Electrochemical hydrogenation of 3-(methoxyphenyl)propenoic acids

Article abstract of DOI:10.1007/s11172-011-0009-y

Electrosynthesis can successfully be used for double bond hydrogenation in 3-(methoxyphenyl)propenoic acids. The corresponding 3-(methoxyphenyl)propanoic acids were produced in a virtually quantitative yield under the conditions of both electrocatalytic hydrogenation at the Ni cathode modified by electrodeposited dispersed nickel in a DMF-H₂O mixture in the presence of AcOH and direct electroreduction using mercury and glassycarbon cathodes in DMF with Bu₄NClO₄ as the supporting electrolyte, although the mechanisms of these processes are different.

Full text of DOI:10.1007/s11172-011-0009-y

Russian Chemical Bulletin, International Edition, Vol. 60, No. 1, pp. 63—68, January, 2011
63
Electrochemical hydrogenation of 3ꢀ(methoxyphenyl)propenoic acids
L. M. Korotaeva, T. Ya. Rubinskaya, I. A. Rybakova, and V. P. Gultyai
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: klm@ioc.ac.ru
Electrosynthesis can successfully be used for double bond hydrogenation in 3ꢀ(methꢀ
oxyphenyl)propenoic acids. The corresponding 3ꢀ(methoxyphenyl)propanoic acids were proꢀ
duced in a virtually quantitative yield under the conditions of both electrocatalytic hydrogenaꢀ
tion at the Ni cathode modified by electrodeposited dispersed nickel in a DMF—H2O mixture
in the presence of AcOH and direct electroreduction using mercury and glassycarbon cathodes
in DMF with Bu4NClO4 as the supporting electrolyte, although the mechanisms of these
processes are different.
Key words: cinnamic acids, transꢀ3ꢀ(methoxyphenyl)propenoic acids, 3ꢀ(methoxyꢀ
phenyl)propanoic acids, polarography, electrocatalytic hydrogenation, nickel cathode, direct
electroreduction, mercury cathode, glassycarbon cathode.
3ꢀ(Methoxyphenyl)propanoic acids find use in the synꢀ
thesis of cardiac pharmaceuticals1 and antibiotics.2 The
known methods for their synthesis are based on reactions
of the corresponding methoxybenzaldehydes with Meldrum´s
acid3 or malonic acid followed by hydrogenation of interꢀ
mediate products over the catalyst Pd/C(10%).2 The double
bond of cinnamic acid derivatives is directly hydrogenated by
the catalytic method4 in an autoclave under hydrogen presꢀ
sure (3 bar) in the presence of 10% Pd/С in ~80% yield.
In several cases, electrocatalytic hydrogenation (ECH)
of unsaturated organic compounds at cathodes with a modꢀ
erate hydrogen overvoltage competes successfully with hetꢀ
erogeneous catalytic hydrogenation, since ECH proceeds
under mild conditions: at ambient temperature and atmoꢀ
spheric pressure and in nonꢀaggressive media. Therefore,
it seems topical to apply the ECH method to accessible
transꢀ3ꢀ(methoxyphenyl)propenoic acids.
The ECH mechanism consists of the addition of
electrochemically generated atomic hydrogen, which is
adsorbed on the electrode surface,5 to double bonds of an
organic molecule. Unsaturated compounds can undergo
hydrogenation either in the adsorbed state or in the nearꢀ
electrode layer of the solution, depending on the material
of the electrode, state of its surface, and composition of
the medium.6 For the successful ECH, it is essential that
the potential of direct electroreduction (ER) of unsaturatꢀ
ed compound would be substantially more negative than
the potential of hydrogen evolution at the electrode used
for hydrogenation. Note that ECH is not accompanied, as
a rule, by the formation of dimeric products.
