JP2002293770A - Method for producing 2-hydroxy-4-methylthiobutanoic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing 2-hydroxy-4-methylthiobutanoic acid efficiently with excellent operability. SOLUTION: The method for producing 2-hydroxy-4-methylthiobutanoic acid comprises (A) a process for hydrating 2-hydroxy-4-methoylthiobutanenitrile in the presence of sulfuric acid, (B) a process for subjecting 2-hydroxy-4- methylthiobutanamide contained in the reaction liquid obtained in the process (A) to a hydrolysis reaction in the presence of sulfuric acid, (C) a process for condensing a reaction product obtained in the process (B), and (D) a process for separating the condensed liquid obtained in the process (C) into an oil layer containing 2-hydroxy-4-methylthiobutanoic acid and an aqueous layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing 2-hydroxy-4-methylthiobutanoic acid which is useful as a feed additive or the like. Specifically, 2-hydroxy-4-
The present invention relates to a method for producing 2-hydroxy-4-methylthiobutanoic acid by hydrating and hydrolyzing methylthiobutanenitrile in the presence of sulfuric acid.

[0002]

2. Description of the Related Art Conventionally, as a method for producing 2-hydroxy-4-methylthiobutanoic acid, 2-hydroxy-4-methylthiobutanenitrile is subjected to a hydration reaction, and the resulting 2-hydroxy-4-methylthiobutanamide is hydrolyzed. A reaction method is known. For example, Japanese Patent Publication 5-178
No. 7 discloses that after hydrating and hydrolyzing 2-hydroxy-4-methylthiobutanenitrile in the presence of sulfuric acid,
A method of extracting 2-hydroxy-4-methylthiobutanoic acid from a reaction solution with an organic solvent such as isobutyl methyl ketone is described. Also, U.S. Pat.
In the specification, after hydration and hydrolysis of 2-hydroxy-4-methylthiobutanenitrile in the presence of sulfuric acid,
A method is described in which a reaction solution is neutralized with ammonia to separate oil and water by a salting-out effect, and 2-hydroxy-4-methylthiobutanoic acid is recovered from the oil layer.

[0003]

However, in the method disclosed in Japanese Patent Publication No. 5-1787, a large amount of organic solvent is used, which leads to an increase in cost and a decrease in volumetric efficiency, and an increase in organic solvent from products and wastewater. Requires a removal operation. Further, in the method described in the above-mentioned U.S. Pat. No. 4,912,257, although it is not necessary to use an organic solvent, the liquid separating property of oil and water is poor, and the operability and recovery efficiency are not sufficient. An object of the present invention is to solve the above problems and provide a method for efficiently producing 2-hydroxy-4-methylthiobutanoic acid with good operability.

[0004]

Means for Solving the Problems As a result of intensive studies, the present inventors have conducted hydration and hydrolysis of 2-hydroxy-4-methylthiobutanenitrile in the presence of sulfuric acid. The inventors have found that the above object can be achieved without using other components such as an organic solvent and ammonia by concentrating and separating oil and water, thereby completing the present invention.

That is, the present invention includes (A): a step of hydrating 2-hydroxy-4-methylthiobutanenitrile in the presence of sulfuric acid, and (B): a reaction solution obtained in the step (A). A step of hydrolyzing 2-hydroxy-4-methylthiobutanamide in the presence of sulfuric acid, (C):
A step of concentrating the reaction solution obtained in the step (B), and (D): separating the concentrated solution obtained in the step (C) into an oil layer containing 2-hydroxy-4-methylthiobutanoic acid and an aqueous layer. The present invention relates to a method for producing 2-hydroxy-4-methylthiobutanoic acid, which comprises a step.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, a reaction liquid containing 2-hydroxy-4-methylthiobutanamide can be obtained by using 2-hydroxy-4-methylthiobutanenitrile as a raw material and subjecting it to a hydration reaction in the presence of sulfuric acid. [Step (A)]. The starting material, 2-hydroxy-4-methylthiobutanenitrile, can be prepared, for example, by reacting acrolein with methylmercaptan to form 3-methylthiopropionaldehyde, which is then reacted with hydrogen cyanide.

The amount of sulfuric acid used in the reaction of step (A) is 2-hydroxy-4-methylthiobutanenitrile
It is usually in the range of 0.55 to 0.85 mol, preferably 0.6 to 0.8 mol, per mol. Step (A)
Is usually 1 to 100 parts by weight of 2-hydroxy-4-methylthiobutanenitrile.
It is in the range of 5 to 80 parts by weight, preferably 20 to 60 parts by weight.

