Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
4~55
TITLE OF THE INVENTION
Process for producing dihydroxynaphthalenes
BACKGROUND OE THE INVENTION
The present invention relates to a~process for
producing hydroxynaphthalenes useful as starting materials
for the production of synthetic resins, synthetic fibers,
pharmaceuticals, agrichemicals, dyes, etc. More
particularly, the present invention relates to a process
for producing hydroxynaphtalenes of high purity.
2,6-Dihydroxynaphthalene is a compound useful as a
starting material for the production of synthectic resins,
synthetic fibers, pharmaceuticals, agrichemicals, dyes,
etc.
A classical method for the production of 2,6-
dihydroxynaphthalene consists of subjecting 2-naphthol-6-
sulfonic acid to alkali fusion with potassium hydroxide.
This method, however, has the problems of low yield and
difficult separation from the tar content. Furthermore,
the end compound 2,6~dihydroxynaphthalene is prone to
crystallization and the inorganic salt used in a large
amount as a reactant tends to be incorporated in the
crystal of 2,6-dihydroxynaphthalene, making it difficult
to be obtained with high purity.
It is also known that 2,6-dihydroxynaphthalene can be
produced by first oxidizing 2,6-diisopropylnaphthalene
with molecular oxygen in the presence of a base to form
diisopropylnaphthalene dihydroperoxide, then acid-
decomposing this peroxide with an acid catalyst such as
sulfuric acid. A problem with this method is that when
2,6-diisopropylnaphthalene is oxidized with molecular
oxygen in the presence of a base, not only is the end
compound 2,6-diisopropylnaphthalene dihydroperoxide
130~7S5
(hereinafter sometimes abbreviated as DHP) obtained but
also various by-products are formed in large quantities.
Among these by-products are carbinols such as 2-(2-
hydroxy-2-propyl)-6-(2-hydroperoxy-2-propyl)naphthalene
(hereinafter sometimes abbreviated as HHP), 2,6-bis(2-
hydroxy-2-propyl)naphthalene (hereinafter sometimes
abbreviated as DCA) and 2-isopropyl-6-(2-hydroxy-Z-
propyl)naphthalene (hereinafter sometimes abbreviated as
MCA), and monohydroperoxides such as 2-isopropyl-6-(2-
hydroperoxy-2-propyl)naphthalene (hereinafter sometimes
abbreviated as MHP). Furtheremore, when the reaction
product obtained by oxidation of diisopropylnaphthalene
and which contains not only DHP but also various by-
products is subjected to acid decomposition in the
presence of an acid catalyst such as sulfuric acid, the
end compound dihydroxynaphthalene is obtained together
with various products of acid decomposition reaction such
as isopropylnaphthol.
As described above, if 2,6-diisopropylnaphthalene is
oxidized to DHP by reaction with molecular oxygen in the
presence of a base and if the resulting DHP is subjected
to acid decomposition with an acidic catalyst such as
sulfuric acid, the reaction mixture obtained will contain
not only the desired dihydroxynaphthalene but also large
amounts of various by-products of the reaction.
It is known that 2,6-dihydroxynaphthalene can be
purified by recrystallization using solvents such as
alcohol, ether, acetone, acetic acid, benzene and water.
However, none of these solvents are completely
satisfactory for recrystallization purposes because their
ability to dissolve 2,6-dihydroxynaphthalene is either too
high or too low to attain good resùlts.
Under these circumstances, other purification methods
have been reviewed. In one method, cumeme or some other
~304'755
suitable material is added to the reaction product of acid
decomposition or, in some instances, the concentrate
obtained by removing the solvent and other materials that
have been employed in the reaction of acid decomposition,
and the resulting precipitate of crude 2,6-
dihydroxynaphthalene is sublimated to obtain pure 2,6-
dihydroxynaphthalene. Another method comprises using an
aqueous alcohol or hydrous ketone as a solvent for
recrystallization. Use of activated carbon for
decolorizing purposes has also been reviewed. However,
these methods have suffered the problem that satisfactory
values of purity cannot be attained if an attempt is made
to increase the recovery rate and that the decoloring
effect is not high enough for practical purposes.
SUMMARY OF THE INVENTION
The present inventors conducted intensive studies
with a view to solving the aforementioned problems of the
prior art. As a result, the present inventors found that a
hydroxynaphthalene, in particular dihydroxynaphthalene,
could be obtained with high purity by hydrolyzing
diacyloxynaphthalene in the presence of an acid catalyst.
