Ammonia → 1H-Pyrazole-1-ethanol, 5-amino-4-nitroso-

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To a flask having an inner volume of 50 ml and equipped with a stirring device, a thermometer and a reflux condenser were charged 4.59 g (30 mmol) of 3,3-dimethoxy-2-hydroxyiminopropionitrile with a purity of 94.3% by weight synthesized in the same manner as in Example 1, 2.98 g (31.5 mmol) of 2-hydroxyethylhydrazine with a purity of 80.5% by weight, 7.8 ml of methanol and 4.5 ml (54 mmol) of conc. hydrochloric acid, and the mixture was reacted at 50 to 52° C. for 3 hours. After completion of the reaction, 7 ml of water was added to the mixture and the resulting mixture was cooled up to 10° C. Then, 3.5 ml (58 mmol) of 28% by weight aqueous ammonia was gradually added dropwise to the mixture, and the mixture was stirred for 30 minutes while maintaining the liquid temperature to 5° C. or lower. The precipitated crystals were collected by filtration, and then, the crystals were washed with 2.5 ml of cold water and 2.5 ml of cold methanol, and dried under reduced pressure to obtain 3.40 g of 5-amino-1-(2-hydroxyethyl)-4-nitrosopyrazole (Isolation yield: 69.7%) as reddish orange crystals with a purity of 96.0% by weight (absolute calibration curve method by high performance liquid chromatography).

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