title: Stability of superoxide ion in imidazolium cation-based room-temperature ionic liquids.
abstract: The stability of superoxide ion (O(2)(*-)) generated chemically by dissolving KO(2) in dried dimethyl sulfoxide solutions containing imidazolium cation [e.g., 1-ethyl-3-methylimidazolium (EMI(+)) and 1-n-butyl-2,3-dimethylimidazolium (BMMI(+))] based ionic liquids (ILs) was investigated with UV-visible spectroscopic, NMR, and voltammetric techniques and an ab initio molecular orbital calculation. UV-visible spectroscopic and cyclic voltammetric measurements reveal that the O(2)(*-) species reacts with BMMI(+) and EMI(+) cations of ILs to form hydrogen peroxide. The pseudo first order rate constant for the reaction of BMMI(+) and O(2)(*-) species was found to be about 2.5 x 10(-3) s(-1). With a molecular orbital calculation, the O(2)(*-) species is understood to attack the 2-position (C-2) of the imidazolium ring (i.e., BMMI(+)) to form an ion pair complex in which one oxygen atom is bounded to C-2 and the other to the hydrogen atom of -CH(3) group attached to C-2. Eventually, the ion pair complex of BMMI(+) cation and O(2)(*-) species undergoes a ring opening reaction as evidenced with (1)H NMR measurement.
authors.affiliation: Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Mail Box G1-5, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.
authors.forename: Md Mominul
authors.initials: MM
authors.lastname: Islam
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Imase
authors.forename: Takeyoshi
authors.initials: T
authors.lastname: Okajima
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Takahashi
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Niikura
authors.forename: Norimichi
authors.initials: N
authors.lastname: Kawashima
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Takeo
authors.initials: T
authors.lastname: Ohsaka