Preparation process of 4-hydroxythiobenzamide

Abstract

The invention relates to the technical field of benzamide, in particular to a preparation process of 4-hydroxythiobenzamide, which comprises the following steps: S1, preparing raw materials: preparing the 4-hydroxythiobenzamide from the following raw materials in parts by weight: 80-100 parts of formic acid, 80-100 parts of hydrochloric acid, 20-30 parts of 4-hydroxybenzaldehyde, 8-12 parts of hydroxylamine hydrochloride, 8-12 parts of thioacetamide and 4-6 parts of sodium hydroxide. According to the preparation method, after 4-hydroxybenzaldehyde is subjected to activating treatment reaction, part of positive charges on aldehyde carbon are dispersed, oxygen atoms in an acetal structure are connected with the aldehyde carbon through covalent bonds to generate an electron withdrawing induction effect, the reaction sequence and the reaction path of the 4-hydroxybenzaldehyde can be controlled through aldehyde activation, and the reaction efficiency of the 4-hydroxybenzaldehyde is improved. Therefore, the generation of byproducts is reduced, and the purity of a reaction product obtained from 4-hydroxybenzaldehyde is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of benzamide, and specifically to a preparation process of 4-hydroxythiobenzamide. Background Art

[0002] 4-Hydroxythiobenzamide is an organic compound, usually appearing as a white or off-white solid. In the chemical field, it can be used as an organic synthesis intermediate for synthesizing other complex organic compounds.

[0003] In the prior art, during the preparation of 4-hydroxythiobenzamide, impurities are generated during various reactions, affecting the product purity of 4-hydroxythiobenzamide. Based on this, the present invention provides a preparation process of 4-hydroxythiobenzamide. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation process of 4-hydroxythiobenzamide. The 4-hydroxythiobenzamide prepared by the present invention has a high purity and melting point, effectively improving the use effect of 4-hydroxythiobenzamide.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A preparation process of 4-hydroxythiobenzamide, comprising the following steps:

[0007] S1: Raw material preparation. The preparation of 4-hydroxythiobenzamide includes the following raw materials in parts by weight: 80 - 100 parts of formic acid, 80 - 100 parts of hydrochloric acid, 20 - 30 parts of 4-hydroxybenzaldehyde, 8 - 12 parts of hydroxylamine hydrochloride, 8 - 12 parts of thioacetamide, and 4 - 6 parts of sodium hydroxide;

[0008] S2: Activation treatment. Before preparation, 4-hydroxybenzaldehyde is pre-activated to obtain an activated material;

[0009] S2: Reaction treatment to obtain a solid substance;

[0010] S3: Purification treatment. The solid substance is purified to obtain 4-hydroxythiobenzamide.

[0011] Further, the activation treatment method is as follows: 4-hydroxybenzaldehyde and toluene are mixed in a beaker, the mass of toluene is 2 - 4 times that of 4-hydroxybenzaldehyde. After mixing evenly, toluenesulfonic acid is added, and the mixture is further mixed evenly. After standing for reaction for 10 - 20 min, methanol is added, and the mixture stands for reaction for 8 - 12 min. The mass of toluenesulfonic acid is 20 - 30% of the mass of 4-hydroxybenzaldehyde, and the mass of methanol is 10 - 20% of the mass of 4-hydroxybenzaldehyde. The product obtained in the beaker is added to a water bath, and the water bath is set to heat up to 40 - 50 °C and keep warm for reaction for 20 - 30 min to obtain the activated material.

[0012] Further, the preliminary reaction method is as follows: Sodium hydroxide and formic acid are added to a water bath, the set temperature is 60 - 70 °C, and the mixture is kept warm for reaction for 8 - 12 min. Stirring is maintained during the heat preservation process. After the heat preservation ends, it is cooled to room temperature. Activated material and hydroxylamine hydrochloride are added to the water bath, and the water bath is set to heat up to 80 - 90 °C and keep warm for reaction for 2 - 4 h. After the heat preservation ends, it is cooled to room temperature to obtain the reaction solution.

