Halogenated pyrazine-phenanthroline small molecule novel organic corrosion inhibitor and preparation method therefor

Abstract

The present invention provides a halogenated pyrazine-phenanthroline small molecule novel organic corrosion inhibitor and a preparation method therefor. The corrosion inhibitor comprises any one of Dppz-Br, Dppz-Cl, and Dppz-F. The method comprises: step 1, selecting a required phenanthroline-2,9-dione and a required halogenated o-phenylenediamine as starting materials; step 2, adding the starting materials into a reactor containing a required solvent to perform a one-step synthesis of a halogenated pyrazine-phenanthroline small molecule; step 3, determining whether the synthesized halogenated pyrazine-phenanthroline small molecule meets the requirements, and if so, obtaining a desired organic corrosion inhibitor. The halogenated pyrazine-phenanthroline small molecule novel organic corrosion inhibitor and the preparation method therefor provided by the present invention can simplify the synthesis process of the corrosion inhibitor, improve synthesis efficiency, effectively reduce pollution and cost, and enhance the corrosion inhibition effect. In a 15% hydrochloric acid acidification system, the corrosion inhibitor exhibits excellent anti-corrosion performance for carbon steel.

Description

Novel small-molecule organic corrosion inhibitors of halogenated pyrazine-phenanthroline and their preparation methods Technical Field

[0001] This invention relates to the field of corrosion inhibitors in acidification processes, and more specifically, to a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline and its preparation method. Background Technology

[0002] The direct economic losses caused by corrosion each year account for approximately 1% to 4% of the world's GDP. Corrosion damages the physical and chemical properties of metallic materials, leading to the scrapping of about 30% of metal equipment and resulting in a serious waste of resources. Currently, society is increasingly concerned about the economic losses and casualties caused by metal corrosion. In addition to conventional coating protection, the use of organometallic corrosion inhibitors is a highly efficient and low-cost corrosion prevention technology that has been developed in recent years. Pyrazine-phenanthroline can strongly coordinate with various metal ions, such as iron ions, to form various metal ion chelates. These metal ion chelates possess a large conjugated system, which helps them to efficiently adsorb onto metal surfaces. Simultaneously, these materials have a nitrogen-containing rigid bidentate planar structure, where the lone pair electrons on the nitrogen atom can coordinate with the empty orbitals of the metal to form coordinate bonds and a bidentate clamp structure, further facilitating the capture of metal ions. This reduces corrosion active sites and inhibits the formation of corrosion products, ultimately effectively slowing down the corrosion process.

[0003] (1) Foreign technology

[0004] Foreign scientists began studying phenanthroline structures as organometallic corrosion inhibitors earlier. Phenanthroline is a common metal ion chelating agent, and studies have found that it inhibits Fe... 2+ Exhibiting strong coordination and chelation properties, it is widely used in the field of metal ion detection. In 1989, Banerjee discovered that phenanthrene-Fe composites exhibited a corrosion inhibition rate exceeding 90% for soft steel in sulfuric acid solution. Furthermore, IB Obot synthesized a novel phenanthrene-Fe composite corrosion inhibitor, 2-methylnitro-1H imidazolium[4,5-f][1,10]-phenanthrene-Fe composite (MEIP), and investigated its corrosion inhibition performance on carbon steel in 0.5 M sulfuric acid solution using weight loss and UV-Vis spectrophotometry. At 303 K and a concentration of 10 µM, MEIP achieved a corrosion inhibition rate of 87% for carbon steel in sulfuric acid, indicating that MEIP was adsorbed onto the carbon steel surface via physical adsorption. This confirmed the corrosion inhibition properties of the MEIP-Fe composite on metal surfaces.

[0005] (2) Domestic technology

[0006] Domestic research on phenanthrene-based corrosion inhibitors generally lags behind international research, and most studies focus on compound corrosion inhibitors. For example, Mu Guannan et al. found that o-phenanthrene-based inhibitors react with Cl- in phosphoric acid and hydrochloric acid media. -Exhibiting a synergistic effect, the corrosion inhibitor effectively hinders the contact between the corrosive medium and carbon steel through adsorption, thereby significantly improving the corrosion inhibition performance of o-phenanthroline on carbon steel in acid. Wang Lin et al. used the weight loss method to study the interaction between o-phenanthroline and Br. - The synergistic corrosion inhibition performance of o-phenanthroline and potassium bromide was demonstrated experimentally, showing that the corrosion inhibition of cold-rolled steel was significantly improved to 97% after compounding. Xueming L used the weight loss method and electrochemical technology to find that the corrosion inhibition effect of o-phenanthroline on cold-rolled steel in 0.5 M sulfuric acid was significantly improved in the presence of sodium chloride.