(Nidisp/Ni cathode),7 which increased the catalytic activiꢀ
ty of the cathode. A mixture of DMF—H2O, KCl, and
АсОН was an optimum medium8,9 for the hydrogenation
of the conjugated system of the С=С—С=О bonds. The
products of complete hydrogenation of all double bonds,
namely, 2ꢀpropylpiperidines,10 were obtained under simiꢀ
lar conditions by the ECH of transꢀ2ꢀallylꢀ6ꢀRꢀ1,2,3,6ꢀ
tetrahydropyridines (R = Me, All, Ph), i.e., both terminal
(allylic) and intracyclic nonconjugated double bonds are
hydrogenated. Under these conditions, phenyl substituꢀ
ents and isolated sterically hindered double bonds are reꢀ
tained. The results obtained are generalized in the review.11
The purpose of this study is to extend the ECH method
to compounds of another type: α,βꢀunsaturated carboxylꢀ
ic acids having the aromatic ring conjugated with the
double bond. The second purpose is to compare the results
of ECH and direct ER of these compounds at cathodes
with high hydrogen overvoltage, such as mercury and glassy
carbon (GC).
transꢀ3ꢀ(3ꢀMethoxyphenyl)propenoic (1a), transꢀ3ꢀ
(4ꢀmethoxyphenyl)propenoic (1b), and unsubstituted
transꢀ3ꢀphenylpropenoic (cinnamic, 1c) acids were used
as subjects of this study (Scheme 1).
Scheme 1
Earlier, in a detailed study of ECH of citral, we have
proposed a method for preliminary modification of the Ni
cathode surface by electrodeposited dispersed nickel
Х = 3ꢀМеО (a), 4ꢀМеО (b), Н (c)
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 62—67, January, 2011.
1066ꢀ5285/11/6001ꢀ63 © 2011 Springer Science+Business Media, Inc.

64
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 1, January, 2011
Korotaeva et al.
Results and Discussion
Electrocatalytic hydrogenation of acids 1a—c was carꢀ
ried out under the conditions proposed previously11 as the
optimal (DMF(40%)—H2O, 0.1 М KCl) in the presence
of fourfold molar excess of АсОН at the Nidisp/Ni cathode.
Unlike previous works, where ECH was carried out in the
potentiostatic mode at Еconst = –1.0 V (I ≈ 100 mA), in
Bifunctionality is a specific feature of α,βꢀunsaturatꢀ
ed carboxylic acids, i.e., the following directions of
the process are possible, in principle, during ER: hydroꢀ
genation of the double bond or formation of various
dimeric products, hydrogen evolution from the carbꢀ
oxyl group and even its reduction to the carbonyl or
hydroxymethyl group. The possibility of this or another
direction depends mainly on the electrode material and
composition of the medium. It should also be taken into
account that α,βꢀunsaturated carboxylic acids themselves
are proton donors.
the present work we used the galvanostatic mode, Iconst
=
= 100 mA (Е ≈ –1.0 V). The results of ECH of acids 1a—c
are presented in Table 1 (for GLC analysis, a mixture of
acids was preliminarily esterified with diazomethane).
The quantity of electricity (Q) theoretically necessary
for hydrogenation of one double bond is 2 F mol–1, but
a noticeable amount of starting acids 1a—c along with
target saturated acids 2a—c was present in the mixtures
even after an excess quantity of electricity (Q = 6 F mol–1
)
Electrocatalytic hydrogenation
was passed (entries 1—3). Passing of a fourfold excess of
electricity (Q = 8 F mol–1) resulted in quite satisfactory
result: hydrogenated acids were obtained in a yield of
97—98% (entries 4—6).
Taking into account stoichiometry of the ethylene bond
hydrogenation, we may assume that it is sufficient to
use equimolar amount or a twofold excess of АсОН.
Therefore, we carried out experiments on ECH of acid 1c
both in the absence of АсОН and at different contents
of AcOH in solution. Samples were withdrawn during
electrolysis.
As follows from Fig. 2, in the absence of АсОН (curve 1)
the content of the target product in the mixture after ECH
does not exceed 40% even upon passing Q = 8 F mol–1
(conversion is also 40%).
In the presence of an equimolar amount of АсОН with
respect to the starting acid 1c in the electrolyzed solution
(see Fig. 2, curve 2), after ECH the content of the target
product 2c in the mixture increased almost to 80%. The
It has earlier been shown7 that during ECH at the
Nidisp/Ni cathode in a medium DMF(40%)—H2O and
0.1 М KCl in the presence of fourfold excess АсОН, the
current of hydrogen evolution (Iw = 100 mA) is achieved
at comparatively low cathodic potentials ЕН ranging from
–1.0 to –1.1 V (vs SCE). Since not only АсОН or H2O
but also 3ꢀphenylpropenoic acids can be hydrogen sources
in this case, we recorded the corresponding polarization
curves (Fig. 1).
