Electrochemical study of catechol derivatives in the presence of β-diketones: Synthesis of benzofuran derivatives

Article abstract of DOI:10.1149/2.029212jes

The electrochemical oxidation of 4-(1,3-dithiolan-2-yl)benzene-1,2-diol was studied in the presence and absence of acetylacetone (2a), dimedone (2b) and 4-hydroxycoumarin (2c) as nucleophiles in aqueous solution bymeans of cyclic voltammetry and controlle

Full text of DOI:10.1149/2.029212jes

Electrochemical Study of Catechol Derivatives in the
Presence of β-diketones: Synthesis of Benzofuran
Derivatives
Mohammad Mazloum-Ardakani, Alireza Khoshroo, Davood Nematollahi and
Bibi-Fatemeh Mirjalili
J. Electrochem. Soc. 2012, Volume 159, Issue 12, Pages H912-H917.
doi: 10.1149/2.029212jes
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© 2012 The Electrochemical Society

H912
Journal of The Electrochemical Society, 159 (12) H912-H917 (2012)
0013-4651/2012/159(12)/H912/6/$28.00 © The Electrochemical Society
Electrochemical Study of Catechol Derivatives in the Presence
of β-diketones: Synthesis of Benzofuran Derivatives
Mohammad Mazloum-Ardakani,a,z Alireza Khoshroo,a Davood Nematollahi,b
and Bibi-Fatemeh Mirjalilia
aDepartment of Chemistry, Faculty of Science, Yazd University, Yazd 89195-741, Iran
bFaculty of Chemistry, University of Bu-Ali Sina, Hamedan, Iran
The electrochemical oxidation of 4-(1,3-dithiolan-2-yl)benzene-1,2-diol was studied in the presence and absence of acetylacetone
(2a), dimedone (2b) and 4-hydroxycoumarin (2c) as nucleophiles in aqueous solution by means of cyclic voltammetry and controlled-
potential coulometry. The results indicate that these nucleophiles participate in Michael addition reaction with the oxidized form
of catechol derivatives, and then convert it to the corresponding new benzofuran derivatives. The electrochemical synthesis of
compounds has been successfully performed at a carbon rod electrode and in two-compartment cell. The observed homogeneous
rate constants (kobs) of the reaction of oxidized form of catechol derivatives with 2a-c as nucleophiles were estimated by comparing
the experimental cyclic voltammograms with the digital simulated results. The calculated kobs was found to vary in the order
4-hydroxycoumarin (2c) < dimedone (2b) < acetylacetone (2a).
© 2012 The Electrochemical Society. [DOI: 10.1149/2.029212jes] All rights reserved.
Manuscript submitted June 25, 2012; revised manuscript received August 28, 2012. Published October 1, 2012.
Electrochemical methods are more and more widely used for
water. Homogeneous rate constants were estimated by analyzing
the cyclic voltammetric responses, using simulation software.9 3,4-
Dihydroxybenzaldehyde, 1,2-ethanedithiol, acetylacetone, dimedone
and 4-hydroxycoumarin were reagent-grade from Aldrich. Phosphate
salt, sodium hydroxide, solvents and reagents were of pro-analysis
grade from E. Merck. These chemicals were used without further pu-
rification. The peak current ratios (IpC1/IpA1) were determined using
the following equation given in Ref. 10.
the study of electroactive compounds in pharmaceutical forms and
physiological fluids due to their simple, rapid, and economical
properties.1 Catechol derivatives play an important role in mammalian
metabolism, and many compounds of this type are known to be sec-
ondary metabolites of higher plants. Moreover, 2 over 1800 exam-
ined antibiotics of microbial origin contain a catechol sub-structure.
