5-(2,4-Dioxotetrahydro-3-furanylmethyl)norbornane-2,3-dicarboxylic acid anhydride and process for production thereof

A novel compound 5-(2,4-dioxotetrahydro-3-furanylmethyl)norbornane-2,3-dicarboxylic acid anhydride has been provided. The compound is prepared by hydrogenating 5-(2,4-dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-di-carboxylic acid anhydride. The compound may be used as a hardening agent for epoxy resins, a raw material of producing polyimides, polyamides and polyesters, and a raw material for a plasticizer for vinyl chloride polymers.

The present invention relates to a novel tetracarboxylic acid anhydride 
which is useful as an epoxy resin hardening agent and the like, as well as 
to methods of preparing it. 
In general, tetracarboxylic acid anhydrides are used as an epoxy resin 
hardening agent for the purpose of obtaining a heat-resistant hardened 
product, a raw material for polyimide resins, a raw material for a 
plasticizer for vinyl chloride resins, and a raw material for 
water-soluble polyesters, and the field of utilizing them is broad. 
Hitherto, as an epoxy resin hardening agent, there have been used 
pyromellitic acid dianhydride, benzophenonetetracarboxylic acid 
dianhydride, methylcyclohexenetetracarboxylic acid dianhydride and the 
like. However, the former two of pyromellitic acid dianhydride and 
benzophenonetetracarboxylic acid dianhydride are poorly compatible with 
epoxy resins. In addition, since they begin to harden epoxy resins 
immediately after they are dissolved in the resins, the pot life of them 
is short. Therefore, they have a drawback that they cannot be used for 
casting compositions unless they are not blended with maleic anhydride. 
The last one of methylcyclohexenetetracarboxylic acid dianhydride is free 
from the drawback, but it has a high melting point of about 168.degree. C. 
so that the workability of it is poor. In addition, they are all 
high-priced. 
The object of the present invention is to provide a low-priced 
tetracarboxylic acid dianhydride, which is free from the above-mentioned 
drawbacks in the prior art and has a good workability, and to provide a 
method of preparing it. 
First, the present invention provides a tetracarboxylic acid dianhydride 
which is 
5-(2,4-dioxotetrahydro-3-furanylmethyl)norbornane-2,3-dicarboxylic acid 
anhydride of a chemical formula: 
##STR1## 
The compound of the present invention has a low melting point and therefore 
has a good workability. In addition, it is highly compatible with epoxy 
resins so that it can be used singly as a hardening agent even in casting 
of epoxy resins. Moreover, the thus hardened epoxy resin products have a 
heat resistance comparable to those as hardened with the conventional 
tetracarboxylic acid dianhydrides. The compound of the present invention 
can also be used as a raw material for polyimides, polyamides and 
polyester resins, and as a raw material for a plasticizer for vinyl 
chloride polymers. Thus, the technical field to which the compound of the 
invention is applied is broad. 
Secondly, the present invention provides a method of preparing the 
above-mentioned compound. 
Specifically, the compound of the present invention can easily be prepared 
by hydrogenating 
5-(2,4-dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-dicarboxylic acid 
anhydride. 
5-(2,4-Dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-dicarboxylic acid 
anhydride itself is a novel substance and is useful also as an epoxy resin 
hardening agent like the compound of the present invention. The compound 
is prepared by reacting 5-methylenenorbornane-2,3-dicarboxylic acid 
anhydride, or 1-methylnorbornene-2,3-dicarboxylic acid anhydride and/or 
5-methylnorbornene-2,3-dicarboxylic acid anhydride, with maleic anhydride. 
5-Methylenenorbornane-2,3-dicarboxylic acid anhydride which is one starting 
material has a double bond at the terminal thereof and is therefore 
extremely highly reactive to easily react with maleic anhydride to give 
5-(2,4-dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-dicarboxylic acid 
anhydride. The reaction is presumed to proceed as mentioned below. This is 
ene-production of a kind, and such ene-production of itself is described 
in, for example, Japanese Patent Publication No. 58-51955. 
