JPS61118378A - Production of tetrachlorophthalic anhydride - Google Patents

Abstract

PURPOSE:To produce the titled compound facilitating the reuse of reaction solvent and the removal of the solvent from the product, by reacting phthalic anhydride with chlorine as using chlorosulfonic acid as the reaction solvent. CONSTITUTION:The objective compound is produced by dissolving phthalic anhydride in chlorosulfonic acid used as the reaction solvent at a concentration of <=40 wt%, especially 5-20 wt%, and introducing chlorine gas into the solu tion at 50-200 deg.C, preferably 70-130 deg.C, preferably in the presence of a catalyst (e.g. aluminum chloride, ferric chloride, etc., especially iodine) thereby reacting the chlorine gas with the phthalic anhydride. The amount of the chlorine gas is 1-3 times mol, especially, 1.1-2 times mol-of the stoichiometric amount (4 times mol of the charged phthalic anhydride). After the reaction, the reaction liquid is cooled to separate the objective compound in the form of crystal, and the remaining liquid is reused as the reaction solvent. The solvent attached to the product can be removed easily by drying.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing tetrachlorophthalic anhydride, which is useful as a raw material for flame-retardant polymers and phthalocyanine-based organic pigments, and more specifically, a method for producing tetrachlorophthalic anhydride, which is useful as a raw material for flame-retardant polymers and phthalocyanine organic pigments. The present invention relates to a method for producing tetrachlorophthalic anhydride by chlorinating phthalic anhydride with chlorine gas in a solvent.

[Conventional technology]

The general method for producing tetrachlorophthalic anhydride is to chlorinate phthalic anhydride with chlorine gas.
Fuming sulfuric acid is usually used as the reaction solvent.

[Problem that the invention seeks to solve]

The method of producing tetrachlorophthalic anhydride using fuming sulfuric acid has the following drawbacks.

That is, when phthalic anhydride is chlorinated in fuming sulfuric acid, hydrogen chloride is generated, and this hydrogen chloride immediately reacts with sulfur dioxide in the fuming sulfuric acid to produce chlorosulfonic acid as a by-product. The amount produced is more than 1.5 times that of the target product, tetrachlorophthalic anhydride, which is unfavorable from an industrial perspective.Moreover, iodine is sometimes used as a catalyst in this reaction. In that case, it is not easy to separate chlorosulfonic acid by distillation because iodine is sublimable and easily mixed in. Also, in this method, after the reaction is completed, the solvent is a mixture of chlorosulfonic acid and sulfuric acid. However, if such a mixed solution is used again as a reaction solvent after separating the crystals (target product), the reaction will be extremely slow.

(Measures to Solve the Problem Y&) As a result of intensive study, the present inventors have found that using chlorosulfonic acid as a reaction solvent and reacting phthalic anhydride with chlorine gas eliminates the above drawbacks and allows We have discovered that chlorophthalic anhydride can be produced, and have arrived at the present invention.

The method for producing tetrachlorophthalic anhydride according to the present invention will be described in detail below based on its implementation.

The present invention is carried out by first dissolving phthalic anhydride in chlorosulfonic acid, which is a reaction solvent, and then supplying chlorine gas to this solution to cause the phthalic anhydride and chlorine gas to react.

The concentration of phthalic anhydride in chlorosulfonic acid is 40%
Below, it is particularly preferable to set it as 5-201% by weight.

Further, the amount of chlorine gas used in the reaction is 1 to 3 times the mole, preferably 1.1 to 2 times the theoretical amount (4 times the mole of the charged amount of phthalic anhydride). It is advantageous to reduce the amount of chlorine gas supplied as the reaction progresses in order to increase the chlorine reaction rate.

In addition, as a catalyst, acetic acid, aluminum chloride, ferric chloride, antimony pentachloride, etc. can be used.
Among these catalysts, it is most preferable to use iodine, and the amount used is 0.1 based on the amount of phthalic anhydride charged.
When iodine is used as a catalyst, preferably in an amount of 1 to 7ii% by weight, iodine easily reacts with chlorine in this reaction system to form iodine chloride and iodine trichloride, and this form The boiling point and melting point of these iodine chlorides are close to each other, and when the reaction is carried out below the boiling point of chlorosulfonic acid, there is little reflux, so the iodine chloride becomes solid near the exhaust gas outlet of the reactor. Therefore, it is necessary to return this solid to the reaction solution by vigorously stirring the reaction solution from time to time and washing it off. If this is not done, the reaction rate will decrease.

The reaction temperature is preferably 50 to 200°C, particularly 70 to 130°C. Also, the reaction is carried out at normal pressure or under elevated pressure, and there is an advantage that the reaction rate is increased if carried out under elevated pressure.

〔Example〕

The present invention will be explained in more detail with reference to Examples below.

Example 1 Anhydrous phthalate 1 in an 11 volume stainless steel autoclave!
50 g (0.34 mol), chlorosulfonic acid 500
g and 1.5 g of iodine as a catalyst were heated to 100°C.Then, the gauge pressure was set to 5g in the autoclave.
Chlorine gas was introduced until the temperature reached /-, and the reaction was started by stirring. Thereafter, the operation was repeated every 30 minutes to release gas until the gauge pressure in the autoclave reached 1 kg/-, and instead introduce chlorine gas until it reached 5 g/clI, and the reaction was carried out for 10 hours.

After the reaction is complete, the autoclave is evacuated and brought to normal pressure at 0.
Next, dissolved chlorine in the reaction solution was expelled with nitrogen gas, and then the reaction solution was cooled. 1 crystal precipitated! After filtering under a stream of bare air and washing with a small amount of chlorosulfonic acid, the funnel containing the crystals was heated to 60°C, and nitrogen was passed through the funnel for drying to obtain crystals of the desired product, tetrachlorophthalic anhydride. . The yield of this tetrachlorophthalic anhydride is 62.9
g, the melting point was 255-257.5°C.

