Kinetics and mechanism of ligand exchange of coordinated cyanide in hexacyanoferrate(II) by nitroso-R-salt in the presence of mercury(II) as a catalyst

✍ Scribed by R. M. Naik; Joy Sarkar; D. D. Chaturvedi

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 166 KB
• Volume: 37
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20077

✦ Synopsis

Abstract

The kinetics of Hg(II)‐catalyzed reaction between hexacyanoferrate(II) and nitroso‐R‐salt has been followed spectrophotometrically by monitoring the increase in absorbance at 720 nm, the λ~max~ of green complex, [Fe(CN)~5~ N‐R‐salt]^3−^ as a function of pH, ionic strength, temperature, concentration of reactants, and the catalyst. In this reaction, the coordinated cyanide ion in hexacyanoferrate(II) gets replaced by incoming N‐R‐salt under the following specified reaction conditions: temperature = 25 ± 0.1°C, pH = 6.5 ± 0.2, and I = 0.1 M (KNO~3~). The stoichiometry of the complex has been established as 1:1 by mole ratio method. The rate of catalyzed reaction is slow at low pH values and then increases with pH and attains a maximum value between 6.5 and 6.7. The rate finally falls again at higher pH values due to nonavailability of [H^+^] ions needed to regenerate the catalytic species. The rate of reaction increases initially with [N‐R‐salt] and attains a maximum value and then levels off at higher [N‐R‐salt]. The rate of reaction shows a variable order dependence in [Fe(CN)~6~^4−^] ranging from unity at lower concentration to 0.1 at higher concentrations. The effect of [Hg^2+^] on the reaction rate shows a complex behavior and the same has been explained in detail. The activation parameters for the catalyzed reactions have been evaluated. A most plausible mechanistic scheme has been proposed based on the experimental observations. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 222–232, 2005