Preparation method of p-hydroxybenzoic acid

Abstract

The invention relates to the technical field of p-hydroxybenzoic acid preparation, and discloses a p-hydroxybenzoic acid preparation method, which comprises: 1, mixing benzoic acid and a potassium hydroxide solution to form a potassium phenolate solution; 2, in an alkaline aqueous solution system, carrying out a directional hydroxylation reaction with a hydroxylation reagent in the presence of a phase transfer catalyst to generate potassium p-hydroxybenzoate; and step 3, converting the potassium p-hydroxybenzoate into p-hydroxybenzoic acid through acidification treatment. Compared with the prior art, the preparation method of p-hydroxybenzoic acid provided by the invention has the advantages of high efficiency, environmental protection and suitability for industrial production. The method comprises the following steps: reacting a potassium phenolate solution under an alkaline condition to generate potassium p-hydroxybenzoate under the catalysis of a phase transfer catalyst, and acidizing to obtain p-hydroxybenzoic acid. The method has the advantages of mild reaction conditions, high yield, few byproducts, easiness in industrial production and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of p-hydroxybenzoic acid preparation, in particular to a method for preparing p-hydroxybenzoic acid. Background Art

[0002] Parahydroxybenzoic acid, where the R group can be methyl, ethyl, propyl, butyl, or heptyl, is known as methylparahydroxybenzoate, ethylparahydroxybenzoate, propylparahydroxybenzoate, butylparahydroxybenzoate, and heptylparahydroxybenzoate, respectively. These pure products appear as colorless, fine crystals or crystalline powders that are insoluble or slightly soluble in water. Parahydroxybenzoic acid esters are not only effective against fungi, but also possess stronger antibacterial properties than benzoic acid and sorbic acid due to their phenolic hydroxyl group structure. Parahydroxybenzoic acid esters are characterized by lower toxicity than benzoic acid, and their antibacterial activity is independent of pH. However, their relatively low water solubility and distinctive odor limit their application in food preservation. Besides being used as a food preservative, they are primarily used as preservatives in pharmaceuticals and cosmetics. Parahydroxybenzoic acid (p-Hydroxybenzoic acid) is an important organic compound widely used in the fields of medicine, food, and cosmetics.

[0003] Currently, traditional methods for preparing p-hydroxybenzoic acid typically involve direct hydroxylation of benzoic acid, but this method has problems such as harsh reaction conditions, low yield, and the production of many by-products. To address these issues, we propose a method for preparing p-hydroxybenzoic acid. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the above technical difficulties and provide a method for preparing p-hydroxybenzoic acid, which is efficient, environmentally friendly and suitable for industrial production.

[0005] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0006] A method for preparing p-hydroxybenzoic acid comprises the following steps:

[0007] Step 1: mixing benzoic acid with potassium hydroxide solution to form a potassium phenolate solution;

[0008] Step 2: In an alkaline aqueous solution system, a directional hydroxylation reaction is carried out with a hydroxylating agent in the presence of a phase transfer catalyst to produce potassium p-hydroxybenzoate;

[0009] Step 3: converting potassium p-hydroxybenzoate into p-hydroxybenzoic acid through acidification.

[0010] Preferably, in step 1, the molar ratio of benzoic acid to potassium hydroxide is 1:1 to 1:4, and the mass fraction of the potassium hydroxide solution is 40% to 60%.

[0011] Preferably, in step 1, after adding phenol and potassium hydroxide solution into the reaction vessel, it is necessary to heat to 100° C. and stir the mixture to react for 0.6 to 1 hour.

[0012] Preferably, in step 2, the reaction temperature is 50° C. to 80° C., and the reaction time is 2 hours to 5 hours.

[0013] Preferably, in step 2, the phase transfer catalyst is a complex of tetrabutylammonium bromide and polyethylene glycol 6000, the mass ratio of the two is 1:0.5-2, and the total addition amount is 1-3% of the mass of the raw materials; during the reaction process, nitrogen is bubbled for 7-10 minutes every hour to enhance mass transfer.

[0014] Preferably, in step three, the acidification treatment uses hydrochloric acid or sulfuric acid with a concentration of 40% to 60%.

[0015] Preferably, in step three, the pH of the solution needs to be adjusted to 4-5.

