JPH0228173A - Production of lactide - Google Patents

Abstract

PURPOSE:To obtain a high-purity lactide useful as a raw material for polylactic acid readily and in high yield without using high purity lactic acid by reacting an alkaline (earth) metallic salt of 2-halopropionic acid as a raw material in a nonaqueous solvent under heating. CONSTITUTION:An alkali metallic salt of 2-halopropionic acid shown by formula I (A is alkali metal such as Na or K; X is Cl, Br or I) or an alkaline earth metallic salt of 2-halopropionic acid shown by formula II (B is alkaline earth metal such as Ca or Ba) is reacted in a nonaqueous solvent such as ketone, e.g. acetone, ethyl methyl ketone or methyl isobutyl ketone or ether, e.g., dioxane preferably at 100-250 deg.C under pressure approximately self generating pressure by the solvent preferably at the operation temperature for 0.1-6 hours and a prepared crude lactide is recrystallized from ethyl acetate to recover high-purity lactide shown by formula III.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is based on the following formula (1) (where A is an alkali metal, and Xi; IC1B
r or ■) or the following formula (2) % formula % (2) (where B is an alkaline earth metal, X is CI,
Br or 1).

Lactide is a compound useful as a raw material for polylactic acid.

(Prior Art and Problems to be Solved by the Invention) Lactide is usually produced by dehydrating and condensing lactic acid while heating it to about 200'C under reduced pressure of 2 g or less. This method is a method that uses lactic acid as a raw material and is easy to handle, and is therefore often used as a method for synthesizing a reagent amount of lactide. However, in this method, it is necessary to carry out the reaction under a relatively high degree of vacuum, and the reaction rate is slow, so that industrially, a large amount of equipment is required. Furthermore, this method requires highly purified lactic acid in order to obtain even more pure lactide. High-level purification of lactic acid also requires considerable purification costs, making it difficult to industrially produce polymer-grade lactide at low cost.

(Means for Solving the Problems) The present inventors conducted detailed research to solve these problems. As a result, it was discovered that by heating the alkali metal or alkaline earth metal salt of 2-halopropionic acid in a non-aqueous solvent, the halide of the alkali metal or alkaline earth metal salt was converted to lactide, and the present invention was completed.

That is, the present invention is a method for producing lactide, which comprises heating an alkali metal or alkaline earth metal salt of 2-halopropionic acid in a nonaqueous solvent to cause a reaction, and then recovering lactide.

2-halopropionic acid mentioned here refers to 2-chloropropionic acid, 2-bromopropionic acid, or 2-iodopropionic acid. Among these, 2-chloropropionic acid is the most easily available industrially. , which is the intention of the present invention, is preferably used in the method of the present invention.

In addition, the alkali metal or alkaline earth metal salt of 2-halopropionic acid includes lithium, lithium,
Sodium, potassium, rubidium or cesium 1,
Alkali metals such as magnesium, calcium,
Alkaline earth metals such as strontium or barium, or calcium oxide, strontium oxide, magnesium oxide, sodium oxide, lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, calcium hydroxide, barium hydroxide , lithium carbonate, sodium carbonate, potassium carbonate, calcium carbonate, strontium carbonate, barium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, etc., by reacting the oxides, hydroxides, or weak acid salts of the alkali metals or alkaline earth metals. Can be easily manufactured.

Specific examples of alkali metal or alkaline earth metal salts of 2-halopropionic acid produced from such raw materials include lithium 2-chloropropionate, sodium 2-chloropropionate, potassium 2-chloropropionate. , rubidium 2-chloropropionate, cesium 2-chloropropionate, magnesium 2-chloropropionate, calcium 2-chloropropionate, strontium 2-chloropropionate, barium 2-chloropropionate, etc. Alkali metal or alkaline earth metal salts, lithium 2-bromopropionate, sodium 2-bromopropionate, potassium 2-bromopropionate, rubidium 2-bromopropionate, cesium 2-bromopropionate, magnesium 2-bromopropionate , calcium 2-bromopropionate, strontium 2-bromopropionate,
Alkali metal or alkaline earth metal salts of 2-bromopropionic acid such as barium 2-bromopropionate;
-Lithium iodopropionate, sodium 2-iodopropionate, potassium 2-iodopropionate, 2-
Rubidium iodopropionate, cesium 2-iodopropionate, magnesium 2-iodopropionate, 2-
Examples include alkali metal or alkaline earth metal salts of 2-iodopropionic acid such as calcium iodopropionate, strontium 2-iodopropionate, and barium 2-iodopropionate.

