Analytical Methods in Environmental Chemistry Journal Vol 1(2018) 67-74
Journal home page: www.amecj.com/ir
AMECJ
Analytical Methods: Electrochemical azido-selenenylation of some olefins by cyclic voltammetry and controlled-potential coulometry
aChemistry Department, Faculty of Science, K.N. Toosi University of Technology, Tehran 15418, Iran.
Article history:
Received 7 Nov 2018
Revised form 5 Dec 2018
Accepted 15 Dec 2018
Electrochemical azido-phenylselenenylation of some olefins was studied with the oxidation of diphenyl diselenide in the presence of some olefins and sodium azide in dimethyl formamide containing tetra butyl ammonium perchlorate as supporting electrolyte in an H-type cell. The electrochemi-
Available online 17 Dec 2018
2
3
cal oxidation of the mixture of (PhSe) , olefins, and NaN
was studied by
------------------------
Keywords: Electrosynthesis Diphenyl diselenide Markovnikov Cyclic voltammetry
Controlled-potential coulometry
cyclic voltammetry and controlled-potential coulometry. Anti product can be obtained with Markovnikov orientation. This product was characterized
.by 1H, 13C NMR, and IR spectroscopy
Selenium is a biologically essential element for all vertebrates.Anumberoforganoseleniumcompounds have been found in living tissue: Selenocoenzyme A, Selenobiotine, Se-methyl Selenomethionine, Selenosystathione, Selenohomocystine, Selenocy- stine, Selenomethionine, etc. Moreover, Selenium is also known to help prevent cancer and cardio- vascular diseases [1-7]. Despite the similarities between sulfur containing molecules and their selenium congeners, there are several unique
* E-mail: rouhollahi@kntu.ac.ir https://doi.org/ xxxxxxx
© 2018 AMECJ/ All rights reserved
features of organoselenium compounds. They can be used in nucleophilic, in electrophilic, as well as in radical reactions [8]. Organoselenium compounds have found applications as oxygen transfer reagents in organic and organometallic synthesis and as oxygendonor ligands in main and transition metal complexes [9]. Also, diselenides are known as mediators, redox catalyst and important precursors in organic electrosynthesis. It is evident that investigations of reactivity and redox mechanisms of organic Selenium compounds are of great importance today. Diaryl diselenide themselves can serve in electrosynthesis
as mediators in indirect electrolyses of organic compounds, as redox catalysts for reduction of protons, oxidation of water or derivatization of olefins, as a trap for new complexes [1]. The chemistry of organoselenium compounds has been extensively investigated because of their utility in organic synthesis [2, 10-12]. The reaction of carbon-
compounds containing phenylselenoetherification and phenylselenolactonization have been reported [22]. In several papers, diphenyl diselenide is used as a catalyst for electrosynthesis of many organic compounds [12, 14].
In the present work, the electrochemical oxidation of diphenyl diselenide in the presence of some
carbon double bonds with selenium electrophiles
3
olefins and NaN
was examined by cyclic
is performed under mild reaction conditions and the reaction products can be used in a variety of subsequent functionalizations [12]. It is well established that addition to unsymmetrical olefins initiated by electrophilic phenylselenium species proceeds through the formation of seleniranium intermediates which, in the presence of external or internal nucleophiles, usually affords anti adducts with prevalent Markovnikov orientation [13]. In addition, the phenylseleno group is an important functionality in organic synthesis because it can be easily introduced into and removed from unsaturated compounds [2, 14]. The products obtained from the azido-selenenylation of alkenes contain the phenylseleno and azido groups which can be used for several conversions [15]. Electrosynthesis is the optimal method for carrying out redox reactions, because it works at normal temperature and has the following advantages [16, 17]. Also, organic electrosynthesis is not a new technique, and there is considerable knowledge of the types of reactions which take place at cathodes and anodes. One view of organic electrochemistry is that it is a unique non-thermal method for activating molecules .Since the rate of reaction can normally be increased by raising the electrode potential, it is possible to carry out reactions with high activation energy at low temperature. Another view is that electrochemistry is an alternative to chemical redox methods [18]. There are several works of phenylseleno group,s versatility, including the alkoxylation of alkenes [19], carbonyl compounds [20], and fluoriation of alkenes [21]. Electrochemicalcyclization of unsaturated hydroxyl
voltammetry and controlled-potential coulometry. The electrochemical generation of phenylselenenyl cation followed the formation of anti adduct by a Markovnikov reaction. The final product was purified by preparative thin layer chromatography and characterized by 1H NMR, 13C NMR, and IR spectroscopy.
