ELECTROCHEMICAL ANALYSES AND REACTIONS OF MALONONITRILE
DERIVATIVES AND PHENYL AZIDE
A RESEARCH PAPER
SUBMITTED TO THE GRADUATE SCHOOL
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE
MASTERS OF ART
BY
JINYU LIU
DR. CHONG ‐ ADVISOR
BALL STATE UNIVERSITY
MUNCIE, INDIANA
JULY 2013
CONTENT
Abstract
1
Introduction
1
Material
3
4-methoxybenzalmalonoitrile
3
Phenyl azide:
4
Set up
6
Experiment
6
1. 4-methoxybenzalmalonoitrile
6
a. Low concentration experiment to check and determine the potential of
4-methoxybenzalmalononitrile.
b. High concentration experiment to confirm the reaction and the product.
c. Product isolation.
6
8
10
2. Electronic effect for different substituted group
12
3. Phenyl azide reaction.
15
Result
16
Acknowledgement
18
Reference
19
Abstract:
The versatile and relatively inexpensive (low energy cost) synthesis of new organic
molecules is important for pharmaceutical production, polymerization, and other industrially
applicable facets of chemistry. Electrochemical reduction of unsaturated organic compounds
at room temperature to new organic products offers a benign and ambient method for the
production of such molecules. The compounds, (p-methoxybenzal)malononitrile, 1 , E pc =
-1.64 V vs. Ferrocene/Ferrocenium (Cp 2 Fe0/+), its derivatives and phenyl azide, 2 , E pc =
-2.43 V vs. Cp 2 Fe0/+, were investigated for their redox activities with and without alkylation
agents, R-X, via scanning and pulse voltammetric techniques in acetonitrile,
acetonitrile/water and tetrahydrofuran as solvents, using 0.1 M [NBu 4 ][PF 6 ] as the supporting
electrolyte. The redox potentials were measured at glassy carbon and platinum disk
electrodes. Controlled potential electrolysis (CPE) of 1 at E appl = -1.75 V vs. Cp 2 Fe0/+ was
yielding p-methoxybenzaldehyde (> 90%). CPE of 2 at E appl = -2.54 V vs. Cp 2 Fe0/+ in air
gave aniline in good yield. Bulk cathodic electrolyses of 1 and 2 were exhausted in < 0.5 - 1 h,
following the passage of 1 F/mol of analyte. Upon completing bulk reductions at each applied
potential, products were characterized by 1H-NMR and GC-MS data analyses.
Introduction:
Nowadays, the C-C bonds cleavage and the C-C bonds coupling are top prior in the
organic field. However, in the traditional way, the synthesis of aldehyde from olefin is an
oxidation reaction.
In the presence of PdCl 2 (MeCN) 2 , 1, 4-benzoquinone, and t-BuOH, aryl-substituted olefins
can selectively be oxidized to aldehydes. The reaction was as followed. [1]
1
The use of PhI(OAc) 2 in dichloromethane enables a clean oxidative cleavage of 1,2-diols to
aldehydes. Using OsO 4 as catalyst, NMO and 2,6-lutidine, olefinic bonds can be cleaved in
acetone/water to yield the corresponding carbonyl compounds. [2]
Based on the both catalytic reaction, in the reaction, expensive catalyst was used. One
reaction is in the high temperament and another one need a long time to get a good yield.
Also, the hydration can be the first step, and followed by the oxidation to get the aldehyde
from olefin. The olefin was hydrated to alcohol. Then the alcohol was oxidized to aldehyde.
H+
+
H2O
OH
[O]
OH
O
From the above reaction mechanism, after hydration of olefin, only ketone produced, and
it could not cleave the C=C double bond. Depend on the traditional organic synthesis
reaction, it will spends lots of time and energy especially in the conjugated structures, like
the compound in this project, the olefin double bonds conjugated with the phenyl group
which stabilized the C=C bond. In the previous research, to make the
2
p-methoxybenzalmalononitrile, p-methoxybenzaldehyde and malononitrile are reactants, but
no research shows the inverse reactions. However, after checking the potential of
p-methoxybenzaldehyde, one cathodic peak is shown in the cyclic voltammetry graph that
means some reduction reactions can happen on this compound by using bulk electrolysis on
Pt electrode under the room temperature with less than 1h. There is no previous research to
indicate the cathodic reduction induced hydration of olefin. Based on the reaction of
hydration of benzalmalononitrile, the CS-gas which is in the similar family can be easy to
decompose into nontoxic compounds.