The present invention has been accomplished on the basis
of this finding the diacyloxynaphthalene may be obtained
by first decomposing diisopropylnaphthalene
dihydroperoxide with an acid, then reacting the resulting
dihydroxynaphthalene-containing reaction mixture of acid
decomposition with an acyloxylating agent in the presence
of a catalyst.
The principal object of the present invention which
aims at solving the aforementioned problems is to provide
a process for producing a hydroxynaphthalene by which a
hydroxynaphthalene, in particular dihydroxynaphthalene,
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--4--
can be produced from diacyloxynaphthalene both in high
yield and with high purity.
The process of the present invention for producing
dihydroxynaphthalene is characterized by hydrolyzing
diacyloxynaphthalene in a water-containing solvent in the
presence of an acid catalyst to form dihydroxynaphthalene.
Where desired, this dihydroxynaphthalene can be separated from
the reaction mixture.
In accordance with the process of the present
invention for producing dihydroxynaphthalene, a
hydroxynaphthalene is obtained by hydrolyzing
diacyloxynaphthalene in a water-containing solvent in the
presence of an acid catalyst, so a hydroxynaphthalene, in
particular dihydroxynaphthalene, of high purity can be
produced in high yield.
DETAILED DESCRIPTION OF THE INVENTION
The process of the present invention for producing
dihydroxynaphthalene is described hereinafter in a
specific way as an example.
In the present invention, dihydroxynaphthalene is
produced by hydrolyzing diacyloxynaphthalene in a water-
containing solvent in the presence of an acid catalyst.
Each of the acyloxy groups in the
diacyloxynaphthalene as the starting material in the
present invention is represented by the following general
formula:
U
R - C - O -
(where R is a lower alkyl group or an aryl group).
Specific examples of the acyloxy group include formyloxy,
acetoxy, propionyloxy, butyryloxy, valeryloxy, benzoyloxy
and t~ uyloxy, with acetoxy being preferred.
~ ,r
Jl" `
'';; .
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The hydroxynaphthalene to be produced by the present
invention is preferably dihydroxynaphthalene, with 2,6-di
hydroxynaphthalene being particularly preferred.
Also included within the scope of the
hydroxynaphthalene to be produced in the present invention
are 2,4-dihydroxynaphthalene and 2,7-dihydroxynaphthalene.
The term"acyloxynaphthalene" or "hydroxynaphthalene" as
used herein includes acyloxyhydroxynaphthalene in which
one of the two acyloxy groups in the diacyloxynaphthalene
is hydrolyzed, with the other remaining as it is.
Examples of the acid catalysts that can be used to
hydrolyze diacyloxynaphthalene include:
inorganic acids such as sulfuric acid, hydrochloric
acid, perchloric acid and hydrofluoric acid; strong acid
cation-exchnage resins; solid acids such as silica and
silica alumina; organic acids such as chloroacetic acid,
methanesulfonic acid, benzenesulfonic acid and
toluenesulfonic acid; and Lewis acids such as boron fluo-
ride and zinc chloride.
These acid catalysts are used in amounts of 0.05 - 10
wt%, preferably 0.2 - 1.0 wt%, of the reaction solvent.
The above-described reaction for hydrolysis of
diacyloxynaphthalene is performed using a solvent, and it
is particularly preferable to use a solvent that is highly
miscible with water, desirably forming a homogeneous
system, under the reaction conditions employed. Suitable
solvents are alcohols such as methanol, ethanol,
isopropanol and ethylene glycol, carboxylic acids such as
formic acid, acetic acid and propionic acid, ketones such
as acetone and methyl ethyl ketone, etheres such as
dioxanecarbitol, and nitriles such as acetonitrile.
The amount of water that is necessary to hydrolyze
the diacyloxynaphthalene may be defined as follows. If an
alcohol is used as the solvent, not only the reaction of
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hydrolysis but also the reaction of ester exchange occurs
so the amount of water relative to diacyloxynaphthalene is
preferably no greater than 2.0 in molar ratio. However, if
solvents other than alcohols are used, water is used in a
molar ratio to diacyloxynaphthalene of at least 2.0,
preferably at least 5.0, moré preferably at least 10Ø
In carrying out the above-described reaction for
hydrolysis of diacyloxynaphthalene, the solvent is used in
an amount of 3 - S parts by weight, preferably 5 - 10
parts by weight, per part by weight of
diacyloxynaphthalene. The solvent is used in such an
amount that not only the diacyloxynaphthalene but also the-
hydroxynaphthalene produced dissolves completely in the
solvent. However, so long as the diacyloxynaphthalene and
hydroxynaphthalene are dissolved in the solvent used, the
amount of the solvent used is preferably decreased so that
the concentration of the resulting hydroxynaphthalene in
the solvent will be increased.
