JP4073048B2 - Method for producing diaryl carbonate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention uses an aromatic heterocyclic nitrogen compound as a catalyst to react an aromatic monohydroxy compound with phosgene or arylchloroformate to produce a high-purity diarylcarbonate that does not contain arylchloroformate. The present invention relates to a method for producing a diaryl carbonate in which an aromatic heterocyclic nitrogen compound as a catalyst is easily and efficiently recovered and reused.
The diaryl carbonate obtained in the present invention is useful as a raw material for aromatic polycarbonate by the melt transesterification method.
[0002]
[Prior art]
As a method for producing diaryl carbonate, a phase interface phosgenation method (Schotten-Baumann reaction) of an aromatic monohydroxy compound in an aqueous alkali solution is known.
In this case, partial saponification of phosgene occurs with an aqueous alkali solution, and a large amount of sodium chloride is generated as a by-product. Therefore, the effective utilization rate of phosgene and alkali is low, and the by-product salt is not reused as a catalyst. Have difficulty.
As a means for solving this problem, a method has been proposed in which the reaction between an aromatic monohydroxy compound and phosgene is carried out in the presence of a catalytic amount of an aromatic heterocyclic basic nitrogen compound or a salt thereof (Japanese Patent Publication Sho 58- 50977). As a method of reusing the catalyst contained in the reaction mixture, the publication discloses a method of isolating as a readily meltable adduct as a residue material during distillation of the reaction mixture, and a second method that settles at the bottom of the reaction melt. A method for isolating the catalyst from the liquid phase is described. However, the catalyst that can be separated in the form of a readily meltable adduct as the residue of the former still is limited due to the thermal stability and boiling point of the hydrochloric acid adduct. In the case of liquid-liquid separation from the latter reaction melt In this case, a considerable amount of catalyst salt is dissolved in diaryl carbonate, and the hue of aromatic polycarbonate produced by the transesterification method with bisphenol A as a raw material is deteriorated or causes corrosion of the mold.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing a diaryl carbonate which is easily and efficiently recovered and reused, and which is substantially free of aryl chloroformate.
[0004]
[Means for Solving the Problems]
The present invention relates to a process for producing a diaryl carbonate by reacting an aromatic monohydroxy compound with phosgene or an aryl chloroformate in the presence of an aromatic heterocyclic nitrogen-containing basic compound or a salt thereof as a catalyst. the reaction mixture was allowed to contact with an alkaline aqueous solution, the organic phase and the aqueous phase was separated from the organic phase, the aromatic heterocyclic free Yu release by distillation at 50 to 80 ° C. in vacuum 20~40torr The nitrogen basic compound and the unreacted aromatic monohydroxy compound are recovered, and the recovered free aromatic heterocyclic nitrogen-containing basic compound and the unreacted aromatic monohydroxy compound are recycled to the reaction system as they are, followed by Providing a method for producing diaryl carbonate, wherein diaryl carbonate is recovered by distillation A.
[0005]
[Action]
The resulting reaction mixture is neutralized with an aqueous alkali solution, separated into an organic phase and an aqueous phase, and the organic phase is distilled, whereby the free basic catalyst can be recovered almost quantitatively. In addition, by adding an alkali in the neutralization step of the reaction mixture, the aryl chloroformate remaining in a trace amount in the reaction step can be converted into diaryl carbonate and phenol and completely disappeared.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Aromatic monohydroxy compounds:
Aromatic monohydroxy compounds are those in which a hydroxy group is bonded directly to an aromatic ring, and alkyl or aryl via phenol, alkylphenols such as cresol and butylphenol, arylphenols, halogenated phenols and heteroatoms. Group-bound phenols can be used.
Aryl chloroformate:
As the aryl chloroformate, the aromatic monohydroxy compound chloroformate can be used.
[0007]
phosgene:
The phosgene is preferably pure without containing impurities such as methylene chloride and carbon tetrachloride. Phosgene is used in an amount of 1.0 mol or less per 1.0 mol of the aromatic monohydroxy compound.
