JPH10279536A - Method for producing dialkyl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently obtain the subject compound at a high reaction rate using a simple reactor, by reacting an alkyl carbamate with an alcohol in the presence of a catalyst and a high-boiling solvent, even if the boiling point of the alcohol is low. SOLUTION: This compound is obtained by reacting an alkyl carbamate of the formula R<1> R<2> N-CO-OR<3> (R<1> and R<2> are each H or a 1-4C alkyl; R<3> is an alkyl), e.g. methyl carbamate, with an alcohol (normally a 1-10C aliphatic alcohol, esp. preferably a 3-6C alcohol), in the presence of a solvent having a boiling point of 180 deg.C or higher, preferably 195 deg.C or higher, more preferably 220 deg.C or higher (preferably a hydrocarbon such as tetradecane or tetramethylpentadecane or an ether such as diphenyl ether) and a catalyst such as zinc oxide, magnesium oxide, lead acetate, copper acetate, dibutyl tin oxide, or tetrabutoxytitanium, preferably under the atmospheric pressure at 100-250 deg.C or so for 2-10 h 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 an alkyl carbamate 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 an alkyl carbamate with an alcohol is disclosed in JP-A-55-102543 and JP-A-57-26464.
No. 5 has a description. The catalyst for this reaction is described in the aforementioned patent and JP-A-57-175147.

[0003] The conventionally known method for producing a dialkyl carbonate by reacting an alkyl carbamate with an 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 those using high-boiling alcohols such as octanol as raw materials. That is, when synthesizing a dialkyl carbonate from an alcohol having a boiling point of 180 ° C. or less and an alkyl carbamate, 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 process for producing a dialkyl carbonate in which an alkyl carbamate 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 specification, an alkyl carbamate is a compound represented by the following general formula (1).

R ¹ R ² N—CO—OR ³ (1) (wherein R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ³ is an alkyl group. is there.)

Examples of these carbamates include methyl carbamate, ethyl carbamate, propyl carbamate, butyl carbamate, pentyl carbamate,
Hexyl carbamate, heptyl carbamate, octyl carbamate, nonyl carbamate, decyl carbamate, methyl carbamic acid methyl ester, methyl carbamic acid ethyl ester, methyl carbamic acid propyl ester, methyl carbamic acid butyl ester, methyl carbamic acid pentyl ester, methyl carbamic acid hexyl ester, methyl carbamic acid heptyl ester, Octyl methylcarbamate, methyl dimethylcarbamate, ethyl dimethylcarbamate, propyl dimethylcarbamate,
Dimethyl carbamic acid butyl ester, dimethyl carbamic acid pentyl ester, dimethyl carbamic acid hexyl ester, dimethyl carbamic acid heptyl ester,
Dimethylcarbamic acid octyl ester, ethylcarbamic acid methyl ester, ethylcarbamic acid ethyl ester, ethylcarbamic acid propyl ester, ethylcarbamic acid butyl ester, ethylcarbamic acid pentyl ester, ethylcarbamic acid hexyl ester, ethylcarbamic acid heptylester, ethylcarbamine Acid octyl ester, diethyl carbamate methyl ester, diethyl carbamate ethyl ester, diethyl carbamate propyl ester, diethyl carbamate butyl ester, diethyl carbamate pentyl ester, diethyl carbamate hexyl ester, diethyl carbamate heptyl ester, octyl diethyl carbamate Esters, etc. (Each example also includes each isomer That).

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, hexanol, heptanol, octanol, nonanol, decanol and the like (each example includes each isomer). It is preferable to use an alcohol having 1 to 8 carbon atoms because the effect of improving the reaction rate is remarkable.
6 alcohols are particularly preferred.

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

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-55-102543, JP-A-57-26645, JP-A-57-175147 and the like. 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 an alkyl carbamate and an alcohol in the presence of a solvent and a catalyst in a reactor equipped with a reflux condenser. The amount of alcohol
The appropriate amount is about 1 to 10 mol per 1 mol of the alkyl carbamate. The amount of the solvent is suitably about 0.1 to 20 mol per 1 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 0.00 per mole of alkyl carbamate.
1-0.5 mole is suitable.

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 reaction is carried out at a pressure other than the atmospheric pressure, ammonia generated during the reaction (amine when an N-substituted alkyl carbamate is used) needs to be discharged from the system. is necessary. 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, 5.86 g (50 mmol) of n-butyl carbamate, 5.56 g (75 mmol) of 1-butanol,
2,6,10,14-tetramethylpentadecane99.
0 g (369 mmol), 0.46 g (1.9 mmol) of di-n-butyltin oxide and 2.0 g of o-terphenyl as an internal standard were refluxed while flowing hot water at 60 ° C. into the condenser. Was. 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 change over time of the reaction is shown below. The carbonate yield is based on carbamate (the same applies to the following examples).

