An activity scale of cathode materials for the electrochemical cyclisation of allyl 2-bromobenzyl ether

Article abstract of DOI:10.1016/j.electacta.2017.03.016

The electrocatalytic activity of 10 cathode materials (Ag, Au, Cu, Glassy carbon (GC), Ni, Mg, Mn, Pb, Pt and Ti) was examined for the intramolecular cyclisation reaction of allyl 2-bromobenzyl ether to 2-methyl benzopyran. The influence of the cathode materials on the electrocatalytic activity was tested by means of cyclic voltammetry (CV) in an electrolyte solution of allyl 2-bromobenzyl ether (1?mM) + tetrabutylammonium perchlorate (0.1?M) (Bu₄NClO₄) in methanol (MeOH). On Au, GC, Ni, Mg, Mn, Pb and Pt one single reduction wave was measured while Ag and Cu exhibited two cathodic reduction waves. Ti did not show a voltammetric response. The best electrocatalytic activity was obtained on Ag which showed a shift of the reduction peak potential of 771?mV with respect to GC, the most inert material. In addition to the screening, rotating disk experiments (RDE) in combination with Koutecky Levich analysis and product formation during electrosynthesis were performed. Koutecky Levich analysis of the RDE at peak potential showed that one-electron was transferred at Au, GC, Ni, Mg, Mn, Pb and Pt. On Ag and Cu the number of transferred electrons determined with Koutecky-Levich depends on the potential and can be tuned to specific one- or two-electron transfer. Electrosynthesis showed that on Au, GC, Ni, Mg, Mn, Pb and Pt exclusively 5-methyl benzopyran was formed. On Ag and Cu product formation was depended on the potential and 2-methyl benzopyran and allyl benzyl ether (not cyclized product) were both formed.

Full text of DOI:10.1016/j.electacta.2017.03.016

Accepted Manuscript
Title: An activity scale of cathode materials for the
electrochemical cyclisation of allyl 2-bromobenzyl ether
Authors: Bart Vanrenterghem, Tom Breugelmans
PII:
S0013-4686(17)30480-2
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.electacta.2017.03.016
EA 29050
To appear in:
Electrochimica Acta
Received date:
Revised date:
Accepted date:
30-10-2016
3-3-2017
3-3-2017
Please cite this article as: Bart Vanrenterghem, Tom Breugelmans, An activity scale
of cathode materials for the electrochemical cyclisation of allyl 2-bromobenzyl ether,
Electrochimica Acta http://dx.doi.org/10.1016/j.electacta.2017.03.016
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

An activity scale of cathode materials for the electrochemical
cyclisation of allyl 2-bromobenzyl ether
Bart Vanrenterghema* and Tom Breugelmansa
a University of Antwerp, Research Group Advanced Reactor Technology, Universiteitsplein 1, 2610 Wilrijk, Belgium
* Corresponding author: bart.vanrenterghem@uantwerpen.be
1

Abstract
The electrocatalytic activity of 10 cathode materials (Ag, Au, Cu, Glassy carbon (GC), Ni, Mg, Mn, Pb, Pt and
Ti) was examined for the intramolecular cyclisation reaction of allyl 2-bromobenzyl ether to 2-methyl
benzopyran. The influence of the cathode materials on the electrocatalytic activity was tested by means of
cyclic voltammetry (CV) in an electrolyte solution of allyl 2-bromobenzyl ether (1mM) +
tetrabutylammonium perchlorate (0.1 M) (Bu4NClO4) in methanol (MeOH). On Au, GC, Ni, Mg, Mn, Pb and Pt
one single reduction wave was measured while Ag and Cu exhibited two cathodic reduction waves. Ti did not
show a voltammetric response. The best electrocatalytic activity was obtained on Ag which showed a shift of
the reduction peak potential of 771 mV with respect to GC, the most inert material. In addition to the
screening, rotating disk experiments (RDE) in combination with Koutecky Levich analysis and product
formation during electrosynthesis were performed. Koutecky Levich analysis of the RDE at peak potential
showed that one-electron was transferred at Au, GC, Ni, Mg, Mn, Pb and Pt. On Ag and Cu the number of
transferred electrons determined with Koutecky-Levich depends on the potential and can be tuned to
specific one- or two-electron transfer. Electrosynthesis showed that on Au, GC, Ni, Mg, Mn, Pb and Pt
exclusively 5-methyl benzopyran was formed. On Ag and Cu product formation was depended on the
potential and 2-methyl benzopyran and allyl benzyl ether (not cyclized product) were both formed.
2

