Natural anthraquinonoid colorants as platform chemicals in the synthesis of sustainable disperse dyes for polyesters

Article abstract of DOI:10.1016/j.dyepig.2010.04.009

Natural anthraquinonoid dyes (alizarin and purpurin) were used as platform chemicals to synthesise sustainable alternatives to existing synthetic dyes by alkylation of hydroxy groups in the 1- and 2-positions. In comparison with the parent compounds, the

Full text of DOI:10.1016/j.dyepig.2010.04.009

Dyes and Pigments 88 (2011) 7e17
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Natural anthraquinonoid colorants as platform chemicals in the synthesis
of sustainable disperse dyes for polyesters
,
,
b
Ioannis Drivas a b, Richard S. Blackburn a , Christopher M. Rayner
*
a Green Chemistry Group, Centre for Technical Textiles, University of Leeds, Leeds LS2 9JT, UK
b School of Chemistry, University of Leeds, LS2 9JT, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Natural anthraquinonoid dyes (alizarin and purpurin) were used as platform chemicals to synthesise
sustainable alternatives to existing synthetic dyes by alkylation of hydroxy groups in the 1- and 2-
positions. In comparison with the parent compounds, the derivatised dyes were insensitive to pH change,
insoluble in alkali and the lmax for the mono-alkylated derivatives was unchanged and that of the bis-
alkylated derivatives was reduced by 53e54 nm. Melting points decreased with derivatisation as the
ability of the dyes to form inter-molecular interactions decreased. Dye exhaustion and colour strength
values for dyeings on PET were relatively high for the parent and mono-alkylated derivatives and lower
for the larger bis-alkylated derivatives. Mono-alkylation with methyl-4-butanoate groups improved the
dyeing properties of the dyes on PLA. All dyeings displayed excellent wash fastness and the light fastness
was improved in the case of the mono-alkylated derivatives owing to the removal of the photo-sensitive
2-hydroxy group.
Received 16 November 2009
Received in revised form
20 April 2010
Accepted 23 April 2010
Available online 23 May 2010
Keywords:
Alizarin
Purpurin
poly(ethyleneterephthalate)
poly(lactic acid)
Chemical modification
Alkylation
Ó 2010 Elsevier Ltd. All rights reserved.
Madder
Rubia tinctorum, Rubia cordifolia
1. Introduction
has recently caused resurgence in research into the potential use of
natural dyes as alternatives to existing synthetic compounds [3e5].
Natural dyes were universally employed in textile dyeing until
Perkin’s 1856 accidental discovery of the ‘coal-tar’ dye, Mauveine,
[1], which triggered a decline in the dominance of natural dyes in
world markets. Indeed, between 1870 and 1880, virtually all natural
dyes were replaced on an industrial scale by synthetic examples,
with indigo being one of the last to be replaced by its synthetic
equivalent in 1883 [2]. Natural dyes suffered the disadvantage that,
for application to either cellulosic or proteinaceous fibres, many
dyes required the pre- and/or post-application of a mordant
(commonly a metal salt of e.g. AlIII, FeII, CuII, SnII, CrIII) to provide
sufficient substantivity between dye and fibre and secure satisfac-
tory fastness. Synthetic dyes were much more acceptable to the
dyer due to their ease of production, simplicity of the dyeing
process, reproducibility in shade, higher tinctorial strength, wider
colour gamut, brighter colours, superior fastness and lower overall
cost.
Many research projects have evaluated the techno-economic
feasibility of plants from which dyes can be extracted and have
developed novel methods of cultivation to improve dye harvests
[6,7]. Studies in agronomy, biochemistry and the dye production
capacity of several species of plants have led to the conclusion that
some natural dyes can provide a viable alternative to synthetic dyes
on an industrial scale [8,9]. Research being carried out on the
development of extraction techniques and analytical methods to
separate, identify and quantify the components of the different
classes of natural dyes found in plants [10]. However, natural dyes
have their own limitations, including limited availability, low
colour yield, low stability, complexity of dyeing processes involved,
reproducibility of shades, and limited substantivity for textile
fibres, particularly synthetic fibres [5,11,12]. Whilst the introduction
of natural dyes into modern dyeing procedures can be seen as one
step towards increased sustainability by affording at least a partial
replacement of synthetic dyes, the technical aspects of dyeing,
defined by the demands of the modern dyehouse and the producer
of the dye, have to be considered.
Nowadays, the production of synthetic dyes contributes to the
depletion of global supplies of non-renewable fossil fuels, which
One of the oldest dyes used throughout history is the mixture of
compounds extracted from the European madder plant (Rubia
tinctorum L.), which provides an orange-red coloured dye; a red dye
* Corresponding author. Fax: þ44 (0) 113 343 3704.
E-mail address: r.s.blackburn@leeds.ac.uk (R.S. Blackburn).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.04.009

8
I. Drivas et al. / Dyes and Pigments 88 (2011) 7e17
can also be obtained from the Indian madder plant (Rubia cordifolia
L.). Madder plants contain an impressive number of anthraquinone
derivatives; of the thirty-six compounds now identified in madder
roots, fifteen play an important role in dyeing and are grouped
together in the Colour Index as C. I. Natural Red 8. The main col-
ouring species extracted from R. tinctorum and R. cordifolia are
alizarin (1) and purpurin (2); other colorants present are xantho-
purpurin (3), rubiadin (4), pseudopurpurin (5), munjistin (6), and
lucidin (7) [13,14].
enhancing the solubility of the dye [20]. Absorbance at longer
wavelengths (bathochromic shift) at higher pH arises from the
formation of more electron-rich conjugated
those shown in Scheme 1.
p-systems, such as
In 1998, poly(ethyleneterephthalate) (PET; 8), overtook cotton as
having the highest consumption of any fibre in the world. PET is
a highly crystalline linear aromatic polymer with a small number of
amorphous regions available for sorption and diffusion and can only
be dyed practically with hydrophobic disperse dyes [21]. Poly(lactic
acid) (PLA; 9) is a linear aliphatic polymer made from renewable raw
materials which are fermented to produce lactic acid, which is then
polymerised to make the polymer via a dimeric lactide interme-
diate. It has been demonstrated that PLA can be dyed with disperse
dyes designed for use on PET [22]. Disperse dyes are generally non-
ionic and are typically only sparingly soluble in water. It is not
possible to dye hydrophobic fibres with a mixture of the dye and
water alone because the dye particles would not be distributed
uniformly and would precipitate from solution, therefore, disperse
dyeing requires incorporation of a surface-active (dispersing)
agents. Since ester fibres and disperse dyes do not typically contain
any ionic groups, dyeefibre attraction clearly originates in hydrogen
bonding, dipoleedipole interaction, hydrophobic effects and
dispersion forces [23]. Studies have demonstrated that all the polar
groups in a disperse dye molecule can contribute to its substantivity
for an ester fibre, in addition, provided the dye molecule is planar
and can lie flat against the cyclic nuclei in the ester polymer
segments, all polar substituents on the fringes of the rings in the dye
have the potential to contribute to the overall strength of the
dyeefibre multiple bonding [23].
O
OH
1: R1 = OH; R2 = R3 = H
8
1
9
R1
R2
2: R1 = R3 = OH; R2 = H
7
6
2
3: R1 = R3 = H; R2 = OH
4: R1 = CH3; R2 = OH; R3 = H
5: R1 = COOH; R2 = R3 = OH
6: R1 = COOH; R2 = OH; R3 = H
7: R1 = CH2OH; R2 = OH; R3 = H
3
10
4
5
O
R3
Alizarin (1,2-dihydroxyanthraquinone; C. I. Mordant Red 11; 1)
is the main dye (orange-red crystals) extracted from R. tinctorum,
which occurs in the roots of the plant as the glycosylated
compound ruberthyric acid, where a 2-O-primeverose group is
present rather than the 2-hydroxy group in alizarin; the prime-
verose moiety is hydrolysed to the hydroxy group during extraction
and dyeing [15]. Purpurin (1,2,4-trihydroxyanthraquinone; C. I.
