JPH0524152B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high purity 2-mercaptobenzothiazole.

2-Mercaptobenzothiazole is not only useful as a vulcanization accelerator in its own right, but is also a starting material for thiazole-based vulcanization accelerators. This compound is produced industrially, for example, by reacting a mixture of aniline, carbon dioxide, and sulfur in an appropriate molar ratio at high temperature and pressure.

The crude 2-mercaptobenzothiazole produced in this way contains many impurities such as side reaction products and reaction intermediates, unreacted aniline, and even a resinous substance of unknown structure. As it is, it is impossible to use it for many purposes.

As a purification method for such a crude product, after suspending the crude product in an aromatic hydrocarbon,
A method of obtaining 2-mercaptobenzothiazole as an aqueous alkaline salt solution by dissolving the wet cake in an aqueous caustic solution and separating the aromatic hydrocarbon phase (Japanese Patent Publication No. 50-24312), in which the crude product is molten or solidified. A method in which aromatic hydrocarbons or aromatic amines are added to the aqueous solution to separate the aromatic hydrocarbon phase or the aromatic amine phase from the alkaline aqueous solution phase (Japanese Patent Laid-Open No. No. 1983-63076) etc. have been proposed.

However, both of these methods use an alkaline aqueous solution as a purification medium and have associated problems.

The present inventors solved this problem by first cooling and solidifying the high-temperature molten crude 2-mercaptobenzothiazole into flakes, and then washing with an aromatic hydrocarbon or a mixture thereof with an aromatic base. We proposed a purification method characterized by the following.

The present invention takes this method one step further, omitting the cooling and solidification step, and obtaining a product of extremely high purity. The liquid is supplied to a continuous crystallizer in its liquid state without being immediately cooled and solidified, and then cooled without a solvent to precipitate crystals and settle in the device, and the crystals that settle at the bottom of the device are melted. , a method for producing 2-mercaptobenzothiazole, characterized in that a part of the melt is extracted as a product, and the remainder is continuously brought into contact with the precipitated crystals as a reflux liquid in the same apparatus for purification. .

The present invention will be explained in further detail.

First, the crude 2-mercaptobenzothiazole purified by the method of the present invention is a high-temperature molten product obtained by a commonly used industrial method in which aniline, carbon disulfide, and sulfur are reacted at high temperature and high pressure. .

The crude product is precooled to an appropriate temperature if necessary, and then treated in a continuous crystallizer to separate and refine high purity 2-mercaptobenzothiazole and the residual liquid.

The continuous crystallizer used in the present invention may be any countercurrent continuous crystallization purification device. As shown in the drawing, one example of such a crystallizer includes a rigid column 1 with a raw material supply port 2 at an appropriate position, for example, a cooling means 3 such as a jacket at the top, a heating means 4 at the bottom, and a product outlet. 6. It has a structure in which a residual liquid outlet 5 is provided at the top, and a stirrer 7 is further provided for stirring in the same plane to maintain the crystals in a fluid state.

The optionally precooled crude product is charged through the suspension of the vertical column and the stirrer is driven. Cooler 8
A refrigerant is supplied to the jacket part 3 through the refrigerant inlet 9, and cooling of the liquid in the column is started. The refrigerant discharged from the discharge port 10 is returned to the cooler and used for circulation.

As the temperature of the refrigerant is lowered, the temperature of the liquid in the column gradually decreases, and when it reaches around the crystal precipitation temperature of the liquid in the column, crystals of 2-mercaptobenzothiazole begin to precipitate. The precipitated crystals settle because they have a higher density than the surrounding liquid.

The temperature of the cooling zone containing the jacket is further reduced and then held at a constant temperature. The lower the temperature in the cooling zone, the more crystals will be precipitated and the higher the product yield will be. However, if the temperature is lowered too much, the sedimentation of the crystals will deteriorate and the entire liquid in the column in the cooling zone may solidify, which may affect the composition of the raw material. There is a more appropriate level.

Since crystals gradually accumulate in the bottom area of the column, use of the heater is started at an appropriate time. The heater may be any suitable heater that uses steam, high-temperature heat medium, electric power, or the like as a heat source.

When heating begins, the crystals accumulated at the bottom of the column melt and become liquid, rising through the column. During the rising process, the liquid and the settling crystals come into contact with each other in a countercurrent flow, the mother liquor adhering around the crystals is washed away, and the impurities adsorbed on the surface of the crystals are desorbed. At the same time, new crystals are deposited on the surface of the sedimenting crystal in an amount corresponding to the temperature rise of the crystal itself due to sedimentation.

