ABSTRACT Kinetics of the substitution reaction of solvent molecule in uranyl (VI) Schiff base complexes by tri-n-butylposphine as the entering nucleophile in acetonitrile at 10–40 C was studied spectrophotometrically. The second-order rate constants for the substitution reaction of the solvent molecule were found to be (8.8±0.5)× 10− 3,(5.3±0.2)× 10− 3,(7.5±0.3)× 10− 3,(6.1±0.3)× 10− 3,(13.5±1.6)× 10− 3,(13.2±0.9)× 10− 3,(52.9±0.2)× 10− 3, and (88.1±0.6) ...