Electrochemical synthesis of adiponitrile from the renewable raw material glutamic acid

Article abstract of DOI:10.1002/cssc.201100776

Current affairs: Adiponitrile, used to produce nylon 6.6, is prepared from the renewable compound glutamic acid by an electrochemical route, involving electro-oxidative decarboxylation and Kolbe coupling reactions. The new route is an example of the use of glutamic acid as a versatile substrate in the transformation of biomass into chemicals. Also, it highlights the use of electrochemical methods in biomass conversion.

Full text of DOI:10.1002/cssc.201100776

DOI: 10.1002/cssc.201100776
Electrochemical Synthesis of Adiponitrile from the Renewable Raw Material
Glutamic Acid
[
a]
Jian-Jun Dai, Yao-Bing Huang, Chi Fang, Qing-Xiang Guo, and Yao Fu*
Adiponitrile, the precursor of hexamethylenediamine, is an im-
synthesis of adiponitrile via Kolbe coupling of potassium 3-cya-
nopropanoate (CPA-K) generated in situ from 3-cyanopropano-
ic acid methyl ester (CPA-Me) (Scheme 2).
[
1]
portant bulk chemical, and used for the production of the
popular polymer nylon 6.6. In 2005, the global production
volume of adiponitrile amounted to about 1.55 million
Electrochemistry has emerged as a powerful tool for numer-
[
2]
[7]
tonnes. Because of its industrial value many methods have
been developed for its synthesis. In an early industrial route,
adiponitrile is made from adipic acid through dehydration of
adipic diamide. More recently, adiponitrile has also been pro-
duced from butadiene through chlorination/cyanation or
direct cyanation. In addition, adiponitrile can be made through
ous industrial-scale transformations. The Kolbe reaction is an
important synthetic tool for carbon–carbon bond formation in
[8]
organic synthesis, on both laboratorial and industrial scales.
For example, sebacic acid, an important raw material for poly-
meric plasticizers, can be obtained from adipic acid via Kolbe
coupling. This process has been used on an industrial scale by
[3]
[9]
the electrolytic hydrodimerization of acrylonitrile (Scheme 1).
Asahi Chemical. Also, amino acids constitute alternative sour-
[10]
Notably, all of these industrial routes for adiponitrile synthesis
ces of nitrogen for nitrogen-containing bulk chemicals. Glu-
tamic acid is considered the most-abundant non-es-
[11]
sential amino acid in plant proteins, and in addi-
tion has been identified as one of the top 12 bio-
mass-derived platform molecules that can be con-
[12]
verted into a variety of value-added chemicals. It
can be obtained from the waste streams of dried dis-
tillers grains with solubles (DDGS) associated with bi-
[11]
oethanol production from wheat and maize. Gluta-
mic acid can also be produced by microbial fermen-
[13]
tation. By 2020, the production of glutamic acid as
a cheap biobased feedstock is estimated to reach ca.
Scheme 1. Petroleum-based routes towards adiponitrile.
[11]
2
0 million tonnes per year. Recently, Scott and co-
are based on petroleum resources. They all required external
nitrogen sources (i.e., NH , NaCN, or HCN). However, diminish-
3
ing fossil fuel resources and increasing environmental concerns
have emphasized the need to use renewable raw materials as
[
4]
educts in the fuel and chemical industries. Accordingly, re-
searchers have shown considerable interest in the transforma-
[
5]
tion of biomass into transportation fuels. The conversion of
biomass platform molecules into bulk chemicals is also gaining
[
6]
increasing attention. In this context, the production of adipo-
nitrile from renewable materials presents an interesting chal-
lenge.
Scheme 2. Biomass-based adiponitrile synthesis from glutamic acid.
Herein, we demonstrate a biobased synthesis of adiponitrile
from glutamic acid (a renewable compound) by using electro-
chemical methods under mild conditions. The protocol in-
volves (1) the conversion of glutamic acid into glutamic acid 5-
methyl ester (Glu-Me), (2) electro-oxidative decarboxylation of
glutamic acid 5-methyl ester (Glu-Me) to 3-cyanopropanoic
acid methyl ester (CPA-Me), and (3) a one-pot electrochemical
workers have reported a series of papers on the production of
[14]
chemicals from glutamic acid, including g-aminobutyric acid,
[
11]
[15]
acrylonitrile, N-methylpyrrolidone, N-vinylpyrrolidone, and
[16]
succinonitrile. Our study is inspired by the use of electro-
chemical methods in industrial synthesis as well as Scott’s
recent work on the transformation of glutamic acid into value-
added compounds. Our study not only shows an alternative
route for the synthesis of adiponitrile from glutamic acid based
on electrochemical methods, but also gives an additional ex-
ample of the use of electrochemical techniques in the transfor-
[
a] J.-J. Dai, Y.-B. Huang, C. Fang, Prof. Q.-X. Guo, Prof. Y. Fu
Anhui Province Key Laboratory of Biomass Clean Energy
Department of Chemistry, University of Science and Technology of China
Hefei 230026 (PR China)
E-mail: fuyao@ustc.edu.cn
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201100776.
[17]
mation of biomass into chemicals.
ChemSusChem 2012, 5, 617 – 620
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
617

