WO2002008181A1

WO2002008181A1 - Process for producing 2-hydroxy-4-methylthiobutanoic acid

Info

Publication number: WO2002008181A1
Application number: PCT/JP2001/005982
Authority: WO
Inventors: Kenji Ikudome; Tetsuya Shiozaki; Takehiro Otani; Shogo Sudo
Original assignee: Sumitomo Chemical Company, Limited
Priority date: 2000-07-25
Filing date: 2001-07-09
Publication date: 2002-01-31
Also published as: AU2001269501A1; JP4517474B2; JP2002037769A

Abstract

A process for producing 2-hydroxy-4-methylthiobutanoic acid which comprises hydrating 2-hydroxy-4-methylthiobutanenitrile in the presence of sulfuric acid, hydrolyzing the 2-hydroxy-4-methylthiobutanamide contained in the reaction mixture, subsequently separating the resultant reaction mixture into an oil layer containing 2-hydroxy-4-methylthiobutanoic acid and an aqueous layer, and circulating part of the aqueous layer to the hydrolysis step and/or the oil/water separation step. By the process, 2-hydroxy-4-methylthiobutanoic acid can be efficiently obtained in a satisfactory manner without using an organic solvent.

Description

Specification

Method for producing 2-hydroxy-4-methylthiobutanoic acid

The present invention relates to a method for producing 2-hydroxy-4-methylthiobutanoic acid. Background of the Invention

Conventionally, a method for producing 2-hydroxy-4-methylthiobutanoic acid by subjecting 2-hydroxy-4-methylthiobutanenitrile to a hydrolysis reaction in the presence of sulfuric acid is known.

As a method for extracting 2-hydroxy-4-methylthiobutanoic acid from the reaction solution obtained by this sulfuric acid hydrolysis, for example, Japanese Patent Publication No. 5-18787 discloses a method using an organic solvent such as isobutyl methyl ketone. A method for extracting and extracting —hydroxy — 4-methylthiobutanoic acid from a reaction solution is described. However, this method increases the cost of raw materials and decreases the volumetric efficiency due to the use of organic solvents, and also requires the recovery and purification of organic solvents and the removal of organic solvents from final products and wastewater. Equipment and processes are required.

Also, U.S. Pat.No. 4,912,257 discloses a method of neutralizing ammonium bisulfate in a reaction solution with ammonia to form ammonium sulfate, and separating the obtained solution into oil and water by a salting out effect. Has been described. However, this method is not sufficient in terms of oil-water separation properties and the extraction efficiency of 2-hydroxy-4-methylthiobutanoic acid.

An object of the present invention is to provide a method for producing 2-hydroxy-4-methylthiobutanoic acid, which solves the above-mentioned problems and allows 2-hydroxy-4-methylthiobutanoic acid to be efficiently removed from the reaction solution with good operability. It is in.

As a result of intensive studies, the present inventors have found that the above object can be achieved by employing a circulation system in a method for producing 2-hydroxy-4-methylthiobutanoic acid from 2-hydroxy-4-methylthiobutanenitrile using sulfuric acid. And found that the present invention was completed. That is, the present invention

(A) 2-hydroxy-4-methylthiobutane nitrile is hydrated and reacted in the presence of sulfuric acid to obtain a reaction solution containing 2-hydroxy-4-methylthiobutanamide.

(B) hydrolyzing 2-hydroxy-4-methylthiobutanamide contained in the reaction solution obtained in the step (A) to obtain a reaction solution containing 2-hydroxy-4-methylthiobutanoic acid;

(C) The reaction solution obtained in the step (B) is separated into an oil layer and an aqueous layer containing 2-hydroxy-4-methylthiobutanoic acid to obtain an oil layer and an aqueous layer.

(C ′) A method for producing 2-hydroxy-4-methylthiobutanoic acid, wherein a part of the aqueous layer obtained in the step (C) is recycled to the steps (B) and Z or the step (C).

Detailed description of the invention

In the present invention, 2-hydroxy-4-methylthiobutyronitrile is used as a raw material, and a hydration reaction is carried out in the presence of sulfuric acid to obtain a reaction solution containing 2-hydroxy-4-methylthiobutanamide. [Step (A)] 2-Hydroxy-4-methylthiobutyronitrile is prepared, for example, by reacting acrolein with methyl mercaptan to obtain 3-methylthiopropionaldehyde, which is then reacted with hydrogen cyanide. can do.

