DESCRIPTION
TITLE OF INVENTION:
METHOD FOR PRODUCING HIGH PURITY 1,3-DIALKYL CYCLOBUTANE-1,2,3,4-
TETRACARBOXYLIC ACID-1,2:3,4-DIANHYDRIDE
5
TECHNICAL FIELD
The present invention relates to a method for producing a high purity 1,3-dialkyl
cyclobutane-1,2,3,4-tetracarboxylic acid-1,2:3,4-dianhydride, which can be a raw
material monomer for e.g. a polyimide for an optical material.
10
BACKGROUND ART
In general, polyimide resins are widely used as electronic materials such as
protective materials or insulating materials, in liquid crystal display elements or
semiconductors, by virtue of their characteristics such as high mechanical strength, heat
resistance, insulating properties and solvent resistance. Further, they are recentl15 y
expected to be used as optical communication materials such as optical waveguide
materials.
In recent years, developments in this field are remarkable, and along with such
developments, materials to be used are also required to have increasingly higher
20 properties. That is, they are expected not only to be excellent in heat resistance and
solvent resistance but also to have various properties depending upon the particular
applications.
However, in the case of a wholly aromatic polyimide resin obtained from an
aromatic tetracarboxylic acid anhydride and an aromatic diamine as raw materials, it
25 has a deep amber color, which brings about a problem in its use where high
transparency is required. On the other hand, it is known that a polyimide resin
obtained by imidating a polyimide precursor formed by a polycondensation reaction of
an alicyclic tetracarboxylic acid anhydride and an aromatic diamine, has a high
transparency with relatively little coloration (Patent Documents 1 and 2).
30 Patent Document 3 discloses that, as an alkylcyclobutanoic acid dianhydride
which is one of alicyclic tetracarboxylic acid anhydrides as raw materials for the above
polyamide having high transparency with relatively little coloration, it is possible to
2
obtain a mixture of 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic acid-1,2:3,4-
dianhydride (1,3-DMCBDA) and 1,2-dimethylcyclobutane-1,2,3,4-tetracarboxylic acid-
1,2:3,4-dianhydride (1,2-DMCBDA) by photodimerization reaction of citraconic
anhydride (abbreviated as MMA) as represented by the following scheme.
5
Meanwhile, when 1,3-DMCBDA and 1,2-DMCBDA are compared, it is known that
the former 1,3-DMCBDA having a highly symmetric structure is more useful since it is
possible to produce a polyimide having a higher molecular weight than the latter 1,2-
DMCBDA.
Although Patent Document 3 discloses that it is possible to obtain a mixture of 1,310 -
DMCBDA and 1,2-DMCBDA, it fails to disclose that the former high-utility 1,3-DMCBDA
having a high purity and a high efficiency is obtained.
PRIOR ART DOCUMENTS
15 PATENT DOCUMENTS
Patent Document 1: JP-B-2-24294
Patent Document 2: JP-A-58-208322
Patent Document 3: JP-A-4-106127
Patent Document 4: WO2010/092989
20
DISCLOSURE OF INVENTION
TECHNICAL PROBLEM
The object of the present invention is to provide a method for producing a 1,3-
dialkyl cyclobutane-1,2,3,4- tetracarboxylic acid-1,2:3,4-dianhydride (hereinafter, also
25 referred to as 1,3-DACBDA) with a high purity and a high efficiency, from a mixture
containing 1,3-DACBDA and 1,2-dialkylcyclobutane-1,2,3,4-tetracarboxylic acid-1,2:3,4-
dianhydride (hereinafter, also referred to as 1,2-DACBDA), obtainable by e.g. a
3
photodimerization reaction of a maleic anhydride compound.
SOLUTION TO PROBLEM
The present inventors have conducted extensive studies to solve the above
problems and as a result, have found that 1,3-DACBDA and 1,2-DACBDA ar5 e
significantly different in solubility to an organic solvent in an heated state, especially
solubility to a specific organic solvent, and the solubility of the former is extremely lower
than the latter, and found a method for obtaining a high-purity 1,3-DACBDA with a high
efficiency by using the difference of the solubility to separate 1,3-DACBDA and 1,2-
10 DACBDA, whereby they have accomplished the present invention.
The present invention provides the following.
