Chemistry Reference
In-Depth Information
The Ura-5-yl radical is a vinyl-type radical. It readily adds to, e.g., its parent,
5BrUra (
k
= 2.7
10
8
dm
3
mol
−1
s
−1
; Rivera and Schuler 1983), but vinyl radicals
are also good H-abstractors [cf. reaction (234)] and typically react with, e.g., 2-
PrOH in the rage of 2
×
10
7
dm
3
mol
−1
s
−1
, depending on the substitu-
ent (Mertens 1994; Mertens and von Sonntag 1994a).
10
5
to 2.4
×
×
Their corresponding peroxyl radicals have the unusual property of absorbing
strongly in the visible (Chap. 8.2). The Ura-5-peroxyl radical formed in reaction
(235)
also absorbs in the visible (
λ
max
= 570 nm), and it has been shown by pulse
radiolyis that it decays rapidly (6
10
4
s
−1
), apparently unimoleculary (Mertens
and von Sonntag 1994a). The resulting product is isodialuric acid [Gilbert and
Schulte-Frohlinde 1970; reaction (236)], and it had already postulated by these
authors that a unimolecular process might be involved in the formation of this
product.
Addition of
•
OH to C(5) in 5-haloruacils leads to a rapid release of HX [reac-
tion (237);
k
×
10
6
s
−1
; Bansal et al. 1972; Neta 1972; Patterson and Bansal 1972;
Mori et al. 2001] as is typical for geminal halohydrines (Köster and Asmus 1971;
Mertens and von Sonntag 1994b; Dowideit et al. 1996).
≥
The resulting radicals have only weakly oxidizing properties and react with
TMPD with a rate constant of 2
10
8
dm
3
mol
−1
s
−1
(Mori et al. 2001).
×
Halogenated purines.
8BrdAdo has been used to study some of the steps in the
cyclization reaction that yields the purine cyclonucleosides/tides (Flyunt et al.
2000; Chatgilialoglu et al. 2003). Upon the reaction of e
aq
−
, the very reactive vi-
nylic radical at
C
(8) is formed [reaction (238);
k
= 1.6
10
10
dm
3
mol
−1
s
−1
] which
undergoes rapid H-abstraction from the hydroxymethyl group at
C
(5
×
) [reaction
(239)]. In neither of these reactions are radicals formed which strongly absorb in
the accessible UV/Vis range. Upon addition of the
C
(5
′
′
) radical to
C
(8) [reaction
10
5
s
−1
], an aminyl radical is formed whose UV/Vis spectrum is
(239);
k
= 1.6
×
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