Method of producing biphenyltetracarboxylic esters

A biphenyltetracarboxylic tetraester, especially, 3,3',4,4'-biphenyltetracarboxylic tetraalkyl ester, is produced by oxidative coupling an orthophthalic diester, especially, orthophthalic dialkylester, in a molecular oxygen-containing atmosphere in the presence of a catalyst consisting of a mixture of a palladium salt with 1,10-phenanthroline and/or 2,2'-bipyridyl or a chelating reaction product of a palladium salt with 1,10-phenanthroline or 2,2'-bipyridyl.

FIELD OF THE INVENTION 
The present invention relates to a method of producing 
biphenyltetracarboxylic esters. More particularly, the present invention 
relates to a method for producing biphenyltetracarboxylic tetraesters by 
catalytically oxidative coupling an orthophthalic diester. 
BACKGROUND OF THE INVENTION 
It is known that biphenyl compounds can be produced by oxidative coupling 
an aromatic compound in an oxygen-containing atmosphere in the presence of 
a palladium type catalyst by various methods. For example, Japanese patent 
application Publication (Kokoku) No. 48--1054(1973) discloses a method of 
producing a biphenyl compound by dehydrogenation-dimerizing (oxidative 
coupling) a benzene type aromatic compound in an oxygen-containing 
atmosphere in the presence of an organic palladium salt but in the absence 
of reaction medium under an increased pressure. 
Also, it is known that a conventional oxidative coupling method, for 
example, the above-mentioned method, for the aromatic compounds, is 
applied to an orthophthalic ester, the resultant coupling product 
contains, as major components, 2,3,3',4'-biphenyltetracarboxylic 
tetraester (a-BPTT) and 3,3',4,4'-biphenyltetracarboxylic tetraester 
(S-BPTT), and usually, the amount of the a-BPTT is larger than that of the 
S-BPTT. However, the S-BPTT is useful as a material for producing an 
aromatic carboxylic dianhydride which is useful as an intermediate for 
producing an aromatic polyimide resin having excellent tenacity, thermal 
resistance and electric insulating property. Therefore, the S-BPTT is more 
industrially valuable than the a-BPTT. Accordingly, it is desirable to 
provide a new method of oxidative coupling the orthophthalic ester, which 
method is capable of producing the S-BPTT as a main product with a high 
degree of yield thereof and the a-BPTT as a by-product with a very low 
degree of yield thereof. It is preferable that the yield of the S-BPTT be 
as large as possible and the yield of the a-BPTT be as small as possible. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a method of producing 
biphenyltetracarboxylic esters, which method is capable of producing 
3,3',4,4'-biphenyltetracarboxylic tetraester with a high degree of 
selectivity thereto. 
Another object of the present invention is to provide a method of producing 
biphenyltetracarboxylic tetraester, in which method the formation of a 
by-product, for example, 2,3,3',4'-biphenyltetracarboxylic tetraester is 
restricted. 
The above-mentioned objects can be attained by the method of the present 
invention, which comprises oxidative coupling an orthophthalic diester in 
a molecular oxygen-containing atmosphere in the presence of a catalyst 
consisting of at least one member selected from the group consisting of 
(A) mixtures of at least one palladium salt with at least one member 
selected from 1,10-phenanthroline and 2,2'-bipyridyl in a molar amount of 
0.9 to 4 times that of said palladium salt and (B) chelating reaction 
products of at least one palladium salt with at least one member selected 
from 1,10-phenanthroline and 2,2'-bipyridyl. In the method of the present 
invention, the oxidative coupling operation may be carried out by blowing 
a molecular oxygen-containing gas into the oxidative coupling system to 
bring the molecular oxygen into contact with the orthophthalic diester and 
the catalyst. 
The method of the present invention is effective for producing S-BPTT with 
a high degree of selectivity thereto in such a manner that the molar ratio 
of the resultant a-BPTT to the resultant S-BPTT is in a range of from 0.01 
to 0.6 
DETAILED DESCRIPTION OF THE INVENTION 
The method of the present invention is characterized in that the catalyst 
for oxidative coupling the orthophthalic diester consists of at least one 
member selected from (A) mixtures of (a) at least one palladium salt with 
(b) at least one member selected from 1,10-phenanthroline and 
2,2'-bipyridyl in a molar amount of 0.9 to 4 times that of said palladium 
salt and (B) chelating reaction products of (a) at least one palladium 
salt with (b) at least one member selected from 1,10-phenanthroline and 
2,2'-bipyridyl. 
The orthophthalic diester usable for the present invention is preferably 
selected from those of the formula (I): 
##STR1## 
wherein R.sup.1 and R.sup.2 represent, independently from each other, an 
alkyl radical having 1 to 4 carbon atoms, respectively. 
For example, the orthophthalic diester is selected from the group 
consisting of dimethyl o-phthalate, diethyl o-phthalate, dipropyl 
o-phthalate, dibutyl o-phthalate. The orthophthalic diester can be 
produced by reacting a corresponding hydroxy group-containing compound 
with orthophthalic acid or its anhydride. 
The palladium salt usable for the method of the present invention can be 
selected from the group consisting of palladium salts of organic 
carboxylic acids, palladium chelate salts of .beta.-diketone compounds, 
and palladium salts of inorganic acids. The palladium salt is usually 
selected from the group consisting of palladium salts of aliphatic 
carboxylic acids having 1 to 5 carbon atoms, for example, palladium 
formate, palladium acetate, palladium propionate, palladium butylate, and 
palladium valerate; palladium salts of aromatic carboxylic acids, for 
example, palladium benzoate, palladium terephthalate; palladium chelate 
salts, for example, of acetylacetone, benzoylacetone and 
trifluoroacetylacetone, and; inorganic palladium salts, for example, 
palladium nitrate, palladium nitrite and palladium sulfate. Also, the 
palladium salt usable for the present invention may be in the form of a 
complex salt, for example, palladium nitrate acetate 
[Pd(NO.sub.3)(O.COCH.sub.3)]. The preferable palladium salts for the 
present invention are palladium salts of aliphatic monocarboxylic acids 
having 1 to 3 carbon atoms, more preferably, palladium acetate. 