As follows from Fig. 1, upon the addition of 0.013 М
acid 1c to the supporting solution, the potential of hydroꢀ
gen evolution decreases insignificantly compared to the
supporting solution: Iw = 100 mA is achieved at ЕН
=
= –1.29 V (curve 2). At the same concentration of АсОН,
ЕН = –1.15 V (curve 3), whereas in 0.052 М АсОН the
same value of current is achieved at ЕН = –0.85 V (curve 5).
This indicates that at the Nidisp/Ni cathode АсОН exhibꢀ
its higher activity as a hydrogen source than acid 1c.
Table 1. Results of electrocatalytic hydrogenation of acids 1a—ca
I/mA
5
4
3
2
1
100
80
60
40
20
Entry
Acid
Q/F mol–1
Composition of mixture
after ECH (%)b
1a—c
2a—c
1
2
3
4
5
6
7
1a
1b
1c
1a
1b
1c
1cc
6
6
6
8
8
8
4
8
9
7
15
3
3
2
91
93
85
97
97
98
91
100
9
0
0.4
0.6
0.8
1
1.2
1.4 E/V
a Conditions of ECH: С1a—c = 0.013 mol L–1, Nidisp/Ni cathꢀ
ode, galvanostatic mode. Composition of the medium:
DMF(40%)—H2O, 0.1 М KCl, АсОН (С = 0.052 mol L–1).
b The composition of a mixture of acids after ECH and esterifiꢀ
cation with diazomethane was determined by GLC.
Fig. 1. Polarization curves of hydrogen evolution at the Nidisp/Ni
cathode (Е vs SCE) for supporting electrolyte DMF(40%)—H2O,
0.1 М KCl (1); with addition of 0.013 М 3ꢀphenylpropenoic acid
(1c) (2); with addition of 0.013 М АсОН (3); with addition of
0.026 М АсОН (4); with addition of 0.052 М АсОН (5).
c С1c = 0.027 mol L–1, САсОН = 0.1 mol L–1
.

Electrochemical hydrogenation of cinnamic acids
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 1, January, 2011
65
Y (%)
Direct electroreduction
4
3
100
80
60
40
20
The polarographic behavior of acids 1a—c was studied
in DMF with Bu4NClО4 as the supporting electrolyte at
the mercury dropping electrode. It was shown that the ER
of all three compounds proceeds in two stages (Table 2).
The heights of the first and second waves are close to
the oneꢀelectron level, which follows from the calculation
by the Ilkovic equation.12 Therefore, we may conclude
that the corresponding radical anions (RA), whose subseꢀ
quent reduction occurs at the second wave potentials, are
formed at the first wave potential. Table 2 also contains
the literature data13 obtained in a an aqueousꢀethanolic
buffer medium.
2
1
2
4
6
Q/F mol–1
As can be seen from Table 2, the halfꢀwave potentials
of acids 1a—c differ insignificantly. Upon the addition of
water to DMF or using of a protonꢀdonating medium
ЕtOH(50%)—Н2О, the first wave potentials somewhat
decrease.
As known,14 dimerization is a characteristic reaction
of RA of activated olefins in media with low protonꢀdoꢀ
nating activity. It is also asserted15—18 that the ER of cinꢀ
namic acids at the mercury cathode in acidic and buffer
media mainly affords dimers. Nevertheless, it is known19
that acid 1c is reduced with sodium amalgam to acid 2c in
80—90% yield.
