Electrocarboxylation of CCI4 in MeCN during electrolysis with the sacrificial Zn anode

Article abstract of DOI:10.1007/s11172-010-0005-7

The regularities of galvanostatic electrocarboxylation of CCl₄ in Alk₄NBr/MeCN in an undivided cell with sacrificial Zn anode were studied. The major product of the electrolysis is zinc trichloroacetate, which is formed as a result o

Full text of DOI:10.1007/s11172-010-0005-7

Russian Chemical Bulletin, International Edition, Vol. 58, No. 2, pp. 297—302, February, 2009
297
Electrocarboxylation of CCl4 in МеCN during electrolysis
with the sacrificial Zn anode*
V. L. Sigacheva, S. V. Neverov, and V. A. Petrosyan
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation,
Fax: +7 (499) 135 5328. Eꢀmail: petros@ioc.ac.ru
The regularities of galvanostatic electrocarboxylation of CCl4 in Alk4NBr/MeCN in an
undivided cell with sacrificial Zn anode were studied. The major product of the electrolysis is
zinc trichloroacetate, which is formed as a result of the reaction of the cathodeꢀgenerated
CCl3− anion with СО2. The further trichloroacetate reduction is prevented by cathode passivaꢀ
tion. Therefore, small amounts of zinc dichloroꢀ and monochloroacetates are formed due to
the chemical reduction of zinc trichloroacetate with Zn0 rather than the cathodic reduction.
Zeroꢀvalence zinc is formed in minor amounts when Zn2+ ions are discharged at the cathode
surface because of the low solubility of ZnBr2 in MeCN. The treatment of (Cl3CCOO)2Zn
with H2SO4 in MeOH gives Cl3CCO2Me in 11% yield based on the starting CCl4.
Key words: electrochemical carboxylation, sacrificial zinc anode, tetrachloromethane,
carbon dioxide, trichloroacetic acid.
In the previous work,1 we studied the galvanostatic
electrochemical carboxylation of CCl4 in DMF in an
undivided cell with the sacrificial Zn anode and revealed
regularities of this process. The reduction of CCl4
generating the CCl3– anion was found to be accompanied
by reduction of Zn2+ salts formed thereupon with the
formation of Zn0 on the cathode. The only product of CCl4
electrocarboxylation was zinc dichloroacetate formed
due to the chemical reduction of the corresponding
trichloroacetate (primary product of electrocarboxylation
of CCl4) by Zn0 freshly precipitated on the cathode. In
addition, zinc trichloroꢀacetate turned out to be very
unstable1 in DMF and decomposed to evolve СО2.
It should be emphasized that a reason for the low yield
of dichloroacetate (<10% based on the starting CCl4) is1
predomination of the destruction of zinc trichloroacetate
over its chemical reduction by Zn0. Taking into account
that the competition is also observed between the reducꢀ
tion of Zn2+ salts and CCl4 reduction that occurs only on
the cathode surface unoccupied with Zn0,1 we may sugꢀ
gest that the electrocarboxylation of ССl4 in DMF as a
whole is rather complicated process affected by a combiꢀ
nation of several opposite factors.
systems with the sacrificial anode as, e.g., in Refs 2—4.
Therefore, we focused the development of works on
CCl4 electrocarboxylation first on the selection of solvent
that would provide stability of zinc polychlorocarboxylates
as expected products of CCl4 electrocarboxylation. In the
present work, MeCN was studied as such a solvent, which
as DMF is an aprotic dipolar solvent with the dielectric
constant value close to that of DMF but with lower disꢀ
sociating ability.5
As earlier,1 electrocarboxylation was carried out under
galvanostatic undivided electrolysis of CCl4 with the Zn
anode and steel cathode, bubbling СО2 through an elecꢀ
trolyte at atmospheric pressure.
Results and Discussion
The choice of MeCN as a medium for CCl4 electroꢀ
carboxylation was reasonable, which is substantiated by
the results of preliminary studies of the comparative
chemical stability of the authentic1 zinc polychloroacetate
samples in DMF and MeCN. For this purpose, equiꢀ
molar samples (0.005 mol) of zinc trichloroꢀ and dichloroꢀ
acetate were placed in DMF and MeCN, respectively,
and the mixtures were stirred for certain time. Zinc triꢀ
chloroacetate in DMF solution decomposed intensely to
evolve СО2 (see Ref. 1).
