The water-induced disproportionation of the electrogenerated
superoxide ion (O2
-) in acetonitrile,
dimethylformamide, and dimethyl sulfoxide media containing various
concentrations of water as a Brønsted acid
has been examined by UV−vis spectroscopy. Analysis of the
kinetics as a function of O2
- and
water
concentrations and of the measurement time demonstrated that the
disproportionation of O2
- by water
in
these media obeys a common mechanism: O2
-
+ H2O ⇄ HO2
• +
OH- (k
1,
k
-1) HO2
• +
O2
- → HO2
- +
O2
(k
2) (HO2
•,
hydroperoxyl radical; HO2
-, hydrogen peroxide
anion). The solvent dependence of the obtained
kinetic parameters of
(k
1/k
-1)k
2,
k
1 and
k
-1/k
2 is discussed in
terms of the solvation of O2
- and
H2O as well
as the effective acidities of H2O in different aprotic
solvents.