Therefore, the catechol derivatives are a promising group of com-
pounds worthwhile for further investigation, which may lead to the
discovery ofselective acting biodegradableagrochemicals having high
human, animal and plant compatibility.2 Biologically active hetero-
cyclics, benzofuran derivatives constitute a major group.3–6 They are
usually an important constituent of plant extracts used in medicinal
chemistry for their various biological activities, including insectici-
dal, traditional medicine, antimicrobial, and antioxidant properties.7,8
Thus, development of efficient methods to functionalize heterocyles
is critical for synthetic chemistry and synthesis of organic com-
pounds with both structures of catechol and benzofuran would be
of interest from the point of view of pharmaceutical properties. This
idea prompted us to investigate electrochemical oxidation of 4-(1,3-
dithiolan-2-yl)benzene-1,2-diol (DITHBD; 1 in Scheme 1) in the pres-
ence of acetylacetone (2a), dimedone (2b) and 4-hydroxycoumarin
(2c) as nucleophiles and report a facile electrochemical method for the
synthesis of some new benzofuran compounds. An additional purpose
of this work is to estimate the observed homogeneous rate constants
(kobs) of reaction of electrochemically generated o-benzoquinone with
nucleophiles by digital simulation of cyclic voltammograms.
[Ipc/Ipa = (Ipc)0/Ipa + 0.485(Isp)0/Ipa + 0.086]
where (Ipc)0 and (Isp)0 are cathodic peak current and “switching po-
tential” current with respect to the zero current, respectively, while
Ipc corresponds to the cathodic peak current and Ipa the anodic peak
current.
Synthesis of 4-(1,3-dithiolan-2-yl)benzene-1,2-diol (1).— A mix-
ture of 3,4-dihydroxybenzaldehyde, (1 mmol), 1,2-ethanedithiol
(1.2 mmol) and 37% BF3 · SiO2 (0.3 g) was ground in a pestel at an
ambient temperature. The progress of reaction was monitored by thin
layer chromatography. After completion of the reaction, the product
was dissolved in ethanol, filtered, and the solvent was evaporated. The
obtained solid was recrystalized in chloroform.
Electroorganic synthesis of benzofuran derivatives.— In a typ-
ical procedure, 80 mL of 0.15 M phosphate buffer (pH 7.0) in
water/acetonitrile (85/15 volume ratio), containing 0.7 mmol of
DITHBD and 0.7 mmol acetylacetone (2a) or dimedone (2b) or
4-hydroxycoumarin (2c), was electrolyzed at controlled-potential in a
two compartment cell. The applied potential used in electrosynthesis
was optimized to obtain each product (0.35 vs. SCE). The electrolysis
was terminated when the current decayed to 5% of its original value.
The process was interrupted seven times during the electrolysis and
the carbon anode was washed in acetone in order to reactivate it. The
precipitated solid was collected by filtration and was washed several
times with water. After washing, products were characterized by IR,
1H NMR, 13C NMR.
Experimental
Apparatus and chemicals.— Cyclic voltammetry and preparative
electrolysis were performed using a potentiostat/galvanostat (SAMA
500, electroanalyzer system, Iran). The working electrode used was a
glassy carbon disk (1.8 mm diameter; purchased from AZAR, Iran)
and a platinum wire was used as the counter electrode. The work-
ing electrode used in controlled-potential coulometry and macroscale
electrolysis was an assembly of four carbon rods (total surface
area of the four electrodes: 35 cm2), while a large stainless steel
gauze constituted the counter electrode. The working electrode po-
tentials were measured versus a saturated calomel electrode (SCE;
AZAR, Iran). All electrochemical oxidations were performed under
controlled-potential conditions in a cell with two compartments sep-
arated by a porous fritted-glass diaphragm and equipped with a mag-
netic stirrer. A Metrohm 691 pH/Ion Meter was used for pH mea-
surements. All solutions were freshly prepared using double-distilled
Characteristics
of
products–1-(4-(1,3-dithiolan-2-yl)-6,7-
dihydroxy-2-methylbenzofuran-3-yl)ethanone(5a) (C14H16O4S2).—
Applied potential: 0.35 vs. SCE. Mp = 268-270◦C. IR (KBr)
ν(cm−1): 3420, 3120, 1622, 1570, 1505, 1440, 1390, 1342, 1282,
1234, 1222, 1130, 982, 847, 764. 1H NMR, δ (ppm) (500 MHz,
DMSO): 2.30 (s, 3H, methyl), 2.56 (m, 5H), 2.86 (t, 4H, J = 11 Hz),
5.28 (s, 1H), 6.68 (s, 1H aromatic); 8.42 (broad, 1H hydroxy), 9.10
(broad, 1H hydroxy). 13C NMR, δ (ppm) (DMSO): 18.6, 30.1, 43.3,
52.2, 111.52, 118.2, 122.3, 125.0, 138.7, 140.4, 145.3, 152.0, 185.2.