Under the conditions of direct ER, we carried out the
preparative electrolysis of acid 1c in DMF with 0.1 М
Bu4NClО4 as the supporting electrolyte at the Hg cathode
at the first wave potential (Е = –1.7 V). During electrolyꢀ
sis, the current decreased rapidly to the background level
after approximately Q = 1 F mol–1 was passed. The results
of GLC analysis of the reaction mixture after standard
treatment and esterification with diazomethane showed
that the mixture contains ~50% starting acid 1c and ~50%
hydrogenated product 2c. An attempt to continue elecꢀ
trolysis by increasing Е to approximately –2.0 V demonꢀ
strated a noticeable increase in the current and then its
gradual decrease to the background level. In this case, the
Fig. 2. Current yield (Y) of acid 2c vs quantity of passed electꢀ
ricity (Q) at different compositions of the electrolyte at С1c
= 0.013 mol L–1 in the absence of АсОН (1); at the equimolar
amount, САсОН = 0.013 mol L–1 (2); and at twofold excess of
АсОН, САсОН = 0.026 mol L–1 (3) and fourfold excess of АсОН,
САсОН = 0.052 mol L–1 (4).
=
further increase in the АсОН concentration increases both
the conversion and content of the target product 2c in the
mixture (curves 3 and 4).
A comparison of the curves in Fig. 2 shows that the
initial linear region of the curves extends with an increase
in the АсОН concentration in the electrolyzate. In the
presence of a fourfold molar excess of АсОН over acid 1c
in the electrolyzate, the linear character of this depenꢀ
dence is retained even upon passing Q = 7 F mol–1. Thus,
this excess of АсОН provides stability of the system for
the ECH of acid 1c even after the quantity of electricity
considerably larger than the theoretically necessary value
was passed.
The obtained results show (see Fig. 2) that for the
ECH of acid 1c the use of a fourfold excess of АсОН
is sufficient, because the content of the target prodꢀ
uct in the mixture after ECH reaches 98% at ~98%
conversion, which is very important for preparative elecꢀ
trolysis.
Table 2. First (EI1/2) and second (EII1/2) reduction waves of
3ꢀphenylpropenoic acids at the mercury dropping electrode at
different compositions of the supporting electrolyte. The values
of E1/2 were determined vs SCE
High solubility of acid 1c in the DMF(40%)—H2O
system made it possible to perform ECH (see Table 1,
entry 7) also at a higher concentration in the solution
(C1c = 0.027 mol L–1). It turned out that after passing
Q = 4 F mol–1 the content of hydrogenated acid 2c in the
mixture upon electrolysis was 90.7% and that of the startꢀ
ing compound was only 9.3%.
Thus, taking into account high yield and good reproꢀ
ducibility of the results (at relatively simple renewal of the
electrode surface before electrolysis), accessibility of the
necessary equipment (galvanostatic mode), and low cost
of the used reagents and cathodic material, the conditions
proposed for ECH can be recommended for the hydrogeꢀ
nation of 3ꢀarylpropenoic acids.
Comꢀ
pound
DMF
Н2О(16%)— ЕtOH(50%)—
DMF,
Н2О*
0.1 М Bu4NClО4
0.1 М Bu4NClО4
–EI1/2/V –EII1/2/V
–EI1/2/V
1a
1b
1c
1.69
1.75
1.66
2.49
2.48
2.48
1.59
1.71
1.57
1.61
1.67
1.62
* Data of Ref. 13; conditions: acetate buffer, pH 6.7.

66
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 1, January, 2011
Korotaeva et al.
total amount of passed quantity is Q = ~2 F mol–1. The
single product of this stepwise ER is the corresponding
hydrogenated acid 2c (conversion 98—99%).
unsaturated acid 1c is completely consumed to form satuꢀ
rated product 2c.
The ER of acids 1a and 1b at the Hg cathode in DMF
with Bu4NClО4 as the supporting electrolyte affords the
corresponding hydrogenated acids 2a and 2b as the single
products of "stepwise" reduction, which does not contraꢀ
dict the proposed scheme. Similar results were obtained
by the electrolysis of acids 1a—c at the GC cathode.
Thus, we showed that, under these only formally "aproꢀ
tic" conditions, the ER of acids 1a—c affords no dimeric
and oligomeric products, but only the electrochemical
hydrogenation of the С=С bonds occurs. Note that the
results of preparative electrolysis could not be predicted
on the basis of polarographic studies.
