JPH0558635B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for producing para-aldol. Acetaldol is crotonaldehyde, 1,
Although it is useful as a raw material for 3-butylene glycol, etc., it is a structurally unstable substance, so
When producing 1,3-butylene glycol and the like, various impurities such as butanol, 2-butanone, etc. are produced as by-products, which poses a problem. However, since para-aldol, which is a duplex of acetaldol, is a cyclic compound, it is a structurally stable substance and can be a useful substance in place of acetaldol. <Prior art> The conventional method for obtaining highly pure acetaldol is
J. Amer, Chem. Soc., 65 , 1309 (1943), etc., mix equal volumes (100 ml) of ether and acetaldehyde, cool to 0-5°C, and add 2 drops of dichloromethane. Add butylamine and add 10% aqueous potassium hydroxide solution with stirring, keeping the reaction temperature at 5-10°C. After the reaction is completed, the ether layer is divided into two layers and is neutralized with 5% sulfuric acid.
Wash with water and dry with anhydrous sodium sulfate. Ether is separated by distillation and acetaldol is obtained by distillation under reduced pressure. Needless to say, such a method is industrially expensive and impractical. British Patent No. 853266 describes an industrial method for producing acetaldol through the condensation reaction of acetaldehyde, but it requires a large amount of water as a solvent and the conversion rate of acetaldehyde is kept below 44%, making it difficult to maintain efficiency and cost. It becomes a problem from this point of view. and Ind. Eng Chem., 44 , 1003 (1952)
It is known that the industrially produced acetaldol is mainly composed of aldoxane, which is a trimer of acetaldehyde. On the other hand, it is known that para-aldol can be synthesized by leaving acetaldol at a low temperature (0 to 5°C) for several days (Chemistry Dictionary = Kyoritsu Shuppan); It is clear that this cannot be implemented industrially. <Problems to be Solved by the Invention> Generally, acetaldol, which is a dimer of acetaldehyde, is an unstable substance and therefore dehydrates to produce crotonaldehyde. Furthermore, since aldoxane, which is a stable cyclic substance obtained by adding acetaldehyde to acetaldol, is a trimer of acetaldehyde, it may be difficult to serve as a substitute for acetaldol in some cases. Therefore, the present inventors conducted repeated studies and came up with the idea that para-aldol, which is a duplex of acetaldol and a tetramer of acetaldehyde and is a stable cyclic substance, can be used as a substitute for aldol. As a result of further detailed study of the manufacturing method, the present invention was arrived at. That is, in the present invention, acetaldehyde is subjected to aldol condensation in the presence of an alkali catalyst to obtain a reaction crude solution containing aldoxane (common name for 2,4-dimethyl-1,3-dioxan-6-ol), and then acetaldehyde is This is a method for producing para-aldol, which is characterized in that para-aldol is essentially obtained by thermally decomposing aldoxane while distilling out para-aldol. <Technical basis> By the way, while analyzing the sample liquid in the aldoxane decomposer experiment, it was highly important to accurately capture the presence (presence or absence) and behavior of aldoxane and para-aldol by making full use of instrumental analysis methods. (Example 1), and by analyzing the change over time in the composition of the above bottom liquor, it was possible to connect it to the basis of the present invention. Next, we will show specific data on changes in the composition of bottoms over time in the alkydosan decomposer. (Figure 1) Figure 1 is interpreted as follows. When the temperature of the tank liquid is kept constant at 97°C and the residence time is extended in the range of 6 to 30 minutes, the aldoxane is thermally decomposed and the amount of acetaldehyde distilled increases. However, when the residence time is prolonged, the aldol produced as an intermediate by thermal decomposition of aldoxane undergoes a dehydration reaction and becomes crotonaldehyde. Until the residence time is around 13 minutes, the aldol produced as an intermediate dimerizes to para-aldol.
