Electrosynthesis of adipic acid by undivided cell electrolysis

Article abstract of DOI:10.1023/B:RUCB.0000035658.50123.07

A preparative method for synthesis of adipic acid in 47% yield was developed. The method is based on cyclohexanol oxidation in an undivided cell on the NiOOH electrode in aqueous alkali. A possibility of the step-by-step process was studied: oxidation of cyclohexanol to cyclohexanone (75% yield) and subsequent oxidation of cyclohexanone to adipic acid (52% yield). The electrosynthesis of adipic acid is accompanied by the formation of minor amounts (up to 10%) of glutaric and succinic acids.

Full text of DOI:10.1023/B:RUCB.0000035658.50123.07

688
Russian Chemical Bulletin, International Edition, Vol. 53, No. 3, pp. 688—692, March, 2004
Electrosynthesis of adipic acid by undivided cell electrolysis
B. V. Lyalin and V. A. Petrosyanꢀ
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
4
7 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. Eꢀmail: petros@ioc.ac.ru
A preparative method for synthesis of adipic acid in 47% yield was developed. The method
is based on cyclohexanol oxidation in an undivided cell on the NiOOH electrode in aqueous
alkali. A possibility of the stepꢀbyꢀstep process was studied: oxidation of cyclohexanol to
cyclohexanone (75% yield) and subsequent oxidation of cyclohexanone to adipic acid
(
52% yield). The electrosynthesis of adipic acid is accompanied by the formation of minor
amounts (up to 10%) of glutaric and succinic acids.
Key words: electrosynthesis, adipic acid, nickel/nickel hydroxide anode, cyclohexanol,
cyclohexanone.
Adipic acid is widely used and, hence, researchers
Results and Discussion
are interested in the development of convenient methꢀ
ods of its synthesis.1 Our emphasis is on a possibilꢀ
ity of electrosynthesis of adipic acid by the electroꢀ
oxidation of cyclohexanol in an aqueous alkaline meꢀ
dium on the nickel anode in an undivided cell, beꢀ
cause NiOOH, which is formed on the Ni anode surꢀ
face and selfꢀregenerated during electrolysis, is a sufꢀ
ficiently efficient oxidant. We successfully used this
approach earlier2 for the oxidation of 1ꢀ(2ꢀhydroxyꢀ
ethyl)tetrazole to obtain tetrazolylacetic acid, which is an
intermediate in the synthesis of antibiotic Cefazolin. Note
that the fact of preparation of cyclohexanone (CHN) by
cyclohexanol (CHL) oxidation on the NiOOH electrode
The expected mechanism of cyclohexanol electroꢀ
oxidation in an undivided cell on the NiOOH anode in
an aqueous solution of NаОН can be described by
Scheme 1.
Scheme 1
3
has been described previously. However, data on the
specific features of this process are lacking. A possiꢀ
bility to synthesize adipic acid (AA) by cyclohexanol
electrooxidation was not studied. One of the expected
difficulties is that the oxidation of the secondary hydroxy
group proceeds through the intermediate formation of
ketone, which is poorly oxidized and prone to selfꢀconꢀ
densation.
The study of the regularities of this process revealed
that the yield of cyclohexanone depended slightly on the
CHL
initial alcohol concentration* (С0
) (Table 1, enꢀ
Taking into account these circumstances, we perꢀ
formed this study in two stages. At the first stage, we
studied the factors determining the efficiency of cycloꢀ
hexanol oxidation to cyclohexanone on the NiOOH elecꢀ
trode. At the second stage, we examined a possibility of
cyclohexanone oxidation to adipic acid and revealed the
regularities of this process. We assumed that the successꢀ
ful occurrence of these stages makes it possible to perform
the oneꢀstep transformation of cyclohexanol into adiꢀ
pic acid.
tries 1—3), reaching the maximum value (75.6%) at
CHL
–1
С0
yield vs. current density ( j) passes through a maximum
see Table 1, cf. entries 1, 4, and 5) achieving 75.6% at
= 0.15 mol L . The plot of the cyclohexanone
(
–2
j = 6 mA cm . It is most likely that an increase in j is
*
The solubility of cyclohexanol depends on the alkali concenꢀ
tration. However, the alcohol loaded was completely dissolved
during electrolysis.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 657—660, March, 2004.