Probably, RA is formed at the first stage of electrolysis
at Е = –1.7 V (Scheme 2, reaction 1) and is protonated by
another molecule of acid 1c, which is not only a depolarꢀ
izer but also a proton donor (reaction 2). As a result, the
anion of the starting acid 1c and the free radical species,
which can be reduced at the first stage potential (ЕI =
= –1.7 V), are formed (reaction 3). The anion of the
starting acid should be electroreduced at a more negative
potential (reaction 4). It is known,15 for example, that the
anions are reduced, as a rule, at the potential 0.2—0.4 V
more negative than that for the ER of nonꢀdissociated
molecules of the same acids. The possibility of formation
of the electroactive anionic form of the acids in aqueous
nonꢀbuffer media has been considered earlier.13
Taking into account that the protonation of primary
RA is the key stage of direct ER, we performed a series of
electrolyses at the GC cathode at different compositions
of the electrolyte (Table 3).
It turned out that the corresponding hydrogenated
acids are also the major products in aqueousꢀorganic
(DMF—Н2О) or protonꢀdonating (EtOH) media. Experꢀ
iment 1 was performed at Е = –1.7 V and stopped after the
current dropped to the background level. It was found that
in the presence of 16% H2O about 2/3 of starting acid 1c is
reduced to form product 2c at this potential. Experiments
2—4 were carried out at the specified initial Е = –1.7 V
and its subsequent stepwise increase to Е = –2.0 V. As can
be seen from a comparison of the results of entries 1 and 2,
an increase in the potential during electrolysis in the presꢀ
ence of H2O also does not result in the complete conꢀ
sumption of the starting compound. Moreover, with an
increase in the amount of Н2О in the electrolyzate (see
Table 3, entries 2 and 3) the conversion even decreases
after the theoretically necessary quantity of electricity
(Q = 2 F mol–1) was passed, while hydrogen evolution is
observed at Е = –2.0 V.
Scheme 2
The addition of a lithium salt to the electrolyzed soluꢀ
tion of acid 1a (see Table 3, entry 4) results in the situation
that the ER occurs only at Е. = –1.7 V, whereas with an
increase in the potential to Е = –2.0 V deposition of
lithium begins on the electrode, and the conversion does
not exceed 50% in this case.
For the ER of acid 1c in the protonꢀdonating solvent
EtOH (entry 5) (galvanostatic mode), a large amount of
the starting acid remains in the electrolyzate in spite of the
knowingly excessive amount of passed electricity. The proꢀ
cess is apparently accompanied by hydrogen evolution
from acid 1c (entry 5), while in entry 6 hydrogen is addiꢀ
tionally evolved from АсОН, which strongly decreases
conversion. Note that the measured value of Е. does not
exceed –1.55 V under these conditions (entries 5 and 6).
As follows from the obtained experimental data, the
direct ER of acids 1a—c at the Hg and GC cathodes with
high hydrogen overvoltage makes it possible to obtain tarꢀ
get 3ꢀphenylpropanoic acids 2a—c in a virtually quantitaꢀ
At the same time, it should be taken into account that
DMF initially contains 0.2—0.3% water (~0.16 mol L–1),
which is more than an order of magnitude higher than
the substrate concentration. Although water molecules
are bound by hydrogen bonds with DMF molecule, at
this molar excess water still can be a proton donor (alꢀ
though weak) for anionic species formed upon electroꢀ
lysis. Therefore, a complex of the anion of the startꢀ
ing acid with water can be formed or it can slowly be
protonated during electrolysis. This explains the increase
in the current with the stepped increase in the potential to
–2.0 V during electrolysis. As a consequence, the starting

Electrochemical hydrogenation of cinnamic acids
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 1, January, 2011
67
Table 3. Results of direct electroreduction of acids 1a and 1c at the GC cathode at different compositions of the medium (supporting
salt 0.1 М Bu4NClО4)
Entry
Acid
C/mol L–1
Mode
Medium
Q/F mol–1 Composition of mixture after ER (%)
Starting
Products
1a or 1c
2a or 2c
1
2
3
4
1c
1a
1a
1a
0.013
0.013
0.013
0.013
Еconst = –1.7 V
H2O(16%)—DMF
H2O(16%)—DMF
H2O(30%)—DMF
H2O(10%)—DMF +
+ 0.1 М LiClO4
EtOH
1.5
2
2
26
16
22
49
74
84
78
51
Е = –1.7 → 2.0 V
Е = –1.7 → 2.0 V
Е = –1.7 → 2.0 V
2
5
6
1c
1c
0.027
0.027
Iconst = 70 mA
Iconst = 70 mA
3
3
61
45
39
55
EtOH + 0.05 М AcOH
potentiostat. All electrolyzers were equipped with a porous glass
membrane. Cathodes were as follows: a cylindrical nickel plate
(visible surface ~0.9 dm2, Vcell = 50 mL), bottom mercury with
the working surface Sw ≈ 0.16 dm2 (Vcell = 15 mL), or a beaker of
glass carbon (SUꢀ2000), which served as an electrolyzer with
Sw ≈ 0.20 dm2 (Vcell = 30 mL). A Pt net was used as an anode,
and a saturated calomel electrode was a reference electrode.
