Preparation method of pyrogallic acid

Abstract

The invention discloses a preparation method of pyrogallic acid, which specifically comprises the following steps: (1) catalytic dehydration reaction: adding gallic acid and deionized water in a mass ratio of 1: (5-10) into a reaction kettle, stirring and heating to 70-100 DEG C, adding 100-400-mesh expanded graphite accounting for 50-200% of the mass of the gallic acid, and reacting for 30-120 minutes; (2) solid-liquid separation: filtering the reaction liquid in the step (1), and separating to obtain a filter cake; (3) sublimation purification: transferring the filter cake obtained in the step (2) into a sublimation reaction kettle, slowly heating to 130-230 DEG C, and reacting for 30-120 minutes; and (4) vacuum collection: starting a vacuum system, and collecting a distilled sublimation product until no product is distilled, so that the sublimation product is the pyrogallic acid. According to the method, through the catalysis / adsorption effect of the expanded graphite, the gallic acid conversion rate and the product purity are remarkably improved, and meanwhile efficient recovery of the catalyst is achieved. The method is suitable for large-scale production and has remarkable economic benefits and environmental protection values.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical synthesis, in particular to a preparation method of pyrogallic acid. BACKGROUND

[0002] Pyrogallic acid is an important organic compound, which is widely used in the fields of medicine, pesticide and photographic developer. At present, the preparation methods of pyrogallic acid mainly include two kinds: 1. Direct high-temperature decarboxylation method: gallic acid is heated to 175-200℃ for decarboxylation reaction, which needs high-concentration hydrochloric acid to participate in the reaction, resulting in a large amount of high-salinity wastewater after reaction, which increases the treatment cost and causes environmental pollution.

[0003] 2. Quinoline-copper catalytic decarboxylation method: gallic acid is subjected to normal pressure catalytic decarboxylation in quinoline solution in the presence of copper metal or copper salt, which has high yield and simple operation process, but trace amounts of catalyst are easily left in the product, affecting the purity.

[0004] These methods generally have the following problems: a. Serious environmental pollution: high-salinity wastewater is difficult to treat, which does not meet the environmental protection requirements; b. Low product purity: many side reactions occur, which need complex refining steps; c. High energy consumption: high-temperature operation leads to high energy consumption; d. Risk of equipment corrosion: strong acid or metal catalysts have corrosion effect on equipment.

[0005] In view of the above problems, there is an urgent need for an efficient and environmentally friendly preparation method of pyrogallic acid. SUMMARY

[0006] This section aims to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, abstract and title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0007] Therefore, in order to solve the above technical problems, the present application provides the following technical scheme: a preparation method of pyrogallic acid, specifically comprising the following steps: (1) Catalytic dehydration reaction: gallic acid and deionized water are added to a reaction kettle, the mass ratio of gallic acid to deionized water is 1:5-10, stirring is carried out to heat to 70-100℃, 100-400 mesh expanded graphite accounting for 50-200% of the mass of gallic acid is added, and reaction is carried out for 30-120 min; (2) Solid-liquid separation: the reaction liquid of step (1) is filtered to separate and obtain a filter cake; (3) Sublimation purification: the filter cake obtained in step (2) is transferred into a sublimation reactor, slowly heated to 130-230 DEG C, and reacted for 30-120 min; (4) Vacuum collection: the vacuum system is opened, and the sublimated product distilled is collected until no product is distilled, which is pyrogallic acid.

[0008] As a preferred scheme of the preparation method of pyrogallic acid, wherein: the expanded graphite is 100-400 mesh.

[0009] The beneficial effects of the present application are: 1. The expanded graphite is used as adsorption / catalytic material in the present application, and high conversion rate is achieved under mild conditions of 70-100 DEG C, which is much higher than that of traditional methods. The expanded graphite with high mesh number can achieve nearly 100% conversion rate in a short time.

[0010] 2. The pyrogallic acid obtained in the present application has a purity of ≥95% verified by high performance liquid chromatography (HPLC), which meets the pharmaceutical standard.

[0011] 3. The expanded graphite in the present application can be reused after simple washing (deionized water) and drying, and the recovered catalyst still maintains high activity, which reduces the production cost. No structure breakage or swelling phenomenon occurs during the recovery process, which prolongs the service life.

[0012] 4. The present application does not need to add any harmful solvent in the whole process, which avoids the discharge of toxic waste liquid. No acid-base neutralization step is needed, which avoids the generation of high-salt wastewater, and meets the development trend of green chemical industry. The excess deionized water can be directly recycled and reused, which reduces resource waste. DETAILED DESCRIPTION

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them: Fig. 1 It is the overall process flow chart of the present application.

[0014] Fig. 2 It is the IR spectrum of the product of example 1 of the present application.

[0015] Fig. 3 It is the HPLC spectrum of the product of example 1 of the present application.

[0016] Fig. 4 It is the HPLC spectrum of the product of example 2 of the present application.

[0017] Fig. 5 HPLC profile of the product of Example 3 of the present application.

[0018] Fig. 6 HPLC profile of the product of Example 4 of the present application. DETAILED DESCRIPTION

[0019] In order to make the above objectives, features and advantages of the present application more obvious and comprehensible, the specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0020] In the following description, a lot of specific details are set forth in order to provide a thorough understanding of the present application, however, the present application can also be implemented in other different ways from those described herein, and those skilled in the art can make similar generalizations without departing from the concept of the present application, therefore, the present application is not limited by the specific embodiments disclosed below.

[0021] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is independent of or selected from other embodiments.