##STR2## 
For effecting the reaction, in general, 
5-methylenenorbornane-2,3-dicarboxylic acid anhydride and maleic anhydride 
are fed into a reactor in a molar ratio of from 0.5/1 to 5/1 and are 
heated preferably at a temperature of approximately from 160.degree. to 
220.degree. C. for approximately from 2 to 24 hours with stirring. The 
reaction may be effected in the presence of any desired catalyst. As a 
usable catalyst, Lewis acids such as aluminium chloride or boron fluoride 
are preferred, which, however, are not limitative. The reaction does not 
need a solvent, but may be effected in any desired solvent. As preferred 
solvents, there are mentioned chlorobenzene, xylene, mesitylene, 
triethylbenzene, etc. 
5-Methylenenorbornane-2,3-dicarboxylic acid anhydride can be prepared by 
isomerizing 1-methylnorbornene-2,3-dicarboxylic acid anhydride and/or 
5-methylnorbornene-2,3-dicarboxylic acid anhydride in the presence of an 
acid catalyst. "Isomerization" as referred to herein broadly includes 
structural isomerization and stereoisomerization but does not have a 
narrow meaning of geometric isomerization and position isomerization. 
5-Methylenenorbornane-2,3-dicarboxylic acid anhydride includes to 
stereoisomers of endo form and exo form, and the present invention may use 
any of them. A mixture of the two may also be used. 
1-Methylnorbornene-2,3-dicarboxylic acid anhydride and 
5-methylnorbornene-2,3-dicarboxylic acid anhydride (hereinafter referred 
to as "1-MeNA" and "5-MeNA", respectively) of themselves are known. Both 
of the two acid anhydrides each have two stereoisomers of endo form and 
exo form, and both of the two stereoisomers can be used in the present 
invention. 
The starting compounds of 1-MeNA and 5-MeNA can be produced, for example, 
as follows: Precisely, 1-methylcyclopentadiene (hereinafter referred to as 
"1-MeCPD") and 2-methylcyclopentadiene (hereinafter referred to as 
"2MeCPD") are reacted with maleic anhydride (Diels-Alder reaction) to 
produce endo-1-MeNA from 1-MeCPD and endo-5-MeNA from 2-MeCPD. 1-MeCPD and 
2-MeCPD are available generally as a mixture of them, and it is 
unnecessary to isolate the two from each other for the purpose of the 
invention. 
The thus obtained mixture of 1-MeNA and 5-MeNA is isomerized in the manner 
as will be mentioned below, whereby endo-1-MeNA gives 
exo-5-methylenenorbornane-2,3-dicarboxylic acid anhydride via exo-5-MeNA, 
while endo-5-MeNA directly gives 
endo-5-methylenenorbornane-2,3-dicarboxylic anhydride. A part of 
endo-5-MeNA may give exo-5-methylenenorbornane-2,3-dicarboxylic acid 
anhydride via exo-5-MeNA. Where endo1MeNA is heated in the absence of an 
acid in the manner as will be mentioned below, it could be isomerized into 
exo-5-MeNA but is not isomerized further into 
exo-5-methylenenorbornane-2,3-dicarboxylic acid anhydride. 
Methylnorbornene-2,3-dicarboxylic acid anhydride is available as a 
commercial product, and it may be used in the present invention. 
Isomerization may be effected by heating 
1-methylnorbornene-2,3-dicarboxylic acid anhydride and/or 
5-methylnorbornene-2,3-dicarboxylic acid anhydride in the presence of an 
acid. Acids to be used for the isomerization are not specifically defined 
but various known acids can be used. For instance, as usable acids, there 
are mentioned Bronsted acids, for example, aromatic sulfonic acids such as 
benzenesulfonic acid, paratoluenesulfonic acid and paraxylene-2-sulfonic 
acids, mineral acids such as sulfuric acid and hydrochloric acid, 
hetero-polyacids such as molybdic acid, and carboxylic acids such as 
maleic acid; as well as other Lewis acids such as aluminium chloride or 
boron fluoride. Since acid anhydrides such as maleic anhydride may be 
reacted with water to give the corresponding acids, they may also be used 
in place of acids to carry out the isomerization. In the present 
invention, use of Bronsted acids is preferred. The amount of the acid to 
be used in the reaction is preferably approximately from 0.01 to 5% by 
weight, especially preferably approximately from 0.02 to 3% by weight, to 
the methylnorbornene-2,3-dicarboxylic acid anhydride to be reacted. The 
temperature for heating is preferably approximately from 120.degree. to 
250.degree. C., especially preferably approximately from 150.degree. to 
230.degree. C. The isomerization under heat can be effected either by a 
batchwise system or a continuous system. The reaction time is preferably 
approximately from 30 minutes to 10 hours, especially preferably 
approximately from 1 to 5 hours for batchwise reaction. 
