Chemical Constitution and Activity of Bipyridinium Herbicides. XIII. Synthesis, Reduction Potential and Biological Activity of 1-Methyl-4-[[(methylpyridinium-4-yl)Imino]methyl]pyridinium Diiodide

A diquaternary salt from the azomethine N-(pyridin-4- ylmethylene)pyridin-4-amine has been prepared. The salt is slowly reduced by zinc dust in aqueous solution to a red radical cation at a potential (E0) of -0.64 V in the pH range 5.2-8.0. In keeping with its low reduction potential the salt is very much less active than paraquat as a post-emergent herbicide.