Switchable (pH-driven) aqueous biphasic systems formed by ionic liquids as integrated production-separation platforms

Article abstract of DOI:10.1039/c7gc00157f

The ability to induce reversible transitions between homogeneous solutions and biphasic systems is of paramount relevance in separation processes. In this context, pH-triggered aqueous biphasic systems composed of ionic liquids and salts are here disclosed as switchable mono/biphasic systems, and their potential application is further demonstrated through an integrated approach comprising both the production and separation of hydroxymethylfurfural from fructose.

Full text of DOI:10.1039/c7gc00157f

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: A. M. Ferreira, A. F.
Cláudio, M. Valega, F. Domingues, A. Silvestre, R. D. Rogers, J. A. P. Coutinho and M. G. Freire, Green
Chem., 2017, DOI: 10.1039/C7GC00157F.
Volume 18 Number
7
7
April 2016 Pages 1821–2242
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Please do not adjust margins
Green Chemistry
Page 1 of 6
View Article Online
DOI: 10.1039/C7GC00157F
Journal Name
COMMUNICATION
Switchable (pH-Driven) Aqueous Biphasic Systems formed by Ionic
Liquids as Integrated Production-Separation Platforms
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
b
c
Ana M. Ferreira, Ana Filipa M. Cláudio, Mónica Válega, Fernando M. J. Domingues, Armando
a
d
a
a
J.D. Silvestre, Robin D. Rogers, João A. P. Coutinho and Mara G. Freire*
DOI: 10.1039/x0xx00000x
www.rsc.org/
9
-11
The ability to induce reversible transitions between homogeneous systems formed by ILs.
It was demonstrated that phase
solutions and biphasic systems is of paramount relevance in transitions in IL-containing mixtures can be induced by a
1
2-16
separation processes. In this context, pH-triggered aqueous temperature-driven phenomenon or by CO
2 2
/N flushing.
1
7-19
biphasic systems composed of ionic liquids and salts are here Both upper critical solution temperature (UCST)
0-22
and lower
phase behaviours have
2
disclosed as switchable mono/biphasic systems, and their critical solution temperature (LCST)
potential application further demonstrated through an intregated been reported for IL-solvent mixtures, whereas these
aproach comprising both the production and separation of temperature-dependent phase transitions have shown to be
2
advantageous in the selective separation of proteins and
3
hydroxymethylfurfural from fructose.
2
4
metals. Reversible liquid-liquid systems have been also
gathered with molecular solvents that react with CO forming
Liquid-liquid extraction processes are of technological
simplicity and of low cost, and are frequently a preferred
1
strategy in separation processes engineering. Nevertheless,
2
salts and/or ILs, and applied in the separation of aliphatic and
1
2-14
aromatic amines
and in the synthesis/separation of gold
1
Au) porous films. However, common UCST and LCST
5
the use of molecular and volatile organic solvents in separation
routes presents major drawbacks due to their high volatility
2
and recurrent toxicity. In this context, and in addition to their
(
behaviours in systems involving ILs typically occur at
temperatures well above room temperature and a high energy
input is required to trigger their phase switch, while the
CO /N -dependent reversibility pattern requires the use of
tailoring ability, ionic liquids (ILs) represent a viable alternative
3
as a result of their non-volatile nature at ambient conditions.
,
2
2
4
The research in liquid–liquid extractions from aqueous media
using ILs has been focused on two main approaches: (i) the
direct use of non-water miscible hydrophobic ILs; and (ii) the
use of aqueous biphasic systems (ABS) composed of ILs and
organic/inorganic salts. Within the two types of systems, ABS
constitute a “greener” and more benign option since they are
mainly composed of water (up to 70 wt% in the overall
specific equipment. Furthermore, these systems are usually
composed of an IL-rich phase (typically with hydrophobic
characteristics) and a more hydrophilic molecular-solvent-rich
1
8, 20-24
phase.
These systems are thus restricted in polarity
differences amongst the coexisting phases, hindering
improved extraction and selectivity performances to be
obtained when dealing with the separation/fractionation of
complex matrices. In this line, IL-based ABS can be seen as
promising options, although the investigation on their use as
reversible systems lagged behind. To the best of our
5
-8
system). Moreover, a more delicate tuning of the phases
polarities can be achieved with IL-based ABS, resulting in
systems that usually allow the complete extraction and
5
-8
purification of a wide variety of compounds.
knowledge,
only
temperature-dependent
reversible
2
5
More recently, there has been a large interest on the
use/applications of dynamic and reversible mono/biphasic
behaviours of IL-based ABS have been reported. Contrarily to
most IL-based ABS, which display a weak dependence on
2
5
temperature, it was recently found that ABS formed by protic
ILs and polymers are highly temperature dependent, allowing
therefore to trigger reversible phase separations by small
changes in temperature.
Given the potential of applications of switchable (aqueous-
