KR102072785B1 - Preparation Method of Dialkylcarbonate using selenite catalyst and Composition Comprising Dialkylcarbonate Prepared Therefrom - Google Patents

Abstract

The present invention relates to a composition which contains: an alkali metal selenite catalyst of chemical formula 2, an alkali metal alkyl selenite catalyst of chemical formula 3, or dialkyl carbonate (DAC) of chemical formula 1, obtained by an oxidation carbonylation process which conducts a reaction of alcohol of chemical formula 4: ROH with a mixed gas of carbon monoxide (CO) and oxygen (O_2); and a selenium-containing by-product, wherein the content of the selenium-containing by-product is 7,000 ppm or less. In addition, the present invention provides a method for manufacturing DAC of the chemical formula 1. The composition according to the present invention can produce DAC of the chemical formula 1 in an economically feasible yield compared to a conventional carbonylation process.

Description

Preparation method of Dialkylcarbonate using selenite catalyst and Composition Comprising Dialkylcarbonate Prepared Therefrom}

The present invention relates to a process for preparing dialkylcarbonates using selenite catalysts and to compositions comprising dialkylcarbonates prepared therefrom.

Dialkyl carbonates (DACs) are attracting attention because they have environmentally mild characteristics and are capable of various applications such as aprotic solvents, monomers for polycarbonates and alkylating agents. It is also used as a dialkyl carbonate electrolyte solvent and gasoline additive. Such dialkyl carbonates can be readily prepared by the reaction of alcohols with phosgene.

However, the phosgenation reaction causes problems with the use of highly toxic phosgene. To replace this phosgenation reaction, several processes have been developed, including transesterification, methyl nitrile carbonylation, alcoholic decomposition of urea, oxidative carbonylation and carboxylation. Among them, the synthesis of DAC through carboxylation by CO ₂ is most preferable in terms of environmental and economic, but so far, economically feasible process using CO ₂ as a raw material has not been developed.

Meanwhile, a method of producing dimethyl carbonate through oxidative carbonylation using a copper-based catalyst such as CuCl has been commercialized by Enichem (see US Patent 5,536,864). Since then, many efforts have been made to improve the activity of copper-based catalysts. A successful example is the use of PdCl ₂ and ammonium salts with CuCl. Dow Chemical has also issued several patents for the use of activated carbon-supported copper catalysts (see US Patent 5,004,827, US Patent 4,625,044).

Nevertheless, catalyst systems reported so far for oxidative carbonylation reactions still need improvement in terms of activity, selectivity, and catalyst recovery and corrosion.

As an alternative to copper-based catalysts, oxidative carbonylation of amines to substituted ureas and carbamates by catalyzing selenium has been reported (see N. Sonoda, Pure Appl. Chem . 65 (1993) 699706). The oxidative carbonylation is performed by the action of carbonyl selenide (Se / CO) system. Due to the weak π-π bonds of Se / CO, nucleophilic compounds such as amines can attack the carbon atoms that make up the carbonyl of Se / CO. In another study, dialkyl carbonates were synthesized using metal selenium as a catalyst, but this synthesis was carried out in the presence of significant amounts of strongly basic alkali metal alkoxides (K. Kondo, N. Sonoda, H. Sakurai, Bull. Chem . Soc . Jpn. 48 (1975) 108111). In addition, catalyst systems comprising metal selenium and inorganic bases have been used for the synthesis of glycerol carbonate by oxidative carbonylation of glycerol. The base is used to improve the nucleophilicity of glycerol to interact with SeCO (VY Lee, K. McNiece, Y. Ito, A. Sekiguchi, N. Geinik, JY Becker, Heteroatom Chemistry, Volume 25, (2014) ) 313319).

On the other hand, the inventors have found that potassium selenite (K ₂ SeO ₃ ), potassium methyl selenite and dialkylimidazolium methyl selenite are very effective catalysts for the oxidative carbonylation of aromatic amines in alcohols, from which urea and It has been reported that carbamate can be produced in high yield depending on the catalyst used (HS Kim, YJ Kim, JY Bae, SJ Kim, MS Lah, CS Chin, Organometallics . 22 (2003) 24982504).

