Diphenyl oxalate-phenol adduct, process for producing the adduct and method of producing diphenyl oxalate from the adduct

A novel crystalline adduct of diphenyl oxalate and phenol in a molar ratio of 1:2 and having a high purity is produced by melting a mixture containing diphenyl oxalate and phenol at a temperature of 100.degree. C. or more; cooling the melt to a temperature of less than 100.degree. C. to allow a resultant adduct of diphenyl oxalate and phenol in a molar ratio of 1:2 to crystallize and deposit from the melt; and collecting the crystalline adduct. Diphenyl oxalate with a high purity is produced by melting the crystalline adduct to dissociate it into diphenyl oxalate and phenol, and evaporating away the dissociated phenol from the melt to collect the dissociated diphenyl oxalate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a crystalline diphenyl oxalate-phenol 
adduct, a process for producing the adduct and a method of producing 
diphenyl oxalate from the adduct. More particularly, the present invention 
relates to a crystalline adduct of diphenyl oxalate and phenol in a molar 
ratio of 1:2, a process for producing the adduct from a melt of a mixture 
of diphenyl oxalate and phenol by applying a crystallization procedure 
thereto, and a method of producing diphenyl oxalate having a high degree 
of purity from the crystalline diphenyl oxalate-phenol adduct. 
The crystalline adduct of diphenyl oxalate and phenol in a molar ratio of 
1:2 is a novel substance and can be obtained in a high degree of purity. 
Also, the crystalline diphenyl oxalate-phenol adduct can be easily 
decomposed into diphenyl oxalate and phenol by heating the adduct, and 
thus is useful as an intermediate material for producing diphenyl oxalate 
in a high degree of purity. 
The diphenyl oxalate produced by the method of the present invention is 
useful as an intermediate compound for producing various medicines, 
agricultural chemicals, polymers and additive for polymers. 
2. Related Art 
U.S. Pat. No. 5,239,106 to S. J. Shafer discloses a crystalline adduct of 
diphenyl carbonate and phenol. Nevertheless, it has not been known that 
diphenyl oxalate can addition-react with phenol to form a crystalline 
adduct thereof. 
Also, diphenyl oxalate has not yet been produced in a large amount at an 
industrial scale, and it has not been known how to industrially produce 
diphenyl oxalate with a high degree of purity. 
It is known that diphenyl oxalate with a high degree of purity can be 
produced, at a laboratory scale, by distilling a crude material containing 
diphenyl oxalate, for example, an ester-interchange reaction product 
containing diphenyl oxalate and phenol. If this laboratory distillation 
method is carried out at an industrial scale, since the distillation 
procedure must be carried out at a high temperature due to the high 
boiling temperature of diphenyl oxalate of 330.degree. C., diphenyl 
oxalate and other compounds (for example, non-reacted starting compounds 
for the ester-interchange reaction) are deteriorated during the 
distillation so as to reduce the degree of purity and yield of the 
products. 
Also, the distillation procedure for diphenyl oxalate having a high boiling 
temperature must be carried out under vacuum, and thus the distillation 
apparatus is complicated and requires a large amounts of energy to 
operate. Accordingly, the distillation method is unsatisfactory for 
industrial use. 
SUMMARY OF THE INVENTION 
An object of the present invention relates to provide a novel crystalline 
adduct of diphenyl oxalate and phenol, a process for producing the 
crystalline diphenyl oxalate-phenol adduct with a high degree of purity in 
a high yield, and a method of producing diphenyl oxalate with a high 
degree of purity from the crystalline adduct, which method can be carried 
out at an industrial large scale with high efficiency. 
The novel substance of the present invention is a crystalline adduct of 
diphenyl oxalate and phenol in a molar ratio of 1:2. 
The process of the present invention for producing a crystalline adduct of 
diphenyl oxalate and phenol comprises the steps of: 
melting a mixture containing diphenyl oxalate and phenol at a temperature 
of 100.degree. C. or more; 
cooling the melt to a temperature of less than 100.degree. C. to allow a 
resultant adduct of diphenyl oxalate and phenol in a molar ratio of 1:2 to 
crystallize and deposit from the melt; and collecting the resultant 
crystalline diphenyl oxalate-phenol adduct. 