[0007] Although there is considerable research on phenanthrene-based corrosion inhibitors in existing technologies, current mainstream inhibitors still suffer from problems such as high pollution levels, high development costs, and unsatisfactory corrosion inhibition effects in strongly acidic environments. Therefore, researching how to reduce the pollution and cost of corrosion inhibitors and improve their corrosion inhibition effects is of great significance.

[0008] Patent publication number CN118812533A mentions a small-molecule organic corrosion inhibitor of aziridine-phenanthroline and its preparation method. The corrosion inhibitor is Dppz-3py, Dppz-4py, or Dppz-md. The method for preparing the corrosion inhibitor includes: S1, adding o-phenanthroline dione, 3,6-dibromo-1,2-phenylenediamine, and anhydrous ethanol to a flask, refluxing at 80 °C for 4 h under a nitrogen atmosphere, filtering after the reaction, and washing the filter cake with acetone, tetrahydrofuran, petroleum ether, and deionized water to obtain intermediate Dppz-br; S2, adding Dppz-br, reactant A, potassium carbonate, a mixed solvent of tetrahydrofuran and water, and palladium acetate to a two-necked flask, refluxing at 80 °C for 24 h under a nitrogen atmosphere. After the reaction is complete, the mixture is filtered, and the filter cake is washed with petroleum ether, DMF, and deionized water. The washed filter cake is then vacuum dried to obtain crude azirpyrazine-phenanthroline small molecule organic corrosion inhibitor. This patent can solve the problem that the corrosion inhibition effect of o-phenanthroline organic corrosion inhibitors in the prior art is generally poor. However, the preparation of this corrosion inhibitor requires the synthesis of the intermediate product Dppz-br first, and then the synthesis of the final product with the help of the intermediate. The entire synthesis process is complex and the yield is low. Summary of the Invention

[0009] In view of this, the present invention aims to propose a novel small-molecule halogenated pyrazine-phenanthroline organic corrosion inhibitor and its preparation method, to solve the problems of existing mainstream corrosion inhibitors, such as high pollution, high development costs, and unsatisfactory corrosion inhibition effects in strong acid environments. This invention simplifies the corrosion inhibitor synthesis process, improves the efficiency of corrosion inhibitor synthesis, effectively reduces pollution and cost, and enhances the corrosion inhibition effect, enabling the corrosion inhibitor to exhibit excellent anti-corrosion performance on carbon steel in a 15% hydrochloric acid acidification system. Furthermore, the corrosion inhibitor prepared by this application not only enriches the types of small-molecule pyrazine-phenanthroline organic corrosion inhibitors but also improves their corrosion inhibition performance.

[0010] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0011] This invention relates to a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline and its preparation method. The novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline includes any one of Dppz-Br, Dppz-Cl, and Dppz-F; wherein the molecular structural formula of Dppz-Br is: The molecular structural formula of Dppz-Cl is: The molecular structural formula of Dppz-F is: .

[0012] A method for preparing a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline, the method comprising the following steps:

[0013] Step 1: Select the desired phenanthrolinedione and the desired halogenated o-phenylenediamine as initial raw materials;

[0014] Step 2: Add the initial raw materials to a reactor containing the required solvent, set the reaction environment inside the reactor, and control the reaction temperature inside the reactor to T. After the required reaction time t, the initial raw materials are synthesized into small molecules of halopyrazine-phenanthroline in one step.

[0015] Step 3: By testing the corrosion inhibition performance of the halopyrazine-phenanthroline small molecule, determine whether the synthesized halopyrazine-phenanthroline small molecule meets the requirements. If yes, the synthesis is successful, and a novel organic corrosion inhibitor with excellent performance of halopyrazine-phenanthroline small molecule is obtained. If no, adjust the amount of initial raw materials and solvents in Step 2, as well as the reaction conditions of the reactor, and thus adjust the structure of the halopyrazine-phenanthroline small molecule to obtain the novel organic corrosion inhibitor with excellent performance.

[0016] Furthermore, in step one, the volume ratio of the required phenanthrolinedione to the required halogenated o-phenylenediamine ranges from 1:1 to 1:1.5.