[0013] Further, acetamide sulfate and hydrochloric acid are added to the reaction solution, and the water bath is set to heat up to 60 - 70 °C and keep warm for reaction for 2 - 4 h. After the heat preservation ends, it is cooled to room temperature to obtain the mixed solution.

[0014] Further, an equal amount of deionized water is added to the mixed solution. After mixing evenly, filtration is carried out to obtain a filter cake. The filter cake is sent into an oven, and the oven is set to dry at 60 - 70 °C for 1 - 3 h to obtain the solid material.

[0015] Further, the purification treatment method is as follows: The solid material is placed in an oven, the oven is set to 38 - 42 °C, and the solid material is kept warm and left standing for 40 - 50 min to obtain the preheated material.

[0016] Further, the preheated material is added to a mixer, and the mixer is set to stir at 120 - 160 r / min for 6 - 10 min to obtain the powder material.

[0017] Further, the powder material is added to a reaction kettle, a catalyst is added to the reaction kettle, the reaction kettle is set to heat up to 60 - 70 °C, the stirring speed is 80 - 120 r / min, and it is set to keep warm and stir for 10 - 20 min. Nitrogen is introduced into the reaction kettle during the heat preservation and stirring process, and the nitrogen introduction amount is 1 - 3 L / min. After the treatment of the reaction kettle is completed, the treated solution is obtained.

[0018] Further, the treatment liquid is added to a pressure filter for filtration and separation to obtain a filtrate. The filtrate is added to a distillation kettle, and the distillation kettle is set to a vacuum degree of 0.08 - 0.1 MPa, and the water bath temperature is maintained at 40 - 50 °C for continuous distillation. The product obtained by distillation is subjected to an ice - water bath for 4 - 6 min, and then subjected to suction filtration and primary filtration. The obtained product is sent into an oven, and the oven is set to dry at 60 - 70 °C for 2 - 4 h to obtain 4 - hydroxythiobenzamide.

[0019] Further, the catalyst is a mixture of sodium sulfite and hydroquinone, and the mass ratio of sodium sulfite to hydroquinone is 1:(0.2 - 0.4).

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. In the present invention, through the activation treatment of 4 - hydroxybenzaldehyde in the preparation process of 4 - hydroxythiobenzamide, after the activation treatment reaction of 4 - hydroxybenzaldehyde, the partial positive charge on the aldehyde - group carbon is dispersed. The oxygen atom in the acetal structure is connected to the aldehyde - group carbon through a covalent bond, generating an electron - withdrawing inductive effect. The activation of the aldehyde group can control the reaction sequence and reaction path of 4 - hydroxybenzaldehyde, thereby reducing the generation of by - products and improving the purity of the reaction product obtained from 4 - hydroxybenzaldehyde.

[0022] 2. In the present invention, through the purification treatment of the 4 - hydroxythiobenzamide product, the physical properties of the solid material after pre - heating will change, and it is easier to be broken and mixed evenly in the subsequent mixing process. The ice - water bath can quickly cool the product, reducing its residence time at high temperature. The final drying treatment can remove the moisture in the product to obtain high - purity 4 - hydroxythiobenzamide. Specific Embodiments

[0023] The following will clearly and completely describe the technical solutions in the experiments of the present invention in combination with the experiments of the present invention. Obviously, the described experiments are only a part of the experiments of the present invention, rather than all the experiments. Based on the experiments of the present invention, all other experiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by the present invention.