Additionally, 34 g (0°23 mol) of phthalic anhydride was added to 500 g of the filtrate, and chlorine gas was introduced in the same manner as the first time.
After the reaction was completed for 8 hours, the same treatment as the first time was carried out to obtain crystals of tetrachlorophthalic anhydride. The yield of this tetrachlorophthalic anhydride was 62.2 g, and the melting point was 254-257°C.

Example 2 200 g of phthalic anhydride (1,
35 mol), 2000 g of chlorosulfonic acid, and 7 g of iodine as a catalyst were added and stirred.Next, this was heated to 100°C in an oil bath, and chlorine gas was introduced therein with stirring to start the reaction. At this time, starting with the chlorine gas flow rate,
4 hours at cc/sin, then 10 at 130cc/sin
The reaction was carried out by changing the time stepwise, ending with 70 cc/+*in for 12 hours.

After the reaction was completed, dissolved chlorine in the reaction solution was expelled with nitrogen gas, and the same treatment as in Example 1 was carried out to obtain crystals of tetrachlorophthalic anhydride. The yield of this tetrachlorophthalic anhydride was 261 g, and the melting point was 254-256.5°C.

In addition, 135 g of phthalic anhydride (0.9
1 mol) was added thereto, and the reaction was carried out again as follows.

After stirring and dissolving phthalic anhydride in the filtrate, the mixture was heated to 100°C.
Add chlorine gas at 130cc/win for 8 hours while stirring.
After the reaction was completed, the same treatment as the first time was carried out to obtain crystals of tetrachlorophthalic anhydride. The yield of this tetrachlorophthalic anhydride was 258 g.

The melting point was 254-257°C.

Comparative Example 1 200 g of phthalic anhydride (1,
35 mol), 2000 g of fuming sulfur and 7 g of iodine as a catalyst were added and stirred.
The reaction mixture was heated to 00°C, and chlorine gas was introduced therein with stirring to start the reaction. When chlorine gas was first introduced at 225 cc/sin for 4 hours and then at 130 cc/sin for 10 hours, crystals began to precipitate, and around this time the chlorine gas inlet of the flask became noticeably clogged. Chlorine gas flow rate 7
The reaction rate was reduced to 0 cc/win, and the reaction was continued for an additional 6 hours while occasionally interrupting the reaction to remove clogging of the chlorine gas inlet. Then, the end of the reaction is determined from the analytical value of unreacted chlorine in the exhaust gas [i! The company recognized the situation and stopped introducing chlorine gas.

After the reaction was completed, dissolved chlorine in the reaction solution was expelled with nitrogen gas, the reaction solution was cooled, and the precipitated crystals were filtered off. The crystals were washed with a small amount of fuming sulfuric acid, and since the sulfuric acid content is nonvolatile and difficult to remove, they were further washed with water and then dried to obtain crystals of tetrachlorophthalic anhydride. The yield of this tetrachlorophthalic anhydride was 245 g - the melting point was 232-25
The temperature was 2°C. Further, when this tetrachlorophthalic anhydride was analyzed by gas chromatography, it was found to contain 3.5% dichloride and 5.5% trichloride.

In addition, 135 g of phthalic anhydride (0.9
1 mol) was added thereto, and the reaction was carried out again as follows.

After stirring phthalic anhydride to the filtrate, it was heated to 10° C., and chlorine gas was introduced into the filtrate with stirring at 130 cc/win for 8 hours and 70 cc/+++in for 12 hours. When the crystals obtained by pressurizing this into ice water were analyzed by gas chromatography, the reaction was very slow, and compared to the second reaction in Example 2, the reaction was about 1/6 It turned out to be speed.

Comparative Example 2 A reaction was started in the same manner as Comparative Example 1 except that the reaction temperature was changed to 150°C. 225cc/+m including chlorine gas
After introducing chlorine gas for 4 hours at 130 cc/+*in for 10 hours, the analysis of unreacted chlorine in the exhaust gas indicated that the reaction had ended, and the introduction of chlorine gas was stopped. After expelling dissolved chlorine in the reaction solution with gas, the reaction solution was cooled and the precipitated crystals were filtered off. This crystal was treated in the same manner as in Comparative Example 1 to obtain crystals of tetrachlorophthalic anhydride. The yield of this tetrachlorophthalic anhydride was as small as 226g, and the melting point was 249-253°5°C.
Furthermore, when this tetrachlorophthalic anhydride was analyzed by gas chromatography, it was found to contain 2.1% trichloromonoiodophthalic anhydride and 0.5% hexachlorobenzene.

〔Effect of the invention〕

According to the method for producing tetrachlorophthal all anhydride of the present invention, there is no problem of by-products as in the conventional method using fuming sulfuric acid as a reaction solvent, and the liquid crystallized after the reaction is used as a reaction solvent as it is. In addition, in the case of the conventional method using fuming sulfuric acid, the sulfuric acid content is non-volatile, so the obtained crystals must be thoroughly washed with water after separation from the solvent, whereas the method of the present invention can be reused. In this case, since the chlorosulfonic acid is volatile, the solvent can be removed by drying, so the washing step can be omitted, which is very advantageous in terms of equipment for the separation process, its material, and equipment related to wastewater treatment.

Claims (1)

[Claims] A method for producing tetrachlorophthalic anhydride, which comprises reacting phthalic anhydride and chlorine gas using chlorosulfonic acid as a reaction solvent.