Synthetic derivatives of mauveine

Article abstract of DOI:10.3184/174751913X13718370656320

Oxidation of phenosafranin and an excess of aniline gave a novel hydroxylated derivative of pseudo-mauveine. N-Methyl-p-toluidine and bis(4-methylphenyl)amine are efficient building blocks for making mauveine-related chromophores. Their oxidation with K

Full text of DOI:10.3184/174751913X13718370656320

JOURNAL OF CHEMICAL RESEARCH 2013
RESEARCH PAPER 427
JULY, 427–434
Synthetic derivatives of mauveine
M. John Platera* and William T.A. Harrisonb
aUniversity of Malaya, Department of Chemistry, Faculty of Science, Kuala Lumpur 50603, Malaysia
bDepartment of Chemistry, University of Aberdeen, Meston Walk, Aberdeen AB24 3UE, UK
Oxidation of phenosafranin and an excess of aniline gave a novel hydroxylated derivative of pseudo-mauveine.
N-Methyl-p-toluidine and bis(4-methylphenyl)amine are efficient building blocks for making mauveine-related
chromophores. Their oxidation with K2Cr2O7 is believed to form nitrogen centred radicals which then couple with
an aromatic amine by homolytic aromatic substitution of hydrogen. The N-methyl substituent and the p-methyl sub-
stituents are essential for the reaction to proceed. N-Methyl substituted chromophores were not demethylated in the
reaction or by oxidation with K2Cr2O7 in dilute H2SO4. N-Nitroso-bis(4-methylphenyl)amine rearranges smoothly to
the orange compound, (2-nitro-4-methylphenyl)-4-methylphenylamine, when a solution in CH2Cl2 is treated with
montmorillonite at room temperature for 24 h. 2,4-Dimethylaniline has been used to make a mauveine homologue.
The colour of silk dyed with mauveine chromophores has been compared to the colour of silk dyed with authentic
1862 mauveine.
Keywords: mauveine, mauve, N-methyl-p-toluidine, N-phenyl-p-phenylenediamine, montmorillonite, Perkin
In 1856, Perkin filed a patent on a method for making mauve-
ine by the oxidation of aniline sulfate with potassium dichro-
mate in hot water.1 This gave a black precipitate from which
some mauveine was extracted with hot ethanol. The coloured
product was dissolved in hot water and used to dye materials a
purple colour. This invention was exploited by Perkin who set
up a factory for mauveine manufacture with his father and
brother in the years 1857–73 at Greenford Green and began the
coal-tar dye industry.2 Research on the molecular structure of
mauveine was begun by Perkin himself3–6 and later pursued by
others7–10 who showed that a phenazine moiety is the basic
structure of mauveine. The two major components of Perkin’s
mauveine have been identified by NMR spectroscopy as
mauveine A and mauveine B.11,12 It is now known that over 12
homologues are present in mauveine.13,14 The synthesis of
mauveine by Perkin’s method is low yielding and others have
had difficulty repeating it.15 Mechanistic studies suggest that
N-phenyl-p-phenylenediamine derivatives are intermediates
in mauveine synthesis.16,17 We have shown that this cheap
anti-oxidant from the rubber industry can be used for making
mauveine chromophores.16,17 We now report our studies on
new synthetic routes to derivatives of mauveine chromophores
and the chemistry of some novel building blocks. Mauveine is
not commercially available like some early dyes such as fuch-
sine18,19 and the lack of synthetic methods may have restricted
its exploitation.
chromophore 2 was isolated in low yield. The UV showed a
characteristic mauveine absorption at 551 nm17 and the IR
1
showed a broad absorption 2500–3300 cm–1. The H NMR
spectrum showed two downfield doublets at 7.90 and 7.96
(2H, 1 and 9), a multiplet at 7.71–7.81 (3H, m/p-phenyl), a
doublet at 7.47 (2H, o-phenyl) ppm, two doublets at 7.35 (1H,
2 or 8) and 7.23 (1H, 2 or 8) ppm, two doublets at 6.96 (2H,
aryl) and 6.70 (2H, aryl) ppm and two fine doublets at 6.12
(1H, 4 or 6) and 5.99 (1H, 4 or 6) ppm. These data are very
characteristic of a mauveine chromophore.11,13,14 The peaks at
6.9 and 6.7 ppm are coupled doublets (J = 9.0 Hz) and are
moved upfield suggesting an electron rich para-substituted
benzene ring. High resolution mass spectrometry confirmed
the molecular ion.
This reaction is best with a large excess of aniline and
requires a low pH. The acid will activate the oxidant and facil-
itate the hydrolysis of intermediate imminium salts. Scheme 2
shows a possible route firstly involving a coupling of pheno-
safranin 1 and aniline to give compound 3 followed by oxida-
tion to quinone-imine 4 via two intermediates. This would
have to be reduced to product 2 with K2Cr2O7 initially present
and under the acidic conditions. Compound 4 may be a good
oxidant and the excess of aniline will give a polyaniline
precipitate that might act as a reductant. Presumably the build-
up of product 2 is sensitive to the concentration of K2Cr2O7
in solution and may occur once the dichromate has been
consumed. Neither aniline or 4-hydroxyaniline react with
phenosafranin 1 in hot water with or without acid present.
Results and discussion
Synthesis with phenosafranin (1)
Phenosafranin 1 and a large excess of aniline were oxidised
Synthesis with bis(4-methylphenyl)amine (5)
Since the four main components of mauveine (A, B, B2, C)13
with K2Cr2O7 in 10% dilute aq. H2SO4 (Scheme 1). A purple
contain a key building block derived from p-toluidine (at
Scheme 1 The synthesis of p-hydroxypseudo-mauveine 2. The numbering scheme of the phenazine ring is shown.
