2-Hydrazinoethanol → 5-Amino-1-(2-hydroxyethyl)-1H-pyrazole-4-carboxylic acid

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Reaction Steps

Example 4 of U.S. Pat. No. 2,989,537 describes the preparation of 5-amino-4-ethoxycarbonyl-1-(2′-hydroxyethyl)-pyrazole by reacting ethyl(ethoxymethylene)-cyanoacetate with 2-hydroxyethylhydrazine in ethanol and distilling the product under vacuum at high temperature. The isolated solid product then is hydrolyzed by heating with 2N aqueous sodium hydroxide solution followed by acidification with 6N hydrochloric acid to give 5-amino-4-carboxy-1-(2′-hydroxyethyl)-pyrazole. This hydrolysis procedure in water leaves some undissolved material that must be removed by filtration. The carboxy intermediate is, heated at 160-170° C. to complete the decarboxylation and the 5-amino-1-(2′-hydroxyethyl)-pyrazole is purified by distillation under vacuum at high temperature.

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