Electrochemical investigation of the chloroselenobenzene under its atmosphere-sensitive characteristics

Article abstract of DOI:10.1016/j.electacta.2020.137025

Electrochemical oxidation and reduction of the chloroselenobenzene were described in a catalyst-less and mild solution through cyclic voltammetry and controlled-potential electrolysis under air and nitrogen atmosphere. By electrogenerated intermediates and controlling conditions, unique compounds, including a Diselenol, Diselenide, and Polyselenid, were synthesized in good to excellent yields and purities. These compounds can be oxidized at the surface of the carbon electrode to produce reactive precursors with several Michael addition positions for further investigations.

Full text of DOI:10.1016/j.electacta.2020.137025

Electrochimica Acta 360 (2020) 137025
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Electrochimica Acta
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Electrochemical investigation of the chloroselenobenzene under its
atmosphere-sensitive characteristics
a,∗
a
b,c,∗∗
Vahid Khakyzadeh , Parisa Chegini , Fahimeh Varmaghani
a
Department of Chemistry, K. N. Toosi University of Technology, P. O. Box 16315-1618, Tehran 15418, Iran
b
c
Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
Research Center for Basic Sciences & Modern Technologies (RBST), Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Electrochemical oxidation and reduction of the chloroselenobenzene were described in a catalyst-less and
mild solution through cyclic voltammetry and controlled-potential electrolysis under air and nitrogen
atmosphere. By electrogenerated intermediates and controlling conditions, unique compounds, including
a Diselenol, Diselenide, and Polyselenid, were synthesized in good to excellent yields and purities. These
compounds can be oxidized at the surface of the carbon electrode to produce reactive precursors with
several Michael addition positions for further investigations.
Received 6 July 2020
Revised 25 August 2020
Accepted 26 August 2020
Available online 28 August 2020
Keywords:
Organoselenium compound
Electro-oxidation
Electro reduction
Diselenol
©
2020 Elsevier Ltd. All rights reserved.
Diselenide
1
. Introduction
processes [16], for example, glutathione peroxidase, iodothyronine
deiodinase, and thioredoxin reductase are three enzymes in mam-
mals which contain selenols [17]. Selenocysteine, selenomethion-
ine, and selenoglutathione are naturally occurring amino acids and
peptide with selenol group or several chiral ebselen analogs, as a
synthetic organoselenium drug, could easily be synthesized using
The element of selenium is as a nutrient essential for the body
1]. As an antioxidant, it protects the cell membranes from oxi-
[
dants [2]. It is also known that there is a relationship between
selenium and vitamin E for prostate cancer [3]. This element is
used in many purposes like semiconductors [4], photocells [5],
electronics [6], glass industry [7], agricultural [8], and oxidizing
agent in organic transformations [9]. Because of the toxicity of in-
organic selenium forms, using them in many therapeutic purposes
was limited; therefore, recently attend to organic forms of them
is highly desirable. [10]. They are well known as antioxidants [11],
antibacterial agents [12], and radioprotector compounds [13], and
also have a unique role in the development of impressive organic
building blocks, material construction, ligand chemistry, and bio-
logical processes [14]. The toxicity, specificity, and redox proper-
ties of organoselenium compounds can be tuned by the group sub-
stituents also or non-bonding interactions between hetero atoms
and selenium atom [15]. Among organo-selenium compounds, Se-
lenols (RSe-H) and Diselenides play an essential role in biological
ꢀ
2,2 -diselanediyldibenzoic acid [18,19] (Scheme 1).
The selenols are more potent acids in comparison with thiols
(about 1000 times more), and also they account as strong nucle-
ophiles in organic transformations [20]. The reaction of organo-
lithium or Grignard reagents with elemental selenium (Scheme 2,
I) [21], the reaction of organic halides [22], or aromatic diazonium
bromide [23], with nucleophilic selenium species (Scheme 2, II),
reduction of Diselenides to the corresponding selenols (Scheme 2,
III) [24], reduction or hydrolysis of selenocyanates (Scheme 2, IV)
[25], and the reaction of potassium selenides with alkyl sulfate
(Scheme 2, V) [26] are entirely known as general methods for
the preparation of Selenols (Scheme 2). However, in most cases,
the significant drawback of the named methodologies include
harsh condition, low yields, selectivities, significant by-products,
long reaction time, high sensitivity to the atmosphere and op-
eration of environmentally unfriendly starting materials can lead
to undesired and unpleasant results. Electrochemical synthesis has
utilized as a potent strategy to produce complex organic com-
pounds because of dominant advantages. In 2019, Hua and co-
workers performed a direct electrochemical oxidative cyclizayion
of alkynoates and alkynamides with diselenole [27]. Very recently,
∗
Corresponding author at: Department of Chemistry, K. N. Toosi University of
Technology, Tehran, P. O. Box 16315-1618, Tehran 15418, Iran
∗
∗
Corresponding author at: Department of Chemistry, Institute for Advanced Stud-
ies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
E-mail addresses: v.khakyzadeh@kntu.ac.ir (V. Khakyzadeh),
f.varmaghani@iasbs.ac.ir (F. Varmaghani).
