Protolytic Kinetics of Some Pyridine Derivatives in Non-buffered Aqueous Solution

Abstract The deprotonation rates of the conjugate acids of 2,2′-bipyridine and pyridine, and the protonation rates of 2-aminopyridine and 4-aminopyridine were measured in non-buffered aqueous solution by means of a stopped-flow pH jump method. These pyridine derivatives showed quite slow protolytic behavior, similar to that of 1,10-phenanthroline and cyclopentadienes: the deprotonation rate constants of conjugate acids of 2,2′-bipyridine and pyridine are (4.8±0.7)×10−1 and (6.0±2.2)×10−2 s−1, respectively. The deprotonation rates of barbituric acid and acetylcyclopentadiene as authentic samples were also measured. Their deprotonation rate constants are in good agreement with the literature values, this demonstrates the validity and the applicability of the stopped-flow pH jump method. This method is superior to the NMR method for the determination of the protontransfer rates of azaaromatic compounds.