JPH11140045A - Production of thiosalicylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing thiosalicylic acid by reducing dithiosalicylic acid with a reduced amount of a metal without using an organic solvent. SOLUTION: The method for producing thiosalicylic acid comprises reducing dithiosalicylic acid with one or more kinds of metals selected from zinc, aluminum and tin in an aqueous solution of an alkali metal hydroxide and subsequently acidifying the obtained alkali metal thiosalicylate aqueous solution with a strong acid to deposit the thiosalicylic acid. The temperature on the reduction reaction is <=40 deg.C. The pH of the aqueous solution on the acidification of the solution with the strong acid to deposit the thiosalicylic acid is <=2.5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing thiosalicylic acid, a compound useful as an intermediate material for agricultural chemicals, medicines, dyes, and the like.

[0002]

2. Description of the Related Art Hitherto, as a method for producing thiosalicylic acid using dithiosalicylic acid as a raw material, for example, Organic Synthesis Collection, Vol. 2, page 580 (Or)
g. Synth. Coll. Vol. 2,580)
A method is described in which anthranilic acid is used as a starting material and then converted to thiosalicylic acid via dithiosalicylic acid. According to the method, dithiosalicylic acid obtained by disulfide of anthranilic acid is reduced with 2.1 mol of zinc per mol of anthranilic acid in glacial acetic acid to give a yield of 71 to 85%.
(Vs. anthranilic acid) to give thiosalicylic acid. However, there are many problems in industrial practice, such as the use of a stoichiometric amount of zinc or more, and the use of acetic acid as a solvent, which requires its recovery.

[0003]

An object of the present invention is to provide a method for producing thiosalicylic acid by reducing dithiosalicylic acid with a smaller amount of metal without using an organic solvent such as acetic acid.

[0004]

Means for Solving the Problems The present inventors have repeatedly studied a method for producing thiosalicylic acid by reducing dithiosalicylic acid, and as a result, dithiosalicylic acid was mixed with an alkali metal hydroxide to form an alkali metal salt. The dithiosalicylic acid is reduced in an aqueous alkali metal hydroxide solution to thiosalicylic acid by adding one or more metals selected from zinc, aluminum and tin to the aqueous solution of It has been found that thiosalicylic acid can be efficiently produced by an industrially advantageous method by precipitating the thiosalicylic acid thus obtained, and the present invention has been completed.

Hereinafter, the present invention will be described in detail. In the present invention, an alkali metal hydroxide used to convert dithiosalicylic acid into a water-soluble salt, zinc, aluminum,
There is a dual purpose alkali metal hydroxide with the alkali metal hydroxide used to react with each metal of tin. Alkali metal hydroxides that can be used for these purposes include:
There are sodium hydroxide, potassium hydroxide and the like. In use, they may be used alone or as a mixture for each purpose.

For example, for 1.0 mole of dithiosalicylic acid, 1.0 to 4.0 liters of water, preferably 1.5 to 4.0 liters
Dissolve the alkali metal hydroxide and then dithiosalicylic acid in 3.0 liters. The alkali metal hydroxide required for dissolving 1.0 mol of dithiosalicylic acid is 2.0 mol or more. Zinc, aluminum, alkali metal hydroxide for reaction with tin, zinc, aluminum, 1.0 mol or more, based on the total amount of 1.0 mol of tin,
Preferably it is 2.0-8.0 mol. Either add the above-mentioned alkali metal hydroxides in total and dissolve them first, or dissolve dithiosalicylic acid, then add and dissolve the alkali metal hydroxide to react with the metal. There are no obstacles.

In the present invention, dithiosalicylic acid 1.0
The total amount of one or more metals selected from zinc, aluminum, and tin required to reduce the mole is 0.7 to 2.0.
Is a mole. If the amount of metal is less than this, a large amount of unreduced dithiosalicylic acid remains in the product, and the use of more metal is uneconomical. The zinc, aluminum and tin are added intermittently or continuously at such a rate and quantity that they do not sink to the bottom of the reactor. Generally 1
It is preferable to add in about 0 minutes or less. When the addition time is long, the reaction rate decreases. In addition, it is preferable to use powdered zinc.

[0008] The temperature at the time of addition is adjusted to 40 ° C or lower, preferably 0 to 30 ° C. If the reaction is performed at a temperature higher than this, a large amount of unreacted dithiosalicylic acid will remain. Since the temperature rises due to the heat of reaction when the addition of the metal is started, it is preferable to control the temperature so as not to exceed 40 ° C. After completion of the addition, for example, the reaction is carried out for 20 minutes to 5 hours while maintaining the temperature at 0 to 40 ° C., to convert the alkali metal salt of dithiosalicylic acid into the alkali metal salt of thiosalicylic acid.

