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A 250 mL three-necked round bottom flask equipped with a mechanical stirrer and thermometer was charged with 70 mL of anhydrous acetone, 15.0 g of diclofenac was added, mechanical stirring under the conditions of 50 ~ 55 deg. C to completely dissolve, with stirring was slowly added dropwise diethylamine, pH meter, control the pH value between 8.5 and 10.0, then added with diethylamine 5.0 ~ 5.5mL, precipitation of a large number of white crystalline powder (need to add a small amount of seed) the crystallization was continued for 2 hours while stirring, the temperature was lowered to 12 ± 2 ° C with stirring, centrifugation, the resulting filter cake was rinsed three times with anhydrous acetone, and then dried in a vacuum oven at 55 ± 2 ° C for 6 to 8 hours, diclofenac diethylamine 17.5g, yield: 93.7%, content: 99.41%.