Natural Red 16; 2) is a minor component in the roots of R. tinctorum,
but is the main dye (bright red crystals) extracted from R. cordifolia
[6,14]. Both alizarin and purpurin are only sparingly soluble in
water, but are freely soluble in alcohol, ether, acetone and alkaline
solutions. It has been demonstrated that alizarin can be extracted
from the roots of R. tinctorum with methanol at 25 ꢀC with an
extraction yield of 2.9 g kgꢁ1 of dried material [7]; this yield can be
increased to 4.0 g kgꢁ1 by means of Microwave Assisted Extraction
(MAE), with purpurin being extracted from R. tinctorum at a yield of
2.1 g kgꢁ1 by MAE [10]. It has also been demonstrated that
extraction of R. tinctorum in methanol/water mixtures can be
conducted at lower temperatures and in shorter times to obtain
similar yields by application of ultrasound assisted extraction [16].
Electron-donating hydroxy groups in the 1- or 4-positions of
alizarin and purpurin are able to form intramolecular hydrogen
bonds with the keto groups (9- and 10-positions) of the anthra-
quinone moiety; however, the hydroxy group in the 2-position is
unable to form intramolecular hydrogen bonds with the keto
groups [13,14,17,18]. Individual dye molecules are also attracted to
each other through van der Waals forces and inter-molecular
hydrogen bonds, with the result that many dyes exist in solution as
aggregates [19]. The large size of these dye aggregates can lead to
a significant reduction in the rate of fibre sorption, or in some cases
to the precipitation of the dye from solution.
O
O
O
C
*
O
O
*
*
*
CH3
O
8
9
Synthetic fibres are generally not dyeable with natural dyes, yet
synthetic anthraquinonoid compounds constitute 32% of all
commercial disperse dyes designed for use on polyester and other
hydrophobic fibres, hence, there is potential for utilising natural
anthraquinonoid dyes based on alizarin and purpurin as disperse
dyes for such fibres [13,20,24]. The research herein is aimed at
chemically modifying the natural dyes alizarin and purpurin to
increase their substantivity for polyester fibres, specifically PET and
PLA, in order to promote the utilisation of natural dyes as platform
chemicals for the sustainable production of alternatives to existing
synthetic dyes, but which maintain technical performance. The
second goal is to achieve a better understanding of the sorption
properties of disperse dyes on PLA fibres and to encourage the
utilisation of this sustainable fibre.
Alizarin and purpurin vary in aqueous solubility and colour
under different pH conditions; strong alkali will create a violeteblue
colour, dilute alkali a violetered, whilst a strong acid with produce
an orange colour; the compounds are practically insoluble at pH
4e6. This change in colour and increase in solubility with increasing
pH is due to the ability of the hydroxy groups to ionise, forming salts
with greater water solubility. Alkali also reduces inter-molecular
hydrogen bonding, decreasing the extent of aggregation, further
2. Results and discussion
The aim of the synthesis work was to chemically modify the
alizarin and purpurin structures to produce dyes with greater
H
H
O
OH
O
O
O
R
O
O
O
R
O
O
O
R
O
O
O
R
OH
OH
O
OH
O
OH
H
O
R
R = H = alizarin
R = OH = purpurin
Scheme 1. Solubilisation of alizarin and purpurin in alkali.

I. Drivas et al. / Dyes and Pigments 88 (2011) 7e17
9
R
O
O
OH
O
O
O
O
OH
OH
O
O
R
R
X , KOH
DMSO
R
+
O
10a 63% : 10b 19%
11a 17% : 11b 11%
12a 23%
10: R = Et; X = I
11: R =
; X = Br
O
12: R =
; X = Br
O
Scheme 2. Alkylation reactions of alizarin to produce derivatised dyes.
substantivity for synthetic polyester fibres, in comparison with the
parent compound. Natural dyes tend to be hydrophilic and have
limited substantivity for hydrophobic substrates, therefore, the
most important objective was to design compounds with greater
hydrophobicity than alizarin and purpurin. A possible route for
derivatisation of the natural compounds was through alkylation of
the phenolic compounds. Reactions were based on a rapid, mild,
one-step procedure developed by Johnstone and Rose for the
alkylation of phenols, utilising a base (KOH) and a suitable alkyl
halide in DMSO [25]. Ethyl iodide, benzylbromide, and methyl-4-
bromobutyrate were selected as reagents for the proposed reac-
tions to derivatise the hydroxy groups in alizarin (Scheme 2) and
purpurin (Scheme 3). It was envisaged that these reactions would
allow the preparation of derivatives containing simple alkyl, aryl
and ester groups, to help determine the relative importance of
structural characteristics in the dye adsorption process for the two
polymers investigated.
in 1M NaOH solution, none of the derivatised dyes were soluble in
this medium, probably due to their significantly greater hydro-
phobicity. Additionally, in anthraquinonoid compounds a hydroxy
group
value than a hydroxy group
internal hydrogen bond between the
in the case of alizarin the pKa values are 12.0 and 8.2 for the
b
(positions 1, 4, 5, 8) to the carbonyl has a much higher pKa
to the carbonyl group due to an
-OH and the carbonyl group;
and
g
b
b
g
hydroxy group, respectively [15]. Hence, the pKa of the remaining 1-
hydroxy group in the derivatised compounds would be expected to
be significantly higher than that of the 2-hydroxy group in the
parent compound, and solubility in 1M NaOH solution would be
significantly reduced. Neither the parent dyes nor the derivatives
were soluble in distilled water or 1M HCl solution. These results
demonstrate that the derivatised compounds are more suitable for
disperse dye application under a variety of different pH conditions
and are more hydrophobic and less acidic than the parent
compounds.
The derivatives shown in Table 1 were successfully synthesised,
as detailed in the experimental section. Although yields were
modest, these were usually of analytically pure products, and were
unoptimised. It was also envisaged that if promising dyeing results
were obtained, then a more environmentally acceptable alkylation
procedure could be adopted. In all cases the predominant product
resulted from alkylation of the 2-hydroxy position, rather than the
1-hydroxy. Although the precise reason for this is unclear, it is
consistent with literature precedent [26,27]. Substantial amounts
of the bis-alkylated products were also isolated in some cases, and
provided further insight into the influence of structure on the
dyeing process.
When considering the light absorption properties of each
compound, it was observed that the wavelength of maximum
absorption (lmax) in acetone for the mono-alkylated derivatives
(where only the 2-position was derivatised) was almost the same as
the respective parent compound, demonstrating that the alkylated
phenolic compounds have similar electronic properties to the
original phenol. However, when the 1-position was also derivatised
the lmax of all the bis-alkylated derivatives was reduced by
53e54 nm (hypsochromic shift) for both alizarin and purpurin.
Alizarin and purpurin both possess low-lying LUMOs, hence they
are good electron acceptors; the electron-donating hydroxy groups
increase molecular conjugation, in comparison with anthraqui-
Physical properties of the derivatised dyes and their parent
compounds are shown in Table 1. As discussed earlier, alizarin and
purpurin are soluble in alkali, and are subject to colour changes
under different pH conditions, this could cause problems during
dyeing processes in industry, where aqueous solutions in different
pH ranges are used. Although both parent compounds were soluble
none, lowering the energies of the LUMOs. Consequently, p / p*
transitions can occur in the visible region, resulting in intense
visible absorptions and the molecules being coloured [28]. In
anthraquinonoid dyes, an enhanced bathochromic effect (absorp-
tion at longer wavelengths) is observed when a protic group in the
1-position (e.g. eOH or eNHR) is able to hydrogen bond with the
R
O
O
OH
OH
O
O
O
O
O
OH
OH
OH
O
O
R
R
X , KOH
DMSO
R
+
OH
13a 34%
13: R = Et; X = I
14a 22% : 14b 5%
15a 21%
14: R =
15: R =
; X = Br
; X = Br
O
O
Scheme 3. Alkylation reactions of purpurin to produce derivatised dyes.

