JPH1077250A - Production of diphenyl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce diphenyl carbonate of sufficient color phase without development of hydrogen chloride by making phenol with phosgene by using a pyridine compound as a catalyst under specifically controlled conditions, including concentration of the catalyst to the phenol, reaction temperature and reagent composition. SOLUTION: This diphenyl carbonate is produced by reacting 1mol of phenol with 0.5mol or less phosgene at a phenol conversion ratio of 90% by the use of a pyridine compound of formula I (R is H, methyl or methoxy) as a catalyst. The reaction is carried out under the conditions that [C] is 1.2-10mol%, [T] 138-165 deg.C, [X] 1.5-8, where [C]: concentration of the catalyst to phenol (mol%), [T]: reaction temperature ( deg.C), [X]: mol ratio of phenol to phenyl chloroformate present in the reaction system at the end of reaction, and [Y]: mol ratio of phosgene used for the reaction with phenol, and also under conditions that satisfy formulae II and III (A is a constant expressed by formula III; B is a constant expressed by formula IV), thus obtaining the objective compound at a high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing diphenyl carbonate from phenol and phosgene using a pyridine compound as a catalyst. Diphenyl carbonate is an important compound as a raw material of polycarbonate by a solventless transesterification reaction.

[0002]

2. Description of the Related Art Diphenyl carbonate is used in large quantities as a raw material for producing aromatic polycarbonate by transesterification with bisphenol A. Since the obtained aromatic polycarbonate is used for an optical disk substrate or the like, a high-quality polycarbonate without coloring is required. For this reason, there is a demand for a method for producing diphenyl carbonate that does not contain a coloring matter.

As a method for producing diphenyl carbonate by the reaction between phenol and phosgene, a stoichiometric reaction between phenol and phosgene using caustic soda has been known for a long time. However, in this reaction, the use of caustic soda and the production of a large amount of sodium chloride as a by-product increase the cost of raw materials, and have problems such as wastewater treatment.

In order to solve these problems, there has been proposed a method represented by the following reaction formula [I] in which phenol is directly reacted with phosgene in the presence of a catalyst. For this reaction that produces hydrogen chloride, hydrogen chloride is a useful chemical substance and can be reused separately in a chemical plant, eliminating the need to discharge chlorinated substances outside the plant and reducing the burden on wastewater treatment. .

[0005]

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A number of methods are known for the above reaction using a heterogeneous catalyst. However, these methods have problems such as by-products such as phenyl salicylate having a boiling point very close to that of diphenyl carbonate and elution of metal components. Not resolved. The method 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 diphenyl carbonate can be obtained by reacting an aromatic monohydroxy compound with phosgene in the presence of a homogeneous catalyst. For example, U.S. Pat. No. 2,837,555 proposes performing solventless condensation in the presence of tetramethylammonium halide as a catalyst. However, this method requires a relatively large amount of catalyst and requires a relatively high temperature of 180 to 215 ° C. in order to obtain an economic reaction rate, which is thermally unstable. With the risk of decomposition of the tetramethylammonium halide. In addition, phosgene is consumed at a much higher rate than required stoichiometrically.

Also, Japanese Patent Publication No. 58-50977 discloses that
A reaction involving the elimination of hydrogen chloride, if necessary, in a solvent at a temperature of 40 to 180 ° C with respect to 2 moles of an aromatic monohydroxy compound such as phenol, using an aromatic nitrogen-containing heterocyclic compound as a catalyst at a temperature of 40 to 180 ° C. (Hereinafter referred to as a phosgenation reaction) to produce a diaryl carbonate such as diphenyl carbonate, which is carried out at a lower temperature and at least twice as fast as the method described in the above-mentioned U.S. Patent. It is disclosed to do.

