Method for synthesizing pentazole cobalt salt based on electrochemistry

Abstract

The invention discloses a method for synthesizing pentazole cobalt salt based on electrochemical synthesis, which comprises the following steps: carrying out electrochemical reaction on 3, 5-dimethyl-4-hydroxyphenyl pentazole in an electrolyte solution containing an additive; and after the reaction is finished, extracting and separating liquid, adding divalent cobalt salt into a water phase, stirring and dissolving, and crystallizing at low temperature to separate out a target product. According to the method, extra catalysts and oxidants are not needed, the reaction is carried out under relatively mild electrochemical conditions, meanwhile, gram-scale amplification synthesis can be carried out in the reaction, and the method is beneficial to promoting the efficient and green preparation process of the pentazole ionic salt.

Description

Technical Field

[0001] The invention relates to a method for synthesizing pentazole cobalt salt, and belongs to the technical preparation field of high-energy energetic materials. Background Art

[0002] High energy density materials are becoming a research hotspot in the field of energetic materials. Among the numerous candidates, all-nitrogen materials and their derivatives based on nitrogen-nitrogen bonds have an average bond energy of 159 and 419 kJ / mol for N-N and N=N bonds, respectively, which is much lower than the average bond energy of 946 kJ / mol for N≡N bonds. Therefore, they will inevitably release huge amounts of energy during the decomposition process into N2. They are expected to be used as a new generation of high-energy green energetic materials in explosives, propellants, and other fields. At present, in addition to the azide anion (N3ˉ), among the reported nitrogen pentacations (N5 + ), pentazole anion (N5ˉ), all-nitrogen six-membered ring [N6] 4 Among all nitrogen species such as N5ˉ and cubic polymeric nitrogen (cg-N), the N5ˉ ion is considered to be the most likely new generation of high-energy materials for application due to its diaromatic conjugated stable structure and high formation enthalpy.

[0003] Since Huisgen and Ugi successfully synthesized aryl pentazoles using phenyldiazonium salts and sodium azide [Angew. Chem. Int. Ed., 1956, 68(22): 705-706], scientists have made numerous attempts to cleave the CN bond of aryl pentazoles and their derivatives to isolate N5ˉ, but unfortunately, none of them have been successful. Until 2017, Zhang Chong et al. used ferrous glycine and m-chloroperbenzoic acid as cleavage reagents and auxiliary agents to successfully isolate the first room temperature stable pentazole ion salt - (N5)6(H3O)3(NH4)4Cl from 3,5-dimethyl-4-hydroxyphenylpentazole [Science, 2017, 355, 374-376], but the yield was only 19.5%. Subsequently, on this basis, they developed a more efficient cutting system of tetraphenylporphyrin manganese and isopropylbenzene hydroperoxide [Chem.-Eur.J., 2024, 31(1): e202402575], which increased the yield of pentazoline ion salt to 35%. However, the above method has certain limitations, mainly including that the yield of pentazoline ion salt is still low, a certain amount of metal catalyst and excess peroxide need to be used, and the post-processing is cumbersome. It can be seen that the traditional redox cutting method no longer meets the sustainable development needs of high-energy pentazoline ion salts. The development of a new process for the simpler and greener synthesis of pentazoline ion salts is of great significance for broadening its scope of application. Summary of the Invention

[0004] The purpose of the present invention is to provide a simple, green and efficient electrochemical method for synthesizing cobalt pentazole salts.

[0005] The technical solution for achieving the purpose of the present invention is:

[0006] A method for electrochemically synthesizing a cobalt pentazole salt comprises the following steps:

[0007] (1) 3,5-dimethyl-4-hydroxyphenylpentazole is subjected to an electrochemical reaction in an electrolyte solution containing an additive;

[0008] (2) After the reaction is completed, the liquid is separated by extraction, and a divalent cobalt salt is added to the aqueous phase, stirred and dissolved, and the target product is crystallized at low temperature;

[0009]

[0010] Furthermore, in step (1), the additive is any one or more of 2,2,6,6-tetramethylpiperidinyl oxide (TEMPO, CAS: 2564-83-2), 4-acetylamino-2,2,6,6-tetramethylpiperidin-1-oxide (4-NHAc-TEMPO, CAS: 14691-89-5), 4-oxo-2,2,6,6-tetramethylpiperidinyl oxide (4-oxo-TEMPO, CAS: 2896-70-0), N-hydroxyphthalimide (NHPI), ferrocene (FeCp2), sodium tetrachloropalladate (Na2PdCl4) and triphenylamine, preferably TEMPO or 4-NHAc-TEMPO as the additive.