It follows that the choice of DMF as a medium1 for
CCl4 electrocarboxylation was unsuccessful, although this
solvent is rather often used for electrocarboxylation in
We assumed that bis(trichloromethyl)zinc formed
intermediately is also unstable and decomposes further to
give ZnCl2 and dichlorocarbene (Scheme 1).
*On the occasion of the 75th anniversary of the foundation
of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 297—302, February, 2009.
1066ꢀ5285/09/5802ꢀ0297 © 2009 Springer Science+Business Media, Inc.

298
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
Sigacheva et al.
monochloroacetic (MEM) acids. It has previously1 been
shown that the ССl4 electrocarboxylation products are
formed due to both electrochemical and chemical stages
of the electrode process and, hence, their current yields
(especially for dichloroꢀ and chloroacetates) are rather
ambiguous. This impelled us to determine the substance
yield of each (poly)chloroacetate (based on the starting
ССl4) using the 1H NMR spectroscopic data for the
corresponding mixtures. Note that in all experiments
the passed electric charge (Q) was less than the theoretical
value (Qtheor) based on the first twoꢀelectron step (see
Scheme 2, a) and usually did not exceed 6000—7000 C
because of cathode passivation.
The data in Table 2 show that the total yield of
chloroacetates in electrocarboxylation increases 2.5ꢀfold
when DMF is replaced by MeCN, and not MED but
MET is formed as the major product.
We believe that these results are due to both the differꢀ
ence in stability of zinc trichloroacetate in DMF and
MeCN (see Table 1) and the presence of different amounts
of freshly precipitated Zn0 on the cathode in these solꢀ
vents. The freshly precipitated Zn0 acts as a reducing agent
with respect to zinc polychloroacetates.1
It turned out that the electrolysis of 0.1 М Et4NBr in
DMF with Zn anode/Fe cathode system resulted in the
dissolution of the Zn anode and generation of Zn2+ ions
with 100% current efficiency. The solution remained
transparent, and a black film of freshly precipitated Zn0
appeared on the cathode surface. An analogous experiꢀ
ment in MeCN also resulted in the dissolution of the Zn
anode with 100% current efficiency. However, in this
case, the cathode surface was only partly covered with a
black film , while the solution, on the contrary, rapidly
became turbid and transformed into a white suspension.
It can be assumed that ZnBr2 formed during electrolysis is
less soluble in MeCN than in DMF. This minimizes, in
turn, the reduction of Zn2+ ions with Zn0 formation on
the cathode surface. This is the reason why the contriꢀ
bution of chemical reduction of zinc trichloroacetate
Scheme 1
If the proposed scheme of decomposition is correct,
then, after distillation of the easily removed destruction
products and DMF, the weight of the dry residue should
correspond to the amount of ZnCl2 formed calculated
from Scheme 1. This is consistent with our experimental
results. Somewhat larger values (39.6 %, Table 1) comꢀ
pared to the calculated ones (34.6% for dry ZnCl2)
are probably due to difficulties of complete DMF removal.
Moreover, it is seen from the data in Table 1 that the
weight of the residues after solvent was distilled off is the
same in experiments with stirring of zinc trichloroacetate
just in DMF for 1 and 4 h. This means that just 1 h after
zinc trichloroacetate decomposes almost completely.
Unlike DMF, in MeCN zinc trichloroacetate is stable,
no gas release was observed upon stirring of the solution
for both 1 and 4 h, and after MeCN was removed the
weight of the dry residue (see Table 1) was 100% of the
initial sample weight. In the case of zinc dichloroacetate,
no gas release occurred in both DMF and MeCN media.
In these experiments, the weight of the residues after
solvent removal was equal to the weight of the initial
samples, which indicates the stability of zinc dichloroꢀ
acetate in the both solvents.