1. A method for producing a 1,3-DACBDA, which comprises heating a mixture of a
1,3-DACBDA and a 1,2-DACBDA in an organic solvent; cooling the mixture; and then
filtrating the mixture to collect a high-purity 1,3-dialkyl-1,2,3,4-cyclobutane
15 tetracarboxylic acid-1,2:3,4-dianhydride as a solid.
2. The method according to the above 1, wherein the organic solvent is an ester or
an anhydride of an organic carboxylic acid, or a carbonic acid ester, having a boiling
point of from 50 to 200 C.
3. The method according to the above 1, wherein the organic solvent is an acetic
20 anhydride.
4. The method according to any one of the above 1 to 3, wherein the organic solvent
is used in an amount of from 2 to 20 parts by mass to 1 part by mass of the mixture of a
1,3-DACBDA and a 1,2-DACBDA.
5. The method according to any one of the above 1 to 4, wherein the heating of the
25 mixture in the organic solvent is carried out at a temperature of from 10 C to a boiling
point of the organic solvent.
6. The method according to any one of the above 1 to 5, wherein, after the heating,
the mixture is cooled to a temperature of from -10 C to 50 C.
7. The method according to any one of the above 1 to 6, wherein the mass ratio of
30 the 1,3-DACBDA to the 1,2-DACBDA in the mixture is from 50:50 to 99.5:0.5.
8. The method according to any one of the above 1 to 7, wherein the mixture of a
1,3-DACBDA and a 1,2-DACBDA is obtained by subjecting maleic anhydride to a
4
photodimerization reaction.
9. The method according to any one of the above 1 to 8, wherein each alkyl group of
the 1,3-DACBDA and the 1,2-DACBDA is a methyl group.
ADVANTAGEOUS EFFECTS OF INVENTIO5 N
According to the present invention, it is possible to obtain a high purity1,3-dialkyl
cyclobutane-1,2,3,4- tetracarboxylic acid-1,2:3,4-dianhydride (1,3-DACBDA) with a high
efficiency and in a high yield.
10 DESCRIPTION OF EMBODIMENTS
A mixture of 1,3-DACBDA and 1,2-DACBDA as raw materials for the production
method of the present invention, is typically obtainable by subjecting a maleic anhydride
compound represented by the formula (1) to a photodimerization reaction, in
accordance with the following reaction scheme.
15 wherein R is a C1-20, preferably a C1-12, more preferably a C1-6 alkyl group, particularly
preferably methyl.
The C1-20 alkyl group may be a linear or branched saturated alkyl group, or a linear
or branched unsaturated alkyl group. As a specific example, methyl, ethyl, n-propyl, ipropyl,
n-butyl, i-butyl, s-butyl, t-butyl, n-pentyl, 1-methyl-n-butyl, 2-methyl-n-butyl, 3-
20 methyl-n-butyl, 1,1-dimethyl-n-propyl, n-hexyl, 1-methyl-n-pentyl, 2-methyl-n-pentyl,
1,1,-dimethyl-n-butyl, 1-ethyl-n-butyl, 1,1,2-trimethyl-n-propyl, n-heptyl, n-octyl, n-nonyl,
n-decyl, n-dodecyl or n-eicosyl, 1-methylvinyl, 2-allyl, 1-ethylvinyl, 2-methylallyl, 2-
butenyl, 2-methyl-2-butenyl, 3-methyl-2-butenyl, 3-methyl-3-butenyl, 2-hexenyl, 4-
methyl-3-pentenyl, 4-methyl-4-pentenyl, 2,3-dimethyl-2-butenyl, 1-ethyl-2-pentenyl, 3-
25 dodecenyl, propargyl, 3-butynyl, 3-methyl-2-propynyl or 9-decynyl may be mentioned.
O
O
O
R
O O
O
O O
R O
R
2 + O O
O
O O
R R O
(1)
5
Here, n represents normal, i represents iso, s represents secondary, and t
represents tertiary, respectively.
