Electrochemical Reduction of Metribuzin

Abstract

Metribuzin [4-amino-6-tert-butyl-3-methylthio-1,2,4-triazin-5(4H)-one] is a widely used weed controlling agent. In aqueous solutions and in 30 % v/v acetonitrile/water solutions it is reduced in two two-electron steps. In both steps protonated forms of azomethine bonds are reduced, in the more positive the 1,6-bond, in the more negative (by about 0.4 V) the 2,3-bond. At pH > 7 the conjugated base is reduced at considerably more negative potentials in a one-electron step. Reduction of both azomethine bonds is accompanied by acid-base and hydration-dehydration equilibria. The 1,6-dihydrometribuzin, formed in the first reduction step, undergoes acid catalyzed hydrolysis. In many aspects the behavior of metribuzin resembles that of metamitron [4-amino-3-methyl-6-phenyl-1,2,4-triazin-5(4H)-one] investigated earlier. For analytical purposes waves between pH 2 and 4 are best suited.