When the residence time exceeds a certain value, the intermediate aldol is considered to be stabilized by dehydration to become crotonaldehyde rather than dimerization to form para-aldol. Therefore, by setting the residence time within a certain range, it can be expected that para-aldol will be preferentially produced. <Means for solving the problem> Usually, aldol condensation is carried out in the presence of an alkali catalyst by maintaining the reaction temperature of acetaldehyde (with or without water solvent) at a reaction temperature of 20 to 30°C and a residence time in the system of 2 to 3 Hrs. be done. It has been found that lower reaction temperatures are preferred to reduce side reactions. After the reaction is completed, the condensation liquid that flows out is strictly neutralized with acid and sent to the next step. The composition of the obtained reaction crude liquid cannot be generalized because it varies greatly depending on the ratio of raw material acetaldehyde to solvent water, the conversion rate of acetaldehyde, etc. In aldoxane decomposition, unreacted acetaldehyde is recovered (distilled), aldoxane is thermally decomposed, and the accompanying by-product acetaldehyde is recovered (distilled).
I do. Appropriately, the temperature of the can liquid is in the range of 60 to 130°C and the residence time is in the range of 5 to 50 minutes. At this time, the two are correctly correlated (for example, in Figure 1),
It will be comprehensively determined within the above range so that acetaldol produced during decomposition of aldoxane will not dehydrate and produce crotonaldehyde. Further, as an apparatus for decomposing aldoxane, a conventional thin film evaporator, distillation tower, evaporator, etc. is used. <Examples> Hereinafter, the present invention will be specifically explained using Examples, but the present invention is not limited only to these Examples. Example 1 Using the flask with a jacket from 1, charge 500 g of a pre-prepared acetaldehyde aqueous solution (acetaldehyde/water = 85/15) and raise the temperature to 15-20.
Cooled to ℃. While vigorously stirring, 0.5 g of a 10% aqueous sodium hydroxide solution was added dropwise little by little to cause a reaction. During this time, the reaction temperature was maintained at 20°C. After aging for 2 hours, it was strictly neutralized with dilute acetic acid (strictly neutralized using a phenolphthalein indicator according to JIS K8006). The composition of the obtained crude reaction liquid is aldoxane
60.0%, acetaldehyde 25.2%, water 14.8% and sodium acetate 0.01-0.02%. Subsequently, 500 g of the above reaction crude liquid was heated, and acetaldehyde was distilled out by single column distillation until the temperature of the bottom liquid reached 96°C. (Batch type) Distillation time was 30 minutes, and the distillation rate was 42.6%. The composition of the bottoms was 30.5% aldoxane, 55.6% para-aldol, 2.0% crotonaldehyde, etc., and 11.9% water, and only acetaldehyde and water were detected in the distillate. The compositions of the stock liquid and bottom liquid were analyzed using NMR analysis and the like. In NMR analysis, each signal was assigned by ^1H - ^1H homospin decoupling and ^13C - ^1H select coupling.
In particular, para-acetaldol was identified by confirming the triplet splitting of the acetal proton of para-aldol. In addition, for quantitative analysis, ¹³ C−
The abundance ratio was determined from the height ratio of each NMR signal. Example 2 Continuous flash evaporation was carried out using the same reaction crude liquid and equipment as in Example 1. The tank liquid temperature was 117℃, the residence time was 13 minutes, and the distillation rate was
It was 44.2%. The composition of the bottom liquid is aldoxane
The composition of the distillate was 78.2% acetaldehyde and 21.8% water. Example 3 and Comparative Example The same procedure as in Example 2 was carried out except that the operating conditions for aldoxane decomposition shown in Table 1 were changed. The results are shown in Table 2.

【table】

[Table] Reference Example Next, 1,3-butylene glycol was produced by carrying out a catalytic reduction reaction using the para-aldol-containing raw materials obtained in Examples 1 to 3 and Comparative Example. Using autoclave 1, predetermined raw materials
After charging 300 g and adding 15% Raney Nickel, the reaction was carried out at 120° C. for 30 minutes under a hydrogen pressure of 80 Kg/cm ² . The results are shown in Table 2.

【table】 [Brief explanation of the drawing]

FIG. 1 shows the relationship between the residence time and composition of bottoms in an aldoxane decomposer according to the present invention.

Claims (1)

[Claims] 1 In the presence of an alkali catalyst, acetaldehyde is subjected to aldol condensation to form aldoxane (2,4-
A crude reaction solution containing dimethyl-1,3-dioxan-6-ol (common name for dimethyl-1,3-dioxan-6-ol) is obtained, and then aldoxane is thermally decomposed while distilling acetaldehyde, thereby essentially obtaining para-aldol. A method for producing paraaldol.