In the organic synthesis, it is an important reaction to reducing azide to amines. The
methods for converting the azide to amines contain catalytic hydrogenation [3], the
phosphine-based Staudinger reduction [4] and the metal hydride reduction [5]. However, for
these methods, they have significant limitation. [6]
In electrochemistry, voltammetries are important tools to show the nature of the compound
based on different solvents. The solvent effect can affect the behavior of compounds
depended on the donor number and the dielectric constant. [7] The voltammetries can be
related to the thermodynamic and kinetic properties of the compounds. Bulky electrolysis is
a normal tool in electrochemistry to make the reaction happen.
Materials:
4-methoxybenzalmalonoitrile:
Light yellow solid 0.0745g; b.p. less than 220 oC
IR (acetonitrile, cm-1) 3621 (w, hydrocarbon), 2225 (s, nitrile), 1514(s, aromatic double
3
bond), 1038 (m, C-O group)
1
H-NMR (400MHz, acetonitrile) δ 7.95 (singlet, 1H [A]), 7.94 (doublet, 1H [B],
J=8.8Hz), 7.10 (doublet, 1H [C], J= 9.16), 3.88 (singlet, 3H [D])
[M+1]=185.
B
C
H
H
NC
D
CN
H3CO
H
C
H
B
A
H
It is a family member as the malononitrile, which also has the cyanocarbon group. It
can be synthesized by the Knoevenagel condensation. [8] Take the CS gas as an example:
The reaction is catalysed with weak base like piperidine or pyridine. The production
method has not changed since the substance was discovered by Corson and Stoughton.
Other bases, solvent free methods and microwave promotion have been suggested to
improve the production of the substance.
Phenyl azide:
It is an organic compound with the formula C 6 H 5 N 3 . It is one of the prototypical
4
organic azide. It has a pungent odor. The structure consists of a linear azide substituent
bound to a phenyl group.
Molecular formula
C6H5N3
Molar mass
119.12 g/mol
Appearance
Pale yellow, oily liquid
Boiling point
49 °C at 5mm Hg
Main hazards
Explosive
N3
Fig 1: MS spectrum for phenyl azide. [9]
5
Setup:
The photo above is a sample of the e-chem cell which had been set up. Working
electrode as 2mm Pt or 2mm glassy carbon electrode was placed in the middle which was
C, the reference as Ag/ AgCl was placed in part A, and the counter electrode as Pt was
placed in part B. Though the change of the potential and current by using the
potentialstat, it shows the graph for the voltammetry to get and check the potential of the
analysts and using that potential to do the electrolysis to make some unknown reaction in
the e-chem cell.
Experiment：
1. 4-methoxybenzalmalonoitrile reaction.
a. Low concentration experiment to check and determine the potential of
6
4-methoxybenzalmalononitrile.
a
E pc = -1.70V
5μA
i ca
background
pre-electrolysis
i an
post-electrolysis
b
2
1
0
-1
E (V vs
-2
-3
Cp2Fe+/0)
Fig2. CV scan for 2m M of 1 in acetonitrile with 0.1M [NBu 4 ][PF 6 ] as electrolyte at room temperature, the scan
rate was 200mV/s on 2mmPt electrode.
From a which is pre-electrolysis, it showed the peak potential of sample was 1.7V vs
ferrocene on Pt electrode which has a huge peak, and post-electrolysis (b), when it ran in
the same potential range, the huge peak disappeared, which may mean the starting
material was reacted during the bulk electrolysis.
i ca
post-electrolysis
i ca
i an
2μA
0.5
0
E (V vs-0.5
Cp2Fe+/0)
-1
-1.5
7
Fig3. CV scan for 2mM 1 post-electrolysis at room temperature in acetonitrile with 0.1M [NBu 4 ][PF 6 ] as
electrolyte, the scan rate was 200 mV/s on 2mm Pt electrode.
Post electrolysis, two new peaks showed up at -0.33V vs. ferrocene and 0.107V vs.
ferrocene that it did not show up in the pre-electrolysis graph. It means that some
unknown reaction happened and some new stuff came up. If all of the product can
dissolve in the acetonitrile, it may two products there. Also, after electrolysis, the color of
the solution in the working electrode turned to orange like the honey.
SWV
1μA
Half Width=130mV
-1
-1.2
-1.4
-1.6
-1.8
E (V vs Cp2Fe+/0)
-2
-2.2
-2.4
Fig4. Square wave voltammetry for 2mM 1 at room temperature with 0.1M [TBA][PF 6 ] as electrolyte on 2mm Pt
electrode.
This graph showed that the half potential of the sample was -1.65V vs. ferrocene, and by
calculating the half width of the peak, it indicated that the reaction in the cell was
one-electron transfer reaction whose half width was larger than 90mV. Seeing the SWV, it
is found that the half width was 90mV, it is likely a one-electron transfer reaction.
b. High concentration experiment to confirm the reaction and the product.