1 Introduction
In recent years there is been a growing search for clean, catalytic and environmentally friendly methods for
the synthesis of heterocyclic compounds [1]. The great interest for these molecules is due to important
applications in pharmaceuticals [2]–[4], pesticides [5], dyes [6] and synthetic applications [7]. The classical
organic synthesis of heterocycles is of a complex nature, requiring a large number of reaction steps and the
use of auxiliaries which results in a low selectivity [1]. In addition the reaction is often catalysed by tributyl
tinhydride (Bu3SnH) [8]–[10]. The high neurotoxicity and difficulties for a total removal of tin out of the
reaction mixture have triggered the search for other alternative synthesis methods. Organic electrosynthesis
may offer an interesting alternative i.e. the electron being a cheap, clean and energy efficient reagent [11].
Reductive radical cyclisation of aryl halides onto an unsaturated bond is frequently used to construct fused
aromatics in heterocyclic organic synthesis [8], [12]. In Figure 1 the possible reaction mechanism that can
occur is displayed. The reduction of aryl halides, certainly at inert electrodes, occurs through a dissociative
electron transfer leading to the scission of the carbon-halogen bond [13], [14]. This process can occurs
through 2 possible mechanisms. A first possibility, which is shown in equations 1 and 2 is that bond rupture
occurs in a stepwise manner with the formation of an intermediate radical anion. The second possibility is
the concerted way yielding directly in a radical anion (equation 3). After the radical is formed, it can undergo
a cyclisation reaction after which it is reduced (equation 4 and 5) or it can be directly reduced, without
cyclisation reaction (equation 6).
Figure 1: Possible reaction pathways to construct fused aromatic molecules starting from allyl 2-bromobenzyl ether
A disadvantage to the use of organic halides in electrosynthesis is that the electrochemical activation of C-X
bonds, especially in chlorides and bromides, requires application of high negative potentials [15] . In
addition, as shown in the previous equations (1-6), the reaction pathway is complex. The usage of an
appropriate electrocatalyst to stimulate specific product formation is crucial to increase the selectivity.
Several approaches based on homogeneous electrocatalysis, mainly with transition metals complexes [1],
[8], [16]–[19], have been investigated to circumvent the high overpotential and selectivity. When the
3

carbon-halogen bond is reductively cleaved with electron-transfer mediators the potentials correspond to
those of the reduction of the mediator. Although the formal electrode potential of the mediators is generally
more positive than the potential required for direct reduction of carbon-halogen bond, this approach gives
rise to low selectivity and difficulties for the purification of the reaction mixture. Attempts to overcome
these obstacles for carbon-halogen bond activation are directed towards improving the catalytic activity of
the electrode material by changing from homogeneous to heterogeneous catalysts [15].
Studies of the carbon-halogen bond rupture have already indicated the intrinsic potential of several bulk
metals such as Ag, Ni or Cu [13], [15]. Jouikov et all. have for instance shown that functionalized graphene
requires strongly negative potentials of ca. -1.8 V in non-aqueous media [20] . On the other hand Dunach et
all. have shown that by using Ni complexes the high overpotential can be reduced [1], [18], [23]. Despite the
large number of papers for homogeneous catalyst there is little work for the catalytic activity of
heterogeneous bulk materials on the intermolecular cyclisation reaction. Hence there is a need for an
electrochemical activity scale of cathode metals for the synthesis of heterocyclic compounds.
In this context, the aim of the present work will be to investigate the electrocatalytic activity of bulk metals
as cathode material for the intramolecular cyclisation reaction. The electrocatalytic activity will be tested for
the cyclisation reaction of allyl 2-bromobenzyl ether to 2-methyl benzopyran, which can be considered as a
model reaction [8], [22]. The formation of benzopyran is of great importance for the pharmaceutical industry
as it is an important building block for numerous drugs [23]. The purpose of this work is not to show the
detailed reaction mechanism but to look at the overall reaction that occurs meaning the formation of allyl 2-
bromobenzyl ether or 2-methylbenzopyran.
Towards these directions our specific objectives are: (i) screening of Ag, Au, Cu, Glassy carbon (GC), Mg, Mn,
Ni, Pb, Pt and Ti as cathode materials for the intramolecular cyclisation of allyl 2-bromobenzyl ether by
means of cyclic voltammetry; (ii) study of the electron transfer through linear sweep voltammetry (LSV) in
combination with rotating disk experiments (RDE) and (iii) batch electrosynthesis of 2-methyl benzopyran by
means of experiments performed under potential control.
4

