Hydrochloric Acid → 5-n-Butyl-2-(2-chloro-5-nitrophenyl)-2,4-dihydro-3H-1,2,4-triazol-3-one

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By the procedure of Example 4, Step C, 2-chloro-5-nitrophenylhydrazine [generated from the hydrochloride, which was prepared from 2-chloro-5-nitroaniline according to H. Stroh and G. Westphal, Chem. Ber. 96, 184 (1963), by partitioning between ether and 1N sodium carbonate] was reacted with ethyl N-carbethoxyvalerimidate (from Example 4, Step B). Enough THF was added to the reaction mixture to ensure dissolution of all starting material. After work-up, the residue was purified by flash chromatography on silica gel (gradient elution with 0.5-5.0% methanol in CH2Cl2) to give a 19% yield of the title compound as an orange solid, mp 145°-147° C., homogeneous by TLC (19:1 CH2Cl2 --MeOH), mass spectrum (FAB) m/e 297 (M+1)+.

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