Based on these results, one could expect that the
electrocarboxylation of ССl4 in MeCN would be more
efficient. Indeed, the composition and yield of the CCl4
electrocarboxylation products in MeCN differ from those
obtained in DMF (Table 2). For the electrocarboxylation
in DMF (Table 2) the reproducibility of the results was
low,1 whereas it was good for all experiments in MeCN.
For product identification, the obtained mixture of zinc
salts of (poly)chloroacetic acids was transformed into a
mixture of the corresponding methyl esters, which was
analyzed by 1H NMR spectroscopy.
This mixture usually consisted of methyl esters
of trichloroacetic (MET), dichloroacetic (MED), and
Table 2. Influence of the solvent nature on the composition of
the electrolysis productsa and the yield of chloroacetic esters
during electrocarboxyꢀlation (EC) of ССl4
Table 1. Relative stability of salts (Cl3СCOO)2Zn and
(Cl2СHCOO)2Zn in DMF and МеCN
Entry Solvent
Total yield
of chloroꢀ
acetates/g
Composition of EC
productsb (yield (%))
Solvent
t/h
Weight of dry residue*
(% of starting weighed sample)
MET MED MEM
(Cl3СCOO)2Zn
(Cl2СHCOO)2Zn
1
2
DMF
0.46
1.16
0.0
95.3
(6.1)
17.0
(2.8)
4.7
(<1)
5.7
DMF
1
4
1
4
39.6
39.5
100.0
100.0
100.0
100.0
100.0
100.0
MeCN
77.3
(10.1)
МеCN
(1.3)
a СССl = 0.5 mol L–1, 0.1 М Et4NBr, steel St3 cathode, anode
4
* The residue was obtained upon solvent removal after stirring a
weighed sample of the corresponding zinc salt in the solvent for
1 or 4 h (4 h is the maximum electrolysis time).
Zn, j = 9.4 mA cm–2, Т = 20 °C, Q = 6900 C (71.5% of Qtheor
based on the twoꢀelectron process).
b Calculated from the H NMR spectral data.
1

Electrоchemical carboxylation of CCl4
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
299
Table 3. Influence of ZnCl2 additives on the composition of the
and 2, Table 3) and also produced noticeable amounts
of zinc monochloroacetate.
electrolysis productsa upon CCl4 electrocarboxylation (EC)
It is quite obvious that this result is due to an increase
of the amount of the reducing agent Zn0 formed on the
cathode surface and an increase in the fraction of diꢀ and
monochloroacetates, respectively. For the same reason,
additives of ZnCl2 (which is better soluble in this medium
than ZnBr2) for the electrolysis in МеСN increase the
yield of zinc dichloroꢀ and especially monochloroacetate
(cf. entries 3 and 4) and decrease the yield of zinc
trichloroacetate. Some decrease in the total yield of polyꢀ
chloroacetates from 1.16 g (entry 3) to 0.76 g (entry 4) is
evidently due to a change in the ratio and, hence, the
total molecular weight of the target products.
Entry ZnCl2 Solvent Total yield
Composition of EC
products (выход (%))
/mol
of chloroꢀ
acetates/g
MET MED MEM
1
—
DMF
0.46
0.0
0.0
95.3
(6.1)
76.0
4.7
(<1)
24.0
2
3
4
0.015 DMF
MeCN
0.015 MeCN
1.0
(10.6) (4.4)
—
1.16
0.76
77.3
(10.1)
41.7
17.0
(2.8)
31.2
(3.3)
5.7
(1.3)
27.1
(3.7)
(3.6)
The study of factors affecting the yield and composiꢀ
tion of the ССl4 electrocarboxylation products in МеСN,
such as the nature of the supporting electrolyte and its
concentration, concentration of ССl4, cathodic current
density, temperature, and electric charge passed, someꢀ
what improved the characteristics of the process.
a The conditions are given in Note to Table 2.
(primarily formed due to CCl4 electrocrboxylation) to
dichloroacetate by Zn0 was lower in MeCN than in DMF
(see Table 2).
