JPH0364494B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is based on the following general formula [] (Here, R ¹ is an alkyl group having 2 to 5 carbon atoms.) Or general formula [] [Here, X is

【formula】

【formula】

【formula】

【formula】 or

[Formula] (where R ² is hydrogen or a methyl group), n is 5 to 40, and R ¹ is an alkyl group having 2 to 5 carbon atoms. ]
The present invention relates to a method for producing esters, which comprises dimerizing aldehydes using aluminum alkoxide phenoxides represented by the following as a catalyst. Conventionally, the method for producing esters by dimerizing aldehydes is as shown in the following reaction formula.
This reaction is known as the Tischtschenko reaction. RCHO＋R′CHO→RCOOCH ₂ R RCOOCH ₂ R′ R′COOCH ₂ R R′COOCH ₂ R′ (Here, R and R′ may be the same or different,
Indicates hydrogen or a substituted or unsubstituted alkyl group, alkenyl group, aryl group, or cycloalkyl group. ) In this reaction, the reaction is carried out in a homogeneous phase using an alkali metal such as sodium, an alkaline earth metal such as magnesium, or an alkoxide of aluminum as a catalyst.
470 pages (1954), successor organic reaction collection 108 pages (1955)
Asakura Shoten] and a method in which a reaction is carried out in a heterogeneous phase using an oxide of an alkaline earth metal such as barium or strontium as a catalyst (Japanese Chemical Journal, p. 1845 (1973)) are known. However, when the reaction is carried out in the above-mentioned homogeneous phase, in addition to the production of esters through the desired duplication, alcohols, hydroxyaldehydes, unsaturated aldehydes,
Since glycol esters, polyol esters, etc. are produced as by-products, there is a problem in the selectivity of ester production. In addition, this type of conventional catalyst is sent to a reaction tank together with the raw material aldehyde, and after the reaction there, the deactivated catalyst and the product are separated by distillation or the like, and are not reused, which is uneconomical. On the other hand, the reaction carried out in the above-mentioned heterogeneous phase is exclusively limited to the production of esters by dimerization of aromatic aldehydes, and moreover, the reaction temperature also requires a high temperature of 100° C. or higher. The present inventors conducted various studies in order to solve the shortcomings of the method of producing esters by dimerizing aldehydes in the above-mentioned homogeneous phase or heterogeneous phase. As a result, it has been found that a method using the novel aluminum alkoxide/phenoxide compounds represented by the above general formulas [] and [] as a catalyst is an excellent production method that overcomes the above-mentioned drawbacks. That is, since the catalyst has very high activity and causes almost no side reactions, according to the method of the present invention, esters can be efficiently produced from aldehydes under mild conditions such as room temperature. be able to. In addition, among the compounds used as catalysts in the present invention, when the reaction is carried out using a polymer-produced compound, that is, one represented by the general formula [] as a catalyst, the catalyst is placed in a packed column. By filling the tank and continuously passing the raw material aldehyde, esters containing no catalyst component can be continuously produced. This has the advantage that the separation step between the catalyst and the product can be omitted in the process, and the cost of the catalyst can be reduced. Examples of aldehydes that can be used in the present invention include aliphatic saturated aldehydes such as olumaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, hexylaldehyde, heptylaldehyde, octylaldehyde, and hexahydrobenzaldehyde, aliphatic saturated aldehydes such as acrolein, crotonaldehyde, and tetrahydrobenzaldehyde. Examples include unsaturated aldehydes and aromatic aldehydes such as benzaldehyde and cinnamaldehyde, which may be used alone or in combination of two or more. The compound represented by the general formula [] is soluble in the solvent used, the raw material aldehydes, and the produced esters, and in the conventional Teishichenko reaction,
It can be used in a manner similar to that used as a homogeneous phase catalyst. On the other hand, the compound represented by the general formula [] is insoluble in the solvent used, the raw material aldebides, and the produced esters, and can be used as a catalyst as it is, or if necessary, can be used as a catalyst, such as alumina, silica, silica alumina, diatomaceous earth, or activated clay. It can be carried out batchwise or continuously by supporting on or mixing with an inert carrier, suspending them in raw material aldehydes, or filling them into a reaction column and passing raw material aldehydes through them. can produce esters. In the above formula, those in which R ¹ is hydrogen or a methyl group have low catalytic activity and cannot be used as the catalyst of the present invention. Aluminum alkoxides and phenoxides used as catalysts in the present invention are produced by the exchange reaction of alkoxyl groups between divalent phenol and aluminum trialkoxide or by the reaction of divalent phenol and trialkylaluminium, and the resulting alkyl aluminum diphenooxide is It can be produced by reacting with a dihydric aliphatic alcohol to exchange the remaining alkyl groups with alkoxyl groups. Typical examples of divalent phenols used as raw materials are as follows:

