JPH0678330B2 - Method for producing 2-chlorobenzothiazoles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a novel method for producing 2-chlorobenzothiazoles.

More specifically, the formula (I) [In the formula, R represents any one of a methyl group, a halogen group and a hydrogen atom. ] The mixture of 2-mercaptobenzothiazole and sulfur represented by the formula (II) is reacted with chlorine in the presence or absence of an organic solvent to give a compound of the formula (II) [In the formula, R represents any one of a methyl group, a halogen group and a hydrogen atom. ] The present invention relates to a method for industrially and economically producing 2-chlorobenzothiazoles. 2-Chlorobenzothiazole is a compound which has a highly reactive chlorine atom at the 2-position and is an important compound as an intermediate raw material for pharmaceuticals and agricultural chemicals such as plant protection agents.

(B) Conventional technology Conventionally, as a method for producing 2-chlorobenzothiazole, 1), a method of heating 2-mercaptobenzothiazoles, phosphorus pentachloride and phosphorus oxychloride. (Seizo Takahashi, Hyōzo Taniyama, Pharmaceutical Journal 67,42 (1947)) 2), a method of reacting phenyl isocyanate with phosphorus pentachloride. (Large Organic Chemistry, Volume 15, P.152, supervised by Mitsuo Kotake, Asakura Shoten, (1958)) 3), A method of reacting sulfuryl chloride on 2-mercaptobenzothiazoles. (Chemical abstract, 61,
4174) 4), Method for heating 2-mercaptobenzothiazole and -sulfur chloride (G, W, Watt, Journal of Organic Chemistry (J.Org.chem.) 4,436 (1939)) Are known. However, in producing 2-chlorobenzothiazole on an industrial scale and economically, it has the following drawbacks.

That is, in any of the methods 1) to 3), since the raw material is expensive and the raw material is difficult to handle, it cannot be an industrial manufacturing method.

Regarding 4), the raw material is a relatively inexpensive manufacturing method,
Although it can be industrialized, it has a poor yield and is a raw material-sulfur chloride is poor in storage stability and is a compound with an offensive odor and an irritating odor, which makes it difficult to handle.

(C) Problems to be Solved by the Invention When 2-chlorobenzothiazole is produced by the conventional method described above, other than 2-chlorobenzothiazole, which is the target product, in the reaction mixture after completion of the reaction. Hydrogen chloride,
It contains high-viscosity tar substances containing sulfur, sulfur chloride, and benzothiazole-based polymer-like substances. If 2-chlorobenzothiazole is subjected to distillation purification in this state, decomposition of 2-chlorobenzothiazole is promoted during distillation, resulting in a decrease in yield and a decrease in product purity.
A large amount of malodorous waste, which is difficult to handle, is produced as a by-product, and environmental pollution and pollution treatment costs are a problem.

(C) Structure of the Invention In order to overcome the above-mentioned industrial drawbacks, the present inventors have
As a result of earnest research, the present invention was found by finding an industrially and economically advantageous production method of 2-chlorobenzothiazole.

That is, in the presence of 2-mercaptobenzothiazole and cheap sulfur, chlorine is introduced at room temperature or with heating to carry out a solid-gas reaction or a reaction in a suspended state or a dissolved state of an organic solvent in advance. It is a thing. It is presumed that SxCl ₂ active in the reaction system is synthesized and promptly reacted with 2-mercaptobenzothiazole to produce 2-chlorobenzothiazole in good yield.

Further, in the method for producing 2-chlorobenzothiazole, in order to take out with high purity and high yield and to minimize the amount of waste, after-reaction hydrogen chloride and by-produced unreacted sulfur chloride are produced. Is neutralized with a dilute alkali metal carbonate, dilute alkali hydroxide, dilute alkali hydrogen carbonate to precipitate as sulfur, which is then separated and removed. Further, in order to take out 2-chlorobenzothiazole adhering to the separated sulfur and 2-chlorobenzothiazole cloudy in neutralized water, an organic solvent which is incompatible with water or has a low compatibility, for example, By adding benzene, toluene, xylene, carbon tetrachloride, chloroform, dichloroethane, dichloromethane, etc., 2-chlorobenzothiazole can be efficiently extracted and separated into the organic layer. It is also possible to add the present extraction solvent in advance at the start of the reaction and allow it to react.

By performing the above operation, the sulfur dissolved in the tar-like substance is precipitated as a solid and separated and removed.

Next, the organic solvent in the organic layer is recovered by distillation, and then vacuum distillation or recrystallization is performed to obtain the desired product, 2-chlorobenzothiazole. Further, the sulfur separated and removed can be reused as a raw material sulfur for the next reaction, and even if it is reused repeatedly, the purity and yield of the product are not affected at all, so that the waste is significantly reduced. It is possible to reduce and economically manufacture.

As described above, the present inventors provide a method for producing 2-chlorobenzothiazole which is extremely economical and has little industrial waste.