After ZnCl2 was added to a 0.1 М solution of Et4NBr
in MeCN, a black film of Zn0 efficiently precipitated on
the cathode during electrolysis. Evidently, this indicates
that ZnCl2 is better soluble in MeCN than ZnBr2. The
results of these experiments (Table 3) agree completely
with the developed concepts on the effect of the solvent
nature on the regularities of ССl4 electrocarboxylation,
confirming that the main role in the formation of zinc
dichloroacetate from the primarily formed trichloroacetate
belongs to the chemical reduction of the latter by freshly
precipitated Zn0.
For example, it turned out that the replacement of
Et4NBr (∼0.1 М) rather poorly soluble in MeCN by 0.1 М
and then 0.2 М Bu4NBr solution increases the total yield
of (poly)chloroacetates (cf. entries 1, 2, and 3, Table 4)
without substantial influence on their ratio. In addition,
the use (entry 3) of a 0.2 М solution of Bu4NBr made it
possible to decrease the cell voltage from 35 to 10 V
and to reduce cathode passivation (see above) during
electrolysis. Therefore, 0.2 М Bu4NBr were used in
further experiments.
The total yield of chloroacetates increased noticeably
and the current density j increased from 9.4 to 18.8 mA cm–2
(entries 4 and 5) with an increase in the initial concentraꢀ
Additives of ZnCl2 during electrolysis in DMF
increased the yield of zinc dichloroacetate (cf. entries 1
Table 4. Influence of the parameters of undivided galvanostatic electrolysis with the soluble Zn anode and steel cathode in MeCN on
the yield and composition of CCl4 electrocarboxylation (EC) products
Entry
CCCl
Background salt
j
Т
/°С
Q/Qtheor
(%)
Total yield
of chhloromethyl
acetates/g
Composition of EC products
(yield (%))
4
С/mol L–1
/mA cm–2
MET
MED
MEM
1
2
3
4
5
6
7
0.5
0.5
0.5
1.5
1.5
1.5
1.5
Et4NBr
(0.1)
Bu4NBr
(0.1)
Bu4NBr
(0.2)
Bu4NBr
(0.2)
Bu4NBr
(0.2)
Bu4NBr
(0.2)
Bu4NBr
(0.2)
9.4
9.4
20
20
20
20
20
10
ꢀ10
71.5*
71.5*
1.26
1.57
1.60
2.22
3.43
2.66
1.60
77.3
(11.3)
77.8
(13.7)
84.0
(15.1)
84.5
(7.1)
84.6
(10.9)
83.1
(8.3)
88.0
17.0
(2.9)
14.8
(3.2)
9.3
(2.1)
10.1
(1.0)
14.9
(2.4
14.3
(1.8)
9.1
5.7
(1.5)
7.4
(2.2)
6.7
(2.0)
5.4
(0.7)
1.5
(traces)
2.6
(traces)
2.9
9.4
71.5*
9.4
23.8**
23.8**
23.8**
23.8**
18.8
18.8
18.8
(5.3)
(0.7)
(traces)
* Qt = 9650 C (based on the twoꢀelectron process).
** Qt = 28950 C (based on the twoꢀelectron process).

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Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
Sigacheva et al.
tion of CCl4 from 0.5 to 1.5 М (entries 3 and 4). For
instance, in entry 5 the yield of chloroacetates was
already 3.43 g instead of 1.26 g in entry 1. At the same
time, an increase in the CCl4 concentration to the values
СО2 affords zinc trichloroacetate unstable in DMF (see
Scheme 1). The fast decomposition via step b competes
with the chemical reduction of trichloroacetate to the
corresponding dichloroacetate (step d) by Zn0 precipiꢀ
tated on the cathode in step c. These are just the reasons
why no zinc trichloroacetate was observed in the elecꢀ
trolysis products upon ССl4 electrocarboxylation in DMF.
The major product is the corresponding dichloroꢀ
acetate, which is formed in low yield along with trace
amounts of zinc monochloroacetate (see Table 3, entry 1
and Ref. 1).
The reduction of anodeꢀgenerated Zn+2 to Zn0
(step b) occurs simultaneously with the reduction of ССl4
at the cathode. The contribution of Zn+2 reduction
depends on the solubility of ZnBr2. Therefore, for elecꢀ
trolysis in DMF, step b is considerably more efficient
than in МеCN (see above). It is important that Zn0 proꢀ
motes the transformation of zinc trichloromethyl acetate
but cannot reduce ССl4. Moreover, the electroreduction
of ССl4 does not occur1 on the cathode surface covered
with freshly precipitated zinc or occurs with high overꢀ
voltage.