066ꢀ5285/04/5303ꢀ0688 © 2004 Plenum Publishing Corporation
1

Electrosynthesis of adipic acid
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 3, March, 2004
689
Table 1. Influence of the experimental conditions on the yields
of cyclohexanone (CHN) and adipic acid (AA) in the electroꢀ
oxidation of cyclohexanol (CHL) in an undivided cell in an
aqueous solution of NaOH
of cyclohexanone even decreased slightly, and adipic acid
was formed simultaneously. Evidently, cyclohexanone
accumulation in a solution and the temperature increase
favor its further oxidation.
Thus, the first stage of studies made it possible
a
Entry CHL
NaOH T/°C j/mA cm–2
mol L–1
Yield (%)
CHL
NaOH
to optimize the conditions (С0
= 0.15, С
=
b
CHN (AA)
1.0 mol L , Т = 10—30 °С, j = 6 mA cm–2) providing a
high yield (74.5—75.5%) of the target product. Simultaꢀ
neously we established a principal possibility of the oneꢀ
step oxidation of cyclohexanol to adipic acid.
–1
/
I
II
1
2
3
4
5
6
7
8
9
1
1
0.10
0.15
0.30
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
1.00
30
30
30
30
30
30
30
30
30
10
50
6
6
6
3
16
6
6
6
6
6
70.3
75.6
68.6
61.4
64.1
50.1
55.1
67.1
65.4
74.4
32.5
70.3
75.6
68.6
61.4
64.1
50.1
55.1
67.1
65.4
74.4
32.5
1.00
1.00
1.00
1.00
0.30
0.50
0.80
1.20
1.00
1.00
The next stage is related to revealing a possibility of
the electrooxidation of cyclohexanone to adipic acid on
the NiOOH electrode. In general, the expected transforꢀ
mations can be described by Scheme 2.
Scheme 2
0
1
6
(
11.4) (41.8)с
1
2 d
0.15
1.00
10
6
70.3
9.4)
44.6
(23.9)с
(
Note. NiOOH is anode, Ti is cathode, Qtheor = 2 F per 1 mole of
cyclohexanol.
a
I is the substance yield, and II is the current efficiency.
Calculated to the starting cyclohexanol (determined as 2,4ꢀdiꢀ
b
nitrophenylhydrazone).
c
Calculated to the eightꢀelectron oxidation of cyclohexanol.
d
Q = 1.5 Qtheor
.
The results of the studies are presented in Table 2. It is
known that NaOH and KOH induce the croton condenꢀ
accompanied by an increase in the contribution of the
side process on the anode
4
sation of cyclohexanone. Therefore, in the first experiꢀ
ments (see Table 2, entries 1 and 2) solutions of К2СО3
were used instead of NaOH solutions. However, the yield
of adipic acid was very low (2—3%), and the conversion
of cyclohexanone did not exceed 7%. It can be assumed
that the amount of the enolic form (this form is most
probably oxidized) is low in a lowꢀbasicity medium. Thereꢀ
fore, further experiments were carried out in a solution of
NaOH. This increased the yield of adipic acid from 3
to 19%, and the ketone conversion was increased from 7
to 57%. The variation of the experimental conditions
showed that the plot of the acid yield vs. increase in the
NaOH concentration passes through a maximum at
–
4
ОН – 4 е → 2 Н О + О .
2
2
An increase in the alkali concentration in a range of
.3—1.0 mol L–1 also increases the yield of cyclohexanone
see Table 1, entries 2, 6—8). However, at the higher
0
(
NaOH
–1
alkali concentration (С
= 1.2 mol L , entry 9), the
yield of ketone decreases by ~10%. A temperature change
in the 10—30 °С range has virtually no effect on the
cyclohexanone yield (entries 2 and 10), and at 50 °С the
formation of adipic acid was detected in the final reaction
mixture (entry 11). The temperature increase evidently
favors the oxidation of cyclohexanone itself. This is indiꢀ
cated by the fact that acid formation is accompanied by a
considerable decrease in the yield of cyclohexanone when
the amount of passed electricity is equal for all entries
NaOH
–1
С
= 1.0 mol L (see Table 2, cf., entries 3—8). The
optimum j value for ketone oxidation is the same as that
for alcohol oxidation and is equal to 6 mA cm– (see
Table 2, cf. entries 3, 8, and 9). At the same time, it is seen
from the data in Table 2 that only 41% reacted ketone are
transformed into the acid, although the cyclohexanone
conversion reaches 80%.