* Correspondent. E-mail: m.j.plater@abdn.ac.uk

428 JOURNAL OF CHEMICAL RESEARCH 2013
Scheme 2 A possible pathway showing four proposed intermediates leading to compound 2.
position 3), we decided to study the dichromate oxidation of
bis(4-methylphenyl)amine 5 and aniline (Scheme 3). Heating
bis(4-methylphenyl)amine 5 and aniline (3 equiv.) in dilute
sulfuric acid (about 0. 3 mL in 200 mL water) with K2Cr2O7
gave a deep purple solution from which the product was
isolated. Since bis(4-methylphenyl)amine 5 is poorly soluble
in water so acetone was added to solubilise it. This reaction
failed completely using diphenylamine, which showed that the
p-methyl groups are essential for the reaction. The reaction
presumably proceeds by formation of a nitrogen centred diaryl
free radical 7 (Fig. 1) which couples to aniline by oxidative
homolytic substitution of hydrogen. The next stages leading to
mauveine chromophores have been discussed previously.16,17
The UV spectrum showed an absorption maximum at
560 nm which is shifted 10 nm bathochromically from a typi-
cal mauveine absorption maximum of 550 nm. The 13C NMR
spectrum showed the expected 20 aromatic resonances. The
1H NMR was well resolved and included a pair of coupled
doublets (8H, aryl ring) at 7.06 and 7.17 ppm. This proved the
symmetry of the molecule. The rest of the molecule is straight-
forward. Two overlapping doublets at 7.9 ppm (2H, 1 and 9),
7.6–7.7 (3H, phenyl) multiplet, 7.4 (2H, phenyl) doublet,
7.3–7.31 (2H, 2 and 8) multiplets and 5.9/6.0 (2H, 4 and 6)
singlets. High resolution mass spectrometry confirmed the
molecular ion.
Compound 8 rearranges into (2-nitro-4-methylphenyl)-4-
methylphenylamine 9 when treated with montmorillonite in
CH2Cl2 at rt. The reaction mixture begins to turn orange within
minutes. Presumably the N-nitroso group is firstly oxidised to
an N-nitro group which then migrates to an ortho position
since the para positions are blocked. The product 9 appears as
a red solid and has a long wavelength absorption maximum of
441 nm. The structure of 9 was confirmed by a single crystal
structure determination (Fig. 2).
Synthesis with N-methyl-p-toluidine (10)
Again we chose to study a modified derivative of p-toluidine,
N-methyl-p-toluidine 10 (Scheme 5). The oxidation of
N-methyl-p-toluidine 10 and aniline with K2Cr2O7 is a much
better reaction than the oxidation of p-toluidine and aniline.
The reaction turns a deep purple colour within half an hour.
Presumably the N-methyl group serves to favour the formation
of a nitrogen centred radical, as for bis(4-methylphenyl)amine
5, which then reacts with aniline. This reaction fails using
either N-methylaniline or N-ethylaniline showing that the
p-methyl group is necessary to favour the oxidation pathway.
The product showed a characteristic absorption maximum at
1
550 nm and an N-methyl group at 3.32 ppm in the H NMR.
Since this peak is close to the resonance for residual MeOH the
The chemistry of bis(4-methylphenyl)amine 5 was explored
further owing to its facile oxidation. Nitrosation with sodium
nitrite in MeOH/H+ gave N-nitroso-bis(4-methylphenyl)amine
8 (Scheme 4). The asymmetry of nitrosated aromatic amines
has been reported previously.20 This compound shows two
methyl groups at 2.37 and 2.40 ppm in the 1H NMR and a more
complex aromatic region. There are eight aromatic carbons
in the 13C NMR. The asymmetry indicates restricted rotation
around the N, N bond, which must be slow on an NMR time
scale.
Fig. 1 A possible free radical that might react with aniline by
homolytic aromatic substitution.
Scheme 3 The oxidation of bis(4-methylphenyl)amine 5 to give mauveine chromophore derivative 6.

JOURNAL OF CHEMICAL RESEARCH 2013 429
Scheme 4 The nitrosation of bis(4-methylphenyl)amine and its subsequent rearrangement.
This reaction was attempted oxidising N-methyl-p-toluidine
10 and aniline/o-toluidine (Scheme 6) in the same way. As for
Scheme 5 this is a much better reaction for making derivatives
of mauveine than the oxidation of p-toluidine/o-toluidine/
aniline.
To separate mixtures of mauveine chromophores by column
chromatography the counterion was changed from sulfate to
acetate. This is easily achieved by taking the dry methanol
extract from a reaction, agitating with dilute sodium hydroxide
and filtering. The precipitate can be washed with base but
pure water immediately begins to redissolve the dye. After
base treatment the precipitate is extracted with MeOH, then
acidified with a few drops of HOAc and evaporated to dryness.
Chromatography is performed using sec-butanol/EtOAc/H2O/
HOAc (60:30:9.5:0.5).11 By this method the two chromophores
were separated by collecting fractions and characterised. The
yields from reacting o-toluidine and aniline with compound 10
are much higher than the yields from using aniline alone.
N-methylmauveine B 13 elutes first. It gave three methyl
groups in the 13C NMR at 16.2, 16.7 and 19.7 ppm. The N-
methyl group appeared at 39.7 ppm. In the 1H NMR spectrum,
a characteristic singlet was present at 7.81 ppm for the
deshielded proton at position 9. The characteristic methyl
group at position 1 also appeared deshielded at 2.7 ppm. The
high resolution mass spectrum confirmed that the molecular
ion. N-methylmauveineA 12 elutes next. It showed two methyl
groups in the 13C NMR at 16.2 and 19.8 ppm and an N-methyl
group at 39.8 ppm. The 1H NMR spectrum showed a character-
istic doublet at 7.8 ppm for the proton at position 1 and a
singlet at 7.7 ppm for the proton at position 9. High-resolution
mass spectrometry confirmed the molecular ion. For both
N-methylmauveine A and N-methylmauveine B, the central
Fig. 2 The molecular structure of 9 showing 50% displacement
ellipsoids. The intramolecular N–H···O hydrogen bond [H···O =
1.943 (18) Å; N–H···O = 130.0 (15)°] is shown as a double–dashed
line. The dihedral angle between the ring planes is 58.94 (5)°
and the nitro group is close to coplanar with its attached ring
[dihedral angle = 5.14 (11)°]. The only possible intermolecular
interaction in the crystal is a very weak C–H···π bond.
spectrum was run in both CD3OD and D2O. Interestingly, in
D2O, the spectrum showed greater resolution and the expected
methyl group at 3.0 ppm. The compound is more soluble in
water than mauveine chromophores with NH at this position.
The 13C NMR showed 22 peaks and had an N-methyl reso-
nance at 41.2 ppm. The high resolution mass spectrum showed
the correct molecular ion for a structure with the N-methyl
group. Initially we had thought that the N-methyl group might
be oxidatively removed during the course of the reaction but it
is, in fact, quite robust. We also failed to remove it by oxidation
of compound 11 with K2Cr2O7 in dilute acetic acid or in dilute
H2SO4 (1.0 mL in 100 mL H2O).