Zinc trichloroacetate is stable in MeCN, unlike DMF.
However, in MeCN the cathode is completely passivated
at certain electrolysis moment. This effect imposes
quantitative restrictions on the formation of zinc trichloroꢀ
acetate and also prevents its further electroreduction to
dichloroacetate. For these reasons, zinc trichloroacetate
becomes the major product of electrocarboxylation. The
variation of conditions gave more than 3 g of MET during
one electrolysis with a current efficiency of 46% (based
on the twoꢀelectron process), although the yield based on
the initial ССl4 was only 11% (see Table 4, entry 5). It
should be mentioned for comparison that for ССl4
electrocarboxylation in DMF the amount of MED, which
is the major product, did not exceed1 0.5—0.7 g even
under optimal conditions.
CCCl ≥ 3 mol L–1 was accompanied by cathode passivaꢀ
4
tion and an increase in the cell voltage, which induced
the decrease in the yield of (poly)chloroacetates. At the
current density above 18.8 mA cm–2 the cell voltage also
increased sharply.
It is known6 that the decrease in temperature enhances
the solubility of СО2 in an electrolyte solution, thus
increasing the efficiency of electrocarboxylation. In our
case, however, the temperature decrease, contrary to
expectations, resulted in a consecutive decrease in the
total yield of (poly)chloroacetates (cf. entries 5, 6, and 7).
Obviously, in this case, the determining factor is the
decrease in the rate of chemical reactions participating
in the electrode process.
Generalizing the results presented in Table 4, we
can conclude that the variation of the conditions of
ССl4 electrocarboxylation in МеСN using the sacrificial
zinc cathode makes it possible to obtain MET with high
selectivity but exerts an insignificant effect on the ratio of
the reaction products. For example, under the optimal
conditions (see Table 4, entry 5), trichloroacetate can be
isolated as MET in a yield to 11% (3.2 g). Simultaneously
MET is formed in the same reaction mixture in 2.4%
yield (0.09 g), and only trace amounts of MEM are
observed.
As a whole, our studies confirmed validity of the conꢀ
clusions1 that the first steps of ССl4 electrocarboxylation
resulting in the formation of zinc triꢀ and dichloroacetates
using the sacrificial Zn anode represent rather compliꢀ
cated (Scheme 2) process including competitive chemical
and electrochemical steps.
According to Scheme 2, step a corresponds to the
–
generation of the ССl3 anion, whose interaction with
Scheme 2

Electrоchemical carboxylation of CCl4
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 2, February, 2009
301
acetic acid was isolated in almost quantitative yield, m.p. being
57—58 °С. The structure was confirmed by the 13С NMR
spectrum (DMSOꢀd6, δ: 92.0 (CCl3), 164.2 (CO)).
Note that because of the low solubility of ZnBr2 in МеCN
the contribution of steps с and d presented in Scheme 2 is
insignificant and only addition of more soluble ZnCl2
assist a deeper chemical reduction of zinc trichloroacetate
(cf. entries 3 and 4, Table 3).
Thus, the regularities of ССl4 electrocarboxylation preꢀ
sented is Scheme 2 allow one to describe the mechanism
of this process at the qualitative level. It is quite possible
that the real process of ССl4 electrocarboxylation is more
complicated. However, we succeeded to reveal its key
steps. The obtained conclusions are valid regardless
of whether the primary electrocarboxylation product is
(Cl3CCOO)2Zn or Cl3CCOOZnСl.
Synthesis of zinc dichloroacetate was carried out according
to a similar (see above) procedure using ZnO (8.14 g, 0.1 mol)
and dichloroacetic acid (28.37 g, 0.22 mol). After evaporation
the mother liquor was a thick viscous syrup from which the
crystalline salt (31.18 g, 97% based on ZnO) was obtained after
drying (8 h, 2 Torr, 50 °С). Found (%): C, 14.99; Cl, 44.41; Zn,
20.25; H, 0.66 (average of two determinations). C4H2Cl4O4Zn.