https://doi.org/10.1016/j.electacta.2020.137025
0
013-4686/© 2020 Elsevier Ltd. All rights reserved.

2
V. Khakyzadeh, P. Chegini and F. Varmaghani / Electrochimica Acta 360 (2020) 137025
Scheme 1. Some organoselenium compounds as a peptide, amino acid, and drug precursor.
Scheme 2. Classical chemical strategies towards organoselenols (left side), and our strategies (right side).
’
Sun s group developed the electro-induced aminoselenation and
oxyselenation of styrenes in the absence of acids or oxidant ad-
ditives. This transformation lead to difuctionalized organoselenium
compounds [28]. In 2020, He et al. reported electrochemical se-
leno/thiocyanation of arylboronic acids to synthesis corresponding
aryl seleno/thiocyanatid [29].
up involving a glassy carbon disk (1.8 mm diameter) as working
electrode, a Pt wire counter electrode and SCE reference electrode.
A Metrohm-pH meter was utilized to adjust the pH of solutions.
Large-scale electrolysis was performed in a 100 ml home-made cell
2
equipped with three graphite plates (50 cm ) as a working elec-
2
trode and a steel rode (10 cm ) as a counter electrode. The accu-
Based on the introduction above, we wonder to investigate
an organoselenium compound deeply, i.e., phenylselenenyl chlo-
ride in different electrochemical conditions, to find new proto-
cols for the synthesis of organoselenium compounds. Therefore, in
this study, we have presented the first electrochemical synthesis
rate potentials were referred to as the SCE. Chloroselenobenzene
(ClSePh) and the other reagents and solvents were of commer-
cial sources. Synthesized products were identified using 1HNMR,
13CNMR, IR, MS, SEM, EDX, and TGA analysis.
ꢀ
ꢀ
of [1,1 -biphenyl]-4,4 -diselenol by the electrochemical oxidation of
phenylselenenyl chloride in an undivided cell using a carbon elec-
trode and in an aqueous phase under air conditions at room tem-
perature. Also, the electrochemical reduction of phenylselenenyl
chloride in different atmospheres (Air and Nitrogen) gave us differ-
ent products. Activation of phenylselenenyl chloride easily occurs
at electrode surface. However, older non-electrochemical reports
have used chemical reagents such as azide to activate phenylse-
lenenyl chloride [30]. This research study is the first example of
the synthesis of this kind of compounds with advantages of high
atom economy, high yield, high purity, and very low pollution
ꢀ
ꢀ
2.2. Electro-organic synthesis of [1,1 -biphenyl]-4,4 -diselenol
(BPhDSe)
The potentiostat method at the first anodic peak potential (+1.2
V vs. SCE) of ClSePh cyclic voltammogram was exerted to 80 ml of
a solution of acetate buffer (c=0.2 M, pH=4.0)/acetonitrile (50/50)
mixture containing 0.25 mmol of ClSePh in a divided cell. The ad-
vancement of the electrolysis was monitored by cyclic voltamme-
try. The electrolysis was continued until near-complete disappear-
ing of the first anodic peak. After that, the product was purified
using column chromatography (methanol/n-hexane 5:1).
(
Scheme 2, our work).
2
. Experimental
Characteristics of BPhDSe: M.p. = decomposition at 220 °C.