In this way, purification of the settling crystals proceeds by countercurrent contact with the rising liquid. As the purity of the bottom liquid increases, the temperature of the bottom liquid increases.
When the target product's freezing point is reached, the bottom liquid begins to be withdrawn.

The withdrawal amount is selected so as to leave a sufficient amount of liquid rising in the column to ensure the above-mentioned purification effect even after the withdrawal is started. Adjust the heating amount if necessary.

Once the extraction begins, charging of the liquid crude product begins. The charging amount depends on the composition of the crude product, the cooling temperature in the cooling area,
It is determined according to the amount of purified 2-mercaptobenzothiazole extracted. If necessary, pre-cool the liquid crude product.

The residual liquid is extracted from the residual liquid outlet at the top of the tower by overflow. The content of 2-mercaptobenzothiazole in the residual liquid varies depending on the temperature inside the tower in the cooling zone, but it can be extracted outside the system as necessary. It can be recovered by known methods. Since treatment using a continuous crystallizer does not involve chemical changes, it is possible to bring the yield of 2-mercaptobenzothiazole close to the theoretical value by adopting an appropriate method for treating the residual liquid.

In this way, the present invention charges a high-temperature liquid crude product into a continuous crystallizer, and converts the 2-mercaptobenzothiazole precipitated from the melt into the high-purity liquid 2-mercaptobenzothiazole rising from the bottom. It is characterized by being purified by contacting with a countercurrent.

Regarding the previously proposed method for purifying 2-mercaptobenzothiazole, the inventors suggested the presence of impurities in the crude product that have the property of strongly adsorbing to the surface of 2-mercaptobenzothiazole crystals. The method of the present invention makes it possible to obtain high-purity products that could not be obtained conventionally.As the crystals descend in the continuous crystallizer, they are purified by countercurrent flow with the high-temperature, high-purity liquid rising from the bottom. It is much more natural to think that this is due to the precipitation of new crystals on the crystal surface through contact and the accompanying desorption of adsorbed impurities, which are extremely effective, than an explanation that only considers the cleaning effect of the rising liquid.

In addition, crystals precipitated from a melt are usually larger than crystals precipitated from a solution, and the method of the present invention, in which crystals are precipitated directly from a melt in a continuous crystallizer, has a surface area of the crystal that adsorbs impurities. It is also not unreasonable to think that it has the effect of reducing the

As described above, the first feature of the present invention is to directly precipitate 2-mercaptobenzothiazole crystals from a high-temperature melt in a continuous crystallizer to obtain crystals in a shape that is convenient for washing and purification. The precipitated crystals are brought into contact with high-temperature, high-purity liquid 2-mercaptobenzothiazole in a countercurrent flow that rises in the column while maintaining the desired shape, thereby washing the crystals, depositing new crystals on the crystal surfaces, and removing the crystals from the crystal surfaces. The second feature is to utilize the purification effect consisting of desorption of adsorbed impurities.

Example Crude 2-mercaptobenzothiazole (purity 81%, melting point 145.8-177.3°C) obtained by high-temperature, high-pressure reaction of aniline, carbon disulfide, and sulfur was melted and placed in the continuous crystallizer shown in the drawing. I loaded it.

In steady state, the temperature at the product outlet at the bottom of the column is 181℃, the temperature at the residual liquid outlet at the top is 125℃, and the jacket temperature is adjusted to maintain a gentle temperature gradient rising from the bottom of the jacket toward the bottom of the column. Continuous crystallization was performed by adjusting the heater temperature and stirrer rotation speed.

The column diameter of the continuous crystallizer is 80mmφ, and the raw material charging speed is
After continuous operation for 8 hours at 550g/Hr, product withdrawal rate of 200g/Hr, residual oil withdrawal rate of 350g/Hr, and stirrer rotation speed of 60rpm, a product with 2-mercaptobenzothiazole purity of 99.3% was stably obtained. Ta. The content of 2-mercaptobenzothiazole in the residual oil was 70.5%.

[Brief explanation of the drawing]

The drawing shows an example of a continuous crystallizer. Code explanation, 1... Rigid tower, 2... Raw material supply port,
3... Cooling means, 4... Heating means, 5... Residual liquid discharge, 6... Product outlet.

Claims (1)

[Claims] 1 High temperature of aniline, carbon disulfide and sulfur,
Crude 2-mercaptobenzothiazole in a high-temperature molten state obtained by high-pressure reaction is charged into a continuous crystallizer, cooled without solvent to precipitate crystals, and allowed to settle in the continuous crystallizer. The crystals that settle at the bottom are melted, a part of the melt is extracted as a product, and the remainder is used as a reflux liquid in the same device for purification and is brought into continuous contact with the crystals that settle. Method for producing 2-mercaptobenzothiazole.