A method for synthesizing a bis(benzothiadiazole-5-amine)

Abstract

The application discloses a synthesis method of bis(benzothiadiazole-5-amine), which is characterized by controlling the feeding mode, preheating and stirring the reaction substrate, adding the reducing agent stannous chloride in batches, taking 5-nitrobenzo[c][1,2,5]thiadiazole as raw material, and performing continuous reactions including coupling and nitro reduction to obtain the target compound [4,4'-bisbenzo[c][1,2,5]thiadiazole]-5,5'-diamine by one-step method. The method not only simplifies the reaction operation, avoids the use of flammable and explosive reagents and catalysts, and improves the reaction stability, but also is a more economical synthesis route of bis(benzothiadiazole-5-amine) compounds, and provides a new idea for the preparation of the compounds.

Description

Technical Field

[0001] The invention belongs to the field of organic synthesis, and particularly relates to a method for synthesizing bis(benzothiadiazole-5-amine). Background Art

[0002] To address the energy crisis, photovoltaic cells that harvest energy from sunlight have attracted significant attention. Bulk heterojunction (BHJ) polymer solar cells (polymer solar cells) based on composites of electron-donating semiconductor conjugated polymers and electron-accepting fullerenes—where the active layer is a blend of the donor and acceptor materials—offer significant market potential, surpassing traditional inorganic solar cells in terms of cost, portability, and ease of processing. In particular, new bulk heterojunction polymer solar cell materials have been designed in recent years to address two key shortcomings of BHJ: a) the relatively large band gap of the donor polymer in the photoactive layer, which allows access to only a small portion of the solar spectrum; and b) the potential for charge transport and collection in disordered nanoscale mixtures to be hindered by phase boundaries and discontinuities. This has injected new momentum into the development of this energy source.

[0003] Bis(benzothiadiazole-5-amine) is a key intermediate for novel bulk heterojunction polymer solar cell materials. Its downstream product, 7,7'-dibromo-[4,4'-bisbenzo[c][1,2,5]thiadiazole]-5,5'-diamine, is a key molecular building block for the polymer poly{N-alkylcarbazole[3,4-c:5,6-c]bis[1,2,5]thiadiazole-halogen-thiophene} (PCBTT). The molecular formula is shown below:

[0004]

[0005] PCBTT is a novel donor-acceptor integrated structure constructed by directly attaching a pull unit to a push unit to form a fused ring. This donor-acceptor integrated structure ensures tight p-p stacking to facilitate charge transfer. The strong electron-withdrawing ability of the two thiadiazole moieties and a functional thiophene bridge maintains a low HOMO energy level, resulting in a narrow band gap. The interaction between the pull and push units can fine-tune the HOMO / LUMO energy levels to adapt to the solar flux (Journal of Polymer Science, Part A: Polymer Chemistry 2013, 51, 565-574), making it a new solar cell material with high application potential. Given the unique functionality of the thiadiazole moiety in PCBTT, bis(benzothiadiazole-5-amine) compounds, the core structure of key intermediates in the synthesis of PCBTT, is essential for developing advantageous synthetic methods to provide new insights into the development of novel solar cell materials.

[0006] In the prior art, the synthesis of bis(benzothiadiazole-5-amine) compounds usually undergoes a halogen coupling step. Taking the compound 7,7'-dibromo-[4,4'-bisbenzo[c][1,2,5]thiadiazole]-5,5'-diamine as an example, its synthesis undergoes two steps, as shown in the following formula:

[0007]

[0008] The first step involves coupling the bromide A (4,7-dibromo-5-nitrobenzo[1,2,5]thiazole) with copper powder to yield compound B (7,7'-dibromo-5,5'-dinitro-4,4'-bisbenzo[c][1,2,5]thiadiazole). The second step involves nitro group reduction in tin hydrochloride to yield the target compound C (7,7'-dibromo-[4,4'-bisbenzo[c][1,2,5]thiadiazole]-5,5'-diamine). The synthesis process is not only complex but also requires the use of flammable and explosive copper powder, a metal catalyst that poses a certain risk and is relatively uneconomical. This, to a certain extent, limits the application and development of this class of compounds. There is an urgent need to develop a shorter, simpler, and more economical synthetic route for bis(benzothiadiazole-5-amine) compounds. Summary of the Invention

