Res. Chem. Intermed.
, Vol. 30, No. 9, pp. 829–836 (2004)
Also available online - www.vsppub.com
Electron transfer (oxidation) of complexes
between bifunctional phenols and DMSO
in non-polar surroundings
, M. RELE, H. S. MAHAL and T. MUKHERJEE
Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Centre,
Mumbai 400 085, India
Received 20 June 2004; accepted 30 June 2004
Abstract—Pulse-radiolysis reactions were performed to study the effect of hydrogen bonding to
dimethyl sulfoxide (DMSO) on the oxidation of dihydroxy benzene and biphenyl diols to phenoxyl
radicals. It was observed that with DMSO as the hydrogen-bond acceptor, the oxidation process
proceeds via proton-coupled electron transfer in the case of hydroquinone. For resorcinol, DMSO
acts in a similar way as in the case of hydroquinone. For other biphenols, viz.,2,2
- and 4,4
diols, it was found that DMSO had no effect on the electron transfer. The results are explained based
on the ionization potential and structure of the phenol derivatives which probably depends on the
rotation of the OH bond causing different electron distribution in the transient conformation.
Keywords: Phenoxyl radicals; pulse radiolysis; proton transfer; ﬂuorescence.
Redox reactions, both photo-sensitized and radiation-induced, often proceed via
organic radical cations as intermediates . Organic radical cations so produced
are meta-stable species having a deﬁcit of one electron. This leads to the generation
of unpaired spin and charge, thereby causing reduction of strength in key bonds of
the molecule [2–4]. Functional polar groups like
OH and SH in aromatic rings
enhance the above-mentioned properties and one can easily monitor the formation
of phenol radical cations [5– 7]. Interestingly, the meta-stable species can be
monitored only in non-polar solvents [3, 4, 8] as in aqueous media or polar media it
is difﬁcult to monitor phenol radical cations due to their low pK
( 0) value or due
to fast ion–molecule reactions.
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