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The Process Improvement in the Scale-Up Synthesis of Herbicide Metamitron

WANG Yan-ling;CHEN Yi-xing;ZHANG Yi-jun;LI De-jiang;College of Chemistry and Life Science,China Three Gorges University;  
The synthetic process of Herbicide Metamitron was studied. Intermediate 1 was synthesized in 97% by the reaction of dimethyl oxalate with potassium carbonate in the presence of concentrate methanol as solvent. 1 reacted with the three phosgene at dehydration condition for 5 h in the presence of beneze to prepare mixture. Then mixture reacted with benze for Friedel-Crafts acetoxylation to give intermediate 2 in the presence of Aluminum trichloride as catalyst. The two steps yield was 71. 1%. 2 reacted with acetyl hydrazine for condensation in the ethanol to give 3 in 90% yield. Intermediate 4 in 93% yield was prepared by 3 and hydrazine in the presence of acetic acid as catalyst. Finally,in the presence of butylalcohol,the reaction of 4 with sodium acetate for dehydration cyclization to obtain metamitron. Yield: 83. 4%,HPLC purity: 99. 30%. The total yield of the title product was 48. 1%. The structures of metamitron was confirmed by1H NMR.
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