8
50 μA
background
i ca
molanonitrile
post-electrolysis
i an
2
1
0
-1
E (V vs Cp2Fe0/+)
-2
-3
Fig5: 30mM 1 with 0.109M [TBA][PF 6 ] in acetonitrile in the room temperature on 2mm Pt electrode. The scan
rate was 200mV/s.
For the high concentration, a little difference appeared by comparing the low
concentration, at the end of range (about 1V vs. ferrocene) a reversible peak showed up.
So the concentration may have some unknown effect on the reaction. And also at -2.5V vs.
ferrocene, there was a new peak there. Also the two old peaks were at the simile place,
because of the high concentration, the peak potential shifted a little. It showed the
potential more clear in the graph blow.
9
i ca
i an
10μA
1.5
1
0.5
0
-0.5
-1
E （V vs Cp2Fe0/+)
Fig6: 30mM 1 post-electrolysis with 0.109M [TBA][PF 6 ] in acetonitrile in the room temperature on 2mm Pt
electrode. The scan rate was 200mV/s.
Two peaks potentials were -0.169V, 0.182V and the half potential for the last peak
was 7.75V vs. ferrocene. Compared with the background, it means that after
electrolysis, some unknown compound formed in the solution.
c. Product isolation.
After the solution was collected in a small vessel, use nitrogen gas to evaporate the
solvent, stirring and keep the evaporation speed slowed to prevent to lose some of
organic product which has a low boiling point. Then mix benzene (1st experiment) or
ethyl ether (2nd experiment) with the residual. As we know, the electrolyte could not
dissolve in both solvent. After mix very well, filter the solution through the silicon gel.
What’s more, remove the solvent again to get the major product.
By using the NMR and GC-MS, a major was fingered out which was
10
4-mehtoxybenzaldehyde.
4-methoxybenzaldehyde:
light yellow liquid 0.0236 (yield 31.7%); b.p. 248 ℃
IR spectrum (dichloromethane, cm-1) 2926 (m, alkane), 1606 (m, CO double bond),
1464 (m, aromatic double bonds)
1
H-NMR (400MHz, chloroform) δ 9.886 (singlet, 1H [A]) 7.851 (doublet, 1H [B]
J=8.8Hz) 7.015 (doublet, 1H [C] J=8.8Hz) 3.847 (singlet, 3H[d])
[M]=136
c
H
H
b
O
d
H3CO
H a
H
c
H
b
Fig7: MS spectrum for the isolated product. The molar mass is 136g/mol.
11
Fig8: NMR spectrum for the isolated product.
The two spectrums above for NMR and GC-MS, show the evidence to prove the
structure for my one major product. After calculation, the yield is around 80%.
2. Electronic effect for different substituted group.
After
the
cathodic
reduction
of
p-methoxybenzalmalononitrile,
the
methoxybenzaldehyde was formed in the solution with the potential (-1.64V vs.
Ferrocene). However, in the benzalmalononitrile family, series of organic compounds
with different substituted groups was shown the different voltammetry activity. So the
electric effect would be investigated by using some various substituted groups in two
different solvents by using two different electrodes (glassy carbon electrode and Pt
electrode)
Based on the different effects of the substituted group on the phenyl group, both
activated and deactivated groups were investigated in three weeks. Also the position
of substituted groups can stabilize or destabilize the conjugated C=C double bonds.
12
The structures of the five compounds were followed:
CN
NC
NC
CN
MeO
MeO
OMe
OMe
p-methoxybenzalmalononitrile
3,4,5-trimethoxybenzalmalononitrile
NC
CN
NC
CN
MeO
OMe
Cl
m-chlorobenzalmalononitrile
NC
3,4-dimethoxybenzalmalononitrile
CN
MeO
p-methoxybenzalmalononitrile
13
b
a
3.00E-05
3.00E-05
2.00E-05
2.00E-05
1.00E-05
1.00E-05
I (A)
I(A)
0.00E+00
-1.00E-05
0.00E+00
-2.00E-05
-1.00E-05
-3.00E-05
-2.00E-05
-4.00E-05
-5.00E-05
2
1.5
0.5
1
0
-0.5
-1
-1.5
-2
-3.00E-05
-2.5
2
E (V vs. Ferrocene)
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
E ( V vs. Ferrocene)
c
2.50E-05
2.00E-05
1.50E-05
I (A）
1.00E-05
5.00E-06
0.00E+00
-5.00E-06
-1.00E-05
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
E ( V vs. ferrocene)
Fig 9: CV scan for (a) 1mM 3,4,5-trimethoxybenzalmalononitrile (b) 1Mm 3,4-dimethoxymalononitrile (c)
1mM m-methoxybenzalmalononitrile. 0.1M [TBA][PF 6 ] was used as electrolyte in the solvent acetonitrile
on 2mm GC electrode. The scan rates are 200mV/s.