Yield: 81%, 1H NMR (400 MHz, DMSO-d ) δ = 4.84 (broad, 2H,
6
2
.1. Apparatus and reagents
Se-H), 7.48 (d, 4H, Ar-H), 7.73 (d, 4H, Ar-H), 13C NMR (100 MHz,
DMSO-d ) δ = 126.2, 128.9, 131.3, 130.7 ppm. IR(KBr) ν = 642,
6
Recording cyclic voltammograms were conducted with a PG-
730, 788, 1410, 1576, 1644, 3433. MS (EI) m/z (relative intensity):
51 (57), 77 (85), 157 (100), 234 (7), 313 (43).
STAT 30 in a conventional one-component three-electrode cell set-

V. Khakyzadeh, P. Chegini and F. Varmaghani / Electrochimica Acta 360 (2020) 137025
3
Fig. 2. Normalized cyclic voltammograms of 3.0 mM ClSePh in water (acetate
buffer, c = 0.2 M, pH = 4.0)/ acetonitrile (5/5 v/v) mixture at different scan rates.
Fig. 1. cyclic voltammograms of (a and b): 3.0 mM ClSePh at glassy carbon elec-
trode in water (acetate buffer, c = 0.2 M, pH = 4.0)/ acetonitrile (5/5 v/v) mix-
ture restricted to 1.45 and 1.8 V, respectively, (c) blank solution containing (acetate
buffer, c = 0.2 M, pH = 4.0)/ acetonitrile (5/5 v/v) mixture. Scan rate: 100 mVs−1.
−
1
Scan rates are 10, 25, 50, 75 and 250 mVs . Inset: variation of A2/A1 peak current
versus scan rate.
2
.3. Electro-organic synthesis of 1,2-diphenyldiselane (DPhDSe)
0 ml of a mixture of acetonitrile/aqueous phosphate buffer so-
8
lution (c=0.2 M, pH=6.0) consisting of 0.25 mmol ClSePh was elec-
trolyzed in a divided cell by exerting the potential of -1.2 V. The
synthesis was performed under bubbling N2 gas during electroly-
sis. When the electrolysis was terminated, the cell was placed un-
der room atmosphere for an hour. After that, a yellow solid was
filtered and was washed several times with water. No further pu-
rification was exerted to characterize it using spectroscopic meth-
ods.
Characteristics of DPhDSe: M.p. = decomposition at 180 °C.
Yield: 85%, 1H NMR (400 MHz, DMSO-d ) δ = 7.31–7.38 (m, 6H,
6
Ar-H), 7.65 (d, 4H, Ar-H), 13C NMR (100 MHz, DMSO-d ) δ = 128.4.
6
1
29.9, 130.4, 131.3 ppm. IR(KBr) ν = 662, 685, 732, 1081, 1433,
1471, 1569. MS (EI) m/z (relative intensity): 51 (50), 77 (50), 154
(
100), 234 (53), 313 (7).
Fig. 3. Cyclic voltammograms of 3.0 mM ClSePh at glassy carbon electrode in ace-
tonitrile/buffered solutions with various pHs of 2.0, 3.0 and 4.0 with the same ionic
strength (0.2 M) (5/5 v/v) respectively. Scan rate: 25 mVs 1.
−
3
. Results and discussion
3
.1. Electrochemical oxidation of ClSePh
controlled electrode process; (c) the ratio of A /A1 peaks (inset of
2
To attain thoroughly analyze of the electrochemical process of
Fig. 2) decreases upon increasing scan rate. In the EE mechanism,
the current of the redox signals does not undergo a change in nor-
malized cyclic voltammograms. This fact declines the connection
of A1 and A2 peaks to two consecutive electron transfers (EE) dur-
ing the oxidation process. The independency of A1 peak current
and decreasing of A2 peak height upon decreasing time scale of
voltammetry can be in accordance with perturbation of the elec-
ClSePh, cyclic voltammogram of 3.0 mM of ClSePh was recorded
in a wide range of potential from 0 to 1.4 V. Fig. 1, curve a, ex-
hibits an irreversible anodic wave (A ) at +1.2 V in aqueous acetate
1
buffer solution (c=0.2 M, pH=4.0)/acetonitrile (5/5 v/v). By extend-
ing the potential up to 1.8 V, a quite distinct anodic peak (A ) at
2
+
1.6 V was observed (curve b). Two anodic peaks arise from ei-
ther oxidation of ClSePh during two successive electron transfer
steps (EE mechanism) or the oxidation of a product resulted from a
follow-up chemical reaction after the electrode process (ECE mech-
anism). It should be noted that the voltammogram c recorded in a
blank solution rejects the connection of the faradaic responses to
concomitants in the solution. Further support to find out the facts
was achieved by recording the voltammograms at different poten-
tial scan rates. Tracking the normalized voltammograms (current
divided to the square root of scan rate) figures out three expres-
sive evidences (Fig. 2); (a) a regular shift of the A1 and A2 signals
to more positive potentials upon increasing the scan rate can be
inferred as charge transfer controlled of the electrode processes at
the surface of the glassy carbon electrode; (b) conformity of A1
peak currents in all normalized voltammograms reveals diffusion-
trode process by a chemical reaction, the ECE mechanism (E >E ).
