Water-based protonic acid doped diindolylmethane derivative as well as preparation method and application thereof

Abstract

The invention provides a water-based protonic acid doped diindolylmethane derivative as well as a preparation method and application thereof. The preparation method comprises the following step: reacting a mixed reaction system containing indole, pyridylaldehyde and aqueous protonic acid to generate the aqueous protonic acid doped diindolylmethane derivative. A pyridine group is introduced into a diindolylmethane skeleton to form a conjugated diheterocyclic structure, so that the molecular planarity is enhanced, and an indole ring is promoted to form coordinate bond adsorption with a metal surface through pi-electrons, so that good adsorbability on the surface of a metal matrix is achieved; and the corrosion inhibitor has good hydrophilicity and corrosion inhibition performance, especially has an excellent corrosion inhibition effect in a strongly acidic environment, and can provide efficient protection for a metal-containing substrate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal corrosion protection, and particularly relates to a water-based proton acid-doped diindolylmethane derivative, a preparation method and application thereof. BACKGROUND

[0002] In the fields of petroleum refining, chemical production and marine facilities, the corrosion problem of metal equipment in sulfur-containing, chlorine-containing and acidic media is increasingly prominent. Although imidazoline and pyridine corrosion inhibitors are widely used, they have low corrosion inhibition efficiency in strong acid environments and low biodegradability. In recent years, indole compounds have become a research hotspot for corrosion inhibitors due to their environmental friendliness and excellent adsorption performance. However, existing indole derivatives have obvious defects: 1. Poor water solubility: Most indole derivatives have low solubility in water (usually <0.1 g / L), which requires the use of organic solvents for solubilization, increasing the cost and environmental burden. 2. Narrow pH range: The corrosion inhibition efficiency significantly decreases in strong acid environments, making it difficult to meet industrial demands. 3. Instability of film formation: Weak intermolecular forces make it difficult to form a long-acting protective film on the metal surface.

[0003] Diindolylmethane (DIM) and its derivatives have excellent metal surface adsorption properties due to their unique planar conjugated structure. Studies have shown that the electron-rich indole ring in the diindolylmethane derivative molecule can form strong chemical adsorption with the metal surface through π electrons, while the hydrophobic group forms a physical barrier. However, the diindolylmethane derivatives synthesized by existing technologies are mostly oil-soluble, such as the imidazoline corrosion inhibitor based on tall oil fatty acid developed by the existing technology RU2710700C1, which still requires organic solvents for dissolution and is prone to layering at low temperatures. SUMMARY

[0004] To solve all or part of the above technical problems, the present application provides the following technical solutions: The first aspect of the present application provides a preparation method of a water-based proton acid-doped diindolylmethane derivative, which comprises: reacting a mixed reaction system containing indole, pyridine formaldehyde and water-based proton acid to generate a water-based proton acid-doped diindolylmethane derivative.

[0005] The present application forms a conjugated double heterocyclic structure by introducing a pyridine group into the indolylmethane skeleton, enhances the molecular planarity, and promotes the indole ring to form a coordination bond with the metal surface through π-electrons to form an adsorption, thereby imparting good adsorption on the surface of the metal-containing substrate. Meanwhile, the introduction of a hydrophilic functional group (such as a pyridine group, and a sulfonic acid group, a carboxyl group derived from a protonic acid, etc.) makes it have good hydrophilicity, solving the poor water solubility problem of the indole derivative in the prior art. The aqueous protonic acid-doped indolylmethane derivative of the present application has excellent corrosion inhibition performance, especially excellent corrosion inhibition effect in a strong acidic environment (such as an acidic chlorine-containing medium), and can provide efficient protection to the metal-containing substrate. Moreover, the aqueous protonic acid-doped indolylmethane derivative has excellent adsorption film-forming ability and can provide long-acting protection to the metal-containing substrate.

[0006] In some embodiments, the temperature of the reaction is room temperature to 80°C.

[0007] In some embodiments, the reaction time is 16h to 24h.

[0008] In some embodiments, the preparation method comprises: performing the reaction under inert atmosphere protection conditions.