The maleic anhydride compound represented by the formula (1) may, for example,
be citraconic anhydride, 2-ethyl maleic anhydride, 2-isopropyl maleic anhydride, 2-nbutyl
maleic anhydride, 2-t-butyl maleic anhydride, 2-n-pentyl maleic anhydride, 2-5 nhexyl
maleic anhydride, 2-n-heptyl maleic anhydride, 2-n-octyl maleic anhydride, 2-nnonyl
maleic anhydride, 2-n-decyl maleic anhydride, 2-n-dodecyl maleic anhydride, 2-neicosyl
maleic anhydride, 2-(1-methyl vinyl) maleic anhydride, 2-(2-allyl) maleic
anhydride, 2-(1-ethyl vinyl) maleic anhydride, 2-(2-methyl allyl) maleic anhydride, 2-(2-
10 butenyl) maleic anhydride, 2-(2-hexenyl) maleic anhydride, 2-(1-ethyl-2-pentenyl) maleic
anhydride, 2-(3-dodecenyl) maleic anhydride, 2-propargyl maleic anhydride, 2-(3-
butynyl) maleic anhydride, 2-(3-methyl-2-propynyl) maleic anhydride or 2-(9-decynyl)
maleic anhydride.
Examples of the production conditions of a mixture of 1,3-DACBDA and 1,2-
15 DACBDA by a photodimerization reaction of a maleic anhydride compound will be
mentioned below.
A solvent to be used in the photodimerization reaction may, for example, be
methyl formate, ethyl formate, n-propyl formate, i-propyl formate, n-butyl formate, i-butyl
formate, methyl acetate, ethyl acetate, n-propyl acetate, i-propyl acetate, n-butyl
20 acetate, i-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, ipropyl
propionate, ethylene glycol diformate, ethylene glycol diacetate, ethylene glycol
dipropionate, dimethyl carbonate or diethyl carbonate.
The amount of the solvent to be used is from 3 to 300 times by mass, more
preferably from 3 to 100 times by mass to the maleic anhydride compound.
25 Further, in order to increase the reaction rate or the yield of the product, the
amount of the reaction solvent to be used is preferably low. For example, when the
concentration of the maleic anhydride compound becomes high, the reaction rate
increases, and the yield of the product obtainable becomes large. Accordingly, in order
to increase the reaction rate or the yield of the product, the amount of the solvent to be
30 used is preferably from 3 to 10 times by mass to the maleic anhydride compound.
In this photodimerization reaction, a wavelength of light is from 200 to 400 nm,
more preferably from 250 to 350 nm, particularly preferably from 280 to 330 nm. As a
6
light source, a low-pressure mercury lamp, a medium-pressure mercury lamp, a highpressure
mercury lamp, an ultrahigh-pressure mercury lamp, a xenon lamp, an
electrodeless lamp or a light-emitting diode, etc. is used.
Particularly in the case a light emitting diode having a wavelength of from 275 to
500 nm, 1,3-DACBDA was obtained in an improved selectivity. Further, if a ligh5 t
source-cooling pipe is changed from lime glass to Pyrex glass, a colored polymer is less
attached to the light source-cooling pipe and impurities are less produced, and therefore
it is possible to obtain 1,3-DACBDA in an improved selectivity.
If the reaction temperature becomes high, a polymer tends to be produced as a
10 by-product, and on the other hand, if the reaction temperature becomes low, the
solubility of the maleic anhydride compound tends to be low, whereby the production
efficiency will be deteriorated. Therefore, the reaction temperature is preferably from -
20 to 80°C, more preferably from -10 to 50°C. In particular, when the reaction
temperature is from 0 to 20°C, the production of a by-product such as 1,2-DACBDA is
15 suppressed, and therefore it is possible to obtain 1,3-DACBDA in a high selectivity and
a high yield.
The reaction time may vary depending upon e.g. the charged amount of a maleic
anhydride compound, the type of a light source or the irradiation dose, but it is possible
to carry out the reaction until the proportion of an unreacted maleic anhydride
20 compound reaches a range of from 0 to 40%, preferably a range of from 0 to 10%.
Further the conversion rate may easily be measured by analyzing a reaction fluid by
e.g. gas chromatography.