If the reaction is performed at atmospheric pressure,
the reaction temperature is limited by the boiling point
of the solvent used but is normally in the range of 40 -
200C, preferably 60 - 100C.
The reaction time normally ranges from 30 minutes to
10 hours and the reaction is substantially completed in
about 5 hours. If dihydroxynaphthalene is to be obtained
as the reaction product, the end point of the reaction can
be approximated by the time when monoacyloxynaphthalene in
which one of the two acyloxy groups in the
diacyloxynaphthalene remains is no longer detectable. If
the reaction time is unduly long, a dimer of
dihydroxynaphthalene will be formed although its amount is
small. Besides, other by-products will also be generated.`
In the reaction of hvdrolysis of esters, the catalyst
may generally be either an acid or a base. However, if an
i~O4755
acid is used, it serves not only as a catalyst for the
reaction of hydrolysis but also as a catalyst for the
reaction of esterification. Therefore, a base is normally
used as a catalyst. In fact, J. Chem. Soc., 35, 1943
describes that purified 2,6-dihydroxynaphthalene is
obtained by a process comprising ob~aining 2,6-
dihydroxynaphthalene by alkali fusion of sodium 2-hydroxy-
6-sulfonate, converting the dihydroxynaphthalene to 2,6-
diacetoxynaphthalene, hydrolyzing it with an aqueous
alkali in a nitrogen atmosphere and recrystallizing the
hydrolyzate with an excess amount of water.
However, if a solution of a hydroxynaphthalene, in
particular 2,6-dihydroxynaphthalene, in aqueous sodium
hydroxide is left in the air, it gradually assumes a color
with time until it becomes black. As is evidenced by this
fact, 2,6~dihydroxynaphthalene is very unstable in alkali
solutions. The present inventors conducted an
investigation to resolve the reason for the coloring of
the alkali solution of 2,6-hydroxynaphthalene, and found
that the product contained 2,2',6,6'-tetrahydroxy-1,1'-
binaphthyl white is a dimer of 2,6-dihydroxynaphthalene.
Since this dimer is a which crystal, the coloring matter
is assumed to be a higher condensate of this dimer. The
formation of the dimer as a by-product is observed even in
a nitrogen atmosphere under alkaline conditions. Since
this dimer is a solid having a decomposition temperature
of 318 - 320C, it is not easily separable from 2,6-
dihydroxynaphthalene (m.p. 220.9 - 222C). Therefore, in
order to obtain purified 2,6-dihydroxynaphthalene, the
starting material preferably contains the least amount of
this dimer. In other words, if a hydroxynaphthalene,
especially 2,6-dihydroxynaphthalene, is to be obtained by
hydrolysis of diacetoxynaphthalene, the condition for
- ~304'755
hydrolysis must be such that the formation of the by-
product dimer is negligible.
However, according to the finding of the present
inventors, the formation of the dimer as a by-product is
unavoidable if diacetoxynaphthalene is hydrolyzed in the
presence of an alkali catalyst.
In the present invention, a dihydroxynaphthalene is
produced from diacyloxynaphthalene using an acid as a
catalyst for the hydrolysis of diacyloxynaphthalene, so
the resulting dihydroxynaphthalene can be purified by
merely washing it with a solvent.
In the present invention, a dihydroxynaphthalene is
produced by the reaction of hydrolysis of
diacyloxynaphthalene. The diacyloxynaphthalene used as the
starting material may be prepared by any method.
Preferably, it is prepared by the following method:
diisopropylnaphthalene is oxidized with molecular oxygen
in the presence of a base; the resulting product of
oxidation reaction containing diisopropylnaphthalene
dihydroperoxide is decomposed with an acid to obtain the
reaction product of acid decomposition containing
dihydroxynaphthalene; an acyloxylating agent is added to
this reaction product to effect reaction between the
acyloxylating agent and the dihydroxynaphthalene; and the
resulting diacyloxynaphthalene is separated from the
reaction mixture.