The amount of sulfuric acid used in the 7-sum reaction may be about 0.5 mol or more, preferably about 0 mol, from the viewpoint of the reaction rate with respect to 1 mol of 2-hydroxy-4-methylthiobutane nitrile. It is at least 6 mol, and from the viewpoint of the separation of oil and water after hydrolysis, it can be at most about 1 mol, preferably at most 0.9 mol.

The amount of water used in the hydration reaction may be about 15 parts by weight or more, and preferably about 15 parts by weight, based on 100 parts by weight of 2-hydroxy-4-methylthiobutanenitrile, from the viewpoint of the reaction rate. It is not less than 25 parts by weight, and can be not more than about 70 parts by weight, preferably not more than about 50 parts by weight.

In the hydration reaction, 2-hydroxy-4-methylthiobutanenitrile, sulfuric acid and water are supplied from the viewpoint of the reaction rate. It is preferable to supply methylthiobutanenitrile. At this time, water is supplied with 2-hydroxy-4-methylthiobutanenitrile. (I) It may be supplied into sulfuric acid together with 4-methylthiobutane nitrile, or a part may be mixed with sulfuric acid before supplying 2-hydroxy-4-methylthiobutane nitrile, and the remaining part may be supplied in sulfuric acid. — May be fed into sulfuric acid with hydroxy-4-methylthiobutanenitrile.

The reaction temperature of the hydration reaction can be about 40 ° C. to about 70 ° C., and the reaction time can be about 1 hour to about 3 hours. The hydration reaction can be carried out at around normal pressure, but may be carried out under increased or reduced pressure as necessary. The reaction solution containing 2-hydroxy-4-methylthiobutanoic acid can be obtained by hydrolyzing 2-hydroxy-4-methylthiobutanamide in the reaction solution obtained in step (A) [Step (B) ]. By circulating and using a part of the aqueous layer separated in the step (B) described later in the step (B), the obtained reaction solution can be separated into oil and water with good liquid separation properties and high distribution efficiency.

The circulation amount of the aqueous layer was determined based on 1 mol of the sulfuric acid used in the hydration reaction (ie, added in step (A)) or when added to the carohydrate decomposition reaction (ie, sulfuric acid was added in step (B)). In the case of), ammonium sulfate and bisulfuric acid contained in the aqueous layer were used for 1 mol of the total amount of sulfuric acid used in the hydration reaction and the hydrolysis reaction (added in steps (A) and (B)). The amount can be about 1.0 mol to about 2.0 mol, preferably about 1.2 mol to about 1.8 mol, in terms of the total amount of ammonium.

In step (B), water may be added as needed. In this case, the amount of water to be added was the sum of the amount of water contained in the reaction solution obtained in step (A) and the amount of water contained in the circulating aqueous layer used in the hydration reaction (step When sulfuric acid was added to 100 parts by weight of sulfuric acid (added in (A)) or during the hydrolysis reaction (in step (B)), it was used for the hydration reaction and hydrolysis reaction. It may be about 100 parts by weight to about 300 parts by weight, preferably about 200 parts by weight, based on 100 parts by weight of the sulfuric acid (added in steps (A) and (B)). Parts by weight to about 300 parts by weight. In the step (B), sulfuric acid may be added as needed. In this case, the amount of sulfuric acid used in the hydration reaction (added in step (A)) may be reduced compared to when no sulfuric acid is added during the hydrolysis reaction (in step (B)).

When a part of the aqueous layer separated in the step (C) described below is recycled to the step (B), the reaction solution obtained in the step (A) and the circulating aqueous layer are used from the viewpoint of operability. After mixing with water or sulfuric acid as needed, it is preferable to subject the resulting mixture to a hydrolysis reaction. Further, while the reaction solution obtained in the step (A) is subjected to a hydrolysis reaction, an aqueous layer circulated therein and, if necessary, water or sulfuric acid may be gradually added.