When the catalyst for the method of the present invention consists of a 
mixture of at least one palladium salt and at least one member selected 
from 1,10-phenanthroline and 2,2'-bipyridyl, the total molar amount of 
1,10-phenanthroline and/or 2,2'-bipyridyl is in a range of from 0.9 to 4 
times, preferably, from 0.95 to 3 times, that of the palladium salt. 
A total molar amount of 1,10-phenanthroline and/or 2,2'-dipyridyl less than 
0.9 times that of the palladium salt, sometimes results in an oxidative 
coupling reaction which exhibits a poor selectivity to the S-BPTT. 
Therefore, the resultant product contains the S-BPTT in a smaller amount 
that of the a-BPTT. Also, a total molar amount of 1,10-phenanthroline 
and/or 2,2'-bipyridyl more than 4 times that of the palladium salt, 
results in a decreased yield of the resultant biphenyltetracarboxylic 
esters. 
The catalyst of the method of the present invention may consist of a 
chelating reaction product of at least one palladium salt with at least 
one member selected from 1,10-phenonthroline and 2,2'-dipyridyl. The 
chelating reaction product can be prepared in such a manner that the 
palladium salt is mixed with 1,10-phenanthroline and/or 2,2'-bipyridyl by 
dissolving them in an organic solvent, for example, benzene, xylene, 
acetone, methylene dichloride or chlorobenzene, the solution is stirred at 
room temperature for a period of time between one half and ten hours to 
complete the chelating reaction, and then, the resultant product is 
isolated from the reaction mixture by removing the organic solvent. 
In the chelating reaction, it is preferable that the molar ratio of the 
palladium salt to the sum of 1,10-phenanthroline and/or 2,2'-bipyridine be 
in a range of from 1:0.9 to 1:2.5. Also, it is preferable that the 
palladium salt to be subjected to the chelating reaction be selected from 
palladium salts of aliphatic mono-carboxylic acids having 1 to 5 carbon 
atoms and palladium nitrate. The palladium chelate salt is composed of one 
palladium atom and one or two 1,10-phenanthroline or 2,2'-bipyridyl 
molecules. 
In the method of the present invention, the catalyst is preferably used in 
an atomic number of palladium of from 0.0001 to 0.1, more preferably, from 
0.002 to 0.01, per molecule of the orthophthalic diester. 
The oxidative coupling reaction in the method of the present invention may 
be carried out in the presence of at least one organic copper salt. The 
organic copper salt is effective for preventing the palladium from being 
deposited in the form of palladium black from the oxidative coupling 
reaction mixture, even when the molecular oxygen-containing atmosphere has 
a low partial pressure of oxygen. Therefore, in the case where the partial 
pressure of oxygen in the oxidative coupling reaction system is low, the 
organic copper salt is effective for stabilizing the oxidative coupling 
reaction. 
The organic copper salt is preferably selected from the group consisting of 
copper salts of aliphatic carboxylic acids having 1 to 5 carbon atoms, for 
instance, copper formate, copper acetate, copper propionate, and copper 
oxalate, and; copper chelate salts of .beta.-diketones, for example, 
acetylacetone and benzoylacetone. Usually, the organic copper salt is used 
in a molar amount of from 0.5 to 10 times that of the palladium salt or 
the palladium chelate salt. 
In the method of the present invention, the oxidative coupling reaction is 
preferably carried out at a temperature of from 50.degree. to 300.degree. 
C., more preferably, from 100.degree. to 230.degree. C., under a pressure 
of from 1 to 300 atmospheres, more preferably, from 2 to 100 atmospheres. 
When the oxidative coupling reaction temperature is lower than 50.degree. 
C., sometimes, the oxidative coupling reaction occurs to a very poor 
extent. Also, an oxidative coupling reaction temperature higher than 
300.degree. C. sometimes causes undesirable side-reactions to vigorously 
occur and the yield of the desired biphenyl compounds to become remarkably 
poor. 
The oxidative coupling operation in the method of the present invention is 
carried out in an atmosphere containing molecular oxygen gas. The 
oxygen-containing atmosphere may consist of pure oxygen gas. However, in 
order to prevent dangerous accidents, for example, an explosion, it is 
preferable that the oxygen-containing atmosphere consist of a mixture gas 
containing a molecular oxygen gas and an inert gas, for instance, nitrogen 
gas and carbon dioxide gas. 
It is preferable that the molecular oxygen-containing atmosphere have a 
partial pressure of oxygen of from 0.05 to 200 atmospheres, more 
preferably, from 0.1 to 50 atmospheres. When no organic copper salt is 
contained in the oxidative coupling reaction system, it is preferable that 
the partial pressure of oxygen in the system be at least 2 atmospheres, 
more preferably, 3 or more atmospheres, and still more preferably, from 5 
to 100 atmospheres. 
In the method of the present invention, the oxidative coupling mixture must 
not contain a large amount of certain kinds of organic compounds, for 
example, dimethylsulfoxide, dimethylformamide, acetonitrile and acetic 
acid, and inorganic compounds, for example, water. However, it is 
allowable for the reaction mixture to contain a large amount of a reaction 
medium consisting of at least one member selected from the group 
consisting of liquid organic acid esters, for instance, ethylene glycol 
diacetate and methyl adipate, and; liquid ketone compounds, for instance, 
n-butylmethylketone, ethylmethylketone and isopropylethylketone. When the 
organic acid ester and/or the ketone compounds are used as a reaction 
medium, sometimes the yield of the biphenyl compounds is increased. 