This preferred method of preparing the
diacyloxynaphthalene is described below in a more specific
way.
First, diisopropylnaphthalene is oxidized with
molecular oxygen in the presence of a base to form
diisopropylnaphthalene dihydroperoxide, and the product of
oxidation reaction which contains the so formed
diisopropylnaphthalene dihydroperoxide is subjected to
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acid decomposition with an acid catalyst such as sulfuric
acid, thereby preparing the dihydroxynaphthalene-
containing product of acid decomposition.
Specific examples of the diisopropylnaphthalene
include 2,6-diisopropylnaphthalene, 2,7-
diisopropylnaphthalene and 1,4-diisopropylnaphthalene,
among which 2,6-diisopropylnaphthalene is preferred.
As described above, diisopropylnaphthalene is
oxidized and subsequently decomposed with an acid to
produce the dihydroxynaphthalene-containing reaction
product of acid decomposition. The solvent, acid catalyst
and other reaction conditions employed for this purpose
can be varied over a broad range.
OXIDATION REACTION
A preferred embodiment of the production of the
dihydroxynaphthalene-containing reaction product of acid
decomposition from diisopropylnaphthalene is described
below in detail.
The oxidation reaction of diisopropylnaphthalene is
performed by adding diisopropylnaphthalene to an aqueous
solution of a base, mixing them mechanically to form an
emulsion, and bubbling with a gas containing molecular
oxygen.
An alkali metal compound is preferably used as the
base. Specific examples of the alkali metal compound
include sodium hydroxide, potassium hydroxide, sodium
carbonate and potassium carbonate. The concentration of
the alkali metal compound in aqueous solution is
preferably not more than 20wt%. It is normally preferable
for the aqueous base solution to be used in the reaction
mixture in such an amount that it accounts for 5 - 80 wt%
of the reaction mixture, with the range of 20 - 70 wt%
being particularly preferred. If the aqueous base solution
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is used in the amount of less than 5 wt~ of the reaction
mixture, neither the oily unreacted diisopropylnaphthalene
nor its oxidation product will be dispersed satisfactorily
in the reaction liquor made of the aqueous base solution
and only an incomplete emulsion will form to cause adverse
effects on the oxidation reaction. If the aqueous base
solution is used in an amount exceeding 80 wt% of the
reaction mixture, the reaction system also fails to
provide a satisfactory emulsion. In the oxidation
reaction, the pH of the aqueous base solution is normally
held in the range of 7 - 14, preferably 11 - 14.
Diisopropylnaphthalene and its oxidation product can
be normally emulsified in the aqueous base solution to a
satisfactory degree by mechancial agitation but, if
desired, agitation may be effected in the presence of a
known emulsifier such as stearic acid.
Other useful examples of the base are alkaline earth
metal hydroxides such as calcium hydroxide, magnesium
hydroxide and strontium hydroxide. Calcium hydrixide is
particularly preferred. These alkaline earth metal
hydroxides may be used either independently or in
combination with the aforementioned alkali metal
compounds.
Oxygen gas may be used independently as the molecular
oxygen but normally the air suffices for producing good
results. The required amount of molecular oxygen is not
limited to any particular value but it normally is in the
range of 5 - 15 Nl/h in terms of oxygen gas per 100 g of
the diisopropylnaphthalene charged for oxidation reaction.
The reaction temperature normally ranges from 80 to
150C, preferably from 90 to 130C. The reaction time
which varies with the reaction temperature and other
reaction conditions is normally in the range of 6 - 40
hours. The degree of conversion of diisopropylnaphthalene
1304"~55
is preferably at least 80% in order to increase the yield
of dihydroperoxide. The reaction is normally carried out
at atmospheric pressure but may be performed under
superatmosphric or subatmospheric pressure as required.
In the above-described oxidation reaction of
diisopropylpaphthalene a reaction initiator is preferably
employed in addition to a catalyst; For example, besides
the reaction mixture of autoxidation of 2,6-
diisopropylnaphthalene, ~,'-azobis(cyclohexane-1-
carbonitrile) may be used as a reaction initiator. The
induction period of the reaction can be shortened by using
a reaction initiator. The reaction initiator is normally
used in an amount ranging from 0.005 to 1 part by weight
per 100 parts by weight of the charged reaction mixture
containing the starting diisopropylnaphthalene.