Prior to each electrolysis, the nickel cathode was activated by
the electrodeposition of dispersed nickel from a solution of
0.5 М NiCl2•6Н2О (analytically pure grade) on the surface
cleaned, washed with water, and degreased with ether for 1 h at
a cathodic current density of 0.1 A dm–2, Е = –(0.60—0.70) V;
then the electrode was washed with water. The surface of the
nickel electrode was covered with a smooth black precipitate.
Commercial 3ꢀ(3ꢀmethoxyphenyl)propenoic (1a), 3ꢀ(4ꢀmethꢀ
oxyphenyl)propenoic (1b), and 3ꢀphenylpropenoic (1c) acids and
Bu4NClО4 (Acros Organics) were used. Prior to distillation DMF
was stored above К2СО3 and dried with molecular sieves 4 Å
(after distillation anhydrous DMF contained 0.2—0.3% Н2О
determined by the Fischer method). Commercial EtOH conꢀ
tained about 4% Н2О and was not additionally purified. Argon
used for blowing was not additionally dried.
tive yield in DMF with Bu4NClО4 as the background elecꢀ
trolyte. It is important to emphasize that no dimerization
and resinification occur under these conditions. The elecꢀ
trocatalytic hydrogenation of acids 1a—c at the catalytiꢀ
cally active cathode with the moderate hydrogen overvoltꢀ
age (Nidisp/Ni) in a medium of DMF(40%)—H2O, 0.1 М
KCl in the presence of fourfold excess of АсОН makes it
possible to obtain the corresponding saturated acids 2a—c
in high yield.
Thus, we showed that the electrochemical method can
quite successfully be used for the hydrogenation of the
double bond of 3ꢀ(methoxyphenyl)propenoic acids, and
the position of the МеО substituent in the aromatic ring
exerts almost no effect on the results of both ECH and
direct ER. The yield in the ECH and direct ER under the
described conditions is close to the quantitative one, alꢀ
though the mechanisms of these processes are principally
different. Evidently, the mechanism of direct ER of
3ꢀphenylpropenoic acids requires detailed investigation usꢀ
ing other electroanalytical methods.
Electrocatalytic hydrogenation in the galvanostatic mode (genꢀ
eral procedure). Electrolysis of 0.013 М solutions of acids 1a—c
was carried out at the Nidisp/Ni cathode with 0.1 М KCl as the
supporting electrolyte in 40% aqueous DMF (catholyte volume
50 mL) in the presence of 0.052 М АсОН at I. = 100 mA (current
density 0.11 A dm–2, measured Е = –(0.9—1.1) V). Electrolysis
was stopped after passing Q = 6 F mol–1 (0.12 A h) or 8 F mol–1
(0.16 A h). After the end of electrolysis, the solution was conꢀ
centrated in vacuo, water was added, and the solution was acidiꢀ
fied with 10% aqueous HCl to рН 2 and extracted with ether.
The extract was washed with water and dried with MgSO4. Then
the solvent was distilled off in vacuo, and the residue was weighed.
The weight of the extracted residue was ~90% of the weight of
the starting acid. The residue was analyzed by TLC and 1Н NMR.
A sample from the residue was methylated with diazomethane
according to the known procedure.20 A mixture of methyl esters
of the starting acid and hydrogenated product was analyzed by
TLC and GLC.