【formula】

【formula】

【formula】

【formula】

[expression] or

[Formula] (wherein R ² represents hydrogen or a methyl group). As mentioned above, in all of the divalent phenols used for preparing the aluminum alkoxide/phenols used as catalysts in the present invention, the carbon atoms to which the hydroxyl groups are bonded on the aromatic ring are not adjacent to each other. As shown in the comparative examples, aluminum alkoxides/phenoxides derived from aromatic rings with adjacent carbon atoms to which hydroxyl groups are bonded have low catalytic activity and low selectivity, and are therefore undesirable. The aluminum alkoxide/phenoxide is used in a proportion of 0.005 to 10 mol % based on the raw material aldehyde. The reaction is carried out at -30 to +100°C for 15 minutes to 24 hours, preferably 1 hour to 10 hours, if necessary in the presence of a suitable solvent. As the solvent, aliphatic hydrocarbons, aromatic hydrocarbons, etc. are used. In the case of a fixed bed flow system, the raw material aldehyde has a LHSV of 0.1 to 50 hr ^-1 , preferably 1 to 50 hr -1
Supplied at 20hr ^-1 . The esters produced can be purified by conventional means such as distillation. As mentioned above, the catalyst used in the method of the present invention, aluminum alkoxide phenoxide itself, is a new substance. Next, the method of the present invention will be illustrated with specific examples. Reference example 1

Synthesis of [Formula] 10 Benzene solution of triethylaluminum (1Mol/) in a nitrogen-substituted 50ml flask
ml (equivalent to 10 mmol of triethylaluminum)
and 10 ml of 1,4-dioxane were added. to this
10 ml of a 1,4-dioxane solution containing 10 mmol of hydroquinone was slowly added dropwise while stirring. Then, at room temperature for 2 hours and then at 95-98℃ for 1 hour.
Stirring was continued for an hour. Then cool it to room temperature and
While stirring, 10 mmol of isopropanol was slowly added dropwise. As in the above case, at room temperature for 2 hours,
After further stirring at 95-98℃ for 1 hour, the solvent and unreacted substances were removed by heating and vacuum treatment, resulting in powdery I got it. When the above compound was hydrolyzed by refluxing with 1N hydrochloric acid for 10 hours and analyzed by gas chromatography, hydroquinone and isopropanol were produced in a ratio of 1.03:1.00 (mol/mol), respectively. This value supports the above structural formula and corresponds to n'(n'=n-1, the same applies hereinafter)=32 in the following structural formula. IR spectrum The IR spectrum was measured using the so-called nujiol method, in which the powdered compound was mixed with liquid paraffin and measured. Its spectrum differed from that of raw materials isopropanol and hydroquinone,
The following absorption bands of 865, 940, 1000 and 1290 cm ^-1 appeared. The IR spectrum is shown in Figure 1. Reference example 2

Synthesis of [Formula] Synthesis was carried out under the same conditions as in Reference Example 1 except that 10 mmol of 4,4'-dihydroxydiphenyl was used instead of 10 mmol of hydroquinone.

I got [formula]. The above compound was hydrolyzed by refluxing with 1N hydrochloric acid for 10 hours, and the product was analyzed by gas chromatography, and it was found that 4,4'-dihydroxydiphenyl and isopropanol were 1.05:1.00, respectively.
(mol/mol). This value supports the above structural formula and corresponds to n'=19 in the following structural formula. IR Spectrum The IR spectrum of this compound was measured by the nujiol method. The spectra were 865, 935, 1095, 1255 and 1605 cm different from those of the raw materials isopropanol and 4,4'-dihydroxydiphenyl.
A new absorption band of ^-1 appeared. 1095 of these
The absorption of cm ^-1 is

Attributed to [Formula]. The IR spectrum is shown in Figure 2. Reference example 3

Synthesis of [Formula] Synthesis was carried out under the same conditions as in Reference Example 1 except that 10 mmol of resorcinol and 10 mmol of ethanol were used instead of 10 mmol of hydroquinone and 10 mmol of isopropanol.