A catalyst may be employed in the oxidation reaction
and preferred examples of the catalyst are copper, cobalt
salt and palladium. These catalysts are normally used in
amount ranging from 0.5 ppm to 1,000 ppm.
By performing the oxidation reaction of
diisopropylnaphthalene in the manner described above, not
only diisopropylnaphthalene dihydroperoxide (DHP) but also
various by-products are formed. The by-products include
carbinols such 2-(2-hydroxy-2-propyl)-6-(2-hydroperoxy-2-
propyl)naphthalene (HHP), 2,6-bis(2-hydroxy-2-propyl)-
naphthalene (DCA) and 2-isopropyl-6-(2-hydroxy-2-
propyl)naphthalene (MCA), and monohydroperoxides such as
2-isopropyl-6-(2-hydroperoxy-2-propyl)naphthalene (MHP).
The composition of the reaction product resulting
from the above-described oxidation reaction can be
determined by the following procedures: after the
reaction, the organic phase is separated from the aqueous
phase; the aqueous phase is extracted with ether; and the
organic phase and the ether extract are analyzed by liquid
1304'75S
chromatography to determine the quantities of the
unreacted diisopropylnaphthalene and the products of
oxidation reaction such as DHP, HHP, DCA, MHP and MCA.
The oxidation reaction of diisopropylnaphthalene is
preferably performed to attain a conversion of at least
80% and the resulting reaction mixture containing the
unreacted diisopropylnaphthalene, diisopropylnaphthalene
dihydroperoxide and various by-products is subjected to
the subsequent step of acid decomposition. Normally, a
suitable organic solvent such as methyl isobutyl ketone
(MIBK) is added in an appropriate amount to the above-
described oxidation reaction mixture and the organic phase
containing this reaction mixture is separated from the
aqueous phase and subjected to subsequent acid
decomposition. In the following description, this organic
phase is sometimes referred to as the starting material
for acid decomposition.
REACTION OF ACID DECOMPOSITION
Using the thus obtained starting material for acid
decomposition, the diisopropylnaphthalene dihydroperoxide
present in it is acid-decomposed in the presence of an
acidic catalyst so as to produce the dihydroxynaphthalene-
containing reaction product of acid decomposition. The
starting material for acid decomposition contains the
aforementioned carbinols that were formed as by-products
in the previous step of oxidation reaction, so if
necessary, hydrogen peroxide may also be employed in the
reaction of acid decomposition in order to ensure that HHP
and DCA among the by-products carbinols are oxidized to
dihydroperoxides, which are acid-decomposed with an acidic
catalyst together with the diisopropylnaphthalene
dihydroperoxide. This method is preferable for the purpose
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of obtaining the desired dihydroxynaphthalene in high
yield.
If the degree of conversion of diisopropylnaphthalene
is increased to 80~ and above, not only the yield of DHP
but also those of HHP and DCA are increased. If hydrogen
peroxide is employed in the reaction of acid
decomposition, HHP and DCA are converted into DHP, thereby
enabling the desired dihydroxynaphthalene to be obtained
in high yield. Further the use of hydrogen peroxide is
also preferable for the reason that the yield of MHP which
does not contribute to the formation of
dihydroxynaphthalene can be reduced. The yield of
dihydroxynaphthalene can be further increased by ensuring
that the degree of conversion of diisopropylnaphthalene is
at least gO%, more preferably at least 95%.
The hydrogen peroxide used for this purpose may be
anhydrous hydrogen peroxide or a solution thereof in
water. Materials that generate hydrogen peroxide under the
reaction conditions employed, such as sodium peroxide and
calcium peroxide, may also be employed but it is
preferable to use an aqueous solution of hydrogen
peroxide. In particular, the desired dihydroxynaphthalene
can be obtained in high yield by performing the reaction
of acid decomposition using 0.9 - 2 moles, preferably 1.0
- 1.5 moles, of hydrogen peroxide per mole of the
alcoholic hydroxyl group in the carbinols described above.
Using hydrogen peroxide under this condition is preferable
since it also inhibits markedly the formation of by-
products due to the condensation of carbinols.