Cyclic voltammetry and controlled-potential coulometry was performed with an Autolab potentiostat/galvanostat, PGSTAT 30 (Eco Chemie, Utrecht, The Netherlands).
The set-up was used a three-electrode cell with a platinum disc (2 mm diameter) as the working electrode, a saturated Ag/AgCl double junction reference electrode, and a platinum wire as the auxiliary electrode. A platinum rod with a diameter (mm) and length (cm) as working electrode was used in controlled-potential coulometry. The working electrode potential was followed vs. Ag/ AgCl double junction reference electrode (from Azar electrode, Iran). Electrosyntheses have been carried out both undivided and divided cells. NMR spectra were recorded on a Bruker AQS-300 Avance Instruments. Thin layer chromatography (TLC) was performed on plastic sheets pre-coated with silica-gel (Merck), and spots were visualized with UV light and iodine tank.
Diphenyl diselenide, cyclohexene, 1-octene, 1-heptene, styrene, and sodium azide were obtained
from Merck. Tetra butyl ammonium per chlorate (TBAP) and cyclooctene were purchased from Fluka. Dimethyl formamide was prepared from Aldrich.
3.18(dd, 1H, J=6.5 and 12.6 Hz). 13C NM , δ (75
3
MHz, CDCl ): 138.7, 133.3, 129.2, 128.8, 126.8,
127.4, 126.8, 66.0, 33.9.
2.4.3 1-phenylseleno-2-(azido)octane
I (neat) (ν
max
,cm-1) : 2094(N=N-N-), 1570, 1465,
2
The (PhSe)
(0.3 mmol) and excess of olefins and
1259 (=C-H aromatic), 979, 858, 833 and 752 cm-1.
3
NaN
are dissolved in 20 ml dimethyl formamide.
3
1H NM , δ (300 MHz, CDCl ): 7.61-7.55(m, 2H),
Organic solution is contained 1.5 mmol of TBAP as supporting electrolyte. Constant potential electrolysis of the solution was performed in an H-type divided cell under an air atmosphere at room temperature. Constant potential was chosen
1.96 mV (Vs. Ag/AgCl). The electrolysis was terminated when the current decayed to 90% of
7.38-7.32(m, 3H), 3.41(dd, 1H, J=4.0 and 16.0Hz),
3.37(dd, 1H, J=8.0 and 16.0Hz), 3.04-2.94(m, 1H),
3
1.68-0.83(m, 13H). 13C NM , δ (75 MHz, CDCl ):
135.2, 133.0, 129.0, 127.9, 55.9, 44.6, 32.4, 31.5,
28.9, 27.4, 22.5, 13.9.
1-phenylseleno-2-(azido)cyclooctane
initiated current. The progress was monitored by
I (neat) (ν
, cm-1): 2094(N=N-N-), 1572, 1468,
cyclic voltammograms and TLC in different times of reaction. At the end of electrolysis, extraction of the cell solution, afforded an organic phase which its solvent is evaporated. Then, the residue purified by preparative thin layer chromatography over silica gel (eluent was a mixture of n-hexane/ ethyl acetate). The product was characterized by 1H NMR, 13C NMR, and IR spectroscopy.
max
1261 (=C-H aromatic), 984, 863, 835 and 753 cm-1.
3
1H NM , δ (300 MHz, CDCl ): 7.8-7.77(m, 2H),
7.3-7.25(m, 3H), 3.70(dd, 1H, J=4.0 and 16.0Hz),
3.15(dd, 1H, J=8.0 and 16.0Hz), 2.18-1.25(m,
3
12H). 13C NM , δ (75 MHz, CDCl ): 133.3, 129.4,
128.0, 124.4, 124.1, 123.5, 34.9, 34.4, 31.9, 31.6,
30.2, 28.9, 27.1, 22.7.
