Kinetics and mechanism of the reactions of uranyl ion and β-diketones in methanol-water (9:1 v/v)

The rates of ketonization and enolization together with the enol to keto ratios of 1,1,1-trifluoropentane-2,4-dione (Htfpd) and 4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dione (Htftbd) have been determined in a range of methanol-water solutions. The equilibrium constants for formation of [UO₂(tfpd)]⁺ and [UO₂(tftbd)]⁺ have been determined in methanol-water solutions (9:1 v/v). The kinetics and mechanisms of the reactions of uranyl ion with pentane-2,4-dione (Hpd), Htfpd, and Htftbd in methanol-water solutions (9:1 v/v) have been investigated. The [UO₂]²⁺ ion reacts with the enol tautomer of Hpd with a rate constant of 4 928 ± 727 dm³ mol^-1 s^-1, while it reacts with the keto tautomer with a rate constant of 18.1 ± 0.5 dm³ mol^-1 s^-1. However, [UO₂]²⁺ reacts exclusively with the enol tautomers of Htfpd and Htftbd with rate constants estimated to be ≥1 000 dm³ mol^-1 s^-1.