Preparation method of amino acid metal surface corrosion inhibitor

Abstract

The invention provides a preparation method of an amino acid metal surface corrosion inhibitor, which comprises the following specific steps: S1, adding a certain amount of amino acid and phenyl isothiocyanate into a reaction container, adding a solvent, and stirring for reaction at a certain reaction temperature; s2, monitoring the reaction process of S1 through thin layer chromatography, cooling after the reaction is finished, and separating a reaction product to obtain a solid product; and S3, drying the solid product obtained in S2 to obtain the amino acid metal surface corrosion inhibitor. The preparation method of the amino acid metal surface corrosion inhibitor is simple, easy to operate and low in production cost, the metal corrosion inhibition effect of products is good, and the requirement for long-term storage of NTO-based high-energy-density materials can be met.

Description

Technical Field

[0001] The invention belongs to the technical field of metal corrosion prevention and control, and relates to a method for preparing an amino acid metal surface corrosion inhibitor. Background Art

[0002] Since NTO (3-nitro-1,2,4-triazol-5-one) was confirmed as a high energy density material in the last century, it has attracted widespread attention due to its energy release level comparable to that of RDX but with lower sensitivity. Thanks to its insensitive characteristics, it can greatly reduce the risk of personnel and platforms during the use of weapons and equipment, so it is used in various types of equipment as an important component of safe ammunition.

[0003] However, NTO itself has the characteristics of hygroscopicity and acidity. It easily absorbs moisture in the air to form a local acidic solution, which in turn causes the encapsulated metal shell to be corroded. This poses a challenge to the long-term storage of weapons and equipment containing NTO. Organic corrosion inhibitors, as a class of organic substances with heteroatoms such as sulfur, nitrogen, and oxygen and unsaturated functional groups, can form a covering protective film by coordinating with metal atoms on the metal surface, thereby blocking the contact between the metal surface and the corrosive medium. It is a metal corrosion prevention and control technology with application prospects. In the prior art, there are few solutions that clearly define the specific synthetic materials, preparation processes, and reaction conditions of organic corrosion inhibitors. At the same time, there are still defects such as complex preparation processes and high costs of synthetic materials. Therefore, how to effectively improve the preparation process of organic corrosion inhibitors to achieve the industrialization and standardized synthesis of organic corrosion inhibitors is a technical problem that needs to be solved urgently at this stage. Summary of the invention

[0004] In view of this, the present invention provides a method for preparing an amino acid-based metal surface corrosion inhibitor. The corrosion inhibitor material prepared by the method can form a protective film on the metal surface. The formation of the film involves physical or chemical adsorption of functional groups in organic molecules on the metal surface. The film has a dense structure and can block direct contact between NTO and other corrosive media and the carbon steel surface, thereby reducing the progress of corrosion reactions.

[0005] To achieve the above effects, the present invention provides a method for preparing an amino acid-based metal surface corrosion inhibitor, comprising the following specific steps: S1: adding a certain amount of amino acid and phenyl isothiocyanate into a reaction container, and adding a solvent, and stirring the reaction at a certain reaction temperature; S2: monitoring the reaction process of S1 by thin layer chromatography, cooling after the reaction is completed, separating the reaction product, and obtaining a solid product; S3: drying the solid product obtained in S2 to obtain an amino acid-based metal surface corrosion inhibitor.

[0006] Optionally, the amino acid is L-tryptophan, and the amino acid metal surface corrosion inhibitor obtained is N-[(phenylamino)sulfurylmethyl]-tryptophan corrosion inhibitor; or, the amino acid is L-arginine, and the amino acid metal surface corrosion inhibitor obtained is N2-[(phenylamino)sulfurylmethyl]-arginine corrosion inhibitor.

[0007] Optionally, when the amino acid is L-tryptophan, S1 specifically includes: the amount of L-tryptophan is 1-5 mmol, the amount of phenyl isothiocyanate is 1-5 mmol; the solvent is 50-100 mL of tetrahydrofuran; the reaction temperature is 80-90° C., and the stirring time is 7-9 h.

[0008] Preferably, the amount of L-tryptophan is 4.9 mmol, the amount of phenyl isothiocyanate is 4.9 mmol; the solvent is 85 mL of tetrahydrofuran; the reaction temperature is 85° C., and the stirring time is 8 h.

[0009] Optionally, when the amino acid is L-tryptophan, S2 and S3 specifically include: the cooling rate is 12-20°C / h; the separation of the reaction products includes concentrating the mother liquor and separating it by column chromatography after the cooling is completed, and purifying PE:EA to EA; the drying is vacuum drying, and the drying time is 35-45h.

