A bispyrazolyl azo compound

Abstract

The application provides a kind of double pyrazole azo compound, belongs to azo compound technical field. To 4 H Amino-1 tert-butyl pyrazole-1 formate is added with sodium bicarbonate, vacuumed and filled with nitrogen, ethyl acetate is added, and then aqueous solution of potassium hydrogen sulfate is slowly added dropwise, stirred for 6-8 hours, extracted with ethyl acetate, separated, dried with anhydrous sodium sulfate, distilled under reduced pressure, column chromatography, column chromatography product is added with tetrahydrofuran, catalytic amount of acetic acid, heated and reacted overnight, dried with anhydrous sodium sulfate, distilled under reduced pressure, and column chromatography to obtain a double pyrazole azo compound. The above compound is derived from 4-pyrazolyl nitroso with tert-butoxycarbonyl protection as a precursor to obtain a double side substituted pyrazole azo compound functional molecule with long half-life Z Isomers, on the one hand, retains the properties of 4,4'-azo pyrazole super long half-life, on the other hand, can also modify the functional groups, such as water-soluble quaternary ammonium salt.

Description

Technical Field

[0001] The present application relates to a bipyrazolyl azo compound, belonging to the technical field of azo compounds. Background Art

[0002] Disazopyrazoles are a class of photochromic molecules with exceptional properties, exhibiting a longer half-life and a higher ratio of bi-isomeric isomers than traditional azobenzenes. These exceptional properties have provided a broad platform for the development of light-controlled functional devices, attracting significant attention in diverse technological fields such as optical switching, light actuation, and energy and information storage.

[0003] However, for azo-4-pyrazole, excessive water solubility and low preparation yield have become the biggest obstacles to its bilateral functionalization. Although there is a previous literature (“Azobispyrazole Family as Photoswitches Combining (near-)Quantitative Bidirectional Isomerization and Widely Tunable Thermal Half-lives from Hours to Years” Angew.Chem.Int.Ed.2021,60,16539) reporting that it was prepared by ring closure construction and oxidation methods, it is not suitable for large-scale derivatization due to its low yield and difficulty in purification. At the same time, it is difficult to obtain bilaterally isosubstituted compounds using dihydroazo-4-pyrazole as a precursor, which greatly limits the further functionalization application of this excellent mother core. Summary of the Invention

[0004] In view of this, the present application provides a bispyrazolyl azo compound, which not only overcomes the shortcomings of the existing (E)-1,2-bis(1H-pyrazol-4-yl)azo, such as poor solubility and difficulty in derivatization, but also obtains bilaterally symmetrical / asymmetric azopyrazole photoresponsive functional molecules.

[0005] Specifically, this application is implemented through the following solutions:

[0006] A bispyrazolyl azo compound, wherein the bispyrazolyl azo compound has the structural formula:

[0007]

[0008] The compound of the above structural formula is a unilaterally functionalized compound, which is obtained by the following steps:

[0009] Step 1: add sodium bicarbonate to tert-butyl 4-amino-1H-pyrazole-1-carboxylate, evacuate and then fill with nitrogen, add ethyl acetate, and then slowly dropwise add an aqueous solution of potassium persulfate double salt, stir and react for 6 to 8 hours, add ethyl acetate to extract, separate the liquids, dry over anhydrous sodium sulfate, distill under reduced pressure, and perform column chromatography.

[0010] Step 2: Add tetrahydrofuran and a catalytic amount of acetic acid to the column chromatography product, heat and react overnight, dry over anhydrous sodium sulfate, distill under reduced pressure, and perform column chromatography to obtain a bispyrazolyl azo compound.

[0011] The above scheme of this application can realize the derivatization synthesis of tert-butyl 4-amino-1H-pyrazole-1-carboxylate in both single-sided functionalization and double-sided functionalization directions:

[0012]

[0013] Furthermore, as a preference:

[0014] The concentration of the aqueous solution of potassium persulfate double salt is 50-65%.

[0015] The PE:EA ratio of the column chromatography is 1 to 3:1.

[0016] In step 2, the heating reaction temperature is 40-45°C.