[0009] In some embodiments, the content of the aqueous protonic acid solute in the mixed reaction system is 3wt% to 11wt% of the total mass of the indole and the pyridine formaldehyde.

[0010] In some embodiments, the molar ratio of the indole and the pyridine formaldehyde in the mixed reaction system is 1.9 to 3:1, preferably 1.9 to 2:1.

[0011] In some embodiments, the aqueous protonic acid comprises one or a combination of sulfuric acid, hydrochloric acid, trifluoromethanesulfonic acid, and phytic acid. For example, concentrated sulfuric acid and / or concentrated hydrochloric acid with a concentration of 37wt% to 38wt% can be used, or phytic acid can be prepared into an aqueous phytic acid solution, and then mixed with indole and pyridine formaldehyde for reaction.

[0012] In some preferred embodiments, the aqueous protonic acid comprises phytic acid. The protective film formed by the indolylmethane derivative prepared by using phytic acid is more dense, the stability of the film layer is improved, the overall corrosion inhibition effect is obviously improved, and the corrosion inhibition efficiency is improved to nearly 99%.

[0013] In some embodiments, the pyridine formaldehyde comprises one or a combination of pyridine-4-formaldehyde, pyridine-3-formaldehyde, and pyridine-2-formaldehyde.

[0014] In some embodiments, the mixed reaction system further comprises a solvent. The solvent may, for example, be one or a combination of ethanol, water, or DMF, but is not limited thereto.

[0015] In some embodiments, the preparation method specifically comprises: dissolving the indole, pyridine carboxaldehyde and solvent to obtain a mixed solution, and then adding the aqueous proton acid dropwise into the mixed solution to perform the reaction.

[0016] In some embodiments, the preparation method further comprises: recrystallizing the reaction product, and obtaining the purified aqueous proton acid doped diindomethane derivative after filtration and reduced pressure distillation.

[0017] The second aspect of the present application provides an aqueous proton acid doped diindomethane derivative prepared by the preparation method of any one of the above technical solutions.

[0018] The third aspect of the present application provides the application of the aqueous proton acid doped diindomethane derivative as a metal corrosion inhibitor or in the preparation of a metal corrosion inhibitor.

[0019] In particular, the corrosion inhibition effect of the proton acid doped diindomethane derivative in a strong acid environment is suitable for a metal corrosion inhibitor in a strong acid (such as an acidic chlorine-containing medium).

[0020] The fourth aspect of the present application provides a metal material comprising a metal-containing substrate and a protective film formed on the surface of the metal-containing substrate, wherein the protective film is formed by a metal corrosion inhibitor, and the metal corrosion inhibitor comprises the aqueous proton acid doped diindomethane derivative of any one of the above technical solutions.

[0021] The material of the metal-containing substrate can be any known material in the art, including but not limited to carbon steel, aluminum, aluminum alloy, magnesium, magnesium alloy, etc. The aqueous proton acid doped diindomethane derivative provided by the present application has excellent adsorption film-forming properties on these metal-containing substrates, and can provide long-term protection.

[0022] The method for forming the protective film on the metal-containing substrate can comprise: providing a solution containing 5-50 mg / L of the aqueous proton acid doped diindomethane derivative, and immersing the metal-containing substrate into the solution to form the protective film on the metal-containing substrate.