[0016] Preferably, the prepared p-hydroxybenzoic acid product meets the following indicators: purity ≥99%, ignition residue ≤0.05%, o-hydroxybenzoic acid isomer content ≤0.25%, and heavy metal (as Pb) ≤5 ppm.

[0017] The advantages of the present invention compared with the prior art are:

[0018] The present invention provides an efficient, environmentally friendly method for preparing p-hydroxybenzoic acid suitable for industrial production. This method involves reacting a potassium phenate solution under alkaline conditions in the presence of a phase transfer catalyst to produce potassium p-hydroxybenzoate, which is then acidified to obtain p-hydroxybenzoic acid. This method has the advantages of mild reaction conditions, high yield, low by-product count, and ease of industrial production. DETAILED DESCRIPTION

[0019] In the description of the present invention, unless otherwise specified, "a plurality of" means two or more. In addition, the term "include" and any variations thereof are intended to cover non-exclusive inclusions.

[0020] The present invention will be further described in detail below with reference to the embodiments.

[0021] When the embodiment of the present invention is implemented:

[0022] Example 1

[0023] A method for preparing p-hydroxybenzoic acid comprises the following steps:

[0024] Step 1: Mix benzoic acid and potassium hydroxide solution to form potassium phenolate solution. The molar ratio of benzoic acid to potassium hydroxide is 1:1, and the mass fraction of potassium hydroxide solution is 40%. After adding phenol and potassium hydroxide solution to the reaction vessel, it is necessary to heat to 100°C and stir the reaction for 0.6 hours. The potassium phenolate needs to be ground to a particle size of less than 25μm before use;

[0025] Step 2: In an alkaline aqueous solution system, a directional hydroxylation reaction is carried out with a hydroxylating agent in the presence of a phase transfer catalyst at a temperature of 50°C for 2 hours to produce potassium p-hydroxybenzoate. The phase transfer catalyst is a complex of tetrabutylammonium bromide and polyethylene glycol 6000, with a mass ratio of 1:0.5 and a total addition amount of 1% of the raw material mass. During the reaction, nitrogen is bubbled for 7 minutes every hour to enhance mass transfer.

[0026] Step 3: convert potassium p-hydroxybenzoate into p-hydroxybenzoic acid by acidification. The acidification uses hydrochloric acid or sulfuric acid at a concentration of 40%, and the pH of the solution needs to be adjusted to 4.

[0027] The prepared p-hydroxybenzoic acid product meets the following indicators: purity ≥99%, ignition residue ≤0.05%, o-hydroxybenzoic acid isomer content ≤0.25%, and heavy metal (calculated as Pb) ≤5ppm.

[0028] Example 2

[0029] A method for preparing p-hydroxybenzoic acid comprises the following steps:

[0030] Step 1: Mix benzoic acid and potassium hydroxide solution to form a potassium phenolate solution. The molar ratio of benzoic acid to potassium hydroxide is 1:3, and the mass fraction of potassium hydroxide solution is 50%. After adding phenol and potassium hydroxide solution to the reaction vessel, it is necessary to heat to 100°C and stir the reaction for 0.8 hours. The potassium phenolate needs to be ground to a particle size of less than 25μm before use;

[0031] Step 2: In an alkaline aqueous solution, a directional hydroxylation reaction is carried out with a hydroxylating agent in the presence of a phase transfer catalyst at 70°C for 4 hours to produce potassium p-hydroxybenzoate. The phase transfer catalyst is a complex of tetrabutylammonium bromide and polyethylene glycol 6000, with a mass ratio of 1:1 and a total addition amount of 2% of the raw material mass. During the reaction, nitrogen is bubbled for 9 minutes every hour to enhance mass transfer.

[0032] Step 3: convert potassium p-hydroxybenzoate into p-hydroxybenzoic acid by acidification. The acidification uses hydrochloric acid or sulfuric acid at a concentration of 50%, and the pH of the solution needs to be adjusted to 4.5.

[0033] The prepared p-hydroxybenzoic acid product meets the following indicators: purity ≥99%, ignition residue ≤0.05%, o-hydroxybenzoic acid isomer content ≤0.25%, and heavy metal (calculated as Pb) ≤5ppm.