10
I. Drivas et al. / Dyes and Pigments 88 (2011) 7e17
Table 1
Physical properties of anthraquinonoid dyes.
Compound
Name
Structure
Solubility
(1M NaOH)
lmax
3max (dm3
Melting point
(ꢀC)
(nm)
mol-1 cmꢁ1
)
OH
O
O
OH
Soluble
1
alizarin (1,2-dihydroxyanthracene-9,10-dione)
(purple-red
colour)
429
425
4300
6800
278e280
182e185
O
OH
O
10a
2-ethoxy-1-hydroxyanthracene-9,10-dione
Insoluble
O
O
O
O
10b
1,2-diethoxyanthracene-9,10-dione
Insoluble
375
4600
129e132
O
O
O
OH
O
11a
2-(benzyloxy)-1-hydroxyanthracene-9,10-dione
Insoluble
423
3600
170e174
O
O
O
11b
1,2-bis(benzyloxy)anthracene-9,10-dione
Insoluble
375
3700
144e147
O
O
O
OH
O
O
O
methyl-4-(9,10-dihydro-1-hydroxy-9,10-
dioxoanthracen-2-yloxy)butanoate
12a
Insoluble
424
5900
145e148
O
O
OH
OH
OH
Soluble
(purple-red
colour)
2
purpurin (1,2,4-trihydroxyanthracene-9,10-dione)
2-ethoxy-1,4-dihydroxyanthracene-9,10-dione
2-(benzyloxy)-1,4-dihydroxyanthracene-9,10-dione
482
480
480
6200
6500
2200
265e270
199e201
202e205
O
OH
O
13a
14a
Insoluble
Insoluble
O
OH
O
O
OH
O
OH

I. Drivas et al. / Dyes and Pigments 88 (2011) 7e17
11
Table 1 (continued)
Solubility
(1M NaOH)
lmax
3max (dm3
Melting point
(ꢀC)
Compound
Name
Structure
(nm)
mol-1 cmꢁ1
)
O
O
O
O
14b
1,2-bis(benzyloxy)-4-hydroxyanthracene-9,10-dione
Insoluble
429
3600
174e176
OH
O
O
OH
O
O
O
methyl-4-(9,10-dihydro-1,4-dihydroxy-9,10-
dioxoanthracen-3-yloxy)butanoate
15a
Insoluble
480
8100
149e152
OH
adjacent carbonyl group, which assists conjugation of the donor
lone pair electrons with the anthraquinone ring [29,30]. Hence,
derivatisation at the 1-position with substituents that were unable
to hydrogen bond with the 9-ketone group caused a reduction in
conjugation in the chromophore, resulting in absorption at shorter
wavelengths.
temperatures. Additional derivatisation of the 1-hydroxy group to
form the bis-alkylated derivatives reduces the potential for
molecular bonding even further, and even lower melting temper-
atures are observed.
Table 2 shows the results of the dyeing and fastness properties
of the parent and derivatised anthraquinonoid dyes on PET and
PLA; it is observed that, as expected, % exhaustion figures relate
directly to K/S values, insofar as when exhaustion is high, K/S values
are also relatively high. It is apparent that, in the case of PET,
exhaustion >84% and high K/S values were observed for both
In terms of extinction coefficient (3max), it is known that a 2-
methoxy group gives a slightly higher 3max in comparison with
a 2-hydroxy group in substituted anthraquinonoid dyes [30];
accordingly, it is observed that derivatisation of the 2-hydroxy
group in both alizarin and purpurin with 2-ethoxy or methyl-4-
butanoate results in an increase in 3max, which can be explained in
terms of PPP-MO calculations [29]. It is noted that the 1,2-diethoxy
alizarin derivative only gave a slight increase in 3max, in comparison
with alizarin, but a significantly lower 3max, in comparison with its
2-hydroxy counterpart; this is probably because the 1-ethoxy group
is unable to fully conjugate due to steric affects and its inability to
hydrogen bond to the 9-ketone group, which is known to decrease
tinctorial strength [30]. However, derivatisation with a 2-benzyloxy
group caused a decrease in 3max, it is not clear why this occurred, but
is certainly worthy of further investigation. The lmax at longer
wavelengths observed for purpurin and its derivatives, in compar-
ison with alizarin and its derivatives, is as a result of the presence of
two electron-donating groups in the 1,4-positions, which gives rise
to a bathochromic shift (increased lmax) [30].
All derivatives have significantly lower melting points in
comparison with their respective parent compound; it is also evident
that the bis-alkylated derivatives have lower melting points than
their respective mono-alkylated derivative. In the case of alizarin,
Guilhem demonstrated [31] that relatively strong inter-molecular
hydrogen bonds (OeH$$$O; 21 kJ molꢁ1 [32]) cause the formation of
aggregates comprising a ‘triple molecule complex’ of three alizarin
molecules (Fig. 1), wherein the individual triple molecule complexes
are linked together by weaker van der Waals forces.
x
O
O
O
O
OH
OH
OH
HO
OH
O
HO
HO
HO
O
O
O
O
O
HO
HO
HO
O
HO
HO
HO
O
O
triple molecule
complex
HO
OH
O
O
O
HO
HO
HO
O
O
O
Distinct needle-like crystals are formed as a result of the short
length of the b-axis as compared to the other crystal axes of the
monoclinic unit cell [33]. From Fig. 1 it can be seen that the 2-
hydroxy group plays an important role in the formation of this
triple molecule complex (through inter-molecular hydrogen
bonds) and in van der Waals interactions between separate
complexes; the role of the 2-hydroxy group is important in rela-
tion to the crystallinity of solid alizarin. Hence, when this position
is derivatised, and is no longer able to bond with adjacent mole-
cules, it would be expected that lower crystallinity of the solids
would result, which explains the observed reduction in melting
inter-molecular
hydrogen bonds
HO
OH
O
O
O
z
HO
Fig. 1. Molecular bonding in alizarin [15].

12
I. Drivas et al. / Dyes and Pigments 88 (2011) 7e17
parent compounds (1 and 2) and the mono-alkylated derivatives
(10ae15a), we propose that this is due to interactions between
aromatic residues in the dyes and the polymer having the greatest
contribution to dyeefibre substantivity, rather than other forces of
attraction such as hydrophobic interactions, dipolar interactions
and hydrogen bonding. Derivatisation of both alizarin and purpurin
at the 2-hydroxy position with one eOCH2CH3 group (10a, 13a)
did afford a slight increase in % exhaustion values with respect to
their parent compounds, most likely as a result of the a greater
hydrophobicity of upon derivatisation. However, derivatisation 2-
hydroxy position with one eOCH2C6H5 group (11a, 14a) did not
afford any change in % exhaustion values.