[0023] Compared with the prior art, the application has at least the following beneficial effects: the application forms a conjugated double heterocyclic structure by introducing a pyridine group into a diindolylmethane skeleton, enhances molecular planarity, and promotes the indole ring to form a coordination bond with a metal surface through π-electrons to impart good adsorption on a metal-containing substrate surface; and the introduction of a hydrophilic functional group imparts good hydrophilicity, solving the poor water solubility of indole derivatives in the prior art. The water-based proton acid-doped diindolylmethane derivative has excellent corrosion inhibition performance, especially excellent corrosion inhibition effect in a strong acidic environment (for example, an acidic chlorine-containing medium), and can provide efficient protection for a metal-containing substrate. Moreover, the water-based proton acid-doped diindolylmethane derivative has excellent adsorption film-forming capacity and can provide long-acting protection for a metal-containing substrate. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0025] Figure 1 is a preparation flow chart of the water-based proton acid-doped diindolylmethane derivative in Example 1 of the present application; Figure 2a is a nuclear magnetic hydrogen spectrum (H NMR) of the water-based proton acid-doped diindolylmethane derivative prepared in Example 1 and the reaction raw material; 1 Figure 2b is a carbon spectrum (C NMR) of the water-based proton acid-doped diindolylmethane derivative prepared in Example 1 and the reaction raw material; 13 Figure 2c is an FT-IR graph of the water-based proton acid-doped diindolylmethane derivative prepared in Example 1; Figure 2d is a UV-vis graph of the water-based proton acid-doped diindolylmethane derivative prepared in Example 1; Figure 3a is a Tafel curve graph of Q235 low-carbon steel in a 1M HCl solution containing different concentrations of Py-DIM; Figure 3b is an EIS equivalent circuit graph of Q235 low-carbon steel in a 1M HCl solution containing different concentrations of Py-DIM; Figure 4a 、 Figure 4b 、 Figure 4c ​​SEM, EDS and CLSM images of Q235 low carbon steel immersed by blank solution (i.e. control group) respectively.

[0026] Figure 5a , Figure 5b , Figure 5c SEM, EDS and CLSM images of Q235 low carbon steel immersed by test solution 1 (i.e. test group 1) respectively.

[0027] Figure 6a , Figure 6b , Figure 6c SEM, EDS and CLSM images of Q235 low carbon steel immersed by test solution 3 (i.e. test group 3) respectively.

[0028] Figure 7a , Figure 7b , Figure 7c SEM, EDS and CLSM images of Q235 low carbon steel immersed by test solution 4 (i.e. test group 4) respectively.

[0029] Figure 8 SEM and element scanning images of Q235 low carbon steel obtained by test group 4 immersion experiment; Figure 9 XPS full scanning image of Q235 low carbon steel obtained by test group 4 immersion experiment; Figure 10 X-ray photoelectron spectroscopy (XPS) characterization element and bonding information of Q235 low carbon steel obtained by test group 4 immersion experiment. DETAILED DESCRIPTION

[0030] The technical solutions of the present application will be described in detail below with specific examples, so that the skilled in the art can better understand and implement the technical solutions of the present application. The specific functional details disclosed herein should not be interpreted as limiting, but only as a basis for the claims and for teaching those skilled in the art to employ the representative basis of the present application in different ways in any appropriate detailed implementation.

[0031] In addition, unless otherwise specified, the various raw materials used in the following examples can be obtained from the market or other sources, and the various production and testing equipment used are all known in the art, and the methods used are also any known methods in the art.

[0032] Example 1

[0033] The present embodiment provides a water-based protonic acid-doped diindolylmethane derivative and a preparation method thereof, Figure 1 is a preparation flowchart of the present embodiment, which specifically comprises the following steps: 6.71 g of indole was weighed into a 250 mL three-necked flask, and 100 mL of anhydrous ethanol was added as a solvent. After stirring until completely dissolved, 3.2 mL of pyridine-4-carboxaldehyde was added dropwise to the three-necked flask, followed by 1 g of concentrated sulfuric acid (37 wt%–38 wt%). The reaction was carried out at 60 °C under nitrogen protection for 20 h. The reaction product was recrystallized from the reaction mixture using ethanol and water at a volume ratio of 10:1, and then filtered and distilled under reduced pressure to obtain a purified aqueous protic acid-doped diindolemethane derivative, denoted as Py-DIM.

[0034] The structure of the Py-DIM prepared in this embodiment is as follows: .

