JPH0710805A - Production of hydroxycarboxylic acid ester - Google Patents

Abstract

PURPOSE:To obtain a hydroxycarboxylic acid ester in high reaction efficiency and high productivity by esterifying an aqueous solution of a hydroxycarboxylic acid with a >=4c alcohol in the presence of an inorganic salt in a separated liquid state of a water layer and an alcohol layer. CONSTITUTION:A hydroxycarboxylic acid (especially preferably 2-6C aliphatic hydroxycarboxylic acid) is esterified with a >=4c alcohol (e.g. preferably 1-8C alcohol such as 1-butanol hardly miscible with water) in the presence of an inorganic salt such as NaCl or KCl in a separated liquid state of a water layer and an alcohol layer to give a hydroxycarboxylic acid ester (e.g. butyl lactate). The hydroxycarboxylic acid ester is useful as a coating compound, a solvent for photoresist, a food additive such as spices and a synthetic raw material for medicines and agrochemicals.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for efficiently producing a hydroxycarboxylic acid ester from a hydroxycarboxylic acid and an alcohol having 4 or more carbon atoms. Hydroxycarboxylic acid ester is a compound that is frequently used as a solvent for paints, photoresists and the like, food additives such as flavorings, pharmaceuticals, and raw materials for synthesizing agricultural chemicals.

[0002]

BACKGROUND OF THE INVENTION Hydroxycarboxylic acid esters are generally industrially produced by the esterification reaction between an aqueous hydroxycarboxylic acid solution and an alcohol. Since hydroxycarboxylic acid is an organic acid and has an alcoholic property at the same time, cyclization, dimerization and polymer formation easily occur when the aqueous solution is concentrated. Therefore, in the esterification reaction, it is common to proceed the reaction while dehydrating using a solvent which forms an azeotropic mixture with a large amount of alcohol and water such as benzene in the presence of a catalyst such as sulfuric acid (for example, (eg, , FAMcDermott, Organic Syntheses, 2,
p365-366,1943).

However, polymer production is unavoidable even in this method, and the yield of the ester is 60 to 70%.
Further, as an industrial method, a large amount of solvent is used, so that the size of equipment is inevitable.

[0004]

As described above, although the prior art has succeeded in the technical problem of producing a hydroxycarboxylic acid ester, the reaction efficiency,
It has the disadvantage of low productivity. In view of this point, the present invention proposes a method for producing a hydroxycarboxylic acid ester, which has high reaction efficiency and high productivity.

[0005]

The present invention is characterized in that an aqueous solution of hydroxycarboxylic acid and an alcohol having 4 or more carbon atoms are subjected to an esterification reaction in the presence of an inorganic salt in a liquid separation state between an aqueous layer and an alcohol layer. The present invention provides a method for producing a hydroxycarboxylic acid ester with good reaction efficiency and productivity.

As the hydroxycarboxylic acid used in the method of the present invention, aliphatic hydroxycarboxylic acids having 2 to 6 carbon atoms such as lactic acid, glyceric acid, tartaric acid and citric acid are preferably used. For example, lactic acid and glyceric acid. etc,
It is particularly effective since it can be used as an aqueous solution for a substance that cannot be isolated due to its low stability. The hydroxycarboxylic acid is supplied to the reaction as an aqueous solution. The concentration of the hydroxycarboxylic acid aqueous solution is generally 40 to 90.
%, Preferably 50% by weight or more. When the concentration is low, the equipment becomes large, which is not preferable.

As the alcohol, one having 4 or more carbon atoms is used. Specific examples thereof include alcohols such as 1-butanol, 2-pentanol, and 1-hexanol that are difficult to mix with water having 4 to 8 carbon atoms. The ratio of alcohol used to 1 mol of hydroxycarboxylic acid is generally 1 to
The amount is 5 mol, preferably 1.5 to 3 mol.

The esterification reaction is carried out by mixing and stirring an aqueous solution of hydroxycarboxylic acid and an alcohol in the presence of an inorganic salt in a liquid separation state of an aqueous layer and an alcohol layer. As the inorganic salt, specifically, those which are soluble in water and hardly soluble in alcohol, such as sodium chloride, sodium sulfate, potassium chloride, calcium chloride and magnesium sulfate, are used. The amount of the inorganic salt is not less than the solubility of the inorganic salt used in water, and is generally 1.1 times the solubility of the inorganic salt in water at 25 ° C. with respect to the amount of water used in the reaction.
Use about 1.5 times. Specifically, for example, sodium chloride is 26 wt% or more, preferably 26 to
An amount of 28 wt% is added.

It is also effective to add an acid catalyst in order to accelerate the reaction. As the acid catalyst, an acid catalyst such as sulfuric acid or p-toluenesulfonic acid is added in an amount of 0.01 to 1 mol with respect to 1 mol of the hydroxycarboxylic acid. About 0.5 mol is used.

The reaction proceeds at room temperature under normal pressure, and the hydroxycarboxylic acid is initially distributed between the aqueous layer and the alcohol layer, but is extracted into the alcohol layer as a hydroxycarboxylic acid ester produced as the reaction proceeds. . Inorganic salts increase the ion concentration in water, eliminate alcohols and formed esters from aqueous solutions, and improve separability. Stirring must be carried out so as to give a sufficient contact area for reaction and extraction, and it cannot be unconditionally specified depending on the reaction vessel used and the shape of the stirrer, but it is performed in a state where the reaction solution is completely suspended in appearance. Seems to be good.