However, no method of synthesizing dialkyl carbonate (DAC) through oxidative carbonylation of alcohol using the selenite compounds as a catalyst has not been reported.

Accordingly, the present invention is to prepare a dialkyl carbonate (DAC) which is more economically feasible than a conventional alcohol oxidative carbonylation process, and to provide a composition comprising the dialkyl carbonate prepared therefrom.

In one aspect of the present invention, in the presence of an alkali metal selenite catalyst of formula (2), an alkali metal alkyl selenite catalyst of formula (3), or a mixture thereof, the alcohol of formula (4) is mixed with a mixed gas of carbon monoxide (CO) and oxygen (O ₂ ). Dialkyl carbonates (DAC) of formula (I) obtained from the oxidative carbonylation process to react; And a selenium-containing byproduct, the composition having a selenium-containing byproduct of 7,000 ppm or less:

 [Formula 2]

[Formula 3]

[Formula 4]

[Formula 1]

Where

M is lithium, sodium, potassium or cesium,

R is a C ₁ -C ₄ alkyl substituted with CH ₃ or C ₁ -C ₄ alkoxy,

R 'is a C ₁ -C ₄ alkyl or fluorine (F) atom-substituted C ₁ -C ₄ alkyl.

Another aspect of the present invention provides a method for preparing a dialkyl carbonate (DAC) of the formula (1).

The term 'C ₁ -C ₄ alkyl' as used herein refers to a straight or branched monovalent hydrocarbon consisting of 1 to 4 carbon atoms, for example methyl, ethyl, n-propyl, i-propyl , n-butyl, i-butyl, t-butyl and the like can be included. Similarly, the term 'C ₁ -C ₄ alkoxy' may include methoxy, ethoxy, propoxy, butoxy and the like.

The composition according to the present invention can be used to prepare a dialkyl carbonate (DAC) of formula (1) in an economically viable yield compared to the conventional carbonylation process by performing an oxidative carbonylation process of alcohol using a selenite catalyst, Compositions comprising the dialkylcarbonates thus prepared may contain very little selenium-containing byproducts, up to 7,000 ppm.

1A-1D show XRD patterns for potassium bicarbonate (KHCO ₃ ), respectively; XRD pattern of metal selenium; XRD pattern of the solid precipitate recovered after the oxidative carbonylation process according to Example 1; And XRD pattern of the solid precipitate recovered after the oxidative carbonylation process according to Example 3.
Figure 2 shows the results of the GC-MS analysis of the solid precipitate recovered after the oxidative carbonylation process according to Example 1.
3 is a graph showing the effect of temperature on the yield of dialkylcarbonates (DMC and BMEC) obtained after the oxidative carbonylation process according to Examples 1 and 6.
4 is a graph showing the yield of the dialkyl carbonates (DMC and BMEC) of Examples 1 and 6 according to the number of reuse of the catalyst.

Hereinafter, the terms or words used in the present specification and claims should not be construed as being limited to the ordinary or dictionary meanings, and the inventors properly define the concept of terms in order to explain their inventions in the best way. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that it can.

The composition according to one embodiment of the present invention comprises a dialkyl carbonate (DAC) of Formula 1 prepared by carrying out an oxidative carbonylation process of alcohol in the presence of a selenite catalyst; And selenium-containing byproducts, wherein the selenium-containing byproducts are 7,000 ppm or less.

[Formula 1]

Where

R is a C ₁ -C ₄ alkyl substituted with CH ₃ or C ₁ -C ₄ alkoxy,

R 'is a C ₁ -C ₄ alkyl or fluorine (F) atom-substituted C ₁ -C ₄ alkyl.

The selenium-containing byproduct may be dimethyl diselenide, 1,2-dimethoxydiselane, O, Se-dimethyl carboselenoate or a mixture of two or more thereof.

The dialkyl carbonate (DAC) of Chemical Formula 1 is an alkali metal selenite catalyst of Chemical Formula 2, an alkali metal methyl selenite catalyst of Chemical Formula 3, or a mixture thereof, and the alcohol of Chemical Formula 4 is carbon monoxide (CO) and oxygen ( It can be prepared through a process of performing an oxidative carbonylation process of alcohol by reacting with a mixed gas of O ₂ ).

