JPH09227447A - Method for producing sorbic acid - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a method for obtaining sorbic acid with a low tar content, easy purification, and high yield. SOLUTION: When the polyester obtained by the lactonization reaction of crotonaldehyde and ketene is hydrolyzed to obtain sorbic acid, the heat generated during the hydrolysis is terminated and then the heat generated during the hydrolysis is terminated. 4 ° C higher than temperature
Isomerization is carried out at low temperatures and above 25 ° C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an efficient method for producing sorbic acid obtained by hydrolyzing a polyester obtained by a lactonization reaction between crotonaldehyde and ketene.

[0002]

2. Description of the Related Art Conventionally, sorbic acid has been widely used as a preservative for foods and the like because it has an antimicrobial effect.
As a method for producing such sorbic acid, various methods are known, but a polyester obtained through β-lactone as an intermediate by reacting crotonaldehyde with ketene is thermally decomposed (hydrolyzed) with concentrated hydrochloric acid. Method) is industrially important. As a concrete method of such a production method, Japanese Patent Publication No. 44266/1989 discloses a reaction product obtained by adding a catalyst to crotonaldehyde and introducing ketene to heat the reaction product under reduced pressure. A method for obtaining sorbic acid by distilling off unreacted crotonaldehyde and a reaction by-product to obtain a polyester containing a catalyst and then decomposing the polyester with hydrochloric acid to cool the obtained reaction mixture is described. .

[0003]

However, the above-mentioned production method is based on the idea of "hydrolyzing" with hydrochloric acid, and as a result of a detailed study by the present inventor of this method, the "hydrolyzing" step Is divided into a process of "until the end of heat generation during hydrolysis" and a process of "the subsequent isomerization", and various studies on the latter isomerization process yield sorbic acid with low tar content in high yield. It has been found. That is, an object of the present invention is to provide a production method in which tarbic acid is small, purification is easy, and a high yield of sorbic acid can be obtained.

[0004]

However, as a result of earnest studies on the above-mentioned isomerization method, the present inventor hydrolyzed the polyester obtained by the lactonization reaction of crotonaldehyde and ketene to obtain sorbic acid. Therefore, after the heat generation during the hydrolysis is completed, the tar content is reduced by performing isomerization at a temperature of 4 ° C. or more lower than the temperature at the end of the heat generation during the hydrolysis and at a temperature of 25 ° C. or more, It was found that sorbic acid can be easily purified and a high yield can be obtained, and the present invention has been completed. Further, in the present invention, during such isomerization, the temperature of the isomerization is kept constant, or by cooling at a rate of 0.1 to 1.0 ° C./min, the effect of the present invention is expected more. can do.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the production method of the present invention will be specifically described. First, crotonaldehyde and ketene are polymerized to obtain polyester, but the reaction method is not particularly limited, and a known method can be adopted. As an example, a catalyst such as zinc (zinc isovalerate), zinc oxide, cadmium, nickel, copper, copper oxide, and cobalt is used, and the reaction conditions are 3 to 30 at a temperature of 20 to 60 ° C. under normal pressure. Such a polyester can be obtained by carrying out a polymerization reaction for about 8 hours, but is not limited to this method.

Next, the obtained polyester is (hydrolyzed) hydrolyzed in hydrochloric acid. In the present invention, the "hydrolysis" step in hydrochloric acid as described above is carried out by "exothermic heat during hydrolysis". It has the greatest feature in performing a specific operation by dividing it into a process of "until the end" and a process of "the subsequent isomerization", and a known method can be adopted as the method of hydrolysis in the previous step. Yes, for example, 15-40% (preferably 25%
~ 36%) concentration of hydrochloric acid is 2 per 1 mol of polyester
10 to 10 mol (preferably 3 to 6 mol), and 25 to 1
The decomposition can be performed at 10 ° C (preferably 50 to 90 ° C).

Although sorbic acid is obtained by such hydrochloric acid decomposition, in the present invention as described above, after the heat generation during the hydrochloric acid decomposition (hydrolysis) is completed, Isomerization is also performed at a temperature lower than 4 ° C or higher and 25 ° C or higher, and isomerization under such conditions (cis, cis-sorbic acid, cis, tra produced in the above reaction)
The effect of the present invention can be obtained only by isomerizing isomers of sorbic acid such as ns-sorbic acid and trans, cis-sorbic acid into trans, trans-sorbic acid. The term "end of heat generation" as used herein means a point of time when the generation of reaction heat due to hydrolysis ends, specifically, a point of time when the temperature rise of the reaction system stops.

In addition, the fact that the isomerization is carried out at a temperature of 4 ° C. or more lower than the temperature at the end of heat generation during hydrolysis and 25 ° C. or more specifically means at the time when the generation of reaction heat is completed. After lowering the system temperature by 4 ℃ or more (however, 25 ℃ or more),
A method of performing isomerization at that temperature, 0.1 to 1.0 ° C./minute (preferably 0.1 to 1.0 ° C./minute) from the time when the generation of reaction heat ends.
Examples of the method include isomerization while cooling to a temperature of 25 ° C. or higher at a rate of 0.5 ° C./min), but are not limited thereto. In the above isomerization, when the difference between the temperature during isomerization and the temperature at the end of heat generation during hydrolysis is less than 4 ° C, the tar content of sorbic acid produced is large, and the temperature during isomerization is less than 25 ° C. Isomerization does not proceed sufficiently,
It becomes impossible to achieve the object of the present invention.