[0035] Figure 2a , Figure 2b These are, respectively, the aqueous protic acid-doped diindolemethane derivative (hereinafter referred to as Py-DIM) prepared in Example 1 and the 1H NMR spectrum of the reaction raw materials. 1 H NMR) and carbon spectrum ( 13 The chemical shift around 6.25 ppm on C NMR and Py-DIM is attributed to the proton peak on the newly formed methine methyl group from the reaction of indole and aldehyde. Figure 2b As shown, the chemical shift of 101.43 ppm in the carbon spectrum of pyridine formaldehyde corresponds to the para carbon of the nitrogen atom on the pyrrole ring, which does not appear in the carbon spectrum of Py-DIM, indicating the successful synthesis of Py-DIM. Figure 2c This is the FT-IR spectrum of the aqueous protic acid-doped diindolemethane derivative prepared in Example 1. Figure 2c As shown, it can be observed that at 3398cm -1 The absorption band centered at 3277 cm⁻¹ corresponds to the -NH stretching vibration on the indole ring. Py-DIM also exhibits an absorption band at 3277 cm⁻¹. -1 The peak at 1633 cm⁻¹ corresponds to the characteristic peak of free -NH, and the peak at 1633 cm⁻¹ corresponds to the peak of the reaction-produced -NH. -1 The peak at 1705 cm⁻¹ belongs to the methine group, and no peak appears at 1705 cm⁻¹. -1 The corresponding C=O stretching vibration peak of pyridine formaldehyde further confirms the successful preparation of Py-DIM. Figure 2d This is the UV-vis image of the aqueous protic acid-doped diindolemethane derivative prepared in Example 1. From Figure 2d It can be observed that Py-DIM exhibits strong absorption in the 220-280 nm range, corresponding to... Transitions. The introduction of the conjugated substituent pyridine ring may cause a redshift or change in absorption intensity, reflecting intramolecular charge transfer or tautomerism, manifested as an additional absorption band in the 250-300 nm range. UV analysis confirms the successful introduction of the pyridine ring into the diindolemethane structure.

[0036] Example 2

[0037] The present embodiment provides a water-based proton acid-doped diindolylmethane derivative and a preparation method thereof, specifically comprising the following steps: Take 6.71 g of indole in a 250 mL three-necked flask, and at the same time, add 100 mL of anhydrous ethanol as a solvent to stir until completely dissolved. Then, add 3.2 mL of pyridine-4-formaldehyde to the three-necked flask, and add 2 g of a 50 wt% concentration of phytic acid aqueous solution. React at 60°C under nitrogen protection for 20 h. Recrystallize the reaction product obtained from the reaction with ethanol and water in a volume ratio of 10:1, and then filter and distill under reduced pressure to obtain the purified water-based proton acid-doped diindolylmethane derivative.

[0038] Example 3

[0039] The present embodiment provides a water-based proton acid-doped diindolylmethane derivative and a preparation method thereof, specifically comprising the following steps: Take 6.71 g of indole in a 250 mL three-necked flask, and at the same time, add 100 mL of anhydrous ethanol as a solvent to stir until completely dissolved. Then, add 3.2 mL of pyridine-4-formaldehyde to the three-necked flask, and add 1 g of concentrated hydrochloric acid (concentration of 37 wt%-38 wt%). React at 60°C under nitrogen protection for 20 h. Recrystallize the reaction product obtained from the reaction with ethanol and water in a volume ratio of 10:1, and then filter and distill under reduced pressure to obtain the purified water-based proton acid-doped diindolylmethane derivative.

[0040] Example 4

[0041] The present embodiment provides a water-based proton acid-doped diindolylmethane derivative and a preparation method thereof, specifically comprising the following steps: Take 6.71 g of indole in a 250 mL three-necked flask, and at the same time, add 100 mL of anhydrous ethanol as a solvent to stir until completely dissolved. Then, add 3.2 mL of pyridine-4-formaldehyde to the three-necked flask, and add 1 g of trifluoromethanesulfonic acid. React at 60°C under nitrogen protection for 20 h. Recrystallize the reaction product obtained from the reaction with ethanol and water in a volume ratio of 10:1, and then filter and distill under reduced pressure to obtain the purified water-based proton acid-doped diindolylmethane derivative.

