Cathodic dehalogenation with dimerization. Dimerization in the course of reduction of butyl iodide

Article abstract of DOI:10.1023/A:1013170124535

Electrochemical reduction of butyl iodide in methanol with a sodium methylate supporting electrolyte was studied. The yield of the dimeric product, octane, largely depends on the cathode material, with copper and iron (St.3 steel) being the most active. At a current density of 0.03-0.10 A cm^-2, 0°C, and 0.005 M CH₃ONa, the yield of octane, based on butyl iodide, is as high as 83-84%.

Full text of DOI:10.1023/A:1013170124535

Russian Journal of General Chemistry, Vol. 71, No. 7, 2001, pp. 1099 1101. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 7, 2001,
pp. 1165 1167.
Original Russian Text Copyright
2001 by Tomilov.
Cathodic Dehalogenation with Dimerization.
Dimerization in the Course of Reduction of Butyl Iodide
A. P. Tomilov
State Research Institute of Organic Chemistry and Technology, Moscow, Russia
Received January 17, 2000
Abstract Electrochemical reduction of butyl iodide in methanol with a sodium methylate supporting elec-
trolyte was studied. The yield of the dimeric product, octane, largely depends on the cathode material, with
2
copper and iron (St.3 steel) being the most active. At a current density of 0.03 0.10 A cm , 0 C, and
0
.005 M CH ONa, the yield of octane, based on butyl iodide, is as high as 83 84%.
3
According to modern data [1], the general scheme
of cathodic reduction of organic halides can be pre-
sented as follows:
2ICH CH CN + 2e
NC(CH ) CN + 2I .
2 4
2
2
The dimeric product can also be obtained by reduc-
tion of bromoethyl acetate [9]:
e
e
RX
RX
R + X
H+
BrCH CH OOCCH + 2e
X
2
2
3
e
CH COO(CH ) COOCH + 2Br .
R( H) + R(+H)
R R
R
3
2 4
3
S
HS
We found no papers devoted to optimization of
electrolytic reductive dimerization of organic halides.
The above scheme suggests that, to increase the yield
of the dimeric product, the process should be per-
formed at a cathode potential as low as possible, so as
to minimize further reduction of the R radical to the
R anion.
R H
where X is halogen and HS is solvent.
According to this scheme, the major reduction
pathways are substitution of hydrogen for halogen and
dimerization of the free radicals. The latter pathway is
an electrochemical analog of the well-known Wurtz
reaction [2] and is of certain practical interest. At the
same time, data on formation of dimeric products in
the course of electrolytic reduction of organic halides
are scarce. For example, reduction of methylene iodide
in aqueous alcohol gave ethylene in a 30% yield [3]:
Preliminary voltammetric studies showed that the
reduction potential of organic halides appreciably
depends on the cathode material [10]. For example,
in reduction of ethyl bromide the lowest reduction
potential was observed with a copper cathode, espe-
cially with that coated with spongy copper. Therefore,
our work on optimization of dimerization by dehalo-
genation was started with testing of various cathode
materials. As a model compound we chose butyl
iodide.
2CH2I2 + 4e
CH =CH + 4I .
2 2
Reduction of butyl iodide gave butane in approxi-
mately the same yield [4, 5]:
The first series of experiments was aimed at reveal-
ing the effect of the cathode material on the selectivity
of butyl iodide reduction. The major attention was
given to pretreatment of the electrode surface before
each run. Metallic cathodes were etched for a short
time in 5% HCl, washed, wiped with sodium carbo-
nate, and rinsed with distilled water. If spots or streaks
appeared on the electrode surface, the etching was
repeated. The results of the experiments are listed in
Table 1. All experiments were performed at a sodium
methylate concentration of 0.005 M, which was suffi-
2
C H I + 2e
C4H10 + 2I .
2
5
The formation of acetylene compounds in the
course of reduction of 1,1,1-trichloro-2,2-diphenyl-
ethane and its derivatives was reported in [6 8]:
2
Ar CHCCl + 6e
Ar CHC CCHAr + 6Cl .
2 2
2
3
Dimerization of 1-cyano-2-iodoethane gave adipo-
dinitrile in a 6.5% yield [5]:
1
070-3632/01/7107-1099$25.00 2001 MAIK Nauka/Interperiodica

