Base decomposition of decavanadate

Abstract

The reaction of decavanadate(6–)(1·0 × 10^–3 mol l^–1 in [V₁₀O₂₈]^6–) with excess hydroxide ion at an ionic strength of 1·30 mol l^–1 proceeds via base-independent and base-dependent paths. Both paths are strongly dependent upon the cation chosen to maintain constant ionic strength. The base-independent rate constant increases in the order K⁺ Na⁺∼ Li⁺ Me₄N⁺ < Et₄N⁺. Extensive measurements in mixed cation media show that this base-independent rate increases as the strength of the cation–decavanadate(6–) ion pair decreases, the importance of ion pairing decreasing in the order K⁺ > Na⁺ > Me₄N⁺ > Et₄N⁺. In contrast, the base-dependent rate constant shows the reverse trend, decreasing in the order K⁺ Na⁺ > Li⁺ Me₄N⁺∼ Et₄N⁺∼ 0. The same mixed-cation studies show that this base-dependent path proceeds via reactive alkali-metal decavanadate species.