[Formula 2]

[Formula 3]

[Formula 4]

Where

M is lithium, sodium, potassium or cesium,

R is a C ₁ -C ₄ alkyl substituted with CH ₃ or C ₁ -C ₄ alkoxy,

R 'is a C ₁ -C ₄ alkyl or fluorine (F) atom-substituted C ₁ -C ₄ alkyl.

For the oxidative carbonylation process, the reactor is supplied with a selenite catalyst of formula (2) or (3), an alcohol of formula (4), and a mixed gas of carbon monoxide (CO) and oxygen (O ₂ ).

At this time, a typical example of selenite catalyst represented by formula (2) or (3) to promote the carbonylation of the alcohol is Li ₂ SeO3, Na ₂ SeO _3, K ₂ SeO _3, Cs ₂ SeO _3, LiSeO ₂ (OCH _3), NaSeO ₂ (OCH ₃ ), KSeO ₂ (OCH ₃ ), CsSeO ₂ (OCH ₃ ), and the like, which may be used alone or in combination. These selenite catalysts can be obtained and used commercially available or can be prepared and used according to methods known in the art.

In addition, representative examples of the alcohol to be carbonylated include methanol or 2-methoxyethanol. In particular, the use of 2-methoxyethanol is advantageous in that the desired dialkyl carbonate can be produced in high yield while the production of selenium-containing by-products can be suppressed as much as possible.

As described above, the content of selenium-containing by-products in the composition comprising the dialkyl carbonate (DAC) of the general formula (1) of the present invention is 7,000 ppm or less, specifically 6,000 ppm or less, and more specifically 5,500 ppm It may be:

The content of the selenium-containing by-products may be affected depending on the type of alcohol of the general formula (4). For example, when using methanol, several selenium-containing byproducts, including malodorous dimethyl diselenide, 1,2-dimethoxydiselane and O, Se-dimethyl carboselenoate, are up to 7,000 ppm, in particular 6,000 ppm Hereinafter, in more detail, 5,500 ppm or less, while 2-methoxyethanol is used, the amount of the by-product is very small at a level of about 500 ppm to 510 ppm.

The alcohol and the selenite catalyst can be fed in a molar ratio of 100: 1 to 10: 1, specifically 50: 1 to 20: 1, in particular 30: 1.

Meanwhile, the mixed gas of carbon monoxide (CO) and oxygen (O ₂ ) supplied to the reactor is in a ratio of 20: 1 to 4: 1, specifically 8: 1 to 4: 1, especially 4: 1 (v / v). It may be mixed with, and may be supplied until the pressure of the reactor is maintained at 2 to 8 MPa, specifically 3 to 6 MPa, in particular 5 MPa.

In addition, the reaction temperature in the carbonylation process may vary depending on the selenite catalyst. For example, when Li ₂ SeO ₃ , K ₂ SeO ₃ , LiSeO ₂ (OCH ₃ ), NaSeO ₂ (OCH ₃ ), KSeO ₂ (OCH ₃ ), or the like is used as a catalyst, the reaction temperature ranges from 70 ° C. to 100 ° C. Can be. On the other hand, when Na ₂ SeO ₃ is used, the reaction is not inactivated at 70 ° C., so that the reaction temperature is preferably maintained at 100 ° C. As such, the catalytic activity of selenite depends on the type of alkali metal ion and the reaction temperature.

The reaction time of the carbonylation process may be 0.5 to 6 hours, specifically 1 to 4 hours, in particular 2 hours.

The oxidative carbonylation of alcohols in the presence of a selenite catalyst according to the present invention can be summarized in Scheme 1 below.

Scheme 1

The reaction of Scheme 1 is carried out in detail through the steps of Scheme 2 below. Scheme 2 below shows the reaction mechanism of the oxidative carbonylation process of alcohol (ROH) using K ₂ SeO ₃ as selenite catalyst.

Scheme 2

In Scheme 1, the first step of carbonylation is K ₂ Se ^IV O ₃ is continuously reduced by CO to Se (0) through the Se (II) compound (KO-Se ^II -OK, Compound I) will be. During the reduction of K ₂ Se ^IV O ₃ , KHCO ₃ may be co-produced.

