Study of the photoreduction of uranyl ions by triphenylphosphine, triphenylarsine, tri-p-tolylphosphine and tri-p-tolylarsine in acetone

The photochemical reduction of uranyl ions by triphenylphosphine, tri-p-tolylphosphine, triphenylarsine and tri-p-tolylarsine in a dry acetone medium in the presence of trimethylacetic acid, using radiation in the visible region (λ > 365 nm), was investigated. The electron spin resonance and electronic spectral data supported the proposal that uranium(V) was formed. The quantum yields and Stern-Volmer quenching constants were also calculated for all four types of substrate. Keeping in view the available evidence, an electron transfer mechanism was postulated for the formation of uranium(V) which disproportionates into uranium(IV) and uranium(VI) in aqueous acidic media.