Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2002-08-02
2003-11-18
O'Sullivan, Peter (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S581000
Reexamination Certificate
active
06649794
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing 2-hydroxy-4-metylthiobutanoic acid, which is useful as feed additives and the like. Specifically, the present invention relates to a method for producing 2-hydroxy-4-methylthiobutanoic acid, the method comprising the steps of hydrolyzing 2-hydroxy-4-methylthiobutanenitrile and/or 2-hydroxy-4-metylthiobutanamide in the presence of sulfuric acid.
BACKGROUND OF THE INVENTION
It is known that 2-hydroxy-4-metylthiobutanoic acid is generated by hydrolyzing 2-hydroxy-4-methylthiobutanenitrile or 2-hydroxy-4-metylthiobutanamide in the presence of an acid such as sulfuric acid.
An extraction method using an organic solvent is generally known as a method of separating 2-hydroxy-4-methylthiobutanoic acid from a reaction mixture obtained by hydrolyzing 2-hydroxy-4-methylthiobutanenitrile or 2-hydroxy-4-metylthiobutanamide with sulfuric acid (for example, as disclosed in Japanese Examined Patent Publication No. 5-1787 (1993)). This method, however, has problems such that the cost for product increases and the volumetric efficiency in the production decreases due to the use of the organic solvent, as well as problems in that equipments and operations are required for recovering and purifying the organic solvent and for removing the organic solvent from a produced product and a waste water.
In contrast to the above, a method not using an organic solvent has been proposed wherein a reaction mixture is neutralized with ammonia and the resulting mixture is separated into an oil layer and a water layer (see, U.S. Pat. No. 4,912,257 publication). However, this method has problems such that the separatability between the oil layer and the water layer is poor, a large amount of 2-hydroxy-4-methylthiobutanoic acid layer remains in the water layer, resulting in poor efficiency in extraction of 2-hydroxy-4-methylthiobutanoic acid from the reaction mixture.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for producing 2-hydroxy-4-methylthiobutanoic acid with excellent operability and efficiency without using an organic solvent, which solves the above-mentioned problems.
The inventors of the present invention have made special efforts to find that the above object can be achieved by hydrolyzing 2-hydroxy-4-methylthiobutanenitrile and/or 2-hydroxy-4-methylthiobutanamide in the presence of sulfuric acid and post-treating the resulting reaction mixture in a certain manner, and have finally accomplished the above object to complete the present invention.
That is, the present invention provides a method for producing a 2-hydroxy-4-methylthiobutanoic acid, the method comprising the steps of:
(A) hydrolyzing at least one selected from a 2-hydroxy-4-methylthiobutanenitrile and a 2-hydroxy-4-methylthiobutanamide in the presence of a sulfuric acid to obtain a reaction mixture containing a 2-hydroxy-4-methylthiobutanoic acid;
(B) mixing the reaction mixture obtained in step (A) with a basic alkaline metal compound to obtain a mixture comprising an oil layer containing the 2-hydroxy-4-methylthiobutanoic acid and a water layer; and
(C) separating the oil layer containing the 2-hydroxy-4-methylthiobutanoic acid from the mixture obtained in step (B).
DETAIL DESCRIPTION OF THE INVENTION
A method for producing a 2-hydroxy-4-methylthiobutanoic acid in the present invention comprises step (A) in which at least one selected from a 2-hydroxy-4-methylthiobutanenitrile and a 2-hydroxy-4-methylthiobutanamide is hydrolyzed in the presence of a sulfuric acid to obtain a reaction mixture containing 2-hydroxy-4-methylthiobutanoic acid. The starting material used herein is a 2-hydroxy-4-methylthiobutanenitrile, a 2-hydroxy-4-methylthiobutanamide or a mixture thereof. Since ammonium salts such as ammonium sulfate and ammonium bisulfate generate in the above hydrolysis reaction, these ammonium salts are also contained in the reaction mixture. The ratio of the generated ammonium sulfate to the generated ammonium bisulfate varies depending on the amount of the sulfuric acid to be used, the reaction ratio and the like.