After completion of the reduction reaction, unreacted metal is removed by filtration. The filtrate is then acidified with a strong acid. The alkali metal salt of thiosalicylic acid in the filtrate is oxidized and easily becomes the alkali metal salt of dithiosalicylic acid again.Therefore, the operation is performed under a non-oxidizing gas atmosphere. preferable.

The strong acid used in the present invention includes sulfuric acid,
Alternatively, there is hydrochloric acid, and there is no problem in using either.
With the strong acid, the filtrate is acidified to pH 1.0-2.5,
Precipitate free thiosalicylic acid. Due to the heat of neutralization, a considerable amount of heat is generated.

[0011] Zinc, aluminum and tin react with the alkali metal hydroxide to generate hydrogen and ionize while the reduction reaction proceeds. The generated ions cause precipitation as the pH of the reaction solution decreases, and further redissolve.
For this reason, free thiosalicylic acid and hydroxide precipitate during the acidification, so that it is preferable to stir vigorously. In order to reduce the amount of zinc, aluminum and tin contained as impurities in the thiosalicylic acid of the product, it is necessary to completely dissolve the hydroxide, and the acidification is performed at pH 3 or less, preferably at pH 1.0 to 2. 5 is assumed. If the pH is 1.0 or less, it is uneconomical and disadvantageous for washing and removing chloride ions or sulfate ions.

The resulting thiosalicylic acid is collected by filtration, isolated,
Washing purification and drying are performed by a known method. Note that, in each step, in order to avoid oxidation of thiosalicylic acid, it is preferable to carry out the reaction in a non-oxidizing gas atmosphere.

[0013]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Embodiment 1 FIG. In a 100 ml four-necked flask equipped with a stirrer, thermometer and cooling tube, 20 ml of water and 93 ml
Then, 3.44 g (0.08 mol) of sodium hydroxide was charged, and after dissolving sodium hydroxide, the mixture was cooled to room temperature. Then, 3.06 g (0.01 mol) of dithiosalicylic acid was added and dissolved. While stirring, 0.65 g (0.01 mol) of zinc dust was continuously added little by little to 30.
Addition took seconds. After the addition, stirring was continued for 30 minutes to complete the reaction. The temperature before zinc addition was 28.5
C., but the exotherm continued for 3 minutes after the addition was completed,
, The temperature was lowered to room temperature of 25 ° C. Unreacted zinc was removed by filtration, and the filtrate was adjusted to pH 2 at 40 ° C. or lower using 36% hydrochloric acid to precipitate thiosalicylic acid. Filter the thiosalicylic acid, wash with water until the filtrate is neutral,
Drying under reduced pressure gave 2.77 g. The yield based on the starting material dithiosalicylic acid was 89.9%. When this was analyzed by high performance liquid chromatography, thiosalicylic acid 9
5.8%, dithiosalicylic acid 2.9%, and other impurities 1.3%.

Embodiment 2 FIG. 200 ml of water was placed in a 500 ml four-necked flask equipped with a stirrer, thermometer and cooling tube.
33.68 g (0.8 mol) of 5% sodium hydroxide was charged to dissolve sodium hydroxide, and then cooled to room temperature.
Then, 30.64 g (0.1 mol) of dithiosalicylic acid
Was dissolved. Cool to 10 ° C, 6.54g zinc dust
(0.1 mol) is divided into 0.3 to 0.4 g each 20 times,
Added every 10 seconds. The cooling was stopped and stirring was continued for 90 minutes. After filtering off unreacted zinc, at 40 ° C or less,
Acidify to pH 1.5 with 62.5% sulfuric acid. The precipitated thiosalicylic acid was collected by filtration, washed with water until the filtrate became neutral, and dried under reduced pressure to obtain 27.98 g (yield based on dithiosalicylic acid: 90.7%). When this was analyzed using high performance liquid chromatography, it was 97.1% of thiosalicylic acid, 2.3% of dithiosalicylic acid, and 0.6% of other impurities.