[0010] Preferably, the cooling rate is 15°C / h and the drying time is 40h.

[0011] Optionally, when the amino acid is L-arginine, S1 specifically includes: the amount of L-arginine is 5.5-8 mmol, the amount of phenyl isothiocyanate is 5.5-8 mmol; the solvent is 50-100 mL ethanol and 5-15 mL double distilled water; the reaction temperature is 50-70° C., and the stirring time is 4-6 h.

[0012] Preferably, the amount of L-tryptophan is 5.74 mmol, the amount of phenyl isothiocyanate is 5.74 mmol; the solvent is 75 mL of ethanol and 10 mL of double distilled water; the reaction temperature is 60° C., and the stirring time is 5 h.

[0013] Optionally, when the amino acid is L-arginine, S2 and S3 specifically include: the cooling rate is 1-10°C / min; the separation of the reaction product includes washing and filtering the obtained solid with a washing solvent after the cooling is completed, and the washing and filtering solvent is one or more of ethanol, ethyl acetate, and double distilled water; the drying is vacuum freeze drying, and the drying time is 48-72h.

[0014] Preferably, the cooling rate is 5°C / min; the washing solvent is ethyl acetate; and the drying time is 60h.

[0015] The present invention has at least the following beneficial effects:

[0016] (1) The preparation method provided by the present invention has mild reaction conditions, a simple process flow, does not require the use of complex production processes, is easy to control the stirring temperature, and is easy to separate to obtain a pure product, making it easy to achieve industrial production of organic corrosion inhibitors.

[0017] (2) The reactants are easy to obtain, the cost of synthetic materials is low, the product output rate is high, and the corrosion inhibition effect is good, which better meets the requirements of long-term storage of NTO-based high-energy density materials while also saving production costs.

[0018] (3) The product prepared by the method of the present invention can form a protective layer on the metal surface. Specifically, the functional groups in the amino acid organic molecules obtained by the reaction are physically or chemically adsorbed on the metal surface, thereby forming a dense protective film on the metal (such as carbon steel) surface. This film effectively blocks the direct contact between NTO and other corrosive media and the carbon steel surface, effectively reducing the progress of the corrosion reaction.

[0019] In addition, additional advantages, objects, and features of the present invention will be described in part in the following description, and will become apparent to those skilled in the art after studying the following, or may be learned from the practice of the present invention. The objects and other advantages of the present invention may be realized and obtained by the structures and method steps specifically pointed out in the written description and claims and the accompanying drawings.

[0020] Those skilled in the art will appreciate that the objectives and advantages that can be achieved with the present invention are not limited to the above specific description, and the above and other objectives that can be achieved by the present invention will be more clearly understood from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of this application, and do not constitute a limitation of the present invention.

[0022] Figure 1 The figure is a schematic flow chart of a method for preparing an amino acid-based metal surface corrosion inhibitor according to an embodiment of the present invention;

[0023] Figure 2 is the H NMR spectrum of N-[(phenylamino)thioxomethyl]tryptophan in Example 3 of the present invention;

[0024] Figure 3is the infrared spectrum of N-[(phenylamino)thioxomethyl]tryptophan in Example 3 of the present invention;

[0025] Figure 4 is the photoelectron spectrum of N-[(phenylamino)thioxomethyl]tryptophan in Example 3 of the present invention;

[0026] Figure 5 Thermogravimetric analysis of N-[(phenylamino)thioxomethyl]tryptophan in Example 3 of the present invention;

[0027] Figure 6 The molecular structure, frontier orbital and electrostatic potential diagram of N-[(phenylamino)sulfoxymethyl]tryptophan in Example 3 of the present invention;

[0028] Figure 7 This is a graph showing the corrosion rate of carbon steel in a saturated NTO solution to which N-[(phenylamino)thioxomethyl]tryptophan is added in Examples 1-4 of the present invention;

[0029] Figure 8 This is the H NMR spectrum of the N2-[(phenylamino)sulfoxymethyl]-arginine corrosion inhibitor in Example 6 of the present invention;

[0030] Fig. 9 is the infrared spectrum of the N2-[(phenylamino)sulfoxymethyl]-arginine corrosion inhibitor in Example 6 of the present invention;

[0031] Fig.10 This is the photoelectron spectrum of the N2-[(phenylamino)sulfoxymethyl]-arginine corrosion inhibitor in Example 6 of the present invention;