[0017] Furthermore, the desired halogenated o-phenylenediamine is any one of 4,5-dibromo-o-phenylenediamine, 4,5-dichloro-o-phenylenediamine, or 4,5-difluoro-o-phenylenediamine.

[0018] Furthermore, the halogenated o-phenylenediamine is 4,5-dibromo-o-phenylenediamine, and the required phenanthrolinedione is o-phenanthrolinedione; the reaction formula for the synthesis of Dppz-Br from o-phenanthrolinedione and 4,5-dibromo-o-phenylenediamine is as follows:

[0019] .

[0020] Furthermore, the halogenated o-phenylenediamine is 4,5-dichloro-o-phenylenediamine, and the required phenanthrolinedione is o-phenanthrolinedione; the reaction formula for the synthesis of Dppz-Cl from o-phenanthrolinedione and 4,5-dichloro-o-phenylenediamine is as follows:

[0021] .

[0022] Furthermore, the halogenated o-phenylenediamine is 4,5-difluoro-o-phenylenediamine, and the required phenanthrolinedione is o-phenanthrolinedione; the reaction formula for the synthesis of Dppz-F from o-phenanthrolinedione and 4,5-difluoro-o-phenylenediamine is as follows:

[0023] .

[0024] Furthermore, in step two, the required solvent includes any one of methanol, ethanol, and dioxane.

[0025] Furthermore, T ranges from 65℃ to 120℃, and t ranges from 2h to 12h.

[0026] Furthermore, step three includes:

[0027] Step S31: Characterize the basic physicochemical properties of the halopyrazine-phenanthroline small molecule and determine whether the halopyrazine-phenanthroline small molecule meets the requirements. If yes, proceed to step S33; otherwise, proceed to step S32.

[0028] Step S32: Based on the test results, return to step two, adjust the initial amounts of raw materials and solvents, as well as the reaction conditions of the reactor, to obtain the desired novel organic corrosion inhibitor;

[0029] Step S33: Perform electrochemical testing on the halopyrazine-phenanthroline small molecule; determine whether the halopyrazine-phenanthroline small molecule is stable. If yes, prepare the desired novel organic corrosion inhibitor. If no, return to step S32.

[0030] Compared with the prior art, the novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline and its preparation method described in this invention have the following beneficial effects:

[0031] The corrosion inhibitor prepared in this application not only enriches the variety of pyrazine-phenanthroline small-molecule organic corrosion inhibitors but also enhances their corrosion inhibition performance. This allows for effective protection of metal equipment in acidification processes through the addition of a small amount of the inhibitor in industrial applications. Furthermore, the preparation method described in this application simplifies the corrosion inhibitor synthesis process, improves synthesis efficiency, effectively reduces pollution and cost, and enhances the corrosion inhibition effect, resulting in excellent corrosion protection for carbon steel in a 15% hydrochloric acid acidification system. Attached Figure Description

[0032] The accompanying drawings, which constitute a part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0033] Figure 1 shows the corrosion inhibitor molecule Dppz-F. 1 Schematic diagram of H NMR spectrum;

[0034] Figure 2 shows the corrosion inhibitor molecule Dppz-Cl. 1 Schematic diagram of H NMR spectrum;

[0035] Figure 3 shows the corrosion inhibitor molecule Dppz-Br. 1 Schematic diagram of H NMR spectrum;

[0036] Figure 4 shows the Fourier infrared spectra of three halopyrazine-phenanthroline corrosion inhibitors: Dppz-Br, Dppz-Cl, and Dppz-F.

[0037] Figure 5 shows the UV-Vis absorption spectra (in DMF solution) of three halopyrazine-phenanthroline corrosion inhibitors: Dppz-Br, Dppz-Cl, and Dppz-F.

[0038] Figures 6a-6c are schematic diagrams of the DFT density functional calculations (B3LYP, 6-31G,d,p) of three halopyrazine-phenanthroline corrosion inhibitor molecules: Dppz-Br, Dppz-Cl, and Dppz-F.

[0039] Figure 7 shows the open-circuit voltage-time curves of low carbon steel in a blank 15% hydrochloric acid solution and a hydrochloric acid solution with 25 mg / L corrosion inhibitor molecules.

[0040] Figure 8 shows the Nyquist plots of low carbon steel in a blank 15% hydrochloric acid solution and a hydrochloric acid solution with 25 mg / L corrosion inhibitor molecules.

