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The general procedure for the synthesis of 3-acetamido-4-methyl-2-nitrobenzoic acid from 3-acetamido-4-methylbenzoic acid is as follows: in Example 42, 3-acetamido-4-methylbenzoic acid (205 g, 1061 mmol) was added in batches to stirred fuming nitric acid (1 L), keeping the reaction temperature at -5°C during the addition process and ensuring that the entire reaction temperature does not exceed 0 °C throughout the reaction. After the addition was completed, stirring of the reaction mixture was continued for 1 hour. Subsequently, crushed ice (2.5 kg) was added to the reaction mixture and stirring was continued for 30 minutes. At the end of the reaction, the precipitate formed was collected by filtration and washed thoroughly with water. The obtained filter cake was air-dried and suspended in 1 L of acetic acid at 65°C. The suspension was allowed to stand for 1 hour to naturally cool to room temperature and then filtered. The filtrate was washed with acetic acid and ether sequentially to finally obtain 3-acetamido-4-methyl-2-nitrobenzoic acid (160 g, 63% yield) as a white solid. Mass spectrometry analysis showed (M + H)+ of 239.

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