JPH0692900A - Production of ester - Google Patents

Abstract

PURPOSE:To highly selectively produce an ester from an aldehyde compound while maintaining a high catalytic activity. CONSTITUTION:An aldehyde compound such as formaldehyde is reacted in the presence of a Ru complex catalyst so as to produce a corresponding ester such as methyl formate. As the Ru complex catalyst, a complex represented by the following formula is included; formula RuX2[P(OR)3]4 [X is a halogen atom, R is an alkyl group, etc.]. The Ru complex catalyst exhibits a high catalytic activity and a high selectivity. A high catalytic activity can be maintained without an influence of water. Further, this catalyst is soluble in an organic solvent and, therefore, can be used in a liquid phase reaction.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing an ester from an aldehyde compound.

[0002]

The Tichenko reaction is known as a method for producing an ester from an aldehyde compound. In this method, methyl formate is obtained by dimerizing formaldehyde or its equivalent paraformaldehyde in the presence of a metal alkoxide catalyst such as sodium, calcium, magnesium or aluminum.

However, the metal alkoxide has a strong basicity, side reactions such as an aldol condensation reaction and a trimolecular condensation reaction occur, and the production of by-products is remarkable and the selectivity is low. Therefore, the operation of separating and collecting the ester becomes complicated. Further, the metal alkoxide is immediately hydrolyzed by a small amount of water to form a strongly basic hydroxide or oxide. Therefore, the catalytic activity cannot be maintained, the reaction efficiency decreases, and it is difficult to carry out the reaction smoothly.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for efficiently producing an ester with a high selectivity while maintaining a high catalytic activity.

[0005]

As a result of intensive studies, the present inventor has found that the Ru complex catalyst exhibits high catalytic activity, is resistant to hydrolysis and is stable, and is chemically neutral and hardly causes side reactions. It was found that an ester can be produced from an aldehyde compound with high selectivity, and the present invention has been completed.

That is, in the method of the present invention, an ester is produced by reacting an aldehyde compound in the presence of a Ru complex catalyst.

As the Ru complex, various complexes can be used, but a hexacoordinated complex, particularly a complex represented by the following general formula (1) is preferable.

[RuX ₂ (P (OR) ₃ ) ₄ ] (1) [wherein, X represents a halogen atom, R represents an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group] The general formula (1) In, the halogen atom includes fluorine, chlorine,
Contains bromine and iodine atoms. Preferred halogen atoms include chlorine atoms.

Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, isobutyl,
Examples thereof include t-butyl, sec-butyl, pentyl and hexyl groups.

Cycloalkyl groups include, for example, cyclopentyl, cyclohexyl, cyclooctyl groups and the like. The aryl group includes a phenyl group and a naphthyl group. Examples of the aralkyl group include benzyl, phenethyl and benzhydryl groups.

The preferred substituent R includes an alkyl group having 1 to 4 carbon atoms, particularly 1 to 3 carbon atoms, and especially a methyl group.

The complex represented by the general formula (1) is characterized in that it has a high selectivity in producing an ester from an aldehyde compound and hardly causes a side reaction. Also,
It also has the feature that it can maintain high catalytic activity without being affected by moisture.

The Ru complex catalyst represented by the general formula (1) can be prepared by a conventional method, for example, RuX ₂ (PPh ₃ ) ₃ (P
h represents a phenyl group. X is the same as above. ) And P (O
R) ₃ (R is the same as above). (WJ Sime and TA Stephenson, J. Organ)
omet. Chem., 161, 245 (1978)). in this way,
Using Ru and uX ₃ as raw materials, once RuX ₂ (PPh ₃ ) ₃
Is required as an intermediate product, and because of the ligand exchange method, there is a problem that the yield based on RuX ₂ (PPh ₃ ) ₃ is as low as about 45%.

Therefore, RuX _{3 is} used in an inert gas atmosphere.
It is useful to employ a method in which MBH ₄ (M represents an alkali metal) is added to the P (OR) ₃ solution of and the mixture is stirred. As the inert gas, nitrogen, helium, argon gas or the like can be used. Examples of the alkali metal M include lithium, potassium and sodium. Examples of the alkali metal borohydride compound MBH ₄ include, for example,
LiBH ₄ , KBH ₄ , NaBH _{4 and the} like can be used.
This method is performed at 5 to 70 ° C., preferably room temperature (eg 10
Can be performed at about 35 ° C.

In this method, the end point of the reaction is usually
It can be judged that the solution changes color when the borohydride compound is added and stirred. Further, after completion of the reaction, the complex can be obtained in a high yield by filtering, concentrating the filtrate if necessary, and recrystallizing.
Further, it can be further purified by using a suitable solvent such as P (OR) ₃ as a recrystallization solvent.

