Kinetics and mechanism of electron transfer from phenolate anion to hexacyanoferrate (III) in aqueous alkaline media

A kinetic reinvestigation of the title redox system in aqueous alkaline media at 35°C and an ionic strength of 0.5 mol dm −3 shows that the reaction follows a pseudosecond‐order Fe(CN)   6 3−disappearance. While varying [phenol] 0 and [OH − ] exhibit a linear influence on the pseudo‐second‐order rate constant, varying[Fe(CN)   6 3− ] 0 and [Fe(CN)   6 4− ] 0 , initially taken, have a complicated inhibitory effect on the same. The major phenoloxidation products isolated under a chosen condition are 2,2′‐ and 4,4′‐ dihydroxydiphenyl. Results are interpreted in terms of a probable mechanism which envisages a reversible formation, by the first one‐electron transfer, of a reactive phenoxy radical (PhO ˙ ) which on the second one‐electron transfer forms a less reactive ion‐pair intermediate (stabilized by the Fe(CN)   6 4−produced) to decompose rate‐determiningly to phenoxonium cation (PhO + ) and Fe(CN)   6 4− , the product‐formation steps being very rapid and kinetically indistinguishable.