The method of the present invention for producing diphenyl oxalate from the 
above-mentioned crystalline diphenyl oxalate-phenol adduct comprises the 
steps of: 
melting a crystalline diphenyl oxalate-phenol adduct having a molar ratio 
of 1:2 to dissociate the adduct into diphenyl oxalate and phenol; and 
evaporating away the dissociated phenol from the melt to collect the 
dissociated diphenyl oxalate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With respect to the novel crystalline adduct of diphenyl oxalate with 
phenol of the present invention, it has been confirmed by a gas 
chromatographic analysis that diphenyl oxalate and phenol are 
addition-reacted with each other in a molar ratio of 1:2, and the adduct 
is crystalline and has a formular weight of 430.64 and a melting 
temperature of 101.degree. to 103.degree. C. 
Also, the diphenyl oxalate-phenol adduct of the present invention exhibits 
a FT-IR spectrum shown in FIG. 1. 
Also, in a nuclear magnetic resonance spectrum (.sup.1 H-NMR) of the 
diphenyl oxalate-phenol adduct crystals, the peaks as shown in Table 1 
appeared. 
TABLE 1 
______________________________________ 
.delta.(CDCl.sub.3) 
ppm Classification 
______________________________________ 
4.85 2H, s 
6.82 4H, d 
6.92 2H, t 
7.23 8H, m 
7.32 2H, t 
7.46 4H, t 
______________________________________ 
The diphenyl oxalate-phenol adduct in a molar ratio of 1:2 can be produced 
by the process of the present invention which can be advantageously 
utilized for industrial practice. 
In the process of the present invention, a mixture containing diphenyl 
oxalate and phenol is melted. In this melt, preferably, the content of 
diphenyl oxalate is in the range of from 1 to 50% by weight, more 
preferably 2 to 45% by weight, based on the total weight of diphenyl 
oxalate and phenol in the melt, and diphenyl oxalate and phenol are 
uniformly mixed in the state of a liquid. If the content of diphenyl 
oxalate is too high, it may be difficult to crystallize-deposit the 
resultant diphenyl oxalate-phenol adduct from the melt. Also, the melt 
preferably contains diphenol oxalate and phenol in a total content of 50% 
by weight, more preferably 60 to 100% by weight, still more preferably, 65 
to 95% by weight, based on the total weight of the melt. 
In the process of the present invention, the mixture to be melted may 
contain, in addition to diphenyl oxalate and phenol, foreign substances, 
for example, oxalic acid derivatives other than diphenyl oxalate, for 
example, dimethyl oxalate and methylphenyl oxalate, and phenyl derivatives 
other than phenol, for example, carboxylic acid phenyl esters and diphenyl 
carbonate, which substances do not deposit from the melt under the 
conditions suitable for crystallize-depositing the diphenyl oxalate-phenol 
adduct of the present invention, are compatible with diphenyl oxalate and 
phenol and have a melting temperature of lower than 150.degree. C., 
preferably lower than 100.degree. C. The foreign substances are present 
preferably in a total content of less than about 50% by weight, more 
preferably 0 to 40% by weight, still more preferably 0 to 30% by weight, 
based on the total weight of the mixture. 
The mixture containing diphenyl oxalate and phenol may be a reaction 
product mixture obtained from various diphenyl oxalate-producing processes 
and containing diphenyl oxalate and phenol or an admixture of the 
above-mentioned reaction product mixture with an additional amount of 
phenol having a composition adjusted as mentioned above. Alternatively, 
the diphenyl oxalate and phenol-containing mixture can be prepared by 
mixing a diphenyl oxalate mixture having a diphenyl oxalate content of 80 
to 100% by weight with a phenol mixture having a phenol content of 80 to 
100% by weight, in a desired weight mixing ratio. 
The mixture containing diphenyl oxalate and phenol is melted at a 
temperature of 100.degree. C. or more, preferably 120.degree. C. to 
300.degree. C., still more preferably 140.degree. C. to 250.degree. C. to 
provide a uniform melt. 
In an example, the melt of the mixture containing diphenyl oxalate and 
phenol is prepared by ester-interchange reacting dialkyl oxalate with 
phenol or a phenol derivative, for example, a carboxylic acid phenyl ester 
or diphenyl carbonate at a temperature of 100.degree. C. or more. The 
resultant reaction product mixture in the state of a melt can be utilized 
as a melt of the mixture containing diphenyl oxalate and phenol for the 
industrial practice. Also, the reaction product mixture melt may be mixed 
with an additional amount of phenol to control the composition of the 
melt. 