[0032] Fig.11 This is the thermogravimetric analysis of the N2-[(phenylamino)sulfoxymethyl]-arginine corrosion inhibitor in Example 6 of the present invention;

[0033] Fig.12 The molecular structure, frontier orbital and electrostatic potential diagram of the N2-[(phenylamino)sulfoxymethyl]-arginine corrosion inhibitor in Example 6 of the present invention;

[0034] Fig.13 This is a graph showing the corrosion rate of carbon steel in a saturated NTO solution to which N2-[(phenylamino)sulfoxymethyl]-arginine corrosion inhibitor is added in Examples 5-8 of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. The schematic embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention. It should also be noted that, in order to avoid blurring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions according to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0036] It should be emphasized that the term “include / comprises” when used herein refers to the presence of features, elements, steps or components, but does not exclude the presence or addition of one or more other features, elements, steps or components.

[0037] The embodiment of the present invention provides a method for preparing an amino acid metal surface corrosion inhibitor, comprising the following specific steps: S1: adding a certain amount of amino acid and phenyl isothiocyanate to a reaction vessel, adding a solvent, and stirring the reaction at a certain reaction temperature; S2: monitoring the reaction process of S1 by thin layer chromatography, cooling after the reaction, separating the reaction product, and obtaining a solid product; S3: drying the solid product obtained by S2 to obtain an amino acid metal surface corrosion inhibitor. Among them, the amino acid can be one or more finished amino acid materials used for industrial batch production and addition. The special functional groups in the molecular structure of phenyl isothiocyanate (PITC) give it a variety of reaction capabilities, for example, specifically it can undergo a nucleophilic substitution reaction with a nucleophilic reagent, and then by adjusting the specific reactants and reaction conditions, various target organic compounds with characteristic functions can be obtained. At the same time, the materials of amino acids and phenyl isothiocyanate in the present invention are conventional industrial product materials, which is conducive to the batch preparation of the final product of the present invention and the industrial transformation application of the specific preparation method provided by the present invention. In addition, the present invention uses thin layer chromatography (TLC) for reaction monitoring, which can achieve rapid separation and characterization of reaction products, and rapidly realize sample detection by utilizing the differences in physical or chemical properties such as adsorption capacity and diffusion rate of different substances on the stationary phase.

[0038] Optionally, the amino acid is L-tryptophan, and the obtained amino acid metal surface corrosion inhibitor is N-[(phenylamino)sulfurylmethyl]-tryptophan corrosion inhibitor; or, the amino acid is L-arginine, and the obtained amino acid metal surface corrosion inhibitor is N2-[(phenylamino)sulfurylmethyl]-arginine corrosion inhibitor.

[0039] Optionally, when the amino acid is L-tryptophan, S1 specifically includes: the amount of L-tryptophan is 1-5 mmol, the amount of phenyl isothiocyanate is 1-5 mmol; the solvent is 50-100 mL of tetrahydrofuran; the reaction temperature is 80-90° C., and the stirring time is 7-9 h.

[0040] Preferably, the amount of L-tryptophan is 4.9 mmol, the amount of phenyl isothiocyanate is 4.9 mmol; the solvent is 85 mL of tetrahydrofuran; the reaction temperature is 85° C., and the stirring time is 8 h.

[0041] Optionally, when the amino acid is L-tryptophan, S2 and S3 specifically include: a cooling rate of 12-20°C / h; separation of the reaction products includes concentrating the mother liquor and separating it by column chromatography after the cooling is completed, and purifying PE:EA to EA; drying is vacuum drying, and the drying time is 35-45h.

[0042] Preferably, the cooling rate is 15°C / h and the drying time is 40h.

[0043] Optionally, when the amino acid is L-arginine, S1 specifically includes: the amount of L-arginine is 5.5-8 mmol, the amount of phenyl isothiocyanate is 5.5-8 mmol; the solvent is 50-100 mL ethanol and 5-15 mL double distilled water; the reaction temperature is 50-70° C., and the stirring time is 4-6 h.

[0044] Preferably, the amount of L-tryptophan is 5.74 mmol, the amount of phenyl isothiocyanate is 5.74 mmol; the solvent is 75 mL of ethanol and 10 mL of double distilled water; the reaction temperature is 60° C., and the stirring time is 5 h.

[0045] Preferably, when the amino acid is L-arginine, S2 and S3 specifically include: a cooling rate of 1-10°C / min; separating the reaction product includes washing and filtering the obtained solid with a washing solvent after the cooling is completed, and the washing and filtering solvent is one or more of ethanol, ethyl acetate, and double distilled water; drying is vacuum freeze drying, and the drying time is 48-72h.

