Electrochemical synthesis of some 6-amino-5-hydroquinone-1,3-dimethyluracil derivatives: A green, simple and efficient strategy

Article abstract of DOI:10.1149/2.0321702jes

In order to synthesize some of new 6-amino-5-hydroquinone-1,3-dimethyluracil derivatives, the electrochemical oxidation of hydroquinones (1a-c) was carried out in the presence of 6-amino-1,3-dimethyluracil as a nucleophile in an aqueous phosphate buffer solution. The results show that electrogenerated p-benzoquinone moieties (1a′-c′) participate in the reaction with 6-amino-1,3-dimethyluracil via the EC mechanism to form the corresponding uracil derivatives (3a-c). The electrosynthesis of these compounds (3a-c) was performed successfully in an aqueous solution at carbon rod electrodes, without using any toxic reagents, catalyst or solvents and the products were finally produced in high yield and purity. The proposed method has a novel viewpoint in the synthesis of potential anticancer/antiviral uracil-base drugs.

Full text of DOI:10.1149/2.0321702jes

G10
Journal of The Electrochemical Society, 164 (2) G10-G16 (2017)
0
013-4651/2017/164(2)/G10/7/$33.00 © The Electrochemical Society
Electrochemical Synthesis of Some 6-Amino-5-hydroquinone-
,3-dimethyluracil Derivatives: A Green, Simple and Efficient
Strategy
1
a,z
b
a
Mehdi Shabani-Nooshabadi, Mohsen Moradian, and Samira Dadkhah-Tehrani
a
Department of Analytical Chemistry, Faculty of Chemistry, University of Kashan, Kashan, Iran
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, Iran
b
In order to synthesize some of new 6-amino-5-hydroquinone-1,3-dimethyluracil derivatives, the electrochemical oxidation of hy-
droquinones (1a-c) was carried out in the presence of 6-amino-1,3-dimethyluracil as a nucleophile in an aqueous phosphate buffer
ꢀ
ꢀ
solution. The results show that electrogenerated p-benzoquinone moieties (1a -c ) participate in the reaction with 6-amino-1,3-
dimethyluracil via the EC mechanism to form the corresponding uracil derivatives (3a-c). The electrosynthesis of these compounds
(
3a-c) was performed successfully in an aqueous solution at carbon rod electrodes, without using any toxic reagents, catalyst or
solvents and the products were finally produced in high yield and purity. The proposed method has a novel viewpoint in the synthesis
of potential anticancer/antiviral uracil-base drugs.
©
2016 The Electrochemical Society. [DOI: 10.1149/2.0321702jes] All rights reserved.
Manuscript submitted September 7, 2016; revised manuscript received November 28, 2016. Published December 8, 2016.
Dearomatization reactions have been widely recognized as a pow-
erful tactic for the synthesis of complex molecules from simple aro-
this work are the in situ production of quinone in the electrode in-
terface area as an unsoluble reagent in the buffer solution media and
replacing toxic and dangerous oxidizing reagents with electrons and
reduce energy consumption of the reaction.
1
–5
matic substrates. In this way, the controlled oxidation of arenes is
very important for a substitution of different nucleophiles on the oxi-
6
dized component. This tactic can perform in organic synthesis with
an electrochemical method like constant potential coulometry. The
main benefits of using electrochemistry include high atom economy
Experimental
(
conversion efficiency of the process) and reduction of waste gener-
Apparatus and reagents.—Cyclic voltammetry (CV), preparative
electrolysis and controlled-potential coulometry were performed us-
ing a μ-AUTOLAB potentiostat/galvanostat model μIII AUTO 71174
connected to a Pentium IV personal computer through a USB electro-
chemical interface. The pH of the buffer solutions was adjusted using
a pH-meter (Corning, Model 140) with a double junction glass elec-
trode. The working and counter electrodes used in the voltammetry
ated by the several chemical processes as well as of the time and work
required to carry them out.