Especially, in the industrial production of the diphenyl oxalate-phenol 
adduct, the reaction product mixture in the state of a melt prepared by 
the ester-interchange reaction of a dialkyl oxalate with phenol at a 
temperature of 100.degree. C. or more is preferably utilized as a melt of 
the mixture containing diphenyl oxalate and phenol. 
In the production of the crystalline diphenyl oxalate-phenol adduct of the 
present invention, even when the above-mentioned reaction product mixture 
melt containing a catalyst for the ester-interchange reaction is used as a 
diphenyl oxalate and phenol-containing mixture melt, the resultant adduct 
crystals deposited from the melt are substantially free from the catalyst 
and thus have a high degree of the purity. Namely, the process of the 
present invention is advantageous in that the diphenyl oxalate-phenol 
adduct crystals having a high degree of purity can be easily obtained 
without using a complicated refining procedure. 
In the process of the present invention, a uniform mixture containing 
diphenyl oxalate and phenol is melted at a temperature of 100.degree. C. 
or more, the resultant uniform mixture melt is cooled to a temperature of 
less than 100.degree. C., preferably 10.degree. to 95.degree. C. to allow 
a resultant adduct of diphenol oxalate and phenol in a molar ratio of 1:2 
to crystallize and deposit from the melt. The deposited adduct crystals 
are collected from the melt by a conventional crystal-collecting 
procedure, for example, a filtration or centrifugal procedure. 
The crystallization procedures can be carried out by gradually and 
continuously decreasing the temperature of the melt. If necessary, a 
combination of a crystallization procedure with an adduct 
crystal-collection procedure can be repeated two or three or more times at 
different crystallization temperatures, to enhance the collection yield of 
the adduct crystals. 
In the process of the present invention, the crystallize-deposition 
procedure can be carried out in a conventional apparatus, for example, a 
conventional deposition vessel equipped with a conventional stirrer. 
The crystallization procedure is preferably carried out in a temperature 
range in which a matrix portion of the melt other than the resultant 
adduct crystals is maintained at the state of a melt. For example, when 
the adduct crystals are deposited from the melt matrix containing 50% by 
weight or more of phenol, the crystallization and collection procedures 
are preferably carried out at a temperature of 40.degree. C. or more, more 
preferably 45.degree. to 90.degree. C., still more preferably 50.degree. 
to 80.degree. C. 
In the case where the reaction product mixture obtained by the process for 
producing diphenyl oxalate by the ester-interchange reaction of dialkyl 
oxalate with a phenol compound is used as a diphenyl oxalate and 
phenol-containing mixture, and the resultant adduct crystals are collected 
from the melt of the reaction product mixture by a filtration or 
centrifugal separation, the collection residue contains non-reacted 
dialkyl oxalate, alkylphenyl oxalate, diphenyl oxalate and phenol. 
Therefore, the collection residue can be recycled to and reused in the 
diphenyl oxalate-producing process. 
Since the diphenyl oxalate-phenol adduct crystals of the present invention 
produced by the process of the present invention have a high degree of 
purity and can be easily dissociated into diphenyl oxalate and phenol by 
heating the adduct crystals at a temperature higher than the melting 
temperature thereof. Accordingly, in the method of the present invention, 
diphenyl oxalate with a high degree of purity can be produced by melting 
the crystalline diphenyl oxalate-phenol adduct in a molar ratio of 1:2, to 
dissociate the adduct into diphenyl oxalate and phenol; and evaporating 
away the dissociated phenol from the melt to collect the dissociated 
diphenyl oxalate. 
In the method of the present invention, the melting procedure is carried 
out at a temperature equal to or higher than the melting temperature of 
the adduct, namely 101.degree. to 103.degree. C. or more, preferably 
136.degree. C. or more. However, the melting temperature is preferably not 
higher than 300.degree. C., more preferably not higher than 250.degree. 
C., and still more preferably not higher than 220.degree. C., to prevent 
thermal deterioration of diphenyl oxalate. 
Also, the evaporation procedure for removing the dissociated phenol from 
the melt, which procedure may be a distillation procedure, is preferably 
carried out while maintaining the temperature of the melt at 300.degree. 