In the case of the bis-alkylated derivatives (10b, 11b, 14b),
exhaustion on PET was between 55 and 65%, and K/S values were
less than half the value of their respective mono-alkylated deriva-
tive. It might be expected that the introduction of a second
substituent into the anthraquinonoid structure with increased
substantivity for the polyesters should improve exhaustion,
however, the bis-alkylated derivatives have a larger, more bulky,
less planar molecules in comparison with their mono-alkylated
derivative counterparts, which is disadvantageous in disperse
dyeing of crystalline polyesters [34], resulting in the lower sorption
observed. Greater differences in sorption and K/S values are
observed between parent dyes and the various derivatives in the
case of PLA dyeings; the polymer does not have any aromatic
moieties, so hydrophobic interactions, dipolar interactions, and
hydrogen bonding involving other moieties is more important in
dyeefibre substantivity. Karst and Yang demonstrated that the
sorption of substituted anthraquinonoid dyes onto PLA was highest
when the substituents present were eNHR, eNR2, eNHCOR, eCOR,
eOR, eCOOR, or a phenyl, wherein the R group was eCH3,
e(CH2)nCH3, or a phenyl, and when the groups eNO2, eNH2, eOH,
eCN, or a halide were absent [35]. They also demonstrated in later
work that the substituents in dye molecules that form the strongest
interactions with PLA included eN(C2H4OCOCH3)2, e(CO)2N-
C3H6OCH3, and eCH(CO)2C6H4 [21]. As such, it is understandable
that derivatisation of alizarin to form 10a and 11a caused and
improvement in sorption properties by addition of eOCH2CH3 and
eOCH2C6H5 groups, respectively, and removal of one eOH group in
both cases; however, this was not reflected in the respective mono-
alkylated derivatives of purpurin (13a and 14a), and this requires
further investigation to understand the possible reasons. In addi-
tion, the same observations were made with the bis-alkylated
derivatives on PLA as for PET, insofar as no improvement in sorption
was noted due to the increase in molecular size of these derivatised
dyes. Highest sorption on PLA was observed with the two
compounds derivatised with one methyl-4-butanoate group (12a
and 15a) where a significant increase in exhaustion and K/S was
noted for both alizarin and purpurin derivatives. In agreement with
Karst and Yang’s work the presence of a eO(CH2)3COOCH3 group
provides greatest dyeefibre affinity, which is logical as the
considering the interactions with the similar eCOCH(CH3)Oe
repeat units of the polymer.
CIELab data is provided in Table 2, and from calculated saturation
(chroma; C*) values it can be seen that alizarin and purpurin
provided dull shades (relatively low C* values), whereas their mono-
alkylated counterparts provided bright shades (relatively high C*
values). This was probably due to reduced hydrogen-bonding,
resulting from derivatisation of the 2-hydroxy, which decreased the
ability of the dyes to form aggregates; aggregation of dyes can cause
interactions between conjugated systems, resulting in a broadening
of the absorption peak, as observed herein; this is in keeping with
the reduction in melting point upon derivatisation as discussed
above. The lmax values at longer wavelengths observed for purpurin
and its derivatives, in comparisonwith alizarin and its derivatives, is
as a result of the presence of two electron-donating groups in the
1,4-positions, which increases lmax [30]; the higher K/S values
observed for purpurin and its derivatives could also be due to the
presence of two electron-donating groups in the 1,4-positions,
which can increase 3max [30], although this is not always as
straightforward as it has been observed that it is not always possible
to directly relate solution spectral parameters such as molar
extinction coefficient to colorimetric data from dyed fibre [36].
Table 2 shows that, in terms of wash fastness, dyeings on PET with
derivatised dyes display slightly improved wash fastness in
comparison with the parent structures (the level of wash fastness
being excellent) probably as a result of greater dyeefibre interaction.
All dyeings on PLA display excellent wash fastness; and no staining
Table 2
Dyeing and fastness properties of anthraquinonoid dyes on PET and PLA.
Fibre
Compound
Exhaustion
(%)
L*
a*
b*
C*
hꢀ
K/S at lmax
Wash fastness
(colour loss) (1e5)
Light fastness
(1-8)
PET
1
10a
10b
11a
11b
12a
2
13a
14a
14b
15a
91.0
97.5
65.4
90.0
57.1
95.3
85.6
96.6
84.2
55.0
97.3
63.2
75.2
77.4
74.7
81.3
75.3
52.8
62.8
66.8
72.2
50.8
12.2
15.7
9.6
14.6
4.4
14.4
41.4
50.3
49.2
23.7
39.1
66.6
90.5
60.6
87.5
46.4
87.7
51.6
76.5
79.1
71.2
53.3
67.8
91.9
61.4
88.7
46.6
88.9
66.1
91.6
93.2
75.1
66.1
79.6
80.2
81.0
80.5
84.6
80.7
51.3
56.7
58.1
71.6
53.8
15.1
18.1
6.8
17.4
5.4
16.4
17.1
24.8
19.9
8.6
4
5
5
5
5
5
4/5
5
5
5
7
4
6
4
7
4
7
5
3
5
5
4/5
21.9
PLA
1
10a
10b
11a
11b
12a
2
13a
14a
14b
15a
29.9
41.1
17.6
40.1
15.3
82.4
39.8
6.5
82.6
86.4
84.5
82.2
84.8
80.6
63.8
78.1
77.2
79.3
65.1
2.0
1.2
2.0
2.8
2.7
47.6
69.4
59.1
61.6
43.7
75.4
43.7
49.9
55.7
57.4
56.5
47.6
69.4
59.2
61.6
43.8
75.6
53.8
55.1
61.2
61.6
66.8
87.7
89.0
88.0
87.4
86.4
85.6
54.4
65.0
65.5
68.5
57.7
2.3
3.9
2.6
3.9
2.4
8.4
5.7
2.4
2.8
2.7
8.6
5
5
5
5
5
5
5
5
5
5
5
4
7
3
4
1
7
3
4
3
2
4
5.8
31.3
23.3
25.4
22.6
35.7
7.5
6.1
60.1

I. Drivas et al. / Dyes and Pigments 88 (2011) 7e17
13
was observed on any of the adjacent multifibre strip materials for any
dyeing after washing (all grade 5).
stabilises the dye against photo-oxidation), or by virtue of the lower
colour strength of the dyeings, which can often cause a reduction in
light fastness in comparison with dyeings of higher K/S values.
In terms of fastness to light, a noticeable improvement is
observed for all mono-alkylated derivatives on PET and most
mono-alkylated derivatives on PLA in comparison with the parent
structure (no decrease being observed); in some cases very high
light fastness ratings (7) are observed. In the parent structures of
alizarin and purpurin, the presence of an electron-donating group
in the 2-position (the 2-hydroxy group) is undesirable because,
unlike similar groups in the 1- and 4-positions, the group is unable
to form intramolecular hydrogen bonds with the keto groups of
anthraquinone and hence is highly susceptible to photo-oxidation
[37]. With the mono-alkylated derivatives this group has been
replaced with groups with lower electron-donating capacity and so
the dye has higher light fastness. Conversely, when the hydroxy
groups in the 1-position are removed it appears that light fastness
is reduced, in comparison with the parent structure, as observed
herein in the case of the bis-alkylated derivatives. There are two
explanations as to why this is observed: the presence of a 1-
hydroxy group in anthraquinonoid dyes stabilises the compound
against photo-oxidation as a result of the intramolecular hydrogen
bond with the 9-ketone group, which is not possible with the bis-
alkylated derivatives; alternatively, light fastness is also related to
differences in the concentration of dye in fibre, and the apparent
reduction in photostability between those of dyes 10a and 11a
compared to 10b and 11b, could be attributable to a significantly
lower concentration of colorant in the substrate in the case of the
bis-alkylated dyes.
4. Experimental section
4.1. Materials
Spun jersey knitted fabric samples of 100% PLA fibre and 100%
PET fibre of the same fabric construction and weight (155 g mꢁ2
)
were kindly supplied by NatureWorks LLC. A sample of the
dispersing agent Borresperse NA (sodium lignosulfonate) was
supplied by Borregaard Lignotech. Sample of the surfactant Kieralon
MFB (mixture of non-ionic and anionic surfactants) and the anti-
oxidant Ludigol AR were supplied by BASF. A sample of the levelling
agent Levagal DLP was supplied by Lanxess. All other chemicals for
synthesis and dyeing were obtained from SigmaeAldrich. Alizarin
(supplied as 97%) and purpurin (supplied as 90%) were purified
before use by recrystallisation from ethanol (CAUTION: Highly
flammable. Irritating to eyes).
4.2. Analytical procedures
1H and 13C NMR spectra were recorded respectively at 300 MHz
and 75 MHz on a Bruker B-ALS 60 spectrometer using deuterated
DMSO and chloroform (CAUTION: Harmful if swallowed. Irritating
to skin. Limited evidence of a carcinogenic effect), respectively, as
the solvent and residual proton signals of respective solvents as an
internal standard. FT-IR absorbance/transmission spectra were
recorded on a Perkin Elmer Spectrum One spectrometer with the
sample compressed into NaCl discs, and held in a specimen holder.