However, use of the above-mentioned reaction medium can be dispensed with. 
Also, in the method of the present invention, it is not suitable for the 
oxidative coupling reaction for the reaction mixture to contain certain 
kinds of inorganic compounds, for example, sodium acetate, lithium 
chloride, potassium sulfide and sulfuric acid, even in a small amount. 
However, it is allowable for the reaction mixture to contain a 
.beta.-diketone compounds, for instance, acetylacetone and benzoylacetone, 
and an organic peroxide compound, for instance, t-butyl peroxide, 
t-butylhydroxyperoxide and t-butylbenzoate. The above-mentioned -diketone 
and organic peroxide compounds are effective for promoting the 
oxidation-coupling reaction of the orthophthalic diester. Usually, the 
.beta.-diketone compound is preferably used in a molar amount of 0.5 to 10 
times, more preferably, from 0.5 to 4 times, that of the palladium salt or 
chelate salt. Also, it is preferable that the organic peroxide compound be 
used in a molar amount of from 2 to 10 times that of the palladium salt or 
chelate salt. 
In the method of the present invention, the oxidative coupling operation 
may be carried out by blowing a molecular oxygen-containing gas into the 
oxidative coupling system to bring the molecular oxygen into contact with 
the orthophthalic diester and the catalyst. The molecular 
oxygen-containing gas may consist of pure oxygen alone. However, the 
molecular oxygen-containing gas may consist of at least 0.1% by volume, 
preferably, from 0.1 to 90% by volume, more preferably, from 1 to 80% by 
volume, of oxygen gas and the balance consist of an inert gas such as 
nitrogen gas and carbon dioxide. Also, in order to prevent dangerous 
accidents, for example, an explosion of the oxidative coupling system, it 
is preferable that the molecular oxygen-containing gas consist of from 0.5 
to 60% by volume, more preferably, from 0.5 to 25% by volume, still more 
preferably, from 1 to 20% by volume, of oxygen gas and the balance consist 
of the inert gas. The molecular oxygen-containing gas may be natural air 
or a mixture of air with the inert gas or oxygen gas. 
The molecular oxygen-containing gas may be blown into the oxidative 
coupling reaction system in any manner as long as the oxygen is 
effectively brought into contact with the orthophthalic diester and the 
catalyst in the reaction mixture. For example, the molecular 
oxygen-containing gas flows along and/or toward the surface of the 
reaction mixture contained in a vessel. Otherwise, the molecular 
oxygen-containing gas is blown into the reaction mixture through one or 
more blowing nozzles or a perforated plate located below the surface of 
the reaction mixture contained in a vessel. When the reaction mixture 
flows through a reaction tube, the molecular oxygen-containing gas may be 
blown into the reaction tube through at least one hole formed on the 
peripheral wall of the reaction tube. Otherwise, the molecular 
oxygen-containing gas may flow coccurrently with the reaction mixture 
through the reaction tube. 
When the molecular oxygen-containing gas is blown into the reaction 
mixture, the molecular oxygen-containing gas is mixed in the form of a 
number of bubbles with the reaction mixture. This type of mixing is most 
effective for promoting the contact of the oxygen gas with the 
orthophthalic diester and the catalyst in the reaction mixture. It is 
preferable that the flow rate of the molecular oxygen-containing gas be in 
a range of from 1 to 20 liters (under a standard condition, that is, at a 
temperature of 25.degree. C. and a pressure of 1 atmosphere) per minute 
per liter of the reaction mixture. The blowing of the molecular 
oxygen-containing gas into the oxidative coupling system is advantageous 
in that the depositing of palladium as a palladium black from the reaction 
mixture can be prevented even if the partial pressure of oxygen is 5 
atmospheres or less. That is, by blowing the molecular oxygen-containing 
gas into the oxidative coupling reaction system, it becomes possible to 
restrict the production of undesirable by-products and to increase the 
yield of the desired S-BPTT, even under a partial pressure of oxygen of 
from 0.1 to 5 atmospheres. 
The method of the present invention is advantageous in that the 
orthophthalic diester can be converted into biphenyltetracarboxylic 
tetraesters with a high degree of conversion thereof and the desired 
S-BPTT can be produced with a high degree of selectivity thereto. That is, 
the oxidative coupling product from the method of the present invention 
contains 3,3',4,4'-biphenyltetracarboxylic tetraester (S-BPTT) and 
2,3,3',4'-biphenyltetracarboxylic tetraester (a-BPTT), which is in a molar 
amount of 0.6 times or less, usually, from 0.01 to 0.5 times, that of the 
3,3',4,4'-biphenyltetracarboxylic tetraester (S-BPTT). 
After the oxidative coupling reaction is completed, palladium in the 
reaction mixture is preferably recovered by any conventional method. For 
example, hydrogen gas is blown into the reaction mixture to reduce the 
palladium compound into metallic palladium, while allowing the resultant 
metallic palladium to precipitate from the reaction mixture. The 
precipitate of the metallic palladium can be easily separated from the 
reaction mixture. In another method, a reducing agent, for example, sodium 
hydrogen carbonate, is added to the reaction mixture to precipitate 
metallic palladium. The precipitate of metallic palladium can be recovered 
from the reaction mixture by means of filtration. 
Thereafter, the desired 3,3',4,4'-biphenyltetracarboxylic tetraester can be 
isolated from the reaction mixture by a conventional method, for example, 
distillation or crystallization. 
