Thermodynamic and Electrochemical oxidation of some diamine derivatives: Experimental and theoretical investigation

Article abstract of DOI:10.1149/2.0351512jes

Electrochemical oxidation of some diamine derivatives (1H⁺-4H⁺) has been investigated both experimentally and theoretically. Experimental results were obtained using cyclic voltammetry and controlled potential coulometry and the theoretical results were calculated at DFT (B3LYP and BP86) levels of theory and 6-311+G (p,d) basis set. The calculated result indicates that oxidation potential of 1H⁺-4H⁺is directly dependent on theΔG_totand species with more positive oxidation potential (E_pA1) have largerΔG_totvalues. Also in this paper electrochemical oxidations of N,N-diethyl-p-phenylenediamine (3) were studied in the absence and in the presence of some nucleophiles. Mechanistic study of the electrochemical oxidation of 3 indicates that its electrochemical oxidation proceed in the thermodynamically favored direction.

Full text of DOI:10.1149/2.0351512jes

Journal of The Electrochemical Society, 162 (12) H877-H883 (2015)
H877
0013-4651/2015/162(12)/H877/7/$33.00 © The Electrochemical Society
Thermodynamic and Electrochemical Oxidation of Some Diamine
Derivatives: Experimental and Theoretical Investigation
Hadi Beiginejad,a,z Davood Nematollahi,b and Sadegh Khazalpourb
aFaculty of Science, Malayer University, 65174 Malayer, Iran
bFaculty of Chemistry, Bu-Ali-Sina University, 65174 Hamedan, Iran
Electrochemical oxidation of some diamine derivatives (1H+–4H+) has been investigated both experimentally and theoretically.
Experimental results were obtained using cyclic voltammetry and controlled potential coulometry and the theoretical results were
calculated at DFT (B3LYP and BP86) levels of theory and 6–311+G (p,d) basis set. The calculated result indicates that oxidation
potential of 1H+–4H+ is directly dependent on the ꢀGtot and species with more positive oxidation potential (EpA1) have larger ꢀGtot
values. Also in this paper electrochemical oxidations of N,N-diethyl-p-phenylenediamine (3) were studied in the absence and in the
presence of some nucleophiles. Mechanistic study of the electrochemical oxidation of 3 indicates that its electrochemical oxidation
proceed in the thermodynamically favored direction.
© 2015 The Electrochemical Society. [DOI: 10.1149/2.0351512jes] All rights reserved.
Manuscript submitted July 7, 2015; revised manuscript received August 24, 2015. Published September 1, 2015.
Amines are used in a range of different fields, such as chemistry,
biology, medicine and agriculture.1–4 Sulfonamides, which are used
as medicine for human beings, can be produced using electrochemical
oxidation of some amines in the presence of some sulfonyl functional
groups.5,6 Also para-quinonediimines can participate in the hydrol-
ysis and formation of Schiff bases reaction which is important in
biochemical processes.7–11 It was reported that electrochemical oxi-
dation of aromatic amines leads to different products depending on
their structure and electrolysis conditions.12,13 Due to their medicinal
importance and reactivity, amines continue to attract interest. In par-
allel with other branches of chemistry, electrochemical methods are
widely applied to study the reactions of amines.14–16 Using these meth-
ods not only thermodynamic and kinetic data were obtained17 but also
some valuable new amine derivatives have been synthesized,18,19 the
products having been formed via a variety of mechanisms20–25 Hav-
ing high selectivity, controlled-potential coulometry is considered as
a powerful tool for the synthesis of different types of products by
control of the applied potential.25,26 Theoretical study of the electro-
chemical process was done by numerous workers.27–30 Created link
between experimental results and theoretical data shows that com-
putational study is a useful method of considering electrochemical
oxidation of some species.31,32 Along with electrochemical study of
some aminophenol31 and dihydroxybenzene derivatives,32 the elec-
trochemical oxidation of some diamine species has been investigated
both experimentally and theoretically. In the first step, oxidation po-
tentials (EpA1) of diamine derivatives (1H+–4H+) have been obtained
from their cyclic voltammograms in solutions maintained at a pH
of 4.0. Also the total change in Gibbs free energy (ꢀGtot) of the
electrochemical oxidation of studied species (1H+–4H+) was cal-
culated using computational methods. The results show that species
with more positive oxidation potential (EpA1) have larger ꢀGtot values.