Scheme 5 A novel synthesis of N-methyl-C25b from N-methyl-p-toluidine. (C25b is the name given to the chromophore lacking
the N-methyl group).13
Scheme 6 A novel synthesis of N-methylmauveine A 12 and N-methylmauveine B 13 from N-methyl-p-toluidine. (Mauveine A
and mauveine B respectively are the names given to the chromophores lacking the N-methyl group.13)

430 JOURNAL OF CHEMICAL RESEARCH 2013
phenyl ring is apparent because three hydrogens appear as a
multiplet centred around 7.75 ppm and the two ortho protons
appear as a doublet further upfield at about 7.4 ppm. Evidently
the use of an N-alkylated building block favours the incorpora-
tion of a phenyl ring into position 5 (aniline as the building
block). The IR spectra of both dyes show absorptions at
1550 cm–1 and 1408 cm–1 due to asymmetric and symmetric
C–O stretches respectively.21 Both dyes show the same absorp-
tion maximum at 550 nm and stain silk an attractive purple
colour from water. In each case, the N-methyl groups are
masked behind the CD3OD. The N-methyl groups were not
removed by oxidation of purified material with K2Cr2O7 in
hot dilute aq. H2SO4 or in boiling acetic acid with KOAc. The
oxidation of N-allyl-p-toluidine2 and aniline by Perkin was not
successful.
with o-toluidine and either 2,4-dimethylaniline or p-toluidine
and then oxidised. The corresponding mauveineA homologues
17 and 18 were fully characterised spectroscopically and are
shown in Scheme 8. 2,4-Dimethylaniline was incorporated
into a mauveine derivative because it might have been an
impurity in Perkin’s aniline. Hence a homologue from it might
occur in the mauveine archives. The possibility that a xylidine
might have been used in mauveine synthesis has been briefly
considered owing to the occurrence of small amounts of
uncharacterised higher homologues in Perkin’s mauveine.13
m-Xylene is the predominant xylene in benzene from coal
tar22 and would lead to 2,4-dimethylaniline by nitration and
reduction.
Mauveine synthesis in distilled versus tap water
To check if water composition could have an effect on mauve-
ine synthesis, we studied the oxidation of aniline/o-toluidine/
p-toluidine with K2Cr2O7 in either tap water or distilled water
side by side (Scheme 9). In warm distilled water initially the
reaction darkened noticeably faster. Since we have suggested
that free radicals may be involved, some metal ions might
act as inhibitors to the reaction. In the first few minutes or so,
the colour change resembled that seen in the oxidation of
N-methyl-p-toluidine. When purified by chromatography the
long mauveine bands looked similar. The product from using
distilled water as solvent was dark green, pure and more crys-
talline. However, the product from using tap water as solvent
was darker, amorphous and less pure. The yields were both
low as expected (distilled water: 2.5%, tap water: 1.4%). We
Synthesis with N-phenyl-p-phenylenediamine (14)
Previously we reported the use of N-phenyl-p-phenylenedi-
amine 14 for the synthesis of pseudo-mauveine 15 and the
mauveine A homologue 16 (Scheme 7).16 We considered that
the dimer of aniline14 might have been used by Perkin as a
starting material to make pseudo-mauveine. Here the purifica-
tion of compound 16 has been improved by careful washing
of the final product with water. When mauveine forms it
precipitates from water onto the polyaniline by-product. Once
purified from this, it is more water soluble so only a small
volume of water is used.
Two more reactions using N-phenyl-p-phenylenediamine 14
to make mauveine derivatives have been studied. It was mixed
Scheme 7 Two mauveine derivatives (15 and 16) that can be prepared from N-phenyl-p-phenylenediamine 14.16
Scheme 8 The synthesis of two new mauveine derivatives from N-phenyl-p-phenylenediamine.

JOURNAL OF CHEMICAL RESEARCH 2013 431
Scheme 9 A comparison of yields for making mauveine in either distilled water or tap water.
suggest that distilled water is the preferred solvent to use in
mauveine syntheses.
and analysed an as supplied authentic sample by 13C NMR
(CD3OD). The spectrum showed four strong signals for
aromatic methyl groups (17.7, 17.9, 20.9 and 21.0 ppm, one
resonance is missing) a strong resonance at 95.0 ppm for car-
bons 4 and 6, weaker peaks at 93.3 and 94.8 ppm from another
chromophore and strong peaks in pairs at 153.4, 153.6, 158.5
and 159.0 ppm indicating two main chromophores to be pres-
ent. However, there were no N-methyl resonances at 39 ppm
and no methyl groups from an ethyl group at about 11 ppm.
No methyl resonance from an acetate group was present and
a carbonyl group was absent. Apart from the aromatic methyl
groups the spectrum was free of any peaks from 0 ppm down
to 93 ppm. The mass spectrum was very clean showing peaks
at 377(3), 391(73), 405(100), 419(49) and 433(9). No other
peaks were present. Authentic mauveine separates into two
spots on a TLC plate using the eluent sec-BuOH/EtOAc/H2O/
HOAc (60:30:9.5:0.5). We purified a small sample and con-
firmed that the first spot has molecular weights of 405(100),
419(77) and 433(15) then the second spot has molecular
weights of 390(100) and 391(94). The methyl group at posi-
tion 1 will shield N-10 reducing the polarity, which explains
why the compound of molecular weight 405 elutes first.
Compounds 11 and 12 elute as a third more polar spot when
co-spotted with archive mauveine.
Silk dyeing
Pieces of silk were dyed to compare hues and to see if the
colour matched that of various museum artifacts dyed with
mauveine. Both the samples made using either distilled water
or tap water as solvent were purified by chromatography. They
both dye silk the same shade of purple, which is duller and
bluer15 than silk dyed from compounds 11–13 and compounds
15–18 (which lack the methyl group of the 4-methylphenyl-
amino group at position 3). This observation on colour was
first made by W. H. Cliffe back in 1956. He prepared mauveine
by Perkins method but failed to reproduce the red/purple shade
of silk he saw with authentic mauveine obtained from Perkin.15
His mauveine was not purified by chromatography so might
have been less pure but our material has been purified by chro-
matography. With a small sample of Perkin’s 1862 authentic
mauveine we have also confirmed this observation. This
mystery has not yet been solved.