In recent years, organic electrosynthesis has been known as a
7
–10
green methodology in organic chemistry.
used as clean reduction reactants, it is possible to replace toxic and
dangerous reagents
PhI(TFA) , F-PhI(TFA)
Since electrons can be
11–29
2
such as hypervalent iodine (exmp. PhI(OAc) ,
30–32
33
2
2
2
),
Pb(OAc)
4
,
oxone as the source of sin-
experiments were a glassy carbon disc electrode (0.031 cm area) and
34
35
glet oxygen, [{(-)-sparteine}
2
Cu ] complex and other reagents
2
O
2
a platinum wire electrode respectively. The working electrode used
in controlled-potential coulometry and macroscale electrolysis was
an assembly of tree ordinary carbon rods (9 mm diameter and 6 cm
with an electric current. Essential reactions such as carbon-carbon,
carbon-nitrogen, carbon-sulfur and carbon-oxygen bond formation
36
2
and functional group interconversions can be obtained from electron
length). A large platinum gauze cylinder (10 cm area) constituted
37
transfer. These reactions in the electroorganic synthesis technique
can be carried out at high selectivity, can reduce energy consumption,
and can be carried at room temperature and without using of cata-
lyst and toxic reagents. Classical procedures of organic synthesis
take place in organic solvents with low volatility, but electrochemical
synthesis reactions can be performed in an aqueous medium with-
out organic solvents moreover, hydroalcoholic mixtures also are an
excellent media to carry out electrosynthesis reactions.
Due to the biological and environmental significance of hydro-
quinone such as application as antioxidant, production of dyes, phar-
maceutical, cosmetics and photographic industries, the synthesis of
hydroquinone derivatives is very important
has been extensively studied.
Uracil is one of the four nucleobases in the nucleic acid of
RNA (ribonucleic acid) building block. Uracil derivatives are used
as anticancer and antiviral drugs, pesticides and anti-photosynthetic
the counter electrode. The potential of working electrode was mea-
sured versus Ag/AgCl (3.0 M KCl) electrode (all electrodes were from
Azar Electrode Company). The glassy carbon electrode was polished
with a polishing cloth before each measurement. The electrolysis was
performed under a constant-potential condition in a cell with two com-
partments separated by an ordinary porous fritted glass diaphragm (a
tube with 4 cm diameter). During electrolysis, a magnetic stirrer was
38
7
39,40
1
13
used. The final products characterized using H NMR, C NMR,
FT-IR spectroscopic techniques and CHNS analyzer. Fourier trans-
form infrared (FT-IR) spectra were obtained using a Perkin-Elmer
781 spectrophotometer. The NMR spectra were recorded on a Bruker
Avance DPX 400 MHz instrument spectrometer at 400 and 100 MHz
in DMSO as a solvent in the presence of tetramethylsilane as internal
standard.
41–43
and their redox system
44–47
The hydroquinones (hydroquinone, 2-methylhydroquinone and
2,3-dimethylhydroquinone) and 6-amino-1,3-dimethyluracil were
reagent grade material and purchased from Merck chemical com-
pany. The NaH PO , Na HPO and other acids and bases were of
48–54
herbicides.
In the present study, we investigated a simple electrochemi-
cal method for the synthesis of new 6-amino-5-hydroquinone-1,3-
dimethyluracil derivatives by the electrochemical oxidation of some
hydroquinone moieties in the presence of 6-amino-1,3-dimethyluracil.
The reaction was performed in an aqueous media and the target prod-
ucts were produced in excellent yield and purity that enables multiple
transformations in the one-pot reaction sequence. Moreover, the re-
action was carried out at room temperature and using any organic
solvents and catalysts under green conditions. The other novelties of
2
4
2
4
pro-analysis grade from Merck chemical company. These chemicals
and solvents were used without further purification. All experiments
were carried out at room temperature.