[0041] Figure 9 is a schematic diagram of the polarization curves of low carbon steel in a blank 15% hydrochloric acid solution and a hydrochloric acid solution with 25 mg / L corrosion inhibitor molecules. Detailed Implementation

[0042] The inventive concepts of this disclosure will be described below using terminology commonly used by those skilled in the art to communicate the essence of their work to others skilled in the art. However, these inventive concepts may be embodied in many different forms and should not be construed as limited to the embodiments described herein.

[0043] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0044] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0045] To address the problems of existing mainstream corrosion inhibitors, such as high pollution, high development costs, and unsatisfactory corrosion inhibition effects in strong acid environments, this embodiment proposes a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline and its preparation method. The novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline includes any one of Dppz-Br, Dppz-Cl, and Dppz-F.

[0046] The molecular structural formula of Dppz-Br is as follows: The molecular structural formula of Dppz-Cl is: The molecular structural formula of Dppz-F is: .

[0047] A method for preparing a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline, the method comprising the following steps:

[0048] Step 1: Select the desired phenanthrolinedione and the desired halogenated o-phenylenediamine as initial raw materials;

[0049] Step 2: Add the initial raw materials to a reactor containing the required solvent, set the reaction environment inside the reactor, and control the reaction temperature inside the reactor to T. After the required reaction time t, the initial raw materials are synthesized into small molecules of halopyrazine-phenanthroline in one step.

[0050] Step 3: By testing the corrosion inhibition performance of the halopyrazine-phenanthroline small molecule, determine whether the synthesized halopyrazine-phenanthroline small molecule meets the requirements. If yes, the synthesis is successful, and a novel organic corrosion inhibitor with excellent performance of halopyrazine-phenanthroline small molecule is obtained. If no, based on the corrosion inhibition performance test results of the existing halopyrazine-phenanthroline small molecule in Step 3, adjust the amount of initial raw materials and solvents in Step 2, as well as the reaction conditions of the reactor, and then adjust the structure of the halopyrazine-phenanthroline small molecule to meet the requirements, thus obtaining a novel organic corrosion inhibitor with excellent performance.

[0051] In step one, the volume ratio of the required phenanthrolinedione to the required o-phenylenediamine is in the range of 1:1 to 1:1.5. By selecting different o-phenylenediamine halogens, a series of halopyrazine-phenanthroline Dppz-Br, Dppz-Cl, and Dppz-F can be prepared. In this embodiment, the required phenanthrolinedione is o-phenanthrolinedione; the required o-phenylenediamine halogen is any one of 4,5-dibromo-o-phenylenediamine, 4,5-dichloro-o-phenylenediamine, and 4,5-difluoro-o-phenylenediamine.

[0052] Furthermore, in step two, the required solvent includes any one of methanol, ethanol, and dioxane. The value of T is 65℃-120℃; the value of t is 2 h-12 h.

[0053] Leveraging the advantages of organophenanthroline molecules forming stable chelates with ferrous ions, resulting in excellent corrosion inhibition performance of metallic iron, strong structural modifiability, and low development cost, a series of halogen atoms were introduced to the side ends of pyrazinophenanthroline to effectively enhance the synergistic effect between phenanthroline-based small-molecule corrosion inhibitors and halogens. Furthermore, by systematically investigating the influence of halogen substituents on the corrosion inhibition efficiency of o-phenanthroline, novel halogen-substituted phenanthroline-based slow-release agent small-molecule materials with excellent corrosion inhibition performance were obtained.

[0054] Preferably, when the halogenated o-phenylenediamine is 4,5-dibromo-o-phenylenediamine, phenanthrene-rholinedione is synthesized with 4,5-dibromo-o-phenylenediamine to obtain Dppz-Br; when the halogenated o-phenylenediamine is 4,5-dichloro-o-phenylenediamine, phenanthrene-rholinedione is synthesized with 4,5-dichloro-o-phenylenediamine to obtain Dppz-Cl; and when the halogenated o-phenylenediamine is 4,5-difluoro-o-phenylenediamine, phenanthrene-rholinedione is synthesized with 4,5-difluoro-o-phenylenediamine to obtain Dppz-F.