[0046] Preferably, the cooling rate is 5°C / min; the washing solvent is ethyl acetate; and the drying time is 60h.

[0047] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0048] Example 1

[0049] 1mmol of L-tryptophan and 1mmol of phenyl isothiocyanate were added to a 150mL conical flask. Subsequently, 50mL of tetrahydrofuran was added to the conical flask. Later, the mixture was stirred at 80°C for 7h. After the reaction was monitored by thin layer chromatography, the mother liquor was concentrated by cooling at 12°C / h, and then separated by column chromatography, and purified from PE:EA to EA. The obtained solid was vacuum dried at 60°C for 35h and then collected to obtain a tryptophan organic corrosion inhibitor. Finally, the collected tryptophan organic corrosion inhibitor was added to a saturated solution of NTO, and the mass loss of carbon steel immersed in this solution was taken to calculate the corrosion rate to verify the effect of this tryptophan organic corrosion inhibitor.

[0050] Example 2

[0051] 3mmol of L-tryptophan and 3mmol of phenyl isothiocyanate were added to a 150mL conical flask. Subsequently, 70mL of tetrahydrofuran was added to the conical flask. Later, the mixture was stirred at 82°C for 7.5h. After the reaction was monitored by thin layer chromatography, the mother liquor was concentrated by cooling at 18°C / h, and then separated by column chromatography, and purified from PE:EA to EA. The obtained solid was vacuum dried at 60°C for 38h and then collected to obtain a tryptophan organic corrosion inhibitor. Finally, the collected tryptophan organic corrosion inhibitor was added to a saturated NTO solution, and the mass loss of carbon steel immersed in this solution was taken to calculate the corrosion rate to verify the effect of this tryptophan organic corrosion inhibitor.

[0052] Example 3

[0053] 4.9mmol of L-tryptophan and 4.9mmol of phenyl isothiocyanate were added to a 150mL conical flask. Subsequently, 85mL of tetrahydrofuran was added to the conical flask. Later, the mixture was stirred at 85°C for 8h. After the reaction was monitored by thin layer chromatography, the mother liquor was concentrated by cooling at 15°C / h, and then separated by column chromatography, and purified from PE:EA to EA. The obtained solid was vacuum dried at 60°C for 40h and then collected to obtain a tryptophan organic corrosion inhibitor. Finally, the collected tryptophan organic corrosion inhibitor was added to a saturated solution of NTO, and the mass loss of carbon steel immersed in this solution was taken to calculate the corrosion rate to verify the effect of this tryptophan organic corrosion inhibitor.

[0054] Example 4

[0055] 5mmol of L-tryptophan and 5mmol of phenyl isothiocyanate were added to a 150mL conical flask. Subsequently, 100mL of tetrahydrofuran was added to the conical flask. Later, the mixture was stirred at 90°C for 9h. After the reaction was monitored by thin layer chromatography, the mother liquor was concentrated by cooling at 20°C / h, and then separated by column chromatography, and purified from PE:EA to EA. The obtained solid was vacuum dried at 60°C for 45h and then collected to obtain a tryptophan organic corrosion inhibitor. Finally, the collected tryptophan organic corrosion inhibitor was added to a saturated solution of NTO, and the mass loss of carbon steel immersed in this solution was taken to calculate the corrosion rate to verify the effect of this tryptophan organic corrosion inhibitor.

[0056] Comparative Example 1

[0057] The corrosion rate of carbon steel was tested by immersing it directly in a saturated NTO solution without adding N-[(phenylamino)sulfoxymethyl]tryptophan corrosion inhibitor.

[0058] Table 1. Corrosion inhibition performance of N-[(phenylamino)thioxomethyl]tryptophan inhibitor on NTO

[0059] Group Corrosion rate (mm / y) Comparative Example 1 9.03 Example 1 7.65 Example 2 5.93 Example 3 5.48 Example 4 5.87

[0060] from Figure 6 It can be seen that the corrosion of carbon steel by the saturated solution of NTO after adding the organic matter N-[(phenylamino) sulfoxymethyl] tryptophan is significantly slowed down, and its corrosion rate is 5.48mm / y, which shows that the corrosion of NTO to low carbon steel is effectively controlled by N-[(phenylamino) sulfoxymethyl] tryptophan. This is due to the fact that N-[(phenylamino) sulfoxymethyl] tryptophan can form a protective film on the metal surface. The formation of this film involves the physical or chemical adsorption of functional groups in organic molecules on the metal surface. This film has a dense structure, which can block the direct contact between NTO and other corrosive media and the carbon steel surface, and reduce the progress of corrosion reactions. In addition, N-[(phenylamino) sulfoxymethyl] tryptophan may react chemically with NTO to form products with lower corrosiveness. This chemical reaction may include complexation reaction, redox reaction, etc., thereby reducing the corrosiveness of NTO to carbon steel. This reaction can not only slow down the progress of corrosion reaction, but also generate some stable compounds, further improving the corrosion resistance of carbon steel.