Compounds 11–13 and 15–18 dye silk a bright red shade
of purple, which by eye resembles the colour of silk dyed with
authentic mauveine and of various museum items dyed with
mauveine.23 Figure 3 compares silk dyed with compounds
12–13 and the mixture of dyes made by Perkin’s method. Silk
dyed with compounds 15–18 looks similar to silk dyed with
compounds 11–13. Although the absorption maximum is
the same at 555 nm compounds 11–13 show a shoulder in the
UV-Vis spectrum at 500–530 nm, which may account for the
different colour of the dye on silk. Purple consists of red and
blue light so absorption of more blue light will give a redder
shade of purple. Absorption of more red light would give a
bluer shade of purple. A so-called red shade and blue shade
of mauveine have been observed before and photographed,
although the method of synthesis of the dyes was not stated.13
Perkin introduced the concept of red and blue shades of mau-
veine to describe the different shades of purple he obtained
from oxidising aniline containing either a large or small
amount of toluidines respectively.5 He published one further
synthetic patent after his initial disclosure on mauveine,1 which
involved alkylation studies of mauveine leading to a red shade
of mauveine but this method does not appear to have been
exploited.24 An HPLC comparison of Perkin’s mauveine with a
modern repeat synthesis has shown them to be similar, although
mauveine B2 and mauveine C were more dominant in the
modern synthesis.14 In summary a red shade of mauveine
on silk may be explained from compounds 12–13 as a
consequence of a hypsochromic shoulder on the absorption
maximum at 555 nm.
Conclusions
A novel hydroxylated derivative of pseudo-mauveine has been
characterised from an unusual reaction in which the oxidant
would have been expected to react with the product.
Bis(4-methylphenyl)amine 5 and N-methyl-p-toluidine 10 are
efficient building blocks for the synthesis of derivatives of
mauveine chromophores. N-Nitroso-bis(4-methylphenyl)amine
8 undergoes a facile rearrangement and oxidation catalysed by
montmorillonite. 2,4-Dimethylaniline has been used to make a
In a further experiment, we treated authentic mauveine with
base, filtered the precipitate and changed the counterion to
acetate by a standard procedure reported here. The mauveine
salt still dyed silk a red shade of mauveine showing that no
special anion or additive gives the red mauveine shade.
Fig. 3 In each photograph, the purple contrast has changed
slightly through photography. (A) Silk dyed with N-methyl-
mauveine A 12. (B) Silk dyed with mauveine made by oxidising
aniline and o/p toluidines in distilled water. (C) Silk dyed with
N-methylmauveine B 13.
Characterisation of authentic mauveine
The N-methylated compounds 11–13 do not appear to be pres-
ent in archived mauveine because we checked previous work11

432 JOURNAL OF CHEMICAL RESEARCH 2013
(20/80) then elutes a dark band characteristic of mauveine syntheses
followed by the title compound 2 (3.5 mg, 3%) as a purple solid m.p.
> 240 °C; λmax (ethanol)/nm 551 (log ε 4.6) and 279 (4.4); νmax (KBr)/
cm−1 3305–2108 (br), 1648m, 1603vs, 1489vs, 1381s, 1310s, 1254s,
1075vs (br), 865m, 811m and 605s; δH (400 MHz; CD3OD) 5.99 (1H,
d, J = 2.2), 6.13 (1H, d, J = 2.2), 6.70 (2H, d, J = 8.8), 6.9(2H, d,
J = 8.8), 7.24 (1H, dd, J = 9.2 and 2.2), 7.35 (1H, dd, J = 9.2 and 2.2),
7.47 (2H, d, J = 7.4), 7.71–7.81 (3H, m), 7.91 (1H, d, J = 9.3) and
7.95 (1H, d, J = 9.3); m/z (Orbitrap ASAP) 379.1551 (M+, 100%)
C24H19N4O requires 379.1553.
derivative of a mauveine chromophore. A comparison has been
made of the two different shades of silk dyed from mauveine
made by oxidising aniline and o/p-toluidines and by the new
routes reported here. They were compared with the shade of
silk dyed from a sample of authentic mauveine.
Experimental
UV-Vis spectra were recorded with an Agilent Technologies Cary 60
spectrophotometer. IR spectra were recorded with a Perkin-Elmer
FT-IR Spectrum 400 with PIKE Technologies GladiATR diamond
anvil or on an ATI Mattson FTIR spectrometer using potassium bro-
mide discs. Melting points were recorded with a Laboratory Devices
USA MEL-TEMP II instrument. Mass spectra were recorded by the
UK national mass spectrometry service centre with an OrbitrapASAP.
NMR data were recorded using a JEOL model ECA 400 spectrometer.
Coupling constants are in Hz. Carbon 13 data acquisition typically
requires a 16 h run. Phenosafranin was commercially available from
Sigma-Aldrich. Distilled water is recommended as solvent for the
mauveine syntheses reported here. Chromatography was performed
using flash silica Merck grade 9385 (0.040–0.063 mm), a Coralife
Luft Aquarium air pump (5 watts, 7 psi) and a seven star grounded
100 watts stepdown transformer. aqNH3/MeOH (20:80) was used
to elute chromophores with a counterion from a strong mineral acid.
sec-Butanol/EtOAc/H2O/HOAc (60:30:9.5:0.5) was used to elute
chromophores with an acetate counterion. aqNH3/MeOH (20:80)
cannot be used to elute chromophores with an acetate counterion as
they deprotonate and are then too polar. Silk pieces cut from a hand-
kerchief were dyed in hot water (30–50 mL) at 50–60 °C with stirring.
Typically about 10–20 mg of chromophore was dissolved but only a
small amount was consumed. Stirring increases the rate of absorption
of dye onto the silk. CCDC 901034 contains the supplementary
crystallographic data for this paper. The data can be obtained free of
charge from the Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request.cif.