The 5-methylenenorbornane-2,3-dicarboxylic acid anhydride thus obtained by 
the method mentioned above is then reacted with maleic anhydride in the 
manner as mentioned above, to thereby obtain 
5-(2,4-dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-dicarboxylic acid 
anhydride. Apart from this, the above-mentioned isomerization and 
ene-production can be effected as one operation. Briefly, 
1-methylnorbornene-2,3-dicarboxylic acid anhydride and/or 
5-methylnorbornene-2,3-dicarboxylic acid anhydride are/is heated in the 
presence of maleic anhydride to give 
5-(2,4-dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-dicarboxylic acid 
anhydride via successive isomerization and ene-production. 
After the above-mentioned reaction, the product is preferably purified 
prior to hydrogenation thereof. Purification of the product may be 
effected by removing the non-reacted raw materials by simple distillation 
or the like followed by recrystallization of the obtained crude product. 
As solvents usable for the recrystallization, there are mentioned acetic 
anhydride and ketone solvents such as methyl isobutyl ketone and the like, 
which, however, are not limitative. 
The 5-(2,4-dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-dicarboxylic 
acid anhydride thus obtained is hydrogenated to obtain the compound of the 
present invention. 
Hydrogenation for obtaining the compound of the invention is not 
specifically defined but may be effected by various known methods. For 
instance, there are mentioned a method of catalytic hydrogenation of 
5-(2,4-dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-dicarboxylic acid 
anhydride, and a method of applying a combination of hydrogen iodide and 
red phosphorus or a combination of sodium and alcohol to the acid 
anhydride. However, these methods are not limitative. Preferred is the 
former catalytic hydrogenation. In general, the catalytic hydrogenation is 
effected by bringing 
5-(2,4-dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-dicarboxylic acid 
anhydride into contact with hydrogen under heat, preferably in the 
presence of a hydrogenation catalyst. As preferred hydrogenation catalysts 
for the process, there are mentioned palladium, cobalt, nickel, platinum 
and the like, which, however, are not limitative. The catalyst may be in 
the form with a carrier. The heating temperature is preferably 
approximately from 80.degree. to 300.degree. C., more preferably 
approximately from 120.degree. to 250.degree. C. The hydrogen pressure 
during the hydrogenation reaction is preferably approximately from 10 to 
150 kg/cm.sup.2 G. The reaction time is preferably approximately from 1 to 
10 hours, more preferably from 2 to 6 hours. No solvent is necessary in 
the hydrogenation. However, since the starting materials and the product 
are solid at room temperature and in order to smoothly conduct the 
hydrogenation, a solvent such as tetrahydrofuran or the like may be in the 
reaction system. 
It is also possible to hydrogenate the 
5-(2,4-dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-dicarboxylic acid 
anhydride as obtained by the above-mentioned production method, without 
isolation or after simple purification, to obtain the intended product of 
the present invention. 
After the above-mentioned reaction, the product may be purified. 
Purification of the product may be effected by recrystallization with a 
solvent such as methyl isobutyl ketone. 