2 Experimental
2.1 Preparation of the cathode materials
10 cathode materials were selected for the screening; Ag, Au, Cu, Glassy carbon (GC), Mg, Mn, Ni, Pb, Pt and
Ti. The choice of these materials is based on previous research regarding C-X bond rupture [15]. To exclude
the influence of the morphology and consider only the intrinsic catalytic activity of the material all cathode
materials where polished to prior extend. The polishing procedure consisted of a sequential polishing with 1
µm and 0.3 µm alumina powder (Struers). The electrochemical measurements were conducted with an
autolab potentiostat/galvanostat PGSTAT 302F in a standard three-electrode electrochemical cell with a Pt
wire counter electrode and Ag/AgCl (Saturated) reference electrode. The reference electrode was separated
from the working electrode through a salt bride to prevent chloride or water contamination in the
measurement medium.
The electrochemical characterisation of the different cathode materials was tested in a de-aerated
electrolyte solution containing 0.1 M tetrabutylammonium perchlorate (Bu4NClO4) (Acros, 99 %+) + 1 mM
allyl 2-bromobenzyl ether (Sigma Aldrich, 95%) in MeOH (MeOH) (Sigma Aldrich, HPLC-grade). The rotation
rate of the electrode was controlled with a radiometer CTV101.
Electrolysis experiments were carried out in a small volume (10 mL) electrochemical cell. The electrolyte was
purged with nitrogen to remove all dissolved oxygen. Identical working-, reference- and counter electrodes
were used as during the electrochemical characterisation. Experiments were carried out under potential
control and identification and distribution were investigated with a Thermo Trace 1300 GC-FID in a stirred
solution of 10 mM allyl 2—bromobenzyl ether. No additional preparation was done before injecting the
sample on the column. Standards for product identification i.e. allyl benzyl ether (Enamine Store, 95%) and
2-methyl benzopyran (Enamine Store, 95%) were used without further purification steps.
5

3 Results and discussion
3.1.
Screening of the cathode materials
At first the electrochemical behavior at less active cathode materials is investigate to benchmark the system.
Recent research of the C-X bond rupture has indicated that materials such as GC, Pt and Ti can be candidates
for an inert reference material, meaning that they are known to have slow kinetics of electron transfer to
various redox systems and therefore require the highest overpotential for C-X bond activation [15], [24].
Before each experiment the ohmic drop was measured using EIS and compensated. The average ohmic drop
for all experiments was ca. 80 ohms. Figure 2A and Table 1 show the results for the reduction of allyl 2-
bromobenzyl on GC. The current densities have been calculated in respect to the geometric surface area of
the electrodes. A distinct cathodic wave can be observed with a peak potential of -1.92 V. When the
reduction wave is measured at multiple scan rates between 50 mV s-1 and 1 V s-1 a good correlation
(R²=0.9854, Table 1) is found between the peak current density and the square root of the scan rate. The
reduction of allyl 2-bromobenzyl is thus characterized as a process of diffusive nature. When the
concentration is elevated (Figure 2A) from 1 mM until 5 mM allyl 2-bromobenzyl ether, a linear correlation
(0.9956, Table 1) is found with the peak current density while the reduction peak potential remained similar
with maximum variations of 12mV (not shown).
Figure 2: Cyclic voltammetry at 50 mV s-1 of GC (A-B), Ti (B) and Pt (B) in MeOH + Bu4NClO4 (0.1 M) and allyl 2-bromobenzyl ether
1mM (A-B) and 5mM (A)
Table 1: Voltammetric data of GC, Pt and Ti for the reduction of allyl 2-bromobenzyl ether (1mM) + Bu4NClO4 in MeOH measured
at 50 mV s-1
In Figure 2B the CV features of Pt and Ti in comparison with GC are shown. On Pt the reduction peak is less
pronounced and occurs at a potential of -1.71 V. Similar results in respect to GC are obtained when the
relation between peak current density vs. square root of scan rate and concentration are investigated (Table
1).
With Ti no clear cathodic wave is measured even at higher concentrations. To verify that the low catalytic
activity is caused by metallic Ti and not to the presence of a titanium (di)oxide layer, additional Surface
Enhanced Raman Spectroscopy (SERS) measurements are done in this work. These measurements
6