[0061] Example 5

[0062] 5.5 mmol of L-arginine and 5.5 mmol of phenyl isothiocyanate were added to a 250 mL round-bottom flask, and then 50 mL of ethanol and 7 mL of distilled water were added to the flask and placed in an oil bath at 50 ° C for 4 hours. The reaction was monitored by thin layer chromatography and cooled at 2 ° C / min. The obtained solid was filtered and washed with ethanol. Subsequently, the obtained solid was vacuum freeze-dried at 50 ° C for 48 hours and then collected to obtain an arginine organic corrosion inhibitor. Finally, the collected arginine organic corrosion inhibitor was added to a saturated NTO solution, and the mass loss of carbon steel immersed in this solution was taken to calculate the corrosion rate to verify the effect of this arginine organic corrosion inhibitor.

[0063] Example 6

[0064] 5.74mmol of L-arginine and 5.74mmol of phenyl isothiocyanate were added to a 250mL round-bottom flask, and then 75mL of ethanol and 10mL of distilled water were added to the flask and placed in an oil bath at 60°C for 5h. The reaction was monitored by thin layer chromatography and then cooled at 5°C / min. The obtained solid was filtered and washed with ethyl acetate. Subsequently, the obtained solid was collected after vacuum freeze drying at 50°C for 60h to obtain an arginine organic corrosion inhibitor. Finally, the collected arginine organic corrosion inhibitor was added to a saturated NTO solution, and the mass loss of carbon steel immersed in this solution was taken to calculate the corrosion rate to verify the effect of this arginine organic corrosion inhibitor.

[0065] Example 7

[0066] 6.5mmol of L-arginine and 6.5mmol of phenyl isothiocyanate were added to a 250mL round-bottom flask, and then 85mL of ethanol and 12mL of distilled water were added to the flask and placed in an oil bath at 65°C for 5.5h. The reaction was monitored by thin layer chromatography and then cooled at 8°C / min. The obtained solid was filtered and washed with ethyl acetate. Subsequently, the obtained solid was collected after vacuum freeze drying at 50°C for 66h to obtain an arginine organic corrosion inhibitor. Finally, the collected arginine organic corrosion inhibitor was added to a saturated NTO solution, and the mass loss of carbon steel immersed in this solution was taken to calculate the corrosion rate to verify the effect of this arginine organic corrosion inhibitor.

[0067] Example 8

[0068] 8mmol of L-arginine and 8mmol of phenyl isothiocyanate were added to a 250mL round-bottom flask, and then 100mL of ethanol and 15mL of distilled water were added to the flask and placed in an oil bath and stirred at 70°C for 6h. The reaction was monitored by thin layer chromatography and cooled at 10°C / min. The obtained solid was filtered and washed with double distilled water. Subsequently, the obtained solid was vacuum freeze-dried at 50°C for 72h and then collected to obtain an arginine organic corrosion inhibitor. Finally, the collected arginine organic corrosion inhibitor was added to a saturated NTO solution, and the mass loss of carbon steel immersed in this solution was taken to calculate the corrosion rate to verify the effect of this arginine organic corrosion inhibitor.

[0069] Comparative Example 2

[0070] The corrosion rate of carbon steel was tested by immersing it directly in a saturated NTO solution without adding N2-[(phenylamino)sulfoxymethyl]-arginine corrosion inhibitor.