[0034] Example 3

[0035] A method for preparing p-hydroxybenzoic acid comprises the following steps:

[0036] Step 1: Mix benzoic acid and potassium hydroxide solution to form a potassium phenolate solution. The molar ratio of benzoic acid to potassium hydroxide is 1:4, and the mass fraction of potassium hydroxide solution is 60%. After adding phenol and potassium hydroxide solution to the reaction vessel, it is necessary to heat to 100°C and stir to react for 1 hour. The potassium phenolate needs to be ground to a particle size of less than 25μm before use;

[0037] Step 2: In an alkaline aqueous solution, a directional hydroxylation reaction is carried out with a hydroxylating agent in the presence of a phase transfer catalyst at 80°C for 5 hours to produce potassium p-hydroxybenzoate. The phase transfer catalyst is a complex of tetrabutylammonium bromide and polyethylene glycol 6000, with a mass ratio of 1:2 and a total addition amount of 3% of the raw material mass. During the reaction, nitrogen is bubbled for 10 minutes every hour to enhance mass transfer.

[0038] Step 3: convert potassium p-hydroxybenzoate into p-hydroxybenzoic acid by acidification. The acidification uses hydrochloric acid or sulfuric acid at a concentration of 60%, and the pH of the solution needs to be adjusted to 5.

[0039] The prepared p-hydroxybenzoic acid product meets the following indicators: purity ≥99%, ignition residue ≤0.05%, o-hydroxybenzoic acid isomer content ≤0.25%, and heavy metal (calculated as Pb) ≤5ppm.

[0040] The present invention and its embodiments are described above, and such description is not restrictive. If a person skilled in the art is inspired by the above, and does not deviate from the purpose of the present invention, and designs an embodiment similar to the technical solution without creative design, it shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing p-hydroxybenzoic acid, characterized in that: The following steps are involved: Step 1: mixing benzoic acid with potassium hydroxide solution to form a potassium phenolate solution; Step 2: In an alkaline aqueous solution system, a directional hydroxylation reaction is carried out with a hydroxylating agent in the presence of a phase transfer catalyst to produce potassium p-hydroxybenzoate; Step 3: converting potassium p-hydroxybenzoate into p-hydroxybenzoic acid through acidification.

2. The method for preparing p-hydroxybenzoic acid according to claim 1, wherein: In step 1, the molar ratio of benzoic acid to potassium hydroxide is 1:1 to 1:4, and the mass fraction of the potassium hydroxide solution is 40% to 60%.

3. A method for preparing p-hydroxybenzoic acid according to claim 2, characterized in that: In step 1, after adding phenol and potassium hydroxide solution into the reaction vessel, it is necessary to heat to 100° C. and stir the reaction at this temperature for 0.6 to 1 hour.

4. The method for preparing p-hydroxybenzoic acid according to claim 3, wherein: In the step 1, the potassium phenolate needs to be ground to a particle size of less than 25 μm.

5. The method for preparing p-hydroxybenzoic acid according to claim 1, wherein: In step 2, the reaction temperature is 50° C. to 80° C., and the reaction time is 2 hours to 5 hours.

6. The method for preparing p-hydroxybenzoic acid according to claim 5, wherein: In step 2, the phase transfer catalyst is a complex of tetrabutylammonium bromide and polyethylene glycol 6000, the mass ratio of the two is 1:0.5-2, and the total addition amount is 1-3% of the mass of the raw materials; during the reaction process, nitrogen is bubbled for 7-10 minutes every hour to enhance mass transfer.

7. The method for preparing p-hydroxybenzoic acid according to claim 1, wherein: In step three, the acidification treatment uses hydrochloric acid or sulfuric acid with a concentration of 40% to 60%.

8. The method for preparing p-hydroxybenzoic acid according to claim 7, wherein: In step three, the pH of the solution needs to be adjusted to 4-5.

9. The method for preparing p-hydroxybenzoic acid according to claim 1, wherein: The prepared p-hydroxybenzoic acid product meets the following indicators: purity ≥99%, ignition residue ≤0.05%, o-hydroxybenzoic acid isomer content ≤0.25%, and heavy metal (calculated as Pb) ≤5ppm.