1-(Phenylamino)pseudo-mauveine: A new water soluble phenazine dye

Article abstract of DOI:10.3184/174751914X14033559668812

1-(Phenylamino)pseudo-mauveine was prepared by the oxidation of 1,3,5-tris(phenylamino)benzene and p-phenylenediamine with potassium dichromate. The absorption maximum of 535 nm is shifted hypsochromically by about 20 nm compared to that for pseudo-mauvei

Full text of DOI:10.3184/174751914X14033559668812

JOURNAL OF CHEMICAL RESEARCH 2014
VOL. 38 JULY, 437–442
RESEARCH PAPER 437
1-(Phenylamino)pseudo-mauveine: a new water soluble phenazine dye
M. John Plater* and Toby Jackson
Department of Chemistry, University of Aberdeen, Meston Walk, Aberdeen, AB24 3UE
1-(Phenylamino)pseudo-mauveine was prepared by the oxidation of 1,3,5-tris(phenylamino)benzene and p-phenylenediamine
with potassium dichromate. The absorption maximum of 535 nm is shifted hypsochromically by about 20 nm compared to
that for pseudo-mauveine. Condensation of 1,3,5-tris(phenylamino)benzene with 4-nitrosodiphenylamine under strongly
acidic conditions gave 1,3,7-tris(phenylamino)-5-phenylphenazinium sulfate and 10-phenyl-6,8-bis(phenylamino)-2,10-
dihydrophenazin-2-one.
Keywords: pseudo-mauveine, 1,3,5-tris(phenylamino)benzene, p-phenylenediamine, N-phenyl-p-phenylenediamine,
4-nitrosodiphenylamine
Mauveine was characterised as an important phenazine
dye in the nineteenth century by independent syntheses
of pseudo-mauveine 3 from the aromatic building blocks
1–2 and 4–5 by oxidation under mildly acidic conditions
(Scheme 1).1 p-Phenylenediamine 1 was oxidatively condensed
Discussion
(i) Synthesis of 1,3-bis(phenylamino)-5-phenyl-7-amino-
phenazinium sulfate {1-(phenylamino)pseudo-mauveine}
A 10 g sample of 1,3,5-tris(phenylamino)benzene 9 was
available from a previous project5 in the authors’ group on the
synthesis of polyaromatic amines as charge transport materials.
The oxidation of compound 9 and p-phenylenediamine 1 with
K2Cr2O7 in H2O/H+ was unsuccessful owing to the poor water
solubility of compound 9. However, we showed previously
that acetone/water mixtures can be used in these syntheses
for poorly water soluble building blocks.6–8 The oxidation of
compound 9 and p-phenylenediamine 1 with K2Cr2O7 in water/
acetone (1.5:1.0) was successful as the building block is easily
dissolved in a water/acetone mixture (Scheme 3). The acetone
must be evaporated before filtration of the reaction mixture
as it solubilises the mauveine-like product 10. Isolation of the
product 10 is aided by the absorption of the chromophore onto
insoluble by-products. However, because the yield of 35% is
with 1,3-bis(phenylamino)benzene
2
and N-phenyl-m-
phenylenediamine was condensed with N-phenyl-p-
4
phenylenediamine 5. The trimer 7 was used to make pseudo-
mauveine 3 and other derivatives more recently.2 The yields
for these reactions are improved over those for conventional
mauveine syntheses because the building blocks 2, 4 and 5
are pre-assembled as dimers. Pseudo-mauveine 3 was also
converted into phenosafranine 8 by oxidation with lead (IV)
oxide (Scheme 2).3,4 The conversion of an asymmetric dye into
a symmetric one helps to verify the correct structure. Mauveine
was used to dye silk from hot water as the dye is poorly soluble
in cold water which also restricts its use as a biological stain. In
this paper we report a novel synthesis of a phenazinium sulfate
salt which fortuitously has good water solubility.
NH2
+
HN
N
H
H2N
1
2
H2N
N
+
H2N
NH
N
H2N
N
N
H
H
4
5
3
NH2
H
N
+
H2N
N
H
7
6
Scheme 1 1+3 and 2+2 assembly routes to pseudo-mauveine.
* Correspondent. E-mail: m.j.plater@abdn.ac.uk
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438 JOURNAL OF CHEMICAL RESEARCH 2014
N
N
N
lead(IV)oxide
H2N
N
N
H2N
NH2
H
3
8
Scheme 2 Perkin’s oxidation of pseudo-mauveine 3 to phenosafranine 8.
