JPS6340416B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a carboxylic acid ester by reacting an aldehyde and an alcohol in the presence of molecular oxygen under mild conditions. More specifically, the present invention relates to a method for producing a carboxylic acid ester with high selectivity by reacting an aldehyde and an alcohol using a catalyst containing platinum and/or palladium in the presence of a diluted molecular oxygen-containing gas. Conventionally, a catalyst in which platinum or palladium is supported on a carrier such as diatomaceous earth or activated carbon is suspended in a mixture of aldehyde and alcohol, and molecular oxygen-containing gas is blown into this under pressure to oxidize the aldehyde in the liquid phase. It is known that carboxylic acid esters can also be produced by
−34368). However, in this method, very complicated side reactions occur in parallel with the carboxylic ester production reaction, such as an acetal production reaction, an oxidation reaction of the alcohol itself, and a reaction between the alcohol and the aldehyde product, which produces the desired carboxylic ester. It has the disadvantage of low selectivity, especially selectivity based on alcohol. These disadvantages not only increase the raw material consumption rate due to a decrease in selectivity to the product, but also require a large amount of equipment and energy to separate by-products from the desired product, which is extremely disadvantageous from an industrial perspective. . One attempt to solve this problem was published in Japanese Unexamined Patent Publication No. 54-73715.
-73717 and JP-A-54-73723-73725, in which a catalyst is proposed that suppresses the formation of by-products due to oxidation of these alcohols themselves and provides the desired product with high selectivity. However, even when these proposed catalysts are used, large amounts of by-products from the oxidation of the alcohol itself, such as methyl formate, are produced in methanol-based reactions, and Pd--Pb-based catalysts, which produce the desired product in high yields, still produce large amounts of by-products. In this case, the amount of this by-product produced is particularly large. As a result of intensive studies aimed at solving these shortcomings, the present inventors found that the oxygen concentration in the molecular oxygen-containing gas used for the reaction was surprisingly low in the amount of by-products produced due to the oxidation of the alcohol itself. On the other hand, it has little to do with the amount of the desired carboxylic acid ester produced by the reaction between aldehyde and alcohol; in other words, lowering the molecular oxygen concentration dramatically reduces the production of this byproduct. However, the present invention was completed by discovering that the production of the target carboxylic acid ester was almost unchanged. Moreover, the effect of limiting the oxygen concentration of the present invention is most remarkable when the reaction is carried out in the presence of a catalyst containing one or more of platinum or a platinum compound and palladium or a palladium compound. The oxygen concentration in the molecular oxygen-containing gas in the method of the present invention must be 18 mol% or less and 1 mol% or more, preferably 14 mol% or more and 2 mol% or more, more preferably 10 mol% or less. It is mol% or more. When the oxygen concentration increases, by-products resulting from the oxidation of the alcohol itself, such as methyl formate in methanol systems, increase, which is not desirable.
On the other hand, if the oxygen concentration becomes too low, not only will the production rate of the target product, carboxylic ester, decrease, but the amount of oxygen-containing gas supplied to the reaction system will increase, resulting in an enlargement of the equipment and This is undesirable because the cost of power supply increases. The oxygen-containing gas may be pure oxygen diluted with a diluent gas inert to the reaction, such as nitrogen, carbon dioxide, or exhaust gas from the reaction, or air diluted with a diluent gas inert to the reaction. The amount of oxygen-containing gas used naturally varies depending on the oxygen content, but it is sufficient that it is at least the stoichiometric amount of pure oxygen necessary for the reaction, preferably at least 1.5 times the stoichiometric amount. The aldehyde and alcohol used in the method of the present invention must be selected depending on the desired ester. To give an example, aldehydes are HCHO, CH ₃ CHO, C ₂ H ₅ CHO, n-
Aliphatic saturated aldehydes such as C ₃ H ₇ CHO, i-C ₃ H ₇ CHO; CH ₂ =CH-CHO,