[0022] Example 1 Reference Figs. 1-3 For the first embodiment of the present application, a preparation method of pyrogallic acid is provided, and the specific method is as follows: 200 mesh expanded graphite is used in the present embodiment to catalytically synthesize pyrogallic acid, and the specific steps are as follows: In the reaction kettle, 188 kg of gallic acid and 1000 kg of deionized water are added, and stirred to be heated to 80°C. 200 kg of 200 mesh expanded graphite (accounting for 106.4% of the mass of gallic acid) is added, and reacted for 60 min. After the reaction is completed, filtration separation is performed, and the filter cake is washed and transferred to a sublimation reaction kettle, and slowly heated to 180°C, and reacted for 70 min. The vacuum system is opened, and the sublimed product (i.e. pyrogallic acid) is collected until no product is distilled.

[0023] Purity of pyrogallic acid: 99.96% (HPLC); Conversion rate of gallic acid: 99.50%; Chemical structure confirmation: IR spectrum and standard spectrum of pyrogallic acid Fig. 1 .

[0024] Example 2 Reference Fig. 4 For the second embodiment of the present application, the difference between the present embodiment and the first embodiment is that: in the present embodiment, the recovered 200 mesh expanded graphite is used to catalytically synthesize pyrogallic acid, and the specific steps are as follows: 200 kg of 200 mesh expanded graphite (106.4% of the mass of gallic acid) recovered from Example 1 was reacted with 188 kg of gallic acid and 1000 kg of deionized water at 80 °C for 90 min. The subsequent operations were the same as in Example 1 (sublimation temperature 180 °C, reaction time 90 min, vacuum distillation).

[0025] Test results: Purity of pyrogallic acid: 98.30% (HPLC); Conversion of gallic acid: 98.50%.

[0026] Example 3 Reference Fig. 5 For the third embodiment of the present application, which differs from the first embodiment in that it uses 100 mesh expanded graphite to catalytically synthesize pyrogallic acid, the specific steps are as follows: In the reaction kettle, 188 kg of gallic acid and 400 kg of deionized water were added and stirred to 70 °C. 100 kg of 100 mesh expanded graphite (53.2% of the mass of gallic acid) was added and reacted for 30 min. After filtration, the filter cake was transferred to the sublimation reaction kettle and slowly heated to 130 °C, reacted for 30 min. The vacuum system was opened and the sublimation product (i.e. pyrogallic acid) was collected until no product was distilled out.

[0027] Test results: Purity of pyrogallic acid: 95.76% (HPLC); Conversion of gallic acid: 98.10%.

[0028] Example 4 Reference Fig. 6 For the fourth embodiment of the present application, which differs from the first embodiment in that it uses 400 mesh expanded graphite to catalytically synthesize pyrogallic acid, the specific steps are as follows: In the reaction kettle, 188 kg of gallic acid and 1800 kg of deionized water were added and stirred to 100 °C. 360 kg of 400 mesh expanded graphite (191.5% of the mass of gallic acid) was added and reacted for 120 min. After the reaction was completed, it was separated by filtration, and the filter cake was washed and transferred to the sublimation reaction kettle. It was slowly heated to 230 °C and reacted for 120 min. The vacuum system was opened and the sublimation product (i.e. pyrogallic acid) was collected until no product was distilled out.

[0029] Test results: Purity of pyrogallic acid: 99.46% (HPLC); Conversion of gallic acid: 99.20%.

[0030] It is proved by the above examples that the pyrogallic acid preparation method provided by the present application has the following advantages: 1. Excellent catalytic efficiency: By using expanded graphite as adsorption / catalytic material, high-efficiency conversion is realized under mild conditions of 70-100℃, and the conversion rate reaches 98%-99.96% (Example 1: 99.50%; Example 4: 99.20%), which is much higher than that of the traditional method (<85%).

[0031] High-mesh expanded graphite (such as 400 mesh) can reach a conversion rate close to 100% within a short time (within 120 min) (Example 4).

[0032] 2. Excellent product purity: The pyrogallic acid obtained has a purity of ≥95.76% (Example 1: 99.96%; Example 3: 95.76%) verified by HPLC, which meets the pharmaceutical standard.

[0033] 3. Recyclable catalyst: The expanded graphite can be reused after simple washing (deionized water) and drying, and the recovered catalyst still maintains high activity (conversion rate of 98.50% in Example 2), which reduces the production cost; No structure breakage or swelling occurs during the recovery process, which prolongs the service life.

[0034] 4. Outstanding environmental friendliness of the process: No harmful solvents (such as benzene, toluene, etc.) need to be added in the whole process, which avoids the discharge of toxic waste liquid; No acid-base neutralization step is needed, which avoids the generation of high-salinity wastewater, and conforms to the development trend of green chemical industry; Excess deionized water can be directly recycled and reused, which reduces resource waste.

[0035] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A method for preparing pyrogallic acid, characterized in that: Includes the following steps: S1: Add gallic acid and deionized water to the reactor, wherein the mass ratio of gallic acid to deionized water is 1:5-10, and stir until homogeneous; S2: Stir and heat to 70-100℃, add 50-200% gallic acid by weight of expanded graphite, and react for 30-120 minutes; S3: Filter the reaction mixture obtained in step S2 to obtain a filter cake; S4: Transfer the filter cake into a sublimation reactor and slowly heat it to 130-230°C for 30-120 minutes. S5: Turn on the vacuum system and collect the distilled sublimation product until no product is distilled out. The sublimation product is pyrogallic acid.

2. The method for preparing pyrogallic acid as described in claim 1, characterized in that: The expanded graphite has a particle size range of 100-400 mesh.

3. The method for preparing pyrogallic acid according to any one of claims 1 to 2, characterized in that: The pyrogallic acid obtained by this method has a purity of ≥95% and a gallic acid conversion rate of ≥98%.

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