[Formula] was obtained. When the above compound was hydrolyzed by refluxing with 1N hydrochloric acid for 10 hours and analyzed by gas chromatography, resorcinol and ethanol were detected.
It was produced at a ratio of 1.09:1.00 (mol/mol). This value supports the above structure, and also supports the structure below.
Corresponds to n′≒10. IR Spectrum The IR spectrum of this compound was measured by the nujiol method. Its spectrum includes 620, 685, 80,
New absorption bands at 1095, 1170, 1255 and 1590 cm ^-1 appeared. Of these, the absorption of 1095cm ^-1 is

[Formula] Attributed to a bond. The IR spectrum is shown in Figure 3. Reference example 4

Synthesis of [Formula] In Reference Example 1, instead of using 10 mmol of hydroquinone, 10 mmol of 1,1'-bi-
It was synthesized under the same conditions except that 2-naphthol was used, and a solid form was obtained.

I got [formula]. NMR spectrum (measured as dethroloform solution) 3.6δ (b) 〃 1.2δ (c) 〃 Area ratio (a):(b):(c)=12.6:6:1.2 This value is the theoretical value 12:6: Close to 1. The NMR spectrum is shown in Figure 5. IR spectrum The IR spectrum was measured as a carbon disulfide solution using a solution cell with a thickness of 0.1 mm. Its spectrum includes isopropyl alcohol and 1,
395 different from those of 1′-bi-2-naphthol,
460, 520, 550, 585, 615, 690, 840, 870, 995,
New absorption bands at 1030, 1070 and 1210 cm ^-1 appeared. Among these absorptions, the absorption of 1030cm ^-1 is

[Formula] Attributed to a bond. The IR spectrum is shown in Figure 4. Example 1 200 mmol of propionaldehyde was added to a 50 ml Erlenmeyer flask purged with nitrogen and cooled to 0°C. Synthesized in Reference Example 1 under stirring,

Add 0.5 ml (0.5 mmol) of benzene suspension (1Mo/) of [formula],
The temperature was raised to 25°C, and the reaction was continued at that temperature for 4 hours with stirring. After the reaction was completed, the contents were analyzed by gas chromatography, and the amount of unreacted aldehyde was 1.5%.
98.6 mmol of n-propyl propionate were detected. These results are
This corresponds to a conversion of propionaldehyde of 99.3% and a selectivity to converted aldehydes and esters of 99.4%, respectively. Example 2 In Example 1

Synthesized in Reference Example 2 instead of using 0.5 mmol of [Formula] and reacting for 4 hours.

When the reaction was carried out under the same conditions except that 0.5 mmol of [Formula] was used and the reaction was carried out for 5 hours, unreacted aldehyde was
16.9 mmol, n-propyl propionate
88.1 mmol each was detected. These results correspond to a conversion of propionaldehyde of 91.6% and a selectivity of converted aldehyde to ester of 96.2%, respectively. Example 3 100 mmol of propionaldehyde and 100 mmol of acetaldehyde were added to a 50 ml Erlenmeyer flask purged with nitrogen and cooled to 0°C. It was synthesized in Reference Example 1 under stirring.

Add 1 ml (1 mmol) of benzene suspension (1Mo/) of [formula],
The reaction was continued at 0° C. for 5.5 hours under stirring. After the reaction was completed, the contents were analyzed using gas chromatography, and unreacted acetaldehyde was detected.
0.5 mmol, unreacted propionaldehyde 0.5
mmol, ethyl acetate 23.8 mmol, ethyl propionate 17.8 mmol, n-propyl acetate 27.5
mmol, and n-propyl propionate
24.0 mmol each was detected. These results correspond to a conversion of total aldehydes of 99.5% and a selectivity of total converted aldehydes to total esters of 93.6%, respectively. Example 4 In Example 3

Instead of using 1 mmol of [formula] and reacting for 5.5 hours,

When the reaction was carried out under the same conditions except that 1 mmol of [Formula] was used and the reaction was carried out for 5 hours, the unreacted acetaldehyde amounted to 3.3
3.9 mmol of unreacted propionaldehyde, 21.7 mmol of ethyl acetate, 15.9 mmol of ethyl propionate, 27.2 mmol of n-propyl acetate and 23.6 mmol of n-propyl propionate were detected. These results correspond to a conversion of total aldehydes of 96.4% and a selectivity of total converted aldehydes to total esters of 91.7%, respectively. In addition, the adjustment of the catalyst described above is as follows: 10 in Reference Example 1.
Similar conditions were used except that instead of using mmol of hydroquinone, 10 mmol of resorcinol was used. When treated in the same manner as in Reference Example 1, n'=10. Example 5 In Example 3

