Photochemical Decomposition of Diquat and Paraquat

Abstract

The effect of ultraviolet (UV) light (240-260 mL4 range) on 6, 7-dihydrodipyrido (1, 2-a:2',1'-c)-pyrazidiinium salt (diquat) and 1,1'-dimethyl-4,4'-bipyridinium salt (paraquat) was studied. Both dipyridyls were very stable in dark but were altered rapidly in the presence of UV light. Radioassay data collected from plan- chets containing solidified diquat or paraquat indicated a loss of more than 50%o of the C'4 from both compounds after 48 hr and more than 75% after 96 hr. When radioactive aqueous solutions were placed under UV lights, little change in the radioactivity occurred during an 8-day period as determined by liquid scintillation. When the concentration of diquat or paraquat in these solutions was determined by chemical analysis, degradation of the original mole- cules was observed. Information obtained by autoradiography of chromatograms, spotted with radioactive aqueous solutions exposed to UV light, indicated that two or possibly more C'4-containing degradation products were formed from both diquat and paraquat. Co-chroma- tography indicated that one degradation product from paraquat was l-methyl-4-carboxy-pyridinium ion.