Transients formed during reduction of polynuclear aromatics: a pulse radiolysis study

Abstract

Pulse radiolysis studies of the reduction of polynuclear aromatic hydrocarbons naphthalene, anthracene, pyrene and pentacene (ArH) with solvated electron and H atom have been carried out on the nanosecond time scale, using 7 MeV electron pulses in polar organic solvents, both protic and aprotic. Kinetic results of reactions of ArH with e^–_solv show high reactivity (k ca. 10¹⁰ dm³ mol^–1 s^–1) to form the respective radical anions (ArH˙^–), with increasing yields in the presence of primary low molecular weight aliphatic amines and alcohols. In an attempt to follow the individual radical anion reactivity in these solvents, their decay to form the respective monohydro radicals (ArH₂˙) were observed. The measured pseudo-first-order formation rate constants of the respective ArH₂˙(K_fca. 10⁵ to 10³ s^–1) indicate that, in the presence of dissolved alkali metal in THF and amines/ammonia, as in the Birch synthesis, the reduction of these hydrocarbons follows this mechanism.