Preferred examples of the acid catalyst that can be
used in the reaction of acid decomposition include:
inorganic acids such as sulfuric acid, hydrochloric acid,
hydrogen fluoride and phosphoric acid; solid acids such as
strong acid cation-exchange resins, silica gel and silica
13047SS
-14-
alumina; organic acids such as chloroacetic acid,
methanesulfonic acid, benzenesulfonic acid and
toluenesulfonic acid; and heteropolyacids such as
phosphotungstic acid and phosphomolybdic acid. These acid
catalysts may be added per se to the reaction system;
alternatively, if these acid catalysts are soluble in a
certain solvent, they may be added to the reaction system
as solutions in appropriate inert solvents. The amount of
the acid catalysts used varies with their type and the
reaction conditions employed, and it normally is within
the range of 0.01 - 10 wt% of the total reaction mixture.
As already mentioned, it is advantageous for
practical purposes that after the reaction for the
oxidation of diisopropylnaphthalene, the obtained
diisopropylnaphthalene dihydroperoxide and by-products are
transferred from the reaction mixture into an organic
solvent such as methyl isobutyl ketone, with the reaction
of acid decomposition being subsequently performed using
this organic solvent as the reaction solvent. However, the
reaction solvent is by no means limited to methyl isobutyl
ketone and other inert organic solvents may be used as
required, such as ketones (e.g.,acetone and methyl ethyl
ketone), alcohols (e.g., methanol and ethanol), lower
aliphatic carboxylic acids (e.g. acetic acid and propionic
acid), hydrocarbons (e.g., benzene, toluene, xylene,
hexane and heptane), nitriles (e.g., acetonitrile),
phenols (e.g., phenol and cresol) and nitro compounds
(e.g., nitromethane and nitrobenzene). Mixtures of these
solvents may also be used. Using carboxylic acids as
reaction solvents is advantageous for the purpose of
acyloxylating the dihydroperoxide with an acylocxylating
agent (see below) either simultaneously with or subsequent
to the step of acid decomposition.
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-15-
The reaction of acid decomposition is carried out at
a temperature in the range of 0 - 100C, preferably 20 -
80C.
The reaction product of acid decomposition thus
obtained in the present invention contains not only the
desired dihydroxynaphthalene but also by-product
impurities including isopropylnaphthol, acetylnaphthol,
dihydroxynaphthalene dimer and tar, as well the by-product
acetone and the reaction solvents such as methyl isobutyl
ketone and cumene that have been used in the step of acid
decomposition. The mixture which is to be subjected to
acyloxylation reaction as described below normally
contains dihydroxynaphthalene in a proportion ranging from
5 to 30 wt%. The proportion of the reaction product of
acid decomposition (i.e., the mixture minus the by-product
acetone and the reaction solvent) that is occupied by
dihydroxynaphthalene is normally in the range of 40 - 80
wt% and in the present invention the above-characterized
reaction mixture of acid decomposition is preferably
subjected to acyloxylation reaction with an acyloxylating
agent as described below.
DIACYLOXYNAPHTHALENE
An acyloxylating agent is added to the thus obtained
dihydroxynaphthalene-containing reaction mixture of acid
decomposition, and the dihydroxynaphthalene is reacted
with the acyloxylating agent in the presence of a catalyst
to produce the desired diacyloxynaphthalene. In performing
the acyloxylation reaction, low-boiling point substances
such as the by-product acetone and the reaction solvent
employed may optionally be removed in appropriate amounts
from the reaction mixture of acid decomposition by a
suitable method such as distillation.
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The acyloxylating agent is preferably added in an
amount of 1 - 20 moles, preferably 2 - 5 moles, per mole
of the dihydroxynaphthalene in the reaction product of
acid decomposition.
The acyloxylating agent used in the present invention
may be exemplified by lower aliphatic carboxylic acids
such as formic acid, acetic acid, propionic acid, butyric
acid and valeric acid, aromatic carboxylic acids such as
benzoic acid and toluic acid, all being in the anhydrous
form and acid chlorides such as acetyl chloride.
The catalyst for use in the reaction between the
dihydroxynaphthalene and the acyloxylating agent may be
selected from a broad range of acid catalysts that are the
same as those used in the decomposition of the
diisopropylnaphthalene dihydroperoxide. Particularly
preferred examples are inorganic acids such as sulfuric
acid, hydrochloric acid, phosphoric acid and boron
fluoride. Ion-exchange resins as solid acids may also be
used. Bases may also be used as non-acid catalysts and
besides organic bases such as pyridine and quinoline,
sodium acetate and other salts may preferably be used. The
amount of catalysts used varies with their type and the
reaction conditions employed and it normally is preferable
to use them in amounts ranging from 0.01 to 10 wt% of the
total reaction mixture.