The compound of the present invention can be identified by various 
determination means such as IR, NMR, etc. For instance, in IR of the 
compound, there are seen peaks at 1770 to 1780 cm.sup.-1 and at 1850 
cm.sup.-1 to be caused by stretching vibration of C.dbd.O of the 
carboxylic acid anhydride moiety. In .sub.1 H-NMR of the same, there are 
seen peaks 8H's to be caused by four-- CH2--'s at 81.8 to 2.4 (only peaks 
6H's are seen in the starting substance 
5-(2,4-dioxotetrahydro-3-furanyl-methyl)-5-norbornene-2,3-dicarboxylic 
acid anhydride; only peaks 4H's in 5-methylenenorbornane-2,3-dicarboxylic 
acid anhydride; and only peaks 2H's in 1- or 
5-methylnorbornene-2,3-dicarboxylic acid anhydride); and there are seen 
peaks 6H's to be caused by six &lt;CH--'s at 82.0 to 3.6 (only peaks 5H's are 
seen in the starting substance 
5-(2,4-dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-dicarboxylic acid 
anhydride; only peaks 4H's in 5-methylenenorbornane-2,3-dicarboxylic acid 
anhydride and 5-methylnorbornene-2,3-dicarboxylic acid anhydride; and only 
peaks 3H's in 1-methylnorbornene-2,3-dicarboxylic acid anhydride). On the 
other hand, peaks at 85.5 to 5.6 to be caused by .dbd.CH-- in norbornene 
ring moiety (a peak 1H is seen in the starting substance 
5-(2,4-dioxotetrahydro- 3furanylmethyl)-5-norbornene-2,3-dicarboxylic acid 
anhydride and 5-methylnorbornene-2,3-dicarboxylic acid anhydride; peaks 
2H's in 1-methylnorbornene-2,3-dicarboxylic acid anhydride); peaks of 
vinylidene (peaks 2H's are seen in the starting substance 
5-methylenenorbornane-2,3-dicarboxylic acid anhydride); and peaks of 
methyl group (peaks 3H's are seen in the starting substance 1- or 
5-methylnorbornene-2,3-dicarboxylic acid anhydride) are not seen in .sup.1 
H-NMR of the product. 
Next, the present invention will be explained in more detail by way of the 
following examples, which do not whatsoever restrict the scope of the 
present invention.

Unless otherwise specifically indicated, all "%" and "parts" in the 
following examples are by weight. 
EXAMPLE 1 
300 g of endo-methylnorbornene-2,3-dicarboxylic acid anhydride (comprising 
58.5% of 1-methyl form and 41.5% of 5-methyl form) and 0.15 g of 
paratoluenesulfonic acid were introduced into a 500 ml four-neck flask 
equipped with a reflux condenser, a thermometer and a stirrer, and they 
were reacted with stirring at 180.degree. C. for 3 hours. By simple 
distillation of the reaction mixture, 287 g of a pale yellow transparent 
liquid, as separated from the catalyst and heavy by-products, was 
obtained. The composition of the liquid was analyzed by gas 
chromatography, which was clarified to comprise 8.8% of 
endo-5-methylenenorbornane-2,3-dicarboxylic acid anhydride, 63.5% of 
exo-5-methylenenorbornane-2,3-dicarboxylic acid anhydride and 27.7% of the 
non-reacted methylnorbornene-2,3-dicarboxylic acid anhydride. The 
structure of the product was identified by infrared absorption 
spectrography (IR) and .sup.1 H-NMR. For instance, in IR of the product, 
there were seen peaks to be caused by stretching vibration of C.dbd.O of 
the carboxylic acid anhydride moiety at 1770 to 1780 cm.sup.-1 and at 
1850 cm.sup.-1. In .sup.1 H-NMR Of the same, peaks to be caused by H.sub.2 
C.dbd.C&lt; (which were not seen in the starting substance 
methylnorbornene-2,3-dicarboxylic acid anhydride) were seen at .delta.4.8 
to 5.2; peaks 4H's to be caused by --CH.sub.2 -- (these are 2H's in the 
starting substance) were seen at .delta.1.8; and peaks to be caused by 
protons as bonded to the tertiary carbon atoms of the norbornane ring 
moiety were seen at .delta.2.8 to 3.6. No peak to be caused by .dbd.CH-- 
of norbornene ring was seen. 