The Ru complex may be subjected to the reaction as it is, or may be used by supporting it on a carrier, if necessary.
Examples of the carrier include activated carbon, silica, alumina, silica-alumina, clay minerals such as zeolite, copper oxide, bentonite, magnesia, silica-magnesia, titania, inorganic carriers such as zirconia; ion-exchange resins, chelate resins and the like. An organic carrier is mentioned.
Preferred carriers include those having a heat resistance higher than the reaction temperature.

The catalyst supported on the carrier can be prepared by a conventional method such as a precipitation method, an impregnation method or an ion exchange method.
The supported amount of the catalyst is, for example, 100 parts by weight of the carrier,
The amount is 0.1 to 200 parts by weight, preferably 1 to 100 parts by weight. Solid catalysts include powder, granules, pellets,
It may be rod-shaped, elliptical or spherical.

The catalyst can be used for both liquid phase reaction and gas phase reaction, but it is characterized by being soluble in an organic solvent and being almost chemically neutral. Therefore, it is useful to use the Ru complex in a liquid phase reaction that constitutes a homogeneous catalyst.

When an aldehyde compound is reacted in the presence of such a catalyst, an ester corresponding to the aldehyde compound is produced. This reaction is presumed to proceed according to the following reaction formula (2).

2R ¹ CHO → R ¹ COOCH ₂ R ¹ (2) (In the formula, R ¹ represents an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group or a heterocyclic group) Examples of the aldehyde compound include: Formaldehyde, paraformaldehyde, acetaldehyde, paraaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, valeraldehyde, isovaleraldehyde,
Aliphatic saturated aldehydes such as pivalin aldehyde, capronaldehyde, heptaldehyde, capryl aldehyde, waurine aldehyde; aliphatic unsaturated aldehydes such as acrolein, crotonaldehyde, propiol aldehyde; benzaldehyde, tolualdehyde, salicylaldehyde, cinnamaldehyde, Aromatic aldehydes such as naphthaldehyde; and heterocyclic aldehydes such as furfural.

Of these aldehyde compounds, aliphatic aldehydes, particularly aliphatic aldehydes having about 1 to 5 carbon atoms are preferable. When obtaining methyl formate as a precursor of acetic acid or methyl acetate, formaldehyde and its equivalent paraformaldehyde are preferably used.

According to the method of the present invention, the ester corresponding to the aldehyde compound can be obtained with high selectivity.
Preferred methods of the present invention include, for example, a method of reacting formaldehyde or paraformaldehyde to obtain methyl formate or methylal which is useful as a precursor of acetic acid or methyl acetate.

In the liquid phase reaction, the aldehyde compound itself may be used as a solvent, or a solvent inert to the reaction may be used. Examples of the solvent include alcohols such as methanol, ethanol, propanol, butanol, and cyclohexanol; aliphatic hydrocarbons such as hexane, heptane, and octane; alicyclic hydrocarbons such as cyclohexane; aromatics such as benzene, toluene, and xylene. Group hydrocarbons; halogenated hydrocarbons such as dichloromethane, trichloromethane, carbon tetrachloride, ethylene chloride; ketones such as acetone, methyl ethyl ketone, cyclohexanone; carboxylic acids such as acetic acid; esters such as methyl acetate and ethyl acetate; diethyl ether , Ethers such as dimethoxyethane and tetrahydrofuran; nitro compounds such as nitromethane, nitroethane and nitrobenzene; nitrile compounds such as acetonitrile, propionitrile and benzonitrile; di Chill, dimethylacetamide, aprotic polar solvents such as dimethylsulfoxide; and the like and mixed solvents thereof can be exemplified.

The catalyst concentration in the reaction solution can be appropriately selected depending on the solubility of the complex catalyst and the degree of catalytic activity, but is usually 0.0
It is about 01 to 500 mM, preferably about 0.01 to 100 mM. Since the Ru complex has high solubility in the target compound methyl formate and the organic compound such as the solvent,
The catalyst concentration can be increased and the reaction rate can be increased.

The liquid phase reaction can be carried out, for example, at 0 to 300 ° C., preferably at 30 to 200 ° C. The reaction can be carried out under an inert atmosphere of nitrogen, helium, argon or the like, at atmospheric pressure or under pressure. The reaction may be carried out batchwise or continuously.

In the liquid phase reaction, the ratio of the aldehyde compound to the Ru complex catalyst can be appropriately selected within the range where the ester production efficiency does not decrease. The ratio of the aldehyde compound to 1 mol of the complex is, for example, 0.1 to 10,000.
The molar amount is preferably about 1 to 1000 mol.