3-(N,N-4-Methylphenylamino)-5-phenyl-7-aminophenazinium
sulfate (6): Bis(4-methylphenyl)amine 5 (250 mg, 1.27 mmol) and
aniline (360 mg, 3.87 mmol) were added to distilled H2O (300 mL)
acidified with cH2SO4 (six drops, 0.3 mL) in a beaker. Acetone
(100–150 mL) was added to dissolves. The beaker was covered with
an evaporating plate and heated for 4–5 h with vigorous stirring. The
solution was purple because acetone dissolved the dye. Heating was
stopped and stirring was continued overnight with the fan on and the
lid removed to evaporate the acetone. It is essential to evaporate the
acetone prior to filtration. The mixture was filtered through a fine pore
sinter (4–8 µm porosity) to leave a precipitate, which was washed with
water and then extracted with portions of MeOH (40 mL x 8). The
combined extracts were evaporated to dryness in a beaker on a hot-
plate then purified by flash chromatography on silica gel. The column
was loaded by dissolving the product in aliquots of MeOH. MeOH
firstly eluted brown impurities and then aqueous cNH3/MeOH (20/80)
eluted a dark band characteristic of mauveine syntheses followed by
the title compound 6 (24 mg, 4%) as a purple solid, m.p. > 240 °C; λmax
(ethanol)/nm 560 (log ε 4.6) and 283(4.4); νmax (KBr)/cm−1 3328–
2107(br), 1589vs, 1502vs, 1463vs, 1372vs, 1316vs, 1281vs, 1175vs,
1128vs, 875m, 813m, 795m, 693m and 478m; δH (400 MHz; CD3OD)
1.88 (3H, s), 2.33 (3H, s), 5.94 (1H, d, J = 2.5), 6.01 (1H, s), 7.07 (4H,
d, J = 8.0), 7.18 (4H, d, J = 8.0), 7.27 (1H, d, J = 8 and 2.2), 7.31 (1H,
d, J = 9.3), 7.37 (2H, d, J = 7), 7.60–7.68 (3H, m) and 7.95 (2H, d,
J = 9.3); δC (100.1 MHz; CDCl3) 24.2, 94.7, 100.5, 121.9, 123.9,
127.8, 128.6, 131.7, 131.9, 132.4, 133.9, 135.6, 137.0, 137.4, 137.4,
138.8, 139.0, 140.2, 142.8, 156.1 and 160.0; m/z (Orbitrap ASAP)
467.2225 (M+, 100%) C32H27N4 requires 467.2230.
X-Ray crystal structure of compound 9
The X-ray intensity data for 9 were collected on a Bruker Kappa
CCD diffractometer (graphite monochromated MoKα radiation, λ =
0.71073 Å, T = 120 K) with the aid of the COLLECT25 and DENZO26
programs. The unit-cell dimensions were obtained by least-squares
refinement against the positions of 10010 reflections (2.91° < θ 27.5°).
The structure was solved by direct methods with SHELXS-9727 and
the atomic model was refined against |F|2 by full matrix least-squares
with SHELXL-97.27 All the C-bound H atoms were geometrically
placed (C–H = 0.95–0.98 Å) and refined as riding; the N-bound H
atom was located in a difference map and its position freely refined
[N–H = 0.908 (19) Å]. The refined site occupancies of the O atoms of
the nitro group did not differ significantly from unity and were fixed
as 1.00 in the final refinement cycles. Red plates of compound 9 were
obtained from light petroleum 40–60: dichloromethane (50:50):
CAUTION: Suitable precautions should be taken for the prepara-
tions of 8 and 9 as nitrosated aromatic amines are carcinogenic.
N-Nitroso-bis(4-methylphenyl)amine (8): Bis(4-methylphenyl)amine
5 (2.0 g, 0.01 moles) was dissolved in MeOH (200 mL) containing
cHCl (5.0 mL) and was cooled in an ice bath. NaNO2 (1.4 g,
0.02 moles) dissolved in a small amount of H2O (10 mL) was added in
portions with stirring over a few minutes. The reaction was monitored
by TLC (25% DCM/75% light petroleum ether 40–60). Additional
aliquots of NaNO2 were required to make the reaction go to comple-
tion. The product precipitates as a yellow solid. After an arbitrary
period of 1 h, water was added (300 mL) and the product collected by
suction filtration. To dry the product it was dissolved in CH2Cl2, dried
over Na2SO4, filtered then concentrated in vacuo to give the title com-
pound 8 (2.21 g, 96%) as a yellow/orange solid, m.p. 100–100.5 °C;
λmax (ethanol)/nm 292 (log ε 3.14) and 206(sh) (4.62); νmax (diamond
anvil) 1508s, 1458s, 1410m, 1318m, 1191m, 1168m, 1056vs, 814vs,
793s, 723m, 697m, 614m, 539m, 525s, and 469m; δH (400 MHz;
CDCl3) 2.34 (3H, s), 2.40 (3H, s), 6.90 (2H, d, J = 8.3), 7.20 (2H, d,
J = 8.3), 7.28 (4H, m); δC (100.1 MHz; CDCl3) 20.9, 21.2, 119.7,
126.9, 129.8, 130.3, 134.3, 136.9, 139.5 and 140.2; m/z (Orbitrap
ASAP) 227.1179 (M+H, 100%) and 197 (M+H – NO, 60%) C14H15N2O
requires 227.1179.
(2-Nitro-4-methylphenyl)-4-methylphenylamine (9): N-Nitroso-
bis(4-methylphenyl)amine 8 (200 mg, 0.88 mmol) in CH2Cl2 (100 mL)
was treated with montmorillonite (2.0 g) in a beaker and left standing
at room temperature for 24 h. The solution turned orange after a few
minutes. The reaction was filtered and the catalyst was washed with
some CH2Cl2. The filtrate was concentrated and purified by flash
chromatography on silica gel. Light petroleum 40-60:dichlorometh-
ane (75:25) eluted the title compound 9 (127 mg, 60%) as red crystals,
m.p. 82.0–82.5 °C (from light petroleum: dichloromethane); λmax
(ethanol)/nm 441 (log ε 3.6), 259 (3.9), 231 (3.9) and 209 (3.9); νmax
(KBr)/cm−1 1629m, 1564s, 1508vs, 1399s, 1339s, 1261vs, 1218vs,
1196vs, 1148vs, 922m, 820vs, 806vs, 764s, 493s and 478vs; δH
(400 MHz; CDCl3) 2.28 (3H, s), 2.37 (3H, s), 7.90–7.22 (6H, m), 8.00
C14H14N2O2, Mr = 242.27, crystal dimensions 0.68 × 0.58 × 0.16 mm,
–
triclinic, space group P1 (No. 2), Z = 2, a = 8.1009 (2), b = 8.1826 (3),
c = 9.5700 (4) Å, α = 88.204 (2), β = 80.521 (2), γ = 76.094 (2)°, V =
607.34 (4) Å3 at 120 K. Number of measured and unique reflections =
12261 and 2787, respectively (Rint = 0.034). Final R(F) = 0.051,
wR(F2) = 0.132 for 169 parameters and 2341 reflections with I > 2σ(I)
(corresponding R-values based on all 2787 reflections = 0.060 and
0.138, respectively), all C-bound H atoms were geometrically placed
and refined as riding; the N-bound H atom was located in a difference
map and its position freely refined. The refined site occupancies of the
O atoms of the nitro group did not differ significantly from unity.