Instead of using 1 mmol of [Formula], synthesized in Reference Example 4

The reaction was carried out under the same conditions except that 0.3 mmol of [Formula] was used, and the results were as follows: unreacted acetaldehyde 22.8 mmol, unreacted propionaldehyde 10.8 mmol, ethyl acetate 16.7 mmol, ethyl propionate 12.0 mmol, acetic acid-n 24.8 mmol of -propyl and 20.6 mmol of n-propyl propionate were detected respectively. These results correspond to a conversion of total aldehydes of 83.2% and a selectivity of total converted aldehydes to total esters of 89.1%, respectively. Example 6 100 mmol of propionaldehyde and 100 mmol of isobutyraldehyde were added to a 50 ml Erlenmeyer flask purged with nitrogen and cooled to 0°C.
Synthesized in Reference Example 1 while stirring

Add 0.5 ml (0.5 mmol) of benzene suspension (1Mo/) of [formula],
The reaction was continued at 0° C. for 5.5 hours under stirring. After the reaction, the contents were analyzed by gas chromatography and found 1.3 mmol of unreacted propionaldehyde, 0.8 mmol of unreacted isobutyraldehyde,
28.0 mmol of n-propyl propionate, 14.5 mmol of n-propyl isobutyrate, 29.7 mmol of isobutyl propionate and 18.4 mmol of isobutyl isobutyrate were detected. These results correspond to a conversion of total aldehydes of 99.0% and a selectivity of total converted aldehydes to total esters of 91.6%, respectively. Example 7 200 mmol of benzaldehyde was charged into a 50 ml Erlenmeyer flask purged with nitrogen and cooled to 0°C. Synthesized in the catalyst preparation method of Example 4 under stirring.

0.5 ml (0.5 mmol) of a benzene suspension of [Formula] (1 Mo/) was added and the reaction was continued at 80°C for 0.5 hour with stirring.
After the reaction was completed, the contents were analyzed by gas chromatography, and it was found that unreacted benzaldehyde 126
mmol and 34.2 mmol of benzyl benzoate were detected respectively. These results indicate an aldehyde conversion rate of 37.0% and a selectivity of converted aldehydes to esters.
Each corresponds to 92.4%. Example 8 200 mmol of acrolein was charged into a 50 ml Erlenmeyer flask that was purged with nitrogen and cooled to 0°C.
And while stirring,

1 ml (1 mmol) of a benzene suspension (1 Mo/) of the formula was added, and the reaction was continued at 0° C. for 5.5 hours with stirring. After the reaction was completed, the contents were analyzed by gas chromatography, and it was found that unreacted acrolein was detected.
182 mmol and 5.2 mmol of allyl acrylate were detected respectively. These results indicate a conversion rate of aldehyde of 9.0% and a selectivity of converted aldehyde to ester of 58%.
correspond to each. The catalyst was prepared under the same conditions as in Reference Example 1 except that 10 mmol of methylhydroquinone was used instead of 10 mmol of hydroquinone. When treated in the same manner as in Reference Example 1, n'=15. Example 9 100 mmol of acetaldehyde and 100 mmol of acrolein were placed in a 50 ml Erlenmeyer flask purged with nitrogen.
mmol was charged and cooled to 0°C. Synthesized in Reference Example 1 while stirring

Add 1 ml (1 mmol) of benzene suspension (1Mo/) of [formula],
The temperature was raised to 25°C, and the reaction was continued at that temperature for 6 hours with stirring. After the reaction was completed, the contents were analyzed by gas chromatography and found to be 0.4 mmol of unreacted acetaldehyde, 63.8 mmol of unreacted acrolein, 29.5 mmol of ethyl acetate, and allyl acetate.
27.3 mmol, 1.8 mmol of ethyl acrylate and 2.7 mmol of allyl acrylate were detected. These results correspond to a conversion of total aldehydes of 67.9% and a selectivity of total converted aldehydes to total esters of 90.3%, respectively. Example 10 200 mmol of pelargon aldehyde was charged into a 50 ml Erlenmeyer flask purged with nitrogen, and while stirring,

