JP2000063332A - Production of diaryl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a diaryl carbonate by using a dialkyl carbonate and an aromatic hydroxy compound as raw materials, not causing the clogging of a device with a solid. SOLUTION: This method for producing a diaryl carbonate of the general formula: ArO-CO-OAr (Ar is phenyl group which is not substituted or is substituted by an alkyl group, an alkoxy group or a halogen) from a 3-6C dialkyl carbonate of the general formula: RO-CO-OR (R is a 3-6C alkyl group) and an aromatic hydroxy compound of the general formula: ArOH. Therein, an alkyl carbamate of the general formula: RO-CO-NH2 contained in the diaryl carbonate is <=0.5 mol.% based on the 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 dialkyl carbonate from urea and an alkyl alcohol, and further for producing a diaryl carbonate from a dialkyl carbonate and an aromatic hydroxy compound. Diaryl carbonate is a compound useful as a raw material for melt transesterification polycarbonate.

[0002]

2. Description of the Prior Art Diaryl carbonates have hitherto been produced by reacting aromatic hydroxy compounds with phosgene. However, phosgene is highly toxic,
Since the apparatus is highly corrosive and a large amount of alkali is required to neutralize by-produced hydrogen chloride, a method without using phosgene has been desired, and some attempts have been made.

For example, a method of oxidatively carbonylating an aromatic hydroxy compound with carbon monoxide and oxygen has been proposed (JP-A-53-68744). However, since these methods use expensive palladium as a main catalyst and require a cocatalyst, a desiccant, an oxidizing agent, etc., they are very complicated reaction systems. In addition, it is difficult to recover the catalyst, and it is the current situation that the yield and reaction rate have not reached the industrial level.

On the other hand, it has been attempted to directly react urea with phenol to produce diphenyl carbonate, but the yield is low (JP-A-8-92167). There is also known a method in which urea is once converted into diphenylurea, and then this is converted into phenylurethane, followed by disproportionation, but the operation is complicated (JP-A-8-198815).

In addition to the above, a transesterification reaction between an aromatic hydroxy compound and a dialkyl carbonate (Japanese Patent Application Laid-Open No. Sho 5)
1-105032) and a disproportionation reaction of an alkylaryl carbonate (JP-A-51-75044) are known. A method that has been studied for this type of transesterification reaction and disproportionation reaction is mainly a method for producing diphenyl carbonate from dimethyl carbonate. The reason for this is considered to be that dimethyl carbonate is relatively easily available. However, when dimethyl carbonate is used as a raw material, methanol to be distilled off from the reaction system forms an azeotropic mixture with dimethyl carbonate, so that dimethyl carbonate is also removed together with methanol,
There was a problem that the reaction was inefficient. Furthermore, the separation of the distilled dimethyl carbonate and methanol is also a big problem.

Therefore, the inventors of the present invention have previously disclosed Japanese Patent Laid-Open No. 10-
In 152452 and JP-A-10-152456, a method for producing a dialkyl carbonate from urea and an alkyl alcohol having 3 to 6 carbon atoms and further producing a diaryl carbonate from a dialkyl carbonate and an aromatic hydroxy compound was proposed. In this production method, since the by-produced alkyl alcohol does not azeotrope with the dialkyl carbonate, it is possible to distill off high-purity alkyl alcohol. Therefore, the distilled alkyl alcohol can be directly used as a raw material for the dialkyl carbonate.

However, in the above-mentioned production method, since the alkyl carbamate is mixed in the dialkyl carbonate obtained from urea, in order to remove it,
A method of precipitating an alkyl carbamate by cooling or a method of washing with warm water is used. However, according to the study by the present inventors, the dialkyl carbonate obtained by these methods does not have sufficient purity, and when it is reacted with an aromatic hydroxy compound as it is, it is caused by an alkyl carbamate which is an impurity. It became clear that a white solid was generated at the time, causing troubles such as blockage of the device.