General procedure for the electroorganic synthesis of 6-amino-
-hydroquinone-1,3-dimethyluracil.—In a general procedure, phos-
5
phate buffer solution (pH 7.0, 0.1 M) containing of the 0.25 mmol of
hydroquinones (1a-c) and 0.25 mmol of 6-amino-1,3-dimethyluracil
(
2) was electrolyzed at suitable potential (0.40, 0.39 and 0.37 V vs
Ag/AgCl electrode for the 1a, 1b and 1c respectively) in a divided
zE-mail: m.shabani@kashanu.ac.ir
cell. The progress of the reaction was monitored by the method of
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Journal of The Electrochemical Society, 164 (2) G10-G16 (2017)
CV during the electrolysis. In order to reactive surface of the graphite
G11
anode, it washed occasionally in acetone. The electrolysis was termi-
nated when the decay of current became more than 95% of its initial
amount. At the end of electrolysis, the precipitated solid in its sus-
pended form was collected by filtration and it was washed several
times with water. Finally, for further purification, the products were
recrystallized from ethanol.
Characteristic of products.—6-amino-5-(2,5-dihydroxyphenyl)-
1
3
1
1
,3-dimethyluracil (3a).—Isolated in 96% yield as beige solid: m.p. >
◦
00 C, decompose; FT-IR (KBr disc): 519.75, 569.61, 769.86, 972.85,
227.68, 1262.50, 1387.38, 1424.55, 1466.04, 1546.88, 1616.40,
−1 1
641.94, 1679.75, 3258.22 cm ; H NMR (DMSO, 400 MHz): 3.22
), 3.46 (s, 3H, N-CH
), 6.62 (d, 1H, J = 8.47 Hz,
Ar-H), 7.18 (d, 1H, J = 8.47 Hz, Ar-H), 7.22 (s,1H, Ar-H), 9.03
-NH , exchangeable hydrogens), 11.86 (-OH, exchangeable hydro-
(
s, 3H, N-CH
3
3
(
2
13
gens); C NMR (DMSO, 100 MHz): 27.77, 30.97, 91.18, 104.58,
11.46, 112.35, 124.99, 128.55, 145.54, 151.37, 153.27, 158.72; ele-
mental analysis (CHNS) for C10 : calcd: C 54.75, N 15.96, H
.98; found: C 54.39, N 16.09, H 5.048.
1
8 4 3
H N O
4
6-amino-5-(2,5-dihydroxy-4-methylphenyl)-1,3-dimethyluracil
(
3b) and 6-amino-5-(2,5-dihydroxy-3-methylphenyl)-1,3-
ꢀ
dimethyluracil (3b ).—Isolated in 94% yield as gray solid:
m.p. >300 C, decompose; FT-IR (KBr disc): 515.79, 602.01,
◦
7
10.59, 745.68, 771.62, 970.58, 1194.47, 1284.10, 1341.67, 1417.70,
−
1
1
1464.23, 1549.27, 1637.55, 1679.81, 2956.17, 3291.91 cm
; H
Figure 1. Cyclic voltammograms of 1.0 mM hydroquinone in the absence (a)
