Kinetics of the mercury(II)‐catalyzed substitution of coordinated cyanide ion in hexacyanoruthenate(II) by nitroso‐R‐salt

Abstract

The kinetics and mechanism of Hg 2+ -catalyzed substitution of cyanide ion in an octahedral hexacyanoruthenate(II) complex by nitroso-R-salt have been studied spectrophotometrically at 525 nm (λ max of the purple-red-colored complex). The reaction conditions were: temperature = 45.0 ± 0.1 • C, pH = 7.00 ± 0.02, and ionic strength (I) = 0.1 M (KCl). The reaction exhibited a first-order dependence on [nitroso-R-salt] and a variable order dependence on [Ru(CN) 6 4− ]. The initial rates were obtained from slopes of absorbance versus time plots. The rate of reaction was found to initially increase linearly with [nitroso-R-salt], and finally decrease at [nitroso-R-salt] = 3.50 × 10 −4 M. The effects of variation of pH, ionic strength, concentration of catalyst, and temperature on the reaction rate were also studied and explained in detail. The values of k 2 and activation parameters for catalyzed reaction were found to be 7.68 × 10 −4 s −1 and E a = 49.56 ± 0.091 kJ mol −1 , H = = 46.91 ± 0.036 kJ mol −1 , S = = −234.13 ± 1.12 J K −1 mol −1 , respectively. These activation parameters along with other experimental observations supported the solvent assisted interchange dissociative (I d ) mechanism for the reaction.

Kinetics and mechanism of formation of the complex [Ru(CN)5INH]3− through the ligand substitution reaction between the aquapentacyanoruthenate(II) anion and isoniazid

“…This pale yellow solution of the aquapentacyanoruthenate(II) ion, formed during the reaction, showed l max at 310 nm. The [Ru(CN) 5 32 ion undergoes a slow dimerization reaction at higher concentrations (.10 24 M) (K d ' 10 22 M 21 s 21 at pH = 7, 25.0°C) to yield most probably a cyanidebridged Ru 2 (CN) 10 62 ion, 46 as reported in the case of the pentacyanoiron(II) system. 47 The dependence of reaction rate on various reaction variables is discussed below.…”

“…For the preparation of the above-mentioned complex, [Ru(CN) 5 INH] 32 , to a solution of 0.1 mmol K 4 [Ru(CN) 6 ]Á3H 2 O in 5 cm 3 of water, 1 mmol INH was added and further, 1.7 cm 3 of aqueous bromine solution (0.0117 M in Br 2 and 0.0117 M in KBr) was added slowly dropwise. Then, at room temperature, the mixture was left for 30 min and more INH was added (1 mmol) to this solution.…”

“…45 The product was further characterized using elemental analysis along with other techniques such as infrared (IR) spectroscopy, mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. Finally, the formed product was identified as the [Ru(CN) 5 INH] 32 complex (as given in Scheme S1 in the supplemental information).…”

“…A single-beam visible spectrophotometer model DIGI-110 (SISCO) equipped with a circulatory arrangement of water for thermostating the cell compartment was used to observe the kinetics of the reaction between [Ru(CN) 5 H 2 O] 32 and INH spectrophotometrically. All kinetic measurements were performed at 502 nm (l max of light yellow [Ru(CN) 5 INH] 32 formed). All pH measurements were made on a Systronics m pH System (Model-361).…”

“…All pH measurements were made on a Systronics m pH System (Model-361). No absorbance correction was made since at this wavelength the only strongly absorbing species is [Ru(CN) 5 INH] 32 and absorbances due to other reactants, namely, [Ru(CN) 5 H 2 O] 32 , NaClO 4 and INH, have negligible values at 502 nm ( Figure 2).…”