K ₂ SeO ₃ + 2ROH + 4CO + O ₂ → 2KHCO ₃ + Se + CO ₂ + (RO) ₂ C = O (1)

The reduction of Se (II) or Se (0) of Se (IV) appears to be the first to occur in the oxidative carbonylation of methanol by selenite catalyst. In that case, depending on the catalyst used, Na ₂ SeO ₃ And the Se = O bond of NaSeO ₂ (OCH ₃ ) is K ₂ SeO ₃ And will be much stronger than KSeO ₂ (OCH ₃ ), from which the breaking of Se═O bonds by CO is prevented. This depends on the Lewis acidity and the size of the alkali metal. Since Na ⁺ is stronger in Lewis acidity than K ⁺ , Na ⁺ interacts more strongly with basic selenite anions, thereby inhibiting the reduction of Se (IV) by CO. However, the activity of Li ₂ SeO ₃ comparable to K ₂ SeO ₃ at 70 ° C. is difficult to explain by Lewis acidity alone because the Lewis acidity of Li ⁺ is stronger than that of Na ⁺ and K ⁺ . Probably due to the delicate balance between the activity of the alkali metal selenite and the cation-anion interaction.

Se (0) formed by the above chemical reaction is an active site, KHCO ₃ acts as a promoter, and the catalytic action of Se (0) has been demonstrated in various other carbonylation reactions. The formation of metal selenium from this K ₂ SeO ₃ is because the reduction of Se (IV) to Se (0) is readily under oxidative carbonylation conditions. See, eg, S. Hwang, HS Kim, M. Cheong , Bull. Korean Chem . Soc. 33 (2012) 3864-3866 describes that [Se ^IV O ₂ (OCH ₃ )] ^- is easily reduced by CO to give [Se ^II O (OCH ₃ )] ^- in the process of oxidative carbonylation of aromatic amines. Reported. Therefore, further reduction of [Se ^II O (OCH ₃ )] ^- to metal selenium by CO can occur without difficulty, unless strong nucleophiles such as amines or phosphines exist to stabilize the Se (II) compound. have.

In addition, the KHCO ₃ can improve the nucleophilicity of alcohol through hydrogen bonding, even if the weak base of p K _b value of 7.65, from which Se (0) such as alcohol and carbonyl selenide (Se-CO) May promote the interaction of the compounds.

Subsequently, the metal Se obtained above reacts with CO to form carbonyl selenide (Se-CO), which Se-CO interacts with an alcohol molecule and KHCO ₃ to form KSeCO ₂ R (R = CH ₃ OCH ₂ Together with CH _2- , Compound II) to produce CO ₂ and H ₂ O. At this time, the nucleophilic attack of the alcohol on the carbon atom of carbonyl selenide (Se-CO) is weak π-π bond present in Se-CO, and strong hydrogen bond by oxygen atom of KHCO ₃ and hydrogen atom of alcohol. It may be due to the action of.

Compound II is then converted to SeC (OR) ₂ OH (Compound III) as an intermediate by reaction with an alcohol molecule, followed by further formation of a dialkyl carbonate (DAC) of (RO) ₂ CO into a compound of MSeH. Is switched.

Finally, the KSeH (Compound IV) can be converted to metal selenium and KHCO ₃ by CO / O ₂ in the reactor.

This series of reactions can be carried out continuously in the reactor.

As described above, when the oxidative carbonylation of alcohol is carried out in the presence of alkali metal selenite (M ₂ SeO ₃ ) or alkali metal methyl selenite (MSeO ₂ (OCH ₃ )) as a catalyst, the catalysts are elemental selenium. And while converted to MHCO ₃ , it is possible to prepare a dialkyl carbonate (DAC) of formula (1) in economically viable yield compared to the existing carbonylation process.

Hereinafter, examples will be described in detail to help understand the present invention. However, embodiments according to the present invention can be modified in many different forms, the scope of the invention should not be construed as limited to the following examples. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Examples 1-5 and Comparative Examples 1-2: Of dialkyl carbonates (DAC)  Produce

All experiments were performed in a 25 mL stainless steel reactor equipped with a magnetic stirrer, thermocouple and electric heater and pressure transducer.