The method described in Japanese Patent Publication No. 50-50977 is industrially excellent for such a reason. In this method, however, phenyl chloroformate (hereinafter referred to as PCF) which is an intermediate product of diphenyl carbonate is used. Abbreviated.) And the reaction rate of phenol with diphenyl carbonate does not have a sufficient rate compared to the rate of PCF formation.
It was thought that a small amount of PCF remained and caused coloring.

The present inventors have studied various reaction conditions for various aromatic nitrogen-containing heterocyclic compounds in order to suppress PCF by-produced in the phosgenation reaction. It has been found that a relatively simple 6-membered aromatic heterocyclic base such as the pyridine-based compound shown has the lowest selectivity to PCF and at the same time has an industrial reaction rate. However, the reaction using these catalysts did not show a sequential reaction behavior using PCF as a reaction intermediate, but rather PCF was found to be by-produced in parallel with the production of diphenyl carbonate. That is, if the reaction is driven to high phenol conversion (> 90%) under practical reaction conditions, PCF formation is reduced by at least 1%.
It turned out that it cannot be suppressed below. Next, the cause of the coloring when these catalysts were used was examined. The main cause of the coloring was not the coloring by the PCF itself, but the decomposition of the adduct (2) of the pyridine compound as a catalyst and the PCF. Was found to be the cause.

[0010]

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(In the formula, R has the same meaning as in the above formula (1).) Chemical Reviews, 1973, vo
l. 73, No. 1, as described in p77,
The pyridine-based compound is selectively pyridine-based compound-phosgene adduct (3) or (4) under a phosgene atmosphere.

[0012]

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(Wherein R has the same meaning as in the above formula (1)), which quickly reacts with phenol, so that a pyridine compound-PCF adduct is obtained during the phosgenation reaction. The amount of formation and accumulation is substantially small, and their decomposition is negligibly small, so that there is no problem of coloring. However, when all of the phosgene has reacted and disappeared, the pyridine-based compound is rapidly converted into PCF.
It was found that when a specific amount of phenol was not present, it turned into a colored impurity quickly in such a temperature range. That is, in the reaction between phenol and phosgene according to the conventional method, PCF depends on the reaction conditions.
When the phosgene in the reaction solution cannot be completely suppressed and the phosgene in the reaction solution is to be completely reacted, when the phosgene disappears, the catalyst pyridine compound and P
There was a problem that an adduct of CF was formed and quickly changed to a colored product.

[0014]

DISCLOSURE OF THE INVENTION The present invention relates to a method for producing diphenyl carbonate by completely reacting phosgene when producing diphenyl carbonate from phenol and phosgene using the pyridine compound represented by the above general formula (1) as a catalyst. In the process, a pyridine compound as a catalyst and PC
The inventors of the present invention have conducted studies on a method for suppressing the decomposition of the adduct with F and preventing the coloring of diphenyl carbonate, and have obtained a large amount of data to derive the method of the present invention.

[0015]

According to the method of the present invention, a compound represented by the general formula (1):

[0016]

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(Wherein R represents a hydrogen atom, a methyl group, or a methoxy group) and a phenol conversion ratio of 90% or more in the presence of a pyridine compound catalyst represented by the formula:
In a method for producing diphenyl carbonate by reacting less than 0.5 mol of phosgene with respect to mol, [C]: concentration of catalyst to phenol (mol%) [T]: reaction temperature (° C.) [X]: end of reaction When the molar ratio of phenol to phenyl chloroformate present in the reaction system at the time [Y]: the molar ratio of phosgene reacted to phenol, [C] is 1.2 to 10 mol% and [T] Is 13
8 to 165 ° C., [X] is 1.5 to 8, and the following formulas (1) and (2)

[0018]

[Expression 7] log [C] ≧ A−B × T (1)

[0019]

−0.302−0.0828 × log [X] + 0.0448 × [log [X]] ² ≦ log [Y] ≦ −0.303 + 0.0055 × log [X] −0.0386 × [Log [X]] ² (2)

(Where (1) A and B values in the above formula are each X
(3) and (4)

[0021]

A = 5.35 + 0.132 × X−6.68 × 10 ⁻³ × X ² (3)

[0022]

B = 0.0336-6.7 × 10 ^-4 × X-4.433 × 10 ^-5 × X ² (4)

Is a constant represented by A method for producing diphenyl carbonate, characterized in that the reaction is carried out under the conditions satisfying (3).