(supporting information) confirm that no oxide layer is present whereby we believe that the low activity is
due to purely metallic Ti. Since GC exhibits the clearest cathodic wave this will be used as reference material
for all other materials.
Subsequently the electrochemical behavior on Ag, Au, Cu, Mg, Mn, Ni and Pb was studied. The investigated
metals can roughly be divided in two groups: Figure 3A where a single reduction wave is measured (Au Pb,
Mn, Mg and Ni) and Figure 3B where two closely spaced cathodic waves are observed (Ag, Cu).
The single reduction waves can be observed in Figure 3A between a potential window of -1.2 V and -2.5 V.
The influence on the electrocatalytic activity is expressed as an electrocatalytic activity parameter in
reference with GC, the material that requires the highest overpotential (Table 2); Ep, cathode -Ep, GC. This
provides a scale for the electrocatalytic activity for each cathode material. Mn induces the greatest shift in
reduction peak potential (260 mV) followed by Ni (150 mV) and Mg (140 mV). The influence of Au (112 mV)
and especially Pb (39 mV) on the electrocatalytic activity is less pronounced. On all metals a good correlation
is found between the peak current density and the square root of the scan rate and a good correlation is
consistently found between the current density and concentration (Table 2).
Figure 3: Cyclic voltammetry at 50 mV s-1 of Au (A), Ag (B) Cu (B), GC (A), Mg (A), Mn (A), Ni (A) and Pb (A) in MeOH + Bu4NClO4
(0.1 M) and allyl 2-bromobenzyl ether 1mM
The CV features of Ag and Cu (Figure 3B) show an additional second reduction wave. The reduction peak
potentials of Ag are respectively -1.15 V (Ag1, Table 2) and -1.38 V (Ag2, Table 2). At both potentials there is
a linear correlation of the peak current density with square root of the scan rate and the process is of
diffusive nature. At -1.15 V a linear correlation is found with the concentration while on -1.38 V the
correlation is exponential between 1-5 mM allyl 2-bromobenzyl ether. The oxidation peak on Ag present at -
0.68 V is believed to be due from the oxidation (1) of small amounts of H20 present in the electrolyte and (2)
dissolution of small quantities of Ag. Cu also shows two reduction peaks present at -1.68 V (Cu1) and -2.02 V
(Cu2). The upper potential window of Cu is limited to prevent formation of CuO. At both potentials the
process is characterized as diffusion control and a good correlation between the peak current density and
concentration is measured (Table 2).
7

Table 2: Voltammetric data of Ag, Au, Cu, Mg, Mn, Ni and Pb for the reduction of allyl 2-bromobenzyl ether (1mM) + Bu4NClO4
(0,1M) MeOH measured at 50 mV s-1
Regardless of the number of reduction peaks, both Cu and Ag show a good electrocatalytic with shifts of 239
mV and 771 mV respectively in comparison with GC (Table 2). It is the authors believe that the bond
dissociation energy between Ag and Br reaches an optimal. The surface phenomena such as adsorption and
desorption of intermediates and products play a crucial role in the electrocatalytic activity. The obtained
results are in correspondence with previous findings for the electrosorption of halides on Ag and Cu and ion-
metal interaction and their contribution to the beneficial catalytic activity [25]. The smaller current densities
of Ag, compared to the other materials, is believed to be due to adsorption of Br- ions at potentials up to -1.2
V. Previous studies of Ocko et all. [26] have indicated that Br- coverage on Ag can reach up until 50% of the
surface.
In addition to the CV measurements lineair sweep voltammetry was used in combination with rotating disk
experiments (LSV/RDE) to elaborate the screening of cathode materials. The linear sweep voltammogram in
this section is obtained at a scan rate of 1 mV s-1 using a rotating disk electrode. In Figure 4 a rotating disk
experiment is shown on a GC electrode. The potential is swept starting at -1.0 V and scanned in the negative
direction until -2.2 V. The potential window is restricted until -2.2 V to prevent reduction of the solvent.
When the system is scanned in an opposite direction from -2.2V until -1.0 V an identical voltammogram is
obtained. The Koutecky Levich plot (Figure 4) is calculated at the reduction peak potential measured in
previously obtained cyclic voltammogram (Figure 2 and Table 1). Calculations were done using equation 1
with values of - 8.1x10-6 cm²/s [27], ν - 7.37x10-4 cm²/s (kinematic viscosity) and Cbenzylbromide- 1mmol.
(1)
The calculated number of exchanged electrons on a GC cathode material is 1.05 ( Table 3).
Figure 4: LSV recorded at 1mVs-1 with rotation rates of 3OO, 450, 620 and 743 RPM for the reduction of allyl 2-bromobenzyl
ether (1mM) in MeOH + Bu4NClO4 (0,1M).
8