[0042] Example 5

[0043] The present embodiment provides a water-based proton acid-doped diindolylmethane derivative and a preparation method thereof, specifically comprising the following steps: Take 6.71 g of indole in a 250 mL three-necked flask, and add 100 mL of anhydrous ethanol as a solvent. Stir until completely dissolved, then add 3.2 mL of pyridine-3-formaldehyde to the three-necked flask, and add 1 g of concentrated sulfuric acid (concentration of 37%-38%). React at 60°C under nitrogen protection for 20 h. Recrystallize the reaction product obtained from the reaction using ethanol and water in a volume ratio of 10:1, then filter and distill under reduced pressure to obtain the purified aqueous proton acid-doped diindomethane derivative.

[0044] The structure of the aqueous proton acid-doped diindomethane derivative prepared in this example is as follows: .

[0045] Example 6

[0046] This example provides an aqueous proton acid-doped diindomethane derivative and a preparation method thereof, specifically comprising the following steps: Take 6.71 g of indole in a 250 mL three-necked flask, and add 100 mL of anhydrous ethanol as a solvent. Stir until completely dissolved, then add 3.2 mL of pyridine-2-formaldehyde to the three-necked flask, and add 1 g of concentrated sulfuric acid (concentration of 37%-38%). React at 60°C under nitrogen protection for 20 h. Recrystallize the reaction product obtained from the reaction using ethanol and water in a volume ratio of 10:1, then filter and distill under reduced pressure to obtain the purified aqueous proton acid-doped diindomethane derivative.

[0047] The structure of the aqueous proton acid-doped diindomethane derivative prepared in this example is as follows: .

[0048] Example 7

[0049] This example provides an aqueous proton acid-doped diindomethane derivative and a preparation method thereof, specifically comprising the following steps: Take 6.71 g of indole in a 250 mL three-necked flask, and add 100 mL of anhydrous ethanol as a solvent. Stir until completely dissolved, then add 3.2 mL of pyridine-2-formaldehyde to the three-necked flask, and add 2 g of a phytic acid aqueous solution with a concentration of 50 wt%. React at 60°C under nitrogen protection for 20 h. Recrystallize the reaction product obtained from the reaction using ethanol and water in a volume ratio of 10:1, then filter and distill under reduced pressure to obtain the purified aqueous proton acid-doped diindomethane derivative.

[0050] Example 8

[0051] This example provides an aqueous proton acid-doped diindomethane derivative and a preparation method thereof,Figure 1 is a preparation flow chart of the embodiment, specifically comprising the following steps: Indole is weighed in a 250 mL three-necked flask, 100 mL of DMF is added as a solvent, after stirring until complete dissolution, pyridine-4-formaldehyde is added dropwise into the three-necked flask, and a protonic acid is added, the dropwise addition time is 30 minutes, while continuous stirring is carried out, the reaction mixture gradually turns into a deep yellow color, forming a mixed reaction system, wherein the molar ratio of indole to pyridine-4-formaldehyde is 1.9~2:1, and the content of the aqueous protonic acid solute is 3wt%~11wt% of the total mass of indole and pyridine formaldehyde; the reaction is carried out at room temperature under nitrogen protection for 24 h. The reaction product obtained is recrystallized by using ethanol and water in a volume ratio of 10:1, then filtered and distilled under reduced pressure to obtain the purified aqueous protonic acid doped diindomethane derivative.

[0052] Example 9

[0053] The embodiment provides the application of the aqueous protonic acid doped diindomethane derivative in being a metal corrosion inhibitor or preparing a metal corrosion inhibitor, specifically comprising the following steps: 1. Prepare a HCl solution with a concentration of 1 mol / L Different concentrations of Py-DIM prepared in Example 1 are respectively added to form four groups of test solutions with Py-DIM concentrations of 5 mg / L, 10 mg / L, 25 mg / L and 50 mg / L.

[0054] 2. Electrochemical performance test method

[0055] Q235 low-carbon steel is used as a working electrode (exposed area is 1 cm 2 ), a saturated calomel electrode is used as a reference electrode, and a platinum sheet (2.5 cm²) is used as a counter electrode to form a three-electrode system. The working electrode is polished to be smooth and refined by using 400, 800 and 1500 SiC sandpapers in turn, then washed by using ultrapure water and ethanol, and dried by cold air.