Aromatic heterocyclic nitrogen-containing basic compound or salt thereof:
As an aromatic heterocyclic nitrogen-containing basic compound used as a catalyst, a nitrogen atom is present in an aromatic 5- or 6-membered ring, and a strong bond with phosgene or a carbonate ester is caused under the reaction conditions. It is a basic nitrogen compound that does not have a functional group (for example, an amino group or a hydroxy group) that easily occurs, and the ring may have other heteroatoms such as oxygen and sulfur in addition to the nitrogen atom . Specific examples of such catalysts are pyridine, quinoline, picoline, imidazoles, benzimidazoles, pyrazoles, triazoles and benzotriazoles.
[0008]
The aromatic heterocyclic nitrogen-containing basic compound catalyst immediately changes to the corresponding hydrochloride salt in the reaction mixture. Since this hydrochloride is in a dissociation equilibrium with the free basic catalyst, instead of the free basic catalyst, a salt of the basic catalyst, for example, an inorganic acid salt such as hydrochloride or sulfate, formate, etc. And organic acid salts such as acetate can be used.
These catalysts are preferably used in an amount of 0.001 to 0.20 mol, more preferably 0.01 to 0.10 mol, relative to 1.0 mol of the aromatic monohydroxy compound.
alkali:
As the alkali, sodium, potassium, calcium and barium hydroxide, carbonic acid and phosphoric acid sodium salt and ammonium salt can be used.
[0009]
reaction:
The present invention will be described in detail with reference to FIG. 1, taking the reaction of an aromatic monohydroxy compound and phosgene as an example.
In the reaction, a mixture of an aromatic monohydroxy compound (1) and an aromatic heterocyclic nitrogen-containing basic compound or a salt thereof (2) is charged into the reactor (4), and this is heated and melted. This is done by introducing gaseous phosgene (3) into the mixture with sufficient stirring. As reaction temperature, 120-190 degreeC is preferable. The amount of phosgene introduced is preferably 1.0 mol or less, more preferably 0.4 to 0.5 mol, relative to 1.0 mol of the aromatic monohydroxy compound. Although the stoichiometric amount is 0.5 mol, the unreacted aromatic monohydroxy compound is inevitably left by suppressing the introduction amount of phosgene below the stoichiometric amount, and the reaction intermediate aryl The reaction of forming a diaryl carbonate between a chloroformate and an aromatic monohydroxy compound is promoted to obtain a reaction mixture that is substantially free of aryl chloroformate that adversely affects the production of industrial grade uncolored polycarbonate. At that time, if necessary, nitrogen gas (5) is blown into the reaction mixture after introducing phosgene, and hydrochloric acid (6) produced by the reaction is removed out of the system, whereby the arylchloroformate and the aromatic monohydroxy compound are removed. The equilibrium reaction can be further promoted.
The mixture after completion of the reaction contains diaryl carbonate, unreacted aromatic monohydroxy compound, trace impurities and hydrochloride of aromatic heterocyclic nitrogen-containing basic compound which is a catalyst.
[0010]
For catalyst recovery, the reaction mixture (7) is neutralized by contacting with an alkaline aqueous solution (8) at 80 to 95 ° C., and the organic phase and the aqueous phase are separated (9) in the pH range of 7 to 13, and the organic phase is distilled. According to (10), the free basic catalyst (11), the unreacted aromatic monohydroxy compound (12) and the diaryl carbonate (13) are separated.
The distillation temperature is 50 to 80 ° C. when the free basic catalyst is 20 to 40 torr, and 20 to 40 torr when the unreacted aromatic monohydroxy compound is phenol or the like, and the diaryl carbonate is diphenyl carbonate. In the case of 5 to 10 Torr and 140 to 160 ° C.
The alkali amount required for neutralization is sufficient to be equal to or slightly excess (1.1 mole times) that of the catalyst hydrochloride, and when used in a large excess, hydrolysis of the diaryl carbonate is not preferable. The recovered free catalyst and unreacted aromatic monohydroxy compound can be reused as they are.
[0011]
In the present invention, the mixture (7) after completion of the reaction contains almost no arylchloroformate, but even when it contains about several thousand ppm of arylchloroformate, neutralization of the catalyst hydrochloride by addition of the alkaline aqueous solution 8 By passing through the process, the aryl chloroformate can be converted into diaryl carbonate and phenol and completely disappeared.
Purification of the diaryl carbonate (13) is carried out by distillation-purifying the reaction mixture after removing the catalyst, the unreacted aromatic monohydroxy compound and the arylchloroformate again under vacuum.
The production of the diaryl carbonate of the present invention may be a continuous type or a batch type (batch type).
