Ion Pair Formation between Electro-generated 1,2-Naphtoquinone Anion Radicals and Alkali Metal Cations in Acetonitrile

Abstract

Abstract Ion association of 1,2-naphthosemiquinone with the alkali metal cations in acetonitrile has been comprehensively studied by the use of ESR, absorption spectroscopy, polarography and with MO calculation. A continuous flow electrolysis system with a glassy carbon column electrode has been developed for the rapid quantitative preparation of organic free radicals, whose ESR spectrum or absorption spectrum was observed in situ. The formation constants of the ion pair with K+, Na+, and Li+ were estimated as 103.2, 104.5, and 108.0, respectively. By the addition of alkali metal cations, the half-wave potentials shifted to more positive potential in the order of K+<Na+<Li+. The proton hyperfine splitting constants in the ESR also varied in this order. This column electrolysis method is considered to be a powerful technique, particularly for the study of short lived free radicals, because the quantitative electrolysis is performed rapidly even in a solution of extremely diluted supporting electrolyte, such as 0.1 mM (mmol/dm3).