Experimental
1
Н NMR spectra were recorded on a Bruker AM 300 specꢀ
trometer with the working frequency 300 MHz in CDCl3 using
Me4Si as an internal standard. GLC was carried out on an
LKhMꢀ80 instrument, column 2 m × 3 mm with 3% OVꢀ17,
stationary phase Inerton AWꢀDMCS. TLC was carried out on
plates with the fixed layer of SiO2 (Silufol UVꢀ254) using a hexꢀ
ane—ether (3 : 2) mixture as an eluent. The melting point was
determined on a Boеtius heating stage.
Polarographic measurements were carried out on a PUꢀ1
polarograph according to the threeꢀelectrode scheme of switchꢀ
ingꢀon the cell: mercury dropping electrode (m = 1.05 mg s–1
t = 0.8 s) and bottom mercury as an auxiliary electrode. A satuꢀ
rated calomel electrode (SCE) connected with the studied soluꢀ
tion through a salt bridge filled with a solution of 0.1 М Bu4NClО4
in DMF was used as a reference electrode. Oxygen from the cell
was removed by blowing with argon. Measurements were carried
out at 25 °C.
,
The ECH of a 0.013 М solution of acid 1a in the presence of
0.026, 0.052, and 0.078 М АсОН was performed similarly with
sampling during electrolysis. After passing Q = 2, 4, 6, and
8 F mol–1, samples (2 mL each) of the electrolysis solution were
taken without interruption of electrolysis. Electrolysis was ceased
Preparative electrochemical hydrogenation was carried out
under argon atmosphere using a B5ꢀ50 current source or a Pꢀ5848

68
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 1, January, 2011
Korotaeva et al.
after passing Q = 8 F mol–1. Each sample was treated as deꢀ
scribed above and analyzed by GLC.
7. L. M. Korotaeva, T. Ya. Rubinskaya, V. P. Gul´tyai, Izv.
Akad. Nauk, Ser. Khim., 1998, 1531 [Russ. Chem. Bull.
(Engl. Transl.), 1998, 47, 1487].
8. T. Ya. Rubinskaya, L. M. Korotaeva, V. P. Gul´tyai, Izv.
Akad. Nauk, Ser. Khim., 1996, 82 [Russ. Chem. Bull.
(Engl. Transl.), 1996, 45, 74].
9. L. M. Korotaeva, T. Ya. Rubinskaya, V. P. Gul´tyai, Izv.
Akad. Nauk, Ser. Khim., 1997, 480 [Russ. Chem. Bull.
(Engl. Transl.), 1997, 46, 459].
10. L. M. Korotaeva, T. Ya. Rubinskaya, V. P. Gul´tyai, Elektroꢀ
khimiya, 2003, 39, 1344 [Russ. J. Electrochem. (Engl. Transl.),
2003, 39].
Electroreduction at the mercury and glasscarbon cathodes at
the controlled potential (general procedure). Electrolysis of 0.013 М
solutions of acids 1a—c was carried out with 0.1 М Bu4NClО4 as
the supporting electrolyte in anhydrous DMF at Е = –1.7 V for
20 min, and then the potential was increased to Е = –2.0 V (as
a whole, approximately Q = 2 F mol–1 was passed). After the end
of electrolysis, the solution was worked up and analyzed accordꢀ
ing to the procedure described above.
Electroreduction at the glassycarbon cathode in the galvanoꢀ
static mode (catholyte volume 30 mL). Electrolysis of 0.027 М
solutions of acid 1c was carried out with 0.1 М Bu4NClО4 as the
supporting electrolyte in ЕtOH and with an additive of 0.05 М
АсОН, I = 70 mA (current density 0.35 A dm–2, measured
11. L. M. Korotaeva, T. Ya. Rubinskaya, in Focus on Electroꢀ
chemistry Research, Ed. M. Nunes, Nova Science Publishers
Inc., New York, 2005, 145.
Е = –(1.5—1.55) V) for 1 h. After passing Q = 3.0 F mol–1
,
12. J. Heyrovský, J. Kuta, Základy polarografie, Nakladatelstvi
∨
∨
electrolysis was stopped, and the reaction mixture was worked
up as described above.
Сeskoslovenské Academie Véd, Praha, 1962.
13. M. J. D. Brand, B. Fleet, J. Electroanalytical Chem., 1968,
16, 341.