0.5 ml (0.5 mmol) of a benzene suspension (1 Mo/) of the formula was added, and the reaction was continued at 25° C. for 5 hours with stirring. After the reaction was completed, the contents were analyzed by gas chromatography, and 16.8 mmol of unreacted pelargonaldehyde and 89.1 mmol of -n-nonyl pelargonate were detected. These results indicate that the conversion rate of pelargon aldehyde
91.6% and a selectivity of converted aldehydes to esters of 97.3%, respectively. The preparation of the catalyst was the same as in Reference Example 1 except that 10 mmol of 1-methyl-3,7-dihydroxynaphthalene and 10 mmol of sec-phthanol were used instead of 10 mmol of hydroquinone and 10 mmol of isopropanol. It was conducted under the following conditions. When treated in the same manner as in Reference Example 1, n'=8. Example 11 In Example 10

Instead of using 0.5 ml (0.5 mmol) of benzene suspension (1Mo/) of [formula]

When the reaction was carried out under the same conditions except that 0.5 ml (0.5 mmol) of benzene suspension (1Mo/) of [formula] was used, unreacted berargonaldehyde
20.0 mmol and n-nonyl belargonic acid
87.5 mmol each was detected. These results indicate that the conversion rate of berargonaldehyde
90.0% and a selectivity of converted aldehydes to esters of 97.2%, respectively. The catalyst was prepared using 10 mmol of 1-methyl-3,7-dihydroxynaphthalene instead of 10 mmol of 1-methyl-3,7-dihydroxynaphthalene in Example 10.
The same conditions were used except that 6,8-dihydroxynaphthalene was used. When treated in the same manner as in Reference Example 1, n'=5. Example 12

[Formula] 10 ml of a benzene suspension containing 0.5 mmol was thoroughly stirred with 1.2 g of alumina fine powder, and the catalyst was sufficiently adhered to the alumina, and the mixture was filled into a jacketed glass tube with an inner diameter of 8 mmφ. The filling has a height of 30 mm and a volume of 1.51
It was hot in ml. Next, water is passed through the jacket and propionaldehyde is allowed to flow down continuously from the upper part while cooling to approximately 25°C. The product accumulated in the lower receiver is taken out at regular intervals, and each fraction is subjected to gas chromatography. Upon analysis, the results shown in Table 1 were obtained. The catalyst was prepared as follows. 20 ml of benzene, 10 mmol of aluminum triisopropoxide, and 20 ml of a 1,4-dioxane solution containing 10 mmol of hydroquinone were added to a flask with an internal volume of 100 ml that had been purged with nitrogen, and heated with stirring. ，
4-Dioxane and the isopropanol produced by the alcohol exchange reaction are slowly distilled out to form a powder.

I got [formula]. When treated in the same manner as in Reference Example 1, n'=25.

[Table] Comparative Example 1 In Example 1

When the reaction was carried out under the same conditions except that 0.5 mmol of [formula] was used and the reaction was carried out for 4 hours, 0.5 mmol of aluminum triisopropoxide (1Mo/benzene solution) was used and the reaction was carried out for 4.5 hours. 15.1 mmol of unreacted aldehyde and 66.1 mmol of n-propyl propionate were detected. These results indicate that the conversion rate of propionaldehyde
92.5% and a selectivity of converted aldehydes to esters of 71.5%, respectively. Comparative Example 2 In Example 1

[Formula] When the reaction was carried out under the same conditions except that instead of using 0.5 mmol of aluminum triethoxide and reacting for 4 hours, the reaction was carried out under the same conditions. n-
69.2 mmol of propyl was detected in each case. These results indicate that the conversion rate of propionaldehyde
93.3% and a selectivity of converted aldehydes to esters of 74.2%, respectively. Comparative Examples 1 and 2 show that the selectivity of aluminum trialkoxide, which is a known catalyst, is lower than that of the catalyst of the present invention. Comparative Example 3 In Example 3

[Formula] Instead of using 1 mmol and reacting for 5.5 hours,

[Formula] When the reaction was carried out under the same conditions except that 0.5 mmol was used and the reaction was carried out for 4 hours, the amount of unreacted acetaldehyde was 10.3
7.8 mmol of unreacted propionaldehyde, 14.7 mmol of ethyl acetate, 11.7 mmol of ethyl propionate, 22.2 mmol of n-propyl acetate, and 19.1 mmol of n-propyl propionate were detected. These results indicate a total aldehyde conversion rate of 91.0%.
and a selectivity of all converted aldehydes to all esters of 74.4%, respectively. That is, it can be seen that the catalytic performance of naphthoxyaluminum dialkoxide is inferior to that of the catalyst of the present invention. The above catalyst was prepared by using 10 mmol of α instead of using 10 mmol of hydroquinone and 10 mmol of isopropanol in Reference Example 1.
Similar conditions were used except that -naphthol and 20 mmol of isopropanol were used respectively. Comparative Example 4 In Example 3