All compounds including alcohols and catalysts used in the synthesis of dialkyl carbonates (DACs) in each example were obtained from Aldrich chemical. In particular, alkali metal methyl selenite compounds are described in HS Kim, YJ Kim, JY Bae, SJ Kim, MS Lah, CS Chin, Organometallics . 22 (2003) 24982504]. CO and O ₂ were each obtained from Shin Yang Gas (Shin Yang Gas, Korea) having a purity of 99.9%. All catalysts were dried under vacuum before use.

Specifically, the alcohol and the catalyst are added to the reactor in the type and content shown in Table 1 below, pressurized to 2.0MPa using a mixed gas of CO / O ₂ (v / v = 80/20) at room temperature, and then vigorously It was heated to the temperature of Table 1 while stirring. After further pressurization of the reactor to 5.0 MPa at that temperature, the conditions were maintained during the reaction using a gas reservoir equipped with a high pressure regulator and a pressure transducer.

After the reaction was performed for 2 hours, the reactor was cooled to room temperature to obtain a liquid product from the oxidative carbonylation reaction.

On the other hand, when methanol was used as the substrate, the gas emission hood was operated during the progress of the reaction as malodorous dimethyl selenide was formed as a by-product during the reaction.

Alcohol
catalyst
Temperature
yield
Selenium-containing
By-product (ppm)
dimethyl
Carbonate
(DMC)
dimethyl
ether
(DME) A B C
Example 1 MeOH
(150 mmol) K ₂ SeO ₃
(5mmmol)
70 ℃
28.0
2.2
2400
1500
1100
Example 2 MeOH
(150 mmol) Na ₂ SeO ₃
(5mmmol)
100 ℃
32.9
1.5
2500
1400
1100
Example 3 MeOH
(150 mmol) KSeO ₂ (OCH ₃ )
(5mmmol)
70 ℃
22.0
2.6
2300
1600
1200
Example 4 MeOH
(150 mmol) NaSeO ₂ (OCH ₃ )
(5mmmol)
100 ℃
28.8
1.6
2400
1800
1100
Example 5 MeOH
(150 mmol) LiSeO ₂ (OCH ₃ )
(5mmmol)
70 ℃
30.7
1.8
2500
1900
950
Reference Example 1 MeOH
(150 mmol) Se / KHCO ₃₂
(5mmmol)
70 ℃
14.4
0.7
4200
3100
1600
Reference Example 2 MeOH
(150 mmol) Se / K ₂ CO ₃
(5mmmol)
70 ℃
7.3
0
4600
3300
1500
Reference Example 3 MeOH
(150 mmol) Se / NaHCO ₃
(5mmmol)
70 ℃
22.5
1.3
3200
2300
1200
Comparative Example 1 MeOH
(150 mmol) CuCl ₂
(5mmmol)
70 ℃
4.1
1.6
-
-
-
Comparative Example 2 MeOH
(150 mmol) Cu (OMe) ₂ / PdCl ₂ (PPh ₃ ) ₂ / NMe ₄ Cl ²⁾
(5mmmol)
70 ℃
2.0
1.0
-
-
- Reaction pressure: 5MPa (CO / O ₂ = 80/20, v / v)
Reference Example 1: Se / K = 1/2 (molar ratio)
Comparative Example 2: Cu / Pd / N = 5 / 0.1 / 5 (molar ratio)
Selenium-containing byproducts:
A: dimethyl diselenide,
B: 1,2-dimethoxydiselan,
C: O, Se-dimethyl carboselenoate

As can be seen in Table 1, the oxidative carbonylation of methanol using K ₂ SeO ₃ as a catalyst was carried out at 70 ° C. under the condition that the molar ratio of CH ₃ OH / [Se] is 30. In this case, dimethyl carbonate (DMC) was obtained in a yield of 28.1%, and a small amount of byproduct dimethyl ether (DME) was formed.

These results are surprising when compared to using Cu-based catalysts (Comparative Examples 1 and 2 in Table 1) under the same experimental conditions. Interestingly, dimethyloxalate (DMO), a major byproduct of the carbonylation reaction with Cu-based catalysts, was not produced.

In addition, Examples 3 to 5 in which alkali metal methyl selenite (MSeO ₂ (OCH ₃ ) was used as the catalyst had somewhat lower catalytic activity than Examples 1 and 2 in which alkali metal selenite (M ₂ SeO ₃ ) was used. Nevertheless, as the alkali metal methyl selenite is dissolved in methanol, it is more efficient in terms of solid support compared to the alkali metal selenite which is dissolved only in water.