3-(4-Hydroxyphenylamino)-5-phenyl-7-aminophenazinium sulfate
(2): Phenosafranin (100 mg, 0.3 mmol) and a large excess of aniline
(1.5 g, 16 mmol, 50 fold) were dissolved in dilute sulfuric acid (20 ml
cH2SO4 added to 280 ml of distilled H2O) in a beaker. The mixture was
treated with K2Cr2O7 (0.5 g, 1.7 mmol) with stirring and heated at
75 °C for 1 h. The mixture was then cooled and filtered through a fine
pore sinter (4–8 µm porosity). The precipitate was washed with H2O
then extracted about 7–8 times with portions of MeOH (40 mL) each
time agitating the precipitate on the sinter. The combined MeOH
extracts were evaporated to dryness in a beaker on a hotplate followed
by flash chromatography on silica gel. MeOH does not elute the
product so portions of MeOH can be used to load the product onto the
column. MeOH firstly elutes brown impurities. Aqueous cNH3/MeOH

JOURNAL OF CHEMICAL RESEARCH 2013 433
(1H, s) and 9.40 (1H, s); δC (100.1 MHz; CDCl3) 20.2, 21.0, 116.1,
124.4, 125.8, 126.9, 130.3, 132.6, 135.3, 136.3, 137.2 and 141.6; m/z
(Orbitrap ASAP) 243.1131 (M+ + H, 100%) C14H15N2O2 requires
243.1128.
was heated to 50 °C and treated with K2Cr2O7 (100 mg, 0.34 mmol)
for 15 min. After cooling the solution it was treated with dil. NaOH to
precipitate the product. This was filtered, extracted with MeOH and
acidified with HOAc (five drops) then evaporated to dryness in a
beaker on a hotplate. The product had identical spectroscopic proper-
ties to the starting material including accurate mass molecular ions
and the 13C spectrum. A similar method was done in aq HOAc (20 mL
HOAc: 80 mL H2O) giving the same result.
3-[4-Methylphenyl(methylamino)]-5-phenyl-7-aminophenazinium
sulfate (11): N-Methyl-p-toluidine 10 (225 mg, 1.86 mmol) and ani-
line (520 mg, 5.6 mmol) were dissolved in H2O (200 mL) in a beaker
acidified with cH2SO4 (six drops, 0.3 mL) followed by the addition of
K2Cr2O7 (912 mg, 3.1 mmol, 1.67 equiv.). The mixture was stirred and
heated at 70–80 °C for 4 h then cooled and filtered through a fine pore
(4–8 µm porosity) sinter. The precipitate was washed with H2O then
extracted with portions of MeOH (40 mL x8) each time with agitation
in the sinter. The combined extracts were evaporated to dryness by
heating in a beaker on a hotplate followed by flash chromatography on
silica gel. MeOH elutes brown impurities. 20% cNH3/MeOH firstly
elutes a dark band characteristic for these reactions followed by the
title compound 11 (52 mg, 6.3%) as a purple solid, m.p. > 240 °C; λmax
(ethanol)/nm 550 (log ε 4.59) and 278 (4.58); νmax (diamond anvil)
3045(br), 1594vs, 1483vs, 1376m, 1332vs, 1185s, 1077vs(br), 872m,
818m, 696m and 608m; δH (400 MHz; D2O) 2.21 (3H, s), 3.09 (3H, s),
5.17 (1H, s), 5.67 (1H, s), 6.67 (2H, d, J = 8), 6.70 (2H, d, J = 8),
6.87 (1H, d, J = 11), 6.92 (1H, d, J = 14), 7.05 (2H, d, J = 8), 7.30
(1H, d, J = 11), 7.44–7.49 (3H, m) and 7.59 (1H, t, J = 8 and 7); δH
(400 MHz; CD3OD) 2.37 (3H, s), 3.31 (3H, s), 5.82 (1H, s), 5.99 (1H,
s), 7.08 (2H, d, J = 8), 7.25 (4H, m), 7.46 (2H, d, J = 7), 7.74–7.81
(3H, m) and 7.91 (2H, m); δC (100.1 MHz; CDCl3) 21.1, 41.2, 94.9,
96.1, 119.9, 123.3, 127.4, 128.7, 132.0, 132.1, 132.7, 134.0, 135.3,
136.9, 137.3, 137.7, 138.9, 139.0, 139.4, 143.8, 156.4 and 159.8; m/z
(Orbitrap ASAP) 391.1920 (M+, 100%) C26H23N4 requires 391.1917.
3-[4-Methylphenyl(methylamino)]-5-phenyl-7-amino-8-methyl-
phenazinium acetate (N-Methylmauveine A) (12) and 1-Methyl-3-[4-
methylphenyl(methylamino)]-5-phenyl-7-amino-8-methylphenazinium
acetate (N-Methylmauveine B) (13): N-Methyl-p-toluidine (250 mg,
2.10 mmol), aniline (326 mg, 3.50 mmol, 1.5 equiv.) and o-toluidine
(375 mg, 3.50 mmol, 1.5 equiv.) were dissolved in H2O (200 mL) in a
beaker acidified with cH2SO4 (six drops, 0.3 mL) followed by the
addition of K2Cr2O7 (1.15 g, 3.1 mmol, 1.67 equiv.). The mixture was
stirred and heated at 70–80 °C for 3 h then cooled and filtered through
a fine pore (4–8 µm porosity) sinter. The precipitate was washed with
H2O then extracted with portions of MeOH (40 mL × 8) each time
with agitation in the sinter. The combined extracts were evaporated to
dryness by heating in a beaker on a hotplate. The material was stirred
with aqueous NaOH (5.0 g in water 200 mL) then filtered and washed
with aqueous alkali (water begins to redissolve the dyes). The precipi-