[0017] The tert-butyloxycarbonyl-protected 4-pyrazole nitroso group proposed in the present invention can be used as a precursor to derive a functional molecule of a double-substituted pyrazole azo compound with a long half-life Z isomer. Furthermore, the present invention prepares two series of azopyrazole molecules with long half-life Z isomers through simple alkylation and quaternary ammonium reactions. On the one hand, these molecules retain the ultra-long half-life properties of 4,4'-azopyrazole, and on the other hand, they can also be modified with functional groups such as water-soluble quaternary ammonium salts. Specifically, the two series of bispyrazolyl azo compounds are processed as follows:

[0018] Method 1: Using the bispyrazolyl azo compound obtained in step 2 as a raw material, the protecting group is removed under acidic conditions to obtain a dihydropyrazolyl azo compound, which is then reacted with 6-bromo-N,N,N-trimethyl-1-hexanammonium under alkaline conditions for 8 to 10 hours, tetrahydrofuran is added to precipitate excess cesium carbonate, and the product is repeatedly recrystallized using methanol / ethyl acetate and methanol / tetrahydrofuran to obtain a double-sided functionalized bispyrazolyl azo compound. The structural formula of the double-sided functionalized bispyrazolyl azo compound is:

[0019]

[0020] Method 2, using the chromatography column product obtained in step 1 as a raw material, the original step 2 is replaced by: adding tetrahydrofuran to the product obtained by column chromatography in step 1 and 4-amino-1H-pyrazole, and then adding a catalytic amount of acetic acid, heating and reacting overnight, drying over anhydrous sodium sulfate, and distilling under reduced pressure, performing a second column chromatography, removing the protecting group of the second column chromatography product under acidic conditions to obtain a dihydropyrazole azo, and then reacting with 1,3-dibromopropane under alkaline conditions for 8 to 10 hours, drying over anhydrous sodium sulfate, and distilling under reduced pressure, performing a third column chromatography, dissolving the third column chromatography product in an ethanol solution, adding trimethylamine and reflux reaction overnight, adding ethyl acetate to precipitate a yellow solid, and washing with ethyl acetate / n-hexane to obtain a double-side functionalized bispyrazolyl azo compound. The structural formula of the double-side functionalized bispyrazolyl azo compound is:

[0021]

[0022] The above two different treatment methods can achieve the acquisition of products with different chain lengths.

[0023] The obtained bipyrazolyl azo compound realizes E→Z isomerization under 350nm light and realizes Z→E isomerization under 549nm light, and has a half-life of ≥37 days.

[0024] The above-mentioned unilaterally functionalized bispyrazolyl azo compounds and bilaterally functionalized bispyrazolyl azo compounds both have photoisomerization effects, high photoisomerization yields, long half-lives, high energy density for converting light energy into chemical energy, and good energy storage stability. In particular, the bilaterally functionalized bispyrazolyl azo compounds, whose bilaterally modified quaternary amine molecules also have good water solubility, thus giving the overall azo compound excellent water solubility, overcoming the application limitations of most organic molecules in aqueous solutions, and having the potential to store energy in green aqueous solutions, realizing the conversion of light energy into chemical energy. Compared with ordinary azobenzene compounds, the bilaterally functionalized bispyrazolyl azo compounds have greater energy density and can therefore be used as photoswitch molecules for light energy storage and conversion.

[0025] The synthesis of the bispyrazolyl azo derivatives proposed in this invention is simple and uses readily available raw materials. The alkylation and quaternization reactions of these compounds are both classic organic reactions with the advantage of mild conditions. In summary, this invention provides a convenient approach for the functionalization and application of bispyrazolyl azo photoresponsive molecules. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the technical solutions in the embodiments of this application will be further described in detail below. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit the technical solutions of this application. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of this application.

[0027] Example 1

[0028] This example synthesizes tert-butyl (E)-4-((1-methyl-1H-pyrazol-4-yl)azo)-1H-pyrazole-1-carboxylate, and the reaction formula is as follows:

[0029]

[0030] The specific process is as follows:

[0031] Step 1: Add tert-butyl 4-amino-1H-pyrazole-1-carboxylate (2.75 g, 15.0 mmol) to a branched reaction flask, followed by sodium bicarbonate (2.52 g, 2.0 eq.). Evacuate the flask, then fill it with nitrogen, and add 48 mL of ethyl acetate. Potassium persulfate (9.22 g, 1.0 eq.) is then fully dissolved in 96 mL of water. The aqueous solution of potassium persulfate is slowly added dropwise to the reaction flask and stirred for 6 h. Ethyl acetate is then added for extraction and separation. The mixture is dried over anhydrous sodium sulfate at room temperature overnight, evaporated under reduced pressure, and purified by column chromatography (PE / EA = 3:1) to yield blue tert-butyl 4-nitroso-1H-pyrazole-1-carboxylate (613.72 mg, 15.6%).