The 3,3',4,4'-biphenyltetracarboxylic tetraester produced by the 
above-mentioned method can be converted to 
3,3',4,4'-biphenyltetracarboxylic acid by a conventional method, for 
example, by hydrolyzing it at an elevated temperature under an increased 
pressure, or by hydrolyzing it with an acid or alkali. The 
3,3'4,4'-biphenyltetracarboxylic acid can be converted to 
3,3',4,4'-biphenyl tetracarboxylic dianhydride by heating. The 
3,3',4,4'-biphenyltetracarboxylic dianhydride is useful as a material for 
producing an aromatic polyimide resin. 
The specific examples presented below will serve to more fully explain how 
the present invention is practiced. However, it will be understood that 
these examples are only illustrative and in no way limit the scope of the 
present invention. 
In the examples, the composition of reaction mixture was determined by 
means of gas chromatography. From the result of the gas chromatographic 
analysis, the amounts of 2,3,3',4'-biphenyltetracarboxylic tetraester 
(a-BPTT) and 3,3',4,4'-biphenyltetracarboxylic tetraester (S-BPTT) and 
by-products (pitch-like substance having a high boiling point) were 
calculated. 
A percent of conversion of an orthophthalic diester, a percent of yield of 
a product and a percent of selectivity to a product were calculated in 
accordance with the following equation. 
##EQU1##

EXAMPLE 1 
A stainless steel autoclave having a capacity of 270 ml was charged with 
425 millipoles (70 ml) of dimethyl orthophthalate and, then, with 0.42 
millimoles (0.094 g) of palladium acetate [Pd (O.CO.CH.sub.3).sub.2 ] and 
0.42 millimoles (0.083 g) of 1,10-phenanthroline monohydrate, and then, 
closed. The pressure in the inside of the autoclave was increased to 50 
atmospheres by blowing compressed air thereinto and the temperature of the 
reaction system in the autoclave was elevated to 200.degree. C., and then, 
maintained at this level for five hours to carry out an oxidative coupling 
operation for the dimethyl orthophthalate. At the begining of the 
oxidative coupling operation, the partial pressure of oxygen in the 
reaction system was 10 atmospheres. 
After the oxidative coupling reaction was completed the resultant reaction 
mixture was subjected to a gas chromatographic analysis. As a result of 
the analysis, it was found that the reaction product contained 0.238 g of 
2,3,3',4'-biphenyltetracarboxylic tetramethylester, which corresponded to 
a yield of 147% based on the palladium used, and; 2.335 g of 
3,3',4,4'-biphenyltetracarboxylic tetramethylester, which corresponded to 
a yield of 1440% based on palladium used. The molar ratio of the resultant 
a-BPTT to the resultant S-BPTT was 0.10:1. 
In order to recover palladium, hydrogen gas was blown into the reaction 
mixture at a temperature of 200.degree. C., under a pressure of 5 
atmospheres on the gauge, for two hours, while allowing the resultant 
metallic palladium to precipitate from the reaction mixture, and then, the 
precipitated metallic palladium was removed from the reaction mixture by 
means of filtration. The amount of the recovered metallic palladium 
corresponded to about 95% of the amount of palladium contained in the 
reaction mixture. After the recovery of the metallic palladium, it was 
found that the content of palladium in the residual reaction mixture was 
2.9 ppm or less. 
The residual reaction mixture was subjected to a distillation to remove 
non-reacted dimethyl orthophthalate at a temperature of 110.degree. C. 
under a pressure of 2 mmHg, and, then, to recover 
3,3',4,4'-biphenyltetracarboxylic tetramethyl ester at a temperature of 
140.degree. to 270.degree. C. under a pressure of 2 mmHg. Thereafter, the 
resultant fraction containing 3,3',4,4'-biphenyltetracarboxylic 
tetramethylester was subjected to a recrystallizing operation by using 
methyl alcohol. The recrystallized 3,3',4,4'-biphenyltetracarboxylic 
tetramethylester having degree of purity of 98% or more, was obtained in 
an recovery yield of 80% or more. 
EXAMPLE 2 
A solution of 1.01 g of 1,10-phenanthroline in 100 ml of benzene was mixed 
with another solution of 1.12 g of palladium acetate [Pd 
(O.CO.CH.sub.3).sub.2 ] in 100 ml of benzene, and the mixed solution was 
stirred for one hour, while allowing the resultant chelate salt to 
precipitate from the mixed solution. The precipitated chelate salt was 
separated from the mixed solution by means of filtration, washed with 100 
ml of benzene and, then, dried within a temperature range of from 
80.degree. to 90.degree. C., under a reduced pressure, for five hours. 
1.84 g of the chelate salt were obtained. 
An elementary analysis of the chelate salt showed carbon: 47.33%, hydrogen: 
3.34%, nitrogen: 6.80% and palladium: 26.05%. 
The same procedures as those described in Example 1 were carried out, 
except that 0.42 millimoles (0.170 g) of the above-mentioned chelate salt 
were used as a catalyst, in place of the mixture of 1,10-phenanthroline 
and palladium acetate. The resultant product contained 0.280 g of 
2,3,3',4'-biphenyltetracarboxylic tetramethylester (a-type compound) which 
corresponded to a yield of 173% based on palladium used, and 2.101 g of 
3,3',4,4'-biphenyltetracarboxylic tetramethylester (S-type compound), 
which corresponded to a yield of 1300% based on palladium used. The molar 
ratio of the a-type compound to the S-type compound was 0.13:1. 
Comparison Example 1 
The same procedures as those described in Example 1 were carried out, 
except that no 1,10-phenanthroline was used. 
The resultant reaction product contained 0.717 g of the a-type compound (a 
yield of 44.2% based on palladium used) and 0.151 g of the S-type compound 
(a yield of 93% based on palladium used). The molar ratio of the a-type 
compound to the S-type compound was 4.75:1. 