[0024] This embodiment provides a preparation process of 4 - hydroxythiobenzamide, including the following steps:

[0025] S1: Raw material preparation. The preparation of 4 - hydroxythiobenzamide includes the following raw materials in parts by weight: 80 - 100 parts of formic acid, 80 - 100 parts of hydrochloric acid, 20 - 30 parts of 4 - hydroxybenzaldehyde, 8 - 12 parts of hydroxylamine hydrochloride, 8 - 12 parts of thioacetamide, and 4 - 6 parts of sodium hydroxide;

[0026] S2: Activation treatment. Prior to preparation, 4-hydroxybenzaldehyde is pre-activated to obtain an activated material.

[0027] S2: Reaction treatment to obtain a solid substance.

[0028] S3: Purification treatment. The solid substance is purified to obtain 4-hydroxythiobenzamide.

[0029] In some embodiments, the activation treatment method is as follows: 4-hydroxybenzaldehyde and toluene are mixed in a beaker. The mass of toluene is 2 - 4 times that of 4-hydroxybenzaldehyde. After mixing evenly, p-toluenesulfonic acid is added and mixing continues until evenly mixed. Then, it is left to react for 10 - 20 min. Methanol is added and left to react for 8 - 12 min. The mass of p-toluenesulfonic acid is 20 - 30% of the mass of 4-hydroxybenzaldehyde, and the mass of methanol is 10 - 20% of the mass of 4-hydroxybenzaldehyde. The product obtained in the beaker is added to a water bath. The water bath is set to heat up to 40 - 50 °C and keep the temperature for 20 - 30 min to obtain the activated material.

[0030] In some embodiments, the preliminary reaction method is as follows: Sodium hydroxide and formic acid are added to a water bath. The temperature is set to 60 - 70 °C and kept for 8 - 12 min with stirring during the heat preservation process. After the heat preservation ends, it is cooled to room temperature. The activated material and hydroxylamine hydrochloride are added to the water bath. The water bath is set to heat up to 80 - 90 °C and keep the temperature for 2 - 4 h. After the heat preservation ends, it is cooled to room temperature to obtain a reaction solution.

[0031] In some embodiments, acetamide sulfate and hydrochloric acid are added to the reaction solution. The water bath is set to heat up to 60 - 70 °C and keep the temperature for 2 - 4 h. After the heat preservation ends, it is cooled to room temperature to obtain a mixed solution.

[0032] In some embodiments, an equal amount of deionized water is added to the mixed solution. After mixing evenly, it is filtered by suction to obtain a filter cake. The filter cake is sent to an oven, and the oven is set to dry at 60 - 70 °C for 1 - 3 h to obtain the solid substance.

[0033] In some embodiments, the purification treatment method is as follows: The solid substance is placed in an oven. The oven is set to 38 - 42 °C, and the solid substance is kept warm and left standing for 40 - 50 min to obtain a preheated material.

[0034] In some embodiments, the preheated material is added to a mixer. The mixer is set to stir at 120 - 160 r / min for 6 - 10 min to obtain a powder.

[0035] In some embodiments, powder materials are added into a reaction kettle, a catalyst is added into the reaction kettle, the reaction kettle is set to be heated to 60 - 70 °C, the stirring speed is 80 - 120 r / min, the heat preservation and stirring treatment is set for 10 - 20 min, nitrogen is introduced into the reaction kettle during the heat preservation and stirring treatment, the nitrogen introduction amount is 1 - 3 L / min, and after the treatment of the reaction kettle is completed, a treatment liquid is obtained.

[0036] In some embodiments, the treatment liquid is added into a pressure filter for filtration separation to obtain a filtrate. The filtrate is added into a distillation kettle. The distillation kettle is set with a vacuum degree of 0.08 - 0.1 MPa, and continuous distillation is carried out at a water bath temperature of 40 - 50 °C. The distilled product is subjected to an ice - water bath for 4 - 6 min, and then primary filtration by suction filtration is carried out. The obtained product is sent into an oven. The oven is set to dry at 60 - 70 °C for 2 - 4 h to prepare 4 - hydroxythiobenzamide.

