Abstract
The complexation kinetics of Mg2+ with CO =3 and HCO −3 has been studied in methanol and water by means of the stopped-flow and temperature-jump methods. Kinetic parameters were obtained in methanol by coupling the magnesium-carbonato reactions with the metal-ion indicator Murexide. Relatively high stability constants were found in methanol (K=1.0×105 liters-mole−1 for Mg2+-Murexide,K=7.0×104 liters-mole−1 for Mg2+−HCO −3 , andK=2.0×105 for Mg2+−CO =3 liters-mole−1). The corresponding, observed formation rate constants were determined to be
The relaxation times were found to be much shorter (τ≈5–20 μsec) in aqueous solutions, primarily due to the relatively high dissociation rate constants. The data could be interpreted on the basis of a coupled reaction scheme in which the protolytic equilibria are established relatively rapidly, followed by a single relaxation process due to the formation of MgHCO +3 and MgCO3 between pH 8.7 and 9.3. The observed formation rate constants were determined to be
These results, in conjunction with NMR solvent exchange rate constants, are analyzed in terms of a dissociative (S N1) mechanism for the rate of complex formation. The significance of these kinetic parameters in understanding the excess sound absorption in seawater is discussed.
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Patel, R.C., Garland, F. & Atkinson, G. Dynamics of magnesium-bicarbonate interactions. J Solution Chem 4, 161–174 (1975). https://doi.org/10.1007/BF00649156
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DOI: https://doi.org/10.1007/BF00649156