A 2-hydroxy-4-methylthiobutanenitrile can be obtained, for example, by reacting an acrolein with a methylmercaptan to obtain a 3-methythiopropionaldehyde, which is then reacted with a hydrogen cyanide. A2-hydroxy-4-methylthiobutanamide can be obtained, for example, by hydration of a 2-hydroxy-4-methylthiobutanenitrile.
In the case of using a 2-hydroxy-4-methylthiobutanenitrile as a starting material, the hydrolysis reaction to a 2-hydroxy-4-methylthiobutanoic acid comprises a hydration reaction of 2-hydroxy-4-methylthiobutanenitrile to 2-hydroxy-4-methylthiobutanamide and a hydrolysis reaction of the 2-hydroxy-4-methylthiobutanamide to 2-hydroxy-4-methylthiobutanoic acid. These reactions may be carried out in a single step by a single operation, however, since the optimum conditions thereof differ from each other, these reactions are preferably carried out in two step reactions, i.e., the first step reaction mainly for hydration of 2-hydroxy-4-methylthiobutanenitrile to 2-hydroxy-4-methylthiobutanamide and the second step reaction mainly for hydrolysis of 2-hydroxy-4-methylthiobutanamide to 2-hydroxy-4-methylthiobutanoic acid.
The first step reaction can be carried out by allowing 2-hydroxy-4-methylthiobutanenitrile, sulfuric acid and water to react for 1 hour to 3 hours at the temperature of from 40° C. to 70° C. The amount of sulfuric acid used herein may be 0.5 mol to 1 mol, preferably 0.6 mol to 0.8 mol, based on 1 mol of the 2-hydroxy-4-methylthiobutanenitrile. The amount of water used herein may be 20 parts by weight to 70 parts by weight, preferably 25 parts by weight to 50 parts by weight, based on 100 parts by weight of the 2-hydroxy-4-methylthiobutanenitrile. In mixing 2-hydroxy-4-methylthiobutanenitrile, sulfuric acid and water, the water may be used in the state that the water is mixed with the 2-hydroxy-4-methylthiobutanenitrile or the sulfuric acid in advance, that is, the water is contained in the resulting aqueous 2-hydroxy-4-methylthiobutanenitrile solution or the resulting aqueous sulfuric acid solution to be used. In this case, the aqueous sulfuric acid solution may be added to the aqueous 2-hydroxy-4-methylthiobutanenitrile solution, the aqueous 2-hydroxy-4-methylthiobutanenitrile solution may be added to the aqueous sulfuric acid solution, or both of them may be poured concurrently into a container. Preferably, the aqueous 2-hydroxy-4-methylthiobutanenitrile solution is added to the aqueous sulfuric acid solution.
The second step reaction can be conducted by mixing the reaction mixture obtained in the first step reaction with water and allowing them to react with each other for 2 hours to 6 hours at the temperature of from 90° C. to 130° C. The amount of water to be used for the mixing may be 100 parts by weight to 200 parts by weight based on 100 parts by weight of the sulfuric acid which has been used in the first step reaction. In the mixing thereof, the water may be added to the first step reaction mixture, the first step reaction mixture may be added to the water, or both of them may be poured concurrently to a container.
On the other hand, in the case of using a 2-hydroxy-4-methylthiobutanamide as a starting material, the 2-hydroxy-4-methylthiobutanamide may be mixed with a sulfuric acid and water to allow them to react under the same condition as the condition in the above mentioned second step reaction, thereby obtaining 2-hydroxy-4-methylthiobutanoic acid. Herein, the amount of sulfuric acid to be used may be 0.5 mol to 1 mol, preferably 0.6 mol to 0.8 mol, based on 1 mol of the 2-hydroxy-4-methylthiobutanamide. The amount of water to be used may be 40 by weight to 180 parts by weight, preferably 50 by weight to 140 parts by weight, based on 100 parts by weight of the 2-hydroxy-4-methylthiobutanamide.
In the present invention, instep (B), the reaction mixture obtained instep (A) is mixed with a basic alkaline metal compound to obtain a mixture comprising an oil layer containin
Ikudome Kenji
Shiozaki Tetsuya
O'Sullivan Peter
Sumitomo Chemical Company Limited
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