JPS642096B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing α-acetoxypropionic acid by oxygen oxidation reaction of α-acetoxypropionaldehyde. Although α-acetoxypropionic acid is an industrially useful compound as a raw material for lactic acid, lactate salts, and lactic acid esters, an industrial manufacturing method for its precursor α-acetoxypropionaldehyde has not been established. The current situation is that it is still not manufactured on an industrial scale. As a method for producing α-acetoxypropionaldehyde, a method is known in which vinyl acetate is hydroformylated in the presence of a rhodium complex compound catalyst (for example,
-1575, Journal of Chemical Society (A), p. 2753 (1970), JP-A-143617), α-acetoxypropion is thermally and chemically unstable in the conventionally proposed method. No technology has been developed for efficiently separating aldehydes from reaction mixtures and for stably recycling and reusing expensive rhodium complexes. According to the present inventors, it has been found that this technical problem can be solved by performing an extraction operation with an aqueous medium on the reaction mixture containing α-acetoxypropionaldehyde obtained in the hydroformylation reaction of vinyl acetate. (Special Application No. 55-26878). According to the method proposed in Japanese Patent Application No. 55-26878, α-acetoxypropionaldehyde can be efficiently extracted and separated into an aqueous medium.
When the raffinate layer containing the rhodium complex compound is directly recycled to the hydroformylation reaction step, the catalytic activity is substantially maintained, and α-acetoxypropionaldehyde can be obtained in good yield from the aqueous layer by fractional distillation. α-acetoxypropionaldehyde can be produced industrially at low cost by hydroformylation reaction. On the other hand, the production of corresponding carboxylic acids by the oxygen oxidation reaction of aldehydes has been carried out industrially for a long time, and an example of this can be seen in the production of acetic acid from acetaldehyde. Since the α-position of the formyl group in α-acetoxypropionaldehyde is substituted with an acetoxyl group, it is interesting to see whether this compound exhibits the same reactivity as general aldehydes. Regarding the oxygen oxidation reaction of α-acetoxypropionaldehyde, the only known method is to oxidize the aldehyde with oxygen in the absence of a catalyst or in the presence of a catalyst known per se such as a cobalt salt, a manganese salt, or a silver oxide. (Refer to Japanese Unexamined Patent Publication No. 143617/1983). However, according to studies conducted by the present inventors, it has been found that such known methods include various problems as shown below. In the reaction without a catalyst, the selectivity to α-acetoxypropionic acid is high, but the reaction rate is slow and it takes a long time to complete the reaction. When a cobalt salt and/or a manganese salt is used as a catalyst, the reaction rate is significantly improved compared to the reaction without a catalyst, but the decarboxylation reaction occurs significantly, resulting in the formation of α-acetoxypropionic acid. Selectivity decreases significantly. Although the decarboxylation reaction can be suppressed to some extent by lowering the reaction temperature to around room temperature, the reaction at low temperatures significantly promotes the accumulation of peracid. According to the present invention, these problems that occur when α-acetoxypropionaldehyde is oxidized with oxygen to produce α-acetoxypropionic acid can be solved by oxidizing α-acetoxypropionaldehyde with at least one member selected from the group consisting of copper salts, iron salts, and nickel salts. It has been found that the problem can be solved by carrying out the process in the presence of a metal salt. According to the method of the present invention, α-acetoxypropionic acid is not only produced at a high reaction rate and with high selectivity, but also because the accumulation of peracid in the reaction system is extremely small, it is industrially advantageous to produce α-acetoxypropionic acid. Acid can be produced. Copper salts used as catalysts in the process of the invention,
Specific examples of iron salts and nickel salts include cuprous halides, cupric halides, cuprous carboxylates, cupric carboxylates, cuprous sulfates, cupric sulfates, cupric nitrates, Ferrous halides, ferric halides, ferrous carboxylates, ferric carboxylates,
Examples include ferric sulfate, nickel carboxylate, nickel sulfate, and nickel halides, but among these, various points such as solubility of the metal salt in the reaction mixture, catalytic activity, and corrosivity to the reaction equipment are important. In consideration of this, cupric carboxylates, ferrous carboxylates, ferric carboxylates, and nickel carboxylates are particularly preferred. As carboxylic acids forming these carboxylic acid salts, lower carboxylic acids such as acetic acid, propionic acid, and butyric acid are considered.
Each of these metal salts may be used alone,
Alternatively, two or more types may be used in combination. The optimum concentration of the metal salt in the reaction solution varies depending on the reaction temperature and the type of metal salt, but it is generally preferable to range from 0.1 to 50 mmol per reaction mixture. In the method of the present invention, acetic acid,