As the reaction time becomes long, the conversion rate of a maleic anhydride
compound increases and the precipitation amount of 1,3-DACBDA thereby increases,
25 and as a result, 1,3-DACBDA produced tends to attach to an exterior wall (a reaction
fluid side) of a light source-cooling pipe, whereby crystal coloration or a decrease of
light efficiency (unit power × yield per hour) accompanied by decomposition reaction
tends to be observed. Therefore, it is practically undesirable to take a long time in one
batch for increasing the conversion rate of the maleic anhydride compound since the
30 production efficiency decreases. The reaction may be carried out by either a batchtype
or a flow-type, and further, the reaction pressure may be either atmospheric
pressure or elevated pressure.
7
After the photodimerization reaction, a precipitate in a reaction fluid is filtrated, a
product collected by the filtration is washed by an organic solvent, and then dried under
reduced pressure, whereby it is possible to obtain a mixture of 1,3-DACBDA and 1,2-
DACBDA.
The amount of the organic solvent to be used for washing the collected product, 5 is
not limited so long as it is possible to transfer a precipitate remained in a reactor to a
filter, but if the amount of the organic solvent is large, the desired compound tends to be
transferred to a filtrate, whereby the recovery rate tends to decrease. Therefore, the
amount of the organic solvent to be used for washing the collected product, is preferably
10 from 0.5 to 10 times by mass, more preferably from 1 to 2 times by mass, to the maleic
anhydride compound used in the reaction.
The solvent to be used for washing the collected product is not particularly limited,
but if a solvent having high solubility of 1,3-DACBDA as a desired product is used, the
desired compound tends to be transferred to a filtrate, whereby the recovery rate
15 decreases. Therefore, the organic solvent to be used for washing the collected
product may, for example, be methyl formate, ethyl formate, n-propyl formate, i-propyl
formate, n-butyl formate, i-butyl formate, methyl acetate, ethyl acetate, n-propyl acetate,
i-propyl acetate, n-butyl acetate, i-butyl acetate, methyl propionate, ethyl propionate, npropyl
propionate, i-propyl propionate, ethylene glycol diformate, ethylene glycol
20 diacetate, ethylene glycol dipropionate, dimethyl carbonate or diethyl carbonate, as a
solvent to be used for photodimerization reaction, a solvent which does not solve a
product, such as toluene, hexane, heptane, acetonitrile, acetone, chloroform or acetic
anhydride, or a mixed solvent thereof. Among them, ethyl acetate or dimethyl
carbonate is preferred, and ethyl acetate, dimethyl carbonate or acetic anhydride is
25 more preferred.
The photodimerization reaction of a maleic anhydride compound may be carried
out in the presence of a sensitizer. As the sensitizer, benzophenone, anthraquinone,
acetophenone or benzaldehyde is preferred. In particular, benzophenone substituted
with an electron-withdrawing group, acetophenone substituted with an electron30
withdrawing group or benzaldehyde substituted with an electron-withdrawing group is
preferred since a mixture of 1,3-DACBDA and 1,2-DACBDA is produced in a high light
reaction efficiency.
8
The amount of the sensitizer to be used is preferably from 0.1 to 20 mol%, more
preferably from 0.1 to 5 mol% to the maleic anhydride compound.
In the present invention, it is possible to obtain a reaction mixture fluid containing
a mixture of 1,3-DACBDA and 1,2-DACBDA as mentioned above. In the reaction
mixture fluid, both of 1,3-DACBDA and 1,2-DACBDA are present as solids, an5 d
therefore the reaction mixture fluid is filtrated, and 1,3-DACBDA and 1,2-DACBDA are
isolated to be raw materials for obtaining a high purity 1,3-DACBDA in the present
invention.
Further, in a case where an organic solvent contained in a reaction mixture
10 containing a mixture of 1,3-DACBDA and 1,2-DACBDA is an organic solvent which can
be used when a high purity 1,3-DACBDA is subsequently obtained, such a reaction
mixture containing a mixture of 1,3-DACBDA and 1,2-DACBDA may be used as raw
materials. Further, in a case where the mixture of 1,3-DACBDA and 1,2-DACBDA is
isolated from the reaction mixture fluid, and preferably subjected to washing treatment,
15 a high purity 1,3-DACBDA can easily be obtained, such being preferred.