[0055] By using phenanthroline dione and different halo-o-phenylenediamines as starting materials, a series of halopyrazine-phenanthroline derivatives Dppz-Br, Dppz-Cl, and Dppz-F can be synthesized in one step. By constructing a series of pyrazine-phenanthroline derivatives with different halogen substitutions, and by systematically studying the effect of halogen substituents on corrosion inhibition performance, halopyrazine-phenanthroline derivatives with excellent corrosion inhibition performance were obtained.

[0056] Step three includes:

[0057] Step S31: Characterize the basic physicochemical properties of the halopyrazine-phenanthroline small molecule and determine whether the halopyrazine-phenanthroline small molecule meets the requirements. If yes, proceed to step S33; otherwise, proceed to step S32.

[0058] Step S32: Based on the test results, return to step two, adjust the amount of initial raw materials and solvents, as well as the reaction conditions of the reactor, and then adjust the structure of the halopyrazine-phenanthroline small molecule to meet the requirements and obtain the desired novel organic corrosion inhibitor with excellent performance.

[0059] Step S33: Perform electrochemical testing on the halopyrazine-phenanthroline small molecule; determine whether the halopyrazine-phenanthroline small molecule is stable. If yes, prepare the desired novel organic corrosion inhibitor with excellent performance. If no, return to step S32.

[0060] By reacting phenanthrene-based diones with different halogenated o-phenylenediamine reagents, and through continuous experimentation and adjustments to reaction conditions such as reactant ratios, different solvents, reaction temperatures, and reaction times, a high-yield halogenated pyrazine-phenanthrene-based dione was successfully developed after multiple experimental optimizations.

[0061] Step S31 includes:

[0062] Step S311: Characterize the structure of the halopyrazinephenanthrene-line small molecule; determine whether the structure of the halopyrazinephenanthrene-line small molecule is accurate. If yes, proceed to step S312; if no, proceed to step S32.

[0063] Step S312: Measure the UV-Vis absorption spectrum of the small molecule halopyrazinephenanthreneroline; determine whether the peak shape and maximum absorption peak of the UV absorption spectrum of the small molecule halopyrazinephenanthreneroline meet the requirements. If yes, proceed to step S313; if no, proceed to step S32.

[0064] Step S313: Calculate the density functional theory (DFT) of the halopyrazine-phenanthroline small molecule; determine whether the halopyrazine-phenanthroline small molecule is qualified. If yes, proceed to step S33; otherwise, proceed to step S32.

[0065] Step S33 includes:

[0066] Step S331: Perform an open-circuit voltage test (OCP) on the halopyrazine-phenanthroline small molecule to determine whether the halopyrazine-phenanthroline small molecule is in a stable state. If yes, proceed to step S332; otherwise, proceed to step S32.

[0067] Step S332: Perform electrochemical impedance and polarization curve tests on the halopyrazine-phenanthroline small molecule to determine whether the halopyrazine-phenanthroline small molecule meets the corrosion inhibition requirements. If yes, prepare the desired novel organic corrosion inhibitor with excellent performance; otherwise, return to step S32.

[0068] Electrochemical tests on the prepared series of halopyrazine-phenanthroline small molecules showed that the series of corrosion inhibitors still have excellent corrosion inhibition performance in 15% hydrochloric acid solution, and the results can also provide a reference for the subsequent development of high-performance o-phenanthroline corrosion inhibitors.

[0069] In summary, this application conducted a series of exploratory studies on synthesis conditions and successfully synthesized three halo-substituted pyrazine-phenanthroline small molecule corrosion inhibitors. Through continuous experimentation with varying feed ratios, different solvents, reaction temperatures, and reaction times, and after multiple experimental optimizations, high-yield halogenated pyrazine-phenanthroline was successfully developed under optimal reaction conditions. Taking Dppz-Br, Dppz-Cl, and Dppz-F as examples, the final optimized preparation methods and conditions are shown in Examples 1-3:

[0070] 1.00 g (4.75 mmol) of o-phenanthrolinedione and 1.51 g (5.7 mmol) of 4,5-dibromo-o-phenylenediamine were added to a 50 mL double-necked round-bottom flask containing 25 mL of anhydrous ethanol solution. The mixture was stirred at 80 °C for 4 h under a nitrogen atmosphere. After the reaction was completed, the mixture was allowed to cool to room temperature, filtered, and washed with acetone, tetrahydrofuran, petroleum ether, and deionized water. The solution was then dried under vacuum by column chromatography to obtain a white solid, Dppz-Br (yield = 75%), as shown in Table 1 below.

