JPH10259166A - Production of dialkyl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently obtain the subject compound at high reaction rate using a simple apparatus even in the case of using a low-boiling alcohol, by reaction between urea or a derivative therefrom and an alcohol in the presence of a high-boiling solvent and a catalyst. SOLUTION: This compound, a dialkyl carbonate, is obtained by reaction between urea or an urea derivative of the formula R1 R2 N-CO-NR3 R4 (R1 to R4 are each H or a 1-4C alkyl) such as methylurea or ethylurea and an alcohol (normally, a 1-10C aliphatic alcohol, esp. pref. 3-6C alcohol) in the presence of a high-boiling solvent >=180 deg.C, pref. >=195 deg.C, more pref. >=220 deg.C (pref. a hydrocarbon such as tetradecane or tetramethylpentadecane, ether such as diphenyl ether) and a catalyst (e.g. zinc oxide, magnesium oxide, lead acetate, copper acetate, dibutyltin oxide, tetrabutoxytitanium) pref. under the atmospheric pressure at 100-250 deg.C or so for 2-10h or so.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a dialkyl carbonate. More specifically, the present invention relates to a method for producing a dialkyl carbonate by reacting urea or a urea derivative with an alcohol, wherein the reaction is carried out in the presence of a high boiling point solvent. Dialkyl carbonate is a compound useful as a raw material for diaryl carbonate, especially diphenyl carbonate.

[0002]

2. Description of the Related Art A method for producing a dialkyl carbonate by reacting urea or a urea derivative with an alcohol is described in JP-A-55-102542. The catalyst for this reaction is described in JP-A-57-175147 and WO9517369.

[0003] The conventionally known method for producing dialkyl carbonate by reacting urea and alcohol requires a high reaction temperature of 180 ° C or more and a reaction time of 8 hours or more. Also, dialkyl carbonates that can be produced at normal pressure by this method have been limited to high boiling alcohols such as 2-ethylhexanol. That is, when producing a dialkyl carbonate from an alcohol having a boiling point of 180 ° C. or less and urea, it is necessary to allow the reaction to proceed for an extremely long time or to increase the pressure in order to obtain a sufficient reaction temperature.

Japanese Patent Application Laid-Open No. 57-26645 discloses an example in which dibutyl carbonate is produced from butyl carbamate and butanol as raw materials. According to this method,
The reaction is carried out under pressurized conditions of 9 to 10 bar, but the conversion of carbamate after 7 hours is only 40%.
Furthermore, when isobutanol is used, it takes 40 hours to complete the reaction, and a practical reaction rate has not been obtained. When the reaction is carried out under pressure, the generated ammonia must be removed while maintaining the pressure, so that the apparatus becomes complicated and expensive.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a method for producing a dialkyl carbonate which can obtain a high reaction rate and can obtain a dialkyl carbonate with a simple apparatus even when a low-boiling alcohol is used. The purpose is to provide.

[0006]

Means for Solving the Problems The present inventors have made it possible to raise the reaction temperature at a low pressure by conducting the reaction in a solvent having a high boiling point, and to confirm that the reaction proceeds at a high reaction rate. I found it. Moreover, surprisingly,
It has also been found that the solvent of the present invention has the effect of accelerating the reaction, and the reaction rate is improved more than the effect of increasing the temperature.

[0007]

DETAILED DESCRIPTION OF THE INVENTION That is, the present invention is a method for producing a dialkyl carbonate in which urea or a urea derivative is reacted with an alcohol in the presence of a high-boiling solvent having a boiling point of 180 ° C. or higher and a catalyst.

In the present invention, the urea derivative is a compound represented by the following general formula (1).

Embedded image R ₁ R ₂ N—CO—NR ₃ R ₄ (1) (wherein R _1, R _2, R _{3 and} R ₄ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms) In particular, R1 _, R2 _, R
_{3. The} case where all of R ₄ are hydrogen is called urea. )

Examples of such urea or urea derivatives include urea, methyl urea, ethyl urea, propyl urea,
Butyl urea, N, N-dimethyl urea, N, N-diethyl urea, N, N-dipropyl urea, N, N-dibutyl urea, N, N′-dimethyl urea, N, N′-diethyl urea, N, N '-Dipropyl urea, N, N'-dibutyl urea, tetramethyl urea, tetraethyl urea, tetrapropyl urea, tetrabutyl urea and the like (each example also includes each isomer).

