Carbon-Centered Radicals - Free-Radical-Induced DNA Damage and Its Repair - page 99

Table 6. 2 . Rate constants of the oxidation of hydroxycyclohexadienyl radicals by IrCl 6 2 −
and Fe(CN) 6 3 − (unit: 10 9 dm 3 mol − 1 s − 1 )

IrCl 6 2− Fe(CN) 6 3− Substrate Reference

Anisol 3.1 2.3 Buxton et al. (1986)

Acetylaniline 1.5 Buxton et al. (1986)

0.16/0.019 a

Toluene 3.0 Buxton et al. (1986)

Benzene 3.1 0.015 Buxton et al. (1986)

Benzene- d 6 0.012 Buxton et al. (1986)

Fluorobenzene 2.4 0.01 Buxton et al. (1986)

Chlorobenzene 1.6 0.0055 Buxton et al. (1986)

Benzonitrile 0.45 <0.0002 Buxton et al. (1986)

Terephthalate 0.077 Fang et al. (1996)

a Rates of oxidation of two different isomers

IrCl 6 2 − for complete (i.e., sufficiently rapid with respect to the bimolecular decay
of the radicals) oxidation (Fang et al. 1996).

In these oxidation processes, often the kinetically favored rather than the ther-
modynamically favored product is formed. A case in point is the oxidation of
pyrimidine-6-yl radicals by Fe(CN) 6 3 − to an isopyrimidine which is only a short-
lived intermediate that results in the formation of the pyrimidine and its hydrate
(Chap. 10.3).
In pulse radiolysis experiments, TNM is often preferred as an oxidant over
Fe(CN) 6 3 − because the strongly absorbing nitroform anion is formed which can
be used to determine the yield of reducing radicals (Chap. 10.3). TNM is only
capable of oxidizing strongly reducing radicals, but with less reducing radicals
an adduct may be formed which usually absorbs at shorter wavelengths and has
a lower absorption coefficient (Schuchmann et al. 1995). In fact, the formation
of adducts is common in the oxidation of radicals by nitro compounds. These
adducts may decompose into two directions [e.g., reactions (12) and (13)] (Nese
et al. 1995).