Oxidation of 2-alkyl-5,10-dihydrophenazines

Article abstract of DOI:10.1007/s11176-005-0027-2

Oxidation of 2-alkyl-5,10-dihydrophenazines afforded 1:1 molecular complexes of the initial compounds with the corresponding 2-alkylphenazines. 2004 MAIK "Nauka/Interperiodica".

Full text of DOI:10.1007/s11176-005-0027-2

Russian Journal of General Chemistry, Vol. 74, No. 9, 2004, pp. 1433 1434. Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 9, 2004,
pp. 1544 1545.
Original Russian Text Copyright
2004 by Bidman.
Oxidation of 2-Alkyl-5,10-dihydrophenazines
T. A. Bidman
Institute of Chemistry and Chemical Technology, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, Russia
Received July 4, 2002
Abstract Oxidation of 2-alkyl-5,10-dihydrophenazines afforded 1: 1 molecular complexes of the initial
compounds with the corresponding 2-alkylphenazines.
Phenazine derivatives have found wide application
as redox indicators. Their formal redox potentials are
usually low: they range from 0.05 to 0.30 V [1].
Taking into account the scope of application of these
compounds, only water-soluble systems containing
hydrophilic substituents in the aromatic ring have
been extensively studied. Phenazine derivatives with
alkyl substituents in the aromatic ring were not re-
ported. The formal redox potential of alkylphenazine
systems is reduced even more strongly due to the
presence of electron-donor alkyl groups; in addition,
the latter endow such systems with hydrophobic
properties, thus making them suitable for redox ex-
traction processes.
We previously developed a procedure for the syn-
thesis of 2-alkyl-5,10-dihydrophenazines [2]. Their
oxidation could give rise to the corresponding 2-alkyl-
phenazines. However, the use of conventional oxida-
tion methods resulted in decomposition of these com-
pounds. The present communication describes a pro-
cedure for the oxidation of 2-alkyl-5,10-dihydrophena-
zines I to 2-alkylphenazines II with an aqueous solu-
tion of potassium bromate.
NH
N
HO
HO
R
NH2
NH2
R
R
+
2H+, 2e
2H2O
NH
N
Ia If
IIa IIf
I, II, R = H (a), Br (b), t-Bu (c), MeCH2CMe2 (d), Me(CH2)3C(Et)Me (e), cyclo-C6H11 (f).
Compounds II were isolated as 1:1 complexes
with initial dihydrophenazines I, like that derived
from hydroquinone and p-benzoquinone. The corres-
ponding complexes were also obtained in the presence
of a large excess of the oxidant, as well as on extend-
ing the reaction time. In these cases, the fraction of
tarry products increased. Stronger oxidants induced
decomposition of dihydrophenazines I. Presumably,
2-alkylphenazines are less stable than their 5,10-di-
hydro derivatives, and the formation of complexes
with the latter stabilizes the former.
The IR spectra of initial dihydrophenazines I con-
tained absorption bands at 3423 3321 cm , typical of
1
stretching vibrations of free and associated NH groups;
analogous bands are characteristic of the IR spectra of
pyrrole and secondary amines [3]. In the region 1620
1509 cm 1 we observed absorption bands due to vibra-
tions of the aromatic rings and NH bending vibrations.
Unlike compounds I, the NH stretching vibration
bands in the IR spectra of complexes I II are dis-
1
placed to 3389 3303 cm , and additional absorption
1
bands appear in the region 1633 1504 cm due to
stretching vibrations of the conjugated C=C and C=N
bonds in II.
The rate of oxidation of compounds I to II depends
on the alkyl radical structure: it increases with branch-
ing of R. In Experimental, the reaction time is given
for the oxidation of 2-bromo derivative Ib which was
oxidized most slowly. The complexes were formed in
quantitative yield. Unlike colorless initial compounds
I, complexes II are orange substances.
EXPERIMENTAL
The IR spectra were recorded in the range from
1
4000 to 400 cm on an IKS-22 spectrometer from
samples pelleted with KBr. Initial compounds Ia If
1070-3632/04/7409-1433 2004 MAIK Nauka/Interperiodica

1434
BIDMAN
Melting points and elemental analyses of 1: 1 complexes
of 2-alkylphenazines II with 2-alkyl-5,10-dihydrophena-
zines I
The mixture was evaporated at room temperature, and
the residue was extracted with three portions of di-
ethyl ether (until colorless extract). The combined
extracts were filtered and evaporated on a rotary eva-
Found,
C
%
Calculated, % porator, and the product was dried under reduced
pressure (water-jet pump). The yields were quantita-
mp, C
Formula
tive. The products were almost pure; the melting
H
C
H
points were determined from samples recrystallized
from hexane. The complexes were crystalline sub-
stances; their melting points and analytical data are
given in the table.
Ia 88 89 79.31 4.80 C24H18N4
Ib 84 85 55.18 2.78 C24H16Br2N4 55.41 3.10
79.54 5.01
Ic 101 102 80.77 6.98 C32H34N4
Id 99 100 81.03 7.37 C34H38N4
Ie 103 104 81.61 8.24 C40H50N4
80.98 7.22
81.24 7.62
81.87 8.59
82.09 7.27
REFERENCES
If
86 87 81.79 6.95 C36H38N4
1. Indicators, Bishop, E., Ed., Oxford: Pergamon, 1972.
Translated under the title Indikatory, Moscow: Mir,
1976, vol. 2, p. 76.
were synthesized by the procedure reported in [2], and
the corresponding 4-alkyl-1,2-benzenediols were
prepared as described in [4].
2. RU Patent 2171255, 2001; Byull. Izobret., 2001,
no. 21.
3. Bellamy, L.J., The Infra-red Spectra of Complex Mo-
lecules, London: Methuen, 1958. Translated under the
title Infrakrasnye spektry slozhnykh molekul, Moscow:
Inostrannaya Literatura, 1963, p. 364.
2-Alkylphenazine 2-alkyl-5,10-dihydrophena-
zine complexes (general procedure). A 4% solution
of KBrO3 (25 ml, 6 mmol) was added to 2 mmol of
dihydrophenazine Ia If (see table), and the mixture
was kept for 2 days at room temperature. The origi-
nally colorless solution turned persistently orange.
4. RU Patent 2084438, 1997; Byull. Izobret., 1997,
no. 20.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 9 2004