[0009] In view of the problems in the prior art of the synthesis of bis(benzothiadiazole-5-amine) compounds, such as the complicated steps, flammable and explosive reagents used, high safety risks and low economic efficiency, the present invention aims to provide a method for synthesizing bis(benzothiadiazole-5-amine) with short reaction steps, simple operation, high safety and a more economical and ideal synthetic route.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

[0011] The present invention provides a method for synthesizing bis(benzothiadiazole-5-amine), which is carried out according to the following route:

[0012]

[0013] Specifically, the method includes the following steps:

[0014] (1) 5-Nitrobenzo[c][1,2,5]thiadiazole (Compound 1) was dissolved in organic solution I, heated to reflux, and stirred for 0.5-1 h;

[0015] (2) adding a reducing agent to the reaction system obtained in step (1) and keeping the temperature to react for 1 to 5 hours;

[0016] (3) After the reaction is completed, the pH of the reaction system is adjusted to alkaline with alkali solution, extracted with organic solvent II, and post-treated to obtain the target compound 2.

[0017] Furthermore, in step (1), the organic solvent I is one or more of methanol, ethanol, tetrahydrofuran, N,N-dimethylformamide, and dioxane.

[0018] Furthermore, in step (1), the mass volume ratio of the compound 1 to the organic solvent I is 1:1 to 30 g / mL.

[0019] Furthermore, in step (1), the duration of the heat preservation and stirring is 0.5 h.

[0020] Furthermore, in step (2), the reducing agent is stannous chloride dihydrate.

[0021] Furthermore, in step (2), the stannous chloride dihydrate is added in batches, and the addition rate is based on the stable reflux.

[0022] Furthermore, in step (2), the molar ratio of compound 1 to stannous chloride is 1:2-4.

[0023] Furthermore, in step (2), the reaction time is 1 to 2 hours.

[0024] Furthermore, in step (3), the operation steps are: cooling the reaction system to room temperature, adding water to dilute, adjusting the pH to alkaline with alkali solution, extracting with organic solvent II, backwashing with saturated brine, drying, concentrating the organic phase, and purifying the concentrate to obtain the target compound 2.

[0025] Furthermore, in step (3), the alkali solution is an aqueous solution of sodium hydroxide and / or sodium carbonate with a concentration of 3 to 6 mol / L;

[0026] and / or the alkali solution is used to adjust the pH of the reaction system to 8-9;

[0027] And / or the organic solvent II is one or more of ethyl acetate, dichloromethane, and dichloroethane.

[0028] Furthermore, in step (3), the purification operation is solvent beating.

[0029] The synthesis mechanism of bis(benzothiadiazole-5-amine) in the present invention is as follows:

[0030]

[0031] During the preparation process, the organic solution containing compound 1 is brought to reflux and kept warm and stirred for a period of time to allow the reaction substrate to store energy, making it easier to break through the reaction domain energy during the reaction. The reducing agent stannous chloride is then added in batches to extend the retention time of the reduced intermediate azo a. Due to the low stannous chloride content in the system at the beginning of the reaction, azo a is further rearranged to obtain the hydrazine intermediate c through the intermediate b. With the addition and dissolution of stannous chloride, the stannous chloride content in the system increases, and the hydrazine intermediate c continues to undergo proton transfer to obtain the target compound 2.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention provides a method for synthesizing bis(benzothiadiazole-5-amine) compounds. By controlling the addition method, preheating and stirring the reaction substrate, and adding the reducing agent stannous chloride in batches, 5-nitrobenz[c][1,2,5]thiadiazole is used as the raw material. A continuous coupling and nitro reduction reaction is carried out within the system to obtain the target compound [4,4'-bisbenzo[c][1,2,5]thiadiazole]-5,5'-diamine in a one-step process. This method, requiring only one step, not only simplifies the reaction operation and reduces product transfer losses, but also avoids the use of flammable and explosive reagents or catalysts, improving reaction robustness and increasing economic efficiency. The reaction yield can reach up to 91.2%, making it an ideal synthetic route for bis(benzothiadiazole-5-amine) compounds and providing a new approach for the preparation of such compounds. In addition, the numerous substitutable sites on the aromatic ring of [4,4'-bisbenzo[c][1,2,5]thiadiazole]-5,5'-diamine also provide more possibilities for the optimized development of PCBTT-based organic material solar cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the H NMR spectrum of compound 2 in Example 1. DETAILED DESCRIPTION