[0071] The reaction formula for the synthesis of Dppz-Br from phenanthrolinedione (i.e., o-phenanthrolinedione) and 4,5-dibromo-o-phenylenediamine is as follows:

[0072]

[0073] Table 1

[0074]

[0075] 1.00 g (4.75 mmol) of o-phenanthrolinedione and 1.01 g (5.7 mmol) of 4,5-dichloro-o-phenylenediamine were added to a 50 mL double-necked round-bottom flask containing 25 mL of anhydrous ethanol solution, and stirred at 80 °C for 4 h under a nitrogen atmosphere. After the reaction was completed, the mixture was allowed to cool to room temperature, filtered, and washed with acetone, tetrahydrofuran, petroleum ether, and deionized water. The mixture was then dried under vacuum by column chromatography to obtain a yellow solid Dppz-Cl (yield = 86%), as shown in Table 2 below.

[0076] The reaction formula for synthesizing Dppz-Cl from phenanthrolinedione (i.e., o-phenanthrolinedione) and 4,5-dichloro-o-phenylenediamine is as follows:

[0077]

[0078] Table 2

[0079]

[0080] 1.00 g (4.75 mmol) of o-phenanthrolinedione and 0.83 g (5.7 mmol) of 4,5-difluoroo-phenylenediamine were added to a 50 mL double-necked round-bottom flask containing 25 mL of anhydrous ethanol solution, and stirred at 80 °C for 4 h under a nitrogen atmosphere. After the reaction was completed, the mixture was allowed to cool to room temperature, filtered, and washed with acetone, tetrahydrofuran, petroleum ether, and deionized water. The mixture was then dried under vacuum by column chromatography to obtain a yellow solid, Dppz-F (yield = 56%), as shown in Table 3 below.

[0081] The reaction formula for synthesizing Dppz-F from phenanthrolinedione (i.e., o-phenanthrolinedione) and 4,5-difluoro-o-phenylenediamine is as follows:

[0082]

[0083] Table 3

[0084]

[0085] The basic physicochemical properties of the halopyrazine-phenanthroline small molecules prepared in Examples 1-3 were characterized as follows:

[0086] 1) Characterization of the small molecule structure of halopyrazinephenanthreneroline:

[0087] The prepared halopyrazinephenanthreneline was purified by silica gel column chromatography, concentrated to remove solvent, and dried in a vacuum drying oven for 24 h. The solid sample was then subjected to 1H NMR spectroscopy. 1 H-NMR (Figures 1-3) and Fourier transform infrared (Figure 4) were used to verify the correctness of the obtained product structure.

[0088] 2) UV-Vis absorption spectroscopy of small molecules of halopyrazine-phenanthroline:

[0089] The obtained halopyrazine-phenanthroline small molecules were prepared into a dilute solution of N,N-dimethylformamide (DMF) and subjected to UV-Vis absorption spectroscopy. The test scan range was from 250 nm to 600 nm. As shown in Figure 5, it can be seen that the UV absorption spectra of Dppz-Br, Dppz-Cl, and Dppz-F have similar peak shapes, and the maximum absorption peaks are located at 381 nm, 392 nm, and 394 nm, respectively.

[0090] 3) Density functional (DFT) calculations of small molecules of halopyrazinephenanthrene-roline:

[0091] Density functional (DFT) simulations were performed on the molecular conformations and HOMO / LUMO energy levels of Dppz-Br, Dppz-Cl, and Dppz-F using Gaussian (B3LYP / 6-31G, d, p basis sets). As shown in Figures 6a-6c, the electron cloud distribution characteristics of the HOMO / LUMO of Dppz-Br, Dppz-Cl, and Dppz-F molecules are basically consistent. The electron cloud distribution on the LUMO is mainly on the pyrazine ring, while on the HOMO it is mainly on the pyridine ring adjacent to the pyrazine. The calculated parameters for the three molecules are as follows: the band gap size relationship is: Dppz-F > Dppz-Cl > Dppz-Br.

[0092] Electrochemical tests were performed on the halopyrazine-phenanthroline small molecules prepared in Examples 1-3; the corrosion effect of adding three 25 mg / L corrosion inhibitors to a 15% hydrochloric acid solution was tested on the carbon steel electrode, with the blank experimental group consisting of a 15% hydrochloric acid solution.

