Pulse Radiolysis Study of Vitamin K1 Reduction in Ethanolic Solution

A pulse radiolysis study of vitamin K1 reduction was carried out in argon-saturated ethanolic solutions. The α-hydroxyethyl radicals ${\rm CH}_{3}{\rm C}^{\bullet}{\rm HOH}\ ({\rm R}^{\bullet})$ and the solvated electrons (${\rm e}_{{\rm solv}}^{-}$) reduce vitamin K1, leading to the semiquinone transient ${\rm K}_{1}{\rm H}^{\bullet}$. This species, characterized by its absorption spectrum, decays by disproportionation and leads to the formation of the hydroquinone ${\rm K}_{1}{\rm H}_{2}$. The rate constants of the monoelectronic exchanges involved in this reduction have been determined.