Kinetics of Oxygen Exchange Between Bisulfite Ion and Water as Studied by Oxygen-17 Nuclear Magnetic Resonance Spectroscopy

摘要

The nuclear magnetic relaxation times of oxygen-17 have been measured in aqueous sodium bisulfite solutions in the pH range from 2.5 to 5 as a function of temperature, pH, and S(IV) concentration, at an ionic strength of 1.0 m. The rate law for oxygen exchange between bisulfite ion and water was obtained from an analysis of the data, and is consistent with oxygen exchange occurring via the reaction SO sub 2 + H sub 2 O right reversible H exp + + SHO sub 3- . The value of k/sub -1/ is in agreement with relaxation measurements. Direct spectroscopic evidence was found for the existence of two isomers of bisulfite ion: one with the proton bonded to the sulfur (HSO sub 3- ) and the other with the proton bonded to an oxygen (SO sub 3 H exp - ). (The symbol SHO sub 3- in the above chemical equation refers to both isomeric forms of bisulfite ion.) The relative amounts of the two isomers were determined as a function of temperature, and the rate and mechanism of oxygen exchange between the two was investigated. One of the two isomers, presumably SO sub 3 H exp - , exchanges oxygens with water much more rapidly than does the other. A two-pulse sequence was developed which greatly diminished the solvent peak in the NMR spectrum. (ERA citation 09:050302)