Pulse radiolysis of 1,4-dicyanobenzene in aqueous solutions in the presence and absence of thallium(I) ions

Abstract

The rate constants for the reaction of 1,4-dicyanobenzene with the hydrated electron (k₂= 2.4 × 10¹⁰ M^–1 s^–1), the hydroxyl radical (k₂= 7.2 × 10⁸ M^–1 s^–1) and the hydrogen atom (k₂= 3.5 × 10⁸ M^–1 s^–1) have been measured together with the spectra and extinction coefficients of the resulting adducts. By addition of methanol and of oxygen respectively it was possible to observe separately the adduct formed by the hydrogen atom and that formed by the hydroxyl radical. The radical anion of 1,4-dicyanobenzene, formed by reaction with the hydrated electron in neutral, de-aerated solution, can also be produced in acid solution if thallium(I) sulphate is present. Evidence is presented to show that the reduced form of the thallium(I) ions, Tl⁰ or Tl⁺₂, which is formed in reaction with the H atom in acid solution, is capable of reducing 1,4-dicyanobenzene to give the anion at pH values as low as 0.01 (k(T1⁺₂+ DCNB)= 2.7 + 10⁹ M^–1 s^–1). Similar results have been obtained using 1,4-dinitrobenzene and it is suggested that addition of T1⁺ may find further applications as a method of producing radical anions in solution at low pH by pulse radiolysis.