[0037] In some embodiments, the catalyst is a mixture of sodium sulfite and hydroquinone, and the mass ratio of sodium sulfite to hydroquinone is 1:(0.2 - 0.4).

[0038] In this embodiment, through the activation treatment of 4 - hydroxybenzaldehyde during the preparation of 4 - hydroxythiobenzamide, after the activation treatment reaction of 4 - hydroxybenzaldehyde, the partial positive charge on the aldehyde - group carbon is dispersed. The oxygen atom in the acetal structure is connected to the aldehyde - group carbon through a covalent bond, generating an electron - withdrawing inductive effect. Aldehyde - group activation can control the reaction sequence and reaction path of 4 - hydroxybenzaldehyde, thereby reducing the generation of by - products and improving the purity of the reaction product obtained from 4 - hydroxybenzaldehyde. Through the purification treatment of the 4 - hydroxythiobenzamide product, the physical properties of the pre - heated solid substance will change, and it is easier to be broken and mixed evenly during the subsequent mixing process. The ice - water bath can quickly cool the product and reduce its residence time at high temperature. The final drying treatment can remove the moisture in the product to obtain high - purity 4 - hydroxythiobenzamide.

[0039] Based on the foregoing embodiments, the following multiple groups of experiments were carried out:

[0040] It should be noted that the raw materials used in the following experiments are all commercially available raw materials.

[0041] Experiment 1:

[0042] S1: Raw material preparation. The preparation of 4 - hydroxythiobenzamide includes the following raw materials by weight: 80 parts of formic acid, 80 parts of hydrochloric acid, 20 parts of 4 - hydroxybenzaldehyde, 8 parts of hydroxylamine hydrochloride, 8 parts of thioacetamide, and 4 parts of sodium hydroxide;

[0043] S2: Activation treatment. 4 - hydroxybenzaldehyde is pre - activated before preparation to obtain an activated material;

[0044] S2: Reaction treatment to obtain a solid substance;

[0045] S3: Purification treatment, purifying the solid substance to obtain 4-hydroxythiobenzamide.

[0046] The method of activation treatment is as follows: 4-hydroxybenzaldehyde and toluene are mixed in a beaker. The mass of toluene is twice that of 4-hydroxybenzaldehyde. After mixing evenly, toluenesulfonic acid is added, and then mixed evenly again. After standing for reaction for 10 min, methanol is added, and then standing for reaction for 8 min. The mass of toluenesulfonic acid is 20% of the mass of 4-hydroxybenzaldehyde, and the mass of methanol is 10% of the mass of 4-hydroxybenzaldehyde. The product obtained in the beaker is added to a water bath pot, and the water bath pot is set to heat up to 40 °C and keep the temperature for reaction for 20 min to obtain an activated material.

[0047] The method of preliminary reaction is as follows: Sodium hydroxide and formic acid are added to a water bath pot, and the set temperature is 60 °C. Keep stirring during the heat preservation reaction for 8 min. After the heat preservation is completed, cool to room temperature. Then add the activated material and hydroxylamine hydrochloride to the water bath pot, and the water bath pot is set to heat up to 80 °C and keep the temperature for reaction for 2 h. After the heat preservation is completed, cool to room temperature to obtain a reaction solution.

[0048] Ethylsulfonamide and hydrochloric acid are added to the reaction solution. The water bath pot is set to heat up to 60 °C and keep the temperature for reaction for 2 h. After the heat preservation is completed, cool to room temperature to obtain a mixed solution.

[0049] An equal amount of deionized water is added to the mixed solution. After mixing evenly, it is filtered by suction to obtain a filter cake. The filter cake is sent into an oven, and the oven is set to dry at 60 °C for 1 h to obtain a solid substance.

[0050] The method of purification treatment is as follows: The solid substance is placed in an oven, and the oven is set to 38 °C. The solid substance is kept warm and static for 40 min to obtain a preheated material.

