Relative Reactivities of Heteroaromatic Cations toward Ferricyanide Ion Oxidation

Article abstract of DOI:10.1021/jo00361a025

The kinetics of the ferricyanide ion oxidation of the N-methyl cations of pyridine (also N-ethyl cation), quinoline, 5,6-benzoquinoline, 7,8-benzoquinoline, 1,10-phenanthroline, and phenanthridine have been investigated in 20percent acetonitrile- 80percent water over the range pH 12-14 (25 deg C, ionic strength 1.0).The initial rates of oxidation of all of these cations are first order in each of ferricyanide ion and heterocyclic cation.All cations, with the exception of the pyridinium cations, display inhibition by the ferrocyanide ion reaction product, in an analogous manner to that previously analyzed in detail for the oxidation of isoquinolinium cations (accompanying paper).The pH dependences of these oxidations are all consistent with rate-determining attack of ferricyanide ion upon the alkoxide ion of the pseudobase derived from each cation.The relative reactivities of these pseudobase alkoxide ions (of the N-methyl cations) toward ferricyanide ion attack are shown to be isoquinolinium > pyridinium > quinolinium ca. 5,6-benzoquinolinium ca. 7,8-benzoquinolinium > 1,10-phenanthrolinium > phenanthridinium > acridinium.