EXAMPLE 3 
The same procedures as those described in Example 1 were carried out, 
except that the oxidative coupling reaction temperature was changed from 
200.degree. C. to 180.degree. C. 
The reaction product contained 0.053 g of the a-type compound (a yield of 
33% based on palladium used) and 1.067 g of the S-type compound (a yield 
of 658% based on palladium used). The molar ratio of the a-type compound 
to the S-type compound was 0.050:1. 
EXAMPLE 4 
The same procedures as those described in Example 1 were carried out, 
except that the 1,10-phenanthroline was replaced by 0.42 millimoles (0.066 
g) of 2,2'-bipyridyl, and after elevating the temperature of the reaction 
mixture to 200.degree. C., the oxidative coupling reaction was carried out 
at this temperature for two hours. The reaction products contained 0.181 g 
of the a-type compound (a yield of 112% based on palladium used), and 
1.176 g of the S-type compound (a yield of 725% based on palladium used). 
The molar ratio of the a-type compound to the S-type compound was 0.15:1. 
Example 5 
The same procedures as those described in Example 4 were carried out, 
except that the oxidative coupling reaction was carried out at a 
temperature of 180.degree. C. for five hours. The reaction product 
contained 0.110 g of the a-type compound (a yield of 68% based on 
palladium used) and 1.097 g of the S-type compound (a yield of 677% based 
on palladium used). The molar ratio of the a-type compound to the S-type 
compound was 0.10:1. 
EXAMPLE 6 
The same chelate salt-producing procedures as those described in Example 2 
were carried out, except that 1,10-phenanthroline was replaced by 
2,2'-bipyridyl. The same oxidation-coupling procedures as those described 
in Example 5 were carried out, except that the catalyst consisting of the 
mixture of palladium acetate and 2,2'-bipyridyl was replaced by a catalyst 
consisting of the above-mentioned chelate salt. The reaction product 
contained 0.224 g of the a-type compound (a yield of 138% based on 
palladium used) and 1.441 g of the S-type compound (a yield of 889% based 
on palladium used). The molar ratio of the a-type compound to the S-type 
compound was 0.16:1. 
EXAMPLE 7 
A three-necked glass flask having a capacity of 300 ml was charged with 608 
millimole (100 ml) of dimethyl orthophthalate and, then, with 1.20 
millimoles (0.269 g) of palladium acetate [Pd (O.CO.CH.sub.3).sub.2 ], 1.2 
millimoles (0.240 g) of copper acetate monohydrate [Cu 
(O.CO.CH.sub.3).sub.2.H.sub.2 O] and 1.2 millimole (0.238 g) of 
1,10-phenanthroline, to prepare a reaction mixture. The reaction mixture 
was heated at a temperature of 140.degree. C. by placing the flask on an 
oil bath, and bubbled by air blown thereinto at a flow rate of 300 ml 
(which was a value under one atmosphere at a temperature of 25.degree. C.) 
per minute, for seven hours. The reaction product contained 0.17 g of the 
a-type compound (a yield of 37% based on palladium used) and 2.19 g of the 
S-type compound (a yield of 473% based on palladium used). The molar ratio 
of the a-type compound to the S-type compound was 0.08:1. 
EXAMPLE 8 
The same procedures as those described in Example 7 were carried out, 
except that the same chelate salt as that described in Example 2 was used 
as a catalyst in place of the catalyst consisting of palladium acetate and 
1,10-phenanthroline. The reaction product contained 0.19 g of the a-type 
compound (a yield of 41% based on palladium used) and 2.25 g of the S-type 
compound (a yield of 486% based on palladium used). The molar ratio of the 
a-type compound to the S-type compound was 0.08:1. 
EXAMPLE 9 
The same procedures as those described in Example 7 were carried out, 
except that 1,10-phenanthroline was replaced by 2,2'-bipyridyl. The 
reaction product contained 0.31 g of the a-type compound (a yield of 67% 
based on palladium used) and 2.04 g of the S-type compound (a yield of 
440% based on palladium used). The molar ratio of the a-type compound to 
the S-type compound was 0.15:1. 
EXAMPLE 10 
The same procedures as those described in Example 9 were carried out, 
except that the same chelate salt as that described in Example 6 was used 
as a catalyst in place of the mixture of palladium acetate and 
2,2'-bipyridyl. 
The reaction product contained 0.30 g of the a-type compound (a yield of 
65% based on palladium used) and 1.88 g of the S-type compound (a yield of 
406% based on palladium used). The molar ratio of the a-type compound to 
the S-type compound was 0.16:1. 
EXAMPLE 11 
The same procedures as those described in Example 7 were carried out, 
except that the oxidative coupling temperature was changed from 
140.degree. C. to 160.degree. C. The reaction product contained 0.24 g of 
the a-type compound (a yield of 52% based on palladium used) and 2.58 g of 
the S-type compound (a yield of 557% based on palladium used). The molar 
ratio of the a-type compound to the S-type compound was 0.10:1. 
EXAMPLE 12 
The same procedures as those described in Example 1 were carried out, 
except that 1,10-phenanthroline was used in an amount of 0.378 millimoles 
(0.075 g). The resultant product contained 0.89 g of the a-type compound 
(a yield of 549% based on palladium used) and 1.51 g of the S-type 
compound (a yield of 931% based on palladium used). The molar ratio of the 
a-type compound to the S-type compound was 0.59:1. 
COMISON EXAMPLE 2 
The same procedures as those described in Example 3 were carried out, 
except that 1,10-phenanthroline was used in an amount of 0.21 millimoles 
(0.042 g). The resultant product contained 5.407 g of the a-type compound 
(a yield of 3340% based on palladium used) and 1.282 g of the S-type 
compound (a yield of 791% based on palladium used). The molar ratio of the 
a-type compound to the S-type compound was 4.23:1. 