In the present invention, the alcohol is not particularly limited as long as it is an aliphatic alcohol.
-10 aliphatic alcohols are used. Examples of these alcohols include methanol, ethanol, propanol, butanol, pentanol (amyl alcohol), hexanol, heptanol, octanol, nonanol, decanol and the like (each of which includes each isomer). The use of an alcohol having 1 to 8 carbon atoms is preferable because the effect of improving the reaction rate is remarkable, and an alcohol having 3 to 6 carbon atoms is particularly preferable.

[0011] The solvent used in the present invention is preferably a solvent having a boiling point of 180 ° C or higher. A solvent having a boiling point of 195 ° C. or higher is more preferable, and a boiling point of 220 ° C. or higher is more preferable, because the effect of increasing the boiling point is high.

The type of the solvent is not particularly limited, but a solvent that reacts with ammonia (ketones, esters, etc.) is not preferred. An amide-based solvent which is considered to be stable to ammonia can also be used, but a solvent having a high polarity is not preferable because it prevents the discharge of ammonia out of the system.

Preferred solvent species include hydrocarbons and ethers. The hydrocarbon may be an unsaturated hydrocarbon other than the aromatic, but a saturated hydrocarbon having higher stability or an aromatic hydrocarbon is preferable. As the ether, any of an aromatic ether, an aliphatic ether, and an aromatic aliphatic ether can be used.

Examples of preferable hydrocarbon solvents include the following. 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 (each example also includes each isomer).

Examples of preferable ether solvents include the following. Dihexyl ether, dioctyl ether, cyclododecyl 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, ditolyl ether Each isomer is also included).

Known catalysts can be used. As catalysts for this reaction, many catalysts have already been described in JP-A-55-102542, JP-A-57-26645, JP-A-57-175147, etc., and any of these catalysts can be used in the present invention. Can be. Among them, oxides, hydroxides, halides, inorganic salts, organic acid salts, alkoxides, alkyl oxides, and alkyls of one or more metals selected from zinc, magnesium, lead, copper, tin, and titanium are particularly preferred. Alkoxides are preferably used. Specifically, zinc oxide, magnesium oxide, lead acetate, copper acetate, dibutyltin oxide, dioctyltin oxide,
Examples thereof include tin dibutyldibutoxy and titanium tetrabutoxy.

The reaction is carried out by heating urea (or urea derivative) and alcohol in a reactor equipped with a reflux condenser in the presence of a solvent and a catalyst. The amount of the alcohol is 2 to 10 per mole of urea (or urea derivative).
Molar amounts are appropriate. The amount of the solvent is suitably from 0.1 to 20 mol per mol of alcohol. When an alcohol having a low boiling point is used, a higher molar fraction of the solvent is preferred because the boiling point of the reaction solution is higher (that is, the reaction temperature is higher), but the size of the reactor increases as the solvent increases. Therefore, the optimal amount differs depending on the type of alcohol.
The amount of the catalyst is suitably 0.001 to 0.5 mol per 1 mol of urea (or urea derivative).

The reaction is preferably carried out at atmospheric pressure,
It may be carried out in a state of reduced pressure or slight pressure of about 0.001 to 0.5 MPa in absolute pressure. When the process is performed at a pressure other than the atmospheric pressure, a pressure adjusting device is required before the reflux condenser. During the reaction, ammonia (amine when a urea derivative is used) is generated, and it is necessary to take this out of the system. The reaction time is suitably about 2 to 10 hours. The reaction can be carried out continuously.

The reaction temperature is preferably a temperature at which the reaction solution refluxes. Although it is possible to carry out the reaction at a temperature at which no reflux occurs, it is preferable to operate at a temperature close to the boiling point of the reaction solution even in such a case. Since the alcohol concentration decreases as the reaction proceeds, when a low-boiling alcohol is used, the boiling point of the reaction solution increases as the reaction proceeds. Therefore, it is preferable to gradually increase the temperature of the external heat source for heating. The specific reaction temperature is 100
~ 250 ° C.

The dialkyl carbonate obtained by the above operation can be easily obtained from the reaction solution by a known separation operation such as distillation.