1-phenylseleno-2-(azido)heptane
I (neat) (ν
max
, cm-1): 2094(N=N-N-), 1573, 1470,
1-phenylseleno -2-(azido)cyclohexane
1265 (=C-H aromatic), 986, 864, 838 and 756
IR (neat) (ν
,cm-1) : 2095 (N=N-N-), 1576, 1468,
cm-1. 1H NM , δ (300 MHz, CDCl ): 7.61-7.58(m,
max
1263 (=C-H aromatic), 982, 860, 835 and 754 cm-1.
3
2H), 7.39-7.34(m, 3H), 3.37(dd, 1H, J=7.9 and 12.6
3
1H NM , δ (300 MHz, CDCl
): 7.63-7.5 (m,2H),
Hz), 3.25(dd, 1H, J=6.5 and 12.6 Hz), 2.04-0.83(m,
7.33-7.25(m, 3H), 3.3(dd, 1H, J=7.9 and 12.6Hz),
3.08(dd, 1H, J=6.5 and 12.6Hz), 2.15-1.26(m,
3
8H). 13C –NM , δ (75 MHz, CDCl ): 135.8, 134.7,
129.1, 128.0, 127.7, 127.5, 64.5, 33.0, 31.8, 29.7,
25.8, 21.6.
1-azido-1-phenyl-2-(phenylseleno)ethane
3
11H). 13C NM , δ (75 MHz, CDCl ): 143.4, 137.3,
132.9, 129.6, 128.9, 127.3, 62.1, 58.6, 34.8, 32.4,
24.3, 23.4, 21.6.
Cyclic voltammogram of a platinum electrode
I (neat) (ν
, cm-1) : 2103(N=N-N-), 1660(C=C),
to (PhSe)
in anhydrous dimethyl formamide
max
3
1585, 1476, 1268 (=C-H aromatic), 985, 872, 841 and 764 cm-1. 1H NM , δ (300 MHz, CDCl ): 7.60- 7.40 (m, 2H), 7.40-7.15(m, 8H), 4.26(dd, 1H, J=6.5 and 7.9 Hz), 3.23(dd, 1H, J=7.9 and 12.6 Hz),
2
containing M TBAP at a sweep rate of 100 mv s-1 in the absence and presence of cyclohexene and sodium azide (excess amount) is shown in Figure
1. This figure shows an oxidative peak (1a) at 1.75
V (vs. Ag/AgCl), which is consisted with oxidation
confirmed this well. In addition to solving well all
2
of (PhSe)
to the phenylselenenyl cation. Cyclic
reactants, it did not show any oxidation peaks in the
2
voltammogram of (PhSe)
in the presence of
potential limit.
6
3
C H
10
and NaN
shows two oxidative peaks (2a,
By supporting the electrolyte which was optimized
3a) at 1 V and 1.96 V. The cyclic voltammetry
for this reaction, it is suggested by a method for
experiments of the mixture of (PhSe)
, C H
, and
increasing yield with bromide ion of electrolyte
2 6 10
3
NaN
were performed in different potential sweep
Torii et al. This anion obtained the reactive mediator
rates of 40-700 mv s-1(Fig. 2). The results of cyclic voltammogram of figure 2 show an increase in the height of anodic peak and oxidation potential. The linear relation of the peak current of 1V vs. square root of sweep rate obtained with data of figure 2 confirms the departure from diffusion control. The
as PhSeBr with PhSe+ [17]. Tetrabutylammonium bromide (TBAB) as supporting electrolyte could not prepare the expectant results. In figure 5, cyclovoltammogramsconfirmedit, and difference of oxidation peak of TBAB and tetrabutylammonium perchlorate (TBAP) is absolutely. Table 1 shows
2
multi-cyclic voltammograms of 4mM (PhSe)
and
the synthesized products of different alkenes and
6
10
excess amount of C H
3
and NaN show a decrease
their yields.
in second scan of anodic peak. After second scan, anodic peak becomes constant (Fig. 3). We seached several conditions for finding optimum results. Firstly, different solvents are used in the
The controlled-potential coulometry was performed in organic solution which is contained 0.3 mmol of
experiments. Acetonitryl was not suitable solvent
(PhSe)
and excess amount of C H
and NaN at
2 6 10 3
3
because of reaction with phenylselenyl cation. The second oxidation peak shows it in figure 4. Kunai et al. postulated a reaction between PhSe+, CH CN in the presence cyclohexene [9]. So we abandoned this solvent. Dimethyl formamide was very suitable solvent for this reaction. Cyclic voltammetry
constant anodic potential of 1.96 V (vs. Ag/AgCl) with an H-type divided cell. Poor results received with undivided cell. The electrolysis was performed between 3-5 h, depending on the passed charge for the reaction. The monitoring of electrolysis was performed by TLC and cyclic voltammetry.