[0008]

In view of the above problems, an object of the present invention is to block a device with a white solid in a method for producing a diaryl carbonate from a dialkyl carbonate obtained from urea and an aromatic hydroxy compound. Another object of the present invention is to provide a method for producing a diaryl carbonate without causing

[0009]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made extensive studies in order to solve the above-mentioned problems in a method for producing a dialkyl carbonate obtained from urea and an aromatic hydroxy compound. As a result, the white solid formed is cyanuric acid, alkyl allophanate and 2,4-dioxo-dihydro-5,6-benzo-1,3.
-It became clear that oxazine was the main component. The inventors have found that if the amount of the alkyl carbamate contained in the raw material dialkyl carbonate is 0.5% or less, a white solid is not substantially generated and the apparatus is not clogged.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION That is, according to the present invention, in the presence of a catalyst,
When a diaryl carbonate represented by the general formula (3) is produced from a dialkyl carbonate having 3 to 6 carbon atoms represented by the general formula (1) and an aromatic hydroxy compound represented by the general formula (2), This is a method for producing a diaryl carbonate in which the alkyl carbamate represented by the general formula (4) contained in the carbonate is 0.5 mol% or less of the dialkyl carbonate.

Embedded image RO-CO-OR (1) ArOH (2) ArO-CO-OAr (3) RO-CO-NH ₂ (4) (In the formula, R represents an alkyl group having 3 to 6 carbon atoms, Ar represents a phenyl group which is unsubstituted or substituted by an alkyl group, an alkoxy group or a halogen.)

In the present invention, the dialkyl carbonate used is one generally produced from an alkyl alcohol having 3 to 6 carbon atoms and urea. Specific examples of the alcohol include various isomers of propanol, butanol, pentanol, and hexanol. In order to produce an alkylaryl carbonate and a diaryl carbonate, in order to proceed the reaction, it is necessary to remove the by-produced alkyl alcohol from the reaction system. However, the alkyl alcohol having 2 or less carbon atoms has a boiling point of that of the dialkyl carbonate. Since the difference is small, it is difficult to selectively remove only the alkyl alcohol. Further, since the alkyl alcohol having 7 or more carbon atoms has a boiling point close to or opposite to that of the aromatic hydroxy compound, it is also difficult to selectively remove the alkyl alcohol. When the dialkyl carbonate is produced, the alkyl alcohol is used in an amount of 0.1 to 10 times the molar amount of urea.

In the above reaction, an alkyl carbamate is first produced, and this is further reacted with an alkyl alcohol to form a dialkyl carbonate. The reaction from urea to alkyl carbamate is fast, but the reaction from alkyl carbamate to dialkyl carbonate is slow.
Therefore, the preferred reaction conditions are different at each stage,
When carrying out the reaction continuously, it is preferable to connect two or more reactors to carry out the reaction. On the other hand, when it is carried out in a batch system, it can be carried out successively in the same reactor. Since ammonia is produced in this reaction, the reaction is carried out while appropriately discharging ammonia out of the system. In order to selectively discharge only ammonia, it is preferable to install a reflux condenser or a distillation column above the reactor.

The step of producing an alkyl carbamate from urea can be reacted at relatively low temperatures. A preferable reaction temperature is 100 to 200 ° C., and if the temperature is elevated at this stage, a side reaction occurs, which is not preferable. The reaction pressure is suitably atmospheric pressure to 2 MPa. The reaction time is 0.5 to 4 hours.

The preferred reaction temperature is 180 to 260 ° C. because the reaction of producing the dialkyl carbonate from the alkyl carbamate is slow. Reaction pressure is normal pressure ~
3 MPa is suitable. The reaction time is 1 to 20 hours.

