CN103012124A - Preparation method of 3,6-dichloro-2-hydroxybenzoic acid - Google Patents

Abstract

The invention discloses a preparation method of 3,6-dichloro-2-hydroxybenzoic acid, which comprises the following steps in sequence: 1) Salt formation of 2,5-dichlorophenol; 2) Carboxylation: making 2,5-dichlorophenol Chlorophenol salt solution is transferred to the autoclave, add co-catalyst, then pass _CO2 to carry out high-pressure carboxylation reaction, get the reaction product containing 3,6-dichloro-2-hydroxybenzoate; co-catalyst is made of carbonic acid Composed of potassium and activated carbon; 3) Refining: Cool the reaction product containing 3,6-dichloro-2-hydroxybenzoate obtained in step 2) to room temperature, add alkali solution, adjust the pH to 11-13, and stir Evenly, filter and recover activated carbon, take the water phase after the filtrate is layered; add acid solution to the water phase, adjust the pH to 1-3, recover 2,5-dichlorophenol through steam distillation, cool and crystallize, and filter and dry to obtain 3 ,6-Dichloro-2-hydroxybenzoic acid.

Description

The preparation method of 3,6-dichloro-2-hydroxybenzoic acid

technical field

The invention belongs to a dicamba intermediate production process and relates to a synthesis method of 3,6-dichloro-2-hydroxybenzoic acid.

Background technique

3,6-dichloro-2-hydroxybenzoic acid, 3,6-dichlorosalicylic acid, English name 3,6-Dichlorosallicylic Acid, structural formula:

。

.

3,6-dichloro-2-hydroxybenzoic acid is an intermediate in the preparation of the pesticide herbicide dicamba (3,6-dichloro-2-methoxybenzoic acid). Dicamba is a benzoic acid series herbicide first developed by the former American Siebel Chemical Company. With the prohibition and restricted use of chlorsulfuron and metsulfuron-methyl preparations, the demand for dicamba will increase, and the market prospect is promising. At present, the global sales volume of dicamba is about 15,000 t/year, and its production is mainly concentrated in Germany's BASF company and Switzerland's Sandoz company. In China, it is mainly Zhejiang Shenghua Biotech Co., Ltd. and Yangnong Chemical.

The current process for synthesizing 3,6-dichloro-2-hydroxybenzoic acid is generally a solvent high-pressure carboxylation method, namely the klobe-schmitt reaction. That is, under alkaline conditions, 2,5-dichlorophenol forms phenoxide, and then in an organic solvent, a catalyst is added, and _CO2 is introduced to carry out carboxylation reaction to generate 3,6-dichloro-2-hydroxybenzoic acid salt, and finally add water to the reaction mixture, add acid to the water phase product to acidify, separate and recover unreacted 2,5-dichlorophenol by steam distillation, and obtain pure 3,6-dichloro-phenol by suction filtration and drying 2-Hydroxybenzoic acid solid. The reaction is divided into three steps:

In the kolbe-schmitt reaction, potassium carbonate or sodium carbonate are often used as catalysts in the high-pressure carboxylation of phenates. And for 2,5-dichlorophenate, use salt of wormwood as catalyst than the effect with sodium carbonate is much better. Therefore, in the industrial production of 3,6-dichloro-2-hydroxybenzoic acid by the kolbe-schmitt reaction, potassium carbonate is used as a catalyst to catalyze the carboxylation reaction.

Although the existing technology improves the production process of 3,6-dichloro-2-hydroxybenzoic acid from different aspects, it mainly focuses on improving the yield of the reaction and reducing the reaction cost. In the existing technology, the yield of this reaction is about 45%. To increase the yield, the requirements for technological production are very high, and it is difficult to realize in industry. In this reaction, unreacted raw materials can be recovered by steam distillation, and other raw materials are relatively cheap, so the consumption of catalyst potassium carbonate accounts for a large part of the cost of this reaction. Therefore, if the consumption of potassium carbonate is reduced, the cost of this reaction can be reduced, thereby reducing the production cost of the herbicide dicamba. But, according to prior art, if reduce the consumption of potassium carbonate, can cause the unfavorable result that occurs reaction yield to reduce.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing 3,6-dichloro-2-hydroxybenzoic acid with low cost and high yield.

