60 g of N-acetyl-3,5-diiodo-L-tyrosine and 900 mL of absolute ethanol were added to a 2 L reaction flask and stirred at room temperature for 30 minutes, then 5.8 mL of thionyl chloride was added, and then the temperature was raised to 50 ℃. The reaction was stirred for 1 hour, and after the reaction was completed, the mixture was concentrated to dryness under reduced pressure. The crude product was dissolved in 500 mL of dichloromethane and washed twice with 300 mL of saturated sodium hydrogen carbonate solution. The crude product was filtered off with suction, then beaten in 100 mL dichloromethane, and concentrated to dryness. The organic phase was dried over anhydrous sodium sulfate and under reduced pressure. The mixture was washed with 10 mL of dichloromethane, and the obtained cake was dried under vacuum at 40 ℃ for 5 hours to obtain 56.1 g of a white powdery solid N-Acetyl-3,5-diiodo-L-tyrosine ethyl ester. The yield was 88.3%, and the purity was 98.52%.
