Phenylhydrazine → 3-Amino-1-phenylpyrazole

Participants

Reaction Steps

Preparation of the novel 3-substituted amino-1-phenyl-2-pyrazoline and 3-substituted amino-1-substituted phenyl-2-pyrazoline compounds V of the instant invention, which exhibit the pharmaceutical activity as herein described, is accomplished by the adaptation of the procedure of Duffin, G. F. and Kendall, J. D., J. Chem. Soc., 1954, 408; with modifications in accordance with the following reaction scheme: ##STR6## wherein R1, R2 and R3 are as previously defined. In accordance with the above reaction scheme, phenylhydrazine or a halogen-mono or disubstituted phenylhydrazine hydrochloride II such as p-chlorophenylhydrazine hydrochloride, m-chlorophenylhydrazine hydrochloride, m-fluorophenylhydrazine hydrochloride or 3,4-dichlorophenylhydrazine hydrochloride is reacted with an α, β-unsaturated nitrile I, such as acrylonitrile, methacrylonitrile, crotononitrile, cinnamonitrile, butyl acrylonitrile or compounds such as β-ethoxypropionitrile (which can undergo base catalyzed elimination to yield I) in a base catalyzed condensation procedure, with a base such as sodium ethoxide or choline hydrate in absolute ethanol. The reaction mixture is refluxed for a period of from 2-18 hours then the solvent is removed in vacuo. The addition of water gives a filterable solid which is collected, dissolved in dichloromethane and passed through a short column of a hydrous magnesium silicate. The column effluent is then refluxed on a steam bath with the gradual addition of hexane until crystallization is noted. Recrystallization from the same solvent pair (with or without additional treatment with a hydrous magnesium silicate) or from acetone-hexane provides the 3-amino-1-phenyl-2-pyrazoline and 3-amino-1-mono and disubstituted phenyl-2-pyrazoline compounds III. If the pyrazoline III is not soluble in dichloromethane, recrystallization may be accomplished from acetone-hexane, 95% ethanol or benzene with the omission of the hydrous magnesium silicate treatment phase.

Provenance & Evidence