The silver(I)-catalyzed exchange of coordinated cyanide in hexacyanoferrate(II) by phenylhydrazine in aqueous medium

✍ Scribed by R. M. Naik; R. K. Tiwari; P. K. Singh; S. B. S. Yadav

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 328 KB
• Volume: 39
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20258

✦ Synopsis

Abstract

The [Ag]^+^‐catalyzed exchange of coordinated cyanide in [Fe(CN)~6~]^4−^ by phenylhydrazine (PhNHNH~2~) has been studied spectrophotometrically at 488 nm by monitoring increase in the absorbance for the formation of cherry red colored complex [Fe(CN)~5~PhNHNH~2~]^3−^. The other reaction conditions were pH 2.80±,0.02, temperature = 30.0 ± 0.1^°^C, and ionic strength (I) = 0.02 M (KNO~3~). The reaction was followed as a function of pH, ionic strength, temperature, [Fe(CN)^4−^~6~], [PhNHNH~2~], [Ag^+^] by varying one variable at a time. The initial rates were evaluated for each variation using the plane mirror method. The initial rates evaluated as a function of [Fe(CN)^4−^~6~] clearly indicate that the initial rate increases with the increase in [Fe(CN)^4−^~6~] and finally reaches to a limiting value when [Fe(CN)^4−^~6~]/[AgNO~3~] ⩾ 1000. It indicates the formation of a strong adduct between [Fe(CN)~6~]^4−^ and AgNO~3~ prior to the abstraction of CN^−^. The variation in initial rates with [PhNHNH~2~] also showed limiting values at [Fe(CN)^4−^~6~]/[PhNHNH~2~] ⩾ 8.30. The complex behavior due to pH and [Ag^+^] variations on the rate has been explained in detail. The composition of the final reaction product [Fe(CN)~5~PhNHNH~2~] formed during the course of reaction has been found to be 1:1 using the mole ratio method. The evaluated values of activation parameters for the catalyzed reaction are E~a~ = 53.85 kJ mol^−1^, Δ H^≠^, = 51.33 kJ mol^−1^, and Δ S^≠^ = −134.63 J K^−1^ mol^−1^, which suggest an interchange dissociative mechanism. A most plausible mechanistic scheme has been proposed based on the experimental observations. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 447–456, 2007