ISSN 1070-3632, Russian Journal of General Chemistry, 2012, Vol. 82, No. 7, pp. 1315–1316. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © Yu.A. Lisitsyn, A.V. Sukhov, 2012, published in Zhurnal Obshchei Khimii, 2012, Vol. 82, No. 7, pp. 1218–1219.
LETTERS
TO THE EDITOR
Indirect Cathode Amination of Anisole in Dilute Sulfuric Acid
and Acetonitrile Solutions
Yu. A. Lisitsyn and A. V. Sukhov
Butlerov Institute of Chemistry of Kazan (VolgaRegion) Federal University,
ul. Kremlevskaya 18, Kazan, Tatarstan, 420008 Russia
e-mail: Yuri.Lisitsyn@ksu.ru
Received February 14, 2012
DOI: 10.1134/S1070363212070250
Electrochemical cation-radical amination of aromatic
compounds poorly soluble in water and activated towards
electrophilic reagents, in particular, anisole, is carried
out in dilute sulfuric acid containing an organic solvent
inert with respect to the amino radical intermediates
[1–4], e.g., acetonitrile [1] or acetic acid [2, 3], in a
concentration close to the maximum possible. In the
electrolysis performed under these conditions with full
theoretical conversion of NH2OH with the use of one
electron per its molecule, the total efficiency of
aromatic monoamino compounds on the current
corresponds to their yield relative to the source of
amino radicals.
Taking into account the data on the conductivity of
the sulfuric acid solutions [5], as well as the influence
of temperature on the results of the anisole amination
in solution of acetic acid and 4 M H2SO4 [3], we
carried out the electrolyses of Ti(IV)–NH2OH–
C6H5OCH3 system in an electrolyte containing 4 M
H2SO4 and 14.1 M CH3CN at 30, 25, 20, and 15°C. In
this case, in contrast to the experiment performed in 6
M H2SO4 a solution of anisole in the catholyte rather
then emulsion was subjected to the electrolysis.
Total yields of the isomeric anisidines (2 para/ortho
~ 3.9) formed at the mentioned temperatures are 79.6,
81.1, 84.2, and 82.3%, respectively, not inferior to that
obtained in 6 M H2SO4 solution at 40°C. Hence, from
an economy point of view, the electrosynthesis of
aromatic monoamino compounds from substrates, which
are poorly soluble in water, it is apparently desirable to
perform it under the conditions we have found: at
room temperature in 4 M H2SO4 solution contained the
maximal possible concentration of CH3CN.
In this work we show that the amination of anisole
to form the isomeric anisidines can be performed with
a fairly high yield relative to hydroxylamine under the
milder conditions than those used in [1]: at a lower
H2SO4 concentration and temperatures.
The highest total yield of anisidines (78%) was
obtained by the electrolysis of the anisole emulsion in
6 M H2SO4 and 11.6 M CH3CN at 40°C in an electro-
chemical cell having a mercury cathode of 12.3 cm2
area [1]. Since the working electrode area in the cell
we used was 11 cm2 and the efficiency of the target
electrochemical process depended on the concentra-
tions of oxidized and reduced forms of the Ti(IV)/Ti(III)
mediator system [4], we initially duplicated the above-
mentioned electrolysis. The yield of anisidines relative
to hydroxylamine was 80%. The increase in the
amination efficiency with a decrease in the cathode
area is connected with a decrease in the rate of the
competitive reduction of aminyl radicals to ammonia
due to the lower rate of the cathode generation of
Ti(III) at the same current density.
The amination of aromatic substrate was performed
in a glass electrochemical cell having a jacket for the
temperature control and ceramic diaphragm that
separated the cathode and anode chambers. The
catholyte (25 ml) containing 0.1 M of Ti(IV), 0.2 M of
NH2OH, 4 or 6 M of H2SO4, 14.1 or 11.6 M of
CH3CN, and a small amount of water was introduced
with the Ti(IV) solution and was added to achieve the
volume of 25 ml after the dissolution of the system
components. The volume of anisole added to the
catholyte was 5 ml. The electrolysis of anisole as a
solution in 4 M H2SO4 deaerated with argon or as a
highly dispersed emulsion in 6 M H2SO4 was
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Lisitsyn