C. or less, more preferably 250.degree. C. or less, and still more 
preferably 220.degree. C. or less under the ambient atmospheric pressure 
or a reduced pressure. The removal of phenol by the evaporation or 
distillation procedure may be carried out simultaneously with the melting 
procedure of the adduct. 
In the method of the present invention, to obtain diphenyl oxalate with a 
high degree of purity, the evaporation or distillation procedure for the 
removal of phenol is preferably carried out while continuously maintaining 
the adduct at the state of a melt. Since the melting temperature of 
diphenyl oxalate is 136.degree. C., the temperature of the adduct melt is 
preferably maintained at 136.degree. C. or more, more preferably 
140.degree. C. or more, and still more preferably 145.degree. C. or more 
from the initial stage at which the concentration of the dissociated 
diphenyl phenol in the melt gradually increases to the final stage at 
which the dissociation of the diphenyl oxalate-phenol adduct is 
substantially completed. 
Accordingly, in the method of the present invention, the adduct melt is 
heated and maintained preferably at a temperature of 100.degree. to 
300.degree. C., more preferably 140.degree. to 250.degree. C., and still 
more preferably 145.degree. to 220.degree. C. throughout the evaporation 
procedure, to evaporate away the dissociated phenol and collect the 
dissociated diphenyl oxalate having a high degree of purity, usually about 
100%. 
In the melting procedure, the temperature of the melt may be gradually 
increased with an increase in the concentration of the dissociated 
diphenyl oxalate in the melt. For example, the evaporation procedure may 
be carried out in multiple steps, for example, at a temperature of 
100.degree. to 140.degree. C. in the initial step and at a temperature of 
140.degree. to 250.degree. C. in the final step. 
To evaporate away the dissociated phenol at a high efficiency, the melt is 
preferably heated to and maintained at a temperature equal to or higher 
than the boiling temperature of phenol, namely 182.degree. C., more 
preferably 190.degree. C. or more. 
Namely, the evaporation or distillation procedure in the method of the 
present invention is carried out preferably in the temperature range of 
from 182.degree. C. to 300.degree. C., more preferably from 190.degree. to 
250.degree. C., still more preferably from 190.degree. to 220.degree. C. 
Also, in the method of the present invention, to reduce the thermal 
deterioration of the dissociated diphenyl oxalate and phenol, the melting 
and evaporation temperatures are preferably maintained within the range of 
from 100.degree. to 300.degree. C. under a reduced pressure of 270 to 
67,000 Pa (2 to 500 mHg). 
The resultant diphenyl oxalate by the method of the present invention has a 
high degree of purity of 95% by weight or more, usually 97 to 100% by 
weight, and thus is useful for various uses as mentioned above. 
EXAMPLES 
The present invention will be further explained by the following examples. 
Example 1 
A mixture of 100.26 g (0.413 mole) of diphenyl oxalate (made by Wako 
Junyaku K. K.) with 450.0 g (4.80 moles) of phenol (made by Wako Junyaku 
K. K.) was placed in a 500 ml glass round flask equipped with a 
thermometer and a stirrer and arranged on a heating oil bath. The heating 
of the mixture by the oil bath was started while stirring the mixture. 
After heating at a temperature of 150.degree. C. for 30 minutes, a uniform 
melt of the mixture of diphenyl oxalate with phenol was obtained. Then the 
heating was stopped and the mixture melt was gradually cooled. When the 
mixture melt temperature reached 81.degree. C., deposition of crystals was 
started. The mixture melt was stirred at this temperature for 30 minutes, 
and the deposited crystals were collected by filtration. The resultant 
crystals were dried at a temperature of 60.degree. C. under vacuum for 5 
hours. The collected crystals were subjected to the following measurement 
and analysis. 
Measurement of Melting Point 
The crystals exhibited a melting point of 101.degree. to 103.degree. C. 
which is different from the melting points of either diphenyl oxalate or 
phenol. 
Gas Chromatographic Analysis 
The crystals were dissolved in acetonitrile and subjected to gas 
chromatographic analysis. As a result, diphenyl oxalate and phenol were 
detected in addition to acetonitrile, and the detected diphenyl oxalate 
and phenol were found in amounts corresponding to a weight ratio of 1:0.78 
and a molar ratio of diphenyl oxalate to phenol of 1:2. 