UV/visible spectrophotometry was conducted using a Jasco V-530
spectrophotometer using 50:50 (v/v) acetone (CAUTION: Highly
flammable. Irritating to eyes): water as solvent. Concentrations
were calculated from calibration graphs at the wavelength of
maximum absorption (lmax); concentration of residual dye in
solution was calculated from calibration plots, and dye adsorbed by
the fibre calculated from the difference before and after exhaustion.
No difference in the shape of the absorption spectrum before and
after dyeing was noted. Mass spectra were recorded on a VG
Autospec mass spectrometer for electron impact (EI) and fast atom
bombardment (FAB) spectra. Molecular ions are reported as mass
with percentage abundance quoted in brackets. Melting points
were determined on a Reichert Hot Stage apparatus and are
uncorrected. Microanalyses were carried out at the University of
Leeds Microanalytical laboratory; all C and H analytical figures are
expressed in percentage values of total molecular weight. All
solvents used in analytical procedures were purified before use
using established procedures [38].
The research has demonstrated the possibility of using alizarin
and purpurin as platform chemicals for the production of sustain-
able alternatives to existing synthetic dyes, which have very good
technical performance, superior to the dyeing properties of the
parent compounds. The research has also provided additional
understanding of the sorption properties of disperse dyes on of PLA
fibres in terms of insight into which chemical groups provide
greatest substantivity for PLA.
3. Conclusions
The research herein has demonstrated that disperse dyes which
yield high colour strength and high fastness properties on PET and
PLA can be synthesized from natural anthraquinonoid colorants by
derivatisation of the 2-hydroxy position in alizarin and purpurin. It
was also possible to produce derivatives of alizarin and purpurin
where both the 1- and 2-positions were alkylated. In comparison
with parent compounds, the following observations were made for
derivatised dyes: insensitive to pH change; insoluble in alkali; lmax
for mono-alkylated derivatives was the same; lmax for bis-alkylated
derivatives was reduced by 53e54 nm, as a result of reduction in
conjugation in the chromophore; melting points decreased as the
ability of the dyes to form inter-molecular interactions decreased
with derivatisation, yielding less crystalline solids.
4.3. Synthesis
Exhaustion and K/S values for dyeings on PET were high for
parent and mono-alkylated derivatives, and lower for bis-alkylated
derivatives, due to formation of larger, more bulky molecules in
comparison with their mono-alkylated counterparts. Mono-alkyl-
ation with ethoxy, benzyloxy, and, particularly, methyl-4-butanoate
groups improved dyeing properties on PLA. Dyeings on PET with
derivatised dyes displayed slightly improved wash fastness in
comparison with the parent structures; all dyeings on PLA displayed
excellent wash fastness. Light fastness was improved in the case of
the mono-alkylated derivatives due to the removal of the 2-hydroxy
group, which is highly susceptible to photo-oxidation; conversely,
light fastness was reduced in the case of the bis-alkylated derivatives
either due to removal of the 1-hydroxy group (which helps to
2-Ethoxy-1-hydroxyanthracene-9,10-dione (10a) and 1,2-
diethoxyanthracene-9,10-dione
10).
Powdered
potassium
hydroxide (CAUTION: Harmful if swallowed. Causes severe burns)
(164 mmol) was added to DMSO (41 cm3) at 37 ꢀC. After stirring for
5 min, alizarin (20.5 mmol) was added, followed immediately by the
ethyl iodide (CAUTION: Harmful by inhalation. Irritating to eyes,
respiratory system and skin) (82 mmol). Stirring was continued for
24 h, after which the mixture was poured into aqueous hydrochloric
acid solution (1M, 400 cm3) and extracted with dichloromethane
(CAUTION: Limited evidence of a carcinogenic effect) (3 ꢂ 400 cm3).
The combined organic extracts were washed with distilled water
(5 ꢂ 500 cm3), dried (MgSO4) and evaporated in a rotary evaporator.
The residue was dried further under high vacuum (24 h). The solid

14
I. Drivas et al. / Dyes and Pigments 88 (2011) 7e17
contained a mixture of 10a and 10b and was dissolved in dichloro-
methane (100 cm3). Compound 10a was extracted into sodium
hydroxide (1M, 2 ꢂ 20 cm3) which was then neutralised to give the
product: 10a (3.53 g, 13.2 mmol, yield: 63%). m.p. 182e185 ꢀC;
(Found: C, 70.4; H, 4.5; C16H12O4 requires C, 71.6; H, 4.5%); nmax
(solid)/cm-1 (CeH) 3094e2891, (eOH) 3000e2600, (C]O) 1660,
(CeO) 1272; 1H nmr, dH (300 MHz, (CD3)2SO); 12.71 (1H, s, CeOH),
8.22e8.11 (2H, m, H-5,8), 7.92 (2H, m, H-6,7), 7.69 (1H, d, J 7.5, H-4),
7.40 (1H, d, J 8.4, H-3), 4.19 (2H, q, J 6.6, H-15), 1.40 (3H, t, J 6.6, H-16);
13C {1H} nmr, dC (75 MHz, CDCl3); 189.6 (C]O, C-9), 181.9 (C]O,
C-10), 153.9 (quat. Ar.C, C-2), 153.3 (quat. Ar.C, C-1), 135.1 (Ar.C, C-6),
134.5 (quat. Ar.C, C-12),134.2 (Ar.C, C-7),133.8 (quat. Ar.C, C-11),127.8
(Ar.C, C-5), 127.3 (Ar.C, C-8), 125.5 (quat. Ar.C, C-14), 121.5 (Ar.C, C-3),
117.0 (Ar.C, C-4), 116.5 (quat. Ar.C, C-13), 65.3 (OeCH2CH3, C-15), 15.0
(OeCH2CH3, C-16); m/z (ESI) 291 (100%, MNaþ); UV/vis lmax
(CH3COCH3) 425 nm.
Evaporation of the remaining dichloromethane solution in vacuo
gave a solid, which was further dried in a high vacuum to give 10b:
(1.18 g, 3.98 mmol, yield: 19%). m.p. 129e132 ꢀC; (Found: C, 73.1; H,
5.2; C18H16O4 requires C, 73.0; H, 5.4%); nmax (solid)/cmꢁ1 (CeH)
3084e2893, (C]O) 1669, (CeO) 1264; 1H nmr, dH (300 MHz,
(CD3)2SO); 8.27e8.17 (2H, m, H-5,8), 8.04e7.92 (3H, m, H-4,6,7),
7.57 (1H, d, J 6.0, H-4), 4.24 (2H, q, J 6.6, H-15), 4.15 (2H, q, J 6.9, H-
17), 1.45 (6H, m, H-16,18); dC (75 MHz, CDCl3); 182.7 (C]O, C-9),
182.5 (C]O, C-10), 158.8 (quat. Ar.C, C-2), 149.1 (quat. Ar.C, C-1),
135.3 (quat. Ar.C, C-12), 134.1 (Ar.C, C-6), 133.8 (Ar.C, C-7), 133.1
(quat. Ar.C, C-11), 127.3 (Ar.C, C-5), 126.6 (Ar.C, C-8), 125.0 (Ar.C, C-
3), 121.1 (quat. Ar.C, C-14), 116.9 (Ar.C, C-4), 116.8 (quat. Ar.C, C-13),
69.8 (OeCH2CH3, C-17), 64.9 (OeCH2CH3, C-15), 15.7 (OeCH2CH3,
C-18), 14.7 (OeCH2CH3, C-16); m/z (ESI) 319 (100%, MNaþ); UV/vis
lmax (CH3COCH3) 375 nm.
2-(Benzyloxy)-1-hydroxyanthracene-9,10-dione (11a). Powdered
potassium hydroxide (82 mmol) was added to DMSO (82 cm3) at 37 ꢀC.