The reaction in the step (A) is preferably carried out by supplying 2-hydroxy-4-methylthiobutanenitrile in sulfuric acid from the viewpoint of the reaction rate. -4-Methylthiobutanenitrile may be mixed with sulfuric acid before being supplied, may be supplied together with 2-hydroxy-4-methylthiobutanenitrile in sulfuric acid, or may be partially supplied with 2-hydroxy- Before supplying 4-methylthiobutanenitrile, it may be mixed with sulfuric acid and a part thereof may be supplied into sulfuric acid together with 2-hydroxy-4-methylthiobutanenitrile.

The reaction temperature in the step (A) is usually from 40 to 70
° C, and the reaction time is usually in the range of 1 to 3 hours. The reaction in step (A) is usually performed at about normal pressure, but may be performed under increased or reduced pressure as necessary.

[0010] 2 contained in the reaction solution obtained in the step (A)
-Hydroxy-4-methylthiobutanamide is hydrolyzed in the presence of sulfuric acid to give 2-hydroxy-
A reaction solution containing 4-methylthiobutanoic acid can be obtained [Step (B)]. Usually, the reaction is preferably performed by mixing the reaction solution obtained in the step (A) with water and / or sulfuric acid, if necessary, and then treating the mixture at a higher temperature than the step (A).

In the step (B), when the reaction solution obtained in the step (A) is mixed with water, the amount thereof is calculated as the sum of the amount of water used in the step (A) and Usually 110 to 330 parts by weight, preferably 130 parts by weight, per 100 parts by weight of hydroxy-4-methylthiobutanenitrile.
It is in the range of ２３０230 parts by weight. In addition, in the step (B), when the reaction solution obtained in the step (A) is mixed with sulfuric acid, the amount thereof is determined as the sum of the amount of the sulfuric acid used in the step (A) and the amount of 2-hydroxyl used as the raw material. -4-methylthiobutanenitrile 1 mol, usually 0.55 to 0.8
It is in the range of 5 mol, preferably 0.6 to 0.8 mol.

The reaction temperature in the step (B) is usually 90 to 13
The reaction temperature is usually in the range of 2 to 6 hours. In addition, the reaction of step (B) is usually performed at around normal pressure, but may be performed under increased or reduced pressure as necessary.

The 2-hydroxy-4 obtained in step (B)
By concentrating the reaction solution containing -methylthiobutanoic acid, a part of water contained in the reaction solution is distilled off [Step (C)]. By this concentration operation, even if the reaction solution obtained in the step (B) is a mixture in which 2-hydroxy-4-methylthiobutanoic acid and water are uniformly mixed, 2-hydroxy-4- A mixture of an oil layer and an aqueous layer containing methylthiobutanoic acid can be obtained. When the reaction solution obtained in the step (B) is already a mixture of an oil layer and an aqueous layer, the concentration is further increased to increase the distribution ratio of 2-hydroxy-4-methylthiobutanoic acid to the oil layer. be able to.

In the step (C), although it depends on the composition of each component in the reaction solution obtained in the step (B), it is usually 10 to 80% by weight, preferably 15% by weight of water contained in the reaction solution. ~
65% by weight are distilled off. The concentration temperature in the step (C) is usually in the range of 20 to 100 ° C., and the pressure is usually in the range of 0.001 to 0.1 MPa.

The concentrated liquid obtained in the step (C) is separated into an oil layer containing 2-hydroxy-4-methylthiobutanoic acid and an aqueous layer, whereby an oil layer containing 2-hydroxy-4-methyl-4-butyric acid is formed.
Methylthiobutanoic acid can be obtained [Step (D)]. In the reaction solution, when ammonium bisulfate or ammonium sulfate is precipitated, oil-water separation may be performed as it is, but from the viewpoint of liquid separation, it is preferable to heat and dissolve these precipitates. Even when no precipitate is present, liquid separation can be enhanced by heating. The temperature at the time of oil-water separation is usually 30 to 120 ° C,
Preferably it is in the range of 70 to 110 ° C.

In the oil layer separated in the step (D), it depends on the conditions of the steps (A) to (D), but usually, in addition to 2-hydroxy-4-methylthiobutanoic acid, water, ammonium sulfate, Ammonium sulfate and the like. As an operation for obtaining a higher concentration of 2-hydroxy-4-methylthiobutanoic acid from the oil layer, the oil layer was mixed with ammonia to neutralize ammonium bisulfate to ammonium sulfate,
It is preferable to remove insoluble substances such as ammonium sulfate precipitated from the obtained mixture by filtration, decantation, or the like [Step (E)]. By removing the water by concentrating the mixture before removing the insoluble matter, more insoluble matter can be precipitated, and the content of water and ammonium sulfate is reduced in 2-hydroxy-4-methylthio. Butanoic acid can be obtained.

