Citric Acid → Sildenafil Citrate

Participants

Reaction Steps

In a 3-necked flask, 3-(4,7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo(4,3-d)pyrimidin-5-yl)-(4-ethoxyphenyl)benzene sulfonyl chloride (10 g, 0.024 mol) was mixed with acetone (100 ml) and NaOH (0.974 g, 47%) at room temperature. N-methyl piperazine (2.68 g, 0.027 mol) was added dropwise to the mixture. Thereafter, the reaction was stirred for 45 mm, additional acetone (100 ml) was added, and then the mixture was heated to reflux. Citric acid (5 g, 0.024 mol) was added, and a white precipitate appeared immediately. The reaction was maintained at reflux for one hour and then allowed to cool to room temperature over 3 hours. The precipitate was collected by filtration, and dried at 50° C. under 10 mm Hg to give pure sildenafil citrate in 72% yield.

Provenance & Evidence