Determina??o da constante de dissocia??o (Ka) do captopril e da nimesulida: experimentos de química analítica para o curso de farmácia

摘要

This paper presents the determination of the dissociation constant (Ka) of captopril and nimesulide as contextualized experiments to teach chemical concepts to students of Pharmacy. Captopril is an antihypertensive drug, which presents high water-solubility and weak acid properties. The pKa of carboxylic acid group of captopril is 3.7. Nimesulide is a non-steroidal anti-inflammatory drug sparingly soluble in water. It is weakly acidic (pKa ≈ 6.5) because of its methanesulfonamide functional group. The pKa of captopril was determined by potentiometric titration with NaOH 2.0 x 10-2 moL L 1. The pKa of nimesulide was determined by using spectrophotometry and photometric titration. The experimental values of pKa of both drugs are in very good agreement with those from literature