JPS6318941B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing β-mercaptopropionic acid, and more particularly to a method for producing β-mercaptopropionic acid using acrylic acid and thiosulfate as raw materials. β-Mercaptopropionic acid is a compound useful as a raw material for many organic synthetic products including medicines, agricultural chemicals, polymer additives, and photopolymers. Various methods are conventionally known for producing β-mercaptopropionic acid. For example, a method using β-propiolactone and sodium hydrosulfide as raw materials [U.S.
2449989]. According to this method, β-mercaptopropionic acid can be obtained relatively easily. However, this method
Propiolactone is expensive and highly toxic, making it unsatisfactory as an industrial production method. On the other hand, more economical production methods include a method using β-chloropropionic acid and sodium hydrogen sulfide [see German Published Patent No. 2354098] and a method using acrylic acid and hydrogen sulfide [see Dutch Published Patent Application No. 6508594]. There is a reference. In these methods, the raw material β-chloropropionic acid can be easily synthesized from acrylonitrile or acrylic acid, which is industrially produced in large quantities at low cost, and acrylic acid can also be produced in large quantities at low cost by oxidation of propylene. It is something that exists. However, these methods require the reaction to be carried out under pressure and with a large excess of hydrogen sulfide in order to prevent the by-product of thiodipropionic acid due to side reactions. It is necessary to select a special material that can withstand high pressure systems, which is extremely disadvantageous as an industrial manufacturing method. As described above, it is difficult to industrially produce β-mercaptopropionic acid directly from β-chloropropionic acid or acrylic acid, which are inexpensive and available in large quantities. Alternatively, various methods have been proposed in which acrylonitrile or the like is used to easily produce β-mercaptopropionic acid through a precursor. [German Published Patent Application No. 2251717, Japanese Patent Publication No. 47-49600 and Japanese Patent Publication No. 35-1983
See Publication No. 2913]. However, these manufacturing methods use carbon disulfide, which is highly toxic and difficult to handle, and
Since expensive thiourea is used as an industrial raw material, it cannot necessarily be called an economical industrial production method. Under the above circumstances, the present inventors have developed an economical method for producing β-mercaptopropionic acid using acrylic acid, which is produced in large quantities at low cost as an industrial raw material, and also using an inexpensive and less toxic sulfur source. As a result of intensive research to develop an industrial manufacturing method,
This book was based on the discovery that β-mercaptopropionic acid can be easily obtained by generating Bunte salt as a precursor of β-mercaptopropionic acid using thiosulfate as a sulfur source and hydrolyzing this Bunte salt with acid. The invention has been achieved. That is, the present invention involves reacting acrylic acid with thiosulfate in an aqueous medium to produce Bunte salt as a precursor of β-mercaptopropionic acid, and then hydrolyzing the Bunte salt in the presence of an acid. This is a method for producing β-mercaptopropionic acid. The reaction of the present invention is expressed by the following general formula. [However, M is an alkali metal, an alkaline earth metal, or an ammonium ion, and n is the valence or ionic valence of M, which is 1 or 2. Furthermore, in the present invention, the yield of the final product is significantly improved by reducing dithiodipropionic acid, which is produced as a by-product during the hydrolysis of Bunte salt, to β-mercaptopropionic acid, if necessary. be able to. Acrylic acid, the main raw material used in the present invention, may be selected from any source, and is usually an inexpensive industrial raw material obtained by oxidation of propylene or hydrolysis of acrylonitrile. In addition, the thiosulfates used in the present invention include alkali metal thiosulfates such as sodium thiosulfate and potassium thiosulfate, alkaline earth metal salts of thiosulfates such as magnesium thiosulfate and calcium thiosulfate, and ammonium thiosulfate. 1
It may be used as a type or a mixture of two or more types. There is no restriction on the presence or absence of water of crystallization of thiosulfate. Among these thiosulfates, it is most preferable to use sodium thiosulfate pentahydrate (commonly known as "hypo"), which is industrially produced in large quantities and at low cost, for industrial production. Next, general embodiments of the present invention will be described. 1 Formation of Bunte salt Bunte by reaction between acrylic acid and thiosulfate
Salt production is carried out in an aqueous medium using approximately equal moles of both materials, but it is possible to use an excess of either raw material within the range of acrylic acid: thiosulfate = 1:0.5 to 1.5 (molar ratio). Also good. The concentrations of acrylic acid and thiosulfate in the aqueous medium are preferably about 5 to 50% by weight, respectively. As the aqueous medium, for example, water or a mixed liquid such as water-alcohol, water-dioxane, water-tetrahydrofuran or water-dimethyl sulfoxide is used, but industrially, the reaction is carried out in water or a water-alcohol mixed liquid. is advantageous. Also, adjust the pH of the reaction solution to 5 to 5 using a buffer solution, etc.
