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The kinetics of the anation reaction of aquopentaamminecobalt(III) by malonate in acidic aqueous solution
Author(s) -
Joubert P. R.,
Van Eldik R.
Publication year - 1976
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550080308
Subject(s) - malonate , chemistry , malonic acid , reaction rate constant , kinetics , aqueous solution , medicinal chemistry , ionic strength , inorganic chemistry , ion , organic chemistry , physics , quantum mechanics
The Co(NH 3 ) 5 OH 2 3+ ion reacts with malonate to form Co(NH 3 ) 5 O 2 CCH 2 CO 2 H 2+ or Co(NH 3 ) 5 O 2 CCH 2 CO 2 + , depending on the pH of the reaction solution. The kinetics of this anation reaction have been studied as a function of [H + ] for the acidity range 1.5 ≤ pH ≤ 6.0 in the temperature range of 60 to 80°C, the [total malonate] ≤ 0.5 M , and the ionic strength 1.0 M . The anation by malonic acid follows second‐order kinetics, the rate constant being 8.0 × 10 −5 M −1 ·sec −1 at 70°C, and the anations by bimalonate (Q 1 , k 1 ) and malonate ion ( Q 2 , k 2 ) are consistent with an I d mechanism. Typical values at 70°C for the ion pair formation constants are Q 1 = 1.3, Q 2 = 5.4 M −1 ; and for the interchange rate constants k 1 = 5.3 × 10 −4 ; k 2 = 7.3 × 10 −4 sec −1 . The activation parameters for the various rate constants are reported and the results discussed with reference to previously reported data for similar systems.