(D) Examples Hereinafter, the present invention will be specifically illustrated by examples and comparative examples, but the present invention is not limited thereto.

Example 1 (Synthesis of 2-chlorobenzothiazole) In a 300 ml four-necked flask equipped with a thermometer, a stirrer, a gas introduction tube, and a condenser connected to a gas absorption bottle, 2-mercaptobenzothiazole 80 g'powder sulfur 37 g. ′ Is charged and 41 g of chlorine is introduced. During that time, the reaction temperature rose to 96 ° C. due to the heat of reaction. After the introduction of chlorine, further stirring is carried out to complete the synthesis of 2-chlorobenzothiazole.

Then, an aqueous solution of sodium carbonate is gradually poured into the reaction product for neutralization. At that time, since sulfur is deposited,
Separate them separately. Next, in order to recover the 2-chlorobenzothiazole attached to the sulfur separated separately, toluene was used.
Wash the sulfur with 100 ml. The sulfur at this time was 43 g '.

After that, the aqueous layer and the toluene layer in which 2-chlorobenzothiazole was extracted and dissolved were separated, and toluene was distilled and recovered, and distilled at 10 torr to obtain 2 of the target colorless transparent liquid.
63 g (77.6% yield) of chlorobenzothiazole are obtained.

The elemental analysis values were as follows.

Analytical value (%) C: 49.32 H: 2.20 N: 8.20 S: 18.50 Calculated value (%) C: 49.56 H: 2.36 N: 8.26 S: 18.88 The analytical value by gas chromatography (FID) is
The purity was 99.2%.

Example 2 (Synthesis of 2-chlorobenzothiazole) In the same manner as in Example 1, 2-mercaptobenzothiazole 80
g ′ and 43 g ′ of sulfur obtained in Example 1 were charged and chlorine was added.
Introduce 48g '. Using a caustic soda solution for neutralization,
Use 100 ml of ethylene dichloride as the extraction solvent.

By distillation, 61 g '(yield 75.1%) of 2-chlorobenzothiazole, the target product, was obtained.

Analysis by gas chromatography (FID) shows a purity of 99.
It was 2%.

Example 3 (Synthesis of 2,5-dichlorobenzothiazole) 80 g of 5-chloro-2-mercaptobenzothiazole and 30.5 g of powdered sulfur are charged and 34 g 'of chlorine is introduced.

The procedure up to neutralization with the apparatus and the sodium carbonate aqueous solution is carried out in the same manner as in Example 1, and after neutralization, 100 ml of toluene is added to give 2,5
Extract the dichlorobenzothiazole. Toluene was separated and recovered by distillation, and recrystallized with acetone to give the desired product, 2,5-dichlorobenzothiazole, as 5
4 g (yield 67%, melting point 69-71 ° C.) was obtained.

Gas chromatographic (FID) analysis shows a purity of 98.
It was 1%.

Example 4 (Synthesis of 2,5-dichlorobenzothiazole) 80 g of 5-chloro-2-mercaptobenzothiazole, 31 g of powdered sulfur and 100 ml of monochlorobenzene were charged and chlorine 34
introduce g.

After the reaction, the organic layer is neutralized with an aqueous solution of sodium carbonate, and monochlorobenzene is separated and recovered by distillation.

Recrystallization from acetone gave 56 g of the target product, 2,5-dichlorobenzothiazole (yield 69%, melting point 69-71).
C) obtained. The analysis value by gas chromatography (FID) was 99.0% in purity.

Comparative Example 2-mercaptobenzothiazole 80 g to sulfur monochloride 71 g
Is added dropwise and the mixture is stirred again to complete the reaction. After the reaction
By distillation, 51 g (yield 63%) of the desired product, 2-chlorobenzothiazole, is obtained.

Gas chromatographic (FID) analysis shows a purity of 98.
It was 0%. The amount of the by-product of the distillation residue was much larger than that of the example.

(E) Effect of the Invention From the examples, the present invention is useful as a highly economical synthesis method and purification method for 2-chlorobenzothiazoles.

Claims (2)

[Claims] 1. A compound represented by the formula (II), which comprises reacting a mixture of 2-mercaptobenzothiazoles represented by the formula (I) and sulfur with chlorine in the presence or absence of an organic solvent. A method for producing 2-chlorobenzothiazoles. [In the formulas (I) and (II), R represents a methyl group, a halogen group or a hydrogen atom. ] 2. A composition obtained by reacting chlorine with a mixture of 2-mercaptobenzothiazoles represented by the formula (III) and sulfur, to obtain a diluted alkali hydroxide, a diluted alkali metal carbonate or a diluted carbonate. A method for producing 2-chlorobenzothiazoles represented by the formula (IV), which comprises washing with alkali hydrogen and then extracting with an organic solvent. [In the formulas (III) and (IV), R represents a methyl group, a halogen group or a hydrogen atom. ]