After stirring for 5 min, alizarin (41 mmol) was added, followed
immediately by the benzylbromide (CAUTION: Irritating to eyes,
respiratory system and skin) (37.5 mmol). Stirring was continued for
24 h, after which time the mixture was poured into aqueous hydro-
chloric acid (1M, 400 cm3) and extracted with dichloromethane
(3 ꢂ 400 cm3). The combined organic extracts were washed with water
(5 ꢂ 500 cm3), dried (MgSO4) and concentrated in vacuo. The residue
was dried further under high vacuum (24 h). The solid contained
a mixture of 11a, 11b and alizarin (1). The mixture was recrystallised
repeatedly from ethylacetate (CAUTION: Highly flammable. Irritating
to eyes) to give the product 11a (2.3 g, 6.96 mmol, yield: 17%). m.p.
170e174 ꢀC; (Found: C, 75.5; H, 4.2; C21H14O4 requires C, 76.4; H, 4.3%);
nmax (solid)/cmꢁ1 (CeH) 3057e2900, (eOH) 2900e2600, (C]O) 1667,
(CeO) 1262; 1H nmr, dH (300 MHz, (CD3)2SO); 12.75 (1H, s, CeOH),
8.23e8.18 (2H, m, H-5,8), 7.93 (2H, m, H-6,7), 7.73 (1H, d, J 9.0, H-4),
7.56e7.40 (6H, m, H-3,16-21), 5.29 (2H, s, H-15); 13C {1H} nmr, dC
(75 MHz, CDCl3); 189.2 (C]O, C-9),181.5 (C]O, C-10),153.3 (quat. ArC,
C-2),153.1(quat. ArC, C-1),135.7 (quat. ArC, C-16),134.8 (ArC, C-6),134.1
(quat. ArC, C-12), 133.8 (ArC, C-7), 133.4 (quat. ArC, C-11), 128.8 (2 ArC,
C-18,20),128.4 (ArC, C-19),127.4 (2 ArC, C-17,21),127.4 (ArC, C-5),126.9
(ArC, C-8),125.7 (quat. ArC, C-14),120.8 (ArC, C-3),118.1 (ArC, C-4),116.4
(quat. ArC, C-13), 71.2 (eOeCH2ePh, C-15); m/z (ESI) 353 (100%,
MNaþ); UV/vis lmax (CH3COCH3) 423 nm.
vacuum (24 h). The solid contained a mixture of 11a, 11b and
alizarin (1) and was dissolved in dichloromethane (100 cm3). The
compound 11a and alizarin were removed by extraction with
sodium hydroxide (1M, 2 ꢂ 20 cm3). Concentration of the
dichloromethane solution in vacuo gave a solid, which was further
dried in a high vacuum and was proven to be 11b (1.92 g,
4.52 mmol, yield: 11%). m.p. 144-147 ꢀC; (Found: C, 78.4; H, 4.6;
C28H20O4 requires C, 80.0; H, 4.8%); nmax (solid)/cmꢁ1) (CeH)
3067e2873, (C]O) 1668, (CeO) 1260; 1H nmr, dH (300 MHz,
(CD3)2SO); 8.21e8.15 (2H, m, H-5,8), 8.06 (1H, d, J 9.0, H-4),
7.95e7.88 (2H, m, H-6,7), 7.69 (1H, d, J 9.0, H-3), 7.50e7.32 (10H, m,
H-17-21,24-28), 5.32 (2H, s, H-22), 5.04 (2H, s, H-15); 13C {1H} nmr,
dC (75 MHz, CDCl3); 181.6 (C]O, C-9), 181.4 (C]O, C-10), 157.4
(quat. ArC, C-2), 147.6 (quat. ArC, C-1), 136.1 (quat. ArC, C-23), 134.6
(quat. ArC, C-16), 134.2 (quat. ArC, C-12), 132.8 (ArC, C-6), 132.4
(ArC, C-7),132.0 (quat. ArC, C-11),128.0e125.6 (10 ArC),124.5 (quat.
ArC, C-14), 124.2 (ArC, C-3), 116.8 (ArC, C-4), 116.8 (quat. ArC, C-13),
74.2 (eOeCH2ePh, C-22), 70.2 (eOeCH2-Ph, C-15); m/z (ESI) 443
(100%, MNaþ); UV/vis lmax (CH3COCH3) 375 nm.
Methyl-4-(9,10-dihydro-1-hydroxy-9,10-dioxoanthracen-2-
yloxy)butanoate
(12a).
Powdered potassium
hydroxide
(160 mmol) was added to DMSO (80 cm3) at 37 ꢀC. After stirring for
5 min, alizarin (40 mmol) was added, followed immediately by the
methyl-4-bromobutyrate (CAUTION: Harmful if swallowed. Irri-
tating to skin) (100 mmol). Stirring was continued for 72 h, after
which time an additional amount of methyl-4-bromobutyrate was
added (100 mmol). The mixture was stirred for another 24 h and
then it was poured into aqueous hydrochloric acid solution (1M,
400 cm3) and extracted with dichloromethane (3 ꢂ 400 cm3). The
combined organic extracts were washed with water (5 ꢂ 500 cm3),
dried (MgSO4) and concentrated in vacuo. The residue was dried
further under high vacuum (24 h). The solid contained a mixture of
12a, traces of di-derivative (12b) and alizarin (1). The mixture and
was recrystallised twice from ethylacetate to give the product 12a:
(3.2 g, 9.4 mmol, yield: 23%). m.p. 145e148 ꢀC; (Found: C, 66.9; H,
4.7; C19H16O6 requires C, 67.1; H, 4.7%); nmax (solid)/cmꢁ1 (CeH)
3100e2885, (eOH) 3000e2600, (C]O) 1730e1667, (CeO) 1278; 1H
nmr, dH (300 MHz, CDCl3); 13.1 (1H, s, CeOH), 8.32e8.30 (2H, m, H-
5,8), 7.85 (1H, d, J 8.4, H-4), 7.82e7.79 (2H, m, H-6,7), 7.18 (1H, d, J
8.4, H-3), 4.22 (2H, t, J 6.3, H-15), 3.71 (3H, s, H-19), 2.61 (2H, t, J 6.9,
H-17), 2.25 (2H, qu, J 6.6, H-16); 13C {1H} nmr, dC (75 MHz, CDCl3);
189.2 (C]O, C-9), 181.5 (C]O, C-10), 173.4 (quat. eCH2COOCH3, C-
18), 153.4 (quat. ArC, C-2), 153.1 (quat. ArC, C-1), 134.8 (ArC, C-6),
134.2 (quat. ArC, C-12), 133.8 (ArC., C-7), 133.4 (quat. ArC, C-11),
127.4 (ArC, C-5), 126.9 (ArC, C-8), 125.5 (quat. ArC, C-14), 121.0 (ArC,
C-3), 117.2 (ArC, C-4), 116.3 (quat. ArC, C-13), 68.2 (eOCH2CH2CH2-,
C-15), 51.8 (eCH2COOCH3, C-19), 30.3 (eCH2COOCH3, C-17), 24.3
(eCH2CH2CH2-, C-16); m/z (ESI) 363 (100%, MNaþ); UV/vis lmax
(CH3COCH3) 424 nm. Through the work conducted herein, it was
not possible to synthesise significant quantities of the di-derivative
product (12b).
2-Ethoxy-1,4-dihydroxyanthracene-9,10-dione (13a). Powdered
potassium hydroxide (77.6 mmol) was added to DMSO (50 cm3) at
37 ꢀC. After stirring for 5 min, purpurin (19.5 mmol) was added, fol-
lowed immediately by the ethyl iodide (23.4 mmol). Stirring was
continued for 72 h, after which the mixture was poured into hydro-
chloric acid (1M, 400 cm3) and extracted with dichloromethane
(3 ꢂ 400 cm3). The combined organic extracts were washed with
distilled water (5 ꢂ 500 cm3), dried (MgSO4) and concentrated
in vacuo. The residue was dried further under high vacuum (24 h). The
solid contained 13a as well as impurities. Column chromatography,
using DCM as eluent gave 13a (1.90 g, 6.68 mmol, yield: 34%). m.p.