zE-mail: mazloum@yazduni.ac.ir

Journal of The Electrochemical Society, 159 (12) H912-H917 (2012)
H913
Scheme 1. Proposed mechanism for the electrochemical oxidation of DITHBD (1) in the presence of acetylacetone (2a), dimedone (2b) and
4-hydroxycoumarin (2c).
reaction in reaction side such as hydroxylation,11,12 dimerization13–15
9-(1, 3-dithiolan-2-yl) -6, 7- dihydroxy-3, 3-dimethyl-3, 4-dihydro-
or oxidative ring cleavage16 is increased.
dibenzo[b,d]furan-1(2H)-one(5b)(C17H18O4S2).— Applied poten-
tial: 0.35 vs. SCE. Mp = 286-288◦C. IR (KBr) cm−1: 3270, 3140,
2950, 2910, 1630, 1588, 1473, 1448, 1372, 1292, 1248, 1138, 1112,
1087, 983, 823, 776. 1H NMR, δ (ppm) (500 MHz, DMSO): 1.03 (s,
6H), 2.22 (s, 2H); 2.56 (s, 2H); 2.86 (t, 4H, J = 11 Hz), 5.58 (s, 1H),
6.48 (s, 1H aromatic), 8.69 (broad, 1H, hydroxy), 9.18 (broad, 1H,
hydroxy). 13C NMR, δ (ppm) (DMSO): 22.1, 29.1, 32.0, 45.2, 52.2,
57.1, 110.3, 114.2, 122.1, 127.3, 143.1, 144.4, 146.3, 161.4, 177.2.
Comparison of the two cyclic voltammograms in Figure 1 appears
to indicate that the peak current ratio IpC1/IpA1 is dependent on the
7-(1, 3-dithiolan-2-yl)-9, 10-dihydroxy-6H-benzofuro[3, 2-c]chro-
men-6-one(5c)(C18H12O5S2).— Applied potential: 0.35 vs. SCE. Mp
= 308-310◦C. IR (KBr) cm−1: 3380, 3290, 2984, 2880, 1730, 1628,
1610, 1514, 1356, 1325, 1280, 1265, 1232, 1050, 980, 872. 1H NMR,
δ (ppm) (500 MHz, DMSO): 2.42 (2 H, t, J = 11 Hz), 2.66 (2 H, t,
J = 11 Hz), 5.23 (s, 1H), 6.12 (s, 1H, aromatic), 7.24 (m, 4H), 8.91
(broad, 1H, hydroxy), 9.26 (broad, 1H, hydroxy). 13C NMR, δ (ppm)
(DMSO): 30.1, 52.2, 109.1, 113.2, 115.4, 122.3, 123.6, 125.2, 126.4,
127.2, 129.5, 146.2, 149.1, 153.2, 159.6, 160.2.
Results and Discussion
Electrochemical study.— As DITHBD is produced using 3,4-
dihydroxybenzaldehyde (DIBZ), the electrochemical behavior of
these two compounds are compared. Cyclic voltammetry was used
to study the effect of the change from an aldehyde group to 1,2-
ethanediothiol in DIBZ. Cyclic voltammogram of a 1.0 mM aqueous
solution of DIBZ in 0.15 M phosphate buffer (pH 7.0) is shown in
Fig. 1 curve a. As can be seen, one anodic (A1) and two cathodic peaks
C1 and C2 were obtained. Fig. 1 curve b, shows the cyclic voltammo-
gram of 1.0 mM DITHBD in conditions similar to those used to obtain
curve a. This compound is a catechol derivative, which can be electro-
chemically oxidized to quinone (A1 in Figure 1a and Figure 1b). The
change from two cathodic peaks in curve a to one cathodic peak in
curve b can be explained as follows: The electron withdrawing charac-
ter of an aldehyde group is stronger than that of an ethanedithol group,
leading to the formation of more reactive quinone. Then, the rate
Figure 1. Cyclic voltammograms of 1.0 mM 3,4-dihydroxybenzaldehyde (a),
1.0 mM DITHBD (b) at glassy carbon electrode, in phosphate buffer solution
(pH = 7.0, c = 0.15 M). Scan rate: 100 mV s−1.t = 25 1◦C.