A facile procedure for the conversion of glutamic acid into
glutamic acid 5-methyl ester (Glu-Me) was previously reported
tion of the solvents revealed that a mixture of MeOH/H O in
2
a 4:1 ratio (v/v) was a better solvent, increasing the yield of
CPA-Me 2 to 60% (entries 2–9). Next, we examined other bro-
[
18]
by Baldwin and co-workers. Hence, we investigated the elec-
trochemical synthesis of adiponitrile starting from (Glu-Me). In
order to make 3-cyanopropanoic acid methyl ester (CPA-Me)
from Glu-Me, Scott and co-workers recently demonstrated oxi-
dative decarboxylation of Glu-Me by using sodium hypochlor-
mide salts, and found that the use of salts including LiBr·H O,
2
KBr, Me NBr, Et NBr, and Bu NBr could also effect the reaction,
4
4
4
but the yields of CPA-Me 2 remained low (entries 10–14). Also,
when other halide salts such as NaCl or NaI were employed,
the yields of the desired CPA-Me 2 were only 19% and 16%,
respectively (entries 15 and 16). When platinum was used as
cathode instead of graphite, the yield of CPA-Me 2 increased
dramatically (entries 17 and 19–21). To our delight, when the
reaction was conducted at 08C, the desired product CPA-Me 2
was obtained in 91% yield (entry 18).
[16]
ite in the presence of a catalytic amount of sodium bromide.
However, the need for stoichiometric amounts of sodium hy-
[
16,19]
pochlorite is considered a drawback of this method.
Elec-
trochemical methods generally enable transformations to
occur under mild conditions without the use of strong, hazard-
[
20]
ous chemical reagents. Thus, oxidative decarboxylation with-
out the use of sodium hypochlorite may be achieved by the
application of electro-organic synthesis techniques.
With these results in hand, we turned our attention to the
electrochemical synthesis of adiponitrile via Kolbe coupling
from CPA-Me 2. First, CPA-Me 2 was converted to CPA-K 3 by
Our work started with the electro-oxidative decarboxylation
of Glu-Me 1 to CPA-Me 2. We initially chose platinum and
graphite as anode and cathode, respectively. Notably, bromide
salts have served both as the supporting electrolyte and as
[
22]
saponification (see Supporting Information).
Because the
[23]
current density plays an important role in Kolbe coupling,
we next optimized the current density for the electrochemical
synthesis of adiponitrile 4 via Kolbe coupling of CPA-K 3. Ini-
tially, the MeOH solution of CPA-K 3 was electrolyzed at current
[
21]
mediator in anodic oxidations. Treatment of Glu-Me 1 with
À2
sodium bromide at a current density of 80 mAcm in MeOH
À2
at room temperature led to electro-oxidative decarboxylation,
densities of 60, 120, 180, 240, 300, and 360 mAcm , respec-
[24]
providing CPA-Me 2 in 33% yield (Table 1, entry 1). Optimiza-
tively. The desired product adiponitrile 4 was obtained after
À1
6
.7 Fmol of electricity passed, however, the yields were only
0 to 45%. This can be attributed to the poor solubility of the
3
product forming at the surface of the platinum anode, decreas-
ing the efficiency of the Kolbe coupling. In order to keep the
surface of the platinum anode clean, we chose acetone as
Table 1. Electro-oxidative decarboxylation of glutamic acid 5-methyl
