a 1 : 1 by volume mixture of acetonitrile
and dioxane as the solvent instead of dioxane in
Example 3, 3.8 g of crude BON-6 was obtained.
~7~
E~PLE 5:
After dissolving 0.1 g of the same mixture
of NCC and NMCA-HPO as in Example 2 into 2 g of
acetonitrile, 0.1 g of an aqueous 30 % solution of
hydrogen peroxide and 0.2 g of an aqueous 40 ~ solu-
tion of perchloric acid were successively added to the
thus prepared solution, and the thus obtained mixture
was stirred at 50C for 2 hours.
By examining the reaction liquid by HPLC, it
was confirmed that BON-6 was obtained in a yield of
g6 ~.
COlMPARATIVE EXAMPLE 1:
After dissolving 1 g of NCC in 20 ml of
acetic acid, 1 g of an aqueous 30 % solution of
hydrogen peroxide and 2 g of an aqueous 70 % solution
of perchloric acid were successively added to the
solution, and the thus prepared mixture was stirred
at 50C for 30 min. After the reaction was over,
the reaction mixture was examined by HPLC to confirm
that only a small amount of BON-6 was formed while
almost all of the starting substance was consumed.
COl~IPARATIVE EXAMPLE 2:
-
In the same procedures as in ComparativeExample 1 except for using ethanol as a solvent
instead of acetic acid in Comparative Example 1, the
reaction was carried out. After the reaction was over,
79~
the reaction mixture was examinéd by HPLC to confirm
that the yield of the thus obtained BON-6 was 10 %.
COMPARATIVE EXAMPLE 3:
In the same procedures as in Comparative
Example 1 except for using toluene as a solvent instead
o~ acetic acid in Comparative Example 1, the reaction
was carried out. Both the starting substance and the
reaction product scarcèly dissolved in toluene and
accordingly, the yield of BON-6 was as low as 16 %.
COMPARATIVE EXMAPLE 4:
After dissolving 1 g of a mixture of 20 % by
weight of NCC and 80 % by weight of NMCA-HPO into 20 g
of ethanol, 2 g of an aqueous 30 % of hydrogen peroxide
and 2 g of an aqueous 70 % solution of perchloric acid
were successively added to the thus prepared solution,
and the mixture was stirred at 50C for 30 min. The
yield of BON-6 was 10 % and the most part of the
starting substance remained unreacted.
COMPARATIVE EXAMPLE 5:
In the same procedures as in Comparative
Example 1 except for using 2 g of an aqueous 70 %
solution of sulfuric acid instead of 2 g of the
aqueous 70 % solution of perchloric acid, the reaction
was carried out. Although the starting substance was
consumed with the progress of the reaction, BON-6 was
scarcely formed.
- 15 -
~79~
REFERENCE EXA~PLE:
To 20 ml of acetone, 1 g of an aqueous 30 %
solution of hydrogen peroxide and 2 g of an aqueous
70 % solution of perchloric acid were successively
added, and the mixture was stirred for 30 min at
50C to obtain a white precipitate. The thus obtained
precipitate had a stimulative odor and was seemed to
be a condensate of acetone. It was thus found that
acetone was unsuitable as the reaction solvent of the
present invention.
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