Then in the second step, electrochemical oxidations of N,N-diethyl-
p-phenylenediamine (3) in the absence and in the presence of some
nucleophiles have been studied. The results show that depending on
the ꢀGtot of the electrochemical oxidation, the products which are
produced during controlled-potential coulometry will participate in
the subsequent electrochemical and chemical reactions. ꢀGtot of the
electrochemical oxidation of diamine derivatives, such as intermedi-
ates and products, were calculated at DFT (B3LYP and BP86) levels
of theory using 6–311+G (p,d) basis set according to the Born-Haber
cycle.
coulometry. The working electrode used in the voltammetry exper-
iments was a glassy carbon disk (1.8 mm diameter) and a platinum
wire was used as the counter electrode. The working electrode used in
controlled-potential coulometry was an assembly of four carbon rods
(31 cm2) and a large platinum gauze was used as counter electrode. The
working electrode potentials were measured vs. Ag/AgCl. Diamine
species (1-4) and other chemicals were prepared from E. Merck and
Aldrich. More details are described in our previous papers.24
Computational study.— The geometries of all species in the gas
phase were fully optimized at Density functional theory (B3LYP and
BP86) using the Gaussian 03.33 The standard 6–311+G (p,d) basis
set was used for all species. Vibrational frequency analysis, calcu-
lated at the same levels of theory, indicates that optimized structures
are at the stationary points corresponding to local minima without
any imaginary frequency. A starting molecular-mechanics structure
for the ab initio calculations was obtained using the HyperChem 5.02
program.34 To calculate solvation energies the Conductor-like Polar-
izable Continuum Model (CPCM)35 with the setting ICOMP = 0,
have been used at the above levels of theory. The optimized atomic
radii were invoked via the solvent keyword RADII = UAHF. Then
solvation free energies were obtained using the SCFVAC keyword.
We have used −6.28 kcal/mol for Gibbs free energy of H+ at gas
phase (ꢀG0(g,H+))36 and −262.5 kcal/mol for its solvation energy
(ꢀG0(s,H+)) in solution.37 Also the value energy “0.86 kcal/mol”
was used for a free electron at 298 K in our calculations.38
Results and Discussion
Voltammetric study.— Electrochemical oxidation of some
diamine derivatives (N,N-Dimethyl-4-nitrosoaniline (1H+), 4-
morpholinoaniline (2H+), N,N-diethyl-p-phenylenediamine (3H+)
and 2,5-diethoxy-4-morpholinoaniline (4H+) (Scheme 2)) has been
studied in aqueous solution using cyclic voltammetry (Fig. 1). Cyclic
voltammogram (CV) 1.0 mM of N,N-dimethyl-4-nitrosoaniline (1H+)