GC-MS Analysis 
The crystals were subjected to GC-MS analysis. As a result, diphenyl 
oxalate having a molecular weight of 242 and phenol having a molecular 
weight of 94 were confirmed. 
Elemental Analysis 
The crystals were subjected to elemental analysis. The analytical results 
shown in Table 2 corresponded to an adduct of diphenyl oxalate and phenol 
in a molar ratio of 1:2. 
TABLE 2 
______________________________________ 
Analytical value 
Theoretical value 
Element (% by weight) 
(% by weight) 
______________________________________ 
C 71.98 72.55 
H 5.23 5.12 
O 22.78 22.33 
______________________________________ 
FT-IR Analysis 
The crystals exhibited a FT-IR spectrum shown in FIG. 1. 
.sup.1 H-NMR Analysis 
The crystals were subjected to .sup.1 H-NMR analysis. The resultant .sup.1 
H-NMR spectrum exhibited the following peaks. 
______________________________________ 
.delta.(CDCl.sub.3) ppm 
______________________________________ 
4.85 (2H, s) 
6.82 (4H, d) 
6.92 (2H, t) 
7.23 (8H, m) 
7.32 (2H, t) 
7.46 (4H, t) 
______________________________________ 
From the above-mentioned analytical results, it was confirmed that the 
crystals consist of a novel adduct of diphenyl oxalate and phenol in a 
molar ratio of 1:2. 
Example 2 
A mixture containing diphenyl oxalate and phenol in the state of a melt was 
prepared by the following procedures. 
A round glass flask having a capacity of 1000 ml and equipped with a 
thermometer and a stirrer was charged with a mixture of 118.0 g (1.00 
mole) of dimethyl oxalate (made by Wako Junyaku K. K.) with 470.2 g (5.00 
moles) of phenol (made by Wako Junyaku K. K.) and 1.01 g (0.0024 mole) of 
tetraphenoxytitanium and placed on a heating oil bath. The mixture in the 
flask was heated by the oil bath to a temperature of 180.degree. C. to 
200.degree. C. and maintained at this temperature for 8 hours, while 
stirring the mixture and distilling away the generated methyl alcohol due 
to an ester-interchange reaction of dimethyl oxalate with phenol. 
After completion of the reaction, a portion of the resultant reaction 
product mixture was subjected to gas chromatographic analysis. It was 
confirmed that the reaction product mixture contained 21.38% by weight of 
diphenyl oxalate, 12.47% by weight of methylphenyl oxalate, 3.86% by 
weight of dimethyl oxalate and 62.05% by weight of phenol. 
The reaction product mixture in the state of a melt and containing diphenyl 
oxalate and phenol uniformly mixed with each other was stopped to be 
heated and gradually cooled from the temperature of 180.degree. to 
200.degree. C. When the temperature of the melt reached about 85.degree. 
C., it was found that deposition of crystals started. The temperature of 
the melt was further decreased to 60.degree. C. to continue the deposition 
of the crystals. The deposited crystals were collected at the temperature 
of 60.degree. C. by filtration, rinsed with about 50 ml of phenol and 
dried at a temperature of 60.degree. C. for 5 hours under a reduced 
pressure. The filtrate contained 3.05% by weight of diphenyl oxalate, 
18.42% by weight of methylphenyl oxalate, 5.72% by weight of dimethyl 
oxalate and 72.80% by weight of phenol. 
The resultant crystals were subjected to the same measurement and analysis 
as in Examples 1. It was confirmed by the measurement and analysis results 
that the resultant crystals consisted of a diphenyl oxalate-phenol adduct 
in a molar ratio of 1:2. 
Example 3 
The same diphenyl oxalate-phenol adduct as in Example 2 in an amount of 150 
g and in the wetted condition was placed in a single distillation 
apparatus and heat-melted at a temperature of 110.degree. to 120.degree. 
C. under a reduced pressure of 2700 Pa (20 mmHg), and the dissociated 
phenol was distilled away from the melt. The distillation residue in an 
amount 74.3 g consisted essentially of diphenyl oxalate having a degree of 
purity of 99% or more determined by gas chromatography. 
In the present invention, a new adduct of diphenyl oxalate and phenol in a 
molar ratio of 1:2 can be produced in a high degree of purity by a simple 
and easy process and apparatus, and can be utilized to produce diphenyl 
oxalate with a high degree of purity by a simple and easy method and 
apparatus.