Electron transfer reaction between 1,3-dinitrobenzene and methyl 1-ethylpyridine-4-carboxylate radical

Abstract

The rate constant (k₂) for the reaction of 1,3-dinitrobenzene (DNB) with the title radical (Py˙) in acetonitrile is 0·29 l mol^–1 s^–1 and in isopropyl alcohol is 10·5 l mol^–1 s^–1. Solvent sensitivity criteria confirm that the reaction involves electron transfer but the magnitude of k₂ is much lower than that for the reaction of Py˙ with 4-nitrobenzyl chloride (k₂ 24,000 l mol^–1 s^–1 in acetonitrile). The polarographic reduction potential of DNB and the life-time of the radical anion were also determined in order to elucidate the mechanism of the reaction. The proposed mechanism is (a) Py˙+ DNB ⇄ Py⁺, DNB^–(fast, reversible electron transfer); (b) Py⁺, DNB-⇄ Py⁺+ DNB^–(fairly fast, reversible ion-pair dissociation); (c) Py⁺+ DNB^–→ Py–DNB (rate-limiting nucleophilic addition to the ring); (d) Py–DNB + Py˙→ Py–DNB–Py (fast radical combination). Absorption maxima are reported for K⁺DNB^– and Na⁺DNB^–.