[0032] Step 2: tert-Butyl 4-nitroso-1H-pyrazole-1-carboxylate (591 mg, 3.0 mmol) and 4-amino-1-methyl-1H-pyrazole (436.50 mg, 1.5 eq.) were added to 10 mL of tetrahydrofuran, and a catalytic amount of acetic acid was added. The mixture was heated to about 40° C. and reacted overnight. The mixture was then dried over anhydrous sodium sulfate at room temperature overnight, evaporated under reduced pressure, and purified by column chromatography (PE / EA=3:1) to give yellow tert-butyl (E)-4-((1-methyl-1H-pyrazol-4-yl)azo)-1H-pyrazole-1-carboxylate (422.74 mg, 51.0%).

[0033] 1 H NMR (400MHz, CDCl3) δ8.55 (s, 1H), 8.09 (s, 1H), 7.91 (d, J = 12.0Hz, 2H), 3.96 (s, 3H), 1.67 (s, 9H); 13C NMR (101MHz, CDCl3) δ147.3,142.4,141.8,135.9,132.9,127.4,126.9,86.2,39.6,27.9.

[0034] Example 2

[0035] In this example, (E)-3,3'-(diazo-1,2-diylbis(1H-pyrazole-4,1-diyl))bis(N,N,N-trimethylpropane-1-amino) was synthesized. The reaction formula is as follows:

[0036]

[0037] The specific process is as follows:

[0038] Step 1: Add tert-butyl 4-amino-1H-pyrazole-1-carboxylate (2.75 g, 15.0 mmol) to a branched reaction flask. Add sodium bicarbonate (2.52 g, 2.0 eq.), evacuate, and then fill with nitrogen. Add 48 mL of ethyl acetate. Then, thoroughly dissolve potassium persulfate (9.22 g, 1.0 eq.) in 96 mL of water. The aqueous solution of potassium persulfate was slowly added dropwise to the reaction flask and stirred for 6 h. Extraction with ethyl acetate was then performed, and the mixture was separated. The mixture was dried over anhydrous sodium sulfate at room temperature overnight, evaporated under reduced pressure, and purified by column chromatography (PE / EA = 3:1) to yield blue tert-butyl 4-nitroso-1H-pyrazole-1-carboxylate (613.72 mg, 15.6%).

[0039] Step 2: tert-Butyl 4-nitroso-1H-pyrazole-1-carboxylate (591.00 mg, 3.0 mmol) and 4-amino-1H-pyrazole (373.50 mg, 1.5 eq.) were added to 10 mL of tetrahydrofuran, and a catalytic amount of acetic acid was added. The mixture was heated to about 40° C. and reacted overnight. The mixture was then dried over anhydrous sodium sulfate at room temperature overnight, evaporated under reduced pressure, and purified by column chromatography (PE / EA=1:1) to give yellow tert-butyl (E)-4-((1H-pyrazol-4-yl)azo)-1H-pyrazole-1-carboxylate (326.53 mg, 41.5%).

[0040] 1 H NMR (400MHz, DMSO) δ13.47(s,1H),9.08(s,2H),8.85(s,1H),8.15(s,1H),1.61(s,9H); 13 C NMR(101MHz,DMSO)δ147.2,142.4,141.4(2),135.7,128.5,125.3,86.2,27.9.HRMS calculated for[C 11 H14 N6O2+Na] + :285.1178,found:285.1071.

[0041] Step 3. (E)-4-((1H-pyrazol-4-yl)azo)-1H-pyrazole-1-carboxylic acid tert-butyl ester (325.22 mg, 1.24 mmol) was adjusted to pH 1 using hydrobromic acid and the protecting group was removed to obtain a yellow dihydropyrazole azo. Subsequently, cesium carbonate was added to adjust the pH to around 8, and the mixture was reacted with 1,3-dibromopropane (751.03 mg, 3.0 eq.) for 8 h. The mixture was dried over anhydrous sodium sulfate, evaporated under reduced pressure, and subjected to column chromatography (PE / EA=1:1) to obtain a yellow (E)-1,2-bis(1-(3-bromopropyl)-1H-pyrazol-4-yl)azo (184.40 mg, 36.8%).