Calculated (%): C, 14.935; Cl, 44.183; Zn, 20.346; H, 0.622.
13С NMR (DMSOꢀd6), δ: 67.53 (CHCl2), 168.31 (CO).
The following data finally convince that the zinc dichloroꢀ
acetate was obtained (the elemental analysis results give some
error on Zn determination): after the salt obtained it was acidified
with concentrated HCl followed by extraction with ether and
evaporation, dichloroacetic acid was isolated, whose structure
was confirmed by the 13С NMR spectrum (DMSOꢀd6, δ: 66.3
(CHCl2), 167.3 (CO)).
Testing of the stability of zinc triꢀ and dichloroacetates in
DMF and MeCN. A weighed sample (0.005 mol) of Zn trichloroꢀ
acetate (1.95 g) or Zn dichloroacetate (1.61 g) was placed in the
corresponding solvent (40 mL), the mixture was stirred at room
temperature for certain time (1 or 4 h), and then the solvent was
distilled off at reduced pressure, and the resulting residue
was weighed. The results obtained are given in Table 1.
Experimental
Electrolysis was carried out in an undivided cell equipped
with a thermometer, a magnetic stirrer, a cooling jacket, and a
device for СО2 bubbling including the system of its drying over
H2SO4 followed by purification from acid traces. In addition,
СО2 flow was passed through a vessel with CCl4 before its inlet
into the electrochemical cell. As it was shown by special test,
this made it possible to avoid CCl4 losses due to blowing out
when СО2 bubbling during electrolysis.
Electrocarboxylation of CCl4 in DMF. Experiments on
electrocarboxylation in DMF are given in Tables 2 and 3 for
comparison. These procedures, as well as procedures for product
isolation, have earlier been described1 in detail and remained
almost unchanged when MeCN was used as the solvent.
Electrocarboxylation of CCl4 in MeCN (general procedure
using entry 5 (Table 4) as an example). A 0.2 М solution
(100 mL) of Bu4NBr in MeCN and CCl4 (23.0 g, 0.15 mol) were
placed in the cell, and this solution was saturated with CO2 for
10 min. Then, continuing CO2 bubbling, electrolysis with the
current I = 0.6 A was carried out at Т = 20 °C. In some
experiments, additives were introduced to the electrolyte, for
example, ZnCl2 (2.0 g, 0.015 mol) (entry 4, Table 3). After
6900 C charge (23.8% Q) was passed, the electrolysis was
stopped, the electrodes were dried and weighed, and MeCN
was distilled off from the electrolyte in a water bath at reduced
pressure. After MeCN was removed, a solid residue containing
chloroacetates, which were transformed into methyl esters of
the corresponding chloroacetic acids for identification, was
formed.
Methyl esters of (poly)chloroacetic acids (exemplified by
entry 5, Table 4). After MeCN was distilled off, the solid residue
was dissolved in MeOH (25 mL) and treated with a solution
of H2SO4 in MeОН (8 mL of concentrated H2SO4 in 50 mL of
MeОН) with stirring. The mixture was stored at room temperaꢀ
ture for 24 h, diluted with water to 500 mL, and extracted with
ether (3×80 mL). The ethereal extract was washed with a
saturated aqueous solution of NaHCO3 and water (2×50 mL),
dried for 24 h over MgSO4, and filtered. The ether was distilled
off, and the residue was distilled in vacuo (45—65 °С at 40 Torr).
The product, a mixture of methyl esters of trichloroꢀ, dichloroꢀ,
and monochloroacetic acids, was obtained (3.43 g). The methyl
esters were identified by 1H NMR spectroscopy (solvent DMSOꢀd6)
by comparing their spectra with the spectra of the authentic
samples. Methyl trichloroacetate (MET). 1Н NMR (DMSOꢀd6),
Electrocarboxylation was carried out in the galvanostatic
regime, using the B5ꢀ49 dc source and passing a specified quantity
of electricity. The process was monitored with a coulometer
designed at the workshop of the Institute of Organic Chemistry.