[0051] The preheated material is added to a mixer, and the mixer is set to stir at 120 r / min for 6 min to obtain a powder.

[0052] The powder is added to a reaction kettle, and a catalyst is added to the reaction kettle. The reaction kettle is set to heat up to 60 °C, the stirring speed is 80 r / min, and it is set to keep stirring and reacting for 10 min. During the process of keeping stirring and reacting, nitrogen is introduced into the reaction kettle, and the nitrogen introduction amount is 1 L / min. After the reaction kettle is processed, a treatment solution is obtained.

[0053] The treatment solution is added to a pressure filter for filtration separation to obtain a filtrate. The filtrate is added to a distillation kettle. The distillation kettle is set to a vacuum degree of 0.08 MPa and continuously distilled at a water bath temperature of 40 °C. The product obtained by distillation is placed in an ice-water bath for 4 min, and then filtered by suction for preliminary filtration. The obtained product is sent into an oven, and the oven is set to dry at 60 °C for 2 h to obtain 4-hydroxythiobenzamide.

[0054] The catalyst is a mixture of sodium sulfite and hydroquinone, and the mass ratio of sodium sulfite to hydroquinone is 1:(0.2).

[0055] Experiment 2:

[0056] S1: Raw material preparation. The preparation of 4-hydroxythiobenzamide includes the following raw materials in parts by weight: 90 parts of formic acid, 90 parts of hydrochloric acid, 25 parts of 4-hydroxybenzaldehyde, 10 parts of hydroxylamine hydrochloride, 10 parts of thioacetamide, and 5 parts of sodium hydroxide;

[0057] S2: Activation treatment. 4-Hydroxybenzaldehyde is pre-activated before preparation to obtain an activated material;

[0058] S2: Reaction treatment. A solid substance is prepared;

[0059] S3: Purification treatment. The solid substance is purified to obtain 4-hydroxythiobenzamide.

[0060] The method of activation treatment is as follows: 4-Hydroxybenzaldehyde and toluene are mixed in a beaker. The mass of toluene is 3 times that of 4-hydroxybenzaldehyde. After mixing evenly, toluenesulfonic acid is added, and the mixture is continuously mixed evenly. After standing for 15 min, methanol is added, and then standing for 10 min. The mass of toluenesulfonic acid is 25% of the mass of 4-hydroxybenzaldehyde, and the mass of methanol is 15% of the mass of 4-hydroxybenzaldehyde. The product obtained in the beaker is added to a water bath. The water bath is set to heat up to 45 °C and keep the temperature for 25 min to obtain an activated material.

[0061] The method of preliminary reaction is as follows: Sodium hydroxide and formic acid are added to a water bath. The temperature is set to 65 °C and keep the temperature for 10 min. Stirring is maintained during the heat preservation process. After the heat preservation is completed, it is cooled to room temperature. The activated material and hydroxylamine hydrochloride are added to the water bath. The water bath is set to heat up to 85 °C and keep the temperature for 3 h. After the heat preservation is completed, it is cooled to room temperature to obtain a reaction solution.

[0062] Thioacetamide and hydrochloric acid are added to the reaction solution. The water bath is set to heat up to 65 °C and keep the temperature for 3 h. After the heat preservation is completed, it is cooled to room temperature to obtain a mixed solution.

[0063] An equal amount of deionized water is added to the mixed solution. After mixing evenly, it is filtered by suction to obtain a filter cake. The filter cake is sent to an oven. The oven is set to dry at 65 °C for 2 h to obtain a solid substance.

[0064] The method of purification treatment is as follows: The solid substance is placed in an oven. The oven is set to 40 °C, and the solid substance is kept standing for 45 min to obtain a preheated material.

[0065] The preheated material is added to a mixer. The mixer is set to stir at 140 r / min for 8 min to obtain a powder.

