Herbicidal Activity of an Aromatic Analogue of Diquat

Abstract

THE mode of action of the herbicide diquat is thought^1–4 to be associated with its ability to be reduced to a stable radical cation at a potential (E₀) of −0.36 V by a one electron transfer which is quantitatively reversed by oxygen. To examine further^5–7 the relationship between properties of one electron transfer and phytotoxicity in bipyridylium compounds, we have investigated the behaviour on reduction and the herbicidal activity of the fully aromatic system, dipyrido[1,2-a : 2′,1′-c]pyrazinium dibromide (I), which has recently been synthesized in another connexion by groups in Australia⁸ and England⁹. The melting point of our sample of (I), > 350° C, agreed with that of the British group.