[Formula] CH ₃ - CH= CH - Aliphatic unsaturated aldehydes such as CHO; C ₆ H ₅ CHO, CH ₃ C ₆ H ₄ CHO,
Aromatic aldehydes such as C ₆ H ₅ CH ₂ CHO and C ₆ H ₄ (CHO) ₂ or their derivatives are used, but the method of the present invention is difficult to apply ordinary autoxidation reactions due to their high polymerizability. It can be particularly suitably applied to the oxidation of unsaturated aldehydes. On the other hand, alcohols include CH ₃ OH, C ₂ H ₅ OH,
Aliphatic saturated alcohols such as C ₃ H ₇ OH, C ₄ H ₉ OH, and C ₈ H ₁₇ OH; Diols such as ethylene glycol and butanediol; Aliphatic unsaturated alcohols such as allyl alcohol; Aromatics such as benzyl alcohol Alcohol etc. are used. The molar ratio of aldehyde to alcohol is preferably in the range of 10 to 1/100, particularly preferably in the range of 2 to 1/50. If the molar ratio exceeds 10, side reactions such as decomposition of aldehydes, for example, polymerization reactions such as dimerization and multimerization in the case of unsaturated aldehydes, become significant, and the selectivity of the reaction decreases, which is not preferable. On the other hand, if it is less than 1/100, by-products due to oxidation of the alcohol itself will be produced significantly, and the selectivity based on alcohol will decrease. The catalyst that exhibits the most remarkable effect in the method of the present invention using diluted oxygen is a catalyst containing platinum and/or palladium, particularly (i) one selected from platinum, palladium and their compounds and (ii) tellurium. ,lead,
Those consisting of one or more selected from mercury, thallium, and their compounds can be suitably used, and in addition to these, Rb, Cs, Mn, As,
A catalyst containing one or more components selected from the group consisting of Sb, Se, and these compounds can also be suitably used. As the platinum compound, platinum chloride (2), platinum chloride (2), chloroplatinic acid, platinum oxide, etc. are used, but it is preferable that at least a part of it becomes metallic platinum in the reaction system. Palladium compounds include palladium nitrate,
Palladium salts such as palladium chloride and palladium sulfate, palladium oxide, and palladium complexes such as palladium phthalocyanine are used, but it is preferable that at least a part of them be converted to metallic palladium in the reaction system. Tellurium compounds include tellurium oxide (), oxides such as tellurium oxide (), sodium tellurate,
Examples include tellurates such as potassium tellurate, tellurites such as sodium tellurite and potassium tellurite, tellurite, and orthotelluric acid; examples of lead compounds include carboxylates such as lead acetate and lead formate; Examples include inorganic lead (), () compounds such as lead nitrate, lead oxide (), oxide salts (), lead hydroxide (), (), etc., and mercury compounds such as mercury acetate, mercurous chloride, oxidized Examples include mercury compounds (), () such as mercury and mercury nitrate, and as thallium compounds, thallium compounds () and () such as thallium acetate, thallium nitrate, thallium sulfate, thallium chloride, and thallium oxide can be used. I can do it. Although these catalytic metal components may be present separately in the reaction system, they are preferably present in the reaction system in a form that allows them to have some effect on each other. For example, these metal components can be activated carbon, silica, alumina, titania, zirconia, diatomaceous earth, silicon carbide, silica-alumina,
A carrier supported on a general carrier such as barium sulfate or calcium carbonate can be suitably used from the viewpoint of handling and reaction activity, but it is particularly preferable to use a carrier having a specific surface area of 70 m ² /g or less. The ratio of each component of these catalysts can be arbitrarily selected within a wide range depending on the type and amount of reaction raw materials, reaction conditions, catalyst preparation method, etc., and is not particularly limited.
Generally, supported catalysts contain 0.05 to 20% by weight of platinum or palladium metal, preferably 0.2 to 20% by weight of platinum or palladium metal, based on the weight of the catalyst.
10% by weight, tellurium, lead, mercury, thallium and their compounds from 0.01 to 30% by weight for each metal.
Preferably, it is in the range of 0.02 to 20% by weight. There is no particular restriction on the amount of catalyst used relative to the raw material aldehyde, but it is usually about 1/100 to 10 times the weight ratio. However, the present invention is not limited to this range, and particularly when the present invention is implemented in a distribution system, it is not limited to the above range. Supported catalysts can be prepared according to conventional methods. For example, when preparing a catalyst in which palladium and lead compounds are supported on an alumina carrier, alumina is impregnated with an aqueous palladium salt solution, reduced with an appropriate reducing agent, immersed in an aqueous solution of lead acetate, and evaporated. It can be dried to dryness and used for reaction. The reaction is usually carried out at a temperature of 0 DEG C. or higher and 120 DEG C. or lower, but in consideration of the reaction rate and the formation of by-products, the reaction temperature range is preferably 20 DEG to 80 DEG C. The reaction can be carried out under reduced pressure, atmospheric pressure or increased pressure. Moreover, this reaction can be carried out either batchwise or continuously. Next, the method of the present invention will be specifically explained with reference to Examples. In addition, the carboxylic acid ester yield and selectivity in Examples and Comparative Examples are all based on aldehyde, and the conversion rate, selectivity, and yield are based on molar basis. Further, the O ₂ concentration in the air-nitrogen mixed gas was expressed in mol%. Example 1 10 g of commercially available 5% by weight palladium-α-alumina (manufactured by Engelhard Japan) was added to an aqueous solution of 0.25 g of lead acetate [(CH ₃ CO ₂ ) ₂ Pb・3H ₂ O] dissolved in 20 ml of distilled water. Add and evaporate to dryness slowly on a hot water bath. Thereafter, it was thoroughly dried under reduced pressure at 100°C to prepare a catalyst. 4 g of this catalyst was placed in a 200 cc.