[0056] After the pretreated working electrode is packaged, it is immersed in the four groups of test solutions or a blank solution prepared above, and electrochemical tests are carried out at a temperature of (25℃±2℃).

[0057] 3. Surface corrosion analysis method

[0058] The above pretreated Q235 low-carbon steel is immersed in the four groups of test solutions or a blank solution prepared above at a temperature of 25℃. The steel (with a size of 1×1×1 cm 3The surface morphology was characterized by X-ray photoelectron spectroscopy (XPS).

[0059] According to Example 9, after Q235 low carbon steel was immersed in the test solution, the open circuit potential (OCP) was recorded at fixed intervals, and then the electrochemical impedance spectroscopy (EIS) measurement was carried out in the frequency range of 100 kHz to 0.01 Hz with an alternating current signal of 10 mV amplitude. In addition, the polarization (Tafel) curve was collected at a scan rate of 1 mV / s within the OCP value range of ±300 mV, and the whole process was carried out at room temperature (298 K).

[0060] The EIS curve was analyzed by Zsimpwin fitting to obtain the equivalent circuit diagram and related electrochemical parameters. All electrochemical tests were repeated at least three times to ensure repeatability. The corrosion inhibition efficiency can be calculated by the formula: (1) (2) In the formula: and are the corrosion current densities corresponding to the blank solution and the test solution, respectively; R0 and R ct are the charge transfer resistances corresponding to the blank solution and the test solution in the equivalent circuit diagram, respectively.

[0061] Figure 3a are the Tafel curves of Q235 low carbon steel in 1M HCl solution containing different concentrations of Py-DIM. As shown in Figure 3a , with the increase of the concentration of Py-DIM corrosion inhibitor, the corrosion potential of the sample polarization curve moves to a more negative direction, and the sample polarization curve also moves to a lower current density direction, and with the increase of the content of Py-DIM corrosion inhibitor, the cathode branch and the anode branch do not change completely, obviously the slope change degree of the cathode branch curve is larger, which shows that the prepared corrosion inhibitor belongs to a mixed type corrosion inhibitor, which can inhibit the cathode reaction and the anode reaction at the same time. With the increase of the concentration of the corrosion inhibitor in the hydrochloric acid solution, the protection ability of Py-DIM for Q235 low carbon steel gradually increases, and the corrosion inhibition efficiency of the test group 4 is as high as 98.98%.

[0062] The anode / cathode reaction kinetics of the Py-DIM corrosion inhibitor prepared in Example 1 was studied by potentiodynamic polarization technology. The experimental data were processed by linear extrapolation method and listed in Table 1, including corrosion potential (E corr ), corrosion current density (i corr ), cathode Tafel slope (β c ), anode Tafel slope (β a ) and corrosion inhibition efficiency (IE PDPTafel parameters of the corrosion inhibitor. Wherein the corrosion inhibition efficiency (IE PDP ) is calculated by formula (1).

[0063] Table 1 Tafel curve parameter table

[0064] The present application also analyzes the EIS test data, Figure 3b is the EIS equivalent circuit diagram of Q235 low carbon steel in 1M HCl solution containing different concentrations of Py-DIM, and the obtained electrochemical parameters are shown in Table 2.

[0065] In Table 2, R s is the solution resistance, R ct is the charge transfer resistance, CPE is the constant phase element, and Cdl is the double-layer capacitance, which are obtained by calculation, and the calculation formula is as follows:

[0066] Wherein, Z CPE is the impedance modulus, wherein Y0, j, ω and n respectively represent CPE constant (Ω cm -2 s -n ), imaginary number (J 2 =-1), angular frequency (rad s -1 ) and index.

[0067] Table 2 EIS fitting data

[0068] As can be seen from Table 2, test groups 1-4 verify that the corrosion inhibition efficiency IE of the diindole methane derivative corrosion inhibitor prepared in Example 1 of the present application can reach more than 95%, which indicates that its performance of delaying metal corrosion is very excellent.

