JPH09278714A - Production of diaryl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a diaryl carbonate having low aryl chloroformate content. SOLUTION: This process for the production of a diaryl carbonate by reacting an aromatic monohydroxy compound with phosgene in the presence of a nitrogen-containing aromatic heterocyclic compound catalyst comprises two reaction steps consisting of the 1st step to react 1 equivalent of an aromatic monohydroxy compound with 0.44-0.5 equivalent of phosgene to produce a diaryl carbonate and an aryl chloroformate in an amount less than the equivalent amount based on the unreacted aromatic monohydroxy compound and the 2nd step to perform dehydrochlorination reaction of the aryl chloroformate and the aromatic monohydroxy compound of the reaction liquid obtained by the 1st step to obtain the objective diaryl carbonate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a diaryl carbonate. More specifically, the present invention relates to a method for producing a diaryl carbonate in which the by-product of aryl chloroformate, which is difficult to separate, is suppressed.

[0002]

2. Description of the Related Art Diaryl carbonate is used in large amounts as a raw material for producing aromatic polycarbonate by transesterification with bisphenol A. From the viewpoint of preventing the resulting aromatic polycarbonate from being colored and preventing the metal from being corroded when it is used as an optical disk substrate, it is desirable that the by-product aryl chloroformate is not contained in the diaryl carbonate.

As a method for producing a diaryl carbonate by reacting an aromatic monohydroxy compound with phosgene, a stoichiometric reaction between phenol and phosgene using caustic soda has long been known. However, in this reaction,
Since caustic soda is used and a large amount of sodium chloride is produced as a by-product, the raw material cost becomes high and there are problems such as wastewater treatment.

In order to solve these problems, there has been proposed a method represented by the following reaction formula (1) in which an aromatic monohydroxy compound is directly reacted with phosgene in the presence of a catalyst. For this reaction, which produces hydrogen chloride as a by-product, hydrochloric acid can be reused separately in a chemical plant, there is no need to discharge the chlorinated product outside the plant, and the burden on wastewater treatment can be reduced.

[0005]

Embedded image 2PhOH + COCl ₂ → Ph-CO-Ph + 2HCl (1)

A number of methods are known for the above reaction using a homogeneous or heterogeneous catalyst. In these methods, by-products such as aryl salicylate having a boiling point extremely close to that of diaryl carbonate or recovery of the catalyst in the case of a homogeneous catalyst, Heterogeneous catalysts have not solved problems such as elution of metal components. The method of using activated carbon as a catalyst has no problem of elution of metal components, but does not have an industrially advantageous reaction rate.

It is also known that diaryl carbonate can be obtained by reacting an aromatic monohydroxy compound with phosgene. For example, U.S. Pat. No. 2,837,555 proposes performing solventless condensation in the presence of tetramethylammonium halide as a catalyst. However,
In order to obtain an economical reaction rate in this method, it is necessary to use a relatively large amount of catalyst and to use a relatively high temperature of 180 to 215 ° C., which is a thermally unstable halogenation. There is a risk of decomposition of tetramethylammonium. In addition, phosgene is consumed at a much higher rate than required stoichiometrically.

Further, Japanese Patent Publication No. 58-50977 discloses that
1 mol of phosgene is used at a temperature of 40 to 180 ° C. with respect to 2 mol of an aromatic monohydroxy compound (phenol) using an aromatic nitrogen-containing heterocyclic compound as a catalyst, with desorption of hydrogen chloride in a solvent if necessary. A method for carrying out a reaction to produce a diaryl carbonate (diphenyl carbonate) is proposed, which is at a lower temperature than the method described in the above-mentioned US Patent, and
It is disclosed that the reaction rate is doubled or more.

The method described in Japanese Patent Publication No. 58-50977 is industrially excellent for the above reason, but in this method, it depends on the reaction between phenyl chloroformate, which is an intermediate product of diphenyl carbonate, and phenol. Since the production rate of diphenyl carbonate is not sufficient as compared to the production rate of phenyl chloroformate, a small amount of phenyl chloroformate remains with diphenyl carbonate at the end of the reaction. Such residual phenyl chloroformate adversely affects the aromatic polycarbonate as described above.

