SELECTIVE CHLORINATION OF 1-(2-FLUOROPHENYL)-4,5-DIHYDRO-3-METHYL-5-OXO-1H-1,2,4-TRIAZOLE Russian patent published in 2001 - IPC

FIELD: organic chemistry, chemical technology. SUBSTANCE: invention describes the novel method of chlorination of 1-(2-fluorophenyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazole at position 4 of phenyl ring. Method involves the following stages: (a) addition of 0.8-1.6 molar equivalents of chlorine to suspension of 1-(2-fluoro- -phenyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazole at stirring in solvent taken among acetonitrile, N,N-dimethyl-formamide, nitromethane and nitrobenzene at the range of temperature from environment to 50 C and at the rate not exceeding 50 C and stirring continues at 30-50 C for 1-10 h; (b) major part of hydrogen chloride as a by-side product is removed for 1-6 h by pressure decrease in reaction vessel but retaining boiling solvent and by maintenance temperature at 30-50 C; (c) reaction vessel is blown with nitrogen optionally to decrease hydrogen chloride concentration in reaction mixture to value below 1%; (d) stages (a), (b) and (c) are repeated twice; and (e) 1-(4-chloro-2-fluorophenyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazole is isolated. EFFECT: increased yield of end product. 4 cl, 2 ex