[0071] Table 2. Corrosion inhibition performance of N2-[(phenylamino)sulfoxymethyl]-arginine inhibitor on NTO

[0072] Group Corrosion rate (mm / y) Comparative Example 2 9.03 Example 5 7.05 Example 6 6.13 Example 7 7.08 Example 8 7.27

[0073] from Fig.12 It can be seen that the corrosion of low carbon steel by NTO saturated solution after adding N2-[(phenylamino) thioxomethyl]-arginine corrosion inhibitor was significantly inhibited, and its corrosion rate was 6.13mm / y. This is due to the presence of thioxomethyl functional groups in N2-[(phenylamino) thioxomethyl]-arginine molecules, which can chemically adsorb with the metal surface to form a dense protective film. At the same time, the arginine group in the arginine molecule may form coordination bonds or hydrogen bonds with the metal surface, enhancing the adhesion of the film, thereby forming a stable and indestructible protective layer. This film can block the entry of corrosive media such as NTO and water molecules, slowing down the corrosion reaction. In addition, N2-[(phenylamino) thioxomethyl]-arginine can also synergistically adsorb with NTO molecules on the carbon steel surface, strengthening the adsorption capacity of the body on the carbon steel surface while weakening the adsorption and dissociation of NTO molecules on the carbon steel surface, further hindering the corrosion caused by the reaction of NTO molecules on the carbon steel surface.

[0074] In addition, the N-[(phenylamino)sulfurylmethyl]tryptophan corrosion inhibitor and N2-[(phenylamino)sulfurylmethyl]-arginine corrosion inhibitor prepared by the present invention can effectively inhibit the corrosion of NTO without reducing its energy level, and the preparation method is simple, easy to operate, and has low production cost. It meets the requirements for long-term storage of NTO-based weapons and equipment and has high industrial application value.

[0075] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an amino acid-based metal surface corrosion inhibitor, characterized in that: The specific steps include: S1: adding a certain amount of amino acid and phenyl isothiocyanate into a reaction vessel, adding a solvent, and stirring the reaction at a certain reaction temperature; S2: Monitor the reaction process of S1 by thin layer chromatography, cool down after the reaction is completed, separate the reaction product, and obtain a solid product; S3: Dry the solid product obtained in S2 to obtain an amino acid metal surface corrosion inhibitor.

2. The preparation method according to claim 1, characterized in that: The amino acid is L-tryptophan, and the amino acid metal surface corrosion inhibitor obtained is N-[(phenylamino)thioxomethyl]-tryptophan corrosion inhibitor; Or, the amino acid is L-arginine, and the amino acid metal surface corrosion inhibitor obtained is N2-[(phenylamino)sulfoxymethyl]-arginine corrosion inhibitor.

3. The preparation method according to claim 2, characterized in that: When the amino acid is L-tryptophan, S1 specifically includes: the amount of L-tryptophan is 1-5 mmol, the amount of phenyl isothiocyanate is 1-5 mmol; the solvent is 50-100 mL of tetrahydrofuran; the reaction temperature is 80-90° C., and the stirring time is 7-9 h.

4. The preparation method according to claim 3, characterized in that: The amount of L-tryptophan is 4.9 mmol, the amount of phenyl isothiocyanate is 4.9 mmol; the solvent is 85 mL of tetrahydrofuran; the reaction temperature is 85° C., and the stirring time is 8 h.

5. The preparation method according to claim 2, characterized in that: When the amino acid is L-tryptophan, S2 and S3 specifically include: the cooling rate is 12-20°C / h; the separation of the reaction products includes concentrating the mother liquor and separating it by column chromatography after the cooling is completed, and purifying PE:EA to EA; the drying is vacuum drying, and the drying time is 35-45h.

6. The preparation method according to claim 5, characterized in that: The cooling rate is 15°C / h, and the drying time is 40h.

7. The preparation method according to claim 2, characterized in that: When the amino acid is L-arginine, S1 specifically includes: the amount of L-arginine is 5.5-8 mmol, the amount of phenyl isothiocyanate is 5.5-8 mmol; the solvent is 50-100 mL ethanol and 5-15 mL double distilled water; the reaction temperature is 50-70° C., and the stirring time is 4-6 h.

8. The preparation method according to claim 7, characterized in that: The amount of L-tryptophan is 5.74 mmol, and the amount of phenyl isothiocyanate is 5.74 mmol; the solvent is 75 mL of ethanol and 10 mL of double distilled water; the reaction temperature is 60° C., and the stirring time is 5 h.

9. The preparation method according to claim 2, characterized in that: When the amino acid is L-arginine, S2 and S3 specifically include: the cooling rate is 1-10°C / min; the separation of the reaction product includes washing and filtering the obtained solid with a washing solvent after the cooling is completed, and the washing and filtering solvent is one or more of ethanol, ethyl acetate, and double distilled water; the drying is vacuum freeze drying, and the drying time is 48-72h.

10. The preparation method according to claim 9, characterized in that: The cooling rate is 5°C / min; the washing solvent is ethyl acetate; and the drying time is 60h.

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