Therefore, in order to industrially obtain high quality polycarbonate, a process for producing a high-purity diaryl carbonate free of aryl chloroformate is desired. The present inventors have examined various aromatic nitrogen-containing heterocyclic compounds and reaction conditions described in the patent publication, but due to these factors, the aryl chloroformate concentration is substantially below the detection limit in the early to middle stages of the reaction. Even if there is, if the reaction is pushed to the range of at least 98% or higher conversion rate of the aromatic monohydroxy compound, the production rate of aryl chloroformate increases near the end of the reaction, resulting in a high conversion rate. It was found that the yield of diaryl carbonate decreased even when the above was obtained. Thus, it was confirmed that when the aromatic monohydroxy compound was reacted with phosgene at a high conversion rate, a considerable amount of aryl chloroformate remained without exception by the conventional method. That is, it is difficult to produce a diaryl carbonate without an aryl chloroformate impurity at a high conversion rate from the reaction conditions only by reacting an aromatic monohydroxy compound with phosgene by a conventional method.

[0011]

DISCLOSURE OF THE INVENTION The present invention provides a method for producing a diaryl carbonate from an aromatic monohydroxy compound and phosgene using an aromatic nitrogen-containing heterocyclic compound as a catalyst, which is industrially advantageous even at a high conversion rate. Moreover, it aims at providing the method of manufacturing the diaryl carbonate which suppresses the content of aryl chloroformate.

[0012]

The present invention relates to a method for producing a diaryl carbonate by reacting an aromatic monohydroxy compound with phosgene in the presence of an aromatic nitrogen-containing heterocyclic compound catalyst. 1 equivalent of group monohydroxy compound
Reacting phosgene 0.44 to 0.5 equivalents to produce diaryl carbonate and aryl chloroformate in an equivalent amount or less with respect to the unreacted aromatic monohydroxy compound,

Second step: a step of producing a diaryl carbonate by subjecting the reaction solution obtained in the first step to a dehydrochlorination reaction of an aryl chloroformate and an aromatic monohydroxy compound, the above two-step reaction The present invention provides a method for producing a diaryl carbonate, which is characterized by undergoing steps.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The process of the present invention is represented by the following chemical formula using phenol and phosgene as raw materials.

[0015]

Embedded image Catalyst first step: PhOH + COCl ₂ → DPC + HCl + PhOH + RCF Second step: PCF + PhOH → DPC + HCl (wherein RCF is phenyl chloroformate, DPC
Represents diphenyl carbonate. )

The details of the invention will be described below. Catalyst: The catalyst used in the first step and the second step is an aromatic nitrogen-containing heterocyclic compound having a 6-membered ring or 5-membered ring skeleton. The ring may contain a hetero atom other than nitrogen (sulfur, oxygen, or a second nitrogen atom). The heterocyclic group may also be fused with another aromatic heterocyclic group or aromatic carbocyclic group.

Examples of such catalysts are as follows. Pyridine, quinoline, isoquinoline, picoline, acridine, pyrazine, pyrimidine, imidazole, 2-
Methylimidazole, 2-methoxypyridine, and 2-hydroxypyridine, preferably pyridine, α-picoline, β, γ-mixed picoline, isoquinoline, 2-hydroxypyridine, and imidazole. Further, the above-mentioned compound molded into a polymer such as polyvinyl pyridine can be similarly used.

Since the aromatic nitrogen-containing heterocyclic compound which is generally active in the first step is also active in the reaction in the second step, the reaction solution in the first step is used as it is, and the reaction solution in the second step is used. A method is also used in which the reaction is continuously performed with the same catalyst. However, the reactions in the first step and the second step do not necessarily have to proceed with the same catalyst, and different catalysts may be used.

The amount of the catalyst is preferably 0.1 to 10 mol%, more preferably 0.5 to 5 mol%, based on the aromatic monohydroxy compound as the substrate. It is preferable. Also, these catalysts quickly convert to the corresponding hydrochloride salt in the reaction mixture. Therefore,
Even if it is used in the reaction in the form of the hydrochloride, the same reactivity and selectivity can be obtained. It is also possible to use strong acid salts such as bromate, sulfate and nitrate. It is also possible to substitute weak acid salts such as formate, acetate, phosphate, caproate, pivalate and the like because they are easily converted into hydrochloride during the reaction.

Aromatic Monohydroxy Compounds: The aromatic monohydroxy compounds used in the present invention include, for example, phenol, cresol (isomer), and isopropylphenol (isomer), chlorophenol (isomer) and methoxyphenol (isomer). Body) and halogenated phenols as well as alkoxyphenols. It is also a heterocyclic monohydroxy compound having a 5- or 6-membered ring which may be condensed with or substituted by an aromatic cyclic group and a carbonate cyclic group, for example, 4-hydroxyquinoline. Particularly, phenol is preferably used.