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Journal of The Electrochemical Society, 159 (12) H912-H917 (2012)
Figure 3. Cyclic voltammograms of 1.0 mM DITHBD (1), at glassy car-
bon electrode, in water (buffered solutions with various pHs and same ionic
strength)/acetonitrile (85/15 v/v). pH values from (a) to (h) are 2.0, 3.0, 4.0,
5.0, 6.0, 7.0 and 8.0 respectively. Scan rate: 50 mV s−1. Inset: Variation of
half-wave potential (E1/2) of DITHBD (1) as a function of pH. t = 25 1◦C.
oxidation of DITHBD (1) to its quinonic form (1a).
DITHBDQ + mH+ + 2e−
ꢀ
ꢁ
DITHBD
DITHBDQ denotes the quinone of DITHBD (1a); and m is the number
of proton(s) involved in the reaction. The half-wave potential (E1/2),
is given by:17
Figure 2. Cyclic voltammograms of 1.0 mM DITHBD (1) at glassy carbon
electrode, in phosphate buffer solution (pH = 7.0, c = 0.15 M). Scan rate:
50 mV s−1. t = 25 1◦C.
E1/2 = E1ꢀ /2 − (2.303 mRT/2F) pH
where Eꢀ1/2 at pH = 0.0, and R, T, and F have their usual meanings.
The half-wave potentials (E1/2) were calculated as the average of the
anodic and cathodic peak potentials of the cyclic voltammograms
{(Epa + Epc)/2}.17
electron-withdrawing character. In the presence of the aldehyde group
with more electron-withdrawing character in the structure of DIBZ,
the peak current ratio, IpC1/IpA1, of DIBZ is smaller than peak current
ratio in DITHBD. Also, in the presence of the ethanedithiol group,
the potential of peak A1 in curve b has shifted negatively by 170 mV
compared to that in curve a.
Next, cyclic voltammetry of 1.0 mM DITHBD (1) in wa-
ter/acetonitrile (85/15 volume ratio) was conducted in 0.15 M phos-
phate buffer (pH 7.0) and the result is show in Fig. 2.
The values of E1/2 as a function of solution pH are plotted in the
inset of Fig. 3. As can be seen, E1/2 shifted to negative potentials with
the slope of 53 mV/pH, which is in agreement with the theoretical
slope (2.303 mRT/2F) of 59 mV/pH when m = 1.8 ≈ 2. This is
expected because DITHBD has a catechol ring with two-electron
two-proton ꢀredox behavior.18 Extrapolation of the plot to pH = 0
yields the E 1/2 = 0.51 V versus SCE.
As can be seen, one anodic (A1) peak arising from the oxidation
of DITHBD to its quinone and one cathodic (C1) peak arising from
the reduction of the quinone back to DITHBD were obtained.
Fig. 3 shows the cyclic voltammograms of DITHBD (1) in
water/acetonitrile (85/15 volume ratio) obtained at different pH.
Between pH 2.0 and 7.0, the cyclic voltammograms show one anodic
(A1) and a corresponding cathodic peak (C1). Under these conditions,
peak current ratio (IpC1 = IpA1) of nearly unity was obtained, support-
ing a degree of stability of DITHBD (1) produced at the electrode
surface under the specified experimental conditions. In other words,
any hydroxylation,11,12 dimerization13–15 or oxidative ring cleavage16
reactions are too slow to be observed on the time scale of cyclic
voltammetry. When the potential sweep rate was decreased from
The oxidation of DITHBD (1) was also studied in the presence of
β-diketones (acetylacetone (2a), dimedone (2b)) and β-ketoester (4-
hydroxycoumarin (2c)) as nucleophiles. In Fig. 4, the cyclic voltam-
mograms of 1 mM DITHBD (1) obtained in the presence of 1 mM
acetylacetone (2a), 1 mM dimedone (2b) and 1 mM 4- hydroxycour-
marin (2c) are shown in I, II and III, respectively. In each study, the
first cyclic voltammetric scan is represented by trace b. These voltam-
mograms exhibit an anodic peak (A1) and a cathodic peak (C1).