And, K ₂ SeO ₃ can be completely converted to metal selenium (Se) and KHCO ₃ (Se / KHCO ₃ = 1/2, molar ratio). Thus, K ₂ SeO ₃ showed similar activity to the catalyst in which Se and KHCO ₃ were mixed in a molar ratio of 1: 2.

On the other hand, the catalytic activity of the alkali metal selenite may vary depending on the reaction temperature. For example, Li ₂ SeO ₃ And K ₂ SeO ₃ gave DMC in a yield of about 30% at 70 ° C. when oxidative carbonylation of methanol was carried out in the presence of them. On the other hand, when Na ₂ SeO ₃ is used as a catalyst, no reaction occurs at 70 ° C., but when the temperature is increased to 100 ° C., DMC is obtained in a yield of 32.9%.

In addition, Examples 1 to 5 it can be seen that the selenium-containing by-product according to the use of the selenite catalyst is 7000 ppm or less.

Example 6 and Comparative Examples 3 to 5:

The same procedure as in Example 1 was performed, but the reaction conditions (change in type of alcohol) shown in Table 2 were applied.

It is well known that volatile selenium compounds are odorous, and the generation of volatile dimethyl diselenide as a by-product during oxidative carbonylation of methanol is quite uncomfortable. Therefore, it is necessary to reduce the occurrence of malodorous selenium compounds by using low volatility alcohol. To this end, oxidative carbonylation reactions for various alcohols were carried out at 70 ° C. in the presence of K ₂ SeO ₃ as catalyst and the results are shown in Table 2.

Alcohol
catalyst
yield
(Corresponding DAC)
p Ka
Selenium-Containing Products (ppm)
A
B
C
Example 1 MeOH
(150 mmol) K ₂ SeO ₃
(5mmmol)
28.1
15.5
2400
1500
1100
Example 6 MeOC ₂ H ₅ OH
(150 mmol) K ₂ SeO ₃
(5mmmol)
29.6
14.8
350
99
54
Comparative Example 3 ethanol
(150 mmol) K ₂ SeO ₃
(5mmmol)
8.4
15.9
950
350
250
Comparative Example 4 1-propanol
(150 mmol) K ₂ SeO ₃
(5mmmol)
2.8
16.1
650
340
160
Comparative Example 5 1-butanol
(150 mmol) K ₂ SeO ₃
(5mmmol)
1.1
16.1
-
-
-
Comparative Example 6 2-chloroethanol
(150 mmol) K ₂ SeO ₃
(5mmmol)
0
14.3
-
-
-
Comparative Example 7   2,2,2-trifluoroethanol K ₂ SeO ₃
(5mmmol)
0
12.5
-
-
- Reaction pressure: 5MPa (CO / O ₂ = 80/20, v / v)
Reaction temperature: 70 ℃
Selenium-containing byproducts:
A: dimethyl diselenide,
B: 1,2-dimethoxydiselan,
C: O, Se-dimethyl carboselenoate

As can be seen in Table 2 above, depending on the type of alcohol, the corresponding dialkyl carbonate was obtained via carbonylation, but the yield varied significantly depending on the alcohol used. The activity of K ₂ SeO ₃ on the carbonylation of C ₂ C ₄ alcohols such as ethanol, 1-propanol and 1-butanol was significantly lower compared to methanol, yielding dialkyl carbonate yields of 1-8%. On the other hand, 2-methoxyethanol (MEG) produced a bis (2-methoxyethyl) carbonate in a yield of 29.6% with similar reactivity to methanol. The reactivity of the alcohol was found to decrease with increasing chain length of the alcohol.

In particular, the activity of K ₂ SeO ₃ was fully quenched to 2-chloroethanol and 2,2,2-trifluoroethanol by electron-withdrawing functionality. These results indicate that the reactivity of the alcohol may be related to the p K _a value or nucleophilicity of the alcohol used. With regard to the reactivity of the alcohols, only alcohols with a p K _a value closest or somewhat lower to methanol (p K _a = 15.5) are reactive for oxidative carbonylation, resulting in 20-30% of the corresponding dialkyl carbonate. It is believed to have been produced in yield.