In the present invention, a mixture of 1,3-DACBDA and 1,2-DACBDA is heated in
an organic solvent, cooled, and then filtrated to collect a high purity 1,3-dialkyl-1,2,3,4-
cyclobutane tetracarboxylic acid-1,2:3,4-dianhydride as a solid, whereby it is possible to
obtain 1,3-DACBDA in a high yield and a high purity.
20 As an organic solvent to be used here, in a heated state, many organic solvents
may be used since they are not reactive with 1,3-DACBDA and 1,2-DACBDA, and have
a small solubility in 1,3-DACBDA but have high solubility in 1,2-DACBDA.
Such an organic solvent is preferably one having a boiling point of preferably from
30 to 200 C, more preferably from 50 to 180 C. As such an organic solvent, hexane,
25 heptane, acetonitrile, acetone, chloroform or toluene. In particular, the organic solvent
is preferably an ester or an anhydride of an organic carboxylic acid, or a carbonic acid
ester.
As the ester of an organic carboxylic acid, it is suitably a fatty acid alkyl ester
represented by the formula: R1COOR2 (wherein R1 is hydrogen, or preferably a C1-4
30 alkyl group, more preferably a C1-2 alkyl group, and R2 is a C1-4 alkyl group, more
preferably a C1-3 alkyl group.)
A preferred example of the ester of an organic carboxylic acid may be ethyl
9
formate, n-propyl formate, i-propyl formate, n-butyl formate, i-butyl formate, methyl
acetate, ethyl acetate, n-propyl acetate, i-propyl acetate, n-butyl acetate, i-butyl acetate,
methyl propionate, ethyl propionate, n-propyl propionate, i-propyl propionate, n-butyl
propionate or i-butyl propionate. Further, ethylene glycol diformate, ethylene glycol
diacetate or ethylene glycol dipropionate may, for example, be used5 .
Further, the anhydride of an organic carboxylic acid is preferably one represented
by the formula: (R1CO)2O (wherein R1 is the same as the above including a preferred
embodiment). As a preferred specific example, propionic anhydride, butyric anhydride,
trifluoroacetic anhydride or acetic anhydride may be mentioned. Among them, acetic
10 anhydride is preferred from the viewpoint that it is possible to obtain 1,3-DACBDA in a
higher yield.
The carbonic acid ester may suitably be a carbonic acid dialkyl ester having a C1-3
alkyl group, more preferably a C1-2 alkyl group. As a preferred example, dimethyl
carbonate, diethyl carbonate, or a mixture thereof may be mentioned.
15 Further, a mixture of 1,3-DACBDA and 1,2-DACBDA may partly be hydrolyzed
during taking out or storing the mixture, but in a case where carboxylic anhydride is
used, a high purity 1,3-DACBDA can stably be obtained since such a partly hydrolyzed
mixture can also be anhydrized by heating and stirring, such being preferred.
Further, many solvents may partly be decomposed during purification if the water
20 content in the solvent is large, and therefore they are needed to control a water content
in the solvent, but in the case of the anhydride of an organic carboxylic acid, a ring
closure of a hydrolyzate can be carried out, and therefore a high purity 1,3-DACBDA
can be obtained without adjusting the water content in the solvent, such being preferred.
The amount of an organic solvent is preferably from 2 to 20 parts by mass to one
25 part by mass of a mixture of 1,3-DACBDA and 1,2-DACBDA, and in view of purification
efficiency or volume efficiency, it is more preferably from 3.5 to 6 parts by mass,.
The temperature at the time of heating in an organic solvent is usually a
temperature of from 10 C to a boiling point of the organic solvent to be used, and with a
view to efficiently dissolve 1,2-DACBDA, it is preferably a temperature of from 50 C to a
30 boiling point of the organic solvent to be used. The heating time is preferably from 30
minutes to 10 hours, and if it is too short, the purity may decrease, and therefore it is
preferably from 1 to 6 hours.
10
After the above heating, the mixture is cooled to a temperature of preferably from
-10 to 50 C, more preferably from -10 to 20 C, whereby crystals of 1,3-DACBDA were
precipitated as a solid. A liquid containing such a solid of 1,3-DACBDA is filtrated, and
crystals of 1,3-DACBDA are collected by filtration, whereby it is possible to separate it
from 1,2-DACBDA which dissolved in the liquid, and thereby to obtain a high purity 1,35 -
DACBDA.