The voltammograms exhibit one anodic peak, and the cathodic (C1)
decreases. This could be indicative of the fact that electrochemically
generated 1a is removed by chemical reaction with nucleophiles (2a-
c). The observed shift (<10 mV) of the A1 and C1 peaks in curve b
(Fig. 4), relative to curve a (Fig. 4) are probably due to the formation
of a thin film of product at the surface of the electrode, inhibiting to a
certain extent the performance of the electrode process.19,20
In the second cycle, parallel to the shift of the peak A1 in a positive
direction, a new peak (A0) appears (Fig. 4 curve b, 2nd scan). This new
peak is related to electrochemical oxidation of intermediate (3a-c). It
is seen that, proportionally to the augmentation of the potential sweep
rate, the peak current ratio (IpC1/IpA1) increases (Fig. 5). A similar
situation is observed when the concentration ratio of nucleophiles
(2a-c) to DITHBD (1) decreased.
50 mV s−1 (IpC1 = IpA1) to 10 mV s−1, A peak current ratio (IpC1/IpA1
)
obtained are 0.8, 0.8, 0.76, 0.7, 0.6, and 0.46 for the pH of 2.0–7.0,
respectively. At pH 8.0 (scan rate: 50 mV s−1), a peak current ratio
(IpC1/IpA1) of 0.73 (<1) was obtained (Fig. 3). A peak current ratio of
0.38 was also obtained when the potential sweep rate was decreased
from 50 mV s−1 to 10 mV s−1. With increasing pH, the peak current
ratio (IpC1 = IpA1) becomes less than unity as well as decreasing poten-
tial sweep rate. These changes in the peak current ratio can be related
to the occurrence of side reactions such as hydroxylation, dimerization
or oxidative ring cleavage under the experimental conditions. These
reactions are enhanced by increasing pH. Also, it was found that the
peak potential for peak A1 (EpA1) shifted negatively as a function of
pH. This is expected because of the participation of proton(s) in the
Al
The current function for the peak A1 (IP /ν1/2) decreases with an
increasing scan rate and such behavior is adopted as indicative of an
ECEC mechanism.19–22

Journal of The Electrochemical Society, 159 (12) H912-H917 (2012)
H915
Figure 4. (a) Cyclic voltammograms of 1.0 mM DITHBD (1) in the absence of nucleophiles. (b) Cyclic voltammograms of 1.0 mM DITHBD (1) in the presence
of 1 mM 2a (curve I); 1 mM 2b (curve II) and 1 mM 2c (curve III), at glassy carbon electrode, in aqueous solution containing phosphate buffer (pH = 7.0,
c = 0.15 M). Scan rate: 25 mV s−1. t = 25 1◦C.
Controlled-potential coulometry was performed in aqueous solu-
tion containing 0.7 mmol of 1 and 0.7 mmol of nucleophiles (2a-c)
at the chosen potential (see section 2.4.). The electrolysis progress
was monitored using cyclic voltammetry (Fig. 6). It is shown that,
as coulometry progresses, the anodic peak A1 decreases and disap-
pears when the charge consumption reaches approximately 4e− per
molecule of DITHBD (1), and the new anodic peak (A0) which is re-
lated to the transformation of intermediate (3a) to the corresponding
quinonicform (4a) (Scheme 1, Eq. (III, a), appears. These observations
allow us to propose the pathway in Scheme 1 for the electrochemical
oxidation of DITHBD (1) in the presence of 2a-c as nucleophiles.
According to our results, it seems that the Michael addition reac-
tion of the enolate anion of nucleophiles (2a-c) to electrochemically
generated 1a is faster than the other secondary reactions, leading
to the intermediate 3a-c. The oxidation of these compounds (3a-
c) is easier than the oxidation of the DITHBD (1) by virtue of the
presence of an electron-donating group. The intramolecular reaction
(Scheme 1, reaction (IV, a-c)), occurring via a 1,6-addition reaction,
because of the existence of the ethanedithiol group at the C-4 position
of the o-quinone ring, leads to the formation of the final products (5a-
c).21 It can be seen from the mechanism shown in Scheme 1 that, as
the chemical reaction (Eq. (III, a-c) occurs, quinone 1a is regenerated
through homogeneous oxidation (Eq. (V) and hence, can be reoxidized
at the electrode surface. Thus, as the chemical reaction takes place,
the apparent number of electrons transferred increases from n = 2 to n
= 4 electrons per molecule. The reaction products (5a-c) can also be
oxidized at a lower potential than the starting compound (DITHBD).
