Electrochemical Reduction of Aza-heteroaromatic Compounds. Part II. Effect of Cationic Charge on the Formation of Aza-phenanthrenyl Radicals

Abstract

p-Phenanthroline di-methiodide (l_a) and its related compounds, such as p-phenanthroline mono-methiodide (ll_a), 5, 6-benzoquinoline methiodide (lll_a), and 3, 4-benzoquinoline methiodide (lV_a), were electrolyzed at the potentials corresponding to the first d.c, polarographic reduction waves and the reduction products were characterized by polarography, cyclic voltammetry, ultraviolet and visible spectroscopy, and NMR spectroscopy. Only the one-electron electrochemical reduction product of Ia was a stable radical because of the electrostatic (cationic) repulsion between charged molecules, and was highly sensitive to oxidants. The same cation radical was also obtained by reduction with sodium dithionite. The same one-electron reduction products of ll_a, lll_a and lV_a were immediately coupled to produce dimers. The two-electron electrochemical reduction product of l_a was not so sensitive to oxidants as the one-electron reduction product of l_a.