Adjustment to 9, preferably 6 to 8 is effective in preventing side reactions. The reaction temperature is usually in the range from 40°C to the boiling point of the reaction solution, and the reaction time is sufficient to be about 30 minutes to 5 hours. After the reaction, it is preferable to separate the obtained Bunte salt from the inorganic salts by solvent extraction or the like before proceeding to the next hydrolysis, but industrially it is preferable to continue the hydrolysis by adding an acid without isolation. There is no problem.
When Bunte salt is isolated and purified, thermal extraction with alcohol can be used. 2 Hydrolysis Acids used for hydrolysis of Bunte salt include mineral acids such as hydrochloric acid, sulfuric acid, and phosphoric acid, organic carboxy acids such as formic acid and oxalic acid, organic sulfonic acids such as P-toluenesulfonic acid, and strong acid ions. Although there are solid acids such as exchange resins, mineral acids such as sulfuric acid and hydrochloric acid are preferable from an industrial perspective, considering the reaction rate and the separation process after the reaction. The amount of acid used is based on acrylic acid, and is selected in the following range: acrylic acid: acid = 1:1.0 to 6.0 (molar ratio), preferably acrylic acid: acid = 1:2 to 5 (molar ratio). The acid concentration is preferably in the range of 10 to 40% by weight. The temperature of the hydrolysis reaction is usually in the range from 60°C to the boiling point of the reaction solution, and the reaction time is sufficient to be about 15 minutes to 8 hours. 3. Reduction Treatment As mentioned above, if dithiodipropionic acid, which is produced as a by-product during the hydrolysis of Bunte salt, is reduced and converted to β-mercaptopropionic acid, the yield of the final product can be greatly improved. As a reduction method, a method using a hydrogenating agent such as lithium aluminum hydride or sodium boron hydride, a method using a combination of a metal such as zinc or tin and an acid (sulfuric acid, hydrochloric acid, acetic acid, etc.), or a method using electrolytic reduction may be used. However, considering that a large amount of the acid used during hydrolysis remains in the reaction solution,
Reduction methods using zinc or tin are industrially advantageous. 4 Recovery After the reaction is completed, β-mercaptopropionic acid can be separated and purified from the reaction mixture by extraction with an organic solvent and distillation of the extract.
Any extraction solvent may be used as long as it dissolves β-mercaptopropionic acid and is immiscible with water, but in particular benzene, toluene, dichloromethane, 1,2-dichloroethane, 1,
1,1-trichloroethane, chloroform, ether, etc. are used. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way. Example 1 1 Production of Bunte salt A reactor equipped with a thermometer, stirrer, cooling condenser, and dropping funnel was charged with 62.7 g of sodium thiosulfate pentahydrate and 100 g of water, and after dissolving, heated to 80°C. did. Add 18.1g of acrylic acid to this solution through a dropping funnel for approximately 1 hour while keeping the liquid temperature at 80-85℃.
It was added dropwise over a period of time, and then aged at the same temperature for 30 minutes. After cooling, insoluble matter was separated, and then the solvent and the like were distilled off under reduced pressure, followed by vacuum drying at 80°C. As a result, as a pale yellow, highly hygroscopic solid
47.3 g (yield 90.9%) of Bunte salt was obtained. 2 Hydrolysis The Bunte salt thus obtained was dissolved in 100 g of water, then 60 g of 36% hydrochloric acid was added and the mixture was heated at 80°C for 1 hour.
The mixture was heated and reacted for an hour. Further, this reaction solution was subjected to reduction treatment using 8 g of zinc powder at the same temperature. A portion of this reaction solution was collected and analyzed by gas chromatography, and as a result, it was found that 11.8 g (reaction yield: 49.0%) of β-mercaptopropionic acid was produced. The overall yield of reactions 1) and 2) was 44.5%. Example 2 In a reactor similar to Example 1, 62.7 g of sodium thiosulfate pentahydrate and 100 g of a 0.2 M potassium phosphate-sodium hydroxide buffer solution adjusted to pH 7 were charged and heated to 80°C. To this solution, 18.1 g of acrylic acid was added dropwise from a dropping funnel over about 1 hour while maintaining the liquid temperature at 80 to 85°C, and then aged at the same temperature for 30 minutes. Next, 63 g of 98% sulfuric acid was added to this reaction solution, and the mixture was reacted at 90° C. for 1 hour, followed by reduction treatment at 80 to 90° C. using 8 g of zinc powder. A portion of this reaction solution was analyzed in the same manner as in Example 1, and 17.6 g (reaction yield: 66.3° C.) of β-mercaptopropionic acid was found to be produced. . Example 3-5 The same operation as in Example 2 was carried out except that the type and amount of thiosulfate used were changed, and the results shown in Table 1 were obtained. 【table】

Claims (1)

[Claims] 1 Reacting acrylic acid with thiosulfate in an aqueous medium to form the Bunte salt as a precursor of β-mercaptopropionic acid, and then
A method for producing β-mercaptopropionic acid, which comprises hydrolyzing this Bunte salt in the presence of an acid.