10.7 g of methyl N-[5-amino-2-chlorobenzyl]carbamate was dissolved in 33 g of 14% hydrochloric acid, followed by stirring at room temperature for 1 hour. 7 ml of an aqueous solution of 3.8 g of sodium nitrite was dropwise added to the solution with stirring at from 0 to 5° C. The formed diazonium salt was dropwise added to a mixed solvent of water/ethyl acetate/toluene (80 ml/40 ml/40 ml) of 21.7 g of sodium acetate, 2.6 g of copper sulfate and 5.9 g of acetaldoxime with vigorously stirring at from 0 to 5° C. over a period of 15 minutes, followed by stirring at room temperature further for 2 hours. The reaction solution was acidified with hydrochloric acid, extraction with ethyl acetate was carried out, followed by washing with water, and the organic layer was dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure, the obtained crude crystals were washed with a mixed solvent of ether/ethyl acetate to obtain 2.8 g of methyl N-[2-chloro-5-(1-hydroxyiminoethyl)benzyl]carbamate as colorless crystals (m.p. 124-127° C.).