Here, the ratio of a mixture of 1,3-DACBDA and 1,2-DACBDA used above is not
particularly limited, but if the ratio of 1,2-DACBDA becomes high, there is a possibility
that the purity will become low. Therefore, the mass ratio of 1,3-DACBDA to 1,2-
10 DACBDA in a mixture used in the present invention is preferably from 50:50 to 99.5:0.5,
more preferably from 70:30 to 99.5:05.
EXAMPLES
Now, the present invention will specifically be described with reference to
15 Examples, but it should be understood that the present invention is by no means
restricted thereto. Further, analytical methods employed in Examples are as follows.

Apparatus: GC-2010 Plus (manufactured by SHIMADZU Corporation),
Column: DB-1 (manufactured by GL Sciences Inc.) diameter 0.25 mm × length
20 30 m, film thickness 0.25 um,
Carrier gas: He,
Detector: FID,
Sample injection amount: 1 um,
Inlet port temperature: 160°C,
25 Detector temperature: 220°C,
Column temperature: 70°C (20 min)-40°C/min-220°C (15 min),
Split ratio: 1:50,
Internal standard substance: butyl lactate.
<1H NMR analytical conditions>
30 Apparatus: Fourier transform superconducting NMR spectrometer (FT-NMR)
INOVA-400 (manufactured by Varian) 400 MHz,
Solvent: DMSO-d6,
11
Internal standard substance: tetramethylsilane (TMS).

Apparatus: DSC1 (manufactured by Mettler-Toredo International Inc.),
Temperature: 35°C-5°C/min-400°C,
Pan: Au (closed)5 .
REFERENCE EXAMPLE 1: Preparation of 1,3-DACBDA and 1,2-DACBDA
In a nitrogen atmosphere, into a 300 mL Pyrex (registered trademark) glass fivenecked
flask, 35.0 g (312 mmol) of a citraconic anhydride (CA), 152 g (1720 mmol, 4.33
times by weight to citraconic anhydride (CA)) of ethyl acetate were charged, and
10 dissolved with stirring by a magnetic stirrer. Then, the resultant was irradiated with a
100 W high-pressure mercury lamp for 48 hours with stirring at a temperature of from 5
to 10°C. A reaction fluid was analyzed by gas chromatography, and the remaining ratio
of the raw material was confirmed to be 16.4%. Thereafter, a white crystal precipitated
was obtained by filtration at a temperature of from 5 to 10°C, and this crystal was
15 washed twice with 43.8 g (497 mmol, 1.25 times by weight to the citraconic anhydride
(CA)) of ethyl acetate. Then, this crystal was dried under reduced pressure to obtain
5.8 g (yield: 16.6%) of a white crystal.
This crystal was analyzed by 1H NMR and confirmed to be a mixture (1,3-DMCBDA:
1,2-DM-CBDA = 92.2.3:7.8) containing 1,3-DM-CBDA and 1,2-DM-CBDA.
20 Further, a crystal, a filtrate and a washing liquid obtained were quantitatively analyzed
respectively by 1H NMR analysis and gas chromatography. Mass balance to the
charged amount was 93.1%.
EXAMPLE 1: Production of high-purity1,3-DM-CBDA (Acetic anhydride)
In a nitrogen stream, into a 200 mL four-necked flask, 18.3 g of a mixture (1,3-DMO
O
O
h
1,3-DM-CBDA
O O
O O
O O
CA 1,2-DM-CBDA
O O
O O
O O
AcOEt
1,3-DM-CBDA
O O
O O
O O
1,2-DM-CBDA
O O
O O
O O
Ac2O
1,3-DM-CBDA
O O
O O
O O
reflux
12
CBDA:1,2-DM-CBDA = 85:15) containing 1,3-DM-CBDA and 1,2-DM-CBDA, obtained in
the same manner as in Reference Example 1, and 92 g of acetic anhydride were
charged and suspended at 25°C with stirring by a magnetic stirrer, followed by heat
reflux (130°C) for 4 hours, and then cooled so that the internal temperature would be
20°C, followed by stirring for one hour at a temperature of 205 °C.
