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New Journal of Chemistry
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ARTICLE
yellow solid that is separated by filtratioDnOfIr:o10m.10b3l9u/eC8sNoJlu00ti1o3n1F.
The solid was recrystallized in hot ethanol. Rendering pure
E-O2NC6H4CH=CHC6H4NO2 (40% and 67%yield from
4-nitrotoluene and 4.4’dinitrobibenzyl, respectively).
DFT Calculations
The well-known B3LYP hybrid functional has been chosen with
the split-valence 6-31+G(d,p) basis set that includes
polarization functions on all atoms and diffuse sp functions on
all atoms other than hydrogens. Geometries have been fully
optimized and the transition states have been approximately
located by means of a distinguished coordinate calculation
that simultaneously enlarges the two C-H bonds that must be
cleaved. All calculations have been carried out using the
GAUSSIAN09 suite of programs.(53)
Scheme 7.
Experimental
Chemicals
All reagents, ACN, DMF and NBu4BF4 were of the highest purity
were commercial origin and used as received.
CV and Electrolysis Experiments
Conclusions
Voltammetry and electrolysis experiments were carried out in
a jacketed five neck conical cell at 20 C. Three of the necks
o
The anion radicals from the electroreduction of
Z-O2NC6H4CH=CHC6H4NO2,
O2NC6H4CH2-CH2C6H4NO2
E-O2NC6H4CH=CHC6H4NO2,
and O2NC6H4CMeH-
were used for the working, counter, and reference electrodes,
while the other two necks were used for the argon inlet and
outlet.
For cyclic voltammetry experiments a glassy carbon disk with a
1 mm diameter was used as working electrode, with the
counter electrode being a 1 mm diameter Pt disk. The
reference electrode is a saturated calomel electrode (SCE),
separated from the working electrode compartment by a salt
bridge with a ceramic frit.
The number of electrons transferred in an electron transfer
step is calculated as the quotient between the function current
[Ip c-1 v-1/2] of the electroactive substance and the function
current, [Ip c-1 v-1/2]0 value of fluorenone (number of electrons
transferred=1) in the same experimental conditions (solution
and working electrode), were Ip is the peak current for
reduction wave, c is the concentration of solution, and v the
scan rate.
Electrolysis were performed at controlled potential (ca. 100
mV more negative than peak potential) using a carbon
graphite rod as a working electrode (8.0 cm2 of surface), a Pt
rod as a counter electrode, and a saturated calomel electrode
(SCE) as a reference electrode. The counter electrode and the
SCE were isolated from the working electrode compartment by
a salt bridge, with a glass frit for the counter electrode, and a
ceramic frit for the reference electrode.
CMeHC6H4NO2undergo disproportion into the neutral and
dianionic species with equilibrium constants ranging from 0.06
and 0.55. In the time scale of the CV (θ≤0.5 s), the
corresponding dianions do not evolve by any chemical
reaction, except for the disproportionation. Also, the anion
radical 4-nitrotoluene remains stable in these conditions.
However, in time scale of electrolysis (from minutes to hours),
2-
only the dianion O2NC6H4CMeH-CMeHC6H4NO2 remains
2-
stable, since the reduced species, Z-O2NC6H4CH=CHC6H4NO2
,
O2NC6H4CH2-CH2C6H4NO22- or O2NC6H4Me•-, evolve totally or in
part to the E-O2NC6H4CH=CHC6H4NO2 dianion. This dianion,
2-
after the work-up with water, is recovered as the neutral
species E-O2NC6H4CH=CHC6H4NO2, with concomitant water
reduction.
2-
In the case of the Z-O2NC6H4CH=CHC6H4NO2 anion, the
negative charge diminishes the bond order of the central C=C
bond, allowing the cis- to trans- isomerization.
2-
On the other hand, the O2NC6H4CH2-CH2C6H4NO2 dianion
spontaneously
E-O2NC6H4CH=CHC6H4NO22-, as demonstrated by combined
electrolysis CV experiments, spectroelectrochemical
releases
H2
to
produce
experiments and theoretical calculations.
Therefore, in spite of being in electroreductive conditions, the
oxidized species E-O2NC6H4CH=CHC6H4NO2 can be obtained
from O2NC6H4CH2-CH2C6H4NO2. A similar situation takes place
in the electroreduction of 4-nitrotoluene, but with a previous
step. The corresponding anion radical, O2NC6H4Me•- is
converted by intermolecular H-transfer reaction into the
After electrolysis in DMF and at constant potential were
complete after the chosen quantity of coulombs was circulated
or electrolysis were exhaustive (i.e. final current was 5% or less
than the initial current), the reaction mixture was extracted,
on air, with water/toluene. The organic layer was dried with
Na2SO4 and evaporated yielding a residue that was analyzed by
GC, GC-MS and H1-NMR.
The electrolysis experiments in ACN+0.10 M NBu4BF4 were
performed at 10 °C in N2:O2 (99.9:0.1) atmosphere in solutions
of reagents with concentration
-
benzylic anion O2NC6H4CH2 , which dimerizes to O2NC6H4CH2-
2-
CH2C6H4NO2 that evolves as previously described. Again, in
this case the oxidized E-O2NC6H4CH=CHC6H4NO2 can be
obtained from 4-nitrotoluene under electroreductive
conditions.
20mM in the same
electrochemical cell and electrodes described. The exhaustive
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J. Name., 2013, 00, 1-3 | 9
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