[0093] 1) Open circuit voltage test (OCP):

[0094] To ensure the accuracy of electrochemical measurements during the experiment, the electrochemical tests must be performed under stable conditions in the three-electrode system. When the OCP curve tends to be a horizontal straight line, it indicates that the test system has reached a steady state. As shown in Figure 7, after immersion in acid solution for 45 min, the OCP curves of the Dppz-Br, Dppz-Cl, Dppz-F, and blank hydrochloric acid systems tend to be horizontal straight lines, indicating that the test system is in a stable state.

[0095] 2) Electrochemical impedance and polarization curve testing:

[0096] Electrochemical impedance spectroscopy is one of the most commonly used methods to study the corrosion inhibition performance of corrosion inhibitors. By analyzing impedance curves and polarization curves, the interfacial corrosion of the working electrode can be obtained.

[0097] As shown in Figure 8, compared with the blank group, the impedance arc radius of the group with added corrosion inhibitors was significantly increased. Dppz-Cl had the largest impedance arc radius, followed by Dppz-Br and Dppz-F. This result indicates that the addition of corrosion inhibitors suppressed the corrosion of carbon steel in 15% hydrochloric acid solution. Furthermore, the corrosion inhibition rates of the halopyrazine-phenanthroline small molecule derivatives followed the order: Dppz-Cl > Dppz-Br > Dppz-F. In addition, circuit fitting of the impedance diagrams showed that the corrosion inhibition rates of Dppz-Br, Dppz-Cl, and Dppz-F on carbon steel in 15% hydrochloric acid solution were 60.7%, 68.8%, and 46.2%, respectively. In conclusion, all three corrosion inhibitors exhibit excellent corrosion inhibition properties in strong acids, with the corrosion inhibition rate in the order of Dppz-Cl > Dppz-Br > Dppz-F.

[0098] As shown in Figure 9, the polarization curve of Dppz-Cl showed the most significant decrease, followed by Dppz-Br and Dppz-F. The corrosion inhibition order of the three inhibitors was consistent with the order obtained from the electrical impedance measurements, with the corrosion inhibition rate order being Dppz-Cl > Dppz-Br > Dppz-F. The halophenanthroline corrosion inhibitor molecule developed in this invention can effectively reduce the current density during the corrosion process of carbon steel in hydrochloric acid solution, thereby providing significant corrosion inhibition and protection for carbon steel.

[0099] Electrochemical impedance spectroscopy was performed on the prepared Dppz-Br, Dppz-Cl, and Dppz-F corrosion inhibitor molecules. In a three-electrode system, the corrosion inhibition effect of the carbon steel electrode when the three 25 mg / L corrosion inhibitors were added to a 15% hydrochloric acid solution was significantly better than that of the blank hydrochloric acid solution. The specific implementation methods and results are shown in Table 4 below.

[0100] Table 4 Product test results of Examples 1-3

[0101] Through one-step organic synthesis, small-molecule organic corrosion inhibitors of brominated, chlorinated, and fluorinated pyrazine-phenanthroline (Dppz-Br, Dppz-Cl, and Dppz-F) were successfully developed. Comparative testing revealed that chlorinated pyrazine-phenanthroline exhibited the best corrosion inhibition performance in a 15% (w / w) hydrochloric acid solution. Leveraging the high designability of organic corrosion inhibitor molecules, three different halogenated structures were introduced into the phenanthroline structure, all demonstrating excellent corrosion inhibition performance. This not only effectively broadens the application scenarios and scope of phenanthroline-based organic corrosion inhibitors but also provides a new construction strategy for the subsequent synthesis and design modification of highly efficient phenanthroline-based corrosion inhibitor molecules.

[0102] Unlike patent CN118812533A, this application simplifies the synthesis process by synthesizing corrosion inhibitors in a single step, which not only improves yield but also reduces cost. Furthermore, the intermediate products in the aforementioned patent are not used as corrosion inhibitors in the field of corrosion inhibitors. Therefore, this application is not repetitive or substitutable with the aforementioned patent, and while meeting corrosion inhibition performance requirements, it possesses the advantages of simplicity and high efficiency. In addition, this application successfully synthesized three small-molecule halogenated pyrazine-phenanthroline organic corrosion inhibitors through a simple one-step organic chemical reaction and by screening and optimizing experimental conditions. In the structure of this series of molecular materials, the lone pair electrons of the nitrogen atom and the π electrons of the large conjugated aromatic ring on the phenanthroline coordinate with the empty orbitals of the iron atom to form coordinate bonds, thereby effectively adsorbing onto the metal surface and effectively inhibiting the corrosion of carbon steel in a 15% hydrochloric acid solution. This application has successfully developed a series of halogenated pyrazine-phenanthroline corrosion inhibitors that are simple to synthesize, have high yields, and exhibit significant anti-corrosion effects, and have broad application prospects and practical value in fields such as oil extraction, metal pickling, and machinery manufacturing.