HN
HN
9
NH2
1
N
N
2
3
2Cr2O7/H+/H2O/acetone
8
K
+
H2N
HN
N
H2N
N
7
H
5
H
6
4
1
10
9
Purple dye λmax 535 nm
Scheme 3 Synthesis of 1,3-bis(phenylamino)-5-phenyl-7-aminophenazinium sulfate 10 (the ring positions are numbered).
much higher than the typical yields of 1–5% obtained for the
assembly of four aromatic amine building blocks,6–8 more
material remains in solution. The product was purified by usual
chromatographic methods. On a silica gel column, MeOH
successfully eluted front running impurities first, then cNH3/
MeOH (20:80) eluted the pure product.
Presumably a larger dipole enhances the water solubility as
the extra phenylamino nitrogen lone pair conjugates to the
chromophore and molecular rotation may affect packing in the
solid state.
(ii) Synthesis of 1,3,7-tris(phenylamino)-5-phenylphenazinium
sulfate
Thestructureofcompound10wasestablishedbyspectroscopic
methods including high resolution mass spectrometry. The
1H NMR spectrum showed upfield singlets for the protons at
positions 2, 4 and 6 and a downfield doublet for the proton at
position 9 (see experimental). The 13C NMR spectrum showed
the required 24 signals. The UV spectrum was unusual because
the λmax of 535 nm was shifted hypsochromically by 15 nm
compared to mauveine chromophores, which have λmax around
550–555 nm. The phenazine core has four sites (positions 1, 3, 7
and 9) where substituents can conjugate to the positive charge.
The new phenylamino group is therefore conjugated to the
chromophore and we had expected a bathochromic shift in the
absorption maximum. The conjugation of the two phenylamino
groups is therefore not additive. A second surprise came from
the water solubility of this compound. It freely dissolves
in water with stirring despite having an extra phenyl ring.
Owing to the success of this synthesis to make compound 10
an attempt was made to prepare further derivatives of pseudo-
mauveine 3 substituted with more phenylamino groups. A
mixture of 1,3,5-tris(phenylamino)benzene 9 and N-phenyl-
p-phenylenediamine 5 was oxidised in the same way using
K2Cr2O7 in water/acetone (1.5:1.0) with some acid (Scheme 4).
One product was formed and this was isolated and
characterised as 1,3,7-tris(phenylamino)-5-phenylphenazinium
sulfate 11 by spectroscopic methods including high resolution
1
mass spectrometry. Much of the H NMR data for compound
11 is similar to that for compound 10 owing to the similarity in
structure and an extra set of phenyl protons are present. This
compound is less soluble and acquisition of 13 C NMR data was
not possible. This compound is now blue rather than purple,
the characteristic colour of pseudo-mauveine 3. The absorption
HN
HN
N
NH2
2Cr2O7/H+/H2O/acetone
K
+
HN
N
N
N
N
N
H
H
H
H
5
9
11
Blue dye λmax 562 nm
Scheme 4 Synthesis of 1,3,7-tris(phenylamino)-5-phenylphenazinium sulfate 11.
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JOURNAL OF CHEMICAL RESEARCH 2014 439
O
N
N
+
EtOH/cHCl
air
N
N
N
HN
N
N
H
H
H
H
12
13
2
Scheme 5 Fischer and Hepp’s synthesis of compound 13.
maximum occurred at 562 nm which is shifted 10 nm
bathochromically compared to pseudo-mauveine 3. However,
the absorption is very broad extending out into the red end
of the spectrum, which will account for the change in colour
from purple to blue. Since the absorption maximum of pseudo-
mauveine 3 is bathochromically shifted compared to that of
phenosafranine 8, the bathochromic shift in the absorption
maximum observed here was anticipated.
11 (11%) and the other was a hydrolysis product tentatively
assigned as structure 14 (18%). The UV spectrum of compound
14 showed an absorption maximum at 519 nm. The IR spectrum
showed no conventional carbonyl group around 1700 cm–1 but
a stretch at 1585 cm–1 which is low for a carbonyl group. It
showed a carbonyl group in the 13C NMR at 172 ppm and the
expected 24 peaks in total. An expected molecular ion and high
resolution mass spectrum for M+ +H was obtained. Treatment
of compound 11 under the same acidic conditions did not
give compound 14 which showed that compound 11 is not a
precursor to it. Treatment of 1,3,5-tris(phenylamino)benzene 9
with 4-nitrosophenol 15 under the same acidic conditions failed
to form compound 14 (Scheme 6) which ruled out an initial
hydrolysis of 4-nitrosodiphenylamine 12 to 4-nitrosophenol
15 (Scheme 7). Scheme 8 describes a proposed route to the
formation of compounds 11 and 14.