[0066] The powder is added into the reaction kettle, and a catalyst is added into the reaction kettle. The reaction kettle is set to heat up to 65 °C, the stirring speed is 100 r / min, and it is set to be kept warm and stirred for 15 min. Nitrogen is introduced into the reaction kettle during the heat preservation and stirring process, and the nitrogen introduction amount is 2 L / min. After the treatment of the reaction kettle is completed, a treatment liquid is obtained.

[0067] The treatment liquid is added into a pressure filter for filtration and separation to obtain a filtrate. The filtrate is added into a distillation kettle. The distillation kettle is set to have a vacuum degree of 0.09 MPa, and the water bath temperature is 45 °C for continuous distillation. The distilled product is subjected to an ice-water bath for 5 min, and then subjected to primary suction filtration. The obtained product is sent into an oven, and the oven is set to dry at 65 °C for 3 h to prepare 4-hydroxythiobenzamide.

[0068] The catalyst is a mixture of sodium sulfite and hydroquinone, and the mass ratio of sodium sulfite to hydroquinone is 1:(0.3).

[0069] Experiment Three:

[0070] S1: Raw material preparation. The preparation of 4-hydroxythiobenzamide includes the following raw materials in parts by weight: 100 parts of formic acid, 100 parts of hydrochloric acid, 30 parts of 4-hydroxybenzaldehyde, 12 parts of hydroxylamine hydrochloride, 12 parts of thioacetamide, and 6 parts of sodium hydroxide.

[0071] S2: Activation treatment. 4-Hydroxybenzaldehyde is pre-activated before preparation to obtain an activated material.

[0072] S2: Reaction treatment. A solid substance is prepared.

[0073] S3: Purification treatment. The solid substance is purified to prepare 4-hydroxythiobenzamide.

[0074] The activation treatment method is as follows: 4-Hydroxybenzaldehyde and toluene are mixed in a beaker. The mass of toluene is 4 times the mass of 4-hydroxybenzaldehyde. After mixing evenly, toluenesulfonic acid is added, and the mixture is continuously mixed evenly. After standing for 20 min, methanol is added, and the mixture stands for 12 min. The mass of toluenesulfonic acid is 30% of the mass of 4-hydroxybenzaldehyde, and the mass of methanol is 20% of the mass of 4-hydroxybenzaldehyde. The product obtained in the beaker is added into a water bath kettle, and the water bath kettle is set to heat up to 50 °C and keep the reaction for 30 min to obtain an activated material.

[0075] The preliminary reaction method is as follows: Sodium hydroxide and formic acid are added into a water bath kettle, and the temperature is set to 70 °C and the reaction is kept for 12 min. Stirring is maintained during the heat preservation process. After the heat preservation ends, it is cooled to room temperature. The activated material and hydroxylamine hydrochloride are added into the water bath kettle, and the water bath kettle is set to heat up to 90 °C and keep the reaction for 4 h. After the heat preservation ends, it is cooled to room temperature to obtain a reaction solution.

[0076] Ethyl acetamide sulfate and hydrochloric acid were added to the reaction solution. The water bath was set to heat up to 70 °C and keep the temperature for 4 h. After the heat preservation ended, it was cooled to room temperature to obtain a mixed solution.

[0077] An equal amount of deionized water was added to the mixed solution. After mixing evenly, it was filtered by suction to obtain a filter cake. The filter cake was sent into an oven, and the oven was set to dry at 70 °C for 3 h to obtain a solid substance.

[0078] The purification method was as follows: The solid substance was placed in an oven, and the oven was set to 42 °C. The solid substance was kept warm and static for 50 min to obtain a preheated material.

[0079] The preheated material was added to a mixer, and the mixer was set to stir at 160 r / min for 10 min to obtain a powder.

[0080] The powder was added to a reaction kettle, a catalyst was added to the reaction kettle, the reaction kettle was set to heat up to 70 °C, the stirring speed was 120 r / min, and it was set to keep warm and stir for 20 min. Nitrogen was introduced into the reaction kettle during the heat preservation and stirring process, and the nitrogen introduction amount was 3 L / min. After the reaction kettle treatment was completed, a treated solution was obtained.