2 1
Cyclic voltammetric response of 3.0 mM ClSePh was studied
more toughly over the pH range of 2–4. Despite A1 peak exhib-
ited to be insensitive to proton limitation, gradually shift of A2
peak potential to negative values reflects facilitating in the electro-
oxidation. This data confirms that the first anodic signal is pH-
independent, and the second electrode process has proton-coupled
nature (Fig. 3).
Controlled-potential coulometry was performed in a mixture
of acetate buffer solution (c=0.2 M, pH=4.0)/acetonitrile (5/5
v/v) containing 0.25 mmol of ClSePh at +1.2 V into the two-
compartment cell to obtain an accurate picture on the oxidation
mechanism. The progress of the electrolysis was traced by record-
ing cyclic voltammograms up to the second oxidation peak. Fig. 4

4
V. Khakyzadeh, P. Chegini and F. Varmaghani / Electrochimica Acta 360 (2020) 137025
Fig. 4. I: Cyclic voltammograms of ClSePh (0.25 mmol) in water (acetate buffer, c = 0.2 M, pH = 4.0)/acetonitrile (50/50% v/v) mixture during controlled-potential coulometry
at +1.2 V versus SCE. Inset: A cyclic voltammogram of 5 mM isolated product (BPhDSe). II: variation of the peak current (IpA1) versus charge consumed.
represents that parallel to gradually decrease of A1 current during
electrolysis, the second peak increases. This observation points out
that the first and the second peaks originate from ClSePh and the
product, respectively. Only A2 peak remained after the exhaustive
electrolysis at +1.2 V. The coulometry was run out after the dis-
appearing of A1 peak. The plotting of I -charge curve represents
A1
the exchange of nearly two electrons per molecule of ClSePh with
the electrode. Diagnostic criteria of the cyclic voltammograms: a
decrease of A2 peak current by increasing scan rate (Fig. 2) and
increasing of the A2 signal during electrolysis confirms the gov-
erning of the ECE mechanism (E >E ). In addition, building on
2
1
1HNMR, 13CNMR, FT-IR, and a sharp signal of 313 in the MS spec-
ꢀ
ꢀ
trum, [1,1 -biphenyl]-4,4 -diselenol (BPhDSe) is introduced as the
isolated product (Scheme 3). ClSePh is converted to its correspond-
+
•
−
ing cation radical (ClSePh ) at the surface of the electrode via 1e
oxidative process followed by leaving of Cl from the molecule. Sub-
+
sequent intermolecular attack of ClSePh to ClSePh produces inter-
mediate 1. By leaving chlorides in the next step in the presence of
water, intermediate 2 is generated. The final product, BPhDSe, is af-
forded by the H-transfer process. HOCl undergoes oxidation at the
−
−
+
applied potential of +1.2 V to produce ClO
during the 2e /3H
2
electrode process. The oxidation of BPhDSe at +1.6 V at the surface
of the glassy carbon electrode is responsible for the appearance of
A2 peak, as is clear from the inset of Fig. 4 correspondings to ox-
idative voltammograms of the isolated product. The inset of Fig. 4I
indicates a recorded voltammogram of the isolated product. The
oxidative A2 peak (+1.6 V) arises from the oxidation of BPhDSe to
BPhDSeox (Scheme 3).
The next step was to apply the same approach of the
controlled-potential coulometry of ClSePh at the identical condi-
tion of Fig. 4. After the disappearing of A1 peak, the electroly-
sis was continued with switching the applied potential to +1.5 V.
Scheme 3. Proposed mechanism for the electrochemical oxidation of ClSePh.