199e201ꢀC; (Found: C, 67.6; H, 4.2; C16H12O5 requiresC,67.6;H, 4.2%);
nmax (solid)/cmꢁ1 (CeH) 2987, (eOH) 3000e2600, (C]O) 1619, (CeO)
1281; 1H nmr, dH (300 MHz, (CD3)2SO); 13.49 (1H, s, C(-4)eOH), 13.22
1,2-Bis(benzyloxy)anthracene-9,10-dione (11b). Powdered
potassium hydroxide (164 mmol) was added to DMSO (82 cm3) at
37 ꢀC. After stirring for 5 min, alizarin (41 mmol) was added, fol-
lowed immediately by the benzylbromide (102.5 mmol). Stirring
was continued for 24 h, after which the mixture was poured into
aqueous hydrochloric acid (1M, 400 cm3) and extracted with
dichloromethane (3 ꢂ 400 cm3). The combined organic extracts
were washed with distilled water (5 ꢂ 500 cm3), dried (MgSO4) and
concentrated in vacuo. The residue was dried further under high

I. Drivas et al. / Dyes and Pigments 88 (2011) 7e17
15
(1H, s, C(-1)eOH), 8.28e8.25 (2H, m, H-5,8), 8.00e7.95 (2H, m, H-6,7),
6.97(1H, s,H-3), 4.23(2H, q, J8.7, H-15), 1.41 (3H, t, J8.7, H-16); 13C{1H}
nmr, dC (75 MHz, CDCl3); 186.2 (C]O, C-9), 183.3 (C]O, C-10), 160.0
(quat. Ar.C, C-4), 156.1 (quat. Ar.C, C-2), 149.5 (quat. Ar.C, C-1), 133.5
(Ar.C,C-6),133.1(quat. Ar.C, C-12),132.8(Ar.C, C-7),132.3(quat.Ar.C,C-
11), 126.0 (Ar.C, C-5), 125.8 (Ar.C, C-8), 111.4 (quat. Ar.C, C-13), 106.3
(Ar.C, C-3),105.0 (quat. Ar.C, C-14); m/z (ESI) 285 (100%, MHþ); UV/vis
lmax (CH3COCH3) 480 nm. Through the work conducted herein, it was
not possible to synthesise significant quantities of the di-derivative
product (13b).
organic extracts were washed with distilled water (5 ꢂ 500 cm3),
dried (MgSO4) and concentrated in vacuo. The residue was dried
further under high vacuum (24 h). The viscous product was tritu-
rated with diethylether and was recrystallised twice from ethyl-
acetate to give 15a (2.9 g, 8.13 mmol, yield: 21%). m.p. 149e152 ꢀC;
(Found: C, 63.8; H, 4.4; C19H16O7 requires C, 64.0; H, 4.4%); nmax
(solid)/cmꢁ1 (CeH) 2954e2887, (eOH) 2900e2600, (C]O) 1730,
(CeO) 1278; 1H nmr, dH (300 MHz, CDCl3); 13.52 (1H, s, C(-4)eOH),
13.45 (1H, s, C(-1)eOH), 8.33e8.30 (2H, m, H-5,8), 7.82e7.78 (2H,
m, H-6,7), 6.67 (1H, s, H-3), 4.18 (2H, t, J 6.0, H-15), 3.71 (3H, s, H-
19), 2.60 (2H, t, J 6.0, H-17), 2.25 (2H, q, J 6.0, H-16); 13C {1H} nmr, dC
(75 MHz, CDCl3); 186.2 (C]O, C-9), 183.5 (C]O, C-10), 172.2 (quat.
eCH2COOCH3, C-18), 159.8 (quat. ArC, C-4), 155.9 (quat. ArC, C-2),
149.6 (quat. ArC, C-1), 133.5 (ArC, C-6), 133.1 (quat. ArC, C-12), 132.8
(ArC., C-7), 132.3 (quat. ArC, C-11), 126.0 (ArC, C-5), 125.9 (ArC, C-8),
111.5 (quat. ArC, C-13), 106.7 (ArC, C-3), 105.2 (quat. ArC, C-14), 67.4
(eOCH2CH2CH2-, C-15), 50.7 (eCH2COOCH3, C-19), 29.2
(eCH2COOCH3, C-17), 23.0 (eCH2CH2CH2-, C-16); m/z (ESI) 379
(100%, MNaþ); UV/vis lmax (CH3COCH3) 480 nm. Through the work
conducted herein, it was not possible to synthesise significant
quantities of the di-derivative product (15b).
2-(Benzyloxy)-1,4-dihydroxyanthracene-9,10-dione (14a) and
1,2-bis(benzyloxy)-4-hydroxyanthracene-9,10-dione
(14b).
Powdered potassium hydroxide (156 mmol) was added to DMSO
(80 cm3) at 37 ꢀC. After stirring for 5 min, purpurin (39 mmol) was
added, followed immediately by the benzylbromide (195 mmol).
Stirring was continued for 24 h, after which the mixture was
poured into hydrochloric acid (1M, 400 cm3) and extracted with
dichloromethane (3 ꢂ 400 cm3). The combined organic extracts
were washed with distilled water (5 ꢂ 500 cm3), dried (MgSO4) and
concentrated in vacuo. The residue was a viscous mixture of 14a,
14b and impurities. The mixture was purified using column chro-
matography (DCM as eluent) to give two major fractions. The first
fraction was a viscous oil which solidified on trituration with
diethylether (CAUTION: Extremely flammable. May form explosive
peroxides. Harmful if swallowed). Recrystallisation twice from
ethylacetate to give 14a. (2.9 g, 8.37 mmol, yield: 22%). m.p.
202e205 ꢀC; (Found: C, 73.0; H, 4.1; C21H14O5 requires C, 72.8; H,
4.1%); nmax (solid)/cmꢁ1 (CeH) 3065e2954, (eOH) 3000e2600,
(C]O) 1674, (CeO) 1274; 1H nmr, dH (300 MHz, (CD3)2SO); 13.45
(1H, s, C(-4)eOH), 13.21 (1H, s, C(-1)eOH), 8.27 (2H, m, H-5,8), 7.97
(2H, m, H-6,7), 7.52e7.39 (5H, m, H-16-21), 7.12 (1H, s, H-3), 5.34
(2H, s, H-15); 13C {1H} nmr, dC (75 MHz, CDCl3); 186.3 (C]O, C-9),
183.5 (C]O, C-10), 159.7 (quat. Ar.C, C-4), 155.7 (quat. Ar.C, C-2),
149.7 (quat. Ar.C, C-1), 133.9 (quat. Ar.C, C-16), 133.6 (Ar.C, C-6),
133.1 (quat. Ar.C, C-12), 132.8 (Ar.C, C-7), 132.3 (quat. Ar.C, C-11),
127.9 (2 ArC), 127.6 (2 ArC), 126.5 (2 ArC), 126.0 (Ar.C, C-5), 125.9
(Ar.C, C-8),111.7 (quat. Ar.C, C-13),107.4 (Ar.C, C-3),105.4 (quat. Ar.C,
C-14), 70.3 (eOeCH2ePh, C-15); m/z (ESI) 369 (100%, MNaþ); UV/
vis lmax (CH3COCH3) 480 nm.
4.4. Preparation of dye dispersions
Both the parent dyes (alizarin and purpurin) and derivatives
were insoluble in water under the pH required for the dyeing of
these fibres (pH 4.5e5.0). Consequently, the addition of
a dispersing agent (surfactant; Borresperse NA) was required to
produce a dispersion of the dye in water for dyeing. Each dye
compound was ground into a fine powder by hand using a mortar
and pestle. A 100 cm3 jar was filled with 6 mm diameter steel ball
bearings to one third of its height and 1 g of Borresperse NA and 1 g
of dye were added. Distilled water was added until the balls were
just below the surface. The jar was placed in a milling apparatus for
three days, where the jar was rolled; at the end of the milling
process the dispersed colorant was washed from the jar with
50 cm3 of distilled water into a 100 cm3 volumetric flask which was
then filled to 100 cm3.