and in the presence (b) of 1.0 mM 6-amino-1,3-dimethyluracil, and (c) 1.0
mM 6-amino-1,3-dimethyluracil singly. Conditions: glassy carbon electrode,
3
(3b)), 2.42 (s, 3H,
ꢀ
ꢀ
3
−1
phosphate buffer solution (pH 7.0, 0.1 M), scan rate = 100 mVs , T = 25 ±
ꢀ
◦
2
,
1 C.
1
1.27 (-OH, exchangeable hydrogens), 11.74 (−OH, exchangeable
13
Electrochemical oxidation of hydroquinone (1a) in the ab-
sence and presence of 6-amino-1,3-dimethyluracil (2).—The cyclic
voltammogram of 1.0 mM hydroquinone in the aqueous phosphate
buffer solution (pH 7.0, 0.1 M) is shown in Fig. 1, curve a. In this
hydrogens); C NMR (DMSO, 100 MHz): 16.71, 17.01, 27.32,
30.57, 30.89, 90.71, 91.25, 101.64, 103.68, 112.30, 112.63, 119.63,
121.73, 122.21, 124.31, 127.34, 128.03, 144.54, 145.08, 150.96,
151.02, 151.11, 152.86, 158.22, 158.33; elemental analysis (CHNS)
condition, the voltammogram shows one anodic peak (A
1
) in the pos-
for C11
10 4 4
H N O : calcd: C 56.31, N 15.15, H 5.45; found: C 56.87, N
itive going scan and corresponding cathodic peak (C ) in the negative
1
14.89, H 5.478.
going scan. These anodic and cathodic peaks represent the transfor-
ꢀ
mation of hydroquinone (1a) to p-benzoquinone (1a ) and vice versa
6-amino-5-(2,5-dihydroxy-3,4-dimethylphenyl)-1,3-dimethylur-
55
within a quasi-reversible two electron process. It is notable that the
oxidation of hydroquinone to quinone is not a single electron transfer
step (E reaction) and it is a series of electron transfer protonation reac-
acil (3c).—Isolated in 95% yield as yellowish gray solid: m.p.
>
◦
300 C, decompose; FT-IR (KBr disc): 423.53, 518.85, 612.58,
7
48.25, 979.96, 1084.66, 1212.88, 1285.09, 1336.61, 1448.07,
56–58
−
1
1
tions (ECEC, EECC or ECEEC) depending on the pH value.
The
1
547.99, 1611.32, 1642.10, 1687.57, 2954.77, 3418.82 cm
), 2.40 (s, 3H, Ar-
), 7.20 (s, 1H, Ar-H),
, exchangeable hydrogens), 11.09 (-OH, exchangeable
; H
electrochemical oxidation of hydroquinone (1a) in the presence of 1.0
mM 6-amino-1,3-dimethyluracil (2) as a nucleophile was investigated
in some details (Fig. 1, curve b). It shows that the current of cathodic
peak C counterpart of the anodic peak A reduced and the current of
NMR (DMSO, 400 MHz): 2.14 (s, 3H, Ar-CH
CH ), 3.25 (s, 3H, N-CH ), 3.56 (s, 3H, N-CH
.95 (-NH
hydrogens); C NMR (DMSO, 100 MHz): 11.82, 13.98, 27.33,
3
3
3
3
8
2
13
1
1
the anodic peak counterpart of A
these evidences confirm this fact that the p-benzoquinone (1a ) formed
1
increased in the presence of 2. Both
3
1
0.93, 91.17, 101.35, 114.74, 118.01, 120.17, 121.27, 127.91, 144.64,
51.05, 158.29; elemental analysis (CHNS) for C11 : calcd:
ꢀ
10 4 3
H N O
at the surface of the electrode is consumed by a chemical reaction with
C 57.72, N 14.42, H 5.88; found: C 57.91, N 14.51, H 5.989.
2
2
. The cathodic shift potential of the peak C , when uracil derivative
is present, is due to the change from a chemically reversible electron
transfer reaction to a chemically irreversible reaction (Fig. 1, curve
b), (last term of the Nernst equation is changing). The voltammo-
Results and Discussion
The electrochemical synthesis for the production of novel 6-
amino-5-hydroquinone-1,3-dimethyluracil compounds was outlined
in Scheme 1.
gram exhibits two anodic peaks A
1
and A
2
and one cathodic peak C
1
.
Comparison of the voltammograms b and c reveals that the peak A
2
(
(
curve b) corresponds to the oxidation of 6-amino-1,3-dimethyluracil
2). The Fig. 1, curve c, shows the cyclic voltammogram of 1.0 mM
of 2 in the absence of hydroquinone under the optimum conditions.