Propionic acid, methyl acetate, α-acetoxypropionic acid, and mixtures of these in arbitrary proportions can be used, but in the subsequent step, the product α-acetoxypropionic acid also functions as a solvent. most preferred in relation to When α-acetoxypropionic acid is used as a solvent, there is no problem if it contains, for example, a small amount of acetic acid. As this reaction is accompanied by extreme heat generation like the usual oxygen oxidation reaction of aldehydes, it is necessary to control the reaction temperature, so the reaction is carried out by continuous or intermittent addition of α-acetoxypropionaldehyde. The reaction is carried out while keeping the aldehyde concentration in the reaction mixture at a low concentration. The oxidation reactor is generally a stirred reactor or, in some cases, a bubble column, and the reaction is carried out while blowing an oxygen-containing gas such as oxygen gas, air, or a nitrogen/oxygen mixed gas in any proportion into the reactor. It is carried out under stirring. The reaction can be carried out in either a continuous method or a batch method, but when a continuous method is adopted, it is also a preferred embodiment of the method of the present invention to provide a follow-up reaction tank and drive the reaction to a desired level in the tank. one of. The pressure of oxygen gas or oxygen-containing gas varies depending on the oxygen gas concentration, but it is practical to select it within the range of 1 to 20 atmospheres. The reaction temperature varies depending on the type of catalyst and its concentration, but is generally selected within the range of about 45 to about 100°C. When using high-purity α-acetoxypropionic acid as the reaction solvent, the reaction temperature is 60 to approximately 100°C, taking into account the melting point of α-acetoxypropionic acid (57 to 60°C).
selected from within the range. The α-acetoxypropionaldehyde used in the process of the invention is advantageously obtained as an aqueous solution by water extraction of the vinyl acetate hydroformylation reaction mixture according to the method proposed in Japanese Patent Application No. 55-26878. . However, according to the studies conducted by the present inventors, when an aqueous solution of α-acetoxypropionaldehyde is used in an oxygen oxidation reaction, the amount of water in the reaction mixture affects the reaction rate, reaction selectivity, and amount of peracid accumulated. Therefore, it is desirable to suppress the amount of water in the reaction mixture to a molar ratio of 2 or less to α-acetoxypropionaldehyde. α-acetoxypropionic acid produced by the method of the present invention can be obtained by performing peracid decomposition by treating the reaction mixture after the reaction with mineral acid as necessary, and then distilling the mixture. I can do it. When α-acetoxypropionic acid is used as a raw material for lactic acid, lactate, or lactic acid ester, the oxidation reaction mixture or the mixture after peracid decomposition is used as it is in the next hydrolysis step or esterification step without purification. You can also. The present invention will be explained in more detail in the following examples. Example 1 100 ml of acetic acid, 26 mg of ferrous acetate (reaction mixture
The addition funnel was charged with 50 ml of an acetic acid solution containing 17.4 g of α-acetoxypropionaldehyde.
When the temperature inside the reactor became constant at 60°C, α-acetoxypropionaldehyde was added from the dropping funnel over 1 hour while stirring the contents at a rotational speed of 800 rpm and introducing oxygen gas at a flow rate of 15 l/hr. An oxidation reaction was carried out by continuously adding an acetic acid solution. After the addition of aldehyde is completed, 1 more time is added at the same temperature.
Stirring was continued for an hour. The internal temperature was kept constant at 60°C during the reaction period. The aldehyde conversion rates immediately after the addition of α-acetoxypropionaldehyde (1 hour after the start of the reaction) and at the end of the oxidation reaction (2 hours after the start of the reaction) were measured by gas chromatography and were 82% and 98%, respectively. Furthermore, the selectivity to α-acetoxypropionic acid (based on converted α-acetoxypropionaldehyde) at the end of the reaction was 98%. Determined by analysis with E. 20 minutes, 40 minutes and
Reaction start 1 determined from sampling results after 60 minutes
The average carbon dioxide concentration in the off-gas up to 0.03
%, and from this the carbon dioxide generation rate (conversion α-
(based on acetoxypropionaldehyde) was 1.2 mol%. After the reaction was completed, the reaction solution was cooled to room temperature, a portion of it was collected, and the amount of active oxygen was determined by the iodine titration method [according to the perbutyl PV method, p. 136 of "Organic Peroxides" edited by the Organic Peroxide Research Group]. However, it was 0.027%. The results are shown in Table 1. Examples 2 to 8 and Comparative Examples 1 to 9 The type and amount of catalyst, type of solvent, concentration of α-acetoxypropionaldehyde, and amount of water relative to α-acetoxypropionaldehyde were determined in the same manner as in Example 1. The oxidation reaction of α-acetoxypropionaldehyde was carried out by varying the oxygen-containing gas, reaction temperature, and reaction time as shown in Table 1. The results are also listed in Table 1.

[Table] 3) Catalyst concentration is expressed in millimoles per 1 reaction mixture.

Claims (1)

[Claims] 1. Oxidizing α-acetoxypropionaldehyde with oxygen gas or oxygen-containing gas in the liquid phase in the presence of at least one metal salt selected from the group consisting of copper salts, iron salts, and nickel salts. A method for producing α-acetoxypropionic acid.