Electrochemical methoxylation of anethole on a graphite anode

Article abstract of DOI:10.1134/S1070427206120275

A procedure is suggested for electrochemical methoxylation of anethole in an electrolyzer with a graphite cathode and potassium p-toluenesulfonate in methanol as supporting electrolyte; a mixture of two products is formed in the process.

Full text of DOI:10.1134/S1070427206120275

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 12, pp. 2035 2036.
Pleiades Publishing, Inc., 2006.
Original Russian Text
I.M. Osadchenko, A.P. Tomilov, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 12, pp. 2059 2060.
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Electrochemical Methoxylation of Anethole on a Graphite Anode
I. M. Osadchenko and A. P. Tomilov
Volgograd Research and Technological Institute of Meat-and-Milk Cattle Breeding and Animal Product Processing,
Russian Academy of Agricultural Sciences, Volgograd, Russia
Received October 3, 2006
Abstract A procedure is suggested for electrochemical methoxylation of anethole in an electrolyzer with
a graphite cathode and potassium p-toluenesulfonate in methanol as supporting electrolyte; a mixture of two
products is formed in the process.
DOI: 10.1134/S1070427206120275
Electrochemical alkoxylation of organic com-
pounds on platinum, carbon, and graphite anodes has
been reported [1]. The source of the methoxylating
agent was methanol, acting as a solvent for both the
organic substance and the electrolyte. Alcoholic solu-
tions of alkalis and alcoholates were recommended
for electrochemical alkoxylation of hydrocarbons, ter-
tiary amines, and ethers. The alkoxylation pathway is
strongly influenced by the concentration of the organ-
ic substrate [1]. If dimerization occurs concurrently
with alkoxylation, the contribution of the former pro-
cess, as a rule, increases with the concentration of
the organic substrate.
The goal of this study is to simplify this process
and extend its potentialities.
Previously [3] we have demonstrated the possi-
bility in principle of electrochemical methoxylation
of anethole at 55 65 C on a graphite anode in meth-
anol, with potassium p-toluenesulfonate as support-
ing electrolyte. An advantage of this system is that
the salt crystallizes and precipitates on cooling, and
it can be readily separated by filtration. The filtrate
is treated with 10% sulfuric acid and extracted with
toluene; the extract is washed with a sodium car-
bonate solution and vacuum-distilled. In the process,
anethole is gradually added to the electrolyte, because
at low concentrations its oxidative dimerization is
suppressed.
The methoxylation of aryl-substituted unsaturated
hydrocarbons, styrene and its derivatives, has been
studied in detail; it was shown that electrochemical
methoxylation of styrene gives dimethoxyphenylethane
in 30% yield [1]. Anodic methoxylation of anethole
(1-methoxy-4-propenylphenol) is of interest as a route
to anisaldehyde (aubepine) diacetal, which can be
readily converted by hydrolysis into the free aldehyde,
a valuable fragrance compound and an intermediate
for organic synthesis. Methoxylation of alkenylarenes,
including anethole, in a methanolic solution of potas-
sium or sodium trifluoroacetate in a diaphragmless
electrolyzer with graphite electrodes was reported in
[2]. However, the electrolyses may be complicated by
anodic decomposition of trifluoroacetate.
We examined the influence exerted on the methox-
ylation by the temperature, current density, amount of
electricity, and electrolyte concentration. The best
results were obtained under the following conditions:
2
55 65 C, anodic current density 0.02 0.05 A cm ,
amount of electricity 5.5 6 F per mole of anethole,
3 5% supporting electrolyte concentration, and up to
0.4 M concentration of anethole in the electrolyte.
Anisaldehyde and methyl p-methoxybenzoate were
obtained in yields of up to 70 and 25%, respectively.
The electrochemical methoxylation and hydrolysis
follow the scheme
6 F, CH3OH
CH3O
CH=CH CH3
CH3O
CH3O
CH(OCH3)2 + CH3O
H
C(OCH3)3
OCH3
C O
C O
CH3O
2035

2036
OSADCHENKO, TOMILOV
It should be noted that methyl p-methoxybenzoate
and pest control [6, 7]. Anisaldehyde can be isolated
from the product via bisulfite derivative. The product
components were identified by gas chromatography
(comparison of the retention times with those of
the authentic samples).
(anisic acid methyl ester) is used as a stabilizer for
fragrance compounds. As a target product we obtained
a mixture of anisaldehyde and methyl p-methoxyben-
zoate. Their boiling points are close (248 and 256 C,
respectively [4]), making difficult their separation by
distillation.
CONCLUSION
EXPERIMENTAL
The procedure developed for electrochemical meth-
oxylation of anethole in methanol on a graphite anode
with potassium p-toluenesulfonate as supporting elec-
trolyte, yields a mixture of two valuable products,
anisaldehyde and methyl p-methoxybenzoate and al-
lows simplification of the process and extension of
its potentialities.
Anethole, toluene, and potassium p-toluenesulfo-
nate were reagent-grade. The electrolyzer was a cy-
lindrical glass vessel with a temperature-control
jacket. Current leads and tubes for the stirrer, addition
of anethole, and removal of the gas were fixed on the
lid. The electrolyzer was charged with a mixture of
150 g of methanol and 3.5 g of potassium p-toluene-
sulfonate; the mixture was stirred at 55 65 C until
the salt dissolved completely, and the electrolysis was
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performed at a current density of 0.03 A cm (3 A
current) with gradual addition of anethole (15 g in
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and vapor temperature of 120 125 C. An oily liquid
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benzoate (total yield based on anethole 94%). The
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RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 79 No. 12 2006