The positive shift of the A peak in the presence of 2 (Fig. 1, curve
b), which is enhanced during the repetitive recycling of potential (Fig.
), confirms the quinones produced electrochemically at the electrode
1
2
interface and then consumed during the reaction with 6-amino-1,3-
dimethyluracil and led to the formation of the product 3.
In the curves of a-j in Fig. 3 are shown the effect of different poten-
tial sweep rate on the cyclic voltammograms of 1.0 mM hydroquinone
in the presence of 1.0 mM 2 at pH 7.0. It can be seen, upon increasing
Scheme 1. The electrochemical synthesis of new 6-amino-5-hydroquinone-
1,3-dimethyluracil.
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Journal of The Electrochemical Society, 164 (2) G10-G16 (2017)
Figure 4. Double potential step chronoamperometry of 1.0 mM hydroquinone
a) in the absence of 1.0 mM 6-amino-1,3-dimethyluracil and (b) in the pres-
(
ence of 1.0 mM 6-amino-1,3-dimethyluracil, at a glassy carbon electrode in
phosphate buffer solution (pH 7.0, 0.1 M). Pulse length, 12 s. The first potential
step was from E0 = 0.00 V to E1 = 0.40 V and the second step from E1 =
◦
Figure 2. Multi-cyclic voltammograms of 1.0 mM hydroquinone in the pres-
0.40 V to E2 = −0.14 V vs. Ag/AgCl. T = 25 ± 1 C.
ence of 1.0 mM 6-amino-1,3-dimethyluracil, at a glassy carbon electrode, in
−1
phosphate buffer solution (pH 7.0, 0.1 M); scan rate, 100 mVs
.
The determination of the existence of chemical reaction be-
tween electrochemically generated p-benzoquinone and 6-amino-1,3-
dimethyluracil is also prove by the double potential step chronoam-
perometry. The curve a in Fig. 4, shows the double potential step
chronoamperogram of 1a in the absence of 2 that it is correspond-
ing to an E mechanism, also, curve b in this Figure, shows dou-
ble step chronoamperogram of 1a in the presence of 2. As can
be seen in the figure, the currents of hydroquinone oxidation are
equal in the absence and presence of 2. While the current of
the reduction of p-benzoquinone decreases in the presence of 6-
amino-1,3-dimethyluracil. These behaviors adopt the EC mechanism
1
the potential sweep rate, the height of cathodic peak C increases. The
aforesaid increasing at higher scan rates is related to reducing the time
needed for the chemical reaction of 6-amino-1,3-dimethyluracil (2)
ꢀ
with p-benzoquinone (1a ). A similar situation is also observed when
the concentration ratio of 2 to 1a was decreased. Furthermore, the
C1
A1
peak current ratio (I
p
/I
p
) slightly intensifies with increasing scan
rates (Fig. 3, inset), which confirms a chemical reaction immediately
after the electron transfer step.
59,60
(electrochemical-chemical reaction)
in the reaction between 1a
and 2 (Scheme 2).