It is desirable that each step of the above reaction is carried out in a high boiling point solvent. Preferred high boiling point solvent species include hydrocarbons and ethers having a boiling point of 180 ° C. or higher. Specifically, undecane, dodecane,
Tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane, tetramethylpentadecane, dicyclohexyl,
Hexylbenzene, cyclohexylbenzene, heptylbenzene, octylbenzene, nonylbenzene, decylbenzene, undecylbenzene, diisopropylbenzene, triisopropylbenzene, pentamethylbenzene, methylnaphthalene, diphenylmethane, ethylbiphenyl, bibenzyl, dihexylether, dioctylether, cyclo Dodecyl methyl ether, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, butyl phenyl ether, benzyl phenyl ether, dibenzyl ether, diphenyl ether or ditolyl ether (each example includes each isomer) Are exemplified. Further, it is possible to lower the melting point of the high boiling point solvent by mixing and using these high boiling point solvents.

As the catalyst for producing dialkyl carbonate from urea, known catalysts can be used. As catalysts for this reaction, JP-A-55-102542 and JP-A-5-102542 are available.
5-102543, JP-A-57-26645, JP-A-SHO-5
Many catalysts are already described in 7-175147 and the like, but any catalyst can be used in the present invention. Among them, particularly, oxides, hydroxides, halides, inorganic salts, organic acid salts, alkoxides, alkyl oxides, or oxides of one or more metals selected from zinc, lead, copper, tin, titanium, gallium, and indium. Alkyl alkoxides are preferably used. Specific examples thereof include zinc oxide, lead acetate, copper acetate, dibutyltin oxide, dioctyltin oxide, dibutyldibutoxytin, tetrabutoxytitanium and gallium tributoxide.
A suitable amount of this catalyst is 0.1 to 20 mol% with respect to urea.

In addition to the dialkyl carbonate, the reaction solution prepared from the dialkyl carbonate from urea contains an intermediate alkyl carbamate, a catalyst, an unreacted alkyl alcohol and a high boiling point solvent when used. It takes a long reaction time to carry out the reaction until all the alkyl carbamate is converted to the dialkyl carbonate, which is not practical. Therefore, the alkyl carbamate, the catalyst, the alkyl alcohol and the high boiling point solvent are preferably separated by distillation and reused.

Since the dialkyl carbonate and the alkyl carbamate azeotrope, it is difficult to completely separate them by a usual distillation operation. Therefore, as a method for separating the dialkyl carbonate and the alkyl carbamate, (1)
A method of breaking the azeotrope by adding an aromatic hydroxy compound for distillation, (2) a method of distilling under two kinds of operating pressures having different azeotropic compositions, (3) a method of cooling to crystallize an alkyl carbamate, (4) There is a method of removing the alkyl carbamate by washing with warm water, but the content of the alkyl carbamate needs to be 0.5 mol% or less. Therefore, it is preferable to separate by the methods of (1) and (2).

The aromatic hydroxy compound which is the raw material of the present invention means phenol, an alkyl group, an alkoxy group,
Phenol substituted with halogen or the like, and specifically, phenol, cresol (each isomer), xylenol (each isomer), ethylphenol (each isomer), methoxyphenol (each isomer), fluorophenol (each isomer) Isomer), chlorophenol (each isomer) and the like. The aromatic hydroxy compound is usually used in an amount of 0.2 to 10 times, and more preferably 1 to 5 times the mol of the dialkyl carbonate.

The production of the diaryl carbonate from the dialkyl carbonate is carried out by a disproportionation step following the transesterification step. In the transesterification step, an alkylaryl carbonate (or diaryl carbonate) and an alkyl alcohol are produced from the dialkyl carbonate (or alkylaryl carbonate) and the aromatic hydroxy compound. In the disproportionation process,
Diaryl carbonate and dialkyl carbonate are produced from the alkyl aryl carbonate. Both reactions are equilibrium reactions, so in order to proceed the reaction,
It is necessary to distill off the generated alkyl alcohol or dialkyl carbonate. Therefore, it is preferable to carry out the reaction in a reactor having a distillation column installed above.