The reaction between the dihydroxynaphthalene and the
acyloxylating agent such as a carboxylic acid anhydride is
performed at a temperature in the range of 0 - 200C,
preferably 80 - 140C. The reaction time ranges from about
30 minutes to about 5 hours, preferably from about 1 to
about 2 hours.
As described above, an acyloxylating agent such as a
carboxylic acid anhydride is added to the
dihydroxynaphthalene-containing reaction product of acid
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decomposition and the dihydroxynaphthalene is reacted with
the acyloxylating agent such as a carboxylic acid
anhydride. Thereafter, the resulting reaction mixture is
left to stand or otherwise cooled to obtain
diacyloxynaphthalene as a precipitate from the reaction
mixture.
The acyloxylation reaction may be performed on the
acid decomposition product in the presence of a solvent
such as an aromatic hydrocarbon (e.g. cumene), a dialkyl
ketone (e.g., methyl isobutyl ketone) or a carboxylic
acid. It is particularly preferable to perform the
acyloxylation using methyl isobutyl ketone as the solvent
because when the desired diacyloxynaphthalene is separated
from the reaction mixture, the impurities remain in the
latter as a result of extraction with the solvent, thereby
allowing the diacyloxynaphthalene to be obtained with a
higher purity.
The thus obtained diacyloxynaphthalene has a very
high purity (2 99~) and its yield is also very good, as
high as 99% on a dihydroxynaphthalene basis. In addition,
the recovery of diacyloxynaphthalene crystal is from is as
high as 95 mol%.
EXAMPLES
The following examples are provided for the purpose
of further illustrating the present invention but are in
no way to be taken as limiting.
Example 1
A 100-ml round-bottom flask equipped with a condenser
pipe was charged with 2.0 g of 2,6-diacetoxynaphthalene,
20 g of methanol (solvent), 1.5 g of water and 0.12 g of
conc. sulfuric acid (acid catalyst), and reaction was
performed at 65~C for 5 hours in a nitrogen atmosphere
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-18-
under stirring with a magnetic stirrer. Analysis of the
reaction liquor by gas chromatography showed that 2,6-
dihydroxynaphthalene had been produced in an amount o~ 5.5
wt% (yield, 99%) and 2,6-dihydroxynaphthalene dimer in an
amount of 0.01 wt%.
.
Examples 2 - 5
The procedures of Example 1 were repeated except for
the solvent and reaction temperature. The results are
shown in Table 1.
Comparative Example 1
The procedures of Example 1 were repeated except for
the solvent and reaction temperature. The results are
shown in Table 1.
TABLE 1
Run Solvent Reaction Yield of 2,6-di-
temperature hydroxynaphthalene
( C) (wt%)
Example 2 acetic acid 80 98
Example 3 methyl acetate 60 97
Example 4 dioxane 80 97
Example 5 acetonitrile 78 95
Comparative methyl isobutyl 76 87
Example 1 ketone
Example 6
An apparatus of the same type as that used in Example
1 was charged with 2.0 g of 2,6-diacetoxynaphthalene, 20 g
of methanol, 0.3 g of water and 0.12 g of conc. sulfuric
acid, and reaction was performed at 65C for 5 hours with
1304755
, g
stirring in a nitrogen atmosphere. The yield of 2,6-
dihydroxynaphthalene was 97%.
Examples 7 and 8
The procedures of Example 6 were repeated except that
conc. sulfuric acid was replaced by the catalysts shown in
Table 2.
TABLE 2
Run Catalyst Yield of 2,6-dihydroxy-
naphthalene
(wt%)
_ _
Example 6 sulfuric acid 97
Example 7 hydrochloric acid 95
Example 8 zinc chloride 94
Comparative Example 2
The procedures of Example 6 were repeated except that
conc. sulfuric acid was replaced by sodium hydroxide.
Analysis of the reaction liquor by gas chromatography
showed that 2,6-dihydroxynaphthalene had been produced in
an amount of 4.9 wt% (yield, 84%) and 2,6-
dihydroxynaphthalene dimer in an amount of 0.9 wt%.
In accordance with the process of the present
invention, dihydroxynaphthalenes of high purity are
obtained in high yield and the obtained
dihydroxynaphthalenes of high purity are useful as
starting materials in the production of synthetic resins,
synthetic fibers, pharmaceuticals, agrichemicals, dyes,
etc.