Fischer and Hepp previously reported the synthesis of
3,7-bis(phenylamino)-5-phenylphenazinium
sulfate
13
by the condensation of 4-nitrosodiphenylamine 12 with
1,3-bis(phenylamino)benzene 2 in cHCl/EtOH with air as
oxidant (Scheme 5).9–11 They also reported other condensations
using 4-nitrosoaniline.12–15
We
therefore
attempted
the
condensation
of
4-nitrosodiphenylamine 12 with 1,3,5-tris(phenylamino)
benzene 9 under similar conditions (Scheme 6). Two products
were isolated. One was the expected product, compound
This involves an initial acid-catalysed condensation of
1,3,5-tris(phenylamino)benzene 9 onto the nitroso group of
11
EtOH/cHCl
HN
HN
O
N
N
N
EtOH/cHCl
11
+
+
N
O
H
HN
N
N
H
H
14
12
9
HO
NO
EtOH/cHCl
15
HN
HN
N
H
9
Scheme 6 Synthesis with 4-nitrosodiphenylamine 12 and attempted synthesis with 4-nitrosophenol 15.
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440 JOURNAL OF CHEMICAL RESEARCH 2014
OH
N
OH
N
NO
EtOH/cHCl
+
N
H
N
NH2
17
O
6
16
12
HO
NO
15
Scheme 7 A possible in situ hydrolysis of 4-nitrosodiphenylamine 12 to 4-nitrosophenol 15, which was not observed.
4-nitrosodiphenylamine 12 and the elimination of water to
give intermediate 19. In principle, there are three different
phenylamino groups, one of which might hydrolyse off from
the molecule. Only one hydrolysis product is formed. The facile
hydrolysis of the phenylamino group, drawn on intermediate 19
as an imminium salt, to give intermediate 20 is the most likely
because molecular twisting will favour this canonical form and
the 1,3,5-tris(phenylamino)benzene ring is more stable. This
molecular twisting is likely owing to steric congestion in the
planar form. Cyclisation and aerial oxidation to compound 14
can then occur.
Since two chromophores were isolated in the
condensation reaction of 4-nitrosodiphenylamine 12 with
1,3,5-tris(phenylamino)benzene 9 caution should be taken in
interpreting Fischer and Hepp’s studies with nitrosated building
blocks as similar hydrolysed products might also occur under
the strongly acidic conditions used.9–15
The TLC spot is also purple using cNH3/MeOH as eluent
and blue using secBuOH/EtOAc/H2O/HOAc as eluent. These
observations are rationalised by assuming that protonation
occurs in mild acid and deprotonation occurs in mild base or
water. This behaviour is different from pseudo-mauveine 3
and other mauveine chromophores which do not deprotonate
with cNH3/MeOH. The rapid elution of compound 14 with
MeOH, and its purple rather than blue colour when purifying
it after its synthesis from compounds 9 and 12, suggests that it
is deprotonated during precipitation or filtration and washing
with water. It is only weakly basic. A strong dipole would
suggest canonical form 22, resembling a meso-ionic structure,
and this might explain the lack of an IR carbonyl stretch.
Conclusion
Two new derivatives of pseudo-mauveine 3 have been prepared
which are substituted with phenylamino groups. Both have
an additional phenylamino group in the 1 position. This
substitution causes good water solubility at room temperature
in compound 10. The syntheses of these compounds require
the use of an acetone/water mixture to solubilise the starting
material 1,3,5-tris(phenylamino)benzene 9.
The TLC characteristics of compound 14 are quite unusual
(Scheme 9). At first we were puzzled as compound 14 eluted
from a column ahead of compound 11 using MeOH as eluent
but then ran more slowly up a TLC plate behind compound
11 using secBuOH/EtOAc/H2O/HOAc as eluent (Scheme 9).
HN
HN
OH
N
air
N
11
+
12
9
H
N
HN
N
HN
HN
N
H
H
19
18
HN
air
N
14
HN
N
O
H
20
Scheme 8 Proposed route to both compounds 11 and 14.