When the insoluble matter is removed by filtration,
It is preferable to heat from the viewpoint of filterability, and the filtration temperature is usually in the range of 50 to 90 ° C. In addition, when the insoluble matter is removed by decantation, it is preferable that the insoluble matter is sufficiently settled by standing or centrifugation.

The insoluble matter removed by filtration, decantation or the like usually contains 2-hydroxy-4-methylthiobutanoic acid on the surface or contained in the inside. To recover 4-methylthiobutanoic acid, at least a part of the insolubles is
It is preferred to recycle to step (E). In this case, the insolubles may be washed with water to elute 2-hydroxy-4-methylthiobutanoic acid, and the obtained washing liquid may be circulated.

[0019]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples. In addition, 2-hydroxy-
The analysis of 4-methylthiobutanoic acid was performed by potentiometric titration, and the analysis of water was performed by Karl Fischer method.

Example 1 60 g of sulfuric acid containing 2% by weight of water [58.8 g of sulfuric acid (0.
6 mol) and 1.2 g of water, and 168.2 g of 2-hydroxy-4-methylthiobutanenitrile containing 22% by weight of water in 131.2 g of 2-hydroxy-4-methylthiobutanenitrile (11.2 g of water) with stirring. Mol), water 37.0 g]
Was added dropwise at 50 ° C. over 30 minutes,
Hold for hours. 141.0 g of water was added to the hydration reaction liquid, and the mixture was stirred at 115 ° C. for 6 hours. The obtained hydrolysis reaction solution (369.2 g) was made up of 39.5% by weight of water (14
5.8 g) of the aqueous solution of 2-hydroxy-4-methylthiobutanoic acid.

The hydrolysis reaction solution was concentrated at a temperature of 70 ° C. and a pressure of 0.01 MPa, heated to 115 ° C., allowed to cool, and separated at 90 ° C. into an oil layer and an aqueous layer. Next, the oil layer and the aqueous layer are mixed, and a hydrolysis reaction solution is prepared again.
Further, the operations of concentration, heating, cooling, and oil-water separation were repeated in the same manner as described above. Thereafter, the operations of mixing, concentrating, heating, cooling, and separating oil and water from the oil layer and the aqueous layer were repeated once again. Table 1 shows the amount of distilled water (total) at the time of concentration, the amount of the oil layer and the aqueous layer after oil-water separation, and the temperature at which salt precipitated from the aqueous layer in each of the first, second, and third operations.

[0022]

[Table 1]

Example 2 The oil layer and the aqueous layer obtained in the third oil-water separation in Example 1 were mixed, 14 g of water was added, and the mixture was separated again at 90 ° C. into an oil layer and an aqueous layer. 4.1 g of 25% by weight aqueous ammonia solution
, And concentrated under reduced pressure until the water content became 1% by weight or less, and then filtered through a glass filter. Each of the re-separated oil layer and aqueous layer, the filtrate and the filtration residue obtained by the filtration, and the 2-hydroxy-
Table 2 shows the content of 4-methylthiobutanoic acid and the yield based on the starting material 2-hydroxy-4-methylthiobutanenitrile.

[0024]

[Table 2]

Example 3 70 g of sulfuric acid containing 2% by weight of water [68.6 g of sulfuric acid (0.
7 mol) and 1.4 g of water, 168.2 g of 2-hydroxy-4-methylthiobutanenitrile containing 13% by weight of 2-hydroxy-4-methylthiobutanenitrile containing 22% by weight of water. Mol), water 37.0 g]
Was added dropwise at 50 ° C. over 30 minutes,
Hold for hours. 121.7 g of water was added to the hydration reaction solution, and the mixture was stirred at 115 ° C. for 4 hours. The obtained hydrolysis reaction liquid (359.9 g) was obtained by adding 35.0% by weight of water (126
g) containing a homogeneous aqueous solution of 2-hydroxy-4-methylthiobutanoic acid.

The hydrolysis reaction solution was concentrated at a temperature of 70 ° C. and a pressure of 0.01 MPa, heated to 115 ° C., allowed to cool, and separated at 90 ° C. into an oil layer and an aqueous layer. Next, the oil layer and the aqueous layer are mixed, and a hydrolysis reaction solution is prepared again.
Further, the operations of concentration, heating, cooling, and oil-water separation were repeated in the same manner as described above. Thereafter, the operations of mixing, concentrating, heating, cooling, and separating oil and water from the oil layer and the aqueous layer were repeated once again. Table 3 shows the amount of distilled water (total) at the time of concentration, the amounts of the oil layer and the aqueous layer after oil-water separation, and the temperature at which salts precipitated from the aqueous layer in each of the first, second, and third operations.