In order to solve the problems of the technologies described above, the invention provides a kind of preparation method of 3,6-dichloro-2-hydroxybenzoic acid, comprising the following steps successively:

1) Salt formation of 2,5-dichlorophenol:

Dissolving 2,5-dichlorophenol in alkali solution for salt-forming reaction, then adding an organic solvent and mixing evenly to obtain a mixed solution; dehydrating the mixed solution to obtain a 2,5-dichlorophenol salt solution; 2,5 -The mol ratio of dichlorophenol and alkali is 1:0.9～1.1;

2), carboxylation:

Transfer the 2,5-dichlorophenolate solution to the autoclave, add a co-catalyst, and then pass in _CO2 for high-pressure carboxylation reaction to obtain a reaction containing 3,6-dichloro-2-hydroxybenzoate product; the reaction temperature is 140~160°C, the reaction pressure is 6~8Mpa, and the reaction time is 6~12h; the co-catalyst is composed of potassium carbonate and activated carbon, and the mass ratio of potassium carbonate to 2,5-dichlorophenol is 0.01~0.2 :1 (preferably 0.04~0.1:1); the mass ratio of activated carbon to 2,5-dichlorophenol is 0.01~0.2:1 (preferably 0.04~0.2:1);

3), refined:

After cooling the reaction product containing 3,6-dichloro-2-hydroxybenzoate obtained in step 2) to room temperature (generally 10~25°C), add alkaline solution to adjust the pH to 11~13 (preferably pH12), stir evenly, filter and recover activated carbon, take the water phase after the filtrate is separated; add acid solution to the water phase, adjust the pH to 1~3, recover 2,5-dichlorophenol by steam distillation (steam distillation , until no more 2,5-dichlorophenol is distilled out), after cooling, it crystallizes naturally, and is filtered and dried to obtain 3,6-dichloro-2-hydroxybenzoic acid.

As an improvement of the preparation method of 3,6-dichloro-2-hydroxybenzoic acid of the present invention: in step 1): the mixed solution is heated to 140~145°C to realize azeotropic dehydration until no water is evaporated, and dehydration End; 2,5-dichlorophenolate solution is obtained.

As a further improvement of the preparation method of 3,6-dichloro-2-hydroxybenzoic acid of the present invention: in step 1): the organic solvent is a high boiling point solvent;

High boiling point solvents are toluene, xylene, dimethyl sulfoxide, N,N-dimethylformamide, n-octanol. Xylene is more preferred.

As a further improvement of the preparation method of 3,6-dichloro-2-hydroxybenzoic acid of the present invention: in step 1): the base is sodium hydroxide or potassium hydroxide. Potassium hydroxide is preferred.

In step 3) of the present invention, the alkali solution used for pH adjustment is sodium hydroxide solution, and the acid solution is hydrochloric acid solution (for example, concentrated hydrochloric acid).

The specific process operation and control conditions of the carboxylation reaction in step 2) of the present invention are as follows: transfer the 2,5-dichlorophenolate solution to the high-pressure reactor, then add the co-catalyst, open the inlet valve and feed CO to _remove After exhausting the air in the kettle, heat up the reactor, start stirring at the same time, and feed a certain amount of CO ₂ into the kettle to stabilize the temperature and pressure in the kettle at 140~160°C and 6~8Mpa respectively. State reaction 6-12h.

The present invention provides a method for preparing 3,6-dichloro-2-hydroxybenzene by klobe-schmitt reaction of 2,5-dichlorophenate and CO ₂ under the co-catalysis of potassium carbonate (K ₂ CO ₃ ) and activated carbon. Formic acid technology. In the present invention, the activated carbon recovered in step 3) can be recycled.

Remarks: In the refining step, potassium carbonate cannot be recovered due to the need to add alkali solution and acid solution to adjust the pH accordingly.