Next, 270 g of the pale yellow transparent liquid as obtained in the 
above-mentioned process and 294 g of maleic anhydride were put in a 1000 
ml four-neck flask as equipped with a reflux condenser, a thermometer and 
a stirrer, and stirred for 6 hours at 180.degree. C. Next, the reaction 
system was subjected to simple distillation under a reduced pressure of 5 
mmHg until the temperature of the bath became 180.degree. C., whereby the 
non-reacted 5-methylenenorbornane-2,3-dicarboxylic acid anhydride, 
methylnorbornene-2,3-dicarboxylic acid anhydride and maleic anhydride were 
removed. As a result, 126 g of a product was obtained. 
The structure of the compound obtained was identified by infrared 
absorption spectrography (IR) and .sup.1 -NMR. For instance, in IR of the 
compound, peaks to be caused by stretching vibration of C.dbd.O of the 
carboxylic acid anhydride were seen at 1770 to 1780 cm.sup.-1 and at 1850 
cm.sup.-1. In .sup.1 H-NMR of the same, there were seen peaks 6H's to be 
caused by three --CH2--'s at .delta.1.8 to 2.2 (only peaks 2H's were seen 
in the starting substance 1- or 5-methylnorbornene-2,3-dicarboxylic acid 
anhydride; and only peaks 4H's in 5-methylenenorbornane-2,3-dicarboxylic 
acid anhydride); there were seen peaks 5H's to be caused by five &gt;CH--'s 
at .delta.2.8 to 3.6 (only peaks 4H's were seen in the starting substance 
5-methylenenorbornane-2,3-dicarboxylic acid anhydride and 
5-methylnorbornene-2,3-dicarboxylic acid anhydride; and only peaks 3H's in 
1-methylnorbornene- 2,3-dicarboxylic acid anhydride); and were seen a peak 
1H to be caused by .dbd.C--H-- of norbornene ring moiety at .delta.5.5 to 
5.6; while there were seen neither peak or methyl group moiety (peaks 3H's 
to be caused by methyl group moiety were seen in the starting substance 1- 
or 5-methylnorbornene-2,3-dicarboxylic acid anhydride) nor peak to be 
caused by vinylidene group moiety (peaks 2H's to b caused by vinylidene 
group moiety were seen in the starting substance 
5-methylenenorbornane-2,3-dicarboxylic acid anhydride). From these 
results, the product was identified to be 
5-(2,4-dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-dicarboxylic acid 
anhydride. 
120 g of the product obtained by the above-mentioned process, 2.4 g of a 
palladium catalyst (carrying 5 wt. % palladium metal) and 120 g of 
tetrahydrofuran as a solvent were put in a 500 ml-autoclave as equipped 
with a stirrer, and the inside of the autoclave was substituted by 
hydrogen and then heated up to 120.degree. C. under hydrogen pressure of 
80 kg/cm.sup.2 G whereupon the compound in the autoclave was hydrogenated 
for 4 hours with stirring. After completion of reaction, the catalyst was 
removed by filtration under reduced pressure and the residue was then 
gradually heated up to 150.degree. to 170.degree. C. under normal pressure 
(this is because the residue is solidified if not heated) and subjected to 
distillation under normal pressure. After the solvent of tetrahydrofuran 
was completely removed therefrom by distillation under reduced pressure, 
112 g of a product was obtained. 
The results of analysis of the product are shown in Table 1 below. 
TABLE 1 
______________________________________ 
Identification or 
Item Date Theoretical Value 
______________________________________ 
IR 1770 to 1780 cm.sup.-1 
Stretching vibration of 
1850 cm.sup.-1 
C = O in carboxylic 
acid anhydride moiety 
1H-NMR* 1.8 to 2.4 (8H) 
-C .sub.-- H.sub.2 -(8H) 
2.0 to 3.6 (6H) 
&gt;C .sub.-- H-(6H) 
Neutralization Value 
760 803 
lodine Value 2.6 0 
______________________________________ 
*.sub.-- (unit, ppm): The parenthesized value indicates the number of 
protons corresponding to the integrated intensity. 