Fig. 1. Cyclic voltammogram of 4 mM (phSe)
(A) , 4 mM (phSe) in the presence of C H
(B), 4 mM (phSe)
2 2 6 10 2
in the presence of C H
and NaN
(C), C H
(D) , NaN (E) with 0.2 M TBAP at a platinum electrode. Potential
6 10
3 6 10 3
sweep rate was 100 mVs-1.
Fig. 2. Cyclic voltammograms of 4 mM (phSe) and 0.2 M TBAP in the presence of excess amounts of C H
and
3
NaN
2
at a platinum electrode and at different potential sweep rates (40-700 mVs-1).
6 10
Fig. 3. Multi-cyclic voltammograms of 4 mM (phSe) and 0.2 M TBAP in the presence of excess amounts of C H
3
and NaN
2
at a platinum electrode. Potential sweep rate was 100 mV.s-1.
6 10
Fig. 4. Cyclic voltammogram of 4 mM (phSe) and 0.2 M TBAP in CH CN at a platinum electrode. Potential sweep
2 3
rate was 100mVs-1.
2
Fig. 5. Cyclic voltammograms of 4 mM (phSe)
6
10
in the presence of excess amounts of C H
3
and NaN
at a platinum
electrode. Supporting electrolytes were tetrabutylammonium bromide (A), tetrabutylammonium Perchlorate (B). Potential sweep rate was 100 mV.s-1.
Table 1. The synthesized products of different alkenes and their yields.
Entry | Alkene | Product | Time (h) | Isolated yield (%) | Theoriticalyield (%) | Current efficiency (%) |
1 |
|
| 3 | 57 | 68 | 90 |
2 |
|
| 3.5 | 60 | 70 | 90 |
3 |
|
| 3 | 54 | 63.5 | 84 |
4 |
|
| 4 | 53 | 62 | 86 |
5 |
|
| 3 | 58 | 69 | 84 |
Moreover, it was shown a decrease in the anodic peak current of the product during various times of
selenenylation of olefins proposed EC reaction which the olefins react with the phenylselenenyl
the electrolysis progressing (Fig. 6).
2
cation of the oxidative (PhSe)
in a nucleophilic
N-value of about 2 electrons calculated for controlled-potential coulometry at the potential of
1.96 V. The mechanism of electrochemical azido-
addition fashion. This reaction generated the intermediate of selenyranium cation which was reacted with Sodium azide for synthesis of the
Fig. 6. Cyclic voltammograms of 4 mM (phSe) and 0.2 M TBAP in the presence of excess amounts of C H
and
2 6 10
3
NaN
at a platinum electrode during controlled potential coulometry versus Ag/AgCl. Potential sweep rate was 100
mV.s-1.
product (scheme 1). The results of IR spectroscopy of the final product show removal of C=C band for vinylil group in 1662 cm-1. A relatively strong adsorption band disappeared for N-N=N group of
In comparison of organic reactions, the present electrochemical method considers being ineffective because of easier conditions (room temperature and atmosphere pressure), using lower amounts
3
NaN
in 2095 cm-1.
of reactants, not used catalysts, relatively short reaction times, high purity, and selectivity.
2
In this paper, olefins and Sodium azide as nucleophile reacted with phenylselenenyl cation derived from electrochemical oxidation of (PhSe) . This progress was leading to the formation of azido-phenylselenenyl functionalized product with Markovnikov reaction. The final product was received a relatively good yield (60%). Like prior papers [4], regeneration of diphenyl diselenide was caused low yield of the product. The study of cyclic voltammograms and coulometric data was confirmed EC mechanism for electrochemical azido-selenenylation of olefins. The results and conditions of this project are better of the organic azido-selenenylation reactions [13, 20].
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