On all other investigated cathode materials a single well-formed reduction wave is observed. The LSV curves
can be consulted in the supporting information. To assess the influence of the cathode material on the
reaction mechanism Koutecky-Levich analysis was applied to the reduction peak potentials measured in the
previous section (Figure 3 and Table 2). Results of these calculations are shown in Table 3. The minimum
correlation coefficient obtained in all these measurements is 0.9602. On Ag, Au, Cu, Mg, Mn, Ni ,Pb and Pt
ca. one-electron is transferred. When Koutecky-Levich analysis is performed at the first reduction peak
potential of Ag and Cu results show that, as with the other cathode materials, one-electron is transferred.
However when Koutecky Levich analysis is applied to the second reduction peak potential 2 electrons are
transferred.
Table 3: Koutecky Levich analysis on investigated cathode materials performed at the reduction peak potential of allyl 2-
bromobenzylether
3.2.
Product identification on different electrochemical materials
The mechanism of dissociative electron transfer of aryl halides is already previously reported and is known
to proceed in a stepwise manner. Once more the authors like to stipulate that it is not our intention to give a
detailed description of reaction mechanism but to clarify the overall processes which occur at different
electrocatalytic materials. The product identification was done by GC-FID of experiments performed under
potential control.
The experiments are performed under potential control i.e. the reduction peak potential (Table 1-2). The
results of the experiments under potential control are divided in two groups: (1) where a single reduction
peak is visible in the CV measurements (Figure 3A), shown in Figure 5 and (2) where two cathodic waves are
observed (Figure 3B), shown in Figure 6.
In Figure 5A-B where the potential is set at the reduction peak potential, the yield of 2-methyl benzopyran
on Au, GC, Mg, Mn, Ni, Pb and Pt is shown. For Ti the potential is set on -2.2 V since literature reports this as
the potential where C-X bond activation takes place [15]. Analysis shows that only 2-methyl benzopyran is
9

formed on all of these cathode materials. The results are in correspondence with the previously performed
Koutecky Levich analysis. The highest yield (Table 4) is obtained with Au (48 mol%), Mg (46 mol%), Ni (50
mol%) and Glassy carbon (44 mol%). Mn, Ti, Pb, Pt display a lower yield of respectively 35 mol%, 5 mol%, 32
mol% and 6 mol% (Table 4). This is as expected according to Faradays law, since the current densities
recorded during the CV (Figure 2-3) are proportional with the yield. Next to the formed product, on all
electrodes, also unreacted allyl 2-bromobenzyl ether was found.
Figure 5: Product formation at Ep on Au (B), GC (A), Mg (B), Mn (B), Ni (B), Pt (A), Pb (B) and Ti (A) in MeOH + Bu4NClO4 (0.1 M) and
allyl 2-bromobenzyl ether (10 mM)
Table 4: Yield of 2-methyl benzopyran formed at the reduction peak potential
At Ag and Cu product formation is studied at both the first and second reduction wave. On Ag at the first
reduction wave only the formation of 2-methyl benzopyran occurs resulting in a yield of 48 mol% for Ag
(Table 4-Figure 6, Ag1). At the second reduction peak potential (Ag2) 15 mol% 2-methyl benzopyran is
formed (Table 4, Ag2). After 180 minutes an equilibrium is obtained for both curves with a maximum
conversion. At the potentials of the second reduction wave, however, both the formation of 2- methyl
benzopyran and allyl benzyl ether occurs. In fact, as already indicated with the Koutecky Levich analysis, a
different number of electrons was transferred. Results indicate that the yield of allyl benzyl ether (52 mol%)
exceeds that of 2-methyl benzopyran (15 mol%) (Table 4). By varying the potential with 243 mV the reaction
can be controlled to specifically the formation of allyl 2-bromobenzyl ether of 2-methyl benzopyran on Ag.
On Cu similar results are obtained. At the first reduction wave only the formation of 2-methyl benzopyran
appears with a yield of respectively 56 mol% (Table 4, Cu1). The second reduction wave mainly gives rise to
the formation of allyl 2-bromobenzylether with a yield of 73 mol% while conversion until 2-methyl
benzopyran is decreased until 8 mol%.
Figure 6: Product formation of 2-methyl benzopyran at Ep of Ag1 and Cu1 in MeOH + Bu4NClO4 (0.1 M) and allyl 2-bromobenzyl
ether (10mM) until
10

