Synthesis
In a 2L three-necked flask, add 140.1g of o-fluorobenzoic acid and 1000ml of dichloromethane, then add 138.2g of m-phenylenediamine. Cool to 5-10℃, and slowly add 133.3g of anhydrous aluminum trichloride. The system gradually releases a large amount of heat. Control the temperature below 10℃ and slowly add the aluminum trichloride. The system will gradually precipitate from a yellowish-brown clear liquid to a yellowish-brown solid. Remove the ice bath and react at room temperature for 6 hours. TLC monitoring shows that the o-fluorobenzoic acid is almost completely consumed.
After the reaction was completed and cooled to below 5°C, the system was slowly added to 500g of ice water to quench the reaction. During this process, a large amount of heat was released and gas was released. After quenching, 500ml of 6N hydrochloric acid was added and stirred for 10 minutes. The mixture was separated, and the resulting organic phase was washed once with 500ml of saturated sodium bicarbonate solution. The mixture was then separated, and the organic phase was washed once with 500ml of saturated sodium chloride solution. The mixture was then separated, dried with anhydrous magnesium sulfate, decolorized with activated carbon, and filtered to obtain a pale yellow liquid. The liquid was then vortexed until a large amount of white solid precipitated. 2L of petroleum ether was added and the mixture was stirred in an ice bath for 1 hour. The mixture was then filtered to obtain a white solid, which was dried under vacuum to obtain 210g of intermediate (single-step molar yield 80.7%, melting point around 80°C). In a 2L three-necked flask, 210g of the intermediate and 1200g of hydrobromic acid aqueous solution were added. Under nitrogen protection, the mixture was heated to 95℃ and reacted for approximately 8 hours. During this time, the solid gradually dissolved into a clear yellow liquid, and the color of the system deepened with increasing reaction time. TLC monitoring confirmed the absence of the intermediate, and the reaction was considered complete. The system was concentrated, precipitating a large amount of pale yellow crude solid. The crude solid was dissolved in 1500ml of ethanol under reflux, decolorized with activated carbon, and filtered. The resulting filtrate was cooled to room temperature, and 3000ml of water was added to slurry the mixture. Filtering yielded a white to white solid, which was then vacuum dried to obtain 145.5g of the product, Siber linkage agent (single-step molar yield 85.1%, HPLC: 98.6%, melting point: 251-253℃). 
The reaction products were characterized by nuclear magnetic resonance (NMR), and the data are as follows:
H NMR (400MHz, DMSO): δ6.89(d, 1H), δ6.92(dd, 1H), δ7.46(td, 1H), δ7.63(d, 1H), δ7.77(td, 1H), δ8.02(d, 1H), δ8.12(dd, 1H), δ11(br, OH)
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