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION

<Catalyst> As the catalyst used in the present invention, pyridine, methylpyridine (2-methylpyridine, 3-methylpyridine, 4-methylpyridine) or mixed picoline (3-methylpyridine)
Methylpyridine, a mixture of 4-methylpyridine), methoxypyridine (2-methoxypyridine, 3-methoxypyridine, 4-methoxypyridine), or a hydrochloride thereof can be used.

<Phenol> For efficient reaction of phosgene, it is preferable to use anhydrous phenol. <Phosgene> Phosgene is preferably as pure as possible, and preferably does not contain impurities such as carbon tetrachloride and methylene chloride. The reaction amount of phosgene is less than 0.5 mol, preferably 0.450 to 0.499, per mol of phenol.
Is a mole. <Catalyst concentration, reaction temperature, and phosgene reaction amount> The catalyst concentration is increased, the reaction temperature is increased, and the catalyst concentration with respect to the reaction temperature is calculated as in the above formula (1). By limiting, the decomposition and coloring of the pyridine-based compound-PCF adduct can be suppressed, so that the selectivity to PCF can be reduced synergistically. Practically, conditions under which all the supplied phosgene completely reacts are preferable.

When the value of [C] is less than 1.2 mol% with respect to the phenol catalyst concentration, a high temperature condition exceeding 165 ° C. is required to obtain a phenol conversion of 90% or more. The problem of coloration of the target product, which may be due to decomposition, is inevitable. On the other hand, if the concentration exceeds 10 mol%, the burden of separation and purification of the target product becomes excessively large, which is not desirable. Further, since the phenol is surely present in an excess amount in the reaction system until the end of the reaction, the molar ratio of phenol to PCF is set to 1.5 (molar ratio) or more. A large amount of phenol remains in the reaction system, which is extremely disadvantageous industrially. At a temperature exceeding 165 ° C., the reaction between the substantially generated PCF and the pyridine-based compound occurs to a non-negligible extent, and this is decomposed. At temperatures below 138 ° C, P
Since the catalyst concentration must be extremely high in order to suppress the formation of CF, the burden of separating and purifying the target product is undesirably increased as described above. Therefore, from the viewpoint of suppressing coloring of diphenyl carbonate, 138 to 165 ° C
The following reaction temperature is used. More preferably 150 to 160
It is a temperature of ° C. However, the A and B values are X (1.5 ≦ X ≦
8) quadratic function expressions (3) and (4)

[0027]

A = 5.35 + 0.132 × X−6.68 × 10 ⁻³ × X ² (3)

[0028]

B = 0.0336-6.7 × 10 ⁻⁴ × X-4.433 × 10 ⁻⁵ × X ² (4)

[X] is preferably 2 to 5, and in this range, it is a constant approximately expressed by the functional formulas (5) and (6) of X (2 ≦ X ≦ 5).

[0030]

A = 5.22 + 0.241 × X−0.0259 × X ² (5)

[0031]

B = 0.0335−4.47 × 10 ⁻⁴ × X (6)

At the end of the phosgenation reaction, the reaction solution is quickly subjected to an inert gas (eg, nitrogen, argon) stream to remove hydrogen chloride in the reaction solution and suppress undesired side reactions. By further reacting, a reaction [II] between the by-product PCF and phenol is performed, and the by-product PCF
Can be effectively reduced, which is industrially advantageous.