However, the oxidation of products 5a-c was circumvented during the
preparative reaction because of the insolubility of the product in mix-
ture of water–acetonitrile (85:15) containing phosphates as the buffer
and supporting electrolyte (pH = 7.0, c = 0.15 M).
Kinetic study.— Electrochemical oxidation of DITHBD (1) in the
presence of 2a-c as nucleophiles was tested by digital simulation. The
simulation was carried out assuming semi-infinite one-dimensional
diffusion and planar electrode geometry. The experimental parame-
ters entered for digital simulation consisted of the following: Estart
,
Figure 5. Cyclic voltammograms of 1.0 mM DITHBD (1) in the presence of 2a (I), 2b (II) and 2c (III) at a glassy carbon electrode, in phosphate buffer solution
(pH = 7.0, c = 0.15 M). Scan rates from (a) to (f) are: 10, 25, 50, 100, 250 and 500 mV s−1, respectively. Inset: Variation of peak current ratio (IPAl /IPC1) versus
scan rate. t = 25 1◦C.

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Journal of The Electrochemical Society, 159 (12) H912-H917 (2012)
neous rate constants (kobs) of reaction of DITHBD (1) with 2a-c have
been estimated by comparison of the simulation results (Fig. 7, curve
Si) with experimental cyclic voltammograms (Fig. 7, curve Ex).
The calculated values of observed homogeneous rate constants,
kobs, for Michael addition reaction of nucleophiles (2a-c) with
quinonic form DITHBD (1a) are 267 6 M−1s−1, 178 3 M−1s−1
,
46 2 M−1s−1 (standard deviation of five independent simulations)
for the nucleophile of acetylacetone (2a), dimedone (2b) and 4-
hydroxycoumarin (2c), respectively.
As can be seen, kobs was found to vary in the order acetylacetone
(2a) > dimedone (2b) > 4-hydroxycoumarin (2c). This is related to
the lower nucleophilicity of 2c, which can be explained as follows.
Notably, 2c is basically a β-ketoester, and the resonance of C = O
of ester with oxygen and, also resonance of keto tautomer of C-
OH with aromatic ring lead to decrease of enol form, therefore the
nucleophilicity of 2c is lower than 2a and 2b. Acetylacetone (2a) is
an open chain β-diketone and dimedone is a cyclic β-diketone. Hence,
the nucleophilicity of 2a is higher than 2b.23 To omit the effect of
the side reactions on the calculation of kobs, the homogeneous rate
constant for side reactions is firstly calculated for DITHBD (1) in the
absence of 2a-c and then it subtracted from the data in the presence
of 2a-c.
Conclusions
The results of this work show that DITHBD (1) is oxidized in
aqueous solution to their respective o-quinone. The quinones are
then attacked by the enolate anion of nucleophiles (2a-c) to form
benzofuran derivatives (5a-c). The overall reaction mechanism for
anodic oxidation of DITHBD (1) in the presence of (2a-c) as the
nucleophiles is presented in Scheme 1. According to our results, it
seems that the Michael reaction of these nucleophiles to the o-quinone
formed leads to the formation of new benzofuran derivatives as final
products. Also, we studied the kinetics of the reaction of the elec-
trochemically generated o-quinone 1a with 2a-c by cyclic voltamme-
try. The simulated cyclic voltammograms show good agreement with
those obtained experimentally. The maximum value of kobs is calcu-
lated in electrochemical oxidation of DITHBD (1) in the presence of
acetylacetone (2a).
Figure 6. Cyclic voltammograms of 0.7 mmol DITHBD (1) in the presence
of 0.7 mmol acetylacetone, at a glassy carbon electrode during controlled
potential coulometry. After consumption of: (a) 0, (b) 40, (c) 70, (d), 95 (e),
130, (f), 160, (g) 190, and (h) 230 C. Inset: Variation of the peak A1 current
(IpA1) vs. consumed charge. scan rate: 100 mV s−1 · t = 25 1◦C.
