Electroreduction of Organic Compounds with Two Reactive Centers. I. 1,2,4-Triazines
In most organic molecules a conjugation of two adjacent double bonds facilitates the electroreduction of the more easily reducible group. An exception of this rule has been observed for some 1,2,4-triazines In two model compounds metamitron(I) (4-amino-3-methyl-6-Phenyl-1,2,4-triazin-5(4H)-one) and metribuzin(II) (4-amino-6-tert-butyl-3-methylthio-1,2,4-triazin-5(4H)-one), which cannot undergo tautomeric changes, two azomethine bonds are present. Their electrochemical reduction on mercury electrodes occurs in two two-electron steps. The 1,6-bond C=N is reduced in protic solvents in the protonated form at potentials by about 0.5 V more positive than the protonated C=N bond in position 2, 3. Potentials of both reduction steps are shifted with increasing pH to more negative values, limiting currents of both steps decrease with increasing pH in a potential range where the protonotion becomes insufficiently fast. Limiting currents of both steps are affected by covalent hydration.