Phosgene: Phosgene is preferably as pure as possible and preferably does not contain impurities such as carbon tetrachloride and methylene chloride.

Reaction: The most effective factor in the present invention is to control the amount of phosgene reacted. That is, in the first step, 0.5 equivalent or less, preferably 0.44 to 0.5 equivalent of phosgene is completely reacted with the aromatic monohydroxy compound. In this condition, any other reaction conditions (catalyst species, catalyst concentration,
Regardless of reaction temperature and phosgene supply rate)
At the end of the process, the relationship of (concentration of aryl chloroformate) ≦ (concentration of aromatic monohydroxy compound) is established. However, even if the condition of (aryl chloroformate concentration) = (aromatic monohydroxy compound concentration) is obtained by reacting 0.5 equivalent of phosgene with respect to the aromatic monohydroxy compound, the arylchloroform is used in the second step. It may take a long time for the formate to completely react.

Therefore, usually, after the first step, a condition is selected in which the aromatic monohydroxy compound is present in the reaction solution in a molar ratio of 1 to 5 with respect to the aryl chloroformate. At this time, the amount of phosgene to be substantially reacted is 0.44 to 0.5 equivalent with respect to the aromatic monohydroxy compound. Preferably, the conditions are selected such that 0.48 to 0.5 equivalents of phosgene can be completely reacted.

In the first step, it is possible to supply phosgene in excess of 0.5 equivalent to the aromatic monohydroxy compound to the reaction solution and recycle unreacted phosgene which escapes into the gas phase. At the end of the first step, it is desirable that the unreacted phosgene does not remain in the reaction solution, but if it remains, the phosgene is allowed to continue to react in the second step so that the amount of phosgene that reacts is substantially zero. ．
It should not exceed 5 equivalents. Alternatively, after the first step, the reaction solution is quickly purged with an inert gas,
Dephosgene can also prevent the reaction of phosgene in the second step.

The reaction pressure in the first step and the second step is usually atmospheric pressure, but it can be carried out under pressure or under reduced pressure if necessary. As the reaction device, either a gas-liquid batch reaction system or a continuous reaction system equipped with an ordinary stirring device can be adopted. The reaction is
Both steps are carried out in the liquid phase, preferably in the molten state, at a reaction temperature above the melting point of the aromatic hydroxy compound and the diaryl carbonate. The temperature range is usually 80 to 180 ° C., preferably 130 to 170.
° C.

As shown in FIG. 1, phosgene 1 is passed through a tubular gas blowing tube or a gas blowing tube 2 having pores,
It is preferable that the phenol 2 in the phosgenation tank 4 is directly blown into the molten substrate 5. It is also possible to use a bubble column reactor without a stirrer in the first step. Further, it is not always necessary to use the separate reactors of the two tanks 4 and 7 in the first and second steps, and the second step may be continuously performed in the same reaction tank after the first step. Good, let the reaction liquid 6 flow through, and the dehydrochlorination tank 7 of the second step
A method in which the reaction solution 6 is fed to
It is also possible to continuously produce the diaryl carbonate 9 in a large amount according to the method (see). The number of reactors in each step is not limited in the present invention.

Regarding the dehydrochlorination reaction in the second step, an arbitrary inert gas 8, for example, nitrogen, argon or the like is circulated in the reaction solution, and the hydrochloric acid 10 in the reaction solution is positively excluded to carry out the reaction. It can also be promoted. First and second
If necessary, a solvent can be used in the reaction of the process. Such solvents include aliphatic and aromatic hydrocarbons such as pentane, hexane, octane, benzene,
Solvents such as xylenes (isomers), diethylbenzene, alkylphthalenes, biphenyl, halogenated hydrocarbons such as dichloromethane, trichloroethylene and the like can be mentioned.

Separation of diaryl carbonate: The final reaction solution obtained through the above-mentioned two steps can be separated into a catalyst and a product by, for example, the method shown below. Liquid (diaryl carbonate) -solid (aromatic nitrogen-containing heterocyclic compound hydrochloride) separation by filtration, extraction separation by a solvent utilizing the polarity difference between diaryl carbonate and aromatic nitrogen-containing heterocyclic compound hydrochloride, and aromatic-containing For example, the nitrogen heterocyclic compound hydrochloride is directly separated by distillation.