On the other hand, in the case of MeOC ₂ H ₅ OH (2-methoxyethanol, MEG) used in Example 6, the total content of the malodorous selenium-containing by-products in oxidative carbonylation was 503 ppm. Thus, in Example ₁ where CH ₃ SeCO ₂ CH ₃ and (CH ₃ O) ₂ Se together with (CH ₃ ) ₂ Se ₂ were observed in an amount of 5,000 ppm in oxidative carbonylation of methanol with K ₂ SeO ₃ . It may be advantageous for the preparation of polyalkyl carbonates (DACs). This is believed to be due to the reduced alkylation capacity of bis (2-methoxyethyl) carbonate (BMEC) finally obtained upon the use of MEG.

Evaluation Example 1 Catalyst Characteristics

In order to understand the catalytic properties of alkali metal selenite, XRD and FT-IR analyzes were performed on fresh and spent catalysts.

Specifically, a grayish black solid precipitate was filtered from the reaction mixture after the oxidative carbonylation process according to Example 1, washed with CH ₃ OH, and dried under vacuum at room temperature. The grayish black solid precipitate thus obtained was measured using XRD-6000 (Shimadzu) (nickel-filtered CuKα, 2θ 10 to 90 ^o ) as an X-ray diffractometer, and then the results were measured. It is shown in Figure 1c. This was compared with the XRD pattern for potassium bicarbonate (KHCO ₃ ) of FIG. 1A and the XRD pattern of metal selenium of FIG. 1B. The results show that the precipitate consists mostly of potassium bicarbonate (KHCO ₃ ) and metal selenium.

Meanwhile, FT-IR analysis of the precipitate was performed using a Nicolet FT-IR spectrometer (iS10, USA) and SMART MIRACLE Accessory, and the presence of potassium bicarbonate (KHCO ₃ ) was confirmed from the FT-IR spectrum.

In addition, XRD analysis of the grayish black solid precipitate obtained from the reaction mixture after the oxidative carbonylation process of Example 3 showed similar X-ray patterns (FIG. 1D).

As such, K ₂ SeO ₃ And KSeO ₂ (OCH ₃ ) are all converted to KHCO ₃ during the carbonylation process and the Se (IV) compounds are reduced to Se (0).

The Na ₂ SeO ₃ of Example 2 was completely inert at 70 ° C. and recovered unchanged after oxidative carbonylation, and activated at 100 ° C. to recover the solid precipitate recovered after carbonylation of NaHCO ₃ and metal selenium. Converted to a mixture, which corresponds to a precipitate formed by K ₂ SeO ₃ and KSeO ₂ (OCH ₃ ) at 70 ° C.

Evaluation Example 2 : By- Product Formation

One disadvantage of the oxidative carbonylation of methanol by selenite catalysts is the formation of malodorous organic selenium-containing byproducts, which leads to inconvenience in carrying out the reaction. To identify the byproducts, a grayish black solid precipitate was filtered from the reaction mixture after the oxidative carbonylation process according to Example 1, followed by gas chromatography / mass spectrometry (GC-MS) on the remaining solution. The analysis was performed. At this time, GC-MS analysis was performed using Agilent 6890 GC (with FID and DB-5 capillary column) and Agilent 6890-5973 GC-MSD (with HP-MS capillary column), and the results are shown in FIG. 2.

As can be seen in FIG. 2, at least three selenium-containing compounds such as (CH ₃ ) ₂ Se ₂ (dimethyl diselenide or 1,2-dimethyldiselan), CH ₃ SeCO ₂ CH ₃ ( O , Se -dimethyl carnoselenoate), and (CH ₃ O) ₂ Se ₂ (1,2-dioxydicelan) were produced. The mechanism for the formation of these Se-containing byproducts is shown in Scheme 1.

In addition, the above three selenium-containing compounds were also observed in Example 2 in which oxidative carbonylation was performed at 100 ° C. using Na ₂ SeO ₃ as a catalyst. Among these, dimethyl diselenide was found to mainly cause the odor observed from the reaction mixture.

