Russian Journal of General Chemistry, Vol. 73, No. 5, 2003, pp. 829 830. Translated from Zhurnal Obshchei Khimii, Vol. 73, No. 5, 2003,
pp. 875 876.
Original Russian Text Copyright
2003 by Lisitsyn, Kargin.
LETTERS
TO THE EDITOR
Efficiency of Radical-Cation Amination
of Aromatic Compounds in Sulfuric Acid Solutions
Yu. A. Lisitsyn and Yu. M. Kargin
Kazan State University, Kazan, Tatarstan, Russia
Received January 8, 2002
One of the reasons why the Mn+ NH2OH system,
where Mn+ is a transition metal ion (one-electron
reducer), has not found application in chemical syn-
thesis of primary amines is that deprotonated aminyl
radicals are very fast reduced to ammonia [scheme (1)].
by treatment with aqueous sodium hydroxide, and
neutralized with NaHCO3. The amination products
were extracted with chloroform and analyzed by
chromatography on a Chrom-4 gas chromatograph
with a flame-ionization detector. The temperature of
the glass column [2500 3 mm, 5% XE-60 na Chro-
maton N-AW-DMCS (0.160 0.200 mm)] was 150 C,
carrier gas helium.
H+
NH2 + Mn+
NH3 + M(n+1)+
.
(1)
Despite long-standing efforts [1 4] at aminating
unsaturated and aromatic substrates in aqueous and
aqueous-organic media with amine cations [Eq. (2)],
the hydroxylamine-based yields of amination products
still remain relatively low.
The highest efficiency of the radical-cation amina-
tion is observed at low Q values, when the concentra-
tion of Ti(III) ions in the solution is low and, con-
sequently, reaction (1) is slow. Benzene amination in
sulfuric acid media occurs by a chain mechanism
[5, 6], and the total current yields (one electron per
one hydroxylamine molecule) in electrolytes 1 and 2
are hundreds percent. Thus, for example, on passing
10 C of electricity through the electrolytes, the yields
of amination products are higher than 900 and 1200%,
respectively.
+
NH2 + H+
NH3.
(2)
In the present work we used the example of the
Ti(IV) NH2OH C6H6 system to show that ammonia
formation can be suppressed by using electrochemical
radical-cation amination; thus we synthesized aniline
and isomeric phenylenediamines with a total hydroxyl-
amine-based yield of about 100%.
Upon completion of the electrolyses accomplished
with passing the quantity of electricity theoretically
required for complete consumption of hydroxylamine
in a one-electron process (Qt 482.4 C), electrolytes 1
and 2 have a stable violet color characteristic of Ti(III)
solutions. These solutions are decolorized by addition
of hydroxylamine, which implies complete conversion
of the latter in the electrochemical processes (the fact
that the cathodic potential and the yields of amines
depend on Q suggests that the amination of benzene
in catholytes 1 and 2 is largely complete on the
consumption of 80 and 60% of Qt). Consequently,
the overall current yield of aniline and isomeric
phenylenediamines in the electrosyntesis with the
consumption of Qt simply the total yield of amines
with respect to hydroxylamine. In our experiments,
the hydroxylamine-based yields of benzene amination
products were 95.6% in the first solution and 99.6%
in the second.
The amination of benzene was performed in an
electrochemical cell equipped with a reflux condenser,
a thermostating shell, and a ceramic diaphragm
between the cathodic and anodic compartments. The
object of electrolysis was a highly dispersed emulsion
of 5 ml of the aromatic substrate in 25 ml of a ca-
tholyte, specifically, 11 M aqueous H2SO4 containing
0.1 M Ti(IV) sulfate, 0.2 M NH2OH or 5 M
CH3CO2H (electrolyte 1), or 5.5 M CH3CN (electro-
lyte 2). The reaction temperatures in electrolytes 1 and
2 were 60 and 50 C, respectively. Titanium(III) ions
were generated on a platinum cathode at a current
density of 2 mA/cm2. The quantity of electricity (Q),
passed through the electrolyte, was varied from 5 to
482.4 C.
After the electrochemical process had been com-
plete, the catholyte was cooled, made weakly acidic
1070-3632/03/7305-0829$25.00 2003 MAIK Nauka/Interperiodica
Lisitsyn