[0081] The treated solution was added to a pressure filter for filtration separation to obtain a filtrate. The filtrate was added to a distillation kettle. The distillation kettle was set to a vacuum degree of 0.1 MPa, and the water bath temperature was 50 °C for continuous distillation. The distilled product was subjected to an ice-water bath for 6 min, and then subjected to suction filtration and primary filtration. The obtained product was sent into an oven, and the oven was set to dry at 70 °C for 4 h to obtain 4-hydroxythiobenzamide.

[0082] The catalyst was a mixture of sodium sulfite and hydroquinone, and the mass ratio of sodium sulfite to hydroquinone was 1:(0.4).

[0083] Comparative Example 1. The difference between this comparative example and Experiment 1 was that: This comparative example did not contain a covering material.

[0084] Comparative Example 2. The difference between this comparative example and Experiment 1 was that: This comparative example did not perform the treatment of soaking in the film-forming solution.

[0085] Comparative Example 3. The difference between this comparative example and Experiment 1 was that: This comparative example did not add vanadyl sulfate when preparing the film-forming solution.

[0086] Comparative Example 4. The difference between this comparative example and Experiment 1 was that: This comparative example did not perform the treatment of the soaking solution.

[0087] Performance test: The 4-hydroxythiobenzamide prepared in Experiment 1, Experiment 2, Experiment 3, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 was subjected to a performance test, and the obtained test data were recorded in the following table:

[0088] It can be seen that the purity performance and melting point data of the aluminum alloy plates after being treated in Comparative Examples 1, 2, 3, and 4 are all lower than those in Experiments 1, 2, and 3. This shows that: by activating 4-hydroxybenzaldehyde during the preparation process of 4-hydroxythiobenzamide, after the activation treatment of 4-hydroxybenzaldehyde in the reaction, the partial positive charge on the aldehyde carbon is dispersed. The oxygen atom in the acetal structure is connected to the aldehyde carbon through a covalent bond, generating an electron-withdrawing inductive effect. Aldehyde activation can control the reaction sequence and reaction path of 4-hydroxybenzaldehyde, thereby reducing the generation of by-products and improving the purity of the reaction products obtained from 4-hydroxybenzaldehyde.

[0089] By comparing and analyzing the relevant data in the table, it can be seen that the 4-hydroxythiobenzamide prepared by the present invention has a high purity and melting point. This indicates that the preparation process of the 4-hydroxythiobenzamide provided by the present invention has a broader market prospect and is more suitable for promotion.

[0090] In the description of this specification, the description referring to terms such as "one experiment", "example", "specific example", etc. means that the specific features, structures, materials, or characteristics described in connection with that experiment or example are included in at least one experiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same experiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more experiments or examples.

[0091] The preferred experiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred experiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. The present specification selects and specifically describes these experiments in order to better explain the principle and practical application of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A preparation process of 4-hydroxythiobenzamide, characterized in that: It includes the following steps: S1: Raw material preparation. The preparation of 4-hydroxythiobenzamide includes the following raw materials in parts by weight: 80-100 parts of formic acid, 80-100 parts of hydrochloric acid, 20-30 parts of 4-hydroxybenzaldehyde, 8-12 parts of hydroxylamine hydrochloride, 8-12 parts of thioacetamide, and 4-6 parts of sodium hydroxide; S2: Activation treatment. 4-hydroxybenzaldehyde is pre-activated before preparation to obtain an activated material; S2: Reaction treatment. A solid substance is obtained; S3: Purification treatment. The solid substance is purified to obtain 4-hydroxythiobenzamide.