Eswitch, Eend, t = 25◦C and analytical concentration of DITHBD (1)
and 2a-c. The transfer coefficient (α) was assumed to be 0.5 and
the formal potentials were obtained experimentally as the midpoint
potential between the anodic and cathodic peaks (Emid). All these
parameters were kept constant throughout the fitting of the digitally
simulated voltammogram to the experimental data. The parameter ho-
mogeneous rate constants (kobs) was allowed to change through the
fitting processes. On the basis of Scheme 1, the observed homoge-
Acknowledgments
The authors wish to thankful the Yazd University Research Coun-
cil, IUT Research Council and Excellence in Sensors for financial
support of this research.
Figure 7. Experimental (Ex) and simulated (Si) cyclic voltammograms of 1 mM DITHBD (1), in the presence of 1 mM 2a (I); in the presence of 1 mM 2b (II)
and in the presence of 1 mM 2c (III), at a glassy carbon electrode, in aqueous solution containing phosphate buffer (pH = 7.0, c = 0.15 M). Scan rate: 20 mV s−1
.
t = 25 1◦C.

Journal of The Electrochemical Society, 159 (12) H912-H917 (2012)
H917
References
11. L. Papouchado, G. Petrie, J. H. Sharp, and R. N. Adams, J. Am. Chem. Soc., 90, 5620
(1968).
1. M. Ebadi, Electrochim. Acta, 48, 4233 (2003).
2. AMICBASE-ESSOIL, Database on Natural Antimicrobials, Review Science,
Germany (1999–2002).
12. T. E. Young, J. R. Griswold, and M. H. Hulbert, J. Org. Chem., 39, 1980 (1974).
13. M. D. Ryan, A. Yueh, and C. Wen-Yu, J. Electrochem. Soc., 127, 1489 (1980).
14. D. Nematollahi, M. Rafiee, and A. Samadi-Maybodi, Electrochim. Acta, 49, 2495
(2004).
15. H. Salehzadeh, D. Nematollahi, and M. Rafiee, J. Electroanal. Chem., 650, 226
(2011).
16. F. Varmaghani and D. Nematollahi, Electrochim. Acta, 56, 6089 (2011).
17. K. Izutsu, Electrochemistry in Nonaqueous Solutions, p. 87 and p. 229, Wiley-VCH,
Weinheim (2002).
18. D. Nematollahi, M. Rafiee, and L. Fotouhi, J. Iran. Chem. Soc., 6, 448 (2009).
19. D. Nematollahi and H. Goodarzi, J. Electroanal. Chem., 510, 108 (2001).
20. D. Nematollahi and H. Goodarzi, J. Org. Chem., 67, 5036 (2002).
21. S. M. Golabi and D. Nematollahi, J. Electroanal. Chem., 430, 141 (1997).
22. D. Nematollahi and S. M. Golabi, Bull. Electrochem., 14, 97 (1998).
23. F. A. Carey and R. J. Sundberg, Advanced Organic Chemistry Part A: Structure and
Mechanisms, 3rd ed., Plenum Press, New York (1990).
3. B. A. Keay, Comprehensive Heterocyclic Chemistry II, A. R. Katritzky, C. W. Rees,
and E. F. V. Scriven, Eds., p. 395, Vol. 2, Pergamon, Oxford (1996).
4. G. E. Schneiders and R. J. Stevenson, J. Org. Chem., 44, 4710 (1979).
5. Z. Yang, P. M. Hon, K. Y. Chui, Z. L. Xu, H. M. Chang, C. M. Lee, Y. X. Cui,
H. N. C. Wong, C. D. Poon, and B. M. Fung, Tetrahedron Lett., 32, 2061
(1991).
6. T. Murare and T. Takahashi, Tetrahedron, 24, 2177 (1968).
7. R. S. Ward, Nat. Prod. Rep., 16, 75 (1999).
8. J. Schopfer, H. Fretz, B. Chaudhuri, L. Murri, E. Seeber, L. Meijer, O. Lozach,
E. Vangrevelinghe, and P. Furet, J. Med. Chem., 45, 1741 (2002).
9. M. Rudolph, J. Electroanal. Chem., 529, 97 (2002). (http://www.digielch.de).
10. A. J. Bard and L. R. Faulkner, Electrochemical Methods, 2nd ed., p 240, Wiley, New
York (2001).