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JOURNAL OF CHEMICAL RESEARCH 2014 441
HN
HN
HN
N
N
N
N
N
N
O
N
HO
N
N
O
H
H
H
14
22
21
Blue
Purple
secBuOH:EtOAc:H2O:HOAc
(60/30/9.5/0.5)
cNH3:MeOH
(20/80)
Scheme 9 Protonation and deprotonation of compound 14 in different TLC solvents.
dryness then purified by chromatography on silica gel. After elution
with MeOH, elution with cNH3/MeOH (20/80) gave the title compound
(198 mg, 34%) as a dark blue solid, m.p.>230 °C. λmax (ethanol)/nm 562
(log ε 4.9) and 287 (4.9); νmax (diamond anvil) 2977w, 2903w, 1584s,
1463s, 1355s, 1302s, 1229s, 1191s, 1066vs, 876s, 823s, 747vs, 596vs,
757vs and 458; δH (400 MHz; CD3OD) 5.68 (1H, d, J=2.0 Hz), 6.31 (1H,
d, J=2.0 Hz), 6.80 (1H, d, J=2.0 Hz), 7.09 (3H, d, J=8.0 Hz), 7.13 (2H,
d, J=12.0 Hz), 7.28 (5H, t, J=8.0 Hz), 7.40–7.45 (4H, m), 7.48 (2H, d,
J=6.0 Hz), 7.68 (2H, t, J=4.0 Hz), 7.75 (3H, t, J=7.20 Hz) and 8.08 (1H,
d, J= 9.20 H z); δC (100.1 MHz; CDCl3) m/z (Orbitrap ASAP) 530.2323
(M+, 100%) C36H28N5 requires 530.2339. The compound was not soluble
enough to record a carbon 13 spectrum.
Experimental
IR spectra were recorded on a PerkinElmer Spectrum Two diamond
anvil IR spectrometer. UV spectra were recorded using a PerkinElmer
Lambda 25 UV-VIS spectrometer with EtOH as the solvent. 1H and 13
C
NMR spectra were recorded at 400 MHz and 100.5 MHz respectively
using a Varian 400 spectrometer. Chemical shift values, δ, are given
in ppm by reference to the residual solvent, and coupling constants, J
are given in Hz. Low resolution and high resolution mass spectra were
obtained at the University of Wales, Swansea using electron impact
ionisation and chemical ionisation. Melting points were determined
on a Kofler hot-stage microscope. 4-Nitrosodiphenylamine and
4-nitrosophenol were purchased from TCI Europe.
10-Phenyl-6,8-bis(phenylamino)-2,10-dihydrophenazin-2-one
(14): 1,3,5-tris(Phenylamino)benzene 9 (100 mg, 0.285 mmol) and
4-nitrosodiphenylamine 12 (56 mg, 0.285 mmol) in EtOH (10 mL) and
cHCl (5 mL) were heated to dryness in a beaker over 3 h in a fume hood.
After the addition of water the product was filtered off and purified
by chromatography on silica gel. MeOH eluted the title compound
(23 mg, 18%) as a dark green solid, m.p.>220 °C. λmax (ethanol)/nm 519
(log ε 4.39) and 295 (4.45); νmax (diamond anvil) 1585vs, 1557s, 1489s,
1436s, 1304s, 1239s, 1218vs, 1175s, 1124s, 874w, 815w, 751s and 695vs;
δH (400 MHz; CD3OD) 5.32 (1H, s), 6.20 (1H, d, J=2.0), 6.26 (1H, d,
J=1.6), 7.04 (2H, d, J=8.0), 7.09–7.12 (4H, m), 7.20 (2H, d, J=7.6),
7.23 (3H, dd, J=8 and 7.6), 7.38 (2H, d, J=7.6), 7.62 (1H, t, J=7.2 and
7.2), 7.71 (2H, t, J=7.6 and 7.6) and 7.93 (1H, d, J= 8.8); δC (100.1 MHz;
CDCl3) 86.4, 94.9, 97.8, 115.7, 120.9, 122.7, 123.7, 124.7, 127.7, 128.8,
128.9, 129.9, 131.0, 133.1, 136.0, 137.2, 137.6, 138.9, 139.7, 140.5,
150.5, 157.7, 157.8 and 172.6; m/z (Orbitrap ASAP) 455.1863 (M+ +H,
100%) C30H23N4O requires 455.1866. cNH3/MeOH (20:80) eluted
1,3,7-tris(phenylamino)-5-phenylphenazinium sulfate 11 (18 mg, 11%)
as a blue solid with identical spectroscopic properties to the material
reported previously.