COMISON EXAMPLE 3 
The same procedures as those mentioned in Comparison Example 2 were carried 
out, except that 2,2'-bipyridyl was used instead of 1,10-phenanthroline. 
The reaction product contained 5.38 g of the a-type compound (a yield of 
3320% based on palladium used) and 1.51 g of the S-compound (a yield of 
931% based on palladium used). The molar ratio of the a-type compound to 
the S-type compound was 3.56:1. 
EXAMPLES 13 THROUGH 23 AND COMISON EXAMPLE 4 
In each of Examples 13 through 23, a stainless steel reaction vessel having 
a capacity of 500 ml was charged with 295 g (250 ml, 1.52 moles) of 
dimethyl orthophthalate, and then, with palladium acetate [Pd 
(O.CO.CH.sub.3).sub.2 ] and 1,10-phenanthroline monohydrate, each in an 
amount as indicated in Table 1, to prepare a reaction mixture. The 
reaction mixture was heated to a temperature as indicated in Table 1, and 
compressed air was blown into the heated reaction mixture through the 
bottom of the reaction vessel for seven hours, while maintaining the 
reaction pressure, the partial pressure of oxygen, the supply rate of the 
compressed air and the reaction temperature at values as indicated in 
Table 1, and while stirring the reaction mixture by rotating stirring 
paddles at a rotation velocity of 300 r.p.m. 
After the above-mentioned oxidative coupling operation was completed, the 
reaction mixture was subjected to a gas chromatographic analysis. As a 
result of the analysis, it was found that the percents of yield of and 
selectivity to the resultant a-type compound, S-type compound and 
by-product having a high boiling point were as indicated in Table 1. Table 
1 also shows the percent of conversion of dimethyl orthophthalate in each 
example. 
In Comparison Example 4, the same procedures as those described in Example 
13 were carried out, except that no 1,10-phenanthroline was used. 
The results are shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Comparison 
Example No. Example 
Item 13 14 15 16 17 18 19 20 21 22 23 4 
__________________________________________________________________________ 
Oxidation-coupling reaction 
Amount of palladium acetate (m mol) 
3.00 
3.00 
3.00 
3.00 
3.00 
3.00 
6.00 
3.00 
3.00 
3.00 
1.50 
3.00 
Amount of 1,10-phenanthroline (m mol) 
2.25 
3.00 
3.75 
4.50 
3.00 
3.00 
6.00 
3.00 
3.00 
3.00 
1.50 
0 
Reaction pressure on the gauge (atm) 
5 5 5 5 10 20 5 5 5 10 10 5 
Partial pressure of oxygen (atm) 
1.2 
1.2 
1.2 
1.2 
2.2 
4.2 
1.2 
1.2 
1.2 
2.2 
2.2 
1.2 
Supply rate.sup.(*)1 of air (.sup.l /min.) 
1 1 1 1 2 3 2 1 1 2 2 1 
Reaction temperature (.degree.C.) 
200 
200 
200 
200 
200 
200 
200 
180 
160 
180 
180 
200 
Conversion of DMP.sup.(*)2 (%) 
6.20 
8.61 
8.74 
4.45 
8.98 
8.90 
14.06 
5.51 
3.60 
5.40 
4.03 
3.37 
Yield and selectivity of product 
a-type.sup.(*)3 
compound 
Yield (%) 
0.4 
0.4 
0.1 
0.1 
0.6 
0.7 
0.7 
0.3 
0.2 
0.2 
0.2 
0.6 
Selectivity 
(%) 
6 5 1 2 6 8 5 5 4 4 5 17 
S-type.sup.(*)4 
compound 
Yield (%) 
5.2 
7.6 
7.6 
3.5 
7.3 
6.1 
11.1 
4.5 
2.6 
4.2 
3.5 
0.3 
Selectivity 
(%) 
84 
88 87 80 82 68 79 82 73 79 87 8 
By-product Yield (%) 
0.6 
0.7 
1.0 
0.8 
1.1 
2.1 
2.3 
0.7 
0.8 
0.9 
0.3 
2.5 
Selectivity 
(%) 
10 
7 11 18 12 24 16 13 23 17 8 75 
__________________________________________________________________________ 
Note 
.sup.(*) This value is under one atmosphere at a temperature of 25.degree 
C. 
.sup.(*)2 Dimethyl orthophthalate 
.sup.(*)3 2,3,3',4biphenyltetracarboxylic tetramethylester 
.sup.(*)4 3,3',4,4biphenyltetracarboxylic tetramethylester 
EXAMPLE 24 THROUGH 28 
In Example 24, the same procedures as those described in Example 22, were 
carried out, except that 2,2'-bipyridyl was used in place of 
1,10-phenanthroline. 
In Example 25, the same procedures as those described in Example 24 were 
carried out, except that 2,2'-bipyridyl was used in an amount of 3.75 
millimoles. 
In Example 26, the same procedures as those described in Example 14 were 
carried out, except that 1,10-phenanthroline was replaced by 
2,2'-bipyridyl. 
In Example 27, the same procedures as those described in Example 24 were 
carried out, except that the reaction pressure was changed to 5 
atmospheres and the supply rate of air was changed to 1 liter/min. 
In Example 28, the same procedures as those mentioned in Example 24 were 
carried out, except that the reaction temperature was changed to 
200.degree. C. 
The results of Examples 24 through 28 are indicated in Table 2. 
TABLE 2 
__________________________________________________________________________ 
Example No. 