[0021]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 In a 200 ml four-necked flask equipped with a Liebig condenser, 2.50 g (41.7 mmol) of urea, 7.71 g (104 mmol) of 1-butanol, and 82.7 g (417) of n-tetradecane Mmol), 0.38 g (1.53 mmol) of di-n-butyltin oxide, and 2.0 g of bibenzyl as an internal standard.
Refluxing was performed while flowing warm water at ℃. The reaction temperature is the temperature at which the liquid refluxes, and the temperature of the oil bath used for heating is
The temperature was always adjusted to be about 20 ° C. higher than the liquid temperature.
The reaction solution was sampled every hour, and the change in the product was monitored by gas chromatography. The time course of the reaction is shown below. The yield of carbonate is based on urea (the same applies to the following examples).

Reaction time Liquid temperature Dibutyl carbonate yield 1 h 175 ° C. 6.4% 2 181 21.6 3 186 36.5 4 193 52.4 5 199 64.9 6 205 75.5 7 206 76.7

Example 2 A 3 L SUS316 autoclave equipped with a stirrer was fitted with a reflux condenser having an inner diameter of 34 mm and a length of 500 mm to prepare a reactor. A pressure control valve was provided at the end of the reflux condenser, so that the pressure in the reactor could be kept constant. In this reactor, 45.2 g (0.753 mol) of urea, 139.5 g (1.88 mol) of 1-butanol, 747 g (3.77 mol) of n-tetradecane, 6.93 g of di-n-butyltin oxide ( 0.028 mol), and 24.0 g of bibenzyl as an internal standard. After the inside of the reactor was pressurized to 0.2 MPa with nitrogen, heating was started and the temperature was adjusted so that the reaction solution was refluxed. During the reaction, the pressure in the reactor increased due to the generation of ammonia. However, the pressure in the reactor was maintained at about 0.2 MPa as a gauge pressure by discharging the ammonia out of the system through a pressure control valve. The results are shown below.

Reaction time Liquid temperature Dibutyl carbonate yield 1 h 191 ° C. 0.4% 2 207 17.6 3 218 37.6 4 223 51.6 5 227 67.9 6 230 72.3 7 230 73.9

Comparative Example 1 In the same reactor as used in Example 2, urea 94.
9 g (1.58 mol), 1170 g of 1-butanol (1
5.8 mol), 13.1 g of di-n-butyltin oxide
(0.053 mol), 50 g of bibenzyl as an internal standard
And pressurize the reactor to 0.9 MPa with nitrogen,
Heating was started and the temperature was adjusted so that the reaction liquid was refluxed. During the reaction, the pressure inside the reactor rises due to the generation of ammonia. However, the pressure inside the reactor is reduced to about 0.9 by gauge pressure by discharging ammonia through the pressure control valve.
Mpa was maintained. The results are shown below, and it can be seen that the reaction rate decreases when no solvent is used.

Reaction time Liquid temperature Dibutyl carbonate yield 1 h 188 ° C. 0.3% 220 201 5.6 4 199 17.3 6 200 29.1 8 200 39.2 10 200 49.4 12 200 57.8 14 199 63.2 16 200 67.6 18 200 71.2 20 200 72.7

Example 3 Instead of tetradecane as a solvent, 2,6,10,1
The same experiment as in Example 1 was performed, except that 82.7 g (308 mmol) of 4-tetramethylpentadecane was used and the internal standard was changed from bibenzyl to 2.0 g of o-terphenyl. The results are shown below.

Reaction time Liquid temperature Dibutyl carbonate yield 1 h 173 ° C. 3.9% 2 184 17.7 3 191 37.2 4 202 54.9 5 213 67.0 6 220 81.2 7 224 83.6

Example 4 Instead of tetradecane as a solvent, bibenzyl
The same experiment as in Example 1 was performed except that 0 g (417 mmol) was used and the internal standard was changed from bibenzyl to 2.0 g of o-terphenyl. The results are shown below.

Reaction time Liquid temperature Dibutyl carbonate yield 1 h 182 ° C. 6.6% 2 188 21.8 3 195 38.3 4 201 53.0 5 207 66.3 6 210 73.2 7 219 81.4 8 224 84.6

Example 5 The same experiment as in Example 1 was carried out except that 71.0 g (417 mmol) of diphenyl ether was used instead of tetradecane as a solvent and the internal standard was changed from bibenzyl to 2.0 g of o-terphenyl. Was. The results are shown below.