1-(Phenylamino)pseudo-mauveine (10) [1,3-bis(phenylamino)-
5-phenyl-7-amino-phenazinium
sulfate]:
A
mixture
of
1,3,5-tris(phenylamino)benzene 95 (382 mg, 1.10 mmol) and
p-phenylenediamine (118 mg, 1.10 mmol) in water and acetone
(150 mL/100 mL) with cH2SO4 (six drops, 0.3 mL) was treated with
K2Cr2O7 (320 mg, 1.10 mmol) and heated at 40–50 °C for 1 h with
stirring in a beaker covered with a petri dish. The petri dish was then
removed and heating and stirring continued for a further 2–3 h to
evaporate the acetone. The acetone must be evaporated before the
mixture is filtered. After allowing the mixture to cool it was filtered
through a fine pore sinter and washed with H2O. The precipitate was
extracted with MeOH (6×50 mL) in the sinter each time agitating
the precipitate. The combined MeOH extracts were evaporated to
dryness then purified by chromatography on silica gel. After elution
with MeOH elution with cNH3/MeOH (20/80) gave the title compound
(194 mg, 35%) as a dark purple glistening solid, m.p.>230 °C. λmax
(ethanol)/nm 535 (log ε 4.9) and 276 (5.3); νmax (diamond anvil)
1607w, 1585s, 1470s, 1388w, 1354w, 1302s, 1225s, 1163s, 1021s,
875w, 824s, 749s, 689s and 591s; δH (400 MHz; CD3OD) 5.57 (1H, s),
5.85 (1H, s), 6.73 (1H, s), 7.01 (2H, d, J=7.6 Hz), 7.06–7.09 (2H, m),
7.10 (1H, t, J=6.8 Hz), 7.21 (2H, d, J=7.6 Hz), 7.30–7.38 (4H, m), 7.41
(2H, d, J=7.6 Hz), 7.68–7.76 (3H, m) and 7.82 (1H, d, J= 8.8 H z); δC
(100.1 MHz; CDCl3) 87.3, 93.0, 93.8, 119.4, 122.3, 122.4, 124.4, 125.0,
127.5, 128.9, 129.2, 129.9, 130.5, 131.2, 132.8, 133.4, 136.6, 137.3, 137.5,
138.6, 139.3, 145.1, 154.9 and 157.5; m/z (Orbitrap ASAP) 454.2021
(M+, 100%) C30H24N5 requires 454.2026.
Attempted synthesis of 10-phenyl-6,8-(phenylamino)-2,10-
dihydrophenazin-2-one (14) Method 1: 1,3,7-tris(Phenylamino)-
5-phenylphenazinium sulfate 11 (10 mg, 0.017 mmol) was heated
to dryness in EtOH (2 mL) and cHCl (1 mL). The dry product
(10 mg, 100%) had the same spectroscopic properties as the starting
material and was pure by TLC (secBuOH:EtOAc:H2O:HOAc)
(60:30:9.5:0.5)
1,3,7-tris(Phenylamino)-5-phenylphenazinium sulfate (11):
A
mixture of 1,3,5-tris(phenylamino)benzene 9 (382 mg, 1.10 mmol)
and N-phenyl-p-phenylenediamine (200 mg, 1.10 mmol) in water and
acetone (150 mL/100 mL) with cH2SO4 (6 drops, 0.3 mL) were treated
with K2Cr2O7 (320 mg, 1.10 mmol) and heated at 40–50 °C for 1 h
with stirring in a beaker covered with a petri dish. The petri dish was
then removed and heating and stirring continued for a further 2–3 h
to evaporate the acetone. The acetone must be evaporated before the
mixture is filtered. After allowing to cool the mixture was filtered
through a fine pore sinter and washed with H2O. The precipitate was
extracted with MeOH (6×50 mL) in the sinter each time agitating
the precipitate. The combined MeOH extracts were evaporated to
Attempted synthesis of 10-phenyl-6,8-(phenylamino)-2,10-
dihydrophenazin-2-one (14) Method 2: 1,3,5-tris(Phenylamino)
benzene 9 (100 mg, 0.285 mmol) and 4-nitrosophenol 15 (35 mg,
0.285 mmol) in EtOH (10 mL) and cHCl (5 mL) were heated to dryness
in a beaker over 3 h in a fume hood. After the addition of water the
reaction was filtered and the precipitated material was purified by
chromatography on silica gel. None of the title compound had formed.
We are grateful to the EPSRC national mass spectrometry
service centre for mass spectra.
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442 JOURNAL OF CHEMICAL RESEARCH 2014
5
M.J. Plater, M. McKay and T. Jackson, J. Chem. Soc. Perkin Trans 1, 2000,
2695.
M.J. Plater, J. Chem. Res., 2013, 37, 427.
M.J. Plater, J. Chem. Res., 2011, 35, 304.
M.J. Plater, J. Chem. Res., 2014, 38, 163.
Received 21 March 2014; accepted 8 June 2014
Paper 1402544 doi: 10.3184/174751914X14033559668812
Published online: 12 July 2014
6
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9
O. Fischer and E. Hepp, Justus Liebigs Ann. Chem., 1895, 286, 193.
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