Regarding the method for separating these catalysts, an appropriate method may be selected in consideration of the chemical properties (boiling point, melting point, polarity) of the aromatic nitrogen-containing heterocyclic compound or salt used as a catalyst. The obtained crude diaryl carbonate may be optionally further purified by, for example, distillation, washing with water or crystallization depending on the use.

[0030]

The present invention will be described with reference to the following examples.
The present invention is not limited to the following examples. Example 1 Using 0.025 mol (1.98 g) of pyridine as a catalyst,
Phosgene was continuously blown into 0.5 mol (47 g) of molten phenol at 130 ° C. in a reaction vessel at a feed rate of 0.9 g / min using a gas blowing tube made of a G2 glass filter, and reacted at 130 ° C. for 35 minutes. Let At the end of this reaction, the reaction mixture was analyzed by gas chromatography.
0.147 mol of phenol remained, 0.136 mol of phenyl chloroformate and 0.11 mol of diphenyl carbonate were produced. The amount of phosgene reacted at this time was 0.246 equivalent (0.246 mol) with respect to phenol (0.5 mol).

The blowing gas was changed to nitrogen gas, and the reaction was further continued at 130 ° C. for 30 minutes while purging with nitrogen. The final composition of the reaction solution was 0.011 mol of phenol and 0.245 mol of diphenyl carbonate, and phenyl chloroformate was below the detection limit (see FIG. 2).
The product obtained by cooling and solidifying the reaction liquid had a pure white color.

Comparative Example 1 0.025 mol (1.98 g) of pyridine was used as a catalyst,
Phosgene was continuously blown into 0.5 mol (47 g) of molten phenol at 130 ° C. in a reaction vessel at a feed rate of 0.6 g / min using a gas blowing tube made of G2 glass filter, and reacted at 130 ° C. for 60 minutes. Let At the end of this reaction, when the reaction solution was analyzed by gas chromatography, 0.094 mol of phenol remained, and 0.103 mol of phenyl chloroformate and 0.152 mol of diphenyl carbonate were produced. The amount of phosgene reacted at this time was 0.2 with respect to 0.5 equivalent of phenol (0.5 mol).
It was 55 equivalents (0.255 mol).

The blowing gas was changed to nitrogen gas, and the reaction was carried out at 130 ° C. for 30 minutes while purging with nitrogen.
The final composition of the reaction solution is 0.003 mol of phenol,
0.013 mol of phenyl chloroformate, 0.24
It was 2 moles of diphenyl carbonate. The product obtained by cooling and solidifying the reaction liquid had a light brown color. As shown in Comparative Example 1, if more than 0.5 equivalent of phosgene is reacted with phenol relative to 1 equivalent of phenol, phenyl chloroformate remains in the reaction solution, which causes coloring of diphenyl carbonate. .

[0034]

INDUSTRIAL APPLICABILITY According to the method for producing a diaryl carbonate according to the present invention, it is possible to provide a high-quality diaryl carbonate that does not contain a by-product phenyl chloroformate.

[Brief description of drawings]

FIG. 1 is a flow sheet diagram for continuously implementing the present invention.

FIG. 2 is a diagram showing the composition of a reaction solution over time in the practice of the present invention.

Claims (3)

[Claims] 1. A method for producing a diaryl carbonate by reacting an aromatic monohydroxy compound with phosgene in the presence of an aromatic nitrogen-containing heterocyclic compound catalyst, wherein the first step is: relative to 1 equivalent of the aromatic monohydroxy compound. ,
A step of reacting 0.44 to 0.5 equivalents of phosgene to produce diaryl carbonate and aryl chloroformate in an equivalent amount or less with respect to the unreacted aromatic monohydroxy compound, the second step: obtained in the first step A process for producing a diaryl carbonate by subjecting a reaction solution to a dehydrochlorination reaction of an aryl chloroformate and an aromatic monohydroxy compound, and a method for producing a diaryl carbonate, which comprises the above-mentioned two-step reaction process. 2. The method for producing a diaryl carbonate according to claim 1, wherein the second step is carried out while blowing an inert gas into the reaction solution. 3. The diaryl carbonate according to claim 1, wherein the molar ratio of the aromatic monohydroxy compound to the aryl chloroformate in the reaction solution obtained in the first step is in the range of 1 to 5. Manufacturing method.