The Kinetics and Mechanism of Ligand Substitution Reaction of Aquapentacyanoruthenate(II) with Nitroso-R-salt and α-Nitroso-β-Naphthol in Presence of Anionic Surfactant Micelle

Abstract

The kinetics and mechanism of ligand substitution reaction of coordinated water in complex, [Ru(CN)₅H₂O]³⁻ by two incoming naphthalene substituted ligands [Lⁿ], that is, Lⁿ = nitroso-R-salt (NRS) and α-nitroso-β-naphthol (αNβN) have been studied spectrophotometrically by following an increase in absorbance at λ_max = 525 nm in aqueous medium in presence of anionic surfactant micelle, sodium dodecyl sulphate (SDS) at 25.0 ± 0.1°C as a function of pH, [nitro-R-salt], [α-nitroso-β-naphthol], [Ru(CN)₅H₂O³⁻], [SDS] and ionic strength(I) under pseudo-first-order conditions by taking excess [L]. The values of pseudo-first-order rate constants (k_obs) were evaluated from the slope of ln(A_∞ − A_t) versus time plots for each variation. Both systems were found to follow a dissociative mechanism (D), through the formation of an intermediate, [Ru(CN)₅]³⁻. The activation parameters, that is, enthalpy of activation (ΔH^≠) and entropy of activation (ΔS^≠) were computed from the slope and intercept of ln(k_f/T) versus (1/T) plot, which support the proposed mechanistic scheme.

Keywords:

• Critical micelle concentration (CMC)
• dissociative mechanism (D)
• kinetics
• kinetics and mechanism in micellar medium
• ligand substitution kinetics
• sodium dodecyl sulphate (SDS)

Acknowledgments

The authors are grateful to Dr. S. K. Singh, Senior Scientist Pharmacokinetic Division Central Drug Research Institute (CDRI), Lucknow for extending support to record repetitive spectral scan on UV-visible spectrophotometer.