The degradation kinetics of a new organometallic coordination compound, aquadichlor0(2,6-diaminopyridine)palladium(11), were studied in acidic and acid halide media. In acidic solutions, the degradation was first order with respect to the complex concentration; e.g., at 77', the apparent rate constants at pH 1.00,1.22, and 1.50 were 0.00395, 0.00292, and 0.00225 min-', respectively. Furthermore, a plot of log (apparent rate constant) uersus pH gave a straight line with an approximate slope of 0.5, indicating pseudo-first-order catalysis with respect to complex concentration at a specified pH. Activation energies obtained from Arrhenius plots varied from 43 to 57 kcal/deg/mole for pH 1.00 and 1.50, respectively. The pH-iadependent activation energy was 15 kcal/ deg/mole. In acid halide solutions, utilizing the method of initial rates, the degradation was first order with respect to complex concentration.
A plot of log (initial rate) uersus log (chloride-ion concentration) gave a straight line with an apparent slope of 1.0. A plot of log (initial rate) versus pH resulted in a straight line with a slope of 0.5. Thus, pseudofirst-order catalysis with respect to complex concentration at a specified pH and pC1 occurred. When the method of curve stripping was applied to the data, a plot of log (complex concentration undegraded) versus time resulted in a biexponential relationship; e.g., at pH 1.50,0.10 M chloride concentration, and 57O, the biexponential relationship between undegraded complex uersus time giving the best fit to the data was: complex concentration = 0.237e-0.065:3t + 2.213e-0-00276f. A general mechanistic explanation of the acid-and acid halide-catalyzed degradation of the complex is proposed. Keyphrases Palladium(I1) coordination compound-degradation kinetics in acidic and acid halide media 0 Aquadichloro(2,6-diaminopyridine)palladium(II)-degradation kinetics in acidic and acid halide media 0 Coordination compounds-aquadichloro(2,6-diaminopyridine)palladium(Ir), degradation kinetics in acidic and acid halide media Degradation kinetics-aquadichloro(2,6-diaminopyridine)palladiurn(I1) in acidic and acid halide media 0 Stability-aquadichloro(2,6diaminopyridine)palladium(II) in acidic and acid halide media Previously referred to in the literature as palladium dichloride [2,6-diamino yridine)-H20. ?Model 202, Perkin-Elmer Corp., Norwalk, Conn.