Kinetics of Oxygen Exchange between the Two Isomers of Bisulfite Ion, Disulfite Ion (S2O5^2-), and Water As Studied by Oxygen-17 Nuclear Magnetic Resonance Spectroscopy

The nuclear magnetic transverse relaxation time of oxygen-17 in aqueous sodium bisulfite solutions in the pH range from 2.5 to 5 was measured over a range of temperatures, pH, and S(IV) concentrations at an ionic strength of 1.0 m. From these data the rate law for oxygen exchange between bisulfite ion and water was determined and found to be consistent with oxygen exchange occurring via the reactions SHO3- + H^+ - SO2 + H2O, SO3H- + K16a -SHO3- SO3^2- + SO2 + H20, and SOsH- + SHOs" ^ 3205^ + H2O, where the symbol SHO3- refers to both isomeric forms of bisulfite ion, one in which the hydrogen is bonded to the sulfur (denoted HSO3-) and another in which the hydrogen is bonded to an oxygen atom (denoted SO3H-). The SO3H- isomer exchanges oxygen atoms with water much more rapidly than does the HSO3- isomer. The value of k-1 was determined and is in essential agreement with the results of a previous determination by relaxation measurements. The value of K16a + K16b was also found, and k16b is at least as large as K16a. The rate and mechanism of oxygen exchange between the two bisulfite ion environments were studied by analyzing the broadening of the HSO3- resonance. Oxygen exchange occurs through isomerization caused by proton transfers.