[0069] The present application also performs CLSM / SEM characterization on Q235 low carbon steel after immersion test in test solutions 1-4, blank solution at 298K. Figure 4a 、 Figure 5a 、 Figure 6a 、 Figure 7a are SEM images of Q235 low carbon steel immersed in blank solution (i.e. control group), test solution 1 (i.e. test group 1), test solution 3 (i.e. test group 3) and test solution 4 (i.e. test group 4) for 3 hours, respectively. Figure 4b 、 Figure 5b 、 Figure 6b 、 Figure 7bEDS energy spectrum analysis graphs of Q235 low-carbon steel after 3 hours of immersion in the control group, test group 1, test group 3 and test group 4, respectively. Figure 4c , Figure 5c , Figure 6c , Figure 7c CLSM graphs of Q235 low-carbon steel after 3 hours of immersion in the control group, test group 1, test group 3 and test group 4, respectively.

[0070] In combination with Figures 4a-4c , Figure 4a shows the typical morphology of low-carbon steel immersed in a hydrochloric acid solution, the surface of the low-carbon steel is severely damaged due to corrosion by the hydrochloric acid solution, the surface is rough and loose. The 3D morphology of the corroded Q235 low-carbon steel in the control group was evaluated, as shown in Figure 4c , the surface roughness (Ra) was as high as 2.123 µm, which was caused by the continuous erosion of corrosive ions. In combination with reference to Figure 5a , Figure 6a , Figure 7a and Figure 5c , Figure 6c and Figure 7c , after the addition of Py-DIM, the surface roughness Ra of the Q235 low-carbon steel in the test groups was reduced to 1.596 µm (test group 1), 1.206 µm (test group 3), and 0.476 µm (test group 4), respectively, the surface morphology was relatively flat, and the polishing marks were still visible, and the surface only showed slight granular corrosion. It shows that as the concentration of Py-DIM in the test solution increases, the corrosion of Q235 low-carbon steel gradually weakens. As shown in Figure 7c , only a small amount of corrosion product deposition was observed on the surface of the Q235 low-carbon steel in test group 4, and the surface was relatively smooth (Ra was 0.476 µm). In combination with reference to Figure 4b , Figure 5b , Figure 6b , Figure 7b , it can be seen that the content of oxygen (O) and chlorine (Cl) decreases with the increase of the concentration of Py-DIM, which indicates that the dissolution of the negative steel and the cathodic hydrogen evolution reaction are continuously delayed, and the corrosion inhibition degree gradually increases. This test further shows that the water-based proton acid-doped diindolylmethane derivative corrosion inhibitor provided by the present application can effectively inhibit the corrosion of Q235 low-carbon steel in an acidic solution.

[0071] Figure 8 is the SEM and element scanning graph of Q235 low-carbon steel obtained by the immersion experiment of test group 4. Figure 9 is the XPS full scan graph of Q235 low-carbon steel obtained by the immersion experiment of test group 4, Figure 10 is the element and bonding information characterized by X-ray photoelectron spectroscopy (XPS). The steel surface immersed in HCl does not show obvious nitrogen signal. In contrast, Figure 10(d) The substrate treated with Py-DIM acid solution in (d) showed a clear N peak, which can be fitted into two parts, the first part is likely to be N-Fe bond (400.0 eV), and the second part is likely to be C-N and =N-bond (392.2 eV) due to the coordination of pyridine N in Py-DIM molecule in test group 4 with Fe on the steel surface. The presence of different forms of nitrogen species means that Py-DIM is chemisorbed on the steel substrate with nitrogen atom as the active site, thereby forming a multiple anchoring barrier to protect the steel from corrosion. The present application selects diindolylmethane skeleton as the main corrosion inhibitor component, forms a coordination bond with the Fe-3d empty orbital on the steel surface through the lone pair of electrons of the heteroatom on the indole ring, forms a protective film, and at the same time uses pyridine formaldehyde as an auxiliary modification, multiple mechanism synergy promotes, enhances the corrosion inhibition and water-soluble effect, so that the overall corrosion inhibitor has very outstanding corrosion inhibition effect in strong acid.