Moreover, since these 2-halopropionate salts can be easily made to high purity by operations such as recrystallization, it is also possible to increase the purity of the obtained lactide by purification at this stage.

Water can be used as a solvent during the synthesis of these salts or during the purification by recrystallization of these salts, but low boiling point alcohols, ketones, esters, ethers, etc. are also preferably used to obtain crystals.

Particularly preferred examples include alcohols with low boiling points such as methanol, ethanol, and isopropyl alcohol.

In the method of the present invention, the non-aqueous solvent has the ability to dissolve even a small amount of the alkali metal or alkaline earth metal salt of 2-halopropionic acid under the reaction conditions, and also has the ability to dissolve even a small amount of the alkali metal or alkaline earth metal salt of 2-halopropionic acid. It is necessary that the yield is not reduced. In particular, those having a low boiling point, high solubility of lactide, and low solubility of alkali metal or alkaline earth metal halides are preferred in order to obtain highly pure lactide.

Examples of such solvents include ketones, esters, or ethers, and specific examples of preferred solvents include acetone, ethyl methyl ketone, methyl isobutyl ketone, isopropyl acetate, diethyl ether, dioxane, tetrahydrofuran, and the like.

Among these solvents, ketones such as acetone, ethyl methyl ketone, and methyl isobutyl ketone are particularly preferably used. The heating temperature of the alkali metal or alkaline earth metal salt of 2-halopropionic acid in these solvents is preferably in the range of 100 to 250°C.

Further, since the vapor pressure of the preferably used solvent at the temperature in the above range is relatively high, the pressure at this time is preferably under pressure, particularly around the self-generated pressure by the solvent at the operating temperature.

The reaction time under these temperature and pressure conditions depends on the reaction temperature, but is usually preferably from 0.1 to 6 hours, particularly preferably from 0.5 to 2 hours.

Another advantage of the present invention is that the obtained rough 1,000 Y can be easily converted to even higher purity lactide by recrystallization. This is because most of the impurities that may exist in the lactide obtained by the method of the present invention are unreacted 2-halopropionic acid, etc., and cannot be easily removed by recrystallization. Attributable to something. The solvent that can be used for recrystallizing lactide is preferably a ketone, ester, ether or alcohol, with acetone, ethyl methyl ketone, methyl isobutyl ketone, methyl acetate, ethyl acetate, isopropyl acetate, diethyl ether and the like being particularly preferred.

(Example) Hereinafter, the method of the present invention will be explained in more detail with reference to Examples.

Reference Example 1 108.5 g (1 mol) of 2-chloropropionic acid was dissolved in 10,100 O of methanol, and a methanol solution of sodium hydroxide (approximately 1N) was added dropwise thereto to neutralize it.
- Methanol of sodium salt of chloropropionic acid/8
I got the liquid.

Next, the 78 liquid was distilled at 50° C. under reduced pressure to distill off the entire amount of methanol to obtain about 130 g of crystals of sodium salt of 2-chloropropionic acid. .

Example 1 10 g of sodium 2-chloropropionate obtained by the method of Reference Example 1 was dispersed in 100 ml of acetone and heated at 200° C. for 2 hours in an autoclave. At this time, the pressure inside the autoclave was approximately 25 atmospheres. Then,
After the autoclave was cooled to room temperature, the lid was opened and the contents were taken out. The contents consisted of a liquid phase (acetone layer) and a solid (salt), so the solid was separated by filtration, and the acetone layer was condensed by distillation under reduced pressure (40°C) to obtain about 6 g of crude lactide crystals. Ta. The yield of lactide was 76% based on the raw material 1-lium 2-chloropropionate, as determined by acid-base titration analysis after hydrolysis.

By recrystallizing this crude lactide with ethyl acetate, about 1.7 g of purified lactide with a purity of 99.7% or higher was obtained.

