Identification of the photolysis products of nitrofurazone irradiated with laboratory illumination

Illumination of aqueous or organic solutions of nitrofurazone, 1, with fluorescent or tungsten light caused the appearance of two new compounds, 2 and 3. Compound 2, which eluted just before nitrofurazone on a reverse phase hplc column, had a mass spectrum identical to that of 1 and converted back to 1 at a rate proportional to the temperature and the polarity of the solvent when allowed to sit in the dark. High resolution proton nmr spectroscopy provided conclusive evidence that compound 2 is the syn isomer of 1. Compound 3 had a retention time, ultraviolet spectrum, and mass spectrum that were indistinguishable from those of synthetic 5-nitrofuraldehyde azine. The toxicity of 3 to E. coli was determined to be the same as 1 while its mutagenicity was over 10-fold lower. No detectable cross-links were formed in the DNA of E. coli in the presence of compound 3. Thus, it is unlikely that the relatively small amounts of the azine 3 formed have much influence on the antibacterial potency or mutagenicity of nitrofurazone solutions. However, these results do confirm the desirability of conducting experiments with these agents in the dark or under yellow light. Photochemical formation of syn isomers was also observed with two other Schiff 's base nitrofuran derivatives, nitrofurantoin and furazolidone.