JPS6163637A - Production of lactic acid ester - Google Patents

Abstract

PURPOSE:Lactic acid and an alcohol are heated in a specific temperature range in the presence of an ion-exchange resin to enable high-yield production of the titled substance which is used in food industry or as an intermediate of medicines or agricultural chemicals easily without trouble of racemization in lactic acid. CONSTITUTION:The objective compound is obtained by reaction between lactic acid and an alcohol in the presence of an ion-exchange resin as a catalyst at 50-170 deg.C, preferably 70-120 deg.C. An alcohol, is cited methanol, ethanol, n- propanol, iso-propanol or n-butanol. The ion-exchange resin is, e.g., H-type strong acid anion-exchange resin, preferably bearing sulfonic acid groups. The form of the resin is, e.g., beads, or fibrils. The amount used is 0.01-1 equivalent, preferably 0.05-0.3 equivalent based on lactic acid. The amount of the alcohol is optimally 2-4 equivalents.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing lactic acid ester.

[Prior art] Lactic acid has a good sour taste and has good bactericidal properties, so it is widely used in the food industry.However, in recent years, its use as an intermediate for pharmaceuticals, medicinal products, etc. has increased, and lactic acid has been used in an anhydrous state. Lactic acid has come to be considered essential.

(There are various methods for converting lactic acid in an anhydrous state to 1!7, and one method is to esterify lactic acid. This method involves converting lactic acid and alcohol into hI in the presence of sulfuric acid.) It is a method of ripening ( □ rganicSyn
theses Colective Volume 2 No. 365
page).

[Problem to be solved by the invention] This 1j method is
However, the sulfuric acid used as a catalyst was concentrated during the reaction, and after the reaction with concentrated sulfuric acid, bQ M was neutralized and removed as a salt from the reaction compound 714. There is a problem that you have to do it. This removal operation is complicated because the generated sulfate often becomes fine crystals, and side reactions also occur. It is also possible to directly purify the 7L acid ester by distillation without neutralizing the sulfuric acid, but lllllIS! in the distillation system! Concentrates and corrodes the material of the system.

In addition, when handling optically active lactic acid, the milk
There are problems such as the possibility of miniaturization. Furthermore, when halogen salts such as common salt and chloride/J lucium coexist in the varnish formation reaction system, a salt exchange reaction proceeds, and IIi! In addition to the i-acid not functioning effectively as a catalyst, the volatile l-p is emitted,
Therefore, the object of the present invention is to solve the above-mentioned problems. 2 ester production provided by 57 people.

[Means for Solving the Problems] The above objects of the present invention are achieved by employing a method of heating lactic acid and alcohol at 50 to 170°C in the presence of an ion exchange resin. By adopting this method, high purity lactic acid can be obtained.1.
The object of the present invention can be efficiently achieved by using a strongly acidic cation exchange resin of the type 1) as the ion exchange resin. The development of the invention will be explained in detail below.

The lactic acid used as a raw material may be produced by either fermentation or synthesis. Lactic acid may be accompanied by water. When accompanying, it is preferably 5 to 50% by weight.

Alcohol J-tanol, n-propanol, isopropanol,
11゛1 /. :
i. For L-branched fats: Preferably (methanol, ethanol, 11-propanol, isopropyl)
, 1panol, (1-butanol, llI3 and isobutanol).

As the H-type strong acidic ion exchange resin as a catalyst, known ones can be used, but sulfone Iilt I is preferably used.
Those to the right of S are used.

The resin can be used in any desired shape, such as beads, short fibers, knitted fabrics, and woven fabrics.

The reaction may be carried out by heating lactic acid and alcohol in the presence of the resin, but in order to carry out the method of the present invention more effectively, the following two methods are adopted.

One method is to simultaneously charge lactic acid, alcohol, and nQ ion exchange resin, and use the Digi-Stark method (D e
The product filtrate is separated by azeotropic distillation using a water separator, so-called azeotropic distillation, and the other is a column filled with the resin, in which lactic acid and alcohol are continuously separated. This is a so-called reactive distillation method in which the lactic acid ester is supplied and the lactic acid ester is continuously flowed out.

The reaction is 50-170, preferably 70-120"C c
It is done. In order to arbitrarily adjust the reaction temperature within the above range, a method is employed in which an azeotropic solvent is omitted from the reaction system or a pressure reduction system is used. .

Reaction +1. Although the time period varies depending on the reaction temperature and the amount of ion exchange resin used, it is the time until the reaction is substantially completed, which is usually 2 to 15 hours. The amount of the auxiliary raw material used relative to the raw material may be equimolar, but in order to increase the reaction rate, it is 1 to 10, preferably 2 to 4 molar. Ion exchange I! The amount of resin to be used is 0.01 to 1 equivalent m, preferably 0, based on lactic acid.