4 Conclusion
An electrochemical activity scale was built up for the intramolecular cyclisation reaction of allyl 2-
bromobenzyl ether to 2-methyl benzopyran in MeOH + 0.1 M Bu4NClO4. CV measurements of GC, Pt, Au, Mg,
Ni and Pb resulted in a single reduction wave. On Ag and Cu two distinct reduction peaks are measured. Ti
did not exhibit a clear reduction peak. Out of all of the investigated cathode materials Ag exhibits the largest
shift of 771mV in reference to GC followed by Mn (260 mV), Cu (238 mV), Ni (150mV), Mg (140), Au
(112mV), and Pb (39mV). Koutecky Levich analysis at the peak potential of Au, GC, Mg, Mn, Ni, Pb, Pt and Ti
showed that one-electron was transferred. On Ag and Cu at the first reduction peak potential similar results
were obtained and results showed one-electron is transferred. However at the second, more negative
reduction peak potential, the process shifted from one-electron transfer. In addition product formation was
studied on the investigated materials. It was shown that on the reduction potential of GC, Pt, Au, Mg, Ni and
Pb only 2-methyl benzopyran was formed. On Ag and Cu 2-methyl benzopyran was formed at the potential
of first reduction peak while at the second reduction peak a mixture of 2-methyl benzopyran but mostly
allyl-2 bromobenzyl ether was found. The highest yield for the electrosynthesis experiments of 2-methyl
benzopyran were obtained at the first reduction peak of Ag (48 mol%) and Cu (56 mol%) and at the
reduction peaks potential of Ni (50 mol%) Au (48 mol%) and Mg (46 mol%).
11

References
[1]
[2]
[3]
[4]
E. Duñach, M. José Medeiros, and S. Olivero, “Intramolecular reductive cyclisations using
electrochemistry: development of environmentally friendly synthetic methodologies,” New J. Chem.,
vol. 30, no. 11, p. 1534, 2006.
L. Pieters, S. Van Dyck, M. Gao, R. Bai, E. Hamel, A Vlietinck, and G. Lemière, “Synthesis and biological
evaluation of dihydrobenzofuran lignans and related compounds as potential antitumor agents that
inhibit tubulin polymerization.,” J. Med. Chem., vol. 42, no. 26, pp. 5475–5481, 1999.
H. F. Roaiah, S. S. El-nakkady, W. S. El-serwy, M. A. A. Ali, and A. H. A. El-rahman, “Studies on some
Benzopyran Derivatives with Expected Antimicrobial and Antiviral Activity,” Nature and Science, vol.
8, no. 7, pp. 20–29, 2010.
M. M. Burbuliene, V. Jakubkiene, G. Mekuskiene, E. Udrenaite, R. Smicius, and P. Vainilavicius,
“Synthesis and anti-inflammatory activity of derivatives of 5-[(2-disubstitutedamino-6-methyl-
pyrimidin-4-yl)-sulfanylmethyl]-3H-1,3,4-oxadiazole-2-thiones,” Farmaco, vol. 59, no. 10, pp. 767–
774, Oct. 2004.
[5]
[6]
[7]
E. Ayranci and N. Hoda, “Adsorption kinetics and isotherms of pesticides onto activated carbon-
cloth.,” Chemosphere, vol. 60, no. 11, pp. 1600–7, Sep. 2005.
A. S. Shawali, “Synthesis and tautomerism of aryl- and hetaryl-azo derivatives of bi- and tri-
heterocycles,” J. Adv. Res., vol. 1, no. 4, pp. 255–290, Oct. 2010.
K. C. Majumdar, P. K. Basu, and S. K. Chattopadhyay, “Formation of five- and six-membered
heterocyclic rings under radical cyclisation conditions,” Tetrahedron, vol. 63, no. 4, pp. 793–826, Jan.
2007.
[8]
[9]
E. Duñach, A. P. Esteves, M. J. Medeiros, C. S. dos Santos Neves, and S. Olivero, “Radical-type
reactions in protic and aprotic media: Comparisons in nickel-catalysed electrochemical reductive
cyclisations,” Comptes Rendus Chim., vol. 12, no. 8, pp. 889–894, Aug. 2009.
K. Mitsudo, Y. Nakagawa, J. Mizukawa, H. Tanaka, R. Akaba, T. Okada, and S. Suga, “Electro-reductive
cyclization of aryl halides promoted by fluorene derivatives,” Electrochim. Acta, vol. 82, pp. 444–449,
Nov. 2012.
[10] M. J. Medeiros, C. S. S. Neves, a. R. Pereira, and E. Duñach, “Electroreductive intramolecular
cyclisation of bromoalkoxylated derivatives catalysed by nickel(I) tetramethylcyclam in ‘green’
media,” Electrochim. Acta, vol. 56, no. 12, pp. 4498–4503, Apr. 2011.
[11] H. J. Schäfer, “Contributions of organic electrosynthesis to green chemistry,” Comptes Rendus Chim.,
vol. 14, no. 7–8, pp. 745–765, Jul. 2011.
[12] C.G. Sowell, R.L. Wollin and R.D. Little, “Electroreductive cyclization reaction, stereoselectino creation
of quaternary centres in bicyclic frameworks and a formal total synthesis of quadrone,” Tetrahedron
letters, vol. 31, no. 4, pp. 95–98, 1990.
[13] A. A. Isse, S. Gottardello, C. Durante, and A. Gennaro, “Dissociative electron transfer to organic
chlorides: electrocatalysis at metal cathodes.,” Phys. Chem. Chem. Phys., vol. 10, no. 17, pp. 2409–16,
May 2008.
[14] A. A. Isse, G. Berzi, L. Falciola, M. Rossi, P. R. Mussini, and A. Gennaro, “Electrocatalysis and electron
transfer mechanisms in the reduction of organic halides at Ag,” J. Appl. Electrochem., vol. 39, no. 11,
pp. 2217–2225, Jan. 2009.
[15] C. Bellomunno, D. Bonanomi, L. Falciola, M. Longhi, P. R. Mussini, L. M. Doubova, and G. Di Silvestro,
12