I checked the peak potentials and half potentials by using CVs, LSVs and DPVs for five
different compounds by using the acetonitrile as the solvent and the [TBA][PF 6 ] as
supporting electrolyte.
14
The data of the potentials as followed:
Glassy Carbon Electrode
Compound
Platinum Electrode
Epc
E1/2.
Half Peak Width
Epc
E1/2
Half Peak Width
（V）
(V)
(V)
(V)
(V)
(V)
m-chlorobenzalmalononitrile
-1.38
-1.32
0.0991
-1.42
-1.33
0.1023
p-methoxybenzalmalononitrile
-1.62
-1.55
0.082
-1.72
-1.68
0.123
m-methoxybenzalmalononitrile
-1.50
-1.43
0.086
-1.60
-1.49
0.16
3,4,5-trimethoxybenzalmalononitrile
-1.53
-1.49
0.096
-1.53
-1.50
0.135
3,4-dimethoxybenzalmalononitrile
-1.61
-1.56
0.087
-1.65
-1.56
0.099
Table1: voltammetry data for different substituted groups on benzalmalononitrile on two different electrodes. The data of
potential was converted to use the ferrocene as a standard.
3. Phenyl azide reaction.
8.00E-05
6.00E-05
i ( A)
4.00E-05
2.00E-05
0.00E+00
-2.00E-05
-4.00E-05
2
1
0
-1
-2
-3
-4
E ( V vs ferrocene)
Fig10: CV scan for 5mM phenyl azide in THF with 0.1M [TBA][PF6] as electrolyte on glassy carbon electrode. The
scan rate was 200mV/s.
In order to get the half potential of phenyl azide, which has an unsaturated group and may
have some reaction on that group based on gaining electrons, the CV scan was used to
check the half potential of this compound in THF. The cathodic peak potential is -3.01V
vs. ferrocence. Then based on the same condition, LSV was used to check the half
potential which was -2.4V vs. ferrocence.
15
2.50E-05
2.00E-05
i ( A)
1.50E-05
1.00E-05
E1/2 = -2.4V
5.00E-06
0.00E+00
-1
-1.5
-2
-2.5
-3
-3.5
-4
E ( V vs ferrocene)
Fig 11: LSV for 5mM phenyl azide in THF with 0.1M [TBA][PF 6 ] as electrolyte on glassy carbon electrode. The scan
rate was 1mV/s.
However, the peak potential shifted a lot when the Glassy Carbon electrode was replaced
by Pt electrode. The peak potential shifted to -3.31V vs. ferrocene
After measuring the half potential of the phenyl azide, controlled potential electrolysis
was running. Aniline was detected by GC-MS which was the product from one electron
reaction, and another product was N 2 which escaped during the process of electrolysis.
Result:
Combining all the voltammetry graphs and the spectrums, for my starting material, it
has some reaction in the cell, and one of the products, 4-methoxybenzalmalononitrile,
formed. However, depended on some unknown reason, only one product can be detected.
So the equation for the reaction is:
16
NC
CN
O
CN
e
MeO
-
H2O
+
CN
MeO
Also, for the electronic effect of different substituted group on this family compound,
the chloro is weakly deactivated group and the methoxy is strongly activated group.
Based on the table, the compound with chloro group has a low half potential. However,
for the chloro, the deactivated group is meta- directors, and the methoxy is ortho or para
directors. The substituted group was used to stabilize the negative charge on the аC to
make the starting material easy to get an electrons. So seeing from the methoxy group,
the lowest one is m-methoxy because it only has one methoxy group on the phenyl group
and the rest is on the meta-position. The largest one is p-methoxy because it has a
activated group, but the rest was connect to the para-position. It decreases the resonance
of the phenyl group and the olefin double bond to increase the energy which is need to
adding the electrons into the bond. For the two other methoxy compounds, the meta
position was decreasing the potential. The otho and para position was increasing the
potential. Also, in these compounds, numbers of methoxy group has some effect on the
potential shift. It can offset the part of the other position’s effect. After this, more
substituted groups will be investigated and electrolysis will be used to investigate the
electronic effect on the reaction product.
For cathodic reduction reaction of phenyl azide, the aniline was detected in the product.
The mechanism was followed. The phenyl azide gains one electron to form the
17
intermediate and release the nitrogen gas. Then gain two protons to form the aniline. [10]
During the reaction, the [PhN]-. anion was formed. In the future, methyl iodide will be
used to do the electrolysis with phenyl azide to try to make N-C bond.
18
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19