Chemical constitution and activity of bipyridylium herbicides: IV.—Diquaternary salts of methyl substituted 1,10‐phenanthrolines

Eight bridged diquaternary salts of methyl substituted 1,10‐phenanthrolines have been prepared. They are reduced in aqueous solution to radical cations at about the same potential as diquat by a one electron transfer which is largely reversed by air. in herbicidal tests they showed slight activity at a rate equivalent to 8 lb/acre. Their relatively poor phytotoxic properties are considered to be due to their large size which hinders their reaching the site of biological action of the bipyridylium herbicides.