Studies on the Photolysis and Hydrolysis of Furosemide in Aqueous Solution

Photolysis and hydrolysis of furosemide were studied in buffere solutions (pH between 1.2 and 12.0). Photolysis experiments were made at room temperature under a Daylight lamp[○!R] or fluorescent lamps as artificial light sources and direct and indirect sunlight as natural light sources by changing the strength of illumination. The photolysis of furosemide was found to follow apparent first-order kinetics under both artificial and natural light sources. In acidic media, the rate of photolysis of furosemide was larger than those in neutral or alkaline media. The pH-rate profile for the photolysis of furosemide indicated that the rate of photolysis of unionized furosemide was much larger than that of ionized furosemide. A hydrolysis experiment of furosemide was made at 37°C in the darkened room. The hydrolysis of furosemide was also found to follow apparent first-order kinetics. Furosemide was stable in neutral or alkaline solutions. In acidic media below pH 3, hydrolysis of furosemide was found to be catalyzed by hydrogen ion with an acid catalyzed rate constant of 0.893 M-1·h-1.