The catalyst used in the above reaction may be any one generally known as a transesterification catalyst, but in particular, an alkoxide of a metal selected from titanium, aluminum, gallium, tin and yttrium. , Aryl oxides, alkyl-substituted oxides, and acetylacetonates are preferably used. Among the above catalysts, particularly Ti (OX) ₄ , R ′ ₂ SnO, R ′ ₂ Sn
(OX) ₂ , Sn (OX) ₄ (in the compound, X has 3 carbon atoms
To 6 are alkyl groups or aryl groups, and R ′ is an alkyl group having 1 to 10 carbon atoms. ) Or a compound thereof and an adduct of a compound represented by XOH (X is the same as above), or a mixture containing at least one of the above compounds is preferably used.

Specific examples of the above catalyst include titanium tetrapropoxide (each isomer), titanium tetrabutoxide (each isomer), titanium tetraphenoxide, dibutyl tin oxide (each isomer), dioctyl tin oxide (each isomer). Isomer), dibutyldibutoxytin (each isomer), dibutyldiphenoxytin (each isomer) and the like. A suitable amount of the catalyst is 0.01 to 10 mol% based on the dialkyl carbonate.

The reaction may be continuous or batchwise. In the case of the continuous system, it is preferable to use one or more reactors for each of the transesterification step and the disproportionation step.
In the case of the batch system, the transesterification step and the disproportionation step can be sequentially performed in the same reactor.

Both the transesterification step and the disproportionation step are 1
It is carried out at a reaction temperature of 60 to 250 ° C. The reaction pressure is 0.0
01-0.5 MPa is suitable. In the disproportionation step, since the dialkyl carbonate having a higher boiling point than the alkyl alcohol is distilled off, the reaction is carried out at a lower pressure than in the transesterification step.

[0025]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples. In this Example, when simply described as butyl, n-
Shall indicate butyl.

Example 1 A distillation column made of glass with a vacuum jacket (Sulzer Lab packing packing, inner diameter 50 mmφ, packing section height 1100 m)
m) was connected to the upper part in a 5 liter round bottom flask, 1816.6 g of the charged liquid [862 g of dibutyl carbonate,
Phenol 932g, Titanium tetraphenoxide 2
0.8 g (1 mol% based on dibutyl carbonate) and 1.8 g of butyl carbamate (0.3 mol% based on dibutyl carbonate)] were charged. It was heated by a mantle heater while stirring at 300 rpm with a mechanical stirrer. After the temperature at the bottom of the column reached 191 ° C and the reflux started, total reflux was performed for 10 minutes, and then
Distillation was started at a reflux ratio of 30. The reaction was started when the distillation was started, and the yield (mol%) of butylphenyl carbonate based on the charged dibutyl carbonate was analyzed by gas chromatography. As a result, the reaction was 20.3 in 30 minutes
%, 60 minutes 25.8%, 90 minutes 29.7%, 120
It was 33.3% in minutes and 35.8% in 150 minutes. The temperature at the bottom of the column at the start of distillation was 192 ° C, and the temperature after 150 minutes was 198 ° C. 150 minutes after the start of the reaction, the reflux ratio was set to 0.2 and the reaction pressure was gradually changed from normal pressure to 450 mmH.
By lowering to g, mainly unreacted phenol and dibutyl carbonate were distilled off. At this time, the temperature at the bottom of the column was 203 ° C. After 37 minutes, unreacted phenol and dibutyl carbonate were almost distilled off. The temperature at the bottom of the column at this time was 205 ° C. Therefore, the reaction pressure
Dibutyl carbonate was mainly distilled off while gradually lowering the pressure to 100 mmHg. The temperature at the bottom of the column at this time was 202 ° C. The reaction was terminated 2 hours after the reflux ratio was adjusted to 0.2, and the reaction solution was analyzed. As a result, 154 g of diphenyl carbonate was formed. The temperature at the bottom of the column at this time was 207 ° C. No white solid was deposited during or after the reaction. The reaction solution was extracted and the above reaction was repeated 4 times without washing the apparatus, but no white solid was deposited.