The isomerization time is not particularly limited, but is usually 10 minutes to 5 hours (preferably 1 hour to 3 hours).
It is arbitrarily selected from the range of about (time). If the time is less than 10 minutes, isomerization does not proceed sufficiently, and if it exceeds 5 hours, the tar content increases and the yield of sorbic acid decreases, which is not preferable. The sorbic acid containing the hydrochloric acid mother liquor isomerized by the above method is then taken out of the system, and the sorbic acid is isolated by a method such as suction filtration or pressure filtration.

[0010]

EXAMPLES The present invention will be further described with reference to examples.
Unless otherwise specified, the following "%" is used.
Indicates weight basis. Example 1 150 g of purified crotonaldehyde and 0.4 g of zinc isovalerate powder were charged into a reactor, and 54 g of ketene was blown thereinto while maintaining the temperature at 30 to 40 ° C. to cause a reaction. After completion of the reaction, the mixture was heated to 120 ° C. under a reduced pressure of 30 to 40 mmHg to distill off unreacted crotonaldehyde and by-products to obtain 136 g of polyester. Such polyester 100
g (0.89 mol) and 430 g (3.54 mol) of 30% hydrochloric acid were charged into a reactor and reacted for 40 minutes at an internal temperature of 73 to 75 ° C. to end the heat generation of hydrolysis (system temperature rise stopped). Therefore, isomerization was performed while cooling at a rate of about 0.35 ° C./min for 140 minutes to obtain a reaction liquid at 25 ° C. Next, the obtained reaction liquid was separated into sorbic acid and hydrochloric acid mother liquor by suction filtration to obtain hydrous sorbic acid. Such sorbic acid was dried to obtain crude sorbic acid 9 having a purity of 97.3%.
3.7 g were obtained. This contained 0.3% of isomers and 2.4% of tar content, and the yield of sorbic acid based on polyester was 91.2%.

Comparative Example 1 In Example 1, the internal temperature was kept at 7 even after the exothermic heat of hydrolysis was completed.
92.4 g of crude sorbic acid having a purity of 94.2% in the same manner except that the reaction was carried out for another 50 minutes while maintaining the temperature at 3 to 75 ° C.
I got This is 0.3% isomer and 5.5% tar
It was included, and the yield of sorbic acid based on polyester was 87.0%.

COMPARATIVE EXAMPLE 2 The procedure of Example 1 was repeated except that after the exothermic heat of hydrolysis was rapidly cooled to isomerize for 140 minutes while maintaining the internal temperature at 20 ° C., the purity was 94.5%. 91.8 g of crude sorbic acid was obtained. This contained 2.0% of isomers and 3.5% of tar content, and the yield of sorbic acid based on polyester was 86.7%.

Example 2 In Example 1, after the exothermic heat of hydrolysis was completed (the temperature rise of the system was stopped), the temperature was cooled to 53 ° C. over 30 minutes, and then 5
93.9 g of crude sorbic acid having a purity of 97.3% was obtained in the same manner except that isomerization was performed at 0 to 55 ° C. for 20 minutes and then the reaction liquid was obtained at 25 ° C. This is 0.3 isomer
%, The tar content was 2.4%, and the yield of sorbic acid based on polyester was 91.4%.

Example 3 Hydrochloric acid mother liquor separated in Example 1 (hydrochloric acid concentration 29.3%)
To 381 g, 49 g of 35.6% hydrochloric acid was added to prepare 430 g (3.54 mol) of 30% hydrochloric acid. This hydrochloric acid was used as in Example 1 except that the internal temperature during hydrolysis was 66
˜68 ° C.) to obtain 93.6 g of crude sorbic acid having a purity of 97.3%. This contained 0.3% of isomers and 2.4% of tar content, and the yield of sorbic acid based on polyester was 91.1%.

[0015]

In the production method of the present invention, since specific isomerization is carried out at the end of heat generation during hydrolysis, tar content is small, purification is easy, and high yield of sorbic acid can be obtained.

Claims (3)

[Claims] 1. When the polyester obtained by the lactonization reaction of crotonaldehyde and ketene is hydrolyzed to obtain sorbic acid, after the heat generation during the hydrolysis ends, the heat generation ends during the hydrolysis. 4 ℃ than the temperature of
A method for producing sorbic acid, characterized in that isomerization is carried out at a low temperature of 25 ° C. or higher. 2. The method for producing sorbic acid according to claim 1, wherein the temperature at the time of isomerization is kept constant or cooled at a rate of 0.1 to 1.0 ° C./min. 3. The method for producing sorbic acid according to claim 1, wherein the isomerization time is 10 minutes to 5 hours.