The reaction temperature of the hydrolysis reaction can be from about 90 to about 130 ° C, and the reaction time can be from about 2 hours to about 6 hours. Further, the hydrolysis reaction can be carried out at around normal pressure, but may be carried out under increased or reduced pressure as necessary.

The reaction solution obtained in the step (B) is separated into an oil layer containing 2-hydroxy-14-methylthiobutanoic acid and an aqueous layer, and the 2-hydroxy-4-methylthiobutanoic acid can be taken out as an oil layer [Step ( C)]. When ammonium bisulfate / ammonium sulfate is precipitated in the reaction solution obtained in the step (B), oil-water separation may be performed as it is. It is preferable to separate oil and water after dissolving the compound. Further, even when no precipitate is present, liquid separation can be enhanced by heating. The temperature during oil-water separation can be from about 30 ° C to about 110 ° C, preferably from about 70 to about 90 ° C. Further, in order to enhance the liquid separating property, the reaction solution obtained in the step (B) may be subjected to an operation such as concentration before the oil-water separation.

A part of the aqueous layer separated in the step (C) can be recycled to, for example, the step (B) as described above [Step (C ′)]. Since the aqueous layer usually contains ammonium bisulfate and ammonium bisulfate, ammonium sulfate may be recovered from the remaining aqueous layer that is not circulated after neutralizing the included ammonium bisulfate with ammonia. Alternatively, a trace amount of 2-hydroxy-4-methylthiobutanoic acid contained in the aqueous layer may be recovered by an appropriate method. The oil layer separated in step (C) contains water, ammonium sulfate, ammonium bisulfate, etc. in addition to 2-hydroxy-4-methylthiobutanoic acid depending on the conditions in steps (A) to (C). It may be. At this time, although it depends on the required form and quality of the final product, from the viewpoint of increasing the concentration of 2-hydroxy-4-methylthiobutanoic acid in the product, the oil layer separated in step (C) must be separated. The mixture is mixed with ammonia, and the ammonium bisulfate contained therein is neutralized into ammonium sulfate to precipitate insolubles [Step (D)]. [Step (E)].

The amount of ammonia used in the step (D) may be about equimolar to the amount of ammonium bisulfate contained in the oil layer separated in the step (C). In addition, this ammonia is preferably in the form of ammonia gas or liquid ammonia from the viewpoint of reducing the water content in the obtained mixed solution, while it is preferably in the form of an aqueous ammonia solution from the viewpoint of operability. .

When removing the insoluble matter by filtration in the step (E), it is preferable to heat the mixture prior to filtration from the viewpoint of filterability. Filtration temperatures can range from about 50 ° C to about 90 ° C. When removing insolubles by decantation, it is preferable to remove the insolubles by standing and centrifuging to sufficiently settle the insolubles.

Before removing insolubles from the mixture obtained in step (D), the mixture is concentrated to remove water [step (D ')], and more insolubles are precipitated. This is preferred because a final product having reduced moisture and ammonium sulfate content can be obtained. For example, the content of ammonium sulfate in the product is

In order to reduce the amount of water to 1% by weight or less, it is preferable to concentrate the mixture until the amount of water contained in the mixture is about 5% or less, preferably about 2% or less.

In the insoluble matter removed in the step (E), 2-hydroxy-4-methylthiobutanoic acid may adhere to the surface or may be contained in the inside. In order to recover methylthiobutanoic acid, at least a part of the insoluble matter is preferably recycled to the step (D) [Step (F)]. in this case, The insolubles may be washed with water to elute 2-hydroxy-4-methylthiobutanoic acid, and the resulting washing may be recycled to step (D).

In the present invention, even if a part of the aqueous layer separated in the above step (C) is circulated to the step (C) instead of being circulated to the step (B), the operability can be improved efficiently. —Hydroxy 4-methylthiobutanoic acid can be extracted. In this case, the amount of circulation of the water layer and other conditions may be performed in accordance with the case where circulation is performed in the step (B). Further, a part of the aqueous layer separated in the step (C) may be circulated to both the step (B) and the step (C).

As described above, according to the method for producing 2-hydroxy-4-methylthiobutanoic acid of the present invention, 2-hydroxy-4-methylthiobutanoic acid can be efficiently extracted with good operability.

Example

Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto.