“Building up an electrocatalytic activity scale of cathode materials for organic halide reductions,”
Electrochim. Acta, vol. 50, no. 11, pp. 2331–2341, Apr. 2005.
[16] S. Olivero, J. Claude, and E. Dunach, “Electrochemical Intramolecular Reductive Cyclisation catalysed
by electrogenerated Ni(cyclam)2+,” Tetrahedron Letters, vol. 36, no. 25, pp. 4429–4432, 1995.
[17] X. Chaminade, E. Duñach, A. P. Esteves, M. J. Medeiros, C. S. Neves, and S. Olivero, “Electrosynthesis
of nitrogen heterocycles using environmentally friendly methodologies,” Electrochim. Acta, vol. 54,
no. 22, pp. 5120–5126, Sep. 2009.
[18] E. Duñach, a. . Esteves, M. . Medeiros, D. Pletcher, and S. Olivero, “The study of nickel(II) and
cobalt(II) complexes with a chiral salen derivative as catalysts for the electrochemical cyclisation of
unsaturated 2-bromophenyl ethers,” J. Electroanal. Chem., vol. 566, no. 1, pp. 39–45, May 2004.
[19] A. Esteves, A. Freitas, M. Medeiros, and D. Pletcher, “Reductive intramolecular cyclisation of
unsaturated halides by Ni(II) complexes,” J. Electroanal. Chem., vol. 499, no. 1, pp. 95–102, Feb. 2001.
[20] V. Jouikov and J. Simonet, “Graphene: Large scale chemical functionalization by cathodic means,”
Electrochem. commun., vol. 46, pp. 132–136, 2014.
[21] E. Duñach, A. P. Esteves, L. F. M. Leite, M. A. Lemos, M. J. Medeiros, and S. Olivero, “Electrochemical
Study of Nickel ( salen ) and Cobalt ( salen ) Derivatives Complexes in the Presence of Unsaturated
Halides,” Portugaliae Electrochmica Acta, vol 2, no. I, pp. 2–5.
[22] E. Duñach, A. P. Esteves, A. M. Freitas, M. J. Medeiros, and S. Olivero, “Electroreductive cyclisation of
unsaturated halides catalysed by nickel macrocyclic complexes,” Tetrahedron Lett., vol. 40, no. 49, pp.
8693–8696, Dec. 1999.
[23] Rahman A.U. et all., “Current Pharamaceutical design,” Bentham Sci. Publ., vol. 1, no. 4, pp. 395–400,
2000.
[24] A. Gennaro, A. A. Isse, E. Giussani, P. R. Mussini, I. Primerano, and M. Rossi, “Relationship between
supporting electrolyte bulkiness and dissociative electron transfer at catalytic and non-catalytic
electrodes,” Electrochim. Acta, vol. 89, pp. 52–62, Feb. 2013.
[25] G. Valette, “Ionic electrosorption on solid surfaces and congruence with respect to the electrical
variable,” J. Electroanal. Chem. Interfacial Electrochem., vol. 146, no. 2, pp. 439–446, May 1983.
[26] T. Wandlowski, J. X. Wang, and B. M. Ocko, “Adsorption of bromide at the Ag ( 100 ) electrode
surface,” J. Electroan. Chem., vol. 500, pp. 418–434, 2001.
[27] D. Zhou, H. Carrero, and J. F. Rusling, “Radical vs Anionic Pathway in Mediated Electrochemical
Reduction of Benzyl Bromide in a Bicontinuous Microemulsion,” Langmuir, vol. 3, no. c, pp. 3067–
3074, 1996.
13