[0011] Furthermore, in step (1), the molar ratio of 3,5-dimethyl-4-hydroxyphenylpentazole to the additive is 1:0.08 to 1:0.15, preferably 1:0.1.

[0012] Furthermore, in step (1), the solvent of the electrolyte solution is one or more of methanol, acetonitrile, tetrahydrofuran, dichloromethane, N,N-dimethylformamide (DMF), ethylene glycol dimethyl ether and water, and the preferred volume ratio is acetonitrile: ethylene glycol dimethyl ether: water = 3 to 8:1:1, preferably 8:1:1.

[0013] Furthermore, in step (1), the electrolyte of the electrolyte solution is any one of ammonium chloride, ammonium iodide, tetra-n-butylammonium chloride, tetra-n-butylammonium bromide, tetra-n-butylammonium iodide, tetra-n-butylammonium tetrafluoroborate, tetra-n-butylammonium hexafluorophosphate and tetra-n-butylammonium perchlorate, preferably ammonium chloride as the electrolyte.

[0014] Furthermore, in step (1), the equivalent ratio of the electrolyte to 3,5-dimethyl-4-hydroxyphenylpentazole is 1:1.

[0015] Furthermore, in step (1), the positive electrode of the electrochemical reaction is a Pt electrode or a C electrode, preferably a C electrode, and the negative electrode is a Pt electrode.

[0016] Furthermore, in step (1), the electrochemical reaction current is 5 to 15 mA, and the reaction time is 2.8 to 8.4 h, preferably 2.8 to 6 h, and more preferably 6 h.

[0017] Furthermore, in step (2), the divalent cobalt salt is one or more of cobalt nitrate hexahydrate, cobalt dichloride hexahydrate, cobalt dibromide hexahydrate, cobalt sulfate heptahydrate, and cobalt acetate tetrahydrate, preferably cobalt dichloride hexahydrate.

[0018] Furthermore, in step (2), the molar ratio of 3,5-dimethyl-4-hydroxyphenylpentazole to divalent cobalt salt is 1:2.

[0019] Furthermore, in step (2), low-temperature crystallization refers to crystallization at 0-5°C.

[0020] Compared with the prior art, the present invention has the following significant advantages:

[0021] (1) No additional metal catalysts or peroxidants are required, and the reaction can be carried out under relatively mild electrochemical conditions;

[0022] (2) The one-pot reaction increased the yield of cobalt pentazole salt to 37% with a reaction time of only 6 h.

[0023] (3) The atom economy after the reaction is good, the post-processing procedure is relatively simple, and it is environmentally friendly to a certain extent;

[0024] (4) The electrochemical reaction produces hydrogen energy (H2) with additional added value at the cathode.

[0025] The present invention is further described in detail below with reference to the accompanying drawings.

[0026] Attached diagram

[0027] Figure 1 Schematic diagram of the electrochemical synthesis of the cobalt pentazole salt of the present invention.

[0028] Figure 2 This is a high-resolution mass spectrum of the cobalt pentazole salt synthesized by the present invention.

[0029] Figure 3 It is the crystal structure diagram of the penta-synthetic azole cobalt salt of the present invention. DETAILED DESCRIPTION

[0030] The following examples may help those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way. The present invention includes, but is not limited to, the following electrochemical reaction systems consisting of electrolytes, solvents, and electrodes.

[0031] Based on in-depth experimental and mechanistic studies on the selective cleavage of the CN bond of aryl pentazoles catalyzed by transition metals to synthesize pentazole anions, the present invention proposes using an electrochemical method with TEMPO or 4-NHAc-TEMPO as an additive, at an ambient temperature of -10°C and a reaction time of 6 hours, to achieve the selective cleavage of the CN bond of 3,5-dimethyl-4-hydroxyphenylpentazole to obtain the pentazole anion. After being captured by divalent cobalt ions, the pentazole anion is crystallized and precipitated at low temperature to obtain the target product, the cobalt pentazole salt - Co(N5)2(H2O)4·4H2O.