in aqueous solution containing 0.2 M acetate buffer (pH 4.0) is shown
in Fig. 1-curve a. The voltammogram exhibits an anodic peak (A1) at
0.82 V and a cathodic peak (C1) at 0.76 V vs. Ag/AgCl, respectively.
The anodic and cathodic peaks (A1 and C1) are counterpart and cor-
respond to the transformation of 1H+ to the p-quinonediimine 1ox+
and vice versa within a quasi-reversible two-electron process.39 Also,
CVs 1.0 mM of 2H+- 4H+ obtained in aqueous solution containing
acetate buffer (0.2 M, pH 4.0) are shown in Fig. 1 curve b-d respec-
tively. The anodic peaks A1 in all three curves b, c and d are related
to the transformation of 2H+, 3H+ and 4H+ to their corresponding
Experimental
Apparatus and reagents.— Cyclic voltammetry and controlled po-
tential coulometry were performed using a micro Autolab model
TYPE III potentiostat/galvanostat. A divided cell was used for
p-quinonediimines (2ox+, 3ox+ and 4ox+) which were recorded in
20–24
0.44 V, 0.38 V and 0.31 V vs. Ag/AgCl, respectively.
This
>
voltammograms indicate that EpA1 varies in the order EpA1 1H+
EpA1 2H+ > EpA1 3H+ > EpA1 4H+.
zE-mail: h.beiginejad@malayeru.ac.ir
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Journal of The Electrochemical Society, 162 (12) H877-H883 (2015)
Figure 1. Cyclic voltammograms 1.0 mM of a) N,N-Dimethyl-4-nitrosoaniline (1H+), b) 4-morpholinoaniline (2H+), c) N,N-diethyl-p-phenylenediamine (3H+)
and d) 2,5-diethoxy-4-morpholinoaniline (4H+) in acetate buffer solution (c = 0.2 M, pH = 4.0); scan rate: 100 mV s−1, t = 25 1◦C.
Because the total change in Gibbs free energy (ꢀGtot) is one of the
most important parameters influencing the reaction mechanisms,31,32
the effect of the ꢀGtot of the electrochemical oxidation on the electro-
chemical oxidation potential of compounds (1H+-4H+) was studied.
The relationship between potential and ꢀGtot is given by:
The gas-phase contribution to the Gibbs free energy can be de-
termined using DFT calculation. In addition EpA1 was selected as an
indication of the oxidation potential (EA) of species 1H+-4H+ which
is obtained using cyclic voltammograms at pH = 4.0.
ꢀGtot of the electrochemical oxidation of 1H+-4H+ were calcu-
lated and the results indicate that ꢀGtot varies in the order ꢀG
>
1
ꢀGtot = −nF (EC − EA)
[1]
ꢀG 2 > ꢀG3> ꢀG4 (Scheme 2). In other word it can be concluded
that species with more positive oxidation potential (EA) have larger
ꢀGtot values.
Where EA is the oxidation potential of amines 1H+-4H+. By consid-
ering the reduction of water as the cathodic reaction for all studied
amines, ꢀGtot is calculated by Eq. 2.
ꢀGtot = K + nF EA
[2]
Where K is constant and ꢀGtot is the total change of Gibbs free energy
for electrochemical oxidation of amines (1H+-4H+). Eq. 2 shows that
there is a linear relationship between ꢀGtot and EA. Also ꢀGtot was
calculated using 6–311+G (p,d) basis set, and DFT(B3LYP, BP86)
levels of theory according to the Born-Haber cycle (Scheme 1) and
Eq. 3.
redox
gas
redox
sol
ꢀGtot = ꢀG
+ ꢀG
[3]
Where ꢀGgas is the standard Gibbs energy in gas phase and ꢀGsol is
the solvation energy and is defined as follows:
= ꢀG + 2ꢀGHso+l − ꢀG
[4]
Scheme 1. Thermodynamic cycle used to calculate Gibbs free energy.
redox
sol
ox
sol
red
sol
ꢀG
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Journal of The Electrochemical Society, 162 (12) H877-H883 (2015)
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O
N
O
N
-H+, -2e-
ΔGtot= 269.85 kcal/mol
N
NH
1ox2+
1H+
NH
NH2
-2H+, -2e-
N
NH
ΔGtot= 239.58 kcal/mol
O
O
2ox+
2H+
Figure 2. Cyclic voltammogram 1.0 mM of DEPD (3H+) in phosphate buffer
solution (c = 0.2 M, pH = 3.0); scan rate: 100 mV s−1, t = 25 1◦C.