The second anodic wave (A ) was gradually decreased during the
trile/water (aqueous buffer solution with various pHs) (5/5 v/v)
represents that the electrode process of BPhDSe is accompanied by
proton transfer. All voltammograms show the same trend expect to
a regular negative shift of potential of A2 with increasing pH. The
effect of pH was then surveyed in detail by plotting the potential-
pH diagram in a wide pH range of 2 to 10. A careful analysis of the
potential-pH diagram represents two linear segments interrupting
2
progress of coulometry (Fig. 5I). Based on the relation of the I–
Q curve (Fig. 5II), two electrons per molecule of BPhDSe was ap-
proximately calculated to eliminate the A2 peak. The data con-
ꢀ
firms the transformation of BPhDSe to [1,1 -bi(cyclohexylidene)]-
ꢀ
ꢀ
ꢀ
−
2
,2 ,5,5 -tetraene-4,4 -diselenone (BPhDSeox) during 2e process.
Redox properties of the isolated product BPhDSe was more
+
characterized by recording cyclic voltammograms in buffered so-
lutions with various pH values to investigate the general na-
ture of the proton-coupled electron transfer (Fig. 6I). Evidence of
the voltammograms of 3.0 mM of BPhDSe conducted in acetoni-
at pH=7 (Fig. 6II). The oxidation potential is affected by H con-
centration in pH values < 7 by Eq. (1).
2
EPA2 = 1.78 − 0.053pH pH values < 7 R = 0.99
(1)

V. Khakyzadeh, P. Chegini and F. Varmaghani / Electrochimica Acta 360 (2020) 137025
5
in a non-aqueous solvent. Scheme 5 represents the redox behavior
of BPhDSe/BPhDSeox in water and methanol. To survey the main
reason for the difference in the feature of the redox process re-
sponsible for the A2 peak, the voltammograms were recorded by
the addition of consecutive water to the same voltammetric cell.
Despite the dilution of the solution, the intensity of A2 peak in-
creases by the addition of water. Taking into account the increase
of A2 peak current parallel to increasing water content, one can
distinguish the involvement of A2 peak with water.
Indeed, Eq. (2) in Scheme 5 is governed to appear A2 signal. We
have assumed that Eq. (1) is not occurred in the studied potential
range due to weak proton accepting properties of methanol. The
low intense A2 wave in 0.1 M LiClO /methanol (Fig. 7) arises from
4
the PCET in the presence of a small amount of water in methanol
as an impurity. Moreover, the counterpart of the A2 wave (C ) cor-
2
responding to the transformation of BPhDSeox to BPhDSe has ap-
peared. Appearing the cathodic wave of C2 is effectively dependent
on solvent nature. The electrogenerated of BPhDSeox is quite re-
active due to Michael addition positions in the molecule. So the
produced BPhDSeox would be consumed in the time scale of cyclic
voltammetry during some reactions such as hydrolysis and hydrox-
ylation reactions in the water mixture.
Fig. 5. I: Cyclic voltammograms of BPhDSe (0.25 mmol) in water (acetate buffer,
c = 0.2 M, pH = 4.0)/acetonitrile (50/50% v/v) mixture during controlled-potential
coulometry at +1.5 V versus SCE. Part II: variation of the peak current (IpA2) versus
charge consumed.
However, in basic solutions, the potential of A2 indicates no
variation by increasing pH (Eq. (2)).
2
EPA2 = 1.41 R = 1 pH value > 7
(2)
3
.2. Electro-reductive chemistry of ClSePh
−
+
The slope of 53 mV per pH, near to 59 mV/pH for ne /mH
(
n=m) process is attributed to releasing of 2H+ during 2e com-
−
The electrode responses of ClSePh was more characterized by
munication of the electrode/BPhDSe. On the other hand, oxidation
of the di-anionic form of the product (BPhDSe2 ), which is dom-
sweeping the potential toward negative direction up to -1.5 V in
acetonitrile/water (aqueous acetate buffer solution with pH=4.0) at
different scan rates (Fig. 8I). The appearance of a sharp irreversible
−
inant in basic solutions, is not affected by proton concentration
(
Scheme 4).
cathodic wave (C ) is related to the electro-reduction of ClSePh to
2
According to Scheme 4, the electrode process of BPhDSe is
−
benzeneselenolate (PhSe ) at the surface of the glassy carbon elec-
conducted by the proton transfer from the redox-active species
to the solvent. Therefore, the solvent plays a significant role in
facilitating the PCET process. To get more findings on the PCET
nature of BPhDSe, the studies were performed by recording the
cyclic voltammogram of 3.0 mM ClSePh in methanol as solvent
and 0.1 M LiClO4 as indifferent supporting electrolyte (Fig. 7). The
manifest difference between the cyclic voltammograms recorded in
water and methanol has occurred in the waveform of A2 peak. De-
trode (Scheme 6). As is clear, the absence of a corresponding an-
odic peak of C2 at higher scan rates confirms the inherent irre-
versible nature of the electron transfer. Besides, the linear depen-
dence of the current-square root of the scan rate (I/ν1/2) indicates
the diffusion-controlled of the process (inset of Fig. 8).