The preparation method of 3,6-dichloro-2-hydroxybenzoic acid provided by the invention has the following characteristics:

1. Replace the potassium carbonate currently used in production with a small amount of potassium carbonate and activated carbon. The consumption of potassium carbonate is 1/5 of the potassium carbonate used in current production, thereby reducing production costs.

2. The activated carbon in the co-catalyst can be recycled.

In summary, the present invention uses a co-catalyst composed of K ₂ CO ₃ and activated carbon to catalyze the kolbe-schmitt carboxylation reaction, replacing the relatively large amount of potassium carbonate used in traditional production, thereby reducing production costs. The synthesis of 3,6-dichloro-2-hydroxybenzoic acid with K ₂ CO ₃ and activated carbon co-catalyst has not been reported in the literature.

Detailed ways

The present invention will be further described below by way of examples.

The following percentages involved in the present invention are all mass percentages.

Embodiment 1, a kind of preparation method of 3,6-dichloro-2-hydroxybenzoic acid, carries out following steps successively:

1) Weigh 146g (0.83mol) 2,5-dichlorophenol (95% purity) in a 1000ml three-neck flask and dissolve it in 98gKOH aqueous solution (mass concentration 48%, containing 0.84mol KOH), then add Mix 640ml of xylene as a solvent evenly, heat up to 142~145°C, dehydrate with a water separator until almost no water is evaporated, and obtain a solution of potassium 2,5-dichlorophenate.

2) Transfer the potassium 2,5-dichlorophenate solution obtained in the above step 1) to an autoclave, then add 12g K ₂ CO ₃ and 14g activated carbon as a co-catalyst, fill the autoclave with CO ₂ to 3Mpa, and wait for stabilization Afterwards, ventilate and continue the same operation for 3 times to fully replace the air in the kettle; then fill with _CO2 to 5Mpa and heat; finally, control the reaction temperature to 145°C and the reaction pressure to 6Mpa to carry out the carboxylation reaction, and the reaction time is 12h . After the reaction, a reaction product containing potassium 3,6-dichloro-2-hydroxybenzoate was obtained.

3) After cooling the above reaction product containing potassium 3,6-dichloro-2-hydroxybenzoate to room temperature, add 155ml of 40% NaOH aqueous solution and 350ml of water. At this time, the pH is about 12. After fully stirring, filter, Filter cake and filtrate are obtained; the activated carbon recovered after the filter cake is dried weighs 13.8g and can be recycled. The filtrate is divided into the organic phase located in the upper layer and the aqueous phase located in the lower layer, then take the aqueous phase, adjust the pH of the aqueous phase to 1 with concentrated hydrochloric acid with a mass fraction of 36%, and then steam distill (adjust the temperature to 140°C) until the distilled The water is clear, that is, no 2,5-dichlorophenol will be distilled out, and it will naturally crystallize after cooling to room temperature. Chloro-2-hydroxybenzoic acid solid 80.4g (0.388mol), the calculated yield is 46.6%. The steam distillation fraction was filtered and dried to obtain 72.5 g (0.434 mol) of 3,5-dichlorophenol as a solid, and the recovery rate of the raw material was 52.3%. The calculated total yield of starting material and product was 98.9%.

Example 2

14g of activated carbon in Example 1 was changed to 13.8g of recovered activated carbon (obtained in Example 1) + 0.2g of activated carbon, and the rest were the same as in Example 1. The result is:

13.9 g of activated carbon was recovered and 73 g (0.437 mol) of 3,5-dichlorophenol was recovered, and the calculated recovery rate was 52.7%. 80 g (0.386 mol) of 3,6-dichloro-2-hydroxybenzoic acid solid was obtained, and the calculated yield was 46.5%. The total yield of starting material and product was calculated to be 99.2%.

Example 3

Change the activated carbon 14g in Example 1 into 13.9g of recovered activated carbon (obtained in Example 2)+0.1g activated carbon, and the rest are the same as in Example 1. The result is:

13.9 g of activated carbon was recovered and 72.1 g (0.432 mol) of 3,5-dichlorophenol was recovered, with a calculated recovery rate of 52.0%. 80.8 g (0.390 mol) of 3,6-dichloro-2-hydroxybenzoic acid solid was obtained, and the calculated yield was 47.0%. The total yield of starting material and product was calculated to be 99.0%.