NH
NH2
coulometry. Progress of the electrolysis was monitored by the use
of cyclic voltammetry (Fig. 3). As can be seen, in parallel progress
of electrolysis a couple C0/A0 peak appears in the negative potential
(Fig. 3).
-2H+, -2e-
N
NH
ΔGtot= 238.30 kcal/mol
Comparing cyclic voltammograms of the two Figures 2 and 3
indicates that although 3ox+ is stable in the time scale of cyclic
voltammetry, in the larger time scale (controlled-potential coulome-
try) 3ox+ becomes unstable and participates in a subsequent chemi-
cal reaction which couple A0/C0 peak is indication of it. Results of
the controlled-potential coulometry show that electrolysis was ter-
minated after consumption 2e− per molecule of 3H+. Because re-
ported results indicate that some electrogenerated p-quinoneimines
can be hydrolyzed in acidic solutions,24,25,31 obtained cyclic voltam-
mogram in the end of the coulometry was compared with recorded
cyclic voltammogram of hydroquinone (3a) in the same condition
(Fig. 4).
3ox+
3H+
NH
NH2
OEt
OEt
-2H+, -2e-
EtO
EtO
N
NH
O
ΔGtot= 234.19 kcal/mol
O
4ox+
4H+
By comparing the voltammograms of a and b in Fig. 4, it
can be concluded that the C0 peak corresponds to the reduction
of p-benzoquinone (3b). Using this condition, 3ox+ converts to p-
benzoqoinone (3b) following hydrolysis. Our previous works on the
Scheme 2. Proposed mechanism for the electrochemical oxidation of studied
amine derivatives.
Because all four species (1-4) attract a proton in aqueous solution
containing acetate buffer solution (pH = 4.0),20,23,24,39. the protonated
forms of them (1H+-4H+) are considered in the schemes and compu-
tational study.
Mechanistic study.— Electrochemical oxidations of N,N-diethyl-
p-phenylenediamine (3) under various conditions were studied by the
use of cyclic voltammetry and controlled potential coulometery and
different mechanisms were reported for them.21–23
Fig. 2 shows a cyclic voltammogram of 1.0 mM N,N-diethyl-
p-phenylenediamine (DEPD) in aqueous solution containing 0.2 M
phosphate buffer solution (pH = 3.0). The voltammogram shows an
anodic peak (A1) in the positive-direction scan and a cathodic counter-
part peak (C1) in the negative-direction scan which are related to the
transformation of DEPD (3H+) to corresponding p-quinonediimine
(3ox+) and vice versa within a two-electron, two-proton process.22,23
Under these conditions, the peak current ratio (IpC1/IpA1) is nearly
unity.
Recorded cyclic voltammograms in lower scan rates (such as 2 or 5
mV/s) show that the peak current ratio (IpC1/IpA1) is not reduced which
can be considered as a criterion for the stability of p-quinonediimine
(3ox+) produced at the surface of the electrode in time scale of cyclic
voltammetry. 80 ml aqueous solution 0.6 mM of 3H+ was electrolyzed
in a divided cell at 0.48 V vs Ag/AgCl using controlled-potential
Figure 3. Cyclic voltammograms of 0.6 mM DEPD (3H+) during controlled
potential coulometry at 0.48 V versus Ag/AgCl in aqueous solution containing
phosphate buffer (pH = 3.0, c = 0.2 M), after the consumption of: (a) 0 C, (b)
2 C, and (c) 8 C. Scan rate: 50 mV s−1; t = 25 1◦C.
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Journal of The Electrochemical Society, 162 (12) H877-H883 (2015)
Figure 4. a) Cyclic voltammogram of 0.6 mM DEPD (3H+) during controlled
potential coulometry after consumption of 8 C and b) Cyclic voltammogram
0.5 mM of hydroquinone (3a) at a glassy carbon electrode, in phosphate buffer
solution (c = 0.2 M, pH = 3.0). Scan rate: 50 mV s−1, t = 25 1◦C.
electrochemical oxidation of amines17,20–25 and the present data allow
us to propose the following mechanistic scheme for the electrochem-
ical oxidation of DEPD (3H+) and its hydrolysis reaction (Scheme
3). ꢀGtot of the electrochemical oxidation of hydroquinone (3a) were
calculated and is shown in scheme 3. As can be seen ꢀGtot of electro-
chemical oxidation of 3a is lower than 3H+. In other words, having
lower ꢀGtot of oxidation, 3a is oxidized at lower potentials.