Example 2 A potassium salt of 2-chloropropionic acid was produced in the same manner as in Reference Example 1 except that potassium hydroxide was used instead of sodium hydroxide.

The potassium salt of 2-chloropropionic acid thus obtained was heated to 190° in acetone in the same manner as in Example 1.
(After heating for 1.5 hours, about 4 g of crude lactide crystals were obtained.

The yield of lactide was 78% based on the starting potassium salt of 2-chloropropionic acid. Further, this crude lactide was recrystallized in the same manner as in Example 1 to obtain 1.3 g of purified lactide with a purity of 99.7% or more.

Reference Example 2 108.5 g (1 mole) of 2-chloropropionic acid was dissolved in 10,100 O ethanol, and about 28 g (0
, 5 mol) was gradually added and stirred in a hot water bath at about 50°C until the calcium oxide was completely dissolved.

Next, using a rotary evaporator, ethanol was removed by evaporation at 50° C. under slightly reduced pressure to obtain about 128 g of calcium 2-chlorolopionate as a white powder.

Example 3 About 10 g of the calcium salt of 2-chloropropionic acid produced by the method of Reference Example 2 was dispersed in about 1.00 ml of dioxane, heated to 180° C. in an autoclave, and reacted for 1 hour.

It was confirmed by infrared absorption spectrum that lactide was produced in the liquid after the reaction.

Example 4 In the method of Reference Example 2, barium salt of 2-chloropropionic acid was produced using 99 g of barium carbonate instead of calcium oxide.

Next, when the barium salt of 2-chloropropionic acid thus obtained was reacted in the same manner as in Example 3, it was confirmed by infrared absorption spectrum that lactide was produced in the reaction solution. Ta.

Reference Example 3 In Reference Example 1, a sodium salt of 2-bromopropionic acid was produced using the same number of moles of 2-bromopropionic acid instead of 2-chloropropionic acid.

Example 5 10 g of sodium 2-bromopropionate produced in Reference Example 3 was dispersed in 100 ml of ethyl methyl ketone, heated to 160'C in an autoclave, and heated to 0.
．． The reaction was carried out for 5 hours.

It was confirmed by infrared absorption spectrum that lactide was produced in the liquid after the reaction.

Reference Example 4 In Reference Example 1, a sodium salt of 2-iodopropionic acid was produced using the same number of moles of 2-iodopropionic acid instead of 2-chloropropionic acid.

Example 6 Sodium 2-iodopropionate l Og produced in Reference Example 4 was mixed with menal isobutyl ketone l Og.
The reaction was carried out at 140'C for 1 hour in an autoclave.

It was confirmed by infrared absorption spectrum that lactide was produced in the liquid after the reaction.

(Effects of the Invention) The method of the present invention provides a new method for producing lactide. In particular, by the method of the present invention, lactide with a high degree of purity can be obtained without using high purity lactic acid.

Claims (13)

[Claims] (1) A method for producing lactide, which comprises heating an alkali metal or alkaline earth metal salt of 2-halopropionic acid in a nonaqueous solvent to cause a reaction, and then recovering lactide. (2) The method according to claim 1, wherein the 2-halopropionic acid is 2-chloropropionic acid. (3) The method according to claim 1, wherein the alkali metal salt of 2-halopropionic acid is a sodium salt of 2-halopropionic acid. (4) The method according to claim 1, wherein the alkali metal salt of 2-halopropionic acid is a potassium salt of 2-halopropionic acid. (5) Alkaline earth metal salt of 2-halopropionic acid is 2
- The method according to claim 1, wherein the calcium salt is halopropionic acid. (6) Alkaline earth metal salt of 2-halopropionic acid is 2
- a barium salt of halopropionic acid. (7) The method according to claim 1, wherein the heating is performed at a temperature of 100 to 250°C. (8) The method according to claim 1, wherein the non-aqueous solvent is a ketone. (9) The method according to claim 8, wherein the ketone is acetone. (10) The method according to claim 8, wherein the ketone is ethyl methyl ketone. (11) The method according to claim 8, wherein the ketone is methyl isobutyl ketone. (12) The method according to claim 1, wherein the non-aqueous solvent is an ether. (13) The method according to claim 12, wherein the ether is dioxane.