The irreversibility of electro-reduction may be originated from
the slow charge transfer. Limitation in the kinetic of the electron
transfer was evaluated by estimation of the transfer coefficient (α)
extracted from the Tafel plot (Eq. (3)).
spite A , the intensity of the A2 peak was severely suppressed in
1
methanol. This observation is likely due to the role of the proton
on the potential of the electron transfer. The potential of the elec-
trode process may be affected by the difficulty of proton transfer
ꢀ
ꢁ
αnF
.3RT
log I = logI0 −
η
(3)
2
Fig. 6. I: Cyclic voltammograms of BPhDSe at a glassy carbon electrode in water/acetonitrile (50/50% v/v) mixture, with various pH values of 2.8, 3.5, 4.5, 5.0, 6.0., 7.0, 8.0,
9
.0, 10.5. Scan rate: 100 mVs 1. II: The potential–pH diagram for oxidation of BPhDSe.
−

6
V. Khakyzadeh, P. Chegini and F. Varmaghani / Electrochimica Acta 360 (2020) 137025
Scheme 4. Electrochemical oxidation of BPhDSe at different pH range and acid/base equilibrium of BPhDSe.
Scheme 6. Proposed mechanism for the electrochemical reduction of ClSePh under
bubbling of N2 to the electrolysis cell.
transfer coefficient (α) calculated from Eq. (3), was found to be
0
.14. This result supports the notion that a limitation in the kinet-
ics of charge transfer occurred at the electrode surface.
Fig. 7. Cyclic voltammograms of 3.0 mM ClSePh in the presence of different content
3
.2.1. Electro-reduction studies of ClSePh during electrolysis under N2
of water in methanol/0.1 M LiClO4.
bubbling
Controlled-potential coulometry was employed to probe the
where I, I , α, E and n define as the symbol of current, exchange
fate of the electro-reductive generated species. To run the elec-
trolysis, 0.25 mmol ClSePh was added to a mixture of acetoni-
trile/water (aqueous acetate buffer solution with pH=6.0) in a di-
vided cell. After that, the potential of -1.2 V was exerted, and the
electrolysis was performed under bubbling of nitrogen gas. The
0
current, transfer coefficient, potential, and the number of elec-
tron (n=1). R and T have the usual meanings. Fig. 8II represents
the relation of logI vs. potential obtained from by raising part
of the cyclic voltammogram of 3.0 mM ClSePh at 25 mV/s. The
Scheme 5. Electrochemical oxidation of BPhDSe in water and methanol as solvents.

V. Khakyzadeh, P. Chegini and F. Varmaghani / Electrochimica Acta 360 (2020) 137025
7
Fig. 8. I: Cyclic voltammograms of ClSePh (3.0 mM) in water (acetate buffer, c = 0.2 M, pH = 4.0)/acetonitrile (5/5 v/v) at various scan rates of a to e: 25, 50, 75, 100 and
50. II: Tafel plot for the electrochemical reduction of 3.0 mM of ClSePh, with scan rate of 25 mV/s.
1
Fig. 10. Cyclic voltammograms of the solution of elecytrolysis cell of ClSePh
Fig. 9. Cyclic voltammograms of ClSePh (0.25 mmol) in water (phosphate buffer,
c = 0.2 M, pH = 6.0)/acetonitrile (50/50% v/v) mixture during controlled-potential
coulometry at -1.2 V versus SCE. Inset: variation of the peak current (IpC3) versus
charge consumed.