[0042] 1 H NMR (400MHz, CDCl3) δ8.06(s,2H),7.97(s,2H),4.36(t,J=6.0Hz,4H),3.36(t,J=4.0Hz,4H),2.24(t,J=6.0Hz,4H).

[0043] Step 4: (E)-1,2-bis(1-(3-bromopropyl)-1H-pyrazol-4-yl)azo (101.03 mg, 0.25 mmol) was dissolved in 5 mL of ethanol solution, and trimethylamine (44.33 mg, 3.0 eq.) was added and refluxed at 80°C overnight (12 h). Ethyl acetate was added to precipitate a yellow solid, which was washed with ethyl acetate / n-hexane to obtain the product (E)-3,3'-(diazo-1,2-diylbis(1H-pyrazol-4,1-diyl))bis(N,N,N-trimethylpropan-1-amino) (66.25 mg, 73.1%), which has excellent water solubility: ≈52 mg / mL.

[0044] 1 H NMR(400MHz,MeOD)δ8.36(s,2H),7.95(s,2H),4.36(t,J=6.0Hz,4H),3.18(t,J=4.0Hz,4H),3.16(s,18H),2.23-2.18(m,4H).HRMS calculated for[C 18 H 34 N8] 2+ :181.1448,found:181.1450.

[0045] Example 3

[0046] In this example, (E)-6,6'-(diazo-1,2-diylbis(1H-pyrazole-4,1-diyl))bis(N,N,N-trimethylhexan-1-ammonium) was synthesized. The reaction formula is as follows:

[0047]

[0048] The specific process is as follows:

[0049] Step 1: Add tert-butyl 4-amino-1H-pyrazole-1-carboxylate (2.75 g, 15.0 mmol) to a branched reaction flask. Add sodium bicarbonate (2.52 g, 2.0 eq.), evacuate, and then fill with nitrogen. Add 48 mL of ethyl acetate. Then, thoroughly dissolve potassium persulfate (9.22 g, 1.0 eq.) in 96 mL of water. The aqueous solution of potassium persulfate was slowly added dropwise to the reaction flask and stirred for 6 h. Extraction with ethyl acetate followed by separation, drying over anhydrous sodium sulfate, and vacuum distillation followed by column chromatography (PE / EA = 3:1) afforded blue tert-butyl 4-nitroso-1H-pyrazole-1-carboxylate (613.72 mg, 15.6%).

[0050] Step 2: tert-Butyl 4-nitroso-1H-pyrazole-1-carboxylate (591.00 mg, 3.0 mmol) and 4-amino-1H-pyrazole (373.50 mg, 1.5 eq.) were added to 10 mL of tetrahydrofuran, and a catalytic amount of acetic acid was added. The mixture was heated to react overnight, dried over anhydrous sodium sulfate, evaporated under reduced pressure, and subjected to column chromatography (PE / EA = 1:1) to obtain yellow tert-butyl (E)-4-((1H-pyrazol-4-yl)azo)-1H-pyrazole-1-carboxylate.

[0051] Step 3: (E)-4-((1H-pyrazol-4-yl)azo)-1H-pyrazole-1-carboxylic acid tert-butyl ester (325.22 mg, 1.24 mmol) was adjusted to pH 1 with hydrobromic acid and the protecting group was removed to obtain a yellow dihydropyrazole azo. Subsequently, cesium carbonate was added to adjust the pH to around 8 and the reaction was carried out with 6-bromo-N,N,N-trimethyl-1-hexanammonium (830.03 mg, 3.0 eq.) for 8 h. Tetrahydrofuran was added to precipitate the excess cesium carbonate. The product was then recrystallized repeatedly using methanol / ethyl acetate and methanol / tetrahydrofuran to obtain a yellow pure product (E)-6,6'-(diazo-1,2-diylbis(1H-pyrazol-4,1-diyl))bis(N,N,N-trimethylhexan-1-ammonium) (20.0 mg, 3.61%) with good water solubility: ≈43 mg / mL.

[0052] 1H NMR (400MHz, MeOD) δ8.19(s,2H),7.87(s,2H),4.22(t,J=6.0Hz,4H),3.33(t,J=4.0Hz ,4H),3.12(s,18H),1.97-1.90(m,4H),1.79(t,J=8.0Hz,4H),1.44-1.40(m,8H).HRMS calculated for[C 24 H 46 N8] 2+ :223.1917,found:223.1916.

[0053] The optical switch performance of the compounds corresponding to the products of the above examples was tested, and the results are shown in Table 1.