Example 4

The activated carbon 14g in Example 1 was changed to recovered activated carbon 13.9g (obtained in Example 3)+0.1g activated carbon, and the rest were the same as in Example 1. The result is:

13.7 g of activated carbon was recovered and 74 g (0.443 mol) of 3,5-dichlorophenol was recovered, with a calculated recovery rate of 53.4%. 78.9 g (0.381 mol) of 3,6-dichloro-2-hydroxybenzoic acid solid was obtained, and the calculated yield was 45.9%. The calculated total yield of starting material and product was 99.3%.

Comparative example 1,

12g K as co-catalyst in embodiment ₂ CO ₃ and 14g activated carbon are changed into 60g salt of wormwood, and corresponding step 3) in " filter after fully stirring, obtain filter cake and filtrate; Promptly obtain reclaimed after filter cake drying Activated carbon, weighing 13.8g, can be recycled; the filtrate is divided into an upper organic phase and a lower aqueous phase" into "after fully stirring, an upper organic phase and a lower aqueous phase are naturally formed". All the other are with embodiment 1. Finally, 80.4 g (0.388 mol) of 3,6-dimethyl-2-hydroxybenzoic acid solid was obtained, and the calculated yield was 46.6%. The recovered 3,5-dichlorophenol solid was 72.1 g (0.432 mol), and the recovery rate was 52.0%. The calculated total yield of raw materials and products was 98.6%.

Comparative example 2,

Cancel the use of 12gK as co-catalyst ₂ CO ₃ and 14g gac in embodiment 1, corresponding step 3) in " filter after fully stirring, obtain filter cake and filtrate; Get the gac of reclaiming after filter cake drying, weigh 13.8g, can be recycled; the filtrate is divided into an upper organic phase and a lower aqueous phase" into "after fully stirring, an upper organic phase and a lower aqueous phase are naturally formed". All the other are with embodiment 1. Finally, 58.2 g (0.281 mol) of 3,6-dichloro-2-hydroxybenzoic acid solid was obtained, and the calculated yield was 33.9%. The recovered 3,5-dichlorophenol solid was 88.2 g (0.426 mol), and the recovery rate was 63.6%. Calculate the total yield of starting material and product to be 97.5%

Comparative example 3,

Cancel the use of 14g gac in embodiment 1, promptly only 12gK ₂ CO ₃ as catalyzer, corresponding step 3) in " filter after fully stirring, get filter cake and filtrate; Get the gac of reclaiming after filter cake drying, It weighs 13.8g and can be recycled; the filtrate is divided into an upper organic phase and a lower aqueous phase" into "after fully stirring, an upper organic phase and a lower aqueous phase are naturally formed". All the other are with embodiment 1. Finally, 68.7 g (0.332 mol) of 3,6-dichloro-2-hydroxybenzoic acid solid was obtained, and the calculated yield was 40%. The recovered 3,5-dichlorophenol solid was 81.4g (0.487), the recovery rate was 58.7%. The calculated total yield of starting material and product was 98.7%.

Comparative example 4,

Cancel the use of the 14g activated carbon in Example 1, change the weight of _K2CO3 from _12g to 26g, and in the corresponding step 3) "filter after fully stirring to obtain filter cake and filtrate; promptly obtain recovery after filter cake drying The activated carbon weighs 13.8g and can be recycled; the filtrate is divided into an upper organic phase and a lower water phase" into "after fully stirring, an upper organic phase and a lower water phase are naturally formed". All the other are with embodiment 1. Finally, 72.1 g (0.348 mol) of 3,6-dichloro-2-hydroxybenzoic acid solid was obtained, and the calculated yield was 42%. The recovered 3,5-dichlorophenol solid was 74.3 g (0.445 mol), and the recovery rate was 53.6%. The calculated total yield of raw materials and products was 95.6%.