2
(
2 F per 1 mole of starting cyclohexanol (see Table 1,
cf. entries 2 and 11).
Thus, the variation of electrolysis conditions made it
possible to increase the yield of cyclohexanone, although
not higher than 75%. It is most probably that this is caused
by the side process of anodic oxidation of hydroxide ions.
An attempt to suppress this process by an increase in the
electrolysis duration (entry 12) was unsuccessful: the yield
The further optimization of the process showed that
adipic acid formation was favored by a decrease in the
CHN
temperature and an increase in С0
. For instance, the
yield of acid per reacted ketone at 10 °С increased to

690
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 3, March, 2004
Lyalin and Petrosyan
Table 2. Influence of the experimental conditions on the yields of adipic (AA), glutaric (GA), and succinic
(
SA) acids during cyclohexanone electrooxidation in an undivided cell in an aqueous solution of NaOH
a
Entry CHN NaOH
mol L–1
Т/°С Conversion
Q/Qtheor
j/
Yield (%)
of CHN
mA cm–2
AA
GA
SA
(
%)
I
II
I
b
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.21
0.30
0.15
0.15
0.15
0.30
0.3
0.3
0.4
0.6
1.0
1.2
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
30
30
30
30
30
30
30
30
30
50
10
10
10
10
10
10
4
7
6
6
6
6
6
6
6
3
16
6
6
6
6
6
6
6
2.3
3.0
57.5
42.8
33.9
34.7
31.7
41.2
34.5
32.7
37.9
30.2
45.3
53.7
57.4
51.1
48.3
52.3
—
—
—
—
b
1
1
1
1
1
1
1
1
1
1
1
1
1.5
2.3
4.0
56.9
63.3
70.3
80.1
87.1
72.7
27.6
95.0
27.9
34.5
37.3
42.3
58.8
70.2
19.3
22.0
22.3
33.1
30.1
23.8
16.5
28.7
12.6
18.5
21.4
21.6
28.4
36.7
7.1
7.5
8.1
7.8
12.6
8.2
2.8
15.3
4.1
5.9
6.9
6.0
8.5
9.3
3.1
3.2
3.5
3.3
5.5
3.7
1.2
7.1
0.8
1.1
1.2
1.7
2.5
3.7
0
1
2
3
4
5
6
Note. NiOOH is anode, Ti is cathode, Q
= 2 F per 1 mole of cyclohexanone.
theor
a
1
I is the yield with respect to the starting cyclohexanone (calculated from the Н NMR data of an isolated
mixture of the electrolysis products), and II is the yield with respect to the reacted cyclohexanone.
b
K CO was used instead of NaOH.
2
3
4
1
5.3% (cf. entries 6, 10, and 11), whereas it increased by
intermediate cyclohexanone formation. In the genꢀ
eral form, the expected reactions can be described by
Scheme 3.
CHN
2% with an increase in С0
(cf. entries 11—13). Deꢀ
spite a satisfactory yield of acid (45%), the conversion of
cyclohexanone remained rather low (~28%). This disꢀ
advantage was partially eliminated by an increase in
the amount of passed electricity (see Table 2, cf. enꢀ
tries 11, 14—16). For instance, a fourfold (compared to
the theoretical value) increase in Q (entry 16) resulted in
the 70% ketone conversion and simultaneously increased
the acid yield to 52%. Thus, the result of the second stage
of the studies is the optimization of the experimenꢀ
Scheme 3
CHN
–1
tal conditions (С0
= 0.15—0.30 mol L , СNaOH =
1
.0 mol L–1, Т = 10 °С, j = 6 mA cm–2 and Q = 4 Qtheor),
which provided a quite satisfactory yield (>52%) of adiꢀ
pic acid.