The reaction temperature is usually 10 to 30 ° C.,
Heating is also effective for accelerating the reaction, but heating at 100 ° C. or higher is not preferable because polymer production is accelerated due to rapid water reduction due to evaporation of water. The reaction time is usually 1 to 5 hours. After the completion of the reaction, the reaction product liquid is allowed to stand and the layers are separated to separate an aqueous layer containing an inorganic salt and an alcohol layer containing a hydroxycarboxylic acid ester as a reaction product. The layer separation is performed by a conventional method by performing liquid separation using a stationary separation tank or the like.

The obtained alcohol solution of hydroxycarboxylic acid ester is subjected to a conventional distillation method, for example, a vacuum distillation apparatus, at a temperature of 80 to 200 ° C. and a pressure of 70 to 40 m.
The hydroxycarboxylic acid ester can be easily isolated by distillation under mHg conditions to recover a fraction of the hydroxycarboxylic acid ester. Since the aqueous layer contains unreacted hydroxycarboxylic acid, acid catalyst and inorganic salt, these can be reused for the next esterification reaction. The alcohol separated by the distillation method can be reused as well.

[0013]

EXAMPLES The present invention will be described more specifically below by showing experimental examples. Example 1 179 g of 50% lactic acid aqueous solution (1.0 mol as lactic acid) and 155 g (2.0 mol) of 1-butanol were placed in a glass separating funnel (1 L) together with 31 g of sodium chloride and 16 g (0.2 mol) of sulfuric acid. And mixed vigorously at room temperature.

After allowing this to stand for 2 hours to separate the layers, 87 g of the lower aqueous layer was recovered and analyzed by liquid chromatography. From the peak area ratio of lactic acid, 93% of the lactic acid used in the reaction was obtained. Was confirmed to have moved to the 1-butanol layer. Add the 1-butanol layer to the flask,
Distilled under reduced pressure to obtain a 40 ° C (70 mmHg) fraction 1.
-Butanol 60g followed by 100 ° C (40mmH
g) As a fraction, 102 g of butyl lactate (gas chromatography purity of 95% or more) was obtained. Yield to lactic acid is 7
It was 0%.

Example 2 179 g of 50% lactic acid aqueous solution, 155 g of 1-butanol,
31 g of sodium chloride and 16 g of sulfuric acid were placed in a glass flask equipped with a condenser on the upper part, vigorously stirred using a magnetic stirrer, and heated to 60 ° C. Two
After the lapse of time, heating and stirring were stopped, and after cooling to room temperature,
The reaction product was put into a glass separating funnel (1 L) and left standing for 2 hours. 86 g of the aqueous layer was collected, and it was confirmed that 94% of lactic acid had moved to the 1-butanol layer. Distillation under reduced pressure was carried out in the same manner as in Example 1 to obtain 11 g of butyl lactate (purity: 95% or more). The yield was 78%.

Example 3 In 86 g of the aqueous layer separated in Example 2 (containing 0.06 mol of lactic acid, 28 g of sodium chloride and 15 g of sulfuric acid),
127 g added with 41 g of an 85% lactic acid aqueous solution (0.4 mol as lactic acid) and 1 collected by distillation in Example 2
Using 60 g of -butanol, heating and liquid separation were carried out in the same manner as in Example 2, 32 g of the aqueous layer was recovered, and it was confirmed that 94% of lactic acid had moved to the 1-butanol layer. Distillation was performed in the same manner as in Example 2 to obtain 45 g of butyl lactate (purity of 95% or more). The yield was 78%.

Comparative Example 1 Mixing was performed using a separating funnel in the same manner as in Example 1 except that sodium chloride was not added.
The reaction solution was a uniform solution even after standing for 2 hours. The whole amount of this was put into a flask and subjected to vacuum distillation.
When 140 g of a water-1-butanol azeotrope, which was a 8 ° C. (70 mmHg) fraction, was distilled off, it was confirmed that a white solid had precipitated in the flask. Distillation was further continued to obtain butyl lactate 5 as a fraction at 100 ° C (40 mmHg).
4 g (purity of 95% or more) was obtained. The yield was 37%.

[0018]

INDUSTRIAL APPLICABILITY According to the present invention, a hydroxycarboxylic acid, particularly a hydroxycarboxylic acid which cannot be isolated due to its low stability, can be produced with good reaction efficiency and productivity as an ester with an alcohol having 4 or more carbon atoms. be able to. Further, with the obtained hydroxycarboxylic acid ester,
A lower alcohol ester of a hydroxycarboxylic acid such as ethyl lactate can be obtained by a transesterification reaction with an alcohol having a carbon number of 3 or less such as methyl or ethyl.

Claims (1)

[Claims] 1. A hydroxycarboxylic acid aqueous solution and a carbon number of 4
A method for producing a hydroxycarboxylic acid ester, which comprises subjecting the above alcohol to an esterification reaction in a liquid-separated state between an aqueous layer and an alcohol layer in the presence of an inorganic salt.