Res. Chem. Intermed.
, Vol. 27, No. 4,5, pp. 379–391 (2001)
Ó
VSP 2001.
One-electron reduction studies on some
aroyl /heteroacyl-1,4-benzoquinones (RCO-BQ)
M. C. RATH
1
, T. MUKHERJEE
1;¤
, R. GHOSH
2
, S. MUKTAWAT
2
,
P. PARDASANI
2
and R. T. PARDASANI
2
1
Radiation Chemistry & Chemical Dynamics Division, Bhabha Atomic Research Centre, Trombay,
Mumbai 400 085, India
2
Department of Chemistry, University of Rajasthan, Jaipur 302 004, India
Abstract—A series of newly synthesized nine aroyl/ heteroacyl-1,4-benzoquinones (RCO-BQ)
undergoes one-electron reduction in pulse radiolytic reducing conditions in an aqueous– 2-propanol–
acetone mixed solvent (MS). The radical centre is mainly located in the quinone ring, though a small
probability exists for reduction at the carbonyl (CO) group. The intramolecular hydrogen bonding
between the OH group of the semiquinone ring and the adjacent CO group makes the radical more
stable as compared to the simple benzosemiquinone radical. A red-shifted absorption band arises
mainly due to large conjugation in the semiquinone. The substitutions (R), thiophenyl, phenyl and
furanyl groups at the keto position reduce their one-electron reduction potential (E
1
) values from
¡
30 mV for BQ to <
¡
300 mV in some of these quinones.
1. INTRODUCTION
Quinones are known to act as very ef cient electron accepting agents [1– 4]. Most
interesting studies in the eld of electron transfer processes involving quinones
have been carried out by several groups using the pulse radiolysis technique
[5– 8]. This technique is an established methodology for studying one-electron
transfer processes (reduction and oxidation) in liquid media [5, 6, 9]. The one-
electron reduction studies of different unsubstituted quinones starting from 1,4-
benzoquinone (BQ) to its higher analogue 6,13-pentacenequinone (PQ) in an
aqueous– 2-propanol (5 mol dm
¡3
)– acetone (1 mol dm
¡3
) mixed solvent (MS) have
been reported by us [10]. Pulse radiolysis studies of BQ [10] and hydroxy-BQs in
aqueous solution have been reported by Adams and Michael [11]. Pulse radiolysis
¤
To whom correspondence should be addressed. E-mail : mukherji@magnum.barc.ernet.in
@Phil_Robichaud
@deepthiw
@JoseServera