The Reaction of Uranyl Ion with Propionaldehyde in the presence and absence of light

A study was made of the photochemical reduction of the uranyl ion by propionaldehyde in aqueous and nonaqueous media. The products of the photochemical reaction in propionaldehyde solution enter into a reverse reaction following an induction period. Products formed in aqueous media apparently enter into some reaction which prevent them from undergoing a reverse reaction. Conductivity measurements of solutions of UO2(NO3)2 · 6 H2O in propionaldehyde, indicate that dissociation of the uranyl salt occurs. The rate equations for the formation and disapearance of uranous ion in propionaldehyde were discussed. The probable mechanisms for the forward and reverse reactions in terms of only those species which change oxidation states are: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} {\rm Forward}\,\,\,\,{\rm U(VI) + (R) + h}\nu \to {\rm U(V) + (O)} \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\quad{\rm 2}\,{\rm U(V) + acid}\,\,\,\,\quad \to \,{\rm U(IV) + U(VI) + Products} \\ {\rm Reverse}\,\,\,\,\,{\rm U(IV) + (O)}\,\,\,\,\,\,\,\,\quad\to {\rm U(V) + (R)} \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\quad{\rm 2U(V) + acid}\,\,\,\,\,\quad \to {\rm U(VI) + U(IV) + Products} \\ \end{array} $$\end{document} The symbols (R) and (O) refer to the reduced and oxidized forms respectively. The overall quantum yield for the U(VI) to U(IV) reaction was found to be at least 0.72. Es wurde die photochemische Reduktion des Uranylions, UO 22+, durch Propionaldehyd in wäßrigem und nichtwäßrigem Medium untersucht. In Propionaldehyd als Medium gehen die Reaktionsprodukte nach einer Induktionsperiode eine Rückreaktion ein, in wäßrigem Medium dagegen nicht. Leitfähigkeitsmessungen zeigen, daß UO2(NO3)2 · 6 H2O in Propionaldehyd dissoziiert. Das Geschwindigkeitsgesetz der UIV‐Bildung bzw. ‐Wiederabnahme werden diskutiert und der wahrscheinliche Mechanismus der Vorwärts‐ und Rückreaktionen sind in „Summary”︁ formuliert. Die Gesamtquantenausbeute der UVI → UIV‐Reaktion liegt bei mindestens 0,72.