Figure 5. Cyclic voltammograms 1.0 mM of DEPD (3): a) in the absence
and b) in the presence 1.0 mM of TSA (5) in phosphate buffer solution
(c = 0.2 M, pH = 7.5) at a glassy carbon electrode. Scan rate = 50 mV
s
−1; t = 25 1◦C.
Fig. 5, curve-a shows CV of 1.0 mM DEPD (3) in aqueous solution
containing 0.2 M phosphate buffer solution (pH = 7.5). The voltam-
mogram shows an anodic peak (A1) in the positive-direction scan
and a cathodic counterpart peak (C1) in the negative-direction scan
which correspond to the transformation of DEPD (3) to correspond-
ing p-quinonediimine (3ox+) and vice versa within a two-electron
process (Scheme 4). Under these conditions, the peak current ratio
(IpC1/IpA1) is nearly unity. Fig. 5 (curve-b) shows a CV of 1.0 mM
DEPD (3) in the presence 1.0 mM of p-toluenesulfinic acid (TSA)
as a nucleophile. As can be seen a new anodic peak (A0) appears at
more positive potentials and also during the reverse scan the cathodic
peak C1 decreases which are the occurrences of a following chemical
reaction after electron transfer process (Scheme 4).
Controlled-potential coulometry was performed in aqueous so-
lution containing 0.5 mmol of 3 and 0.5 mmol of TSA (5) at 0.2
V versus Ag/AgCl. The electrolysis progress was monitored using
cyclic voltammetry. It was shown that, proportional to the progress of
the electrolysis, the anodic peak A1 decreased and disappeared when
the charge consumption becomes about 2e– per molecule of 3.21 Our
reported result and this data allow us to propose Scheme 4 for the
electrochemical oxidation of DEPD (3) in the presence of TSA (5).
As can be seen TSA (5) as a nucleophile reacts with produced 3ox+
leading to 5a as a final product. In other word, the oxidation of 5a is
more difficult than the oxidation of 3 and the final product is formed
via an EC mechanism. The ꢀGtot of the electrochemical oxidation of
3 and 5a were calculated. The results indicate that the ꢀGtot of the
electrochemical oxidation of 5a is more positive than DEPD (3). This
led to the increase of electrochemical oxidation potential of 5a. So,
NH
NH2
-2e- -2H+
O
NH
S
ΔGtot= 238.30 kcal/mol
N
NH2
NH
O
HN
SO2
-H+, -2e-
(5)
EC
N
3ox+
3H+
N
ΔGtot= 226.69 kcal/mol
N
3ox+
3
5a
Hydrolysis
reaction
O
S
O
O
OH
N
S
O
O
O
HN
-2e- -2H+
-H+, -2e-
N
ΔGtot= 233.59 kcal/mol
N
ΔGtot= 241.93 kcal/mol
OH
3a
5b
3b
5a
Scheme 3. Proposed mechanism for the electrochemical oxidation of 3H+ in
phosphate buffer solution (c = 0.2 M, pH = 3.0).
Scheme 4. Proposed mechanism for the electrochemical oxidation of DEPD
(3) in the presence of p-toluenesulfinic acid (TSA).