[0054] Table 1: Optical switching properties of the corresponding compounds of the final products of different examples

[0055]

[0056] The specific ratios of the Z isomers of the compounds corresponding to the products of the above examples in methanol at different optical equilibrium states are shown in Table 2.

[0057] Table 2: Ratio of Z isomers in final products of different examples

[0058]

[0059] It can be seen from the above embodiments that:

[0060] In terms of photoisomerization yield, the bispyrazolyl azo compounds synthesized in the above examples have good photoisomerization yields: the E→Z yield at 350 nm is about 76.8% for the single-side functionalized product (Example 1), about 78.7% for the short-chain double-side functionalized product (Example 2), and about 79.6% for the long-chain double-side functionalized product (Example 3); the Z→E yield at 549 nm is about 80.1% for the single-side functionalized product, about 84.5% for the short-chain double-side functionalized product, and about 85.6% for the long-chain double-side functionalized product. This shows that the bispyrazolyl azo compounds provided in the above examples all have good photoisomerization yields, and the azo compounds corresponding to the double-side functionalization are slightly better than the azo compounds corresponding to the single-side functionalization, proving that the bispyrazolyl azo compounds provided in this application are beneficial to improving the energy density of conversion of light energy to chemical energy.

[0061] In terms of half-life, the half-life of the bipyrazolyl azo compound provided in the above embodiment is maintained at 36 to 37 days, which can effectively achieve stable energy storage.

[0062] Single-side and double-side functionalization has little effect on the photoswitching properties, and different alkyl chain lengths also have a small effect on the photoswitching properties, and the effect on the photoisomerization ratio and half-life can be ignored.

[0063] In terms of water solubility, it can be seen from the comparison of Example 1 with Examples 2 and 3 that: the single and double-sided functionalization has a greater influence on the polarity and water solubility of the substance, and the water solubility of the double-sided functional compound is significantly better than that of the single side, which significantly improves its application in energy storage in aqueous solution. In addition, the longer alkyl chain has a smaller effect on the water solubility of the product. The corresponding long-chain double-sided functionalized azo compound (Example 3) has a water solubility of about 43 mg / mL, while the short-chain double-sided functionalized azo compound (Example 2) has a water solubility of about 52 mg / mL. It further proves that the energy storage potential of the parent core is good, and the modification of the bilateral quaternary ammonium chain further improves its energy storage potential in aqueous solution.

[0064] The above-described embodiments merely represent several feasible implementation methods of the present invention. The description thereof is relatively specific and detailed, but it should not be understood as limiting the scope of the invention. The embodiments are not intended to limit the scope of protection in the claims of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention. Any equivalent implementation or modification that does not depart from the scope of the present invention should be included in the technology of the present invention.

Claims

1. A bipyrazolyl azo compound, characterized in that The structural formula of the bipyrazolyl azo compound is: ， Obtained by the following steps: Step 1, to 4-amino-1 H -Pyrazole-1-carboxylic acid tert-butyl ester was added with sodium bicarbonate, vacuumed and then filled with nitrogen, ethyl acetate was added, and then an aqueous solution of potassium hydrogen persulfate was slowly added dropwise. After stirring for 6-8 hours, ethyl acetate was added for extraction, separation, drying over anhydrous sodium sulfate, vacuum distillation, column chromatography, Step 2: Add 4-amino-1-methyl-1 H -pyrazole, tetrahydrofuran, and a catalytic amount of acetic acid, heated to react overnight, dried over anhydrous sodium sulfate, distilled under reduced pressure, and subjected to column chromatography to obtain a bispyrazolyl azo compound.

2. A bipyrazolyl azo compound according to claim 1, characterized in that: The concentration of the aqueous solution of potassium persulfate is 50-65%.

3. A bipyrazolyl azo compound according to claim 1, characterized in that: The PE:EA ratio of the column chromatography is 1-3:

1.

4. A bipyrazolyl azo compound according to claim 1, characterized in that: In step 2, the heating reaction temperature is 40~45°C.

5. A bipyrazolyl azo compound according to claim 1, characterized in that: The bispyrazolyl azo compound undergoes E-to-Z isomerization under 350nm light and Z-to-E isomerization under 549nm light, with a half-life of ≥37 days.

6. The bispyrazolyl azo compound according to any one of claims 1 to 5, wherein: Bispyrazolyl azo compounds are used as photoswitch molecules.

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