From the above-mentioned data, the product obtained in the present example 
was identified to be the compound of the present invention being 
5-(2,4-dioxotetrahydro-3furanylmethyl)norbornane-2,3-dicarboxylic acid 
anhydride. The iodine value of the non-hydrogenated compound of 
5-(2,4-dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-dicarboxylic acid 
anhydride was 88.2. Reduction of the iodine value of the hydrogenated 
product to be 2.6 well supports the conclusion. 
USE EXAMPLE 
70 parts of the compound obtained in the previous example 
[5-(2,4-dioxotetrahydro-3-furanylmethyl)norbornane-2,3-dicarboxylic acid 
anhydride] and 100 parts of an epoxy resin (Epikote 828 (trade name), 
product by Yuka Shell Co.) were blended at 140.degree. C. and then cooled 
to 80.degree. C. One part of dimethylbenzylamine was added thereto and 
blended, and the resulting mixture was cast into a casting frame. After 
hardened at 160.degree. C. for 15 hours, the thermal deformation 
temperature of the hardened product was measured in accordance with JIS K 
6911, which was 186.degree. C. 
COMATIVE USE EXAMPLE 1 
50 parts of benzophenonetetracarboxylic acid dianhydride and 100 parts of 
an epoxy resin (Epikote 828 (trade name), product by Yuka Shell Co.) were 
intended to be blended at 140.degree. C. to fail in forming a uniform 
blend. Then, the system was gradually heated with continuously stirring, 
and it gave a uniform layer at a temperature of 170.degree. C. but it soon 
gelled. 
COMATIVE USE EXAMPLE 2 
60 parts of methylcyclohexenetetracarboxylic acid dianhydride (Epikuron 
B-4400 (trade name), product by Dai-Nippon Ink Co.) and 100 parts of an 
epoxy resin (Epikote 828 (trade name), product by Yuka Shell Co.) were 
blended at 140.degree. C. and then cooled to 80.degree. C. One part of 
dimethylbenzylamine was added thereto and blended, and the resulting blend 
was hardened under the same condition as that in Use Example 1 and the 
thermal deformation temperature of the hardened product was measured to be 
169.degree. C. 
Referential Use Example 
70 parts of the intermediate obtained in the previous example 
[5-(2,4-dioxotetrahydro-3-furanylmethyl)-5-norbornene-2,3-dicarboxylic 
acid anhydride] and 100 parts of an epoxy resin (Epikote 828 (trade name), 
product by Yuka Shell Co.) were blended at 120.degree. C. and then cooled 
to 80.degree. C. One part of dimethylbenzylamine was added thereto and 
blended and the resulting blend was cast into a casting frame. After 
hardened for 15 hours at 160.degree. C., the thermal deformation 
temperature of the hardened product was measured to be 176.degree. C. 
From the results of Use Example and Comparative Use Examples 1 and 2, it is 
understood that the compound of the present invention may be blended with 
an epoxy resin and may be processed more easily than the conventional 
epoxy resin hardening agents. In addition, the epoxy resin as hardened 
with the compound of the present invention is noted to have a higher 
thermal deformation temperature than that as hardened with the 
conventional hardening agent. 
Advantage of the Invention 
In accordance with the present invention, there are provided a novel 
compound 
5-(2,4-dioxotetrahydro-3-furanylmethyl)norbornane-2,3-dicarboxylic acid 
anhydride and a method of producing it. The compound has a low melting 
point and has a good workability. In addition, since it is well compatible 
with epoxy resins, it can be used singly as a hardening agent in casting 
of epoxy resins. Moreover, the epoxy resin articles as hardened with the 
compound of the invention have a higher heat resistance than those as 
hardened with any other conventional tetracarboxylic acid dianhydrides 
having a poorer workability. Therefore, the compound of the present 
invention can be used as a hardening agent for epoxy resin sealants for 
electronic parts or electric parts which are to be large scale integration 
circuits and which are desired to have a high heat resistance. In 
addition, the compound of the present invention can also be used as a raw 
material for producing polyimides, polyamides and polyesters and as a raw 
material for a plasticizer for vinyl chloride polymers. The technical 
field to which the compound of the present invention is applied is broad.