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Journal of The Electrochemical Society, 162 (12) H877-H883 (2015)
H881
sponding p-quinonediimine (3ox+), and the cathodic peak C1 is due
to the reduction of the produced 3ox+ to 3, and the cathodic C2 peak
relates to the reduction of a product which is produced on the surface
of the electrode. Under this condition the peak current ratio (IpC1/IpA1
)
is less than unity which can be considered as a criterion for the in-
stability of 3ox+ produced at the surface of the electrode. Obtained
cyclic voltammograms of 3 at various scan rates show that the height
of C1 peak increases upon increasing scan rate and the peak current
ratio (IpC1/IpA1) approaches unity. Also it was shown that the peak
current ratio (IpC1/IpA1) is dependent on the concentration of DEPD
(3) and decreases with increasing concentration of DEPD (3). The
dependence of the peak current ratio (IpC1/IpA1) on the concentration
of DEPD (3) is indication of a second-order reaction after electron
transfer process.23
Controlled-potential coulometry was performed in aqueous solu-
tion (phosphate buffer, 0.2 M, pH 8.0) containing 0.25 mmol of DEPD
(3) at 0.15 V versus Ag/AgCl. Monitoring the electrolysis progress
by cyclic voltammetry was shown that the peak A1 disappeared af-
ter consumption of about 2e– per molecule of DEPD (3).23 Using
our experience in electrochemical oxidation of DEPD (3) at various
conditions we can propose following scheme for the electrochemical
oxidation of 3 (Scheme 5). Based on Scheme 5, 3ox+ participates
in the Michael addition reaction with 3 to form 3c and its oxidation
converted 3c to 3d as the final product. Our computational data show
that the ꢀGtot of the electrochemical oxidation of DEPD (3) is larger
than 3c. In other words, this leads to the oxidation of intermediate
3c during controlled-potential coulometry and the final product 3d is
formed via an ECE mechanism.
The electrochemical oxidation of DEPD (3) was studied in the
presence of phenol (6) as a nucleophile. Fig. 7 shows CVs 1.0 mM
of 3 in the absence and in the presence 1.0 mM of 6. Comparing
curve-a with curve-b indicates that: a) the current of anodic peak A1
increases, b) the peak current ratio (IpC1/IpA1) decreases and c) a new
cathodic peak (C0) appears at the negative potentials, duo to addition
of 6. These behaviors correspond to the participation of produced p-
quinonediimine (3ox+) in the following chemical reaction with 6. The
Figure 6. Cyclic voltammogram 5.0 mM of DEPD (3) in phosphate buffer
solution (c = 0.2 M, pH = 7.5) at a glassy carbon electrode. Scan rate = 10
mV s−1; t = 25 1◦C.
the oxidation of 5a is more difficult than the oxidation of the starting
molecule 3 and the final product is formed via an EC mechanism.
According to Scheme 4, the anodic peaks A1 and A0 correspond to
the oxidation of 3 and 5a to 3ox+ and 5b respectively.
Fig. 6 shows CV of 5.0 mM DEPD (3) in aqueous solution con-
taining phosphate buffer solution (c = 0.2 M, pH = 8.0). The voltam-
mogram indicates an anodic peak (A1) in the positive-going scan and
two cathodic peaks (C1 and C2) in the negative-going scan versus
Ag/AgCl. The anodic peak A1 is due to the oxidation of 3 to its corre-
NH2
N
NH
N
NH2
NH
-H+, -2e-
3
EC
HN
N
ΔGtot= 226.69 kcal/mol
N
3ox+
3c
3
N
Scheme 5. Proposed mechanism for the electro-
chemical oxidation of DEPD (3) in phosphate buffer
solution (c = 0.2 M, pH = 8.0).
N
N
-2H+, -2e-
N
N
NH
NH
E
ΔGtot= 208.03 kcal/mol
N
N
3c
3d
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H882
Journal of The Electrochemical Society, 162 (12) H877-H883 (2015)
Table I. The calculated ꢀGtot of electrochemical oxidation of
studied species.
