A process for the preparation of an organic pigment intermediate

Abstract

The application provides a preparation method of an organic pigment intermediate. The preparation method comprises the following steps: (1) adding Br2 dropwise into a mixture containing p-xylene and a first catalyst, and performing a reaction under a micro-negative pressure until no gas is emitted, and then performing water washing and distillation to obtain an intermediate product I; (2) adding potassium permanganate into an aqueous solution containing the intermediate product I and a second catalyst in batches to perform an oxidation reaction, and then performing filtration to obtain a filtrate containing an intermediate product II; and (3) adding dilute hydrochloric acid into the filtrate containing the intermediate product II to adjust the pH value to 1-4, and then obtaining 2,5-dibromo-p-benzene dicarboxylic acid. The application adopts p-xylene as a raw material, performs a bromination reaction first, and then performs an oxidation reaction and an acidification treatment, the reaction process is mild, the quality of the prepared 2,5-dibromo-p-benzene dicarboxylic acid is good, the yield is high, the generation of by-products can be reduced, the subsequent purification treatment process is simple, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of organic chemical technology, specifically to a method for preparing an organic pigment intermediate. Background Technology

[0002] 2,5-Dibromo-p-benzoic acid (DBTA) is an important intermediate for organic pigments. Two common synthetic methods exist: one is the bromination of phthalic acid (TPA), but this reaction requires fuming sulfuric acid, making product separation and purification difficult and resulting in very low yields. The other method uses 2,5-dibromo-p-xylene as a raw material in an acidic medium, with cobalt and manganese salts as catalysts, and reacts under high temperature and pressure with air. However, this reaction process places extremely high demands on the equipment's temperature, pressure, and corrosion resistance, making it unsuitable for small-batch, low-volume production, especially in laboratory settings. Summary of the Invention

[0003] (a) Technical problems to be solved

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing organic pigment intermediates, which solves the problems mentioned in the background section.

[0005] (II) Technical Solution

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] According to a first aspect of the present invention, a method for preparing an organic pigment intermediate is provided, comprising the following steps:

[0008] (1) Br2 was added dropwise to a mixture containing p-xylene and the first catalyst, and the reaction was carried out under a slight negative pressure until no gas escaped. The mixture was then washed with water and distilled to obtain intermediate product I.

[0009] (2) Potassium permanganate was added in batches to an aqueous solution containing intermediate product I and the second catalyst to carry out an oxidation reaction, and the solution was filtered to obtain a filtrate containing intermediate product II.

[0010] (3) Add dilute hydrochloric acid to the filtrate containing intermediate product II to adjust the pH to 1-4 to obtain 2,5-dibromo-p-dibenzoic acid.

[0011] The reaction equations for steps (1) to (3) in this invention are as follows:

[0012]

[0013] Preferably, in step (1), the first catalyst is selected from at least one of Fe, FeCl3, FeCl3·6H2O or I2.

[0014] Preferably, in step (1), the mass of the first catalyst is 0.5 to 2 wt% of the p-xylene.

[0015] Preferably, in step (1), the mass ratio of Br2 to p-xylene is 2.5 to 3.5:1.

[0016] Preferably, in step (1), the reaction temperature is 40–80°C.

[0017] Preferably, in step (2), the second catalyst is selected from at least one of C16 to C36 aliphatic quaternary ammonium salts, crown ethers, nonionic polyoxyethylene fatty alcohol condensates, and polyoxyethylene alkylphenol condensates.

[0018] Preferably, in step (2), the mass of the second catalyst is 10 to 17 wt% of the intermediate product I.

[0019] Preferably, in step (2), the mass ratio of potassium permanganate to intermediate product I is 3 to 4:1.

[0020] Preferably, in step (2), the oxidation reaction includes a first-stage oxidation reaction and a second-stage oxidation reaction. The temperature of the first-stage oxidation reaction is 80-90°C and the time of the first-stage oxidation reaction is 30-60 min. The temperature of the second-stage oxidation reaction is 95-105°C and the time of the second-stage oxidation reaction is 2-3 h.

[0021] Preferably, the ratio of potassium permanganate added in the first oxidation reaction to the amount added in the second oxidation reaction is 1:1.

[0022] (III) Beneficial Effects

[0023] This invention provides a method for preparing an organic pigment intermediate. It has the following beneficial effects:

[0024] This solution provides a method for preparing an organic pigment intermediate. Using p-xylene as a raw material, the process involves first undergoing a bromination reaction, followed by an oxidation reaction and acidification. The reaction process is mild, and the resulting 2,5-dibromo-p-dibenzoic acid is of good quality and has a high yield. This method can reduce the generation of by-products, and the subsequent purification process is simple, thus reducing production costs. Detailed Implementation

[0025] To better illustrate the content of this invention, the following description is provided in conjunction with specific embodiments.

[0026] Example 1

[0027] Synthesis of 2,5-dibromo-p-xylene: 212 g of p-xylene and 5.4 g of FeCl3·6H2O were added to a four-necked flask and stirred. 639 g of Br2 was slowly added dropwise at 20 °C. Under slight negative pressure, the generated HBr gas was extracted. Then the temperature was raised to 60 °C until no HBr gas escaped. Hot water at 90 °C was added, and the mixture was allowed to stand and separate into layers. The wastewater layer was discarded, and the oil layer was distilled at atmospheric pressure. The fraction at 261 °C was collected to obtain 370 g of intermediate product I, 2,5-dibromo-p-xylene, with a yield of 70%.