The gas phase reaction can be carried out, for example, at a temperature of 20 to 400 ° C., preferably about 50 to 300 ° C. The reaction can be carried out under an inert atmosphere of nitrogen, helium, argon or the like, at atmospheric pressure or under pressure.

The gas phase reaction may be carried out batchwise or continuously. When the reaction is performed in a batch system, the ratio of the raw material components to 1 mol of the complex is, for example, 0.1 to 1
It is about 0000 mol, preferably about 10 to 1000 mol. In the continuous method, the supply amount of the aldehyde compound with respect to 1 mol of the complex is, for example, 0.001 to 1000 mol /
Minutes, preferably in a wide range of about 0.1 to 100 mol / min.

When the reaction is carried out in a gas phase continuous system, a fixed bed,
A conventional method such as a reaction method using a fluidized bed or a reactive distillation method can be adopted.

The ester obtained by the method of the present invention is also useful as a precursor of an organic acid having one more carbon atom than the aldehyde compound or an ester thereof. More specifically, when methyl formate produced from formaldehyde or paraformaldehyde according to the reaction of the present invention is reacted in the presence of a Ru—Sn heteronuclear polynuclear complex catalyst represented by the following general formula (3), high selectivity is obtained. Methyl acetate can be obtained at a rate.

[RuX _a (SnY ₃ ) _b {P (OR) ₃ } _c ] (3) (wherein Y represents a halogen atom, a represents 0 or 1, and b
Indicates 1 or 2. However, a + b = 2, c is 3 when a is 0, and c is 4 when a is 1.
X and R are the same as those described above.) Like the complex represented by the general formula (1), in the complex catalyst represented by the general formula (3), preferable halogen atoms X and Y include a chlorine atom and the like. Included and preferable R includes an alkyl group having 1 to 4 carbon atoms, especially a methyl group.

Specific examples of the complex represented by the general formula (3) include, for example, [RuCl (SnCl ₃ ) {P (O
CH ₃ ) ₃ } ₄ ], [Ru (SnCl ₃ ) ₂ {P (OC
H ₃ ) ₃ } ₃ ] and the like.

Either a liquid phase method or a gas phase method can be adopted for the reaction for producing methyl acetate from methyl formate.
In addition, the amount of the complex catalyst represented by the general formula (3),
The reaction conditions such as the reaction temperature can be the same as those in the present invention.

[0034]

According to the method of the present invention, since a Ru complex catalyst is used, an ester can be efficiently produced from an aldehyde compound with a high selectivity while maintaining a high catalytic activity.

[0035]

EXAMPLES The present invention will be described in more detail based on the following examples.

The catalyst [RuCl ₂ (P (OC
Preparation of H ₃ ) ₃ ) ₄ ] 1.00 g of RuCl ₃ .3H ₂ O was added to 10 ml of P (O).
0.83 g after dissolving in CH ₃ ) ₃ and stirring for 15 minutes
NaBH ₄ was added in small portions and stirring continued until the solution turned yellow. These operations were performed at room temperature.

The solid content in the solution is filtered off, the filtrate is concentrated,
Crystals were precipitated by cooling. The yield of precipitated crystals was 95% based on Ru. The obtained precipitate was dissolved in P (OCH ₃ ) ₃ and purified by a recrystallization method of cooling to prepare the title complex.

[0038] ³¹ P NMR chemical shift: 128.7 ppm (85
% H ₃ PO ₄ standard) Example At room temperature, in an Agon atmosphere, 0.0167 g of the catalyst and 0.0375 g of paraformaldehyde were dissolved in 50 ml of nitromethane and charged into a glass ampoule. The ampoule was degassed by vacuum evacuation, and the ampoule was sealed.
The reaction was allowed for 0 hours. When the reaction product was quantified by gas chromatography, 0.084 g of methyl formate and 0.0002 g of methylal were produced. The conversion of paraformaldehyde into methyl formate was 22.3% based on formaldehyde, and the selectivity was 98%.

Claims (3)

[Claims] 1. A method for producing an ester, which comprises reacting an aldehyde compound in the presence of a Ru complex catalyst. 2. A Ru complex catalyst has the following general formula (1) [RuX ₂ (P (OR) ₃ ) ₄ ] (1) [wherein, X is a halogen atom, R is an alkyl group, a cycloalkyl group, and aryl. Group, which represents an aralkyl group]. 3. The process for producing an ester according to claim 1, wherein methyl formate is obtained by reacting formaldehyde in a liquid phase in the presence of a Ru complex homogeneous catalyst.