Method for synthesizing 6-hydroxy-2-naphthoic acid

Abstract

The invention relates to the technical field of preparation of 6-hydroxy-2-naphthoic acid, and discloses a method for synthesizing 6-hydroxy-2-naphthoic acid, which comprises the following steps: step 1, carrying out hydroxyl protection reaction on 2-naphthol and an acetylation reagent at 50-70 DEG C to generate 2-naphthol ester; step 2, carrying out Fries rearrangement reaction on the 2-naphthol ester obtained in the step 1 under the action of a catalyst to generate 6-acyl-2-naphthol; step 3, hydrolyzing the 6-acyl-2-naphthol obtained in the step 2 under an acidic condition to generate a 6-hydroxy-2-naphthoic acid crude product; and 4, recrystallizing the 6-hydroxy-2-naphthoic acid crude product in the step 3 to generate a 6-hydroxy-2-naphthoic acid refined product. Compared with the prior art, the method has the advantages that 1, a 6-hydroxy-2-naphthoic acid refined product can be prepared only through four-step reaction, and the operation is simple and convenient; 2, the reaction yield of each step is relatively high, and the total yield can reach more than 80%; and 3, reagents and solvents adopted in the method can be recycled, so that environmental pollution is reduced.

Description

Technical Field

[0001] This invention relates to the field of 6-hydroxy-2-naphthoic acid preparation technology, specifically to a method for synthesizing 6-hydroxy-2-naphthoic acid. Background Technology

[0002] 6-Hydroxy-2-naphthoic acid, also known as 2,6-acid, is an important organic intermediate used in engineering plastics, organic pigments, liquid crystal materials, and pharmaceuticals, particularly as a monomer for heat-resistant synthetic materials. It is a off-white crystalline powder with a melting point of 243–246°C. It is weakly acidic, soluble in alkalis, practically insoluble in dry water, and readily soluble in alcohols, ethers, and benzene, among other organic solvents. It has wide applications in pharmaceuticals, dyes, and fragrances.

[0003] Currently, traditional methods for synthesizing 6-hydroxy-2-naphthoic acid generally suffer from cumbersome procedures, low yield, and environmental pollution.

[0004] To address the aforementioned issues, we propose a method for synthesizing 6-hydroxy-2-naphthoic acid. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the above-mentioned technical difficulties and provide a method for synthesizing 6-hydroxy-2-naphthoic acid, which has the advantages of simple steps, high yield and low environmental pollution.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0007] A method for synthesizing 6-hydroxy-2-naphthoic acid includes the following steps:

[0008] Step 1: 2-Naphthol is reacted with an acetylation reagent at 50-70℃ to undergo a hydroxyl protection reaction to generate 2-naphthol ester;

[0009] Step 2: The 2-naphthol ester obtained in Step 1 undergoes a Fries rearrangement reaction under the action of a catalyst to generate 6-acyl-2-naphthol;

[0010] Step 3: Hydrolyze the 6-acyl-2-naphthol obtained in Step 2 under acidic conditions to produce crude 6-hydroxy-2-naphthoic acid;

[0011] Step 4: The crude 6-hydroxy-2-naphthoic acid from Step 3 is recrystallized to produce refined 6-hydroxy-2-naphthoic acid.

[0012] Furthermore, the acetylation reagent in step one is acetic anhydride, acetyl chloride, or glacial acetic acid.

[0013] Furthermore, the catalyst in step two is anhydrous aluminum trichloride, zinc chloride, or a boron trifluoride diethyl ether complex.

[0014] Furthermore, in step two, the temperature of the Fries rearrangement reaction is 80-150℃.

[0015] Furthermore, the acidic conditions in step three employ a mixed oxidation system of H2O2-H2SO4, wherein the amount of 30% hydrogen peroxide used is 1.3-1.6 times the theoretical value.

[0016] Furthermore, in step three, the hydrolysis reaction is carried out at a temperature of 50-100℃.

[0017] Furthermore, in step four, the final purification is carried out by recrystallization using an ethanol-water mixed solvent, wherein the volume fraction of ethanol is 65-75%, and the recrystallization yield is ≥92%.

[0018] The advantages of this invention compared to the prior art are:

[0019] 1. This invention requires only four reaction steps to obtain high-quality 6-hydroxy-2-naphthoic acid, and the operation is simple;

[0020] 2. The reaction yields of each step in this invention are high, with an overall yield of over 80%;

[0021] 3. The reagents and solvents used in this invention can be recycled, reducing environmental pollution. Detailed Implementation

[0022] In the description of this invention, unless otherwise stated, "a plurality of" means two or more. Furthermore, the term "comprising" and any variations thereof are intended to cover non-exclusive inclusion.

[0023] The present invention will now be described in further detail with reference to the embodiments.

[0024] In specific implementation of the embodiments of the present invention:

[0025] Example 1

[0026] A method for synthesizing 6-hydroxy-2-naphthoic acid includes the following steps:

[0027] Step 1: 2-Naphthol is reacted with acetic anhydride at 50°C to undergo a hydroxyl protection reaction to generate 2-naphthol ester;

[0028] Step 2: The 2-naphthol ester obtained in Step 1 is subjected to Fries rearrangement reaction under the catalysis of anhydrous aluminum trichloride at a temperature of 80℃ to generate 6-acyl-2-naphthol.