(
0.25 mmol) in water (phosphate buffer, c = 0.2 M, pH = 6.0)/acetonitrile (50/50%
v/v) at -1.2 V (a) just after the end of electrolysis and (b) an hour passed from the
end of the electrolysis. Inset: cyclic voltammogram of 3.0 mM commercial DPhDSe
in water (phosphate buffer, c = 0.2 M, pH = 6.0)/acetonitrile (50/50%). (For inter-
pretation of the references to color in this figure, the reader is referred to the web
version of this article.)
progress of electrolysis was followed by the recording of cyclic
voltammograms (Fig. 9). A considerable decrease in the cathodic
signal of C3 was a sign of annihilating the starting material. Upon
consuming 50 C (approximately two electrons per molecule), the
cyclic voltammograms (inset of Fig. 9) showed the inconsiderable
C3 peak. On the other hand, a new anodic wave of A4 was ap-
peared and increased during the progress of electrolysis. The new
(Fig. 10b). A dramatic difference between the waveform of voltam-
mogram recorded just after the end of the electrolysis (Fig. 10a)
and the corresponding after an hour passed from electrolysis sup-
ports the notion that a chemical reaction occurred after termina-
tion of the electrolysis. As is evident A4 signal was eliminated,
anodic signal (A ) would be related to the either intermediate or
and a sharp cathodic band (C ) has appeared. The produced yellow
4
5
final product.
solid filtered and was characterized by spectroscopic data. Accord-
ing to the spectroscopic data, 1HNMR, 13CNMR, IR, and MS, 1,2-
diphenyldiselane (DPhDSe) was introduced as an isolated product.
At the end of electrolysis, the bubbling of nitrogen gas to
the cell was interrupted, and the solution of the cell rested for
an hour in-room atmosphere. In the next step, a voltammogram
was recorded after an hour passed from the end of electrolysis
−
According to Scheme 6, benzeneselenolate (PhSe ) was generated
at the surface of the electrode during two successive one-electron

8
V. Khakyzadeh, P. Chegini and F. Varmaghani / Electrochimica Acta 360 (2020) 137025
reductions. At the end of the electrolysis, DPhDSe was produced
−
during air oxidation of PhSe . It is suggested that the production of
−
PhSe is responsible for appearing A4 anodic signal. As expected,
−
the oxidation peak of PhSe is at significant lower potential than
ClSePh because of the negative charge on selenium atom relative
to the presence of electron-withdrawing Cl in ClSePh. To prove the
proposed mechanism, the voltammogram of commercial DPhDSe
was recorded (Fig. 10c). Conformity of the waveform of curves b
and c reflects the same electrode process of commercial DPhDSe
and the resulted product.
The proposed mechanism was also confirmed by conducting the
electrolysis in acidic solution. In this direction, the same procedure
as the previous part (Fig. 9) was utilized in acetonitrile/aqueous
phosphate buffer solution with pH=2.0. Cyclic voltammograms
were recorded to probe differences in the feature of the electrode
process in natural and acidic solutions. Fig. 11 exhibits the anodic
part of cyclic voltammograms recorded at the end of electrolysis
in solution with pHs of 2.0 and 6.0. As is evident, the anodic wave
of A4 tends to increase. This observation reflects the role of the
−
proton on the electrode oxidation process of intermediate (PhSe ).
−
PhSe is protonated in an acidic solution to give phSeH. The pro-
tonated form is oxidized more difficult due to a lack of negative
charge in the structure.
Fig. 11. The anodic part of recorded cyclic voltammograms at the end of electrolysis
of the solution of ClSePh at -1.2 V in acetonitrile/aqueous phosphate buffer with
pHs of 2.0 and 6.0.
3
.2.2. Electro-reductive studies of ClSePh during electrolysis without
N2 bubbling
According to Scheme 6, oxygen proves to affect the reaction
pathways. To future investigate the mechanistic aspects of ClSePh
electron transfer, bulk electrolysis of electrochemical reduction of
ClSePh was performed at the same condition of Fig. 9 expect to
exert no bubbling N2 gas. To elucidate the mechanism of the reac-
tion, cyclic voltammograms of the electrolysis cell were monitored
during the electrolysis progress. Fig. 12 indicates cyclic voltammo-
grams recorded upon coming to the end of electrolysis. It is seen
that the strong cathodic band (C ) decreases in height. Meanwhile,
3
no increase in the height of the anodic wave of A4 is observed dur-
ing electrolysis. The comparison between the voltammograms of
electrolysis under (Fig. 9) and without (Fig. 12) nitrogen gas im-
plies governing different mechanisms during the electro-reduction
step. Contrary to produced the yellow solid observed in the elec-
trolysis under N2 gas, light blue precipitation was formed in the
solution. The difference between the products indicates that oxy-
gen may promote the reaction toward different pathways.