[0032] In the present invention, except for the raw material 3,5-dimethyl-4-hydroxyphenylpentazole which is synthesized according to the literature (J.Energ.Mater., 2016, 34, 103-111.), other reagents and raw materials can be purchased through commercial channels.

[0033] Example 1:

[0034] 27 mg (0.5 mmol) of ammonium chloride, 8 mL of acetonitrile, 1 mL of ethylene glycol dimethyl ether (DME), and 1 mL of water were added to a 25 mL electrochemical reaction cell. After ultrasonic dissolution, the temperature was lowered to -10°C. Then, 95.5 mg (0.5 mmol) of 3,5-dimethyl-4-hydroxyphenylpentazole and 7.81 mg (0.05 mmol) of TEMPO were added. The electrolytic cell was equipped with a graphite rod anode ( 90mm) as the anode, and a Pt sheet (10mm×10mm×0.1mm) as the cathode. The mixed solution was electrolyzed at -10°C with a constant current (7mA) for 6h. After the reaction, the organic solvent was removed by rotary evaporation to obtain a viscous substance, 5mL of ethyl acetate and 2mL of water were added for extraction and separation, the aqueous phase was retained, and a 0.1M dilute hydrochloric acid solution was used to adjust the pH to 3-4, 238mg (1.0mmol) of cobalt dichloride hexahydrate was added, stirred and dissolved, and 32mg of the target product, pentazole cobalt salt, was crystallized at low temperature to precipitate an orange-yellow color. The pentazole anion yield was 37%. The electrochemical synthesis process is as follows: Figure 1 , high-resolution mass spectrometry data such as Figure 2 , the crystal structure is as Figure 3 shown.

[0035] Example 2:

[0036] Other conditions were the same as in Example 1. The effects of different additive types on the yield of the target product were examined. The experimental results are shown in Table 1.

[0037] Table 1: Effect of different additive types on target product yield

[0038]

[0039] Example 3:

[0040] Other conditions were the same as in Example 1. The effect of the amount of additives on the yield of the target product was examined. The experimental results are shown in Table 2.

[0041] Table 2: Effect of the amount of additives on the yield of the target product

[0042]

[0043] Example 4:

[0044] Other conditions were the same as in Example 1. The effects of different solvent systems on the yield of the target product were examined. The experimental results are shown in Table 3.

[0045] Table 3: Effect of different solvent systems on the yield of target products

[0046]

[0047] Example 5:

[0048] Other conditions were the same as in Example 1. The effects of different electrolyte types on the yield of the target product were examined. The experimental results are shown in Table 4.

[0049] Table 4: Effect of different electrolyte types on the yield of target products

[0050]

[0051]

[0052] Example 6:

[0053] Other conditions were the same as in Example 1. The effects of different electrode materials on the yield of the target product were examined. The experimental results are shown in Table 5.

[0054] Table 5: Effect of different electrode materials on the yield of target products

[0055]

[0056] Example 7:

[0057] Other conditions were the same as in Example 1. The effects of different current intensities and reaction times on the yield of the target product were examined. The experimental results are shown in Table 6.

[0058] Table 6: Effects of different current intensities and reaction times on the yield of target products

[0059]

[0060] Example 8:

[0061] Other conditions were the same as those in Example 1. The effect of adding different divalent cobalt salt hydrates after the reaction on the yield of the target product was tested. The experimental results are shown in Table 7.

[0062] Table 7: Effect of the type of added divalent cobalt salt hydrate on the yield of the target product

[0063]

[0064] Example 9:

[0065] Based on Example 1, an amplification experiment was performed, and the process and synthesis route are as follows:

[0066] To a 150 mL electrochemical reaction cell, 320 mg (6 mmol) of ammonium chloride, 80 mL of acetonitrile, 10 mL of ethylene glycol dimethyl ether (DME), and 10 mL of water were added. After sonication, the mixture was cooled to -10°C. Then, 1146 mg (6.0 mmol) of 3,5-dimethyl-4-hydroxyphenylpentazole and 187.5 mg (1.2 mmol) of TEMPO were added. The electrolytic cell was equipped with a graphite rod anode (30 mm × 15 mm × 3 mm) as the anode and a platinum sheet (35 mm × 15 mm × 0.5 mm) as the cathode. The mixed solution was electrolyzed at a constant current (15 mA) for 18 h at -10°C. After the reaction, the organic solvent was removed by rotary evaporation, and 60 mL of ethyl acetate and 20 mL of water were added for extraction. The aqueous phase was retained and the pH was adjusted to 3-4. 2856 mg (12.0 mmol) of cobalt dichloride hexahydrate was added and dissolved with stirring. The mixture was refrigerated at 5°C overnight to crystallize 360 ​​mg of the target pentazolium cobalt salt, Co(N5)2(H2O)4·4H2O, into an orange-yellow solution. The yield of the pentazolium anion was 35%. This scale-up experiment demonstrates the important research value and application potential of electrochemical synthesis technology for promoting the green preparation of high-energy pentazolium ion salts and the further development of pentazolium-based energetic materials.

[0067]

[0068] The above-mentioned implementation cases are only preferred implementation cases in the present invention, but the implementation methods of the present invention are not limited to the above-mentioned implementation cases. For example, various combinations of the schemes in the embodiments and any other changes, modifications, substitutions, and combinations made without departing from the spirit and principles of the present invention should be equivalent replacement methods and are within the scope of protection of the present invention.

Claims

1. A method for electrochemically synthesizing a cobalt pentazole salt, characterized in that: The following steps are involved: (1) 3,5-dimethyl-4-hydroxyphenylpentazole is subjected to an electrochemical reaction in an electrolyte solution containing an additive; (2) After the reaction is completed, the liquid is separated by extraction, and a divalent cobalt salt is added to the aqueous phase, stirred and dissolved, and the target product is crystallized at low temperature; 2. The method according to claim 1, wherein In step (1), the additive is any one or more of 2,2,6,6-tetramethylpiperidinyl oxide (TEMPO, CAS: 2564-83-2), 4-acetylamino-2,2,6,6-tetramethylpiperidinyl-1-oxide (4-NHAc-TEMPO, CAS: 14691-89-5), 4-oxo-2,2,6,6-tetramethylpiperidinyl oxide (4-oxo-TEMPO, CAS: 2896-70-0), N-hydroxyphthalimide (NHPI), ferrocene (FeCp2), sodium tetrachloropalladate (Na2PdCl4) and triphenylamine, preferably TEMPO or 4-NHAc-TEMPO as the additive.

3. The method according to claim 1, wherein The molar ratio of 3,5-dimethyl-4-hydroxyphenylpentazole to the additive is 1:0.08 to 1:0.15, preferably 1:0.

1.

4. The method according to claim 1, wherein The solvent of the electrolyte solution is one or more of methanol, acetonitrile, tetrahydrofuran, dichloromethane, N,N-dimethylamide, ethylene glycol dimethyl ether and water, preferably in a volume ratio of acetonitrile:ethylene glycol dimethyl ether:water = 3 to 8:1:1, preferably 8:1:

1.

5. The method according to claim 1, wherein The electrolyte of the electrolyte solution is any one of ammonium chloride, ammonium iodide, tetra-n-butylammonium chloride, tetra-n-butylammonium bromide, tetra-n-butylammonium iodide, tetra-n-butylammonium tetrafluoroborate, tetra-n-butylammonium hexafluorophosphate and tetra-n-butylammonium perchlorate, and ammonium chloride is preferably used as the electrolyte.

6. The method according to claim 1, wherein The equivalent ratio of the electrolyte to 3,5-dimethyl-4-hydroxyphenylpentazole is 1:

1.

7. The method according to claim 1, wherein The positive electrode of the electrochemical reaction is a Pt electrode or a C electrode, preferably a C electrode, and the negative electrode is a Pt electrode.

8. The method according to claim 1, wherein The electrochemical reaction current is 5 to 15 mA, and the reaction time is 2.8 to 8.4 h, preferably 2.8 to 6 h, and more preferably 6 h.

9. The method according to claim 1, wherein The divalent cobalt salt is one or more of cobalt nitrate hexahydrate, cobalt dichloride hexahydrate, cobalt dibromide hexahydrate, cobalt sulfate heptahydrate, and cobalt acetate tetrahydrate, preferably cobalt dichloride hexahydrate.

10. The method according to claim 1, wherein The molar ratio of 3,5-dimethyl-4-hydroxyphenylpentazole to the divalent cobalt salt is 1:2.

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