Then, a white crystal precipitated was filtrated, the crystal obtained was washed
twice with 18 g of ethyl acetate, and then dried under reduced pressure to obtain 14.4 g
(yield: 92.6%) of a white crystal. The crystal was analyzed by 1H NMR, whereby the
ratio of 1,3-DM-CBDA to 1,2-DM-CBDA was confirmed to be 1,3-DM-CBDA:1,2-DM10
CBDA = 99.5:0.5.
1H NMR (DMSO-d6, ppm) (1,3-DM-CBDA): 1.38 (s, 6H), 3.89 (s, 2H).
1H NMR (DMSO-d6, ppm) (1,2-DM-CBDA): 1.37 (s, 6H), 3.72 (s, 2H).
mp. (1,3-DM-CBDA ): 316-317°C
EXAMPLE 2: Production of high-purity1,3-DM-CBDA (Acetic anhydride)
15 In a nitrogen stream, into a 100 mL four-necked flask, 5 g of a mixture (1,3-DMCBDA:
1,2-DM-CBDA = 70:30) containing 1,3-DM-CBDA and 1,2-DM-CBDA, obtained in
the same manner as in Reference Example 1, and 25 g of acetic anhydride were
charged and suspended at 25°C with stirring by a magnetic stirrer, followed by heat
reflux (130°C) for 4 hours, and then cooled so that the internal temperature would be
20 20°C, followed by stirring for one hour at a temperature of 20°C.
Then, a white crystal precipitated was filtrated, the crystal obtained was washed
twice with 5 g of ethyl acetate, and then dried under reduced pressure to obtain 3.3 g
(yield: 94.3%) of a white crystal. The crystal was analyzed by 1H NMR, whereby the
ratio of 1,3-DM-CBDA to 1,2-DM-CBDA was confirmed to be 1,3-DM-CBDA:1,2-DM25
CBDA = 99.5:0.5.
EXAMPLE 3: Production of high-purity1,3-DM-CBDA (Acetonitrile)
In a nitrogen stream, into a 500 mL four-necked flask, 70 g of a mixture (1,3-DMCBDA:
1,2-DM-CBDA = 89:11) containing 1,3-DM-CBDA and 1,2-DM-CBDA, obtained in
the same manner as in Reference Example 1, and 420 g of acetonitrile were charged
30 and suspended at 17°C with stirring by a magnetic stirrer, followed by stirring for one
hour at 32°C, and then cooled so that the internal temperature would be 10°C, followed
by stirring for one hour at a temperature of 10°C.
13
Then, a white crystal precipitated was filtrated, the crystal obtained was washed
twice with 70 g of acetonitrile, and then dried under reduced pressure to obtain 52.56 g
(yield: 84.3%) of a white crystal. The crystal was analyzed by 1H NMR, whereby the
ratio of 1,3-DM-CBDA to 1,2-DM-CBDA was confirmed to be 1,3-DM-CBDA:1,2-DMCBDA
= 99.5:0.55 .
EXAMPLE 4: Production of high-purity1,3-DM-CBDA (Ethyl acetate)
In a nitrogen stream, into a 500 mL four-necked flask, 80 g of a mixture (1,3-DMCBDA:
1,2-DM-CBDA = 89:11) containing 1,3-DM-CBDA and 1,2-DM-CBDA, obtained in
the same manner as in Reference Example 1, and 800 g of ethyl acetate were charged
10 and suspended at 17°C with stirring by a magnetic stirrer, followed by stirring for one
hour at 50°C, and then cooled so that the internal temperature would be 17°C, followed
by stirring for one hour at a temperature of 20°C.
Then, a white crystal precipitated was filtrated, the crystal obtained was washed
twice with 160 g of ethyl acetate, and a white crystal obtained was dried under reduced
15 pressure to obtain a crystal having a ratio of 1,3-DM-CBDA to 1,2-DM-CBDA being 1,3-
DM-CBDA:1,2-DM-CBDA = 99.0:1. Here, the ratio of 1,3-DM-CBDA and 1,2-DMCBDA
was confirmed by 1H NMR analysis. Thereafter, in a nitrogen stream, into a 500
mL four-necked flask, all amount of the crystal obtained and 800 g of ethyl acetate were
charged and suspended at 17°C with stirring by a magnetic stirrer, followed by stirring
20 for one hour at 50°C.