[0027]

[Table 3]

Example 4 The oil layer obtained in the third oil / water separation in Example 3 was mixed with 6.8 g of a 25% by weight aqueous ammonia solution, and the water content was 1% by weight.
After concentrating under reduced pressure until it became the following, it filtered with the glass filter. The amounts of the oil layer and the aqueous layer obtained in the third oil-water separation in Example 3, the filtrate and the filtration residue obtained by the filtration, and the 2-hydroxy-4 contained therein.
Table 4 shows the content of -methylthiobutanoic acid and the yield based on the raw material 2-hydroxy-4-methylthiobutanenitrile.

[0029]

[Table 4]

Example 5 80 g of sulfuric acid containing 2% by weight of water [78.4 g of sulfuric acid (0.
8 mol) and 1.6 g of water], 168.2 g of 2-hydroxy-4-methylthiobutanenitrile containing 22% by weight of water and 131.2 g of 2-hydroxy-4-methylthiobutanenitrile containing 22% by weight of water. Mol), water 37.0 g]
Is added dropwise at 50 ° C. over 30 minutes,
Hold for hours. 130.0 g of water was added to the hydration reaction solution, and the mixture was stirred at 115 ° C. for 3 hours. The obtained hydrolysis reaction liquid (378.2 g) was obtained by adding 36.0% by weight of water (13
6.2 g) was a homogeneous aqueous solution of 2-hydroxy-4-methylthiobutanoic acid.

The hydrolysis reaction solution was concentrated at a temperature of 70 ° C. and a pressure of 0.01 MPa, heated to 115 ° C., allowed to cool, and separated at 90 ° C. into an oil layer and an aqueous layer. Next, the oil layer and the aqueous layer are mixed, and a hydrolysis reaction solution is prepared again.
Further, the operations of concentration, heating, cooling, and oil-water separation were repeated in the same manner as described above. Thereafter, the operations of mixing, concentrating, heating, cooling, and separating oil and water from the oil layer and the aqueous layer were repeated once again. Table 1 shows the amount of distilled water (total) at the time of concentration, the amount of the oil layer and the aqueous layer after oil-water separation, and the temperature at which salt precipitated from the aqueous layer in each of the first, second, and third operations. Further, the above operation was repeated. In each operation,
Table 5 shows the amount of distilled water (total) at the time of concentration, the amounts of the oil layer and the aqueous layer, and the temperature at which salt was precipitated from the aqueous layer.

[0032]

[Table 5]

Example 6 The oil layer and the aqueous layer obtained in the third oil-water separation in Example 5 were mixed, and after adding 17.4 g of water, the oil layer and the aqueous layer were separated again at 90 ° C. 9. The oil layer is 25% by weight ammonia aqueous solution.
The mixture was mixed with 2 g, concentrated under reduced pressure until the water content became 1% by weight or less, and then filtered with a glass filter. The amounts of the re-separated oil layer and aqueous layer, the filtrate and the filtration residue obtained by the filtration, the content of 2-hydroxy-4-methylthiobutanoic acid contained therein, and the raw material 2-hydroxy-4-methylthiobutanenitrile Table 6 shows the standard yields.

[0034]

[Table 6]

[0035]

According to the present invention, efficient and efficient operability is achieved.
-Hydroxy-4-methylthiobutanoic acid can be produced.

Continued on the front page F term (reference) 2B150 DA32 4H006 AA02 AC46 AD15 AD17 AD30 BA28 BA36 BA66 BE60 TA04 TB38 TB52 4H039 CA65 CE20 CF40

Claims (2)

[Claims] (A) a step of hydrating 2-hydroxy-4-methylthiobutanenitrile in the presence of sulfuric acid;
(B): a step of hydrolyzing 2-hydroxy-4-methylthiobutanamide contained in the reaction solution obtained in the step (A) in the presence of sulfuric acid, and (C): a reaction obtained in the step (B). Condensing the liquid; and (D): separating the concentrated liquid obtained in the step (C) into an oil layer containing 2-hydroxy-4-methylthiobutanoic acid and an aqueous layer. A method for producing -hydroxy-4-methylthiobutanoic acid. 2. The method according to claim 1, further comprising the step of: (E): mixing the oil layer separated in the step (D) with ammonia, and removing insolubles from the obtained mixture.