The heats of dissociation of the 8-quinolinol and substituted 8-quinolinol metal chelates of uranium (VI), thorium (IV) and scandium (III)

Abstract The heats of dissociation, ΔH , were determined for the reaction: M(Ox) n ·HOx(s) → M(Ox) n (s) + HOx(g) for the uranium (VI), thorium (IV), and scandium (III) complexes of 8-quinolinol (HOx) and substituted 8-quinolinols such as 2-methyl-, 5,7-dichloro-, 5,7-dibromo-, 5-iodo, and 5-iodo-7-chloro-8-quinolinol. Also, the heats of sublimation, ΔH v , were determined for the above chelating agents in the temperature range of 35° to 160°. These quantities, as well as the K p , ΔF , and ΔS values, were calculated from dissociation pressure data obtained by a modified Knudsen effusion-cell method. For the 8-quinolinol metal chelates, the order of decreasing ΔH values was: UO 2 2+ > Th 4+ > Sc 3+ . For a given metal ion, Th 4+ , the order of decreasing ΔH values was: HOcCl 2 > HOx > HOxICl > HOxBr 2 > HOxI.