ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 5, pp. 1001–1003. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © E.Sh. Kagan, V.V. Yanilkin, V.I. Morozov, N.V. Nastapova, I.Yu. Zhukova, I.I. Kashparov, V.P. Kashparova, 2009, published in
Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 5, pp. 829–831.
Mechanism of Electrochemical Oxidation
of 1-Chloro-2,2,6,6-tetramethylpiperidine
a
b
b
b
E. Sh. Kagan , V. V. Yanilkin , V. I. Morozov , N. V. Nastapova ,
a
a
a
I. Yu. Zhukova , I. I. Kashparov , and V. P. Kashparova
a
South-Russian State Technical University (Novocherkassk Polytechnical Institute),
ul. Prosveshcheniya 132, Novocherkassk, 346421 Russia
e-mail: kagan29@mail.ru
b
Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center,
Russian Academy of Sciences, ul. Arbuzova 8, Kazan, 420088 Tatarstan, Russia
e-mail: yan@iopc.knc.ru
Received December 4, 2009
Abstract―In contrast to 2,2,6,6-tetramethylpiperidine and other aliphatic amines, at the electrochemical
oxidation of 1-chloro-2,2,6,6-tetramethylpiperidine a sufficiently stable cation-radical is formed. Its formation
is confirmed by the data of cyclic voltammetry and electron paramagnetic resonance. Further transformation of
the cation-radical leads to the formation of 2,2,6,6-tetramethylpiperidin-1-oxyl.
DOI: 10.1134/S1070363209050235
Earlier [1] we showed that electrolysis of 2,2,6,6-
tetramethylpiperidine (I) in the presence of chloride
ions in a diaphragmless elecrolyzer in a two-phase
system methylene chloride–water afforded the respec-
tive nitroxyl radical, 2,2,6,6-tetramethylpiperidin-1-
oxyl (III) (Scheme 1). The same nitroxyl radical is
formed also at the electrolysis under similar conditions
of 1-chloro-2,2,6,6-tetramethylpiperidine (II, Scheme 1).
However, mechanism of this reaction remained
unclear. Scheme 1 shows an oxidation of 2,2,6,6-tetra-
methylpiperidine I into nitroxyl radical III and
oxoammonium salt IV via 1-chloro-2,2,6,6-tetrame-
thylpiperidine II.
with the diaphragm-type electrolyzer, in the organic
phase remains unreacted II, while water phase contains
oxoammonium salt IV. No other product was detected
in the water phase. For the isolation of the reaction
products the oxoammonium salt IV was reduced with
sodium nitrite or sodium hydroxide into the respective
nitroxyl radical III which was readily soluble in
organic solvents and could be easily recovered from
the water phase.
The result obtained probably means that in a
diaphragmless electrolyzer the nitroxyl radical III is
formed in the process of chloroamine II oxidation.
It is suggested [2–4] that in the first step of
oxidation of amines a single electron transfer occurs
and the respective cation-radical is formed, despite the
fact that in the majority of cases the cation-radicals
have not been identified owing to their short life-time,
Preparative synthesis of radical III can also be
performed by oxidation on anode in an electrolyzer
with a diaphragm-separated cells using compound I as
an initial substance (Scheme 1). At the electrolyzis
Scheme 1.
electrolysys
Na SO
electrolysys
Na SO
electrolysys
NaCl
+
N
2
4
N
2
4
N
N
H
Cl
O
O
III
IV
I
II
1001