[0035] To make the technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The following examples synthesize bis(benzothiadiazole-5-amine) using the following synthetic route:

[0037]

[0038] Specifically, the method includes the following steps:

[0039] (1) 5-Nitrobenzo[c][1,2,5]thiadiazole (Compound 1) was dissolved in organic solution I, heated to reflux, and stirred for 0.5-1 h;

[0040] (2) adding a reducing agent to the reaction system obtained in step (1) and keeping the temperature to react for 1 to 5 hours;

[0041] (3) After the reaction is completed, the pH of the reaction system is adjusted to alkaline with alkali solution, extracted with organic solvent II, and post-treated to obtain the target compound 2.

[0042] The following examples synthesize compound 1, and the preparation method is as follows:

[0043]

[0044] (a) Compound 1' (1 eq) was added to SOCl2 (10 eq), and pyridine (0.15 eq) was slowly added dropwise. The temperature was raised to reflux and the reaction was kept at this temperature for 2 h.

[0045] (b) After the reaction was completed, a large amount of SOCl2 was removed by distillation under reduced pressure, and the reaction solution was slowly diluted by pouring into ice water and stirred for 30 min. Solid precipitated and was filtered. The filter cake was washed with water and dried to obtain compound 1.

[0046] The invention will be further described below through specific embodiments.

[0047] Example 1

[0048] This example synthesizes bis(benzothiadiazole-5-amine), specifically as follows:

[0049]

[0050] Compound 1' (100 g, 0.653 mol) was added to 450 mL of 6 mol of SOCl2. Pyridine (8.9 mL, 0.11 mol) was slowly added dropwise, producing a large amount of white smoke. The mixture was then heated to reflux. Once the reaction solution became clear, the mixture was incubated for 2 h. TLC confirmed the reaction was complete. Most of the SOCl2 was removed by vacuum distillation. The residue was then slowly poured into 2 L of ice water and stirred for 15 minutes. Solids precipitated and were filtered. The filter cake was washed with water (200 mL x 2) and then dried at 45°C to yield Compound 1 (116 g, 0.64 mol) as a gray solid in a 98% yield.

[0051]

[0052] Compound 1 (100 g, 0.55 mol) was dissolved in 1000 mL THF, heated to reflux, and stannous chloride dihydrate (500 g, 2.2 mol) was added in portions (after adding a small portion, the reaction was vigorously refluxed, and the next portion was added after the reflux was stable). After the addition was completed, the reaction was allowed to react for 1 hour. After the reaction was completed, the temperature of the reaction system was reduced to room temperature, and then poured into 3 L ice water. The pH of the system was adjusted to weak alkaline (8-9) with 5 mol / L sodium hydroxide solution, 2 L EA was added to dissolve, and the insoluble was filtered. The filtrate was separated, and the obtained organic phase was backwashed with saturated sodium chloride aqueous solution (500 mL x 2). The organic phase obtained by separation was dried with anhydrous sodium sulfate, and the obtained organic phase was distilled under reduced pressure to remove the solvent. The concentrate was slurried with 200 mL PE, filtered, and the filter cake was collected and air-dried to obtain 153.95 g of orange powder of compound 2, with a purity of 98.2% and a yield of 91.2%.

[0053] Compound 2 obtained 1 H NMR (400 MHz, DMSO) δ 7.82 (d, J = 9.4 Hz, 2H), 7.42 (d, J = 9.4 Hz, 2H), 5.55 (s, 4H).

[0054] Examples 2-5 and Comparative Examples 1-3

[0055] Examples 2-5 and Comparative Examples 1-3 were synthesized under the same conditions as Example 1, except that the amount and addition method of stannous chloride were adjusted, as shown in Table 1.

[0056] Table 1

[0057]

[0058] As can be seen from Table 1:

[0059] Examples 2-4 and Comparative Example 1 were compared with Example 1, and the amount of the reducing agent stannous chloride dihydrate was adjusted. From the reaction yield, the optimal amount of stannous chloride dihydrate was 4 eq. When the amount was less than 4 eq, the reaction rate was slower, and part of the product was in an intermediate state, reducing the yield of the target product to only 20.1% when the amount was 1 eq. When the amount was more than 4 eq, the generation of the competitive reaction benzothiadiazole-5-amine was slightly increased, reducing the reaction yield.