1100
TOMILOV
Table 1. Effect of cathode material on reduction of butyl
iodide in methanol
that reduction is partially due to chemical dissolution
of zinc. Data in Table 1 refer to a smooth copper
cathode. For comparison, we performed an experiment
under the same conditions with a cathode coated with
spongy copper. On such an activated electrode no
hydrogen evolution was observed in the first 1.5 h of
the electrolysis, i.e., reduction occured at a high rate;
however, the yield of octane based on butyl iodide
was essentially the same, 80.1%. Further experiments
showed that variation of the current density in the
range 0.03 0.10 A cm 2 has no appreciable effect on
the reduction, whereas, as the sodium methylate con-
centration is increased from 0.005 to 0.7 M, the proc-
ess parameters become worse (despite somewhat
lower working voltage on the electrolyzer), which is
illustrated in Table 2. The yield of octane increases as
the temperature is decreased to 0 C. In the experiment
performed at 0 1 C, the yield of octane based on
butyl iodide was 83 84%.
a
Yield as a function of current,
%
Yield of
octane based
on butyl
Cathode
material
H2
C4H10
C8H18
iodide, %
Pb
Zn
Hg
Sn
Graphite
Cu
St.3 steel
Ni
28
27
4
29
31
21
34
50
29.6
72.2
36.0
30.1
34.0
25.7
19.6
24.7
14.8
17.3
45.6
37.5
18.8
47.8
56.0
79.6
78.0
60.0
a
Catholyte 0.005 M CH ONa in methanol (270 ml), 50 g of
3
butyl iodide; current density 0.028 A cm ; temperature 20
2
2
5 C.
Thus, dimerization of butyl iodide by cathodic
dehalogenation can be performed with a good yield.
The copper cathode shows a high electrocatalytic
activity; the dimeric product can also be obtained with
an iron cathode.
Table 2. Effect of sodium methylate concentration on
reduction of butyl iodide
a
Obtained, g
Yield of octane
based on butyl
iodide, %
[
CH ONa],
3
M
EXPERIMENTAL
C4H10
C8H18
0
.005
2.3
4.15
7.9
5.9
5.1
9.2
7.7
6.0
5.7
5.1
78.0
64.5
42.6
49.1
48.9
Chemically pure grade butyl iodide was distilled
prior to use; the fraction with bp 101 102 C was
collected. Chemically pure grade methanol was used
as solvent without additional purification. Solution of
sodium methylate was prepared by dissolution of the
calculated amount of metallic sodium in methanol.
0
0
0
0
.05
.20
.35
.70
a
The other conditions are the same as for Table 1.
Experiments were performed in a cylindrical glass
electrolyzer equipped with a cooling jacket. The cath-
odic and anodic compartments were separated with a
ceramic diaphragm (Fig. 4 in [11]). The volume of the
cathodic compartment was 300 ml, and the cathode
surface area, 60 cm . The solution was stirred with a
power-driven stirrer.
cient to ensure the conductivity required for prepara-
tive electrolyses. Preliminary experiments showed that
in methanolic solutions of sodium methylate of the
concentration up to 0.7 M butyl iodide is not notice-
ably saponified at room temperature. Experiments
with lead, mercury, tin, and zinc cathodes showed
that these cathodes degrade under the process condi-
tions. From the solution obtained by electrolysis
with a lead cathode, we isolated and identified tri-
2
Gaseous electrolysis products passed through a trap
cooled with an acetone dry ice mixture. Butane con-
densed in the trap. Hydrogen was collected in a Mari-
otte vessel. After electrolysis completion, the catho-
lyte was diluted with a threefold amount of water to
separate crude octane, which was dried and analyzed
chromatographically.
butyllead iodide Bu PbI (found, %: C 28.6; H 5.55;
3
I 25.0. C H PbI. Calculated, %: C 27.9; H 5.30;
1
2
27
I 24.0). Similar organometallic compounds can be
expected to form with the other degradable cathodes,
but we did not isolate and identify them. Table 1
shows that the best yields are attained with copper and
iron cathodes. However, the reduction on iron is slow-
er than on copper, as judged from the higher yield
of hydrogen on the iron cathode. The high yield of
butane on the zinc cathode is probably due to the fact
ACKNOWLEDGMENTS
The study was financially supported by the Russian
Foundation for Basic Research (project no. 97-03-
32265).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 7 2001

CATHODIC DEHALOGENATION WITH DIMERIZATION
1101
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