3ꢀ(3ꢀMethoxyphenyl)propanoic acid (2a), m.p. 42—44 °C
(from hexane) (cf. Ref. 21: m.p. 43—45 °C). 1H NMR (CDCl3),
δ: 2.70 (t, 2 Н, ArCH2CH2, J = 7.7 Hz); 2.95 (t, 2 H, ArCH2CH2,
J = 7.7 Hz); 3.80 (s, 3 Н, OMe); 6.73—6.85 (m, 3 Н, HAr);
7.20—7.30 (m, 1 Н, HAr).
3ꢀ(4ꢀMethoxyphenyl)propanoic acid (2b), m.p. 94—96 °С
(from hexane) (cf. Ref. 21: m.p. 98—100 °C). 1H NMR (CDCl3),
δ: 2.65 (t, 2 Н, ArCH2CH2, J = 7.7 Hz); 2.92 (t, 2 H, ArCH2CH2,
J = 7.7 Hz); 3.80 (s, 3 Н, OMe); 6.85 (d, 2 H, HAr(3), HAr(5),
J = 8.6 Hz); 7.13 (d, 2 Н, HAr(2), HAr(6), J = 8.5 Hz).
3ꢀPhenylpropanoic acid (2c), m.p. 44—46 °С (from hexane)
(cf. Ref. 21: m.p. 47—49 °C). 1H NMR (CDCl3), δ: 2.70 (t, 2 Н,
ArCH2CH2, J = 7.7 Hz); 3.0 (t, 2 H, ArCH2CH2, J = 7.8 Hz);
7.19—7.25 (m, 5 Н, Ph).
14. A. I. Rusakov, A. S. Mendkovich, V. P. Gul´tyai, V. Yu.
Orlov, Struktura i reaktsionnaya sposobnost´ organicheskikh
anionꢀradikalov [Structure and Reactivity of Organic Radical
Anions], Mir, Moscow, 2005, 294 pp. (in Russian).
15. A. P. Tomilov, S. G. Mairanovskii, M. Ya. Fioshin, V. A.
Smirnov, Elektrokhimiya organicheskikh soedinenii [Electroꢀ
chemistry of Organic Compounds], Khimiya, Leningrad, 1968,
592 pp. (in Russian).
16. A. P. Tomilov, M. Ya. Fioshin, V. A. Smirnov, Elekꢀ
trokhimicheskii sintez organicheskikh veshchestv [Electrochemꢀ
ical Synthesis of Organic Substances], Khimiya, Leningrad,
1976, 424 pp. (in Russian).
17. Organic Electrochemistry, Eds M. M. Baizer and H. Lund,
Marcel Dekker Inc., New York—Basel, 1983.
18. Organic Electrochemistry, Eds H. Lund, O. Hammerich, Marꢀ
cel Dekker Inc., New York—Basel, 2001, 1393 pp.
19. A. P. Tomilov, E. Sh. Kagan, V. A. Smirnov, I. Yu. Zhukoꢀ
va, Preparativnaya organicheskaya elektrokhimiya [Preparaꢀ
tive Organic Electrochemistry], YuRGTU, Novocherkassk,
2002, 42 (in Russian).
20. Organikum. Organischꢀchemisches Grundpractikum, Veb
Deutscher Verlag der Wissenschaften, Berlin, 1976.
21. Spravochnik khimicheskikh reaktivov i laboratornogo oborudoꢀ
vaniya "Aldrich" [Manual of Chemical Reagents and Laboratoꢀ
ry Equipment], 2003—2004, The SigmaꢀAldrich Family
(in Russian).
References
1. H. C. Englert, U. Gerlach, S. Scheidler, J. Med. Chem.,
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2. A. J. Pearson, K. Lee, J. Org. Chem., 1994, 59, 2304.
3. G. Toth, K. E. Kover, Synth. Commun., 1995, 25, 3067.
4. L. Tietze, T. Eicher, Reaktionen und synthesen im organischꢀ
chemischen praktikum und forschungslaboratorium, Georg
Thieme Verlag Stuttgart, New York, 1991.
5. A. P. Tomilov, Zh. Org. Khim., 1993, 29, 657 [Russ. J. Org.
Chem. (Engl. Transl.), 1993, 29].
6. V. S. Bagotskii, in Problemy elektrokataliza [Problems of
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(in Russian).
Received June 25, 2010