Phenylurea → 4-Phenylsemicarbazide

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Other known methods for the preparation of 4-aryl-1,2,4-triazol-3-ones involve the use of hydrazine as a raw material. In one such method, phenylurea is reacted with hydrazine to give a 4-phenylsemicarbazide. The semicarbazide is then condensed with ethyl formate to give the 4-phenyltriazolone. The overall yield from this method is about 20%. In another method, a 4-phenylsemicarbazide is reacted with formic acid to form the 1-formyl-4-phenylsemicarbazide intermediate, followed by intramolecular condensation to the 4-phenyltriazolone. The yield obtained by this method is about 40%. In yet another method, a substituted aniline is converted to the phenylcarbamate derivative. The phenylcarbamate is treated with hydrazine to give the phenylsemicarbazide derivative, followed by condensation with formamidine acetate to give the 4-phenyltriazolone. Each of these methods requires the use of the toxic compound hydrazine. In addition, the methods suffer from low overall yield.

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