A second fraction was obtained from the column, and was dis-
solved in dichloromethane (100 cm3) and washed with sodium
hydroxide (1M, 20 cm3). Evaporation of the dichloromethane
solution gave a solid, which was further dried in a high vacuum to
give 14b: (0.9 g, 2.06 mmol, yield: 5%). m.p. 174e176 ꢀC; (Found: C,
77.0; H, 4.5; C28H20O5 requires C, 77.1; H, 4.6%); nmax (solid)/cmꢁ1
(CeH) 3061e2959, (eOH) 3000e2600, (C]O) 1671, (CeO) 1270;
1H nmr, dH (300 MHz, (CD3)2SO); 13.57 (1H, s, C(-1)eOH), 8.25 (2H,
m, H-5,8), 7.95 (2H, m, H-6,7), 7.51e7.29 (10H, m, H-17-21,24-28)
7.13 (1H, s, H-3), 5.32 (2H, s, H-15), 4.98 (2H, s, H-22); 13C {1H} nmr,
dC (75 MHz, CDCl3); 187.0 (C]O, C-9), 182.0 (C]O, C-10), 162.6
(quat. Ar.C, C-4), 161.1 (quat. Ar.C, C-2), 143.8 (quat. Ar.C, C-1), 137.1
(quat. Ar.C, C-16), 135.1 (quat. Ar.C, C-22), 135.0 (quat. Ar.C, C-12),
134.2 (Ar.C, C-6), 133.6 (Ar.C, C-7), 132.9 (quat. Ar.C, C-11),
128.9e126.4 (10 ArC, C-17-21,24-28), 106.9 (ArC, C-3), 75.2
(eOeCH2ePh, C-15), 71.3 (eOeCH2ePh, C-15); m/z (ESI) 459 (100%,
MNaþ); UV/vis lmax (CH3COCH3) 429 nm.
Methyl-4-(9,10-dihydro-1,4-dihydroxy-9,10-dioxoanthracen-
3-yloxy)butanoate (15a). Powdered potassium hydroxide
(160 mmol) was added to DMSO (80 cm3) at 37 ꢀC. After stirring for
5 min, purpurin (40 mmol) was added, followed immediately by
methyl-4-bromobutyrate (100 mmol). Stirring was continued for
72 h, after which time more methyl-4-bromobutyrate (100 mmol)
and potassium hydroxide (160 mmol) was added. After 4 days the
mixture was poured into hydrochloric acid (1M, 400 cm3) and
extracted with dichloromethane (3 ꢂ 400 cm3). The combined
4.5. Pre-treatment of fabrics
Prior to dyeing fabric samples (5 g) were scoured using 2 g dm-3
sodium carbonate (CAUTION: Irritating to eyes) and 1 g dmꢁ3
Kieralon MFB using a 20:1 liquor ratio at 60 ꢀC for 15 min. Samples
were scoured in stainless steel, sealed dye tubes in a laboratory-
scale Roaches Pyrotec 2000 dyeing machine. At the end of the
treatment, the samples were rinsed with water and dried in air.
4.6. Dyeing
Scoured fabric samples (5 g) were dyed at a concentration of 2%
on mass of fibre (omf) using a liquor:fibre ratio (LR) of 10:1 liquor
ratio. Dyeing assistants added were 1 g dmꢁ3 Levagal DLP and
2 g dmꢁ3 Ludigol AR. The pH was adjusted to 4.5e5.0 using acetic
acid/sodium acetate buffer. Samples were dyed in stainless steel,
sealed dye tubes in a laboratory-scale Roaches Pyrotec 2000 dyeing
machine. The dyebath was heated steadily (2 ꢀC minꢁ1) until the
dyeing temperature was achieved (PET, 130 ꢀC; PLA 115 ꢀC), then
held at that temperature for 45 min. After dyeing, the dyebaths
were cooled and the residues retained for analysis; dyed samples
were rinsed with water and left to dry in air under ambient
conditions.

16
I. Drivas et al. / Dyes and Pigments 88 (2011) 7e17
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Reduction clearing was conducted to remove any dye that had
not diffused into the fibres and was deposited on the surface. Dyed
fabric samples were treated with 1.5 g dmꢁ3 sodium carbonate and
2.0 g dmꢁ3 sodium hydrosulfite using a LR of 20:1 in stainless steel,
sealed dye tubes in a laboratory-scale Roaches Pyrotec 2000 dyeing
machine. The dyebath was heated rapidly to 60 ꢀC then held at that
temperature for 15 min. After treatment, the samples were rinsed
with water and left to dry in air under ambient conditions.
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4.8. Colour measurement
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Spectral reflectance factors (taken between 400 and 700 nm
wavelengths in 20-nm increments) of the samples were measured
using a Datacolor Spectraflash SF600 reflectance spectrophotometer
(Datacolor International Ltd, UK) interfaced to a computer. Each fabric
sample was folded twice to give a total of four layers. Four different
areas of each sample were measured and the average colour value
was automatically calculated and saved by the computer. CIELAB
values (under illuminant D65 using the 10ꢀ standard observer) and
K/S values (representing absorption) were automatically calculated
from reflectance factors R at the desired wavelength (usually lmax) by
the software using the KubelkaeMunk equation (1).
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K
S
ð1 ꢁ RlÞ2
2Rl
¼
(1)
of
Coordination
Chemistry
2004;30(5):365e70.
doi:10.1023/B:
RUCO.0000026008.98495.51.
4.9. Wash fastness testing
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Dyed samples were subjected to ISO 105:C06/C2S wash fastness
test [39] using SDC Multifibre as adjacent fabric in a laboratory-scale
Roaches Washtec-P wash fastness testing machine. Dyed samples
were assessed using grey scales according to the ISO 105:A02 [39]
for assessing change in colour. Rating was given using a grey scale
ranging between 1(worst) and 5 (best) with half-points in between.
[22] Blackburn RS, Zhao X, Farrington DW, Johnson L. Effect of D-isomer concen-
tration on the coloration properties of poly(lactic acid). Dyes and Pigments
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4.10. Light fastness testing
[23] McIntyre JE. In: Hawkyard C, editor. In synthetic fibre dyeing. Cambridge:
Woodhead Publishing; 2004.
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onto PLA fiber. Journal of Colloid and Interface Science 2007;310(1):106e11.
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of phenols, alcohols, amides and acids. Tetrahedron 1979;35(18):2169e73.
doi:10.1016/0040-4020(79)87035-0.
Dyed samples were subjected to ISO 105:B02 [39] light fastness
test (Method 2) using a Xenotest Alpha LM apparatus using blue
wool standards as reference. Blue wool standards fade on a scale of
1 (worst) to 8 (best) and dyed samples were assessed against these
references.
[26] Kar P, Suresh M, Kumar DK, Jose DA, Ganguly B, Das A. Preferential binding of
the magnesium ion by anthraquinone based chromogenic receptors. Poly-
hedron 2007;26(6):1317e22. doi:10.1016/j.poly.2006.10.051.
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phenolic and enolic functions with lithium carbonate/alkyl halide. Synthetic
Communications 1988;18(12):1379e84. doi:10.1080/00397918808078806.
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alizarin and purpurin by surface-enhanced resonance Raman spectroscopy
(SERRS) using silver colloids. Journal of Raman Spectroscopy 2004;35
(8e9):800e7. doi:10.1002/jrs.1199.
Acknowledgments
The authors would like to thank The State Scholarships Foun-
dation of Greece (I. K. Y.), Onassis Foundation and EPSRC for the
provision of financial support to Mr. Drivas to allow him to conduct
his PhD studies.
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