Kinetics and Mechanism of the Substitution of Ligand (Urea) of [Ti(ur)6]3+ by H2O and SCN¯ in Ethanol Solution

The kinetics of substitution of [Ti(ur)6]3+ by H2O and SCN¯ ion in ethanol solution have been measured spectrophotometrically by stopped-flow method. Water is a good nucleophile toward Ti(III) substrates. Even the solvent ethanol appears to be a poor ligand when compared to water. Substitution, in general follows two parallel pathways: "direct" (second order) reaction and solvolysis followed by rapid substitution (first order). Both mechanisms are important for H2O substitution, but for SCN¯ reaction is much more rapid and proceeds entirely by the "direct" route, probably because of the greater nucleophilic strength of SCN¯ V.S. H2O.