Comparative Example 1 The reaction was carried out by the same equipment and operation as in Example 1 except that 1820.6 g of a charging solution containing 5.8 g of butyl carbamate (1.0 mol% based on dibutyl carbonate) was charged. . Butylphenyl carbonate yield (mol%) was 20.1% in 30 minutes of reaction and 25.1% in 60 minutes.
%, 90 minutes 29.3%, 120 minutes 32.2%, 15
It was 35.1% in 0 minutes. The temperature at the bottom of the column at the start of distillation was 192 ° C, and the temperature after 150 minutes was 198 ° C. After the reaction was completed, 151 g of diphenyl carbonate was produced. Precipitation of white solid was observed in the reactor and the cooling tube. The reactor solids were filtered, washed with toluene and dried to give 629 mg of a white solid. The white solid was analyzed by liquid chromatography to find that it had 65% by weight of cyanuric acid and 2,4-dioxo-dihydro-5,6-
It contained 17% by weight of benzo-1,3-oxazine and 6% by weight of butyl allophanate. Also, from the cooling pipe 115
Recovered mg of white solid. Similarly, when analyzed by liquid chromatography, butyl allophanate was 74% by weight,
It contained 10% by weight of cyanuric acid.

Comparative Example 2 The reaction was carried out by the same apparatus and operation as in Example 1 except that 1872.8 g of a charging liquid containing 58 g of butyl carbamate (10 mol% based on dibutyl carbonate) was charged. Butyl phenyl carbonate yield (mol%)
Is 18.5% in 30 minutes, 23.7% in 60 minutes, 9
It was 26.9% at 0 minutes and 30.2% at 120 minutes. The temperature at the bottom of the column at the start of distillation was 193 ° C, and the temperature after 120 minutes was 197 ° C. As the reaction proceeded, white solids attached to the cooling tube gradually increased. After 130 minutes, the cooling pipe was blocked and the reaction could not be continued.

[0029]

Industrial Applicability According to the method of the present invention, when a diaryl carbonate produced from urea and an aromatic hydroxy compound are produced, the diaryl carbonate can be produced without causing clogging of the device with a solid. .

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Claims (5)

[Claims] 1. In the presence of a catalyst, a dialkyl carbonate having 3 to 6 carbon atoms represented by the general formula (1) and an aromatic hydroxy compound represented by the general formula (2) are converted into a compound represented by the general formula (3). The method for producing a diaryl carbonate, wherein the alkyl carbamate represented by the general formula (4) contained in the dialkyl carbonate is 0.5 mol% or less of the dialkyl carbonate. Embedded image RO-CO-OR (1) ArOH (2) ArO-CO-OAr (3) RO-CO-NH ₂ (4) (In the formula, R represents an alkyl group having 3 to 6 carbon atoms, Ar represents a phenyl group which is unsubstituted or substituted by an alkyl group, an alkoxy group or a halogen.) 2. The catalyst is Ti (OX)._Four, R '₂Sn
O, R '₂Sn (OX) ₂And Sn (OX)_Four(Compound
Where X represents an alkyl group or an aryl group having 3 to 6 carbon atoms
R'represents an alkyl group having 1 to 10 carbon atoms. ) Noi
Or XOH (where X is the same as above)
Same. ) Is an adduct of a compound represented by
Is also a mixture containing one of the above compounds.
A method for producing the described diaryl carbonate. 3. The method for producing a diaryl carbonate according to claim 1, wherein R is an n-butyl group. 4. The method for producing a diaryl carbonate according to claim 1, wherein Ar is a phenyl group. 5. The dialkyl carbonate in which the dialkyl carbonate and the alkyl carbamate are separated by adding an aromatic hydroxy compound to a mixture of the dialkyl carbonate and the alkyl carbamate and distilling the mixture is used. Method for producing diaryl carbonate.