This high reduction potential indicates that persulfate is a strong aqueous oxidizing
agent that makes many oxidation reactions thermodynamically favorable. However, House
(1962) indicated that many direct reactions occur at rates that are kinetically slow and
that decomposition of the oxidant into free radicals may dramatically improve the rate at
which oxidation reactions occur. Recent evidence indicates that direct reaction of the
persulfate anion with organics that do not involve radical intermediates also may be significant.
For instance, Tsitonaki et al. (2006) reported +99% degradation of methyl tert-butyl
ether (MTBE) in a system at ambient temperature, with onlyMTBE, water, and persulfate ion
present (no activators), suggesting that a direct oxidation reaction may be occurring
(Figure 4.3). It is also possible that a degree of thermal activation can occur at ambient
temperatures.
However, probably the most important electron transfer reaction of persulfate appears
to occur through a one-electron transfer process, typically with a transition metal, radical, or
other reactant, resulting in the production of a sulfate radical (SO4
) via the reaction in
Equation 4.2.
S2O8
2 þ e ! SO4
2 þ SO4
(Eq. 4.2)
These reactions are believed to proceed through a one-electron transfer reaction resulting in
the cleavage of the peroxygen bond within the persulfate molecule. Typically, a sulfate anion
and a sulfate radical are released as products, as well as an oxidized transition metal.
Figure