tate was then washed with MeOH (50 mL × 4), and the filtrate acidi-
fied with HOAc (five drops) and evaporated to dryness. The material
was taken up in sec-butanol and purified by flash chromotagraphy
on silica gel (fractions were collected). Elution with sec-butanol/
EtOAc/H2O/HOAc (60:30:9.5:1) gave firstly the title compound
N-methylmauveine B 13 (59 mg, 6%) followed by the title compound
N-methylmauveine A 12 (68 mg, 7%) as dark purple solids. N-meth-
ylmauveine B λmax (ethanol)/nm 550 (log ε 4.76) and 280 (4.75); νmax
(diamond anvil) 3326(br), 1545(vs), 1407(vs), 1348(vs), 1017(m) and
645(m); δH (400 MHz; CD3OD) 1.87 (CH3CO2), 2.35 (6H, s), 2.70
(3H, s), 5.67 (1H, d, J = 2.0), 6.04 (1H, s), 7.05 (2H, d, J = 8.2), 7.10
(1H, s), 7.23 (2H, d, J = 7.8), 7.42 (2H, d, J = 7.0), 7.71–7.78 (3H, m)
and 7.85 (1H, s); The N-Me resonance is masked by the CD3OD. δC
(100.1 MHz; CDCl3) 16.2, 16.8, 19.8, 22.9 (CH3CO2), 39.7, 93.2,
93.7, 118.0, 126.0, 127.4, 129.9, 130.6, 130.7, 131.2, 132.6, 135.5,
135.9, 136.1, 136.4, 136.7, 137.9, 141.9, 142.5, 154.5, 157.6 and
179.0 (CH3CO2); m/z (OrbitrapASAP) 419.2223 (M+, 100%) C28H27N4
requires 419.2230. N-methylmauveine A λmax (ethanol)/nm 550
(log ε 4.65) and 280 (4.62); νmax (diamond anvil) 3311(br), 1551(vs),
1408(vs), 1017(m) and 651(m); δH (400 MHz; CD3OD) 1.87 (CH3CO2),
2.35 (6H, s), 5.81 (1H, d, J = 3.0), 6.06 (1H, s), 7.05 (2H, d, J = 8.2),
7.23 (3H, d, J = 8.0), 7.44 (2H, d, J = 7.0), 7.70–7.78 (3H, m), 7.83
(1H, s) and 7.92 (1H, d, J = 9.6); The N-Me resonance is masked by
the CD3OD. δC (100.1 MHz; CDCl3) 16.3, 19.8, 22.9 (CH3CO2), 39.8,
93.7, 96.6, 118.6, 126.1, 127.3, 130.6, 130.7, 130.8, 131.3, 132.3,
132.4, 135.5, 135.7, 136.4, 136.4, 137.7, 138.0, 142.5, 154.7, 157.9
and 179.2 (CH3CO2); m/z (Orbitrap ASAP) 405.2074 (M+, 100%)
C27H25N4 requires 405.2074.
3-Phenylamino-5-(2-methylphenyl)-7-amino-8-methylphenazinium
sulfate (16): See general method used here and a previous paper for
other experimental data.16 The product was carefully washed with a
small volume of cold water (4%); δH (400 MHz; CD3OD) 1.92 (3H, s),
2.40 (3H, s), 6.05 (1H, s), 6.30 (1H, s), 7.13 (3H, m), 7.28 (2H, m),
7.40 (1H, d, J = 7.0), 7.47 (1H, d, J = 9.0), 7.65 (3H, m), 7.84 (1H, s)
and 8.0 (1H, d, J = 9.0); δC (100.1 MHz; CDCl3) 16.8, 17.6, 94.3,
94.5, 122.0, 123.3, 126.6, 128.7, 130.3, 130.6, 132.3, 132.5, 133.9,
133.9, 134.6, 136.4, 136.8, 136.9, 137.5, 139.2, 140.1, 154.0 and
159.7 (one resonance is missing).
The acetate salts of compounds 17 and 18 for 13C spectra were
synthesised as for compounds 12 and 13
3-(Phenylamino)-5-(2,4-dimethyphenyl)-7-amino-8-methylphen-
azinium sulfate (17): N-Phenyl-p-phenylenediamine (250 mg, 1.36 mmol),
o-toluidine (145 mg, 1.36 mmol) and 2,4-dimethylaniline (164 mg,
1.36 mmol) were dissolved in distilled H2O (250 mL) treated with
CH2SO4 (six drops, 0.3 mL). The mixture was treated with K2Cr2O7
(535 mg, 1.82 mmol, 1.34 equiv.) and stirred at 70 °C for 5 h. The
mauve-coloured reaction mixture was then cooled and filtered through
a fine pore sinter (4–8 µm porosity). The precipitate was washed with
H2O, then extracted with MeOH (40 mL × 8) on the sinter. The com-
bined extracts were evaporated to dryness in a beaker on a hot plate
then purified by flash chromatography on silica gel (2–3 fractions
were collected and analysed by TLC). MeOH elutes impurities then
20% cNH3/MeOH elutes a dark band followed by the title compound
17 (27.8 mg, 4.5%) as a purple solid, m.p. > 240 °C (from suspending
in a small volume of water and filtration) λmax (ethanol)/nm 553 (log ε
4.6), 281 (4.5), 231 (4.2) and 204 (4.4); νmax (KBr)/cm−1 3500–2100
(br), 1608vs, 1589vs, 1529vs, 1493vs, 1463vs, 1343vs, 1307vs,
1182vs, 1135vs, 1098vs, 1012s, 825m, 753m, 717m, 693m and 610m;
δH (400 MHz; CD3OD) 1.87 (3H, s), 2.37 (3H, s), 2.48 (3H, s), 6.08
(1H, s), 6.32 (1H, s), 7.14 (3H, m), 7.25 (1H, d, J = 7.6), 7.28 (3H, m),
7.41 (1H, d, J = 7.6), 7.47 (1H, s), 7.84 (1H, s) and 8.00 (1H, d,
J = 9.2); δC (100.1 MHz; CDCl3) (acetate salt) 16.7, 17.6, 21.3, 24.2
(CH3CO2), 94.4, 94.8, 121.7, 123.2, 126.6, 128.4, 130.6, 130.7, 132.4,
133.7, 133.9, 134.3, 134.6, 135.9, 137.0, 137.1, 137.5, 139.3, 140.0,
143.1, 153.9, 159.6 and 180.5 (CH3CO2); m/z (Orbitrap ASAP)
405.2073 (M+, 100%) C27H25N4 requires 405.2074.