Item 24 25 26 27 28 
__________________________________________________________________________ 
Oxidation-coupling reaction 
Amount of palladium acetate (m mol) 
3.00 
3.00 
3.00 
3.00 
3.00 
Amount of 2,2'-bipyridyl (m mol) 
3.00 
3.75 
3.00 
3.00 
3.00 
Reaction pressure on the gauge (atm) 
10 10 5 5 10 
Partial pressure of oxygen (atm) 
2.2 2.2 1.2 1.2 
2.2 
Supply rate of air (l/min.) 
2 2 1 1 2 
Reaction temperature (.degree.C.) 
180 180 200 180 
200 
Conversion of DMP (%) 
6.44 
6.08 
6.10 
6.50 
6.25 
Yield and selectivity of product 
a-type compound 
Yield (%) 
0.5 0.4 0.5 0.5 
0.6 
Selectivity 
(%) 
7 7 8 7 9 
S-type compound 
Yield (%) 
5.7 5.4 4.8 5.7 
4.9 
Selectivity 
(%) 
88 89 79 88 79 
By-product 
Yield (%) 
0.3 0.3 0.8 0.3 
0.8 
Selectivity 
(%) 
5 4 13 5 12 
__________________________________________________________________________ 
EXAMPLE 29 
A palladium chelate salt was prepared by the following procedures. A 
solution of 1.01 g of 1,10-phenanthroline monohydrate dissolved in 100 ml 
of benzene was mixed with another solution of 1.12 g of palladium acetate 
[Pd (O.CO.CH.sub.3).sub.2 ] dissolved in 100 ml of benzene. The mixed 
solution was stirred at a temperature of 25.degree. C. for one hour. The 
resultant precipitate was separated from the mixed solution by means of 
filtration, washed with 100 ml of benzene and, finally, dried at a 
temperature of from 80.degree. to 90.degree. C., under a reduced pressure, 
for five hours. The amount of the palladium chelate salt was 1.84 g. An 
elementary analysis of the palladium chelate showed 47.33% of carbon, 
3.34% of hydrogen, 6.80% of nitrogen and 26.05% of palladium. The same 
oxidative coupling procedures as those described in Example 13 were 
carried out, except that 3.00 millimoles (1.214 g) of the above-described 
palladium chelate salt were used as a catalyst instead of the mixture of 
palladium acetate and 1,10-phenanthroline, and the reaction was continued 
for ten hours. 
The degree of conversion of dimethyl orthophthalate was 7.81%, the yield of 
and the selectivity to the resultant a-type compound were 0.4% and 5%, 
respectively, the yield of and the selectivity to the resultant S-type 
compound were 6.9% and 88%, respectively, and yield of and the selectivity 
to the by-product having a high boiling point, were 0.5% and 7%, 
respectively. 
EXAMPLE 30 
A mixture of 3.00 millimoles of palladium acetate, and 3.00 millimoles of 
1,10-phenanthroline with 250 ml of dimethyl orthophthalate was stirred at 
a temperature of 80.degree. C. for 15 minutes. A solution of the resultant 
palladium chelate salt dissolved in dimethyl orthophthalate was obtained. 
The obtained solution was placed in the same reaction vessel as that 
described in Example 13, the oxidation-coupling operation was carried out 
at a temperature of 180.degree. C., under a pressure of 5 atmospheres (a 
partial pressure of oxygen of 1.2 atmosphere), for seven hours, while 
stirring the solution by rotating stirring paddles at a rotating speed of 
300 r.p.m. and while blowing air into the reaction vessel at a supply rate 
of 1 liter/min. through the bottom of the reaction vessel. 
The degree of conversion of dimethyl orthophthalate was 6.39%, the yield of 
and the selectivity to the resultant a-type compound were 0.3% and 5%, 
respectively, the yield of and the selectivity to the resultant S-type 
compound were 5.2% and 81%, respectively, and the yield of and the 
selectivity to the by-product having a high boiling point were 0.9% and 
14%, respectively. 
EXAMPLES 31 THROUGH 35 
In the Examples 31 through 34, the same procedures as those mentioned in 
Example 22 were carried out, except that a mixed gas consisting of 
nitrogen and oxygen in a composition as indicated in Table 3 was used as a 
molecular oxygen-containing gas, and the reaction pressure, the partial 
pressure of oxygen and the reaction temperature were those indicated in 
Table 3. 
In Example 35, a palladium chelate salt was prepared by stirring a mixture 
of a solution of 0.80 g of 2,2'--bipyridyl dissolved in 100 ml of benzene 
with another solution of 1.12 g of palladium acetate dissolved in 100 ml 
of benzene, at a temperature of 25.degree. C. for about one hour. The 
resultant precipitate was separated from the mixture by means of 
filtration, washed with 100 ml of benzene and, then, dried. The amount of 
the resultant palladium chelate salt was 1.70 g. The same 
oxidation-coupling procedures as those described in Example 31 were 
carried out, except that 1.5 millimoles (0.517 g) of the obtained 
palladium chelate salt were used as a catalyst instead of the mixture of 
palladium acetate and 1,10-phenanthroline. 
The results of Examples 31 through 35 are indicated in Table 3. 
TABLE 3 
__________________________________________________________________________ 
Example No. 
Item 31 32 33 34 35 
__________________________________________________________________________ 
Oxidation-coupling reaction 
Reaction pressure on the gauge (atm) 
10 5 5 5 10 
Partial pressure of oxygen (atm) 
1.1 0.55 
0.55 
0.30 
1.1 
Content of oxygen 10 10 10 5 10 
Molecular oxygen-(% by volume) 
containing gas Supply rate (l/min) 
2 2 0.5 2 2 
Reaction temperature (.degree.C.) 