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0104]

Claims

1. A novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline, characterized in that, This includes any one of Dppz-Br, Dppz-Cl, and Dppz-F; among which, the molecular structural formula of Dppz-Br is: The molecular structural formula of Dppz-Cl is: The molecular structural formula of Dppz-F is: .

2. A method for preparing a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline, characterized in that, The method is used to prepare a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline as described in claim 1, and the method includes the following steps: Step 1: Select the desired phenanthrolinedione and the desired halogenated o-phenylenediamine as initial raw materials; Step 2: Add the initial raw materials to a reactor containing the required solvent, set the reaction environment inside the reactor, and control the reaction temperature inside the reactor to T. After the required reaction time t, the initial raw materials are synthesized into small molecules of halopyrazine-phenanthroline in one step. Step 3: By testing the corrosion inhibition performance of the halopyrazine-phenanthroline small molecule, determine whether the synthesized halopyrazine-phenanthroline small molecule meets the requirements. If yes, the research is successful, and a novel organic corrosion inhibitor with excellent performance of halopyrazine-phenanthroline small molecule is obtained. If no, adjust the amount of initial raw materials and solvents in Step 2, as well as the reaction conditions of the reactor, and then adjust the structure of the halopyrazine-phenanthroline small molecule to obtain a novel organic corrosion inhibitor with excellent performance.

3. The method for preparing a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline according to claim 2, characterized in that, In step one, the volume ratio of the required phenanthrolinedione to the required halogenated o-phenylenediamine is in the range of 1:1 to 1:1.

5.

4. The method for preparing a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline according to claim 3, characterized in that, The desired halogenated o-phenylenediamine is any one of 4,5-dibromo-o-phenylenediamine, 4,5-dichloro-o-phenylenediamine, and 4,5-difluoro-o-phenylenediamine.

5. The preparation method of a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline according to claim 4, characterized in that, The halogenated o-phenylenediamine is 4,5-dibromo-o-phenylenediamine, and the required phenanthrolinedione is o-phenanthrolinedione; the reaction formula for the synthesis of Dppz-Br from o-phenanthrolinedione and 4,5-dibromo-o-phenylenediamine is as follows: 。 6. The method for preparing a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline according to claim 4, characterized in that, The halogenated o-phenylenediamine is 4,5-dichloro-o-phenylenediamine, and the required phenanthrolinedione is o-phenanthrolinedione; the reaction formula for the synthesis of Dppz-Cl from o-phenanthrolinedione and 4,5-dichloro-o-phenylenediamine is as follows: 。 7. The preparation method of a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline according to claim 4, characterized in that, The halogenated o-phenylenediamine is 4,5-difluoro-o-phenylenediamine, and the required phenanthrolinedione is o-phenanthrolinedione; the reaction formula for the synthesis of Dppz-F from o-phenanthrolinedione and 4,5-difluoro-o-phenylenediamine is: 。 8. The method for preparing a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline according to claim 2, characterized in that, In step two, the required solvent includes any one of methanol, ethanol, and dioxane.

9. The method for preparing a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline according to claim 8, characterized in that, The value of T is 65℃-120℃, and the value of t is 2 h-12 h.

10. The method for preparing a novel small-molecule organic corrosion inhibitor of halopyrazine-phenanthroline according to claim 2, characterized in that, Step three includes: Step S31: Characterize the basic physicochemical properties of the halopyrazine-phenanthroline small molecule and determine whether the halopyrazine-phenanthroline small molecule meets the requirements. If yes, proceed to step S33; otherwise, proceed to step S32. Step S32: Based on the test results, return to step two, adjust the initial amounts of raw materials and solvents, as well as the reaction conditions of the reactor, to obtain the desired novel organic corrosion inhibitor; Step S33: Perform electrochemical testing on the small molecule of halopyrazine-phenanthroline; determine whether the small molecule of halopyrazine-phenanthroline is stable. If yes, prepare the desired novel organic corrosion inhibitor; if no, return to step S32.

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