Then the internal temperature was cooled to be at most 20°C, followed by stirring
for one hour at a temperature of at most 20°C. Then, a white crystal precipitated was
filtrated, the crystal obtained was washed twice with 160 g of ethyl acetate, and then
dried under reduced pressure to obtain 53.32 g (yield: 74.9%) of a white crystal. The
25 crystal was analyzed by 1H NMR, whereby the ratio of 1,3-DM-CBDA to 1,2-DM-CBDA
was confirmed to be 1,3-DM-CBDA:1,2-DM-CBDA = 99.3:0.7.
INDUSTRIAL APPLICABILITY
The high-purity 1,3-dimethyl-1,2,3,4-cyclobutane tetracarboxylic acid-1,2:3,4-
30 dianhydride obtained in the present invention is a compound useful as a raw material for
e.g. a polyimide, and such a polyimide is widely useful as a resin composition used for
electronic materials such as protective materials or insulating materials, in liquid crystal
14
display elements or semiconductors.
The entire disclosure of Japanese Patent Application No. 2014-007189 filed on
January 17, 2014 including specification, claims and summary is incorporated herein by
reference in its entirety.

CLAIMS
1. A method for producing a 1,3-dialkyl cyclobutane-1,2,3,4-tetracarboxylic acid-
1,2:3T4-dianhydride, which comprises heating a mixture of a 1,3-dialkyl cyclobutane-
1,2,3,4-tetracarboxylic acid-1,2:3,4-dianhydride and a 1,2-dialkyl cyclobutane-1,2,3,4-
tetracarboxylic acid-1,2:3,4-dianhydride in an organic solvent; cooling the mixture; and
then filtrating the mixture to collect a high-purity 1,3-dialkyl-1,2,3,4-cyclobutane
tetracarboxylic acid-1,2:3,4-dianhydride as a solid.
2. The method according to Claim 1, wherein the organic solvent is an ester or an
anhydride of an organic carboxyiic acid, or a carbonic acid ester, having a boiling point
of from 50 to 200°C.
3. The method according to Claim 1, wherein the organic solvent is an acetic
anhydride.
4. The method according to any one of Claims 1 to 3, wherein the organic solvent is
used in an amount of from 2 to 20 parts by mass to 1 part by mass of the mixture of a
1,3-dialkyl cyclobutane-1,2,3,4-tetracarboxylic acid-1,2:3,4-dianhydride and a 1,2-dialkyl
cyclobutane-1,2,3,4-tetracarboxylic acid-1,2:3,4-dianhydride.
5. The method according to any one of Claims 1 to 4, wherein the heating of the
mixture in the organic solvent is carried out at a temperature of from 10°C to a boiling
point of the organic solvent.
6. The method according to any one of Claims 1 to 5, wherein, after the heating, the
mixture is cooled to a temperature of from -10°C to 50°C.
7. The method according to any one of Claims 1 to 6, wherein the mass ratio of the
1,3-dialkyl cyclobutane-1,2,3,4-tetracarboxylic acid-1,2:3,4-dianhydride to the 1,2-dialkyl
cyclobutane-1,2,3,4-tetracarboxyiic acid-1,2:3,4-dianhydride in the mixture is from 50:50
to 99.5:0.5.
8. The method according to any one of Claims 1 to 7, wherein the mixture of a 1,3-
dialkyl cyclobutane-1,2,3,4-tetracarboxylic acid-1,2:3,4-dianhydride and a 1,2-dialkyl
cyclobutane-1,2,3,4-tetra carboxyiic acid-1,2:3,4-dianhydride is obtained by subjecting
maleic anhydride to a photodimerization reaction.
9. The method according to any one of Claims 1 to 8, wherein each aikyl group of
the 1,3-diaikyl eye lo butane-1,2,3,4-tetra carboxyiic acid-1,2:3,4-dianhydride and the 1,2-
dialkyl cyclobutane-1,2,3,4-tetracarboxyiic acid-1,2:3,4-dianhydride is a methyl group.