Nature of the transient species formed by the reactions of reducing radicals with 2- and 3-aminopyridines: A pulse radiolysis study

Abstract

The reactions of e − aq, H-atoms and some one-electron reducing radicals with 2-aminopyridine (2-AmPy) and 3-aminopyridine (3-AmPy) were studied using pulse radiolysis technique. The initial electron adduct of 2-AmPy, was found to react with the parent molecule to give a dimer radical at pH 4.8 and 9 which has entirely different spectrum from the initial adduct. The yield of the dimer radical increased with increasing concentration of the parent compound. The equilibrium constant for dimer formation was found to be 198 and 142 dm 3 mol −1, respectively, at pH 4.8 and 9. In the case of 3-AmPy however, dimer formation was not observed. H-atoms add to both the compounds giving H-adducts as in the case of pyridine. The radicals derived from alcohols were able to reduce 2-AmPy to give pyridinyl type radical. However, in the case of pyridine and 3-AmPy these radicals were unable to give pyridinyl radical but react at acidic pHs by addition to the pyridine ring giving non-reducing species.