[0012]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
Example 1
Three jacketed glass reaction vessels (with an internal volume of 1 L and an overflow pipe installed at a position of 700 ml of actual liquid) connected to an oil circulation external heating device were connected in series. An exhaust pipe with a condenser for removing the generated hydrochloric acid gas out of the system was connected to the second and third reaction vessels.
Molten phenol previously added with 5 mol% of pyridine and stirred was heated to 150 ° C. while being continuously fed to the first reaction vessel at about 700 ml / hr (phenol 716 g / hr, corresponding to pyridine 30 g / hr). Warm up. While sufficiently stirring, phosgene (361 g / hr) of 0.48 molar ratio of supplied phenol was continuously supplied to the first reaction vessel.
[0013]
The reaction mixture flowing out from the first reaction vessel was supplied to the second reactor via the overflow pipe, and the reaction mixture flowing out from the second reactor was similarly supplied to the third reactor. The reaction mixture flowing out of the third reactor was extracted into a polypropylene receiver. A nitrogen gas blowing tube was installed in the third reactor, and 70 N liter / hr of nitrogen gas was continuously supplied into the reaction mixture. 1 kg of the reaction mixture (89% by weight of diphenyl carbonate, 6% by weight of phenol, 5% by weight of pyridine hydrochloride, phenyl chloroformate not detected) extracted after the composition was sufficiently stabilized was connected to an oil circulation external heating device. The temperature was raised to 85 ° C. in a jacketed glass reaction vessel. After adding 124 g of 15% by weight sodium hydroxide aqueous solution and stirring for 20 minutes, the mixture was allowed to stand for 30 minutes, and then the aqueous phase and the organic phase were extracted separately. The pH after addition of the aqueous sodium hydroxide solution was 8.
[0014]
The separated organic phase was purified by distillation in a vacuum distillation column packed with 10 Sulzer Packing (manufactured by Sumitomo Heavy Industries). Specifically, after free form pyridine and phenol are distilled off at a vacuum of 20 to 40 torr, an oil bath temperature of about 220 ° C., a top temperature of 50 to 80 ° C., a vacuum of 10 torr, an oil bath temperature of about 230 ° C., and a top temperature At 150 ° C., 750 g of purified diphenyl carbonate containing no free pyridine and aryl chloroformate (0 ppm) was obtained.
[0015]
【The invention's effect】
According to the method of the present invention, when a diaryl carbonate is produced by reacting an aromatic monohydroxy compound with phosgene or an aryl chloroformate, it has a high purity that does not contain an aryl chloroformate that causes coloring of an industrial polycarbonate. And the aromatic heterocyclic nitrogen-containing basic compound and aromatic monohydroxy compound, which are catalysts, can be easily and efficiently recovered.
[Brief description of the drawings]
FIG. 1 is a flow sheet diagram showing a method for producing a diaryl carbonate of the present invention.

Claims (4)

In a method for producing a diaryl carbonate by reacting an aromatic monohydroxy compound with phosgene or an aryl chloroformate in the presence of an aromatic heterocyclic nitrogen-containing basic compound or a salt thereof as a catalyst, the reaction mixture formed is after contact with the aqueous alkali solution, an organic phase and the aqueous phase was separated from the organic phase, aromatic Yu release by distillation at 50 to 80 ° C. in vacuum 20~40torr heterocyclic nitrogen-containing basic compound and unreacted aromatic monohydroxy compound recovered, along with the recycling of recovered free aromatic heterocyclic nitrogen-containing basic compound and unreacted aromatic monohydroxy compound as it is to the reaction system, a diaryl carbonate and subsequently A method for producing diaryl carbonate, which is recovered by distillation.   An aromatic heterocyclic nitrogen-containing basic compound is used in an amount of 0.001 to 0.20 mol and phosgene is used in an amount of 0.5 to 1.0 mol with respect to 1.0 mol of an aromatic monohydroxy compound, and phosgene is introduced. The process for producing a diaryl carbonate according to claim 1, wherein the temperature of the reaction system is 120 to 190 ° C.   The method for producing a diaryl carbonate according to claim 1, wherein the aromatic heterocyclic nitrogen-containing basic compound is pyridine or imidazole.   The method for producing a diaryl carbonate according to claim 1, wherein the pH of the liquid obtained by contacting the produced reaction mixture with an alkaline aqueous solution is in the range of 7 to 13.

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