[0060] Example 5 was compared with Example 1, and the addition method of the reducing agent stannous chloride dihydrate was adjusted. Due to the one-time addition, the concentration of the reducing agent in unit time was increased, and the generation of the competitive reaction benzothiadiazole-5-amine was slightly increased.

[0061] Comparative Examples 2-3 adjusted the order of material addition. From the reaction results, it can be seen that whether the addition method of compound 1 and the reducing agent is mixed and then heated, or the reducing agent is preheated before adding compound 1, is conducive to the formation of benzothiadiazole-5-amine in the competitive reaction, and the yield of the target compound is extremely low.

[0062] In summary, the present invention controls the feeding method, adopts preheating and stirring of the reaction substrate, and adds the reducing agent stannous chloride in batches. With 5-nitrobenz[c][1,2,5]thiadiazole as the raw material, a one-step continuous reaction of coupling and nitro reduction is carried out in the system to obtain the target compound [4,4'-bisbenzo[c][1,2,5]thiadiazole]-5,5'-diamine. This not only simplifies the reaction operation and reduces the loss of product transfer, but also avoids the use of flammable and explosive reagents or catalysts, improves the reaction stability, is more economical, and has a reaction yield of up to 91.2%. The present invention is an ideal synthetic route for bis(benzothiadiazole-5-amine) compounds.

[0063] The above is a preferred embodiment of the present invention, but the present invention should not be limited to the contents disclosed in this embodiment. Therefore, any equivalent or modified implementations that do not depart from the spirit disclosed in the present invention fall within the scope of protection of the present invention.

Claims

1. A method for synthesizing bis(benzothiadiazole-5-amine), characterized in that: Proceed according to the following synthetic route: The synthesis method comprises the following steps: (1) 5-Nitrobenzo[c][1,2,5]thiadiazole (Compound 1) was dissolved in organic solution I, heated to reflux, and stirred for 0.5-1 h; (2) adding a reducing agent to the reaction system obtained in step (1) and keeping the temperature to react for 1 to 5 hours; (3) After the reaction is completed, the pH of the reaction system is adjusted to alkaline with alkali solution, extracted with organic solvent II, and post-treated to obtain the target compound 2. The reducing agent is stannous chloride dihydrate.

2. The method for synthesizing bis(benzothiadiazole-5-amine) according to claim 1, wherein: In step (1), the organic solvent I is one or more of methanol, ethanol, tetrahydrofuran, N,N-dimethylformamide, and dioxane.

3. The method for synthesizing bis(benzothiadiazole-5-amine) according to claim 1, wherein In step (1), the mass volume ratio of the compound 1 to the organic solvent I is 1:1 to 30 g / mL.

4. The method for synthesizing bis(benzothiadiazole-5-amine) according to claim 1, wherein In step (1), the duration of the heat preservation and stirring is 0.5 h.

5. The method for synthesizing bis(benzothiadiazole-5-amine) according to claim 1, wherein: In step (2), the stannous chloride dihydrate is added in batches, and the addition rate is based on the stable reflux.

6. The method for synthesizing bis(benzothiadiazole-5-amine) according to claim 1, characterized in that: In step (2), the molar ratio of compound 1 to stannous chloride is 1:2-4, and / or the reaction time is 1-2 h.

7. The method for synthesizing bis(benzothiadiazole-5-amine) according to claim 1, characterized in that: In step (3), the operation steps are: cooling the reaction system to room temperature, adding water to dilute, adjusting the pH to alkaline with alkali solution, extracting with organic solvent II, backwashing with saturated brine, drying, concentrating the organic phase, and purifying the concentrate to obtain the target compound 2.

8. The method for synthesizing bis(benzothiadiazole-5-amine) according to claim 7, characterized in that: In step (3), the alkali solution is an aqueous solution of sodium hydroxide and / or sodium carbonate with a concentration of 3 to 6 mol / L; and / or the alkali solution is used to adjust the pH of the reaction system to 8-9; And / or the organic solvent II is one or more of ethyl acetate, dichloromethane, and dichloroethane.

9. The method for synthesizing bis(benzothiadiazole-5-amine) according to claim 7, wherein: In step (3), the purification is solvent beating.

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