Halogenation of vitamin K3 (menadione) (I) by means of bromine and NaOAc in AcOH furnished 3-bromo menadione (II). Subsequent displacement of the halogen of (II) by 2-mercaptoethanol (III) in the presence of imidazole yielded the desired (2-hydroxyethyl) thioether.
In an alternative procedure, the title compound was obtained by addition of 2-mercaptoethanol (III) to vitamin K3 oxide (menadione oxide) (IV) in the presence of imidazole.