180 180 180 180 
180 
Degree of conversion of DMP (%) 
4.83 
4.94 
4.71 
5.67 
3.92 
Yield of and selectivity to product 
a-type compound 
Yield (%) 
0.2 0.2 0.2 0.3 
0.3 
Selectivity 
(%) 
4 4 5 5 8 
S-type compound 
Yield (%) 
3.8 3.9 3.9 4.8 
3.4 
Selectivity 
(%) 
79 78 82 84 88 
By-product 
Yield (%) 
0.8 0.9 0.6 0.7 
0.2 
Selectivity 
(%) 
17 18 13 12 4 
__________________________________________________________________________ 
EXAMPLES 36 THROUGH 42 
In Example 36, the same procedure as those described in Example 1 were 
carried out, excpet that 0.128 g of bis-acetylacetonatopalladium were used 
instead of palladium acetate. 
In Example 37, a stainless steel reaction vessel having a capacity of 100 
ml was charged with 59 g (50 ml, 0.304 millimoles) of dimethyl 
orthophthalate and 0.6 millimoles of a chelate salt consisting of one 
molecule of palladium orthophthalate and one molecule of 
1,10-phenanthroline. The reaction mixture was subjected to an 
oxidation-coupling reaction at a temperature of 180.degree. C., under a 
pressure of 10 atmospheres on the gauge, for seven hours, while blowing a 
mixture gas of 10% by volume of oxygen and 90% by volume of nitrogen at a 
supply rate of 0.4 liter/min. through the bottom of the reaction vessel, 
and while stirring the reaction mixture with stirring paddles at a 
rotation speed of 300 r.p.m. 
In Example 38, a stainless steel reaction vessel having a capacity of 500 
ml was charged with 0.3 millimoles of a chelate salt consisting of one 
molecule of palladium orthophthalate and one molecule of 2,2'-bipyridyl. 
The thus prepared reaction mixture was subjected to an oxidation-coupling 
reaction at a temperature of 200.degree. C., under a pressure of 10 
atmospheres on the gauge, for seven hours, while blowing a mixture gas 
consisting of 90% by volume of nitrogen and 10% by volume of oxygen at a 
supply rate of 0.5 liter/min. through the bottom of the vessel, and while 
stirring the reaction mixture with stirring paddles at a rotation speed of 
1000 r.p.m. 
In each of the Examples 39 through 42, the same procedures as those 
described in Example 38 were carried out, except that the palladium 
chelate salt consisted of one molecule of palladium nitrate and two 
molecules of 2,2'-bipyridyl in Example 39, one molecule of palladium 
nitrate and two molecules of 1,10-phenanthroline in Example 40, one 
molecule of palladium nitrate and one molecule of 2,2'-bipyridyl in 
Example 41 and one molecule of nitrate-acetatepalladium and one molecule 
of 2,2'-bipyridyl in Example 42. 
The results of Examples 36 through 42 are indicated in Table 4. 
TABLE 4 
__________________________________________________________________________ 
a-type S-type By-product 
compound 
compound 
compound 
Percent of 
Selec- Selec- Selec- 
Example conversion 
Yield 
tivity 
Yield 
tivity 
Yield 
tivity 
No. Type of Catalyst 
of DMP 
(%) (%) (%) (%) (%) (%) 
__________________________________________________________________________ 
36 Mixture of bis-acetyl- 
1.40 0.14 
10 1.20 
86 0.06 
4 
acetonatepalladium and 1,10- 
phenanthroline monohydrate 
37 1:1 type chelate salt of 
2.34 0.11 
5 1.62 
69 0.61 
26 
palladium orthophthalate with 
1,10-phenanthroline 
38 1:1 type chelate salt of 
9.64 0.56 
6 5.34 
55 3.74 
39 
palladium orthophthalate with 
2,2'-bipyridyl 
39 1:2 type chelate salt of 
4.79 0.44 
9 3.57 
75 0.78 
16 
palladium nitrate with 2,2'- 
bipyridyl 
40 1:2 type chelate salt of 
1.54 0.05 
3 0.69 
45 0.80 
52 
palladium nitrate with 1,10- 
phenanthroline 
41 1:1 type chelate salt of 
4.13 0.50 
12 2.94 
71 0.69 
17 
palladium nitrate with 2,2'- 
bipyridyl 
42 1:1 type chelate salt of 
4.33 0.38 
9 3.42 
79 0.53 
12 
nitrato-acetatopalladium with 
2,2'-bipyridyl 
__________________________________________________________________________ 
EXAMPLE 43 
A stainless steel reaction vessel having a capacity of 500 ml was charged 
with 295 g (250 ml, 1.52 moles) of dimethyl orthophthalate and 2.0 
millimoles of a chelate salt consisting of one molecule of palladium 
acetate and one molecule of 1,10-phenanthroline. The resultant reaction 
mixture was subjected to an oxidation-coupling reaction at a temperature 
of 200.degree. C., under a pressure of 10 atmospheres on the gauge, for 
2.5 hours, while blowing a mixture gas consisting of 90% by volume of 
nitrogen and 10% by volume of oxygen at a supply rate of 2 liter/min. 
through the bottom of the reaction vessel, and while stirring the reaction 
mixture with stirring paddles at a rotation speed of 800 r.p.m. 
Thereafter, 0.4 millimoles of 1,10-phenanthroline dissolved in 10 g of 
dimethyl orthophthalate were added to the reaction mixture and the same 
oxidative coupling operation as that described above was continued for the 
mixture for eleven hours. 
After the reaction was completed, it was found that the degree of 
conversion of dimethyl orthophthalate was 9.87%. Also, it was found that 
the yield of and the selectivity to the a-type compound were 0.42% and 4%, 
respectively, the yield of and the selectivity to the S-type compound were 
7.89% and 80%, respectively, and the yield of and the selectivity to the 
by-product were 1.56% and 16%, respectively.