a: The starting material, salicylic acid (20 g, 145 mmol), was placed in a 250 mL three-necked round-bottom flask. Acetic acid (120 mL) was added and heated to 50 °C to dissolve the precipitate. The mixture was refluxed and stirred. Then, concentrated nitric acid (10 mL) was slowly added dropwise to the reaction solution over approximately 6 minutes. The mixture was heated and stirred continuously. The reaction was monitored by TLC and was completed in approximately 3 hours. The reaction solution was poured into ice water while still hot, resulting in the precipitation of a large amount of brown solid. After standing for a period of time, the mixture was filtered and the filter cake was washed with ice water to obtain a brownish-yellow solid, 2-hydroxy-5-nitrobenzoic acid.
The filtrate was placed at 0°C to continue precipitating solids. This was filtered again, and the resulting solid was dried to a constant weight of 15.92 g (yield: 60%). This was set aside for the next step. Reaction step b: The product obtained above, 2-hydroxy-5-nitrobenzoic acid (15.92 g, 87 mmol), was placed in a 250 mL three-necked round-bottom flask. Methanol (150 mL) was added, and the mixture was heated to 70°C to dissolve. The mixture was refluxed and stirred. Then, 10 mL of concentrated sulfuric acid was added dropwise to the reaction solution. The reaction was allowed to proceed for 1 day. After TLC detection showed the reaction was complete, the reaction solution was poured into ice water while still hot, resulting in the precipitation of solids. After standing for a period of time, the mixture was filtered, and the filter cake was washed with ice water to obtain a white solid, METHYL 5-NITROSALICYLATE. The filtrate was placed at 0°C to continue precipitating solids. This was filtered again, and the resulting solid was dried to a constant weight. The pure product was then separated by column chromatography (petroleum ether: ethyl acetate, 40:1) to obtain 10.28 g (yield: 60%).