Calculated ꢀGtot using
Calculated ꢀGtot using
Species
B3LYP (kcal/mol)
BP86 (kcal/mol)
1H+
2H+
3H+
4H+
3
3a
3c
5a
6a
269.85
239.58
238.30
234.19
226.69
233.59
208.03
241.93
205.44
267.77
237.25
236.63
234.08
226.25
233.31
205.66
238.45
203.05
the electrochemical oxidation of DEPD (3) leads to the formation
of p-quinonediimine 3ox+. The Michael addition reaction of 6 to p-
quinonediimine 3ox+ and aromatization leads to 6a. The oxidation of
compound 6a is easier than the oxidation of 3 and is converted to 6b
as a final product (Scheme 6). Calculated ꢀGtot of the electrochemi-
cal oxidation of DEPD (3) and 6a were shown in Scheme 6. As can
be seen ꢀGtot of 3 is more than 6a, which led to the oxidation of
intermediate 6a during controlled-potential coulometry.
Electrochemical oxidation of 3, in the condition which was men-
tioned above, was also investigated using BP86 level of theory and
6–311+G (p,d) basis set. Our calculations show that the results using
BP86 level of theory are similar to the results using B3LYP level
of theory (Table I). The theoretical results show that the electro-
chemically generated species which are produced during controlled-
potential coulometry will participate in the subsequent electrochemi-
cal and chemical reactions based on the ꢀGtot of the electrochemical
oxidation. Using calculated results it can be concluded that although
the electrochemical oxidations of 3 in the presence of different nucle-
ophiles have different mechanisms but proceed in the thermodynam-
ically favored directions.
Figure 7. Cyclic voltammograms 1.0 mM of DEPD (3): a) in the absence and
b) in the presence 1.0 mM of phenol (6) in phosphate buffer solution (c = 0.2
M, pH = 8.0) at a glassy carbon electrode. Scan rate = 20 mV s−1; t = 25
1◦C.
new peak (C0) is related to the electrochemical reduction of 6b which
produced on the surface of the electrode.22
Controlled-potential coulometry was performed in aqueous solu-
tion (phosphate buffer, 0.2 M, pH 8.0) containing DEPD (3) and 6
at the peak A1 potential (at 0.15 V versus Ag/AgCl). Monitoring the
electrolysis progress by cyclic voltammetry indicated that the IpA1 de-
creased and disappeared when the charge consumption becomes about
4e− per molecule of DEPD (3). According to the reported results,22
O
O
NH
NH2
NH
EC
-H+, -2e-
(6)
N
N
N
ΔGtot= 226.69 kcal/mol
3
6a
3ox+
Scheme 6. Proposed mechanism for the electro-
chemical oxidation of DEPD (3) in the presence of
phenol (6).
O
N
O
-2H+, -2e-
C
NH
ΔGtot= 205.44 kcal/mol
N
N
6a
6b
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Journal of The Electrochemical Society, 162 (12) H877-H883 (2015)
H883
Conclusions
10. A. S. Kirdant, V. A. Shelke, S. G. Shankarwar, A. G. Shankarwar, and
T. K. Chondhar, J. Chem. Pharm. Res. 3, 790 (2011).
Electrochemical oxidation of some diamine derivatives (1H+–
4H+) has been investigated both experimentally and theoretically
using cyclic voltammetry, controlled potential coulometry and Den-
sity Functional Theory (DFT). The calculated results indicate that the
oxidation potential of 1H+–4H+ is directly dependent on their ꢀGtot
and species with more positive oxidation potential (EpA1) have larger
ꢀGtot values. Also in this paper electrochemical oxidations of N,N-
diethyl-p-phenylenediamine (3) were studied in the absence and in
the presence of some nucleophiles. The results show that the electro-
chemically generated species which are produced during controlled-
potential coulometry, based on the ꢀGtot of the electrochemical oxida-
tion, will participate in the subsequent electrochemical and chemical
reactions. The ꢀGtot of the electrochemical oxidation of intermediates
and products were investigated at DFT (B3LYP and BP86) levels of
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