[0028] Synthesis of potassium 2,5-dibromo-p-dibenzoate: 66 g of intermediate product I, 750 g of water and 10 g of PTC were added to a four-necked flask and heated to 80 °C. Under stirring, 100 g of the first batch of potassium permanganate was added, and the reaction temperature was raised to 100 °C and kept under reflux. When the red color of the reaction solution disappeared, 100 g of the second batch of potassium permanganate was added. The reaction was carried out for 2 h, filtered, and the residue was washed with boiling water. The filtrates were collected and combined to obtain intermediate product II, a solution of potassium 2,5-dibromo-p-dibenzoate.

[0029] Synthesis of 2,5-dibromo-p-dibenzoic acid: 30% dilute hydrochloric acid was added dropwise to the solution containing intermediate II obtained above until the pH of the mixed solution was 2. White crystals were precipitated, filtered, washed with water, and dried to obtain 48.6 g of organic pigment intermediate, 2,5-dibromo-p-dibenzoic acid, with a yield of 60%.

[0030] Example 2

[0031] Synthesis of 2,5-dibromo-p-xylene: 240 g of p-xylene and 9.6 g of FeCl3 were added to a four-necked flask and stirred. 720 g of Br2 was slowly added dropwise at 20 °C. Under slight negative pressure, the generated HBr gas was extracted. Then the temperature was raised to 60 °C until no HBr gas escaped. Hot water at 90 °C was added, and the mixture was allowed to stand and separate into layers. The wastewater layer was discarded, and the oil layer was distilled at atmospheric pressure. The fraction at 261 °C was collected to obtain 420 g of intermediate product I, 2,5-dibromo-p-xylene, with a yield of 72%.

[0032] Synthesis of potassium 2,5-dibromo-2,5-dibenzoate: 130 g of intermediate product I, 1500 g of water and 19.5 g of hexadecyl dimethyl ammonium chloride were added to a four-necked flask and heated to 80 °C. Under stirring, 150 g of the first batch of potassium permanganate was added, and the reaction temperature was raised to 100 °C and kept under reflux. When the red color of the reaction solution disappeared, 150 g of the second batch of potassium permanganate was added. The reaction was carried out for 3 h, filtered, and the residue was washed with boiling water. The filtrates were collected and combined to obtain intermediate product II, a solution of potassium 2,5-dibromo-2,5-dibenzoate.

[0033] Synthesis of 2,5-dibromo-p-dibenzoic acid: 30% dilute hydrochloric acid was added dropwise to the solution containing intermediate II obtained above until the pH of the mixed solution was 2. White crystals were precipitated, filtered, washed with water, and dried to obtain 102g of organic pigment intermediate, 2,5-dibromo-p-dibenzoic acid, with a yield of 63%.

[0034] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an organic pigment intermediate, characterized in that: Includes the following steps: (1) Br2 was added dropwise to a mixture containing p-xylene and the first catalyst, and the reaction was carried out under a slight negative pressure until no gas escaped. The mixture was then washed with water and distilled to obtain intermediate product I. (2) Potassium permanganate was added in batches to an aqueous solution containing intermediate product I and the second catalyst to carry out an oxidation reaction, and the solution was filtered to obtain a filtrate containing intermediate product II. (3) Add dilute hydrochloric acid to the filtrate containing intermediate product II to adjust the pH to 1-4 to obtain 2,5-dibromo-p-dibenzoic acid.

2. The method for preparing an organic pigment intermediate according to claim 1, characterized in that: In step (1), the first catalyst is selected from at least one of Fe, FeCl3, FeCl3·6H2O or I2.

3. The method for preparing an organic pigment intermediate according to claim 1, characterized in that: In step (1), the mass of the first catalyst is 0.5 to 2 wt% of the p-xylene.

4. The method for preparing an organic pigment intermediate according to claim 1, characterized in that: In step (1), the mass ratio of Br2 to p-xylene is 2.5 to 3.5:

1.

5. The method for preparing an organic pigment intermediate according to claim 1, characterized in that: In step (1), the reaction temperature is 40–80°C.

6. The method for preparing an organic pigment intermediate according to claim 1, characterized in that: In step (2), the second catalyst is selected from at least one of C16 to C36 aliphatic quaternary ammonium salts, crown ethers, nonionic polyoxyethylene fatty alcohol condensates, and polyoxyethylene alkylphenol condensates.

7. The method for preparing an organic pigment intermediate according to claim 1, characterized in that: In step (2), the mass of the second catalyst is 10-17 wt% of the intermediate product I.

8. The method for preparing an organic pigment intermediate according to claim 1, characterized in that: In step (2), the mass ratio of potassium permanganate to intermediate product I is 3 to 4:

1.

9. The method for preparing an organic pigment intermediate according to claim 1, characterized in that: In step (2), the oxidation reaction includes a first-stage oxidation reaction and a second-stage oxidation reaction. The temperature of the first-stage oxidation reaction is 80-90℃ and the time of the first-stage oxidation reaction is 30-60 min. The temperature of the second-stage oxidation reaction is 95-105℃ and the time of the second-stage oxidation reaction is 2-3 h.

10. The method for preparing an organic pigment intermediate according to claim 9, characterized in that: The ratio of potassium permanganate added in the first oxidation reaction to that added in the second oxidation reaction is 1:1.

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