2. The preparation process of 4-hydroxythiobenzamide according to claim 1, characterized in that, The method of the activation treatment is as follows: 4-hydroxybenzaldehyde and toluene are mixed in a beaker. The mass of toluene is 2-4 times the mass of 4-hydroxybenzaldehyde. After mixing evenly, toluenesulfonic acid is added, and the mixture is continuously mixed evenly. After standing and reacting for 10-20 min, methanol is added, and the mixture is allowed to stand and react for 8-12 min. The mass of toluenesulfonic acid is 20-30% of the mass of 4-hydroxybenzaldehyde, and the mass of methanol is 10-20% of the mass of 4-hydroxybenzaldehyde. The product obtained in the beaker is added to a water bath pot, and the water bath pot is set to heat up to 40-50 °C and keep the temperature for reaction for 20-30 min to obtain an activated material.

3. The preparation process of 4-hydroxythiobenzamide according to claim 1, characterized in that, The method of the preliminary reaction is as follows: Sodium hydroxide and formic acid are added to a water bath pot, and the temperature is set to 60-70 °C and keep the temperature for reaction for 8-12 min. Stirring is maintained during the heat preservation process. After the heat preservation ends, it is cooled to room temperature. The activated material and hydroxylamine hydrochloride are added to the water bath pot, and the water bath pot is set to heat up to 80-90 °C and keep the temperature for reaction for 2-4 h. After the heat preservation ends, it is cooled to room temperature to obtain a reaction solution.

4. The preparation process of 4-hydroxythiobenzamide according to claim 3, characterized in that, Thioacetamide and hydrochloric acid are added to the reaction solution, and the water bath pot is set to heat up to 60-70 °C and keep the temperature for reaction for 2-4 h. After the heat preservation ends, it is cooled to room temperature to obtain a mixed solution.

5. The preparation process of 4-hydroxythiobenzamide according to claim 4, characterized in that, An equal amount of deionized water is added to the mixed solution. After mixing evenly, it is filtered by suction to obtain a filter cake. The filter cake is sent into an oven, and the oven is set to dry at 60-70 °C for 1-3 h to obtain a solid substance.

6. The preparation process of 4-hydroxythiobenzamide according to claim 1, characterized in that, The method of the purification treatment is as follows: The solid substance is placed in an oven, and the oven is set to 38-42 °C. The solid substance is kept warm and allowed to stand for 40-50 min to obtain a preheated material.

7. The preparation process of 4-hydroxythiobenzamide according to claim 6, characterized in that, The preheated material is added to a mixer, and the mixer is set to stir at 120-160 r / min for 6-10 min to obtain a powder.

8. The preparation process of 4-hydroxythiobenzamide according to claim 7, characterized in that, The powder is added to a reaction kettle, a catalyst is added to the reaction kettle, the reaction kettle is set to heat up to 60-70 °C, the stirring speed is 80-120 r / min, and it is set to keep the temperature and stir for 10-20 min. Nitrogen is introduced into the reaction kettle during the heat preservation and stirring process, and the nitrogen introduction amount is 1-3 L / min. After the reaction kettle treatment is completed, a treatment solution is obtained.

9. The preparation process of 4-hydroxythiobenzamide according to claim 8, characterized in that, The treatment solution is added to a pressure filter for filtration and separation to obtain a filtrate. The filtrate is added to a distillation kettle. The distillation kettle is set to a vacuum degree of 0.08-0.1 MPa, and the water bath temperature is kept at 40-50 °C for continuous distillation. The distilled product is subjected to an ice-water bath for 4-6 min, and then subjected to suction filtration and primary filtration. The obtained product is sent into an oven, and the oven is set to dry at 60-70 °C for 2-4 h to obtain 4-hydroxythiobenzamide.

10. The preparation process of 4-hydroxythiobenzamide according to claim 8, characterized in that, The catalyst selected is a mixture of sodium sulfite and hydroquinone, and the mass ratio of sodium sulfite to hydroquinone is 1:(0.2 - 0.4).