It is in the range of 0.05 to 0.3 equim. 4j, the equivalent weight is determined from the v1 soda exchange capacity of the ion exchange resin.

The reaction can be carried out using the alcohol itself as a solvent, or it may be carried out using a solvent other than the alcohol. )
As a solvent for many people, energy saving, raw materials, 01 originals: 1
Solvents that form an azeotropic composition and can separate water from esters and solvents, such as benzene, toluene, xylene, etc., are used to reduce the amount used, shorten reaction time, and improve conversion rate. Hydrocarbons and aliphatic hydrocarbons such as cyclohexane are used.

After the reaction is completed, the cation exchange resin can be separated from the reaction mixture and the remaining reaction mixture can then be distilled in order to extract Nistyl from the reaction mixture. Furthermore, depending on the case, the reaction mixture may be distilled as it is.

Next, examples of the present invention will be described.

[Example] Implementation)? + 1 In a 1 liter eggplant-shaped flask fitted with a Tween-Stark water separator, add 90% L-lactic acid 1009 liters (1 mole as L-lactic acid), isopropanol 180 (] (3
3 mol, benzene 200ml
Pour 50ml and heat for about 6 hours until water no longer separates)! It was washed away.

After the reaction was completed, the cation exchange resin was filtered off and distilled under normal pressure to recover isopropanol and benzene. 116.2 g of monolactate isoprobyl ester as t
F7. The yield was 87.9%/S ([α]D
9.23" (C-4, Et 0H)). The recovered cation exchanger # could be used again as is.

Example 2 Using the same reactor as in Example 1, 106.8 g of 85% D-lactic acid aqueous solution (1 mol as D-lactic acid), 5.8 g of common salt (0.1 mol), and 222 g of isobutanol.
(37 L), 300 n+l of benzene, and 40 g of knitted cation exchange resin # (strongly acidic cation exchange resin with sulfonic acid group, type 1) were charged, and heated under reflux for about 8 hours until water no longer separated. .

After the reaction is completed, isobutanol and benzene are recovered by distillation under normal pressure in the presence of a lGl physical cation exchange resin. Subsequently, the concentrated liquid was distilled under reduced pressure to obtain b, 0.92-...-
), '3°C/27mmH (as a reservoir of J, a chloride water tip (12, + right side) containing almost no detection
-Lactic acid isobutyl ester 12L8q was obtained.

The yield was 83.0% ([α]D +12.88@
(c = 4.Et 0)-1), CI-containing ffi
10 1111m or less).

Implementation pA3 In a 1 liter eggplant-shaped flask equipped with Zimrow 1, add 108.5 liters of DL-2-chloropropionic acid (17 liters), 60 g of helium hydroxide (1,5 liters) water, 500 m I DL-lactic acid was synthesized by heating and refluxing for 3 vFlip.

At the end of the reaction 1, the contents were concentrated to 300 g (
Add 27 g of concentrated sulfuric acid to 30 f > 17i in ice water.
Stir! ,-6 Isopropatol 24o9 (4 torr) was added to the reaction mixture, stirred, and then filtered to remove inorganic salts. To the filtrate, add 400 ml of toluene and μF1'A ion exchange resin 5K1B (Mitsubishi Kasei H type ion exchange resin > 40
The mixture was heated under reflux for about 6 hours until water no longer separated.

After the reaction is completed, carry out the same procedure as in Example 2, and b.

110.2 g of D-lactic acid isoprobyl ester was obtained as a distillate at 89° C./64 mm Ha. Yield is 83.5
% (C1 content 20 ppm or less).

Comparative Example DL-lactic acid 100.9 (1
85.0-92.0% lactic acid containing aqueous solution>, isobutanol 2001111, benzene 300ml and 5
0% sulfuric acid 511 was charged and heated under reflux for about 3 hours until no water separated into the separator.

Then, after concentrating the content under pressure until the content became 200ml,
Cooled to room temperature. After neutralizing the sulfuric acid by adding 109 h of calcium carbonate, the stagnant calcium sulfate 11 and excess calcium carbonate were separated by filtration. The filtrate was distilled under reduced pressure to give b, 0
．． 105.2 g of D[-lactic acid isopropyl ester was obtained as a distillate of 82-b9. The yield was about 72%.

[Effect of the invention] According to the method of the present invention, high purity lactic acid ester can be produced with high yield of CI?
7. In particular, if Q of a volatile ↑11 acid such as a halogen salt is present in lactic acid, a highly pure lactic acid ester can be obtained even with 6.

Furthermore, even if an optically active lactic acid ester is used, it can be obtained in a reactor without U-milization.

Claims (2)

[Claims] (1) A method for producing a lactic acid ester, which comprises heating lactic acid and alcohol at 50 to 170°C in the presence of an ion exchange resin. (2) The method for producing a lactic acid ester according to claim 1, wherein the ion exchange resin is an H-type strongly acidic cation exchange resin.