case of fatal overdosage. [ 49 ] [ edit ] Chemical synthesis The preparation steps for synthesis of sildenafil are as follows: [ 50 ] Methylation of 3-propylpyrazole-5-carboxylic acid ethyl ester with hot dimethyl sulfate. Hydrolysis with aqueous NaOH to free acid. Nitration with oleum/fuming nitric acid. Carboxamide formation with refluxing