[0033]

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<Reactor> A gas-liquid reactor equipped with a stirrer is usually used. Using a tubular gas blow-in tube or a gas blow-in tube having pores, the gas is blown directly into the molten substrate. In particular, it is preferable to use a gas injection tube having micropores in order to allow the reaction to proceed efficiently. It is also possible to use a bubble column reactor without a stirrer. The reaction pressure is usually carried out at normal pressure,
It can be carried out under pressure or under reduced pressure as necessary. <Separation of diphenyl carbonate>
Liquid catalyst in the form of hydrochloride after the process (diphenyl carbonate)
-Solid (pyridine compound hydrochloride) methods such as hot filtration separation, extraction separation using a solvent, and direct distillation separation of the pyridine compound hydrochloride are possible. The obtained crude diphenyl carbonate may be further purified by distillation, crystallization, or the like.

[0035]

EXAMPLES The present invention will be described with reference to the following examples and comparative examples, but the present invention is not limited to the following examples. Example 1 Mixed picolin 0.0 in 0.5 mol (47 g) of phenol
25 mol (2.34 g, 5 mol% based on phenol)
Was added, and phosgene was continuously supplied at a supply rate of 0.3 g / min using a G2 glass filter gas injection tube, and reacted at 150 ° C. for 84 minutes [The supply amount of phosgene was 24.6 g (approx. 0.2493 mol)]. At the end of the reaction, the composition of the reaction solution was such that 0.04 mol of unreacted phenol remained, and 0.027 mol of PCF and 0.217 mol of diphenyl carbonate were formed. The phenol conversion at this time was 92%, and the actual phosgene reaction amount (phenol 1
Mole per mole) was 0.487. The molar ratio of phenol to PCF was 1.5. The solid that was cooled and solidified had a white color. In addition, the amount of reacted phosgene was equivalent to 0.487 mol with respect to 1 mol of phenol.

COMPARATIVE EXAMPLE 1 Mixed picolin 0.0 in 0.5 mol (47 g) of phenol
25 mol (2.34 g, 5 mol% based on phenol)
Was added, and phosgene was continuously supplied at a supply rate of 0.3 g / min using a gas injection tube made of a G2 glass filter, and reacted at 150 ° C. for 90 minutes [The supply amount of phosgene was 27 g (approximately 0. 273 mol)]. At the end of this reaction,
The composition of the reaction solution was such that 0.012 mol of unreacted phenol remained, and 0.028 mol of PCF and 0.23 mol of diphenyl carbonate were formed. The actual phosgene reaction amount (the number of moles per mole of phenol) determined from the amounts of PCF and diphenyl carbonate generated was 0.516, and the molar ratio of phenol to PCF was 0.43. The reaction solution quickly turned black in the course of cooling.

Comparative Example 2 A reaction was carried out in the same manner as in Example 1, and the reaction was terminated when the molar ratio of phenol to PCF became 1. In the course of cooling this reaction solution, the reaction solution turned brown. Comparative Examples 3 and 6 The reaction was carried out in the same manner as in Example 1 except that the catalyst concentration was 2 mol% and the conditions of the phosgene supply rate and the reaction time were changed. At the end of the phosgenation reaction, the molar ratios of phenol and PCF were 1.5 and 2.39, respectively, and no coloring of the reaction solution was observed. However, under these conditions, the phenol conversion rates were about 83% and 87%, respectively. Yes, less than 90%.

Example 2 Except that the concentration was 8 mol% using pyridine as a catalyst, the phosgene supply rate was 0.4 g / min, and the reaction time was 68 minutes [The supply amount of phosgene was 27.2 g (about 0.275 mol). ] Was carried out in the same manner as in Example 1. At the end of the reaction, the composition of the reaction solution was such that 0.035 mol of unreacted phenol remained, and 0.0171 mol of PCF and 0.224 mol of diphenyl carbonate were formed. Phenol conversion is about 93
%Met. Under these conditions, the molar ratio of phenol to PCF was 2.05, and no coloring of the reaction solution was observed even during the cooling process.