[0029] Step 3: Hydrolyze the 6-acyl-2-naphthol obtained in Step 2 under acidic conditions. The acidic conditions are achieved using a mixed oxidation system of H2O2 and H2SO4, with the amount of 30% hydrogen peroxide being 1.3 times the theoretical value. The hydrolysis reaction temperature is 50℃, producing crude 6-hydroxy-2-naphthoic acid.

[0030] Step 4: The crude 6-hydroxy-2-naphthoic acid from Step 3 is recrystallized to obtain refined 6-hydroxy-2-naphthoic acid. Final purification involves recrystallization using an ethanol-water mixed solvent, with ethanol comprising 65% by volume, achieving a recrystallization yield ≥90%.

[0031] Example 2

[0032] A method for synthesizing 6-hydroxy-2-naphthoic acid includes the following steps:

[0033] Step 1: 2-Naphthol and acetyl chloride undergo a hydroxyl protection reaction at 60°C to generate 2-naphthol ester;

[0034] Step 2: The 2-naphthol ester obtained in Step 1 is subjected to a Fries rearrangement reaction under the catalysis of zinc chloride. The temperature of the Fries rearrangement reaction is 100℃, which generates 6-acyl-2-naphthol.

[0035] Step 3: Hydrolyze the 6-acyl-2-naphthol obtained in Step 2 under acidic conditions. The acidic conditions are achieved using a mixed oxidation system of H2O2 and H2SO4, with the amount of 30% hydrogen peroxide being 1.4 times the theoretical value. The hydrolysis reaction temperature is 50-100℃, producing crude 6-hydroxy-2-naphthoic acid.

[0036] Step 4: The crude 6-hydroxy-2-naphthoic acid from Step 3 is recrystallized to obtain refined 6-hydroxy-2-naphthoic acid. Final purification involves recrystallization using an ethanol-water mixed solvent, with 70% ethanol by volume, achieving a recrystallization yield ≥90%.

[0037] Example 3

[0038] A method for synthesizing 6-hydroxy-2-naphthoic acid includes the following steps:

[0039] Step 1: 2-Naphthol is reacted with glacial acetic acid at 70°C to undergo a hydroxyl protection reaction to generate 2-naphthol ester;

[0040] Step 2: The 2-naphthol ester obtained in Step 1 is subjected to Fries rearrangement reaction under the catalysis of boron trifluoride diethyl ether complex. The temperature of the Fries rearrangement reaction is 150℃, to generate 6-acyl-2-naphthol.

[0041] Step 3: Hydrolyze the 6-acyl-2-naphthol obtained in Step 2 under acidic conditions. The acidic conditions are achieved using a mixed oxidation system of H2O2 and H2SO4, with the amount of 30% hydrogen peroxide being 1.6 times the theoretical value. The hydrolysis reaction temperature is 100℃, producing crude 6-hydroxy-2-naphthoic acid.

[0042] Step 4: The crude 6-hydroxy-2-naphthoic acid from Step 3 is recrystallized to obtain refined 6-hydroxy-2-naphthoic acid. Final purification involves recrystallization using an ethanol-water mixed solvent, with ethanol comprising 75% by volume, achieving a recrystallization yield ≥90%.

[0043] The present invention and its embodiments have been described above, and this description is not restrictive. If those skilled in the art are inspired by this description and design similar embodiments without departing from the spirit of the invention, such embodiments should fall within the protection scope of the present invention.

Claims

1. A method for synthesizing 6-hydroxy-2-naphthoic acid, characterized in that: Includes the following steps: Step 1: 2-Naphthol is reacted with an acetylation reagent at 50-70℃ to undergo a hydroxyl protection reaction to generate 2-naphthol ester; Step 2: The 2-naphthol ester obtained in Step 1 undergoes a Fries rearrangement reaction under the action of a catalyst to generate 6-acyl-2-naphthol; Step 3: Hydrolyze the 6-acyl-2-naphthol obtained in Step 2 under acidic conditions to produce crude 6-hydroxy-2-naphthoic acid; Step 4: The crude 6-hydroxy-2-naphthoic acid from Step 3 is recrystallized to produce refined 6-hydroxy-2-naphthoic acid.

2. The method for synthesizing 6-hydroxy-2-naphthoic acid according to claim 1, characterized in that: The acetylation reagent in step one is acetic anhydride, acetyl chloride, or glacial acetic acid.

3. The method for synthesizing 6-hydroxy-2-naphthoic acid according to claim 1, characterized in that: The catalyst in step two is anhydrous aluminum trichloride, zinc chloride, or boron trifluoride diethyl ether complex.

4. The method for synthesizing 6-hydroxy-2-naphthoic acid according to claim 1, characterized in that: In step two, the temperature of the Fries rearrangement reaction is 80-150℃.

5. The method for synthesizing 6-hydroxy-2-naphthoic acid according to claim 1, characterized in that: The acidic conditions in step three employ a mixed oxidation system of H2O2-H2SO4, wherein the amount of 30% hydrogen peroxide used is 1.3-1.6 times the theoretical value.

6. The method for synthesizing 6-hydroxy-2-naphthoic acid according to claim 5, characterized in that: In step three, the hydrolysis reaction is carried out at a temperature of 50-100℃.

7. The method for synthesizing 6-hydroxy-2-naphthoic acid according to claim 1, characterized in that: In step four, the final purification is achieved by recrystallization using an ethanol-water mixed solvent, wherein the volume fraction of ethanol is 65-75%, and the recrystallization yield is ≥90%.