Reaction time Liquid temperature Dibutyl carbonate yield 1 h 173 ° C. 3.5% 2 184 18.5 3 191 38.9 4 202 58.9 5 213 73.1 6 221 78.0

Example 2 In a 200 ml four-necked flask equipped with a Liebig condenser, 4.88 g of n-butyl carbamate (41.
7 mmol), 4.63 g (62.5 mmol) of 1-butanol, 82.7 g (417 mmol) of n-tetradecane, 0.38 g (1.5 mm) of di-n-butyltin oxide
Mmol), and 2.0 g of bibenzyl as an internal standard
And refluxed 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 was sampled every hour, and the change in the product was monitored by gas chromatography.
The change over time of the reaction is shown below.

Reaction time Liquid temperature Dibutyl carbonate yield 1 h 176 ° C. 15.4% 2 181 29.7 3 186 44.5 4 191 62.05 198 74.8 6 203 78.0

Example 3 In a 200 ml four-necked flask equipped with a Liebig condenser, 7.46 g (63.7 g) of n-butyl carbamate was added.
Mmol), 7.08 g (95.5 mmol) of 1-butanol, 108.4 g (637 mmol) of diphenyl ether, 0.59 g of di-n-butyltin oxide (2.
4 mmol) and 2.0 g of o-terphenyl 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 change over time of the reaction is shown below.

Reaction time Liquid temperature Dibutyl carbonate yield 1 h 180 ° C. 9.5% 2 183 24.7 3 187 41.1 4 193 57.0 5 199 73.5 6 205 78.0

Example 4 In a 200 ml four-necked flask equipped with a Liebig condenser, 5.0 g (38.1 mmol) of isoamyl carbamate and 5.04 g (57.2 g) of isoamyl alcohol were added.
Mmol), 86.0 g (320 mmol) of 2,6,10,14-tetramethylpentadecane, 0.35 g (1.4 mmol) of di-n-butyltin oxide and 2.0 g of o-terphenyl as an internal standard. Then, reflux was performed while flowing hot water of 60 ° C. into the cooler. 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 Diamyl carbonate yield 1 h 207 ° C. 22.7% 2 218 59.1 3 220 67.6 4 222 70.2

Example 5 In a 200 ml four-necked flask equipped with a Liebig condenser, 7.22 g of n-octyl carbamate (41.
7 mmol), 8.15 g of 1-octanol (62.6)
Mmol), 65.2 g (417 mmol) of undecane, 0.38 g (1.5 mmol) of di-n-butyltin oxide.
3 mmol), and bibenzyl 2.0 as an internal standard.
g of water and refluxed 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 was sampled every hour, and the change in the product was monitored by gas chromatography. The results are shown below.

Reaction time Liquid temperature Dioctyl carbonate yield 1 h 176 ° C. 9.0% 2 195 33.7 3 195 53.7 4 195 64.3 5 195 72.5 6 196 73.7

Comparative Example 1 7.22 g (41.7 mmol) of n-octyl carbamate and 1-octanol 6 were placed in the same reactor as in Example 5.
The same experiment as in Example 5 was conducted except that 2.5 g (480 mmol), 0.38 g (1.53 mmol) of di-n-butyltin oxide and 2.0 g of bibenzyl were used as an internal standard. That is, the reaction was performed by replacing all the undecane used in Example 5 with octanol. The results are shown below. The boiling points of octanol and undecane are both 196 ° C. Compared to Example 5, despite the increase in the amount of octanol, the reaction rate was clearly reduced, and it is clear that there is a solvent effect.

Reaction time Liquid temperature Dioctyl carbonate yield 1 h 175 ° C. 3.6% 2 196 8.3 3 196 14.0 4 196 20.0 5 196 25.4 6 196 30.7 7 196 35.8 8196 42.2

[0034]

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 around normal pressure, and the solvent assists the discharge of ammonia out of the system. Since the reaction rate is improved, dialkyl carbonate can be easily obtained with a simple apparatus, and its industrial effect is great.

 ──────────────────────────────────────────────────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 (4)

[Claims] 1. A method for producing a dialkyl carbonate, comprising reacting an alkyl carbonate 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 tetramethylpentadecane, tetradecane and diphenyl ether.