Fig. 12. Cyclic voltammograms of ClSePh (0.25 mmol) in water (phosphate buffer,
c = 0.2 M, pH = 6.0)/acetonitrile (50/50% v/v) mixture during controlled-potential
coulometry at -1.2 V versus SCE. (For interpretation of the references to color in
this figure, the reader is referred to the web version of this article.)
Scheme 7. Proposed mechanism for the electrochemical reduction of ClSePh without N2 gas.

V. Khakyzadeh, P. Chegini and F. Varmaghani / Electrochimica Acta 360 (2020) 137025
9
Fig. 13. FT-IR spectra of I: DPhDSe and II: polyselenobenzene.
FT-IR spectra of the products obtained by two strategies confirm
the observed fact (Fig. 13). A comparison of the FT-IR of the prod-
uct under N2 (Fig. 13I) with the spectrum of the corresponding
solid without N2 gas (Fig. 13II) shows several differences. In con-
trast to the presence of sharp peaks in Fig. 13a some broad bands
The morphology of the polymer was characterized by scanning
electron microscopy (SEM), and the data is shown in Fig. 14. The
SEM images show spherical particles in the range of 200 μM to
200 nm. The average diameter of the nanospheres is estimated
to be 96.4± 6 nm. Also, the elemental analysis of nanostructure
was analyzed using energy dispersive X-ray (EDX) spectrum. The
EDX spectrum (Fig. 14c) confirms the presence of C (81%) and Se
(18%). A comparison of the relative atomic ratio of the elements is
in good agreement with polymer chemical formula. TGA was also
used to examine the thermal decomposition of the polymer. The
curve of weight loss is shown in Fig 14d. The sharp peak of weight
loss is located at almost 280 °C can be attributed to the combus-
tion of carbon content in the sample.
in the range of 500–1750 cm 1 are observed in Fig. 13b. The broad
−
absorption peak in 1058 cm 1 attributed to C-H aromatic stretch-
ing vibrations could be suggested as a polymeric structure of the
final product.
−
According to experimental finds, we proposed a reaction mech-
anism, as shown in Scheme 7. First of all, ClSePh is reduced
at the electrode surface to give the corresponding radical anion
•
−
•−
(
ClSePh ). O2 can serve as an oxidative agent. ClSePh
is oxi-
•
dized following dechlorination to generate intermediate PhSe . In
the next step, a dimmer (SePh)2 is produced by an intermolecu-
It should be noted that the electrochemical properties of
Phenylselenyl bromide (BrSePh) as another substrate was studied.
The behavior of this molecule was very similar to the Benzene-
selenyl chloride. The electrochemical features of BrSePh are pre-
sented in Figs. S8–S10.
•
lar reaction of PhSe and ClSePh. Thereafter a coupling reaction
proceeds between dimmer and ClSePh. Finally, selenobenzene can
polymerize during successive coupling reactions.

10
V. Khakyzadeh, P. Chegini and F. Varmaghani / Electrochimica Acta 360 (2020) 137025
Fig. 14. (a,b) SEM images, (c) EDX analysis, and (d) TGA of synthesized polyselenobenzene.
4. Conclusion
Acknowledgments
In this work, a comprehensive electrochemical study, based on
The authors acknowledge to the K. N. Toosi University of Tech-
nology and the IASBS research council for support this work.
electro-reduction and -oxidation, on Chloroselenobenzene was dis-
closed for the synthesis of new organoselenium compounds in-
cluding a new Diselenol, Diselenide, and polyselenide in good to
excellent yields (81–85%) and purities. All investigations were car-
ried out in a simple cell, consisting of carbon electrodes in wa-
ter/acetonitrile mixture under simple conditions, without using
any catalyst in the presence of air or nitrogen atmosphere. We in-
troduce the first electrochemical pathway for the synthesis of dis-
elenols under oxidation condition also our electroreduction condi-
tion results in different atmospheres, gave us this opportunity to
produce diselenide (under N2 atmosphere) or a polyselenide (un-
der air atmosphere). The applicability of the current protocols are
currently under examination in related chemistries, which will be
released in due course.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.electacta.2020.137025.
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