Comparative example 5,

12gK in embodiment 1 as cocatalyst ₂ CO ₃ and 14g activated carbon are changed into 12gK ₂ CO ₃ and 28g activated carbon, all the other are the same as embodiment 1. Recover activated carbon 27.6g. 78.9 g (0.381 mol) of 3,6-dichloro-2-hydroxybenzoic acid solid was obtained, and the calculated yield was 45.9%. 72.1 g (0.432 mol) of 3,5-dichlorophenol was recovered, and the calculated recovery rate was 52.0%. The calculated total yield of starting material and product was 97.9%.

Comparative example 6,

Change 12gK as co-catalyst 12gK ₂ CO ₃ and 14g gac into 12gK ₂ CO ₃ and 7g gac in embodiment 1, and all the other are the same as embodiment 1. Recover activated carbon 6.9g. 73.7 g (0.356 mol) of 3,6-dichloro-2-hydroxybenzoic acid solid was obtained, and the calculated yield was 42.9%. 76.3 g (0.457 mol) of 3,5-dichlorophenol was recovered, and the calculated recovery rate was 55.1%. The total yield of starting material and product was calculated to be 98.0%.

Comparative example 7,

12gK in embodiment 1 as co-catalyst ₂ CO ₃ and 14g gac into 6gK ₂ CO ₃ and 14g gac, all the other are the same as embodiment 1. Recover activated carbon 13.8g. 74 g (0.357 mol) of 3,6-dichloro-2-hydroxybenzoic acid solid was obtained, and the calculated yield was 43.1%. 75.4 g (0.451 mol) of 3,5-dichlorophenol was recovered, and the calculated recovery rate was 54.4%. The total yield of starting material and product was calculated to be 97.5%.

Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and many variations are possible. All deformations that can be directly derived or associated by those skilled in the art from the content disclosed in the present invention should be considered as the protection scope of the present invention.

Claims (4)

1.3, the preparation method of 6-dichloro-2-hydroxybenzoic acid is characterized in that comprising the following steps successively: 1) Salt formation of 2,5-dichlorophenol: Dissolving 2,5-dichlorophenol in an alkali solution for salt-forming reaction, then adding an organic solvent and mixing evenly to obtain a mixed solution; dehydrating the mixed solution to obtain a 2,5-dichlorophenol salt solution; the 2 , the molar ratio of 5-dichlorophenol to alkali is 1:0.9~1.1; 2), carboxylation: Transfer the 2,5-dichlorophenolate solution to the autoclave, add a co-catalyst, and then pass in _CO2 for high-pressure carboxylation reaction to obtain a reaction containing 3,6-dichloro-2-hydroxybenzoate product; the reaction temperature is 140~160°C, the reaction pressure is 6~8Mpa, and the reaction time is 6~12h; the co-catalyst is composed of potassium carbonate and activated carbon, and the mass ratio of potassium carbonate to 2,5-dichlorophenol It is 0.01～0.2:1; The mass ratio of described activated carbon and 2,5-dichlorophenol is 0.01～0.2:1; 3), refined: Cool the reaction product containing 3,6-dichloro-2-hydroxybenzoate obtained in step 2) to room temperature, add alkali solution, adjust the pH to 11~13, stir well, filter and recover activated carbon, and separate the filtrate Finally, take the water phase; add an acid solution to the water phase, adjust the pH to 1~3, recover 2,5-dichlorophenol by steam distillation, cool and crystallize, filter and dry to obtain 3,6-dichloro-2-hydroxyl benzoic acid. 2. The preparation method of 3,6-dichloro-2-hydroxybenzoic acid according to claim 1, characterized in that in step 1): heating the mixed solution to 140~145°C to achieve azeotropic dehydration until No water was evaporated, and the dehydration was completed; 2,5-dichlorophenolate solution was obtained. 3. The method for preparing 3,6-dichloro-2-hydroxybenzoic acid according to claim 1 or 2, characterized in that in step 1): the organic solvent is a high boiling point solvent; The high boiling point solvent is toluene, xylene, dimethyl sulfoxide, N,N-dimethylformamide, n-octanol. 4. The preparation method of 3,6-dichloro-2-hydroxybenzoic acid according to claim 3, characterized in that in step 1): the alkali is sodium hydroxide or potassium hydroxide.