A stainless steel plate (S = 42 cm2) served as the cathode, and
the anode was a Zn rod (S = 33 cm2). Prior to electrolysis the Zn
electrode was activated, namely, it was stored for 1 min in a
dilute (1 : 4) aqueous hydrochloric acid, washed with distilled
water, and dried.
The supporting electrolyte was a 0.1 or 0.2 М solution of
Et4NBr or Bu4NBr in MeCN or DMF. Before use, quaternary
ammonium salts (pure) were recrystallized from ethanol and
dried by heating on a water bath of a rotary evaporator at reduced
pressure for 6 h; MeCN, DMF, and tetrachloromethane were
purified as described in Refs 7—9, respectively.
To identify and determine the yield of zinc (poly)chloroꢀ
acetates, they were transformed into the corresponding methyl
(poly)chloroacetates according to the earlier1 developed proceꢀ
dure. Mixtures of the esters were analyzed by 1H NMR spectroꢀ
scopy (solvent DMSOꢀd6) on a Bruker ACꢀ200 instrument,
comparing their spectra with the spectra of the authentic
samples.
Synthesis of zinc trichloroacetate. Trichloroacetic acid
(35.94 g, 0.22 mol) was added to a ZnO suspension (8.14 g,
0.1 mol) in water (50 mL), and the mixture was stirred until
ZnO dissolved almost completely. The reaction mixture was
filtered, and the mother liquor was concentrated by evaporation
in vacuo. Residues of water and trichloroacetic acid were removed
from the salt obtained by drying (8 h, 2 Torr, 50 °С). The salt
was obtained in a yield of 38.26 g (98% based on ZnO). Found
(%): C, 12,21; Cl, 54,67; Zn, 16,67 (average of two deterꢀ
minations). C2Cl6O4Zn. Calculated (%): C, 12,29; Cl, 54,56;
Zn, 16,76. 13С NMR (DMSOꢀd6), δ: 95.0 (CCl3), 164.4 (CO).
The salt obtained was acidified with concentrated HCl
followed by extraction with ether and evaporation, and trichloroꢀ

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Sigacheva et al.
δ: 4.0 (s, 3 Н, ОМе). Methyl dichloroacetate (MED). 1Н NMR
(DMSOꢀd6), δ: 5.9 (s, 1 Н, CHCl2); 3.85 (s, 3 Н, ОМе). Methyl
chloroacetate (MEM). 1Н NMR (DMSOꢀd6), δ: 4.22 (s, 2 Н,
CH2Cl); 3.72 (s, 3 Н, ОМе).
The composition of the isolated MET—MED—MEM (84.6 :
14.9 : 1.5%) mixture of products was determined on the basis of
the ratio of integral intensities of signals from the methoxy groups.
The substance yield of MET was 11% and the current efficiency
was 46% (based on the twoꢀelectron process).
3. G. Silvestry, S. Gambino, G. Filardo, NATO ASI Ser.,
Ser. C, 1987, 339.
4. V. G. Koshechko, V. D. Pokhodenko, Teor. Eksp. Khim.,
1997, 33, 268 [Theor. Exp. Chem. (Engl. Transl.), 1997,33].
5. I. M. Kolthoff, Pure Appl. Chem., 1971, 25, 305.
6. O. Stock, M. Troupl, J. Perichon, Tetrahedron Lett., 1985,
26, 1509.
7. F. Olver, Anal. Chem., 1965, 37, 1447.
8. S. B. Brummer, J. Chem. Phys., 1965, 42, 1636.
9. A. J. Gordon, R. A. Ford, The Chemist´s Companion, Wiley,
New York—London—Sidney—Toronto, 1972.
References
1. B. L. Sigacheva, V. A. Frolovskii, V. A. Petrosyan, Elektroꢀ
khimiya, 2005, 41, 1133 [Russ. J. Electrochem. (Engl. Transl.),
2005, 41].
2. J. Chaussard, J.ꢀC. Folest, J. Y. Nedelec, J. Perichon,
S. Sibille, M. Troupel, Synthesis, 1990, 369.
Received October 17, 2008;
in revised form December 30, 2008