Reaction time Liquid temperature Dibutyl carbonate yield 1 h 184 ° C. 10.5% 2 192 30.0 3 201 51.3 4 213 68.2 5 226 80.6 6 231 79.8

Example 6 The same procedure as in Example 1 was carried out except that 92.7 g (417 mmol) of tetraethylene glycol dimethyl ether was used instead of tetradecane as a solvent, and the internal standard was changed from bibenzyl to 2.0 g of o-terphenyl. An experiment was performed. The results are shown below.

Reaction time Liquid temperature Dibutyl carbonate yield 1 h 198 ° C. 2.1% 220 3 8.6 3 209 19.9 4 213 30.6 5 217 39.9 6 219 49.5 7 220 53.5 8 220 55.0

Example 7 In a 200 ml four-necked flask equipped with a Liebig condenser, 2.07 g (34.5 mmol) of urea, 7.30 g (82.8 mmol) of isoamyl alcohol, 2,2
78.1 g of 6,10,14-tetramethylpentadecane
(291 mmol), di-n-butyltin oxide 0.1.
31 g (1.25 mmol) and o- as internal standard
2.0 g of terphenyl was added, and reflux was performed while flowing hot water of 60 ° C. into the condenser. The reaction temperature was a temperature at which the liquid was refluxed, and the temperature of the oil bath used for heating was adjusted to be always about 20 ° C. higher than the liquid temperature. The reaction solution is 1
Samples were taken every hour and the product changes were tracked by gas chromatography. The results are shown below.

Reaction time Liquid temperature Diamil carbonate yield 1 h 203 ° C. 19.8% 2 218 58.3 3 220 68.2 4 220 69.6

Example 8 2.51 g (41.8 mmol) of urea was placed in a 200 ml four-necked flask equipped with a Liebig condenser, and 1-1.
7.71 g (104 mmol) of butanol, 71.1 g (418 mmol) of diphenyl ether, 0.38 g (4.7 mmol) of zinc oxide and o as internal standard
2.0 g of terphenyl was added, and reflux was carried out while flowing hot water at 60 ° C. into the condenser. The reaction temperature was a temperature at which the liquid was refluxed, and the temperature of the oil bath used for heating was adjusted to be always about 20 ° C. higher than the liquid temperature. The reaction solution was sampled every hour, and the change in the product was monitored by gas chromatography. The results are shown below.

Reaction time Liquid temperature Dibutyl carbonate yield 1 h 179 ° C. 13.1% 2 181 18.3 3 184 23.8 4 186 27.3 5 188 33.6 6 191 37.4 7 192 44.9 8 194 49.6 9 195 55.1 10 197 60.3 11 199 65.3 12 200 66.3

Example 9 In a 200 ml four-necked flask equipped with a Liebig condenser, 2.50 g (41.7 mmol) of urea, 13.6 g (104 mmol) of octanol and 6 undecane
5.2 g (417 mmol), 0.38 g (1.53 mmol) of di-n-butyltin oxide, and 2.0 g of bibenzyl as an internal standard were added, and the mixture was refluxed while flowing hot water at 60 ° C. into a condenser. . The reaction temperature was a temperature at which the liquid was refluxed, and the temperature of the oil bath used for heating was adjusted to be always about 20 ° C. higher than the liquid temperature. The reaction solution was sampled every hour, and the change in the product was monitored by gas chromatography. The results are shown below.

Reaction time Liquid temperature Dibutyl carbonate yield 1 h 176 ° C. 3.0% 2 195 29.3 3 195 48.8 4 195 61.25 195 69.0 6 196 70.2

Comparative Example 2 In the same reactor as in Example 9, 2.50 g (41.7 mmol) of urea, 67.8 g (521 mmol) of octanol, 0.38 g (1.5 g) of di-n-butyltin oxide
3 mmol), and bibenzyl 2.0 as an internal standard.
g, and the same experiment as in Example 11 was performed. That is, the reaction was performed by replacing all undecane used in Example 11 with octanol. The results are shown below. still,
Octanol and undecane have boiling points of 196 ° C
It is. Although the amount of octanol was increased as compared with Example 11, the reaction rate was clearly decreased, and it is clear that there was a solvent effect.

