THE EFFECT OF PH ON THE COURSE OF THE PHOTOREACTION OF 2,4-PYRIDINEDICARBONITRILE WITH BENZOPHENONE IN AQUEOUS 2 PROPANOL - REDUCTION VS SUBSTITUTION

The photoinitiated reactions of 2,4‐pyridinedicarbonitrile (1) and benzophenone in neutral, acidic, and basic 3:1 2‐propanol‐water and the kinetics of disappearance of 1, have been studied. Pyridinyl radical anion forms as an intermediate by an electron transfer. In acidic solution substitution of the cyano group in the 2 position and in the 2 and 4 positions with diphenylmethanol occurs. In neutral medium both substitution at the 2‐position and reduction, in which the cyano group at the 4 position is replaced by hydrogen, are observed. In basic solution in which protonation of the radical anion is not likely, only reduction occurs. The rates of formation and relative yields of these products depends on the pH of the solution. A mechanism is discussed. Copyright © 1990 Journal of Heterocyclic Chemistry