It is of interest that glutaric (substance yield 4—9%)
and succinic (substance yield 0.8—3.7%) acids are formed
in minor amounts along with adipic acid by the electroꢀ
oxidation of cyclohexanone under the experimental conꢀ
ditions (see Table 2). It can be assumed that their formaꢀ
tion is induced by the partial oxidative destruction of the
cyclohexanone ring (oxidation of one or two carbon atꢀ
The acid yield increases during electrolysis with an
CHL
increase in С0
(Table 3, entries 1—3) but remains low
(~21%) when the theoretical amount of electricity is
passed. In addition, the solution after electrolysis conꢀ
tains a considerable amount of cyclohexanone due to its
incomplete conversion to adipic acid. An increase in the
amount of passed electricity increased the ketone converꢀ
sion (see Table 3, entries 4—6), and the yield of adipic
acid increased substantially to be already 46.7%. In should
be emphasized that the electrolysis of cyclohexanol (as
oms to СО ) at early steps of electrolysis, because adipic
2
acid is not oxidized under the experimental conditions.
As a whole, the results considered above are a good
prerequisite for the development of oneꢀstep transformaꢀ
tion of cyclohexanol into adipic acid omitting the step of

Electrosynthesis of adipic acid
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 3, March, 2004
691
Table 3. Influence of the experimental conditions on the yields of cyclohexanone (CHN) and
adipic acid (AA) and on the total yield of glutaric (GA) and succinic acids (SA) in the
electrooxidation of cyclohexanol in a 0.1 М aqueous solution of NaOH
Entry
CHL
mol L–1
Q/Qtheor
Yield (%)
AAa,с
II
/
CHNa,b
GAc
SAc
I
II
I
1
2
3
4
5
6
0.10
0.15
0.20
0.15
0.15
0.15
1.0
1.0
1.0
0.8
2.0
4.0
66.8
64.2
39.3
73.8
30.0
17.7
16.70
16.00
9.60
23.80
3.75
19.2
21.1
37.8
21.4
36.9
46.7
19.20
21.10
37.80
34.20
18.20
11.52
6.60
3.30
8.20
2.55
9.40
11.50
1.2
1.1
1.4
0.6
3.7
6.3
1.10
Note. NiOOH is anode, Ti is cathode, Qtheor = 8 F per 1 mole of cyclohexanol, j = 6 mA cm–2
,
a
Т = 10 °C.
a
I is the substance yield, and II is the current efficiency.
b
Per the starting cyclohexanol (determined as 2,4ꢀdinitrophenylhydrazone).
c
1
Per the starting cyclohexanol (calculated by the Н NMR data for an isolated mixture of the
electrolysis products).
for cyclohexanone electrooxidation, see above) affords
glutaric and succinic acids in minor amounts along with
adipic acid (see Table 3).
Electrooxidation of cyclohexanol to cyclohexanone (general
procedure exemplified by entry 12, Table 1). An electrolytic cell
was filled with a 1 М aqueous solution of NaOH (200 mL) and
cyclohexanol (3.1 mL, 0.03 mol), and electrolysis was carried
out at a current of 0.744 A and 10 °C. After 3 F electricity was
passed per 1 mole of cyclohexanol, electrolysis was stopped. The
reaction mixture was stirred for 0.5 h and neutralized with conꢀ
centrated HCl (to рН 6—7). Then an aliquot of this solution was
taken to identify cyclohexanone and to determine its yield, which
was 70.3% (substance yield) and 44.6% (current efficiency).
Concentrated HCl was added to the remaining reaction mixture
It should be noted in conclusion that we showed a
possibility of electrooxidation of ketones to carboxylic
acids on the NiOOH electrode in an aqueous alkaline
medium with a satisfactory yield using cyclohexanone as
an example. This possibility was used for the development
of a preparative method for synthesis of adipic acid by
cyclohexanone electrooxidation under the experimental
conditions.
(
to pH 1—2), and water was distilled off under a reduced presꢀ
sure. The dry salt residue was extracted with acetone (4×25 mL).
After acetone was distilled off, adipic acid (0.41 g) was obtained
and identified by the H NMR spectra (comparing with that of
Experimental
1
the authentic sample) and m.p. 152 °С (Ref. 6: 153 °С). The
substance yield of adipic acid was 9.4% and its current efficiency
was 23.9%.
Electrolysis was carried out in an undivided cell with the Ni
2
2
anode (S = 124 cm ) and Ti cathode (S = 40 cm ) equipped with
a water jacket for temperature control. Electrolysis was carꢀ
ried out in an amperostatic regime using a B5ꢀ8 dc source.