Comparative Examples 4 and 5 The catalyst concentrations were 8 and 5 mol%, and the reaction temperatures were 150 and 1, respectively.
At 30 ° C, the molar ratio of phenol to PCF is 0.50-
The reaction was carried out until it reached 0.55. In this case, the reaction solution slowly turned brown during the cooling process after the completion of the reaction. Comparative Example 7 A reaction was carried out at a reaction temperature of 170 ° C. in the same manner as in Example 1. At this time, brown coloration was already observed during the reaction. Therefore, a temperature of 170 ° C. is not suitable as a reaction temperature in consideration of coloring.

Example 3 A reaction was carried out at a reaction temperature of 165 ° C. in the same manner as in Example 1. At this time, no coloring of the reaction solution observed during the reaction at 170 ° C. was observed. Examples 4 and 5 The reaction was carried out in the same manner as in Examples 1 and 2. After stopping the supply of phosgene, the mixture was further purged with nitrogen (200 hours) at the same temperature for 20 minutes.
ml / min), the phenol conversion was 97.
At 3,96.4%, PCF was not detected by gas chromatography. No coloring of the reaction solution was observed. The conditions and results of the above Examples and Comparative Examples are summarized in Table 1, FIG. 1 and FIG.

[0041]

[Table 1]

[0042]

According to the method of the present invention in which phenol and phosgene are reacted using a pyridine compound as a catalyst, a high phenol conversion rate is obtained and the decomposition of the pyridine derivative-phenylchloroformate adduct is suppressed. Thus, diphenyl carbonate having an improved hue is obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a catalyst concentration for phenol and a reaction temperature in the present invention.

FIG. 2 is a graph showing the relationship between the molar ratio of phosgene to be reacted with phenol and the molar ratio of phenol to phenyl chloroformate present in the reaction system at the end of the reaction in the present invention.

Claims (3)

[Claims] 1. A compound of the general formula (1) (Wherein, R represents a hydrogen atom, a methyl group or a methoxy group) using a pyridine-based compound as a catalyst, and converting phosgene less than 0.5 mol per mol of phenol at a phenol conversion rate of 90% or more. In the method of producing diphenyl carbonate by reacting, [C]: a catalyst concentration (mol%) with respect to phenol [T]: a reaction temperature (° C.) [X]: with respect to phenyl chloroformate present in the reaction system at the end of the reaction When the molar ratio of phenol [Y]: the molar ratio of phosgene to be reacted with phenol, [C] is 1.2 to 10 mol% and [T] is 13
8 to 165 ° C., [X] is 1.5 to 8, and the following equations (1) and (2): log [C] ≧ AB × T (1) −0.302−0.0828 × log [X] + 0.0448 × [log [X]] ² ≦ log [Y] ≦ −0.303 + 0.0055 × log [X] −0.0386 × [log [X ] ² (2) (where A and B values in the above formula (1) are the functional formulas (3) and (4) of X, respectively) A = 5.35 + 0.132 × X−6.68 × 10 ⁻³ × X ² (3) B = 0.0336−6.7 × 10 ⁻⁴ × X−4.433 × 10 ⁻⁵ × X ² (4) This is a constant.) Under the conditions that satisfy
A method for producing diphenyl carbonate, characterized by reacting. 2. The method for producing diphenyl carbonate according to claim 1, wherein [X] is in the range of 2 to 5, and A and B
The method wherein the value is a constant represented by equations (5) and (6). A = 5.22 + 0.241 × X−0.0259 × X ² (5) B = 0.0335−4.47 × 10 ⁻⁴ × X (6) where 2.0 ≤X≤5.0 3. The process for producing diphenyl carbonate according to claim 1, wherein after the phosgene blowing is completed, the phenyl chloroformate composition in the reaction solution is reduced to substantially 1 mol% or less under an inert gas stream. The method characterized by reacting until.