[0072] Five peaks (four peaks from Fe 2p3 / 2 and one peak from Fe 2p1 / 2) were obtained from the Fe 2p spectrum of the corrosion product on the steel surface. The peak value at 707.18 eV (Fe 2p3 / 2) is attributed to metallic Fe; the peak value at 710.33 eV is mainly related to Fe2O3 of Fe 3 + or Fe3O4; the peak located at about 712.68 eV is likely to be due to the presence of a small amount of FeCl3 on the steel surface. It is speculated that the peak value at 722.93 eV is related to the above Fe 3+ compound. The peak value at 724.88 eV is the peak value of Fe 2p1 / 2.

[0073] The present application also tests the corrosion inhibition performance of the water-based proton acid-doped diindolylmethane derivative prepared in other embodiments, and the corrosion inhibition effect is excellent.

[0074] In summary, the water-based proton acid-doped diindolylmethane derivative provided by the present application is a corrosion inhibitor with excellent corrosion inhibition effect in acidic corrosive media, and can achieve good corrosion inhibition effect with less dosage. The preparation method provided by the present application has mild conditions and low cost, and is suitable for large-scale industrial production and application. The present application has very important practical and research significance for developing new functional corrosion inhibitors with high efficiency, environmental protection and non-toxicity.

[0075] In addition, the present inventors have also carried out tests with other raw materials, process operations and process conditions described in the present specification with reference to the foregoing embodiments, and all ideal results have been obtained.

[0076] The aspects, embodiments, features and examples of the present application should be considered illustrative, for explaining and illustrating the present application, but not for limiting the present application, and the scope of the present application is only defined by the claims.

[0077] While the application has been described with reference to the illustrative embodiments, those skilled in the art will appreciate that various modifications, omissions, and / or additions can be made without departing from the spirit or scope of the application. Additionally, many modifications can be made to adapt a particular situation or material to the teachings of the application without departing from its scope. Therefore, the scope of the application should be determined not with reference to the description of the disclosed embodiments but should instead be determined with reference to the appended claims, along with their full scope of equivalents. Further, to the extent that the terms first, second, etc. are used herein to describe various elements, these are also generally to be understood as interchangeable and are not used to denote an order or importance, but are used to distinguish one element from another.

Claims

1. A process for the preparation of an aqueous protonic acid-doped diindolylmethane derivative, characterized in that, The application relates to a preparation method of a water proton acid doped diindolylmethane derivative. The reaction is carried out at room temperature to 80 DEG C, and the reaction time is 16h to 24h; and / or, the reaction is carried out under the protection of an inert atmosphere.

2. The method of claim 1, wherein: The content of the water proton acid solute in the mixed reaction system is 3wt% to 11wt% of the total mass of the indole and the pyridine formaldehyde; 3. The method of claim 1, wherein: And / or, the molar ratio of the indole and the pyridine formaldehyde in the mixed reaction system is 1.9 to 2:

1. The water proton acid comprises one or a combination of sulfuric acid, hydrochloric acid, trifluoromethanesulfonic acid and phytic acid; 4. The method of claim 1, wherein: And / or, the pyridine formaldehyde comprises one or a combination of pyridine-4-formaldehyde, pyridine-3-formaldehyde and pyridine-2-formaldehyde. The water proton acid comprises phytic acid.

5. The method of claim 4, wherein: The mixed reaction system further comprises a solvent.

6. The method of claim 1, wherein: The application further relates to a water proton acid doped diindolylmethane derivative prepared by the preparation method.

7. The preparation method according to claim 1, characterized in that, The application further relates to a purified water proton acid doped diindolylmethane derivative obtained by recrystallization, filtration and vacuum distillation of the reaction product.

9. The water proton acid doped diindolylmethane derivative of claim 8 is used as a metal corrosion inhibitor or in the preparation of a metal corrosion inhibitor.

8. An aqueous protonic acid-doped diindolylmethane derivative, characterized in that: The application further relates to a metal-containing substrate provided with a protective film formed on the surface of the metal-containing substrate, wherein the protective film is formed by a metal corrosion inhibitor, and the metal corrosion inhibitor comprises the water proton acid doped diindolylmethane derivative of claim 8. ​ 10. A metal material, characterized by, ​

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