Embodiment 3 FIG. 200 ml of water was added to a 300 ml four-necked flask equipped with a stirrer, thermometer and cooling tube.
21.47 g (0.51 mol) of 5% sodium hydroxide was charged, and after dissolving sodium hydroxide, the mixture was cooled to room temperature. Next, 30.64 g (0.1 mol) of dithiosalicylic acid was dissolved. After cooling to 10 ° C, 3.06 g (0.11 mol) of aluminum powder was continuously added little by little to about 4
Added in minutes. The mixture was stirred for 90 minutes while maintaining the temperature at 10 ± 2 ° C. After the unreacted aluminum is filtered off, the pH is reduced to 1.5 with 40% or less using 62.5% sulfuric acid.
Until acidified. 28. Precipitated thiosalicylic acid was collected by filtration, washed with water until the filtrate became neutral, and dried under reduced pressure.
03 g (Yield based on dithiosalicylic acid: 92.5%)
I got When this was analyzed using high performance liquid chromatography, it was 94.5% of thiosalicylic acid, 4.9% of dithiosalicylic acid, and 0.6% of other impurities.

Embodiment 4 FIG. 200 ml of water was added to a 300 ml four-necked flask equipped with a stirrer, thermometer and cooling tube.
33.68 g (0.8 mol) of 5% sodium hydroxide was charged to dissolve sodium hydroxide, and then cooled to room temperature.
Then, 30.64 g (0.1 mol) of dithiosalicylic acid
Was dissolved and heated to 50 ° C. While maintaining the temperature at 50 ± 2 ° C., 6.54 g (0.1 mol) of zinc powder was added to 0.3 to 0.4.
The solution was added in increments of 25 g every 10 seconds, and then stirred for 90 minutes. After filtering off the reactive zinc, 4
At 0 ° C. or lower, acidification was performed using 36% hydrochloric acid until the pH reached 2.0. The precipitate was collected by filtration, washed with water until the filtrate became neutral, and dried under reduced pressure to obtain 29.88 g (yield based on dithiosalicylic acid: 96.9%). When this was analyzed using high performance liquid chromatography, it was 80.4% of thiosalicylic acid, 18.8% of dithiosalicylic acid, and 0.8% of other impurities.

Embodiment 5 FIG. 200 ml of water was placed in a 500 ml four-necked flask equipped with a stirrer, thermometer and cooling tube.
21.47 g (0.51 mol) of 5% sodium hydroxide was charged, and after dissolving sodium hydroxide, the mixture was cooled to room temperature. Next, 30.64 g (0.1 mol) of dithiosalicylic acid was dissolved. After cooling to 10 ° C., 3.06 g (0.11 mol) of aluminum powder was continuously added little by little for about 5 minutes.
Added in minutes. The reaction was continued for 120 minutes while maintaining the temperature at 10 ± 2 ° C. After filtering off unreacted aluminum,
Acidification was performed at 40 ° C. or lower using 62.5% sulfuric acid until the pH reached 3.0. The resulting precipitate was collected by filtration, washed with water until the filtrate became neutral, and dried under reduced pressure to obtain 30.04 g (yield based on dithiosalicylic acid of 97.4%). When this was analyzed using high performance liquid chromatography, thiosalicylic acid 90.1% and dithiosalicylic acid 1.
8% and other impurities were 8.1%.

Embodiment 6 FIG. 200 ml of water was added to a 300 ml four-necked flask equipped with a stirrer, thermometer and cooling tube.
After 39.61 g (0.60 mol) of 5% potassium hydroxide was charged and potassium hydroxide was dissolved, the mixture was cooled to room temperature. Next, 30.64 g (0.1 mol) of dithiosalicylic acid was dissolved. Cool to 25 ° C and tin powder 11.87g
(0.10 mol) was added little by little over a period of about 5 minutes. The reaction was continued for 90 minutes while maintaining the temperature at 25 to 30 ° C. After filtering off unreacted tin, at 40 ° C or less, 6
Acidify to pH 1.1 with 2.5% sulfuric acid. The resulting precipitate was collected by filtration, washed with water until the filtrate became neutral, and dried under reduced pressure to obtain 29.94 g (yield based on dithiosalicylic acid: 97.1%). When this was analyzed using high performance liquid chromatography, it was 92.1% of thiosalicylic acid, 0.7% of dithiosalicylic acid, and 7.2% of other impurities.

[0020]

As described above, according to the method of the present invention, thiosalicylic acid can be produced by reducing dithiosalicylic acid without using an organic solvent and with a small amount of metal. It is useful as an industrial production method.

Claims (3)

[Claims] In an aqueous alkali metal hydroxide solution, dithiosalicylic acid is selected from zinc, aluminum and tin.
A method for producing thiosalicylic acid, comprising reducing an alkali metal salt of thiosalicylic acid with an at least one kind of metal to obtain an aqueous solution of an alkali metal salt of thiosalicylic acid, followed by acidification with a strong acid for precipitation. 2. The method according to claim 1, wherein the temperature during the reduction reaction is 40 ° C. or less. 3. The method according to claim 1, wherein the pH at the time of precipitation by acidification with a strong acid is 2.5 or less.