Reaction time Liquid temperature Dibutyl carbonate yield 1 h 175 ° C. 1.5% 2 196 6.1 3 197 12.0 4 197 17.9 5 197 23.4 6 197 28.6 7 197 33.8 8 197 40.1

[0044]

According to the method of the present invention, even when an alcohol having a low boiling point is used, the reaction can be carried out at normal pressure or low pressure, and the solvent assists the discharge of ammonia out of the system. Because the reaction rate is improved, dialkyl carbonate can be easily obtained with a simple apparatus,
The industrial effect is great.

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[Procedure amendment]

[Submission date] March 26, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0038

[Correction method] Change

[Correction contents]

Example 8 2.51 g (41.8 mmol) of urea, 7.71 g (104 mmol) of 1-butanol and 71.1 g (418 mmol) of diphenyl ether were placed in a 200 ml four-necked flask equipped with a Liebig condenser. , Zinc oxide 0.3
8 g (4.7 mmol) and 2.0 g of o-terphenyl were added as an internal standard, and the mixture was refluxed while flowing hot water at 60 ° C into the condenser. The reaction temperature was a temperature at which the liquid was refluxed, and the temperature of the oil bath used for heating was adjusted to be always about 20 ° C. higher than the liquid temperature. The reaction solution was sampled every hour, and the change in the product was monitored by gas chromatography. The results are shown below.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0040

[Correction method] Change

[Correction contents]

Example 9 In a 200 ml four-necked flask equipped with a Liebig condenser, 2.50 g (41.7 mmol) of urea, 13.6 g (104 mmol) of 1-octanol, 65.2 g (417 mmol) of undecane Then, 0.38 g (1.53 mmol) of di-n-butyltin oxide and 2.0 g of bibenzyl as an internal standard were added, and the mixture was refluxed while flowing hot water at 60 ° C into a condenser. The reaction temperature was a temperature at which the liquid was refluxed, and the temperature of the oil bath used for heating was adjusted to be always about 20 ° C. higher than the liquid temperature. The reaction solution was sampled every hour, and the change in the product was monitored by gas chromatography. The results are shown below.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0041

[Correction method] Change

[Correction contents]

Reaction time Liquid temperature Dioctyl carbonate yield 1 h 176 ° C. 3.0% 2 195 29.3 3 195 48.8 4 195 61.2 5 195 69.0 6 196 70.2

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0042

[Correction method] Change

[Correction contents]

Comparative Example 2 In the same reactor as in Example 9, 2.50 g (41.7 mmol) of urea, 67.8 g (521 mmol) of 1-octanol and 0.38 g (1.0 g) of di-n-butyltin oxide were added. 5
3 mmol), and bibenzyl 2.0 as an internal standard.
g, and the same experiment as in Example 9 was performed. That is,
The reaction was performed by replacing all undecane used in Example 9 with 1-octanol. The results are shown below. In addition, 1
Octanol and undecane both have a boiling point of 196
° C. Compared with Example 9, despite the increase in the amount of 1-octanol, the reaction rate clearly decreased, and it is clear that there was a solvent effect.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0043

[Correction method] Change

[Correction contents]

Reaction time Liquid temperature Dioctyl carbonate yield 1 h 175 ° C. 1.5% 2 196 6.1 3 197 12.0 4 197 17.9 5 197 23.4 6 197 28.6 7 197 33.8 8 197 40.1

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Takuro Oshinda 22nd Wadai, Tsukuba, Ibaraki Prefecture Mitsubishi Gas Chemical Co., Ltd. Inside the company research institute

Claims (5)

[Claims] 1. A method for producing a dialkyl carbonate, comprising reacting urea or a urea derivative with an alcohol in the presence of a high-boiling solvent having a boiling point of 180 ° C. or higher and a catalyst. 2. The method for producing a dialkyl carbonate according to claim 1, wherein the high boiling point solvent is a hydrocarbon having a boiling point of 180 ° C. or higher or an ether. 3. The method for producing a dialkyl carbonate according to claim 1, wherein the alcohol is an alcohol having 3 to 6 carbon atoms. 4. The method for producing a dialkyl carbonate according to claim 2, wherein the high boiling point solvent is at least one selected from tetradecane, undecane, tetramethylpentadecane, bibenzyl, diphenyl ether and tetraethylene glycol dimethyl ether. 5. The method for producing a dialkyl carbonate according to claim 2, wherein the high boiling point solvent is at least one selected from tetramethylpentadecane, tetradecane and diphenyl ether.