In order to determine the effect of pH, behavior of the electro-
chemical oxidation of hydroquinone (1a) was studied in the absence
and presence of 6-amino-1,3-dimethyluracil (2) in different pH val-
C1
A1
ues. A peak current ratio (I
P
/I
P
) of hydroquinone in acidic and
neutral conditions is almost constant and near to unity particularly
during recycling of the potential, which it is because of stability of
p-benzoquinone produced at the surface of the electrode under the
experimental conditions. In the other words, in a pH range of 3.0–7.0,
61,62
63–65
the side reactions such as hydroxylation
or dimerization
are
too slow to be observed on the time scale of cyclic voltammetry. In
C1
A1
basic media (pH > 7.0), the peak current ratio (I
P
/I
P
) is less than
unity and decreases with increasing the pH value. These variations
can be related to the increasing of the acidic dissociation reaction of
hydroquinone; consequently, the anionic forms of 1a are produced in
the reaction media. Therefore, the rate of the coupling reaction of the
anionic or dianionic forms of hydroquinone with p-benzoquinones
65
increases (dimerization side reactions). Instead, in acidic solution,
in the presence of 6-amino-1,3-dimethyluracil (2), 2 is inactive toward
a Michael addition reaction with p-benzoquinone due to the protona-
tion of the amino functional group. Accordingly, the peak current ratio
C1
A1
(
I
p
/I
p
) increases with decreasing of the pH values. This behavior
is shown in Fig. 5 for pH values between 4.0 and 7.0. Thus, phosphate
fb ou rf ft eh ri ss or el ua ct it oi on n w. ith pH = 7.0 was selected as the optimum solution
Controlled-potential coulometry was carried out in the phosphate
buffer solution (pH = 7.0, 0.1 M) containing 0.25 mmol hydroquinone
and 0.25 mmol of 6-amino-1,3-dimethyluracil. In order to monitor
the electrolysis progress and determination of the number of electrons
Figure 3. Typical cyclic voltammograms of 1.0 mM hydroquinone in the
presence of 1.0 mM 6-amino-1,3-dimethyluracil at a glassy carbon electrode,
in phosphate buffer solution (pH 7.0, 0.1 M). Scan rates from (a) to (j) are: 20,
−1
5
0, 100, 200, 300, 400, 500, 700, 800 and 1200 mV s , respectively. Inset:
C1 A1
◦
variation of peak current ratio (Ip /Ip ) versus scan rate (ν). T = 25 ± 1 C.
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Journal of The Electrochemical Society, 164 (2) G10-G16 (2017)
G13
Scheme 2. Mechanism of the reaction.
transferred for each hydroquinone molecule, the cyclic voltamme-
try was used during the electrolysis (Fig. 6). The electrolysis was
terminated when the decay of the current become more than 95%
consumption of this electrochemical reaction (ca. 48 C), that it is in
accordance with the general mechanism proposed in Scheme 2.
All of the evidence in Experimental section such as cyclic
voltammetry, controlled potential coulometry, double potential step
of its initial amount. According to our results, all anodic (A
1
and
A
2
) and cathodic (C ) peaks decrease and disappear when the charge
1
−
consumption becomes 2e per molecule of 1a, during the progress
of coulometry. The inset of Fig. 6 shows the number of coulombs
Figure 6. Cyclic voltammograms of 0.25 mmol hydroquinone in the presence
of 0.25 mmol 6-amino-1,3-dimethyluracil, at a glassy carbon electrode during
controlled potential coulometry at 0.40 V versus Ag/AgCl electrode, after
consumption of: (a) 0, (b) 10, (c) 22, (d) 30 and (e) 40 C. Inset: Variation
Figure 5. Cyclic voltammograms of 1.0 mM hydroquinone in the presence of
1.0 mM 6-amino-1,3-dimethyluracil at a glassy carbon electrode in phosphate
A1
of peak current (Ip ) versus charge consumed during controlled potential
buffer solution at various pH values (4.0, 5.0, 6.0 and 7.0); scan rate, 100
−
1
◦
−1
◦
mVs . T = 25 ± 1 C.
Coulometry. Scan rate, 100 mV s . T = 25 ± 1 C.
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Journal of The Electrochemical Society, 164 (2) G10-G16 (2017)
Figure 9. Effect of current density on the yield of product 3a. Charge con-
sumed 50 C.
Figure 7. The potential-time diagram during constant current electrolysis
of 0.25 mmol hydroquinone in the presence of 0.25 mmol 6-amino-1,3-
dimethyluracil, at a glassy carbon electrode in phosphate buffer solution (pH
scribed for controlled-potential coulometry. Due to the effect of cur-
rent density on the yield and purity of the product, it was investigated
◦
7
.0, 0.1 M). Rotation rate: 1000 rpm. T = 25 ± 1 C.