ester to 3-cyanopropanoic acid methyl ester.
[
a]
[25]
a co-solvent with MeOH for Kolbe coupling of CPA-K 3.
Indeed, the yield of adiponitrile 4 was effectively improved. As
shown in Figure 1, the yield of the desired product 4 was 65%
at a current density of 180 mAcm with MeOH/acetone (1:1)
[
b]
Entry
MX
Anode–
cathode
Solvent
Yield
[%]
À2
as solvent at room temperature.
1
2
NaBr
NaBr
NaBr
NaBr
NaBr
NaBr
NaBr
/
Pt–C
Pt–C
Pt–C
Pt–C
Pt–C
Pt–C
Pt–C
Pt–C
Pt–C
Pt–C
Pt–C
Pt–C
Pt–C
Pt–C
Pt–C
Pt–C
Pt–Pt
Pt–Pt
Pt–Pt
Pt–Pt
Pt–Pt
MeOH
33
50
20
55
35
60
36
0
trace
42
46
58
49
In an attempt to increase the efficiency of the conversion of
CPA-Me 2 to adiponitrile 4, we next tried to combine the sapo-
nification reaction and Kolbe coupling in a single step. Treat-
ment of CPA-Me 2 with the corresponding base in MeOH at
3
MeOH/CH CN (1:1)
[
c]
3
4
5
6
7
8
9
0
MeOH/DMF (1:1)
MeOH/H O (1:1)
CH CN/H
2
3
2
O (1:1)
O (4:1)
O (4:1)
O (4:1)
MeOH/H
MeOH/H
MeOH/H
2
2
2
608C for 30 min caused the full conversion of CPA-Me 2 to
[
[
d]
e]
CPA-M (M=K, Li, Me N, etc.). Various conditions for Kolbe cou-
4
NaBr
LiBr·H
KBr
EtOH/H
2
O (4:1)
pling of CPA-M were examined to optimize the reaction condi-
tions (Table 2). Furthermore, it was found that the best ratio of
MeOH/acetone was 1:1 (v/v; entries 2–4). The desired product
1
2
O
MeOH/H
MeOH/H
MeOH/H
MeOH/H
MeOH/H
MeOH/H
MeOH/H
MeOH/H
2
2
2
2
2
2
2
2
O (4:1)
O (4:1)
O (4:1)
O (4:1)
O (4:1)
O (4:1)
O (4:1)
O (4:1)
1
1
1
1
1
1
1
1
2
3
4
5
6
7
Me
Et NBr
Bu NBr
4
NBr
4
was obtained in inferior yields when using H O, CH CN, DME,
2 3
4
or HFIP as the co-solvent (entries 5–10). Temperature is not
considered a critical variable but may improve transport in
electrodecarboxylation. An increase of the temperature usually
4
36
19
16
72
NaCl
NaI
NaBr
NaBr
KBr
[23]
[
f]
[g]
gives a higher yield in Kolbe couplings. Indeed, when the re-
action was carried out at a lower temperature (08C), the de-
sired product 4 was obtained in lower yield (entry 11). In con-
trast, the yield of the desired product 4 increased to 78% at
608C (entry 13). We also used a divided cell to reduce the re-
duction reaction in the undivided cell. Unfortunately the yield
of 4 was not increased effectively (entry 12). The organic base
1
8
MeOH/H
MeOH/H
MeOH/H
2
O (4:1)
O (4:1)
O (4:1)
91 (76)
65
19
20
21
2
Me
4
NBr
2
70
54
NaBr
CH
3
CN/H
2
O (1:1)
[
(
8
a] Reaction conditions: l-glutamic acid 5-methyl ester (2.0 mmol), MX
3.0 mmol) in solvent (10 mL) was electrolyzed at a current density of
0 mAcm in an undivided cell at room temperature. The cell voltage
was 5–10 V. [b] GC yields were determined with the use of succinonitrile
À2
Me NOH also gave the product 4 in a moderate yield
as an internal standard. [c] DMF=N,N-Dimethylformamide. [d] 20 mmol%
4
NaBr was used. [e] 0.5 mmol Bu
4
NPF
6
was used as the supporting electro-
(entry 14).
lyte. [f] Reaction was conducted at 08C. [g] Current efficiency in parenthe-
ses.
Finally, we combined all the reactions and tested the full
process for the synthesis of adiponitrile from glutamic acid
6
18
www.chemsuschem.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2012, 5, 617 – 620