Evaluation example  3: influence of reaction temperature

In order to examine the influence of the reaction temperature according to the type of alcohol, dimethyl carbonate (DMC) and bis (2-methoxy obtained in Example 1 (methanol) and Example 6 (2-methoxyethanol, MEG) The yield of ethyl) carbonate (BMEC) was measured according to temperature, and the results are shown in FIG. 3.

As can be seen in Figure 3, the yield of BMEC increased until the reaction temperature rose to 70 ℃ and remained almost constant up to 100 ℃. However, above 100 ° C., the yield of BMEC gradually decreased. It appears that BMEC is hydrolyzed to MEG and CO ₂ at high temperatures. It also appears that the formation of Se-containing compounds is promoted at temperatures above 100 ° C. Similar trends were observed in the synthesis of DMC, and the yield of DMC decreased sharply above 70 ° C., and it appears that the formation of by-product Se-containing organic compounds increased with increasing temperature.

Evaluation Example 4 Catalyst Recovery

To assess the recoverability of the selenite catalyst, a greyish black solid precipitate was filtered from the reaction mixture after the oxidative carbonylation process according to Examples 1 and 6, and each precipitate was washed with CH ₃ OH, After drying in vacuo at room temperature, it was reused for further reaction of the freshly added corresponding alcohol.

4 is a graph showing the yield of the dialkyl carbonates (DMC and BMEC) of Examples 1 and 6 according to the number of reuse of the catalyst. From this, the catalyst during BMEC synthesis retained most of its initial activity even after five reuses, indicating that the active portion of the catalyst is in a heterogeneous state. However, in the case of the carbonylation reaction of methanol, the yield of DMC gradually decreased as the solid precipitate obtained from K ₂ SeO ₃ recovered after the reaction was a mixture of KHCO ₃ and metal selenium. Eventually, after five reuses, the yield of DMC decreased from 28% to 13.02%. Another cause of this reduction can also be found in the formation of (CH ₃ ) ₂ Se ₂ , CH ₃ SeCO ₂ CH ₃ , (CH ₃ O) ₂ Se ₂ due to methanol.

Claims (14)

delete delete In the presence of an alkali metal selenite catalyst of formula (2), an alkali metal methyl selenite catalyst of formula (3), or a mixture thereof, without using a copper-based catalyst,
Including the reaction of the alcohol of formula 4 with a mixed gas of carbon monoxide (CO) and oxygen (O ₂ ) to perform an oxidative carbonylation process of alcohol,
Process for preparing dialkyl carbonate (DAC) of formula 1:
[Formula 2]

[Formula 3]

[Formula 4]

[Formula 1]

Where
M is lithium, sodium, potassium or cesium,
R is a C ₁ -C ₄ alkyl substituted with CH ₃ or C ₁ -C ₄ alkoxy,
R 'is a C ₁ -C ₄ alkyl or fluorine (F) atom-substituted C ₁ -C ₄ alkyl. The method of claim 3,
The selenite catalyst represented by Formula 2 or Formula 3 is Li ₂ SeO ₃ , Na ₂ SeO ₃ , K ₂ SeO ₃ , Cs ₂ SeO ₃ , LiSeO ₂ (OCH ₃ ), NaSeO ₂ (OCH ₃ ), KSeO ₂ (OCH ₃ ), CsSeO ₂ (OCH ₃ ) or a mixture of two or more thereof. The method of claim 3,
The alcohol is methanol or 2-methoxyethanol. The method of claim 3,
The alcohol and the selenite catalyst are used in a 100: 1 to 10: 1 molar ratio. The method of claim 6,
The alcohol and the selenite catalyst are used in a molar ratio of 50: 1 to 20: 1. The method of claim 3,
The mixed gas of carbon monoxide (CO) and oxygen (O ₂ ) is a mixture of 20: 1 to 4: 1 (v / v) ratio of the production method. delete The method of claim 3,
The pressure in the reactor is maintained at 2MPa to 8MPa. The method of claim 10,
The pressure in the reactor is maintained at 3MPa to 6MPa. The method of claim 3,
The reaction temperature of the oxidative carbonylation process is 70 ℃ to 100 ℃. The method of claim 3,
The reaction time of the carbonylation process is 0.5 hours to 6 hours. The method of claim 13,
The reaction time of the carbonylation process is 1 hour to 4 hours.

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