Ep (V vs.
Ag/AgCl)
Jp
R² (Jp vs.
C)
Cathode
Glassy
(mA/cm²) R² (Jp vs v0,5)
Carbon
Pt
Ti
-1.92
-1.71
/
0.14
0.02
/
0.9854
0.9956
/
0.9872
0.9793
/
14

Ep (V vs.
Ag/AgCl) (mA/cm²)
Jp
Ep,cathode-Ep, GC
(mV)
R² (Jp vs
v0,5)
0.9845
/
0.9955
0.9779
0.9821
0.9891
0.9903
0.9788
0.985
R² (Jp vs.
C)
Cathode
Ag1
Ag2
Au
Cu1
Cu2
Mg
Mn
Ni
Pb
-1.15
-1.38
-1.81
-1.68
-2.02
-1.78
-1.66
-1.77
-1.88
0.08
0.02
0.79
0.41
0.18
0.07
0.29
0.14
0.22
771
/
112
238
/
140
260
150
39
0.9699
0.9772
0.9754
0.9735
0.9817
0.9821
0.9942
0.9837
0.9844
15

R² ( ω-1/2 vs. J-
Cathode
Ag1
Ag2
Au
n
1.07
2.18
1.12
1.05
1.09
2.05
1.13
0.97
0.98
1.20
0.94
/
)
1
0.9789
0.9826
0.9803
0.9694
0.9745
0.9801
0.9924
0.9670
0.9716
0.9602
0.9627
/
GC
Cu1
Cu2
Mg
Mn
Ni
Pb
Pt
Ti
16

Cathode Yield allyl 2-bromobenzylether (mol%) Yield 2-methyl benzopyran (mol%)
Yield allyl benzyl ether (mol%)
Ag1
Ag2
Au
GC
Cu1
Cu2
Mg
Mn
Ni
52
33
52
56
44
19
54
65
50
68
94
95
48
15
48
44
56
8
46
35
50
32
6
0
52
0
0
0
73
0
0
0
0
Pb
Pt
Ti
0
0
5
17

Figure 1
-
CH2
CH2
O
O
+ e_
(1)
(2)
Br
Br
-
CH2
CH2
O
O
Br-
+
+
C
Br
CH2
CH2
+ e_
O
O
Br-
O
(3)
(4)
C
Br
CH2
O
C
CH2
O
O
+ e_
(5)
(6)
CH-2
CH2
CH2
CH2
+ e_
O
O
C-
C

Figure 2A
0,2
0,0
-0,2
-0,4
-0,6
-0,8
-1,0
-1,2
-1,4
-1,6
-1,8
-2,0
-2,2
-2,4
GC 1mM
GC 5mM
-2,6
-2,4
-2,2
-2
-1,8
-1,6
-1,4
-1,2
-1
E vs. (Ag/AgCl)/V

Figure 2B
0,2
0,1
0,0
-0,1
-0,2
-0,3
-0,4
-0,5
GC
Pt
Ti
-2,6
-2,4
-2,2
-2
-1,8
-1,6
-1,4
-1,2
-1
E vs. (Ag/AgCl)/V

Figure 3A
0,2
0,0
-0,2
-0,4
-0,6
-0,8
-1,0
Ni
Au
GC
Pb
Mn
Mg
-2,6
-2,4
-2,2
-2
-1,8
-1,6
-1,4
-1,2
-1
E vs. (Ag/AgCl)/V

Figure 3B
0,2
0,0
-0,2
-0,4
-0,6
-0,8
-1,0
Ag
Cu
-2,6
-2,1
-1,6
-1,1
-0,6
-0,1
E vs. (Ag/AgCl)/V

Figure 4
0,00
-0,50
-1,00
-1,50
-2,00
-2,50
0
-0,2
-0,4
-0,6
-0,8
-1
-1,2
-1,4
0
0,05
0,1
0,15
0,2
ω-1/2 / (rad/s)-1/2
300 RPM
450 RPM
620 RPM
743 RPM
-2,5
-2
-1,5
-1
-0,5
0
E vs. (Ag/AgCl)/V

Figure 5A
50%
45%
40%
35%
30%
25%
20%
15%
10%
5%
Glassy carbon
Pt
Ti
0%
0
50
100
150
200
250
300
350
400
Time/ min

Figure 5B
60%
50%
40%
30%
20%
10%
0%
Au
Mg
Mn
Ni
Pb
0
50
100
150
200
250
300
350
400
Time /min

Figure 6
60%
50%
40%
30%
20%
10%
0%
Ag
Cu
0
50
100
150
200
250
300
350
400
Time/ min