[Formula] Instead of using 1 mmol and reacting for 5.5 hours, a benzene solution of aluminum triisopropoxide (1Mo/)
When the reaction was carried out under the same conditions except that 0.5 ml (0.5 mmol) was used and the reaction was carried out for 5 hours, 10.6 mmol of unreacted acetaldehyde, 58 mmol of unreacted propionaldehyde, and 15.5 mmol of ethyl acetate were obtained.
10.8 mmol of ethyl propionate, 22.7 mmol of n-propyl acetate and 17.8 mmol of n-propyl propionate were detected. These results correspond to a conversion of total aldehydes of 91.8% and a selectivity of total converted aldehydes to total esters of 72.8%, respectively. This Comparative Example, like Comparative Examples 1 and 2, shows that the performance of the aluminum trialkoxide catalyst is inferior to that of the catalyst of the present invention. Comparative Example 5 In Example 6

[Formula] Instead of using 0.5 mmol and 100 moles of isobutyraldehyde

When the reaction was carried out under the same conditions except that 0.5 ml (0.5 mmol) of benzene suspension (1Mo/) of [formula] and 86 mmol of isobutyraldehyde were used, 5.9 mmol of unreacted propionaldehyde was used. , 3.9 mmol of unreacted isobutyraldehyde, 20.4 mmol of n-propyl propionate,
10.0 mmol of n-propyl isobutyrate, 23.9 mmol of isobutyl propionate and 12.8 mmol of isobutyl isobutyrate were detected. These results correspond to a conversion of total aldehydes of 94.7% and a selectivity of total converted aldehydes to total esters of 76.2%, respectively. In the above

[Formula] represents a saturated cycloaliphatic group, and this comparative example uses a saturated cycloaliphatic group instead of an aromatic group, and is superior to the catalyst of the present invention in both conversion rate and selectivity. It shows that it is significantly inferior. The catalyst was prepared under the same conditions as in Reference Example 1 except that 10 mmol of 1,4-cyclohexanediol was used instead of 10 mmol of hydroquinone. When treated in the same manner as in Reference Example 1, n'=35. Comparative Example 6 In Example 3

[Formula] 1 mmol used Instead of doing

[Formula] When the reaction was carried out under the same conditions except that 0.5 mmol was used, unreacted acetaldehyde 73.0 mmol, unreacted propionaldehyde 71.6 mmol, ethyl acetate 4.8 mmol, ethyl propionate 3.4 mmol, acetic acid -n- 7.2 mmol of propyl and 5.3 mmol of n-propyl propionate were detected respectively. These results correspond to a conversion of total aldehydes of 27.7% and a selectivity of total converted aldehydes to total esters of 74.7%, respectively. That is, a catalyst derived from a compound in which two phenolic hydroxyl groups are present adjacent to each other has low activity and low selectivity. In addition, the adjustment of the catalyst described above is as follows: 10 in Reference Example 1.
Similar conditions were used except that instead of using mmol of hydroquinone, 10 mmol of catechol was used.

[Brief explanation of drawings]

Figure 1 shows the IR spectrum of the product obtained in Reference Example 1, and Figure 2 shows the IR spectrum of the product obtained in Reference Example 2.
IR spectrum, Figure 3 is the IR spectrum of the product obtained in Reference Example 3, Figure 4 is the IR spectrum of the product obtained in Reference Example 4, and Figure 5 is the IR spectrum of the product obtained in Reference Example 4.
This is an NMR spectrum.

Claims (1)

[Claims] 1. General formula [] (Here, R ¹ is an alkyl group having 2 to 5 carbon atoms.) Or general formula [] [ ^wherein ,
R ¹ is an alkyl group having 2 to 5 carbon atoms. ] A method for producing esters, which comprises dimerizing aldehydes using an aluminum alkoxide/phenoxide represented by the following as a catalyst. 2. The method according to claim 1, characterized in that the catalyst is used suspended in the reaction system. 3. Claim 1, characterized in that esters are continuously produced by filling a reaction tower with the catalyst and continuously passing the aldehyde through the reactor.
The method described in section. 4 In the reaction, the reaction temperature is -30 to +100°C,
2. The method according to claim 1, wherein the reaction pressure is 0 to 50 atm and the amount of catalyst used is 0.005 to 10 mol based on the aldehyde.