A coulometer designed at the Specialized Design Office of the
Institute of Organic Chemistry of the RAS was connected into
the electric circuit. The temperature was maintained by a
Uꢀ1 thermostat. A magnetic stirrer was used to stir the reaction
mixture during electrolysis. Before experiments, the Ni anode
Electrooxidation of cyclohexanone to adipic acid (general
procedure exemplified by entry 16, Table 2). A cell was filled
with a 1 М aqueous solution of NaOH (200 mL) and cycloꢀ
hexanone (3.1 mL, 0.03 mol), and electrolysis was carried out at
a current of 0.744 A and 10 °С. After 24 F electricity was passed
per 1 mole of cyclohexanone, electrolysis was stopped, and the
cyclohexanone conversion was determined (as described above),
which was 70.2%. After the reaction mixture was treated as
described above, a powder (2.11 g) was isolated, which was,
3
was activated using a known procedure by the preliminary elecꢀ
trolysis in a solution containing 0.1 М NiSO , 0.1 М NaOAc,
4
and 0.005 М NaOH at j = 1 mA cm–2 with a periodical reversal
of electrode polarization. This procedure is necessary to form a
multilayer NiOOHꢀcontaining coating on the Ni anode surface.
A working solution was prepared using distilled water and a
titrated solution of NaOH (pure grade).
according to the data of H NMR spectroscopy, a mixture of
1
adipic, glutaric, and succinic acids. The molar ratio of the prodꢀ
ucts equal to 9.9 : 2.5 : 1 was determined from integrated
intensities of the signals (adipic acid: δ 1.50 (m, 4 H, CH ),
2
glutaric acid: 1.70—1.88 (m, 2 H), and succinic acid: 2.40 (4 H,
To identify cyclohexanone and determine its yield, it was
transformed into 2,4ꢀdinitrophenylhydrazone using a known proꢀ
CH )). The yields of these acids (per loaded cyclohexanone)
2
were 36.7, 9.3, and 3.7%, respectively. To isolate adipic acid
from the mixture, the powder (2.11 g) was rinsed with water
(3×5 mL) and dried. The amount of adipic acid obtained was
0.86 g (60% of the mixture content, according to the data of the
5
cedure. Acids formed (adipic, glutaric, and succinic) were idenꢀ
1
tified by H NMR spectroscopy (solvent DMSOꢀd ) on a Bruker
6
ACꢀ200 instrument using comparison with spectra of authentic
samples.
1
H NMR spectra), m.p. 153—154 °С (Ref. 6: 153 °С).

692
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 3, March, 2004
Lyalin and Petrosyan
Electrooxidation of cyclohexanol to adipic acid (general proꢀ
Technology of General Organic and Petrochemical Synthesis],
2nd ed., Khimiya, Moscow, 1975, p. 736 (in Russian).
2. B. V. Lyalin and V. A. Petrosyan, Elektrokhimiya, 1996, 1, 96
[Russ. J. Electrochem., 1996, 1 (Engl. Transl.)].
cedure exemplified by entry 6, Table 3). A cell was filled with a
М aqueous solution of NaOH (200 mL) and cyclohexanol
3.1 mL, 0.03 mol). Electrolysis was carried out as described
1
(
above, passing 32 F electricity per 1 mole of cyclohexanol. After
the end of electrolysis and isolation of the products as described
above, cyclohexanone and adipic, glutaric, and succinic acids
were obtained with substance yields of 17.7 and 46.7, 11.5, and
3. J. Kauler and H. J. Schaefer, Tetrahedron, 1982, 38, 3299.
4. W. Wayne and H. Adkins, J. Am. Chem. Soc., 1940,
62, 3401.aaa
5. Houben—Weyl, Methoden der Organischen Chemie, Band II,
Analytische Methoden [Methods of Organic Chemistry, vol. 2,
Methods of Analysis], Verlag Georg Thieme, Stuttgart, 1953
6
.3%, respectively.
This work was carried out in the framework of the
(
in German).
Complex Program of the Russian Academy of Sciences
Directed Synthesis of Substances with Specified Properꢀ
6
. Svoistva organicheskikh soedinenii (spravochnik) [Properties of
Organic Compounds (Reference Book)], Ed. A. A. Potekhin,
Khimiya, Leningrad, 1984, 520 (in Russian).
"
ties and Creation of Related Functional Materials".
References
1
. N. N. Lebedev, Khimiya
i
tekhnologiya osnovnogo
Received December 15, 2003;
organicheskogo i neftekhimicheskogo sinteza [Chemistry and
in revised form February 13, 2004