3-(Phenylamino)-5-(4-methylphenyl)-7-amino-8-methylphenazin-
ium sulfate (18): N-Phenyl-p-phenylenediamine (250 mg, 1.36 mmol),
p-toluidine (145 mg, 1.36 mmol) and o-toluidine (145 mg, 1.36 mmol)
were dissolved in distilled H2O (250 mL) treated with cH2SO4
(six drops, 0.3 mL). The mixture was treated with K2Cr2O7 (535 mg,
1.82 mmol, 1.34 equiv.) and stirred at 70 °C for 5 h. After 30 min the
reaction stains silk brown but after 1.5 h it stains silk purple. The
mauve coloured reaction was then cooled and filtered through a fine
pore sinter (4–8 µm porosity). The precipitate was washed with H2O,
then extracted with MeOH (40 mL x 8) on the sinter. The combined
extracts were evaporated to dryness in a beaker on a hotplate then
purified by flash chromatography on silica gel (two or three fractions
were collected and analysed by TLC). MeOH elutes impurities then
20% cNH3/MeOH elutes a dark band followed by the title compound
18 (62 mg, 10.4%) as a purple solid, m.p. > 240 °C (from suspending
in a small volume of water and filtration). λmax (ethanol)/nm 555 (log
ε 4.7) and 280 (4.7); νmax (KBr)/cm−1 3176s, 3036s, 1665m, 1610m,
1591m, 1434vs, 1062vs(br), 983s, 710m and 609vs; δH (400 MHz;
CD3OD) 2.35 (3H, s), 2.51 (3H, s), 6.11 (1H, s), 6.34 (1H, s), 7.12
(3H, m), 7.31 (2H, t, J = 8 and 8), 7.35 (2H, d, J = 8), 7.38 (1H, d,
J = 7), 7.59 (2H, d, J = 8), 7.78 (1H, s) and 7.92 (1H, d, J = 9); δC
(100.1 MHz; CDCl3) (acetate salt) 17.6, 21.3, 24.2 (CH3CO2) 95.1,
95.5, 121.5, 123.1, 123.3, 126.5, 128.5, 129.9, 130.6, 132.1, 132.2,
133.0, 133.6, 134.4, 135.1, 137.6, 139.2, 142.9, 153.4, 159.2 and
180.0 (CH3CO2); m/z (OrbitrapASAP) 391.1920 (M+, 100%) C26H23N4
requires 391.1917.
Oxidation of aromatic amines in tap water or distilled water.
Aniline (174 mg, 1.87 mmol), o-toluidine (200 mg, 1.87 mmol) and
p-toluidine (200 mg, 1.87 mmol) in either distilled water (250 mL) or
Attempted oxidation of N-methylmauveine A and B
The mixture of N-methylmauveine A 12 and N-methylmauveine B 13
(15 mg, 0.04 mmol) in aqueous H2SO4 (0.25 mL H2SO4: 100 mL H2O)

434 JOURNAL OF CHEMICAL RESEARCH 2013
3
4
5
6
7
8
9
W.H. Perkin, J. Chem. Soc., 1896, 69, 596.
W.H. Perkin, Proc. R. Soc., 1863, 12, 713.
W.H. Perkin, J. Chem. Soc., 1879, 35, 717.
W.H. Perkin, J. Chem. Soc., 1862, 14, 230.
O. Fischer and E. Hepp, Ber., 1888, 21, 2617.
O. Fischer and E. Hepp, Ber., 1893, 26, 1194.
O. Fischer and E. Hepp, Liebigs Ann. Chem., 1892, 272, 306.
tap water (250 mL) each acidified with cH2SO4 (six drops, 0.3 mL)
was heated to 75 °C and treated with K2Cr2O7 (917 mg, 3.12 mmol,
1.67 equiv.) for 3 h. Each mixture was cooled and filtered. The pre-
cipitate was extracted with MeOH (40 mL x 5), evaporated in a beaker,
then purified by chromatography. Elution with MeOH gave some
brown impurities then 20% cNH3/MeOH elutes a dark band followed
by a long purple band of mauveine chromophores (20 mg, 2.5%)
from using distilled water as solvent and (12 mg, 1.4%) from using tap
water as solvent.
10 R. Nietzki, Ber., 1896, 29, 1442–1446.
11 O. Meth-Cohn and M. Smith, J. Chem. Soc., Perkin Trans., 1, 1994, 5.
12 O. Meth-Cohn and A.S. Travis, Chem. Brit., 1995, 31, 547.
13 M.M. Sousa, M.J. Melo, A.J. Parola, P.J.T. Morris, H.S. Rzepa and
J. Sergio Seixas de Melo, Chem. Eur. J., 2008, 14, 8507.
14 J. Seixas de Melo, S. Takato, M. Sousa, M.J. Melo and A.J. Parola, Chem.
Commun., 2007, 2624.
The exchange of mauveine counterions
See the general procedure for compounds 12 and 13. For smaller
quantities of material the material on a sinter was not washed with
aqueous alkali.
15 W.H. Cliffe, J. Soc. Dyers Colourists, 1956, 72, 563.
16 M.J. Plater, J. Chem. Res., 2011, 304.
17 C. Heichert and H. Hartmann, Z. Naturforsch, 2009, 6, 747.
18 C. Gordon, A. Van Deun and R. Lumb, Int. J. Tuberc Lung Dis., 2009, 13,
130.
19 M.N. Montes de Oca, I.M. Aiassa, M.N. Urrutia, G.A. Arguello and
C.S. Ortiz, J. Chrom. Sci., 2010, 48, 618.
20 L. Forlani, L. Lunazzi, D. Macciantelli and B. Minguzzi, Tetrahedron Lett.,
1979, 20, 1451.
We are grateful to the EPSRC national mass spectrometry
service centre for mass spectra and to the Manchester Museum
of Science and Industry (MoSI) and the trustees for providing
a sample of authentic mauveine.
21 M. Kakihana, M. Kotaka and M. Okamoto, J. Phys. Chem., 1982, 86,
4385.
Received 5 February 2013; accepted 23 April 2013
Paper 1301773 doi: 10.3184/174751913X13718370656320
Published online: 18 July 2013
22 H.T. Clarke and E.R. Taylor, J. Am. Chem. Soc., 1923, 45, 830.
23 Science and Society Picture Library of the Science Museum, London
http://www.scienceandsociety.co.uk/results.asp?txtkeys1=Mauveine
24 R.W.W. Hooft, COLLECT data collection software, Nonius B.V., Delft,
The Netherlands, 1998.
25 Z. Otwinowski and W. Minor, Macromol. Crystallogr., Part A. 1997, 276,
307.
26 G.M. Sheldrick, Acta Crystallogr., Sect. A: Fund. Cryst., 2008, A64, 112.
27 W.H. Perkin, GB 2762 AD 1863, 1–5.
References
1
2
W.H. Perkin, GB1984, AD 1856, 1–4.
The British coal tar industry, it’s origin, development, and decline, 1915,
W.M. Gardner, ed. Philadelphia, J.B. Lippincott Company and Kessinger
Publishing LLC, pp. 141–187.

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