Solvent effect on the photolysis of 5‐fluorouracil: A kinetic study

Abstract A photodegradation study of 5‐fluorouracil (5‐FU) has been carried out in the water (pH 7.0) and organic solvents (chloroform, ethyl acetate, acetone, 1‐butanol, 1‐propanol, ethanol, methanol, and acetonitrile) using developed and validated high‐performance liquid chromatography (HPLC) method. The test method was found to be simple, accurate (% recovery, 100.25%–101.08%), precise (%RSD < 2.00), and sensitive. The apparent first‐order rate constants are in the range of 0.85 (chloroform) to 4.25 × 10 −4 min −1 (water). The values obtained for k obs were found to be linear as a function of the dielectric constant indicating the involvement of the dipolar intermediate in the reaction. The increase in the rate of degradation of this intermediate is enhanced by the polarity of the medium. Rates of photolysis for 5‐FU show a linear relationship with the solvent acceptor number (AN) which indicates the degree of solute–solvent interaction. The values of k obs were found to be linear to the inverse of the viscosity of the medium due to the diffusion‐controlled process.