Add 79g of air-nitrogen mixed gas (O ₂ concentration 11%) at 30N through the gas inlet at a reaction temperature of 40℃.
The reaction was carried out while blowing at a rate of l/h.
At this time, the reaction mixture was stirred using a magnetic stirrer. The reaction was carried out for 2.5 hours and the results are shown in Table 1.
From this result, it is clear that the amount of methyl formate produced as a by-product was smaller than in Comparative Examples 1 and 2, which will be described later. Example 2 The method of Example 1 was repeated using 4 g of the same catalyst as in Example 1, except that the O ₂ concentration of the air-nitrogen mixture was changed to 7%, and the blowing rate was changed to 45 N-l/h. The reaction results are shown in Table-1. Comparative Examples 1 to 2 Using 4 g of the same catalyst as in Example 1, the blown gases were 3 N-l/h of pure oxygen and 15 N-l/h of air, respectively.
The method of Example 1 was repeated except that the l/h was changed. The reaction results are shown in Table-1. Examples 3 to 4, Comparative Examples 3 to 4 In the same manner as in Example 1, 5 weight % palladium-α-alumina was replaced with 5 weight % palladium.
The catalyst was prepared using _CaCO3 . Using 4g of this catalyst, the blowing gas was 30N-l/air-nitrogen mixed gas ( _O2 concentration 11%).
time, air-nitrogen mixed gas (O ₂ concentration 7%) 45N-
The procedure of Example 1 was repeated, except that the flow rate was 3 N-l/h, pure oxygen 3 N-l/h, and 15 N-l/h air. The reaction results are shown in Table-1. Examples 5-6, Comparative Examples 5-6 Using 2 g of a catalyst prepared in the same manner as in Example 1 using 5% by weight palladium-CaCO ₃ and tellurite,
The blowing gases were air-nitrogen mixed gas (O ₂ concentration 11%) 30N-l/hr, air-nitrogen mixed gas (O ₂ concentration 7%) 45N-l/hr, and pure oxygen 3N-l/hr.
Example 1 except that air was used at 15 N-l/hr.
The method was repeated. The reaction results are shown in Table-1. Example 7, Comparative Example 7 Using 4 g of a catalyst prepared in the same manner as in Example 1 using 5% by weight palladium-Al ₂ O ₃ and mercury acetate,
The procedure of Example 1 was repeated, except that the blowing gases were 45 N-l/h of air-nitrogen mixture (7% O ₂ concentration) and 3 N-l/h of pure oxygen, respectively. The reaction results are shown in Table-1. Example 8, Comparative Example 8 Using 4 g of a catalyst prepared in the same manner as in Example 1 using 5% by weight palladium-SiO ₂ and thallium nitrate, the blowing gas was air-nitrogen mixed gas (O ₂ concentration 7%). 45N-l/hour, pure oxygen 3N-
The method of Example 1 was repeated except that l/h was used. The reaction results are shown in Table-1. Example 9, Comparative Example 9 Using 4 g of a catalyst prepared in the same manner as in Example 1 using commercially available 5% by weight platinum-alumina and mercury acetate, the reaction temperature was changed to 58°C, and the blowing gas was changed to air-nitrogen, respectively. Mixed gas (O ₂ concentration 7%) 45N -
The method of Example 1 was repeated, except that 3N-l/h of pure oxygen was used. The reaction results are shown in Table-1. Comparative Example 10-1, Comparative Example 10-2 Using 4 g of a commercially available 5% by weight palladium-alumina catalyst (manufactured by Engelhard Japan), the blowing gas was air-nitrogen mixed gas (O ₂ concentration 7%).
The method of Example 1 was repeated, except that 45 N-l/h and pure oxygen were used at 3 N-l/h. The reaction results are shown in Table-1. Example 10, Comparative Example 11 Using 4 g of the same catalyst as in Example 1, replacing 3.3 g of acrolein with methacrolein and using 79 g of ethanol with methanol, the blowing gas was air-nitrogen mixed gas (O ₂ concentration 7 %) 45N―
The reaction was carried out for 2.5 hours by repeating the method of Example 1 except that the amount of pure oxygen was 3N-l/hour. The reaction results are shown in Table-1. Example 11, Comparative Example 12 Using 4 g of the same catalyst as in Example 1, using 3.1 g of acetaldehyde instead of methacrolein, and blowing gas with air-nitrogen mixed gas (O ₂ concentration 7%) at 45 N-l/hour, The reaction was carried out for 2.5 hours by repeating the method of Example 1 except that the amount of pure oxygen was 3 N-l/hour. The reaction results are shown in Table-1.

【table】

【table】

Claims (1)

[Scope of Claims] 1. A method for producing a carboxylic acid ester by reacting an aldehyde with an alcohol in the presence of molecular oxygen, comprising: (a) at least one selected from platinum, platinum compounds, palladium, and palladium compounds;
The reaction is carried out at 0 to 120°C using diluted oxygen gas with a concentration of 18 mol% or less in the presence of a catalyst containing a species and at least one selected from (ro)tellurium, lead, mercury, thallium, and their compounds. A method for producing a carboxylic acid ester, characterized by carrying out the following steps. 2. The method according to claim 1, wherein the concentration of the diluted oxygen gas is 1 mol% or more. 3 Diluted oxygen gas is an inert gas for the reaction,
Alternatively, the method according to claim 1 or 2, wherein air is diluted.