Studies of the electrochemical reduction of the isomeric diazines have been mainly concerned with pyrimidine and its derivatives 1" 2. Limited attention has been given to pyrazine 3 and pyridazine. Carrington 4 reported the generation of the radical anion dimer of pyridazine in dimethylsulfoxide. Lund 5, in a recent review, has shown that the reduction of 3,6-disubstituted pyridazines generally yield 1,4-and 4,5dihydropyridazines. Further reduction is complicated by the fact that the different tautomeric forms may be reduced differently and at different potentials and that the rate of transformation of a given tautomer to the most easily reducible one may or may not be fast compared with the rate of further reduction. Furthermore, under appropriate conditions ring contraction can occur.
Millefiori 6 in a recent polarographic study of pyridazine observed a single reduction wave at pH 0-2.5, and attributed this wave to the reduction of pyridazine to 1,4-dihydropyridazine. At pH 2.5 a second wave appeared which initially increased with increasing pH, reaching its maximum height at pH 5.5, after which it decreased until at pH 8 it was no longer present. The product of this wave was reported to be H2N~CH=CHCH2~H=NH. Both waves were characterized as irreversible reductions. In the pH range 8 to 11 the reduction was reported to occur as successive one-electron steps, yielding a mixture of 1,2-and 1,4-dihydropyridazine. In very alkaline media (pH > 11) a single two-electron reduction to 1,4-dihydropyridazine was reported.
The work reported herein was completed before we became aware of Millefiori's study. As will be shown, our experimental data are not in complete agreement with his. Two differences in the experimental conditions could account for the discrepancies. First, the former study was restricted to 0.59 mM pyridazine. Second, we employed only phosphate buffers, whereas Millefiori used both Britton-Robinson and Sorensen~21ark buffer systems. Since both studies indicate the presence of a ring opening reaction, catalysis by some component of the buffers could be involved. This possibility is being investigated and the results will be reported at a later date.