In summary, we demonstrate
electrochemical routes for the
synthesis of adiponitrile from the
biomass-derived compound glu-
tamic acid by using electro-oxi-
dative
decarboxylation
and
Kolbe coupling reactions. This
work serves as another example
of the versatility of the substrate
glutamic acid in the transforma-
tion of biomass into chemicals,
and of the use of electrochemi-
cal methods to effect such trans-
formations. Further studies on
the conversion of biomass into
chemicals by electrochemical
methods are ongoing in our lab-
oratory.
Experimental Section
Figure 1. Optimization of the current density for Kolbe coupling. GC yields were determined with the use of
phthalonitrile as an internal standard.
General experimental procedure
for the electro-oxidative decar-
boxylation: The electro-oxidative
decarboxylation of l-glutamic acid
Table 2. One-pot synthesis of adiponitrile via Kolbe coupling of 3-cyano-
propanoic acid salts form 3-cyanopropanoic acid methyl ester.
5-methyl ester (Glu-Me) was carried out in an undivided cell (ca.
20 mL vial) equipped with two platinum electrodes (1.0ꢁ1.0 cm).
The distance between the electrodes was 5 mm. l-glutamic acid 5-
methyl ester (Glu-Me) (2.0 mmol), sodium bromide (3.0 mmol) was
[
a]
placed in an undivided cell. Then MeOH (8.0 mL) and H O (2.0 mL)
were added with a syringe. A constant current (80 mAcm , the
2
[
b]
À2
Entry
Base
Solvent
Yield [%]
cell voltage 5–10 V) was passed through the cell at the appointed
temperature and the mixture was stirred. After 5.2 Fmol electrici-
1
2
3
4
5
6
7
8
KOH
KOH
KOH
KOH
LiOMe
NaOMe
KOH
KOH
KOH
MeOH
40
65
55
37
11
15
33
42
52
56
42
66
À1
MeOH/acetone (1:1)
MeOH/acetone (4:1)
MeOH/acetone (1:4)
MeOH/H
MeOH/H
MeOH/H
MeOH/CH
MeOH/DME (1:1)
MeOH/HFIP (1:1)
MeOH/acetone (1:1)
MeOH/acetone (1:1)
MeOH/acetone (1:1)
MeOH/acetone (1:1)
ty had passed, the solvents (MeOH/H O) were removed and then
2
diethyl ether (30 mL) was added to the mixture. The organic layers
were washed with water (2ꢁ30 mL), then with brine, dried over
2
2
2
O (4:1)
O (4:1)
O (4:1)
MgSO , and filtered. Then the solvents were removed under re-
4
duced pressure. The residue was purified by flash chromatography
3
CN (1:1)
1
on silica gel to afford the desired product 2 in 88% yield. H NMR
[
[
[
[
c]
d]
e]
f]
9
0
13
(
400 MHz, CDCl ): d=2.62 (m, 4H), 3.68 ppm (s, 3H). C NMR
3
1
Me
4
NOH
(
100 MHz, CDCl ): d=12.87 29.67 52.25 118.53 170.55 ppm. HRMS
3
1
1
KOH
KOH
KOH
(EI) Calcd for C H NO [M]: 113.0477, Found: 113.0476 (Table 1,
5
7
2
1
1
1
2
3
[
g]
[h]
entry 18).
78 (29)
[
g]
General experimental procedure for the one-pot synthesis of
4
Me
4
NOH
75
adiponitrile: 3-cyanopropanoic acid methyl ester (CPA-Me)
[
a] Reaction conditions: 3-cyanopropanoic acid methyl ester (2.0 mmol),
(2.0 mmol), KOH (3.0 mmol), and 5.0 mL MeOH were placed in
base (3.0 mmol) in solvent (10 mL) at 608C for 30 min yield the corre-
sponding 3-cyanopropanoic acid salts and the mixture was electrolyzed
at a current density of 180 mAcm in an undivided cell at room temper-
ature. The cell voltage was 7–15 V. [b] GC yields were determined with
the use of phthalonitrile as an internal standard. [c] DME=1,2-dimethoxy-
ethane. [d] HFIP=Hexafluoroisopropanol. [e] Reaction was conducted at
a 20 mL vial. The mixture was heated at 608C for 30 min, yielding
the corresponding potassium 3-cyanopropanoate (CPA-K) (GC anal-
ysis showed full conversion). After the reaction, another 5.0 mL
acetone as the co-solvent was added by a syringe. Then two plati-
num electrodes (1.0ꢁ1.0 cm) were equipped in the cell with
a 180 mA constant current applied and the mixture was stirred at
À2
0
8C. [f] H-type divided cell with cation exchange membrane was used,
the distance between two platinum electrodes was 8 cm. [g] Reaction
was conducted at 608C (Close to the boiling point of the solvent),
3
6
3
08C. The distance between the electrodes was 5 mm. After
.4 Fmol electricity had passed, the solvents were removed
À1
À1
.4 Fmol of electricity passed. [h] Current efficiency in parentheses.
under reduced pressure. The residue was purified by flash chroma-
tography on silica gel to afford the desired product 4 in 74% yield.
1
H NMR (400 MHz, CDCl ): d=1.77 (m, 4H), 2.38 ppm (m, 4H).
3
13
C NMR (100 MHz, CDCl ): d=16.52 (2C) 24.17 (2C) 118.85 ppm
3
[
24]
(
Figure 2). Although industrial-scale synthesis of adiponitrile
(2C). HRMS (EI) Calcd for C H N [M+H]: 109.0766, Found: 109.0770
6 9 2
is beyond the scope of this Communication, the overall yield
of adiponitrile from glutamic acid was found to be 58%.
(Table 2, entry 13).
ChemSusChem 2012, 5, 617 – 620
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
619

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Received: November 30, 2011
Revised: January 2, 2012
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