−
2
in the range of 0.02 to 2.0 mA cm at the same condition of elec-
trolysis (0.25 mmol of hydroquinone and 0.25 mmol of 6-amino-1,3-
dimethyluracil in phosphate buffer solution at pH = 7.0, 0.1 M and
at room temperature). The effect of current density on the starting
potential during constant-current electrolysis is shown in Fig. 7. Inas-
chronoamperometry and also spectroscopic data of the isolated prod-
uct, proved that the product 3a is formed through anodic oxidation of
hydroquinone and reaction with 6-amino-1,3-dimethyluracil; accord-
ing to the pathway described in Scheme 2 (EC mechanism). In the first
−
2
much as, in current density of 0.9 mA cm , the generation potential is
about 0.40 V and this potential is nearest amount to the oxidation po-
tential of hydroquinone, only the hydroquinone can be oxidized with
an acceptable rate while, 2 and/or product 3a don’t oxidize. Thus, the
ꢀ
ꢀ
step (E), 1a -c would be generated at the surface of the electrode, and
in the second step (C step), these components participate as a Michael
acceptor in a chemical reaction with 6-amino-1,3-dimethyluracil and
produced the intermediate d in the solution. Then, d is rearranged
and converts to the intermediate e. In the final step, the target prod-
ucts 3a-c provide in the media of reaction from tautomerization of e.
The products 3a-c are insoluble in the phosphate buffer media and
precipitate.
−
2
current density of 0.9 mA cm was selected as an optimum value.
To further investigation on galvanostatic studies, constant-current
electrolysis was carried out in an aqueous phosphate buffer solution
(
pH = 7.0, 0.1 M) containing 0.25 mmol of 1a and 0.25 mmol of 2,
−2
under the 0.9 mA cm as optimum current density, in a divided cell.
The monitoring of the electrolysis progress was performed by cyclic
voltammetry. The results show that, proportional to the advancement
Furthermore, the synthesis of product 3a was also performed via
the constant-current electrolysis under the same conditions as de-
of coulometry, the current of anodic peaks A
1
and A
2
decrease. A
A1
nonlinear equation between I
p
and the charge consumed during the
A1
oxidation of hydroquinone in the presence of 2 has been found (I
p
−
0.034Q
2
=
37.26e
, R = 0.9947) (Fig. 8).
The effect of current density on the yield of the reaction is shown
in Fig. 9. In this study, the current density varied between 0.1 and 1.3
−
2
mA cm , while the other parameters were kept constant. The results
−
2
show that, with increasing the current density from 0.9 mA cm , the
yield of product decreases, because higher current density can cause
the addition of side reactions.
Conclusions
The present study is the first reported work in the electrosynthesis
of biologically significant products (3a-c) that have been produced di-
rectly and efficiently from the electrooxidation of hydroquinones (1a-
c) and 6-amino-1,3-dimethyluracil (2). The reaction was carried out
in water as a reaction media without using any toxic solvent, reagent
or catalyst. This reaction was performed in the mild and green condi-
tions at room temperature. Our results indicate that electrochemically
ꢀ
ꢀ
generated of 1a -c act as a Michael acceptor and then are attacked
by 2 and after rearrangement convert to the target compounds (3a-c).
The products obtained in high yield and purity through one-pot pro-
cess and also, this procedure can lead to a minimization of the side
reactions.
Figure 8. Variation of IpA1 versus consumed charge during constant current
electrolysis of 0.25 mmol hydroquinone in the presence of 0.25 mmol 6-amino-
1
,3-dimethyluracil at a glassy carbon electrode in phosphate buffer solution
−2
(
pH 7.0, 0.1 M). Current density: 0.9 mA cm
.
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Journal of The Electrochemical Society, 164 (2) G10-G16 (2017)
G15
Acknowledgments
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