Example 1

The operation consisting of the following (i) to (vi) was repeated four times.

(i): To 74.0 g (0.74 mol) of 98% concentrated sulfuric acid was added 175.4 g (1.0 mol) of a 74.8% aqueous solution of 2-hydroxy-4-methylthiobutanenitrile to 50% under stirring. , And the mixture was kept at 50 ° C for 90 minutes.

(ii): To the reaction solution obtained in (i), add the aqueous layer and water obtained in the previous oil-water separation (iii) in the amounts shown in Table 1 [However, in the first operation, Instead of the aqueous layer and water, an aqueous solution prepared by dissolving 60 g (0.52 mol) of ammonium bisulfate and 38.2 g (0.29 mol) of ammonium sulfate in 114 g of water was added], and at 115 ° C. The mixture was stirred for 4 hours. The concentration of 2-hydroxy-4-methylthiobutanamide in the obtained reaction solution was measured by liquid chromatography, and the change over time in the residual ratio was determined. Table 1 shows the results. (iii): The reaction solution obtained in (ii) was allowed to stand, and separated into an oil layer and an aqueous layer. Table 1 shows the weight of the aqueous layer and the content of ammonium bisulfate and ammonium sulfate in the aqueous layer determined by neutralization titration (using NaOH).

(iv): 6.8 g of a 25% aqueous ammonia solution was added to the oil layer obtained in (iii) (0.

1 mol) and the total amount of the washings obtained in the previous filtration (vi) was added [however, the washings were not used in the first operation], and concentrated under reduced pressure to reduce the water content of the oil phase. A slurry of 2% or less was obtained.

(V): The slurry obtained in (iv) was filtered, and the filtrate was used as a final product. Table 1 shows the weight of the product, the sulfate ion concentration in the product determined by ion chromatography, and the water content in the product determined by the Karl Fischer method.

(vi): The residue separated by filtration in (V) was washed with 10 g of water.

1st 2nd 3rd 4th

Water layer used in (ii) (g)-142.0 150.0 161.5 Water layer and water (g) 74.0 68.0 58.0 Added water

Reaction (ii) 0.5 hour 2.875 2.140 1.864 3.075 1 hour in solution 1.085 0.872 0.680 1.105 2-hydroxy 2 hours 0.168 0.152 0.119 0.178-4-methylthiophene "3 hours 0.077 0.048 0.059 0.053 Remaining tanamide 4 hours 0.037 0.025 0.034 0.030 (%)

Weight in (iii) Weight (g) 261.2 255.7 253.3 259.0 Separated water Ammonium bisulfate

0.911 0.846 0.818 0.874 (mol)

Ammonium sulfate 0.555 0.513 0.450 0.475 Content (mol)

Weight obtained in (V) (g) 109.7 114.8 131.2 140.4 Final sulfate concentration 0.62 0.85 0.60 0.59 Quality (%)

Water content (%) 1.0 1.5 0.8 0.6

Claims

The scope of the claims

1. (A) 2-Hydroxy-1-methylthiobutyronitrile is hydrated in the presence of sulfuric acid to give a reaction solution containing 2-hydroxy-4-methylthiobutanamide.

(B) Hydrolysis of 2-hydroxy-4-methylthiobutanamide contained in the reaction solution obtained in the step (A) to obtain a reaction solution containing 2-hydroxy-4-methylthiobutanoic acid,

(C) separating the reaction solution obtained in the step (B) into an oil layer and an aqueous layer containing 2-hydroxy-14-methylthiobutanoic acid to obtain an oil layer and an aqueous layer;

(C ') Part of the water layer obtained in step (C) is recycled to step (B) and / or step (C)

A method for producing 2-hydroxy-1-methylthiobutanoic acid.

2. (D) The oil layer separated in step (C) is mixed with ammonia to precipitate insolubles in the obtained mixed solution.

The production method according to claim 1, further comprising: (E) a step of removing insolubles from the mixture obtained in the step (D).

3. Between step (D) and step (E),

(D ′) The production method according to claim 2, further comprising a step of removing water from the mixture obtained in the step (D).

4. (F) The production method according to claim 2 or 3, wherein at least a part of the insoluble matter removed in the step (E) is recycled to the step (D).