rich) biphasic systems discussed above, in this work we
demonstrate the reversibility of IL-based ABS attained by a pH-
driven phenomenon and their use as integrated platforms,
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 6
View Article Online
DOI: 10.1039/C7GC00157F
COMMUNICATION
Journal Name
comprising both the production and separation of 5- formation of a two-phase system at given conditions, while
hydroxymethylfurfural (HMF) from fructose.
mixture compositions below the same curve result in the
formation of a homogeneous solution (no phase-separation).
We firstly determined the liquid-liquid ternary phase diagrams
at different pH values of ABS composed of ILs
/C + water. These were determined at pH values
ranging between 5 and 9 for the following hydrophilic ILs:
+
K
3
C
6
H
5
O
7
6 8 7
H O
[C
4
C
1
im]Cl, [C
4 1 1 4 1 4 1 4 1
C C im]Cl, [C C pip]Cl, [C C py]Cl, [C C im]Br and
[
P4444]Cl. The definition of the ILs acronyms is provided as a
footnote‡; details on their purity are given in the ESI†. Further
details on the experimental procedure adopted are provided in
the ESI†.
The ternary phase diagrams at 25 °C for the ABS composed of
[
P4444]Cl at different pH values are illustrated in Fig. 2. The
depicted ABS phase diagrams at the most acidic pH values also
denote the limit in compositions and pH values for which ABS
no longer form. The experimental weight fraction data, as well
as the representation of the phase diagrams for the remaining
ILs, are given in the ESI†. All the phase diagrams were further
characterized by the determination of several tie-lines to infer
on the phases compositions for given mixture compositions
Fig. 1. Ternary phase diagrams of an IL-based ABS at 25 °C, at pH ≈9 (▲) and pH ≈5 (cf. the ESI†). In general, and for all ILs, there is a decrease on
(
ꢀ). In all the investigated ABS, the top phase corresponds to the IL-rich phase while
the ability for ABS formation with the pH decrease - the higher
the pH of the aqueous medium the larger is the biphasic
region, and the lower the IL/salt amounts required to induce
phase separation. Given that ILs with no speciation capability
have been chosen, the observed dependency of the ABS
formation on the pH is related to the speciation performance
of potassium citrate. As discussed before, at pH values lower
than 3.05 and 4.07, the non-charged citric acid and
monovalent dihydrogencitrate anion are, respectively, the
prevalent species, and none of these species is able to form
ABS with the ILs investigated. At pH values above 4.67 and
the bottom phase is mainly composed of salt and water.
Aiming at evaluating the possibility of moving from
monophasic to biphasic regimes (and vice-versa) by a proper
tailoring of the pH of the aqueous media, ABS formed by a
wide range of chloride-based ILs and potassium citrate were
investigated. ILs with no speciation capability were chosen,
and as such, the pH-triggered reversible phenomenon is a
result of the salt (potassium citrate) speciation as a function of
the pH. Citric acid presents 4 pK values, namely 3.05, 4.67,
a
2
.39 and 13.92. The speciation curves of citric acid are
6
5
5
.39 there is the main presence of the divalent and trivalent
depicted in the ESI†. At pH values lower than 3.05, the non-
charged citric acid is the dominant species present, whereas at
pH values above 3.07, 4.67 and 5.39, there is the prevalence of
charged hydrogencitrate and citrate anions, respectively. IL-
based ABS are only formed at pH values higher than 5,
meaning that only the divalent and trivalent citrate-based
anions induce phase separation. This behaviour is in
the
monovalent,
divalent
and
trivalent
charged
dihydrogencitrate, hydrogencitrate and citrate anions,
respectively. All these citrate-based species can be ranked
6
within the Hofmeister series, in which higher charge density
6
agreement with the Hofmeister series since higher charge
density and higher charge valence anions are stronger salting-
out species able to induce the salting-out of the IL, further
resulting in the creation of IL-based ABS.
and higher charge valence anions are better hydrated and
stronger salting-out species, being thus more favourable to the
creation of IL-based ABS. In fact, previous works have been
published on the pH effect towards the formation of IL-based
At a fixed pH, the IL ability to form ABS follows the order:
[
[
P4444]Cl > [C C im]Br > [C C py]Cl ≈ [C C pip]Cl > [C C C im]Cl ≈
4 1 4 1 4 1 4 1 1
2
7-29
4 1
C C im]Cl (cf. the ESI† with all the phase diagrams). More
ABS,
although no investigations on their reversible
hydrophobic ILs, resulting either from cations with longer and
more aliphatic moieties or from anions of lower hydrogen-
behaviour have been carried out hitherto. To be able to
change the pH in the investigated ABS and to trigger the phase
transition while avoiding the introduction of new species into
3
1, 32
bond basicity
, are more capable of forming ABS, i.e. are
able to form two-phase systems at lower pH values or require
lower amounts of the phase-forming components for phase
separation. Examples of this are seen for [P4444]Cl and
6 8 7
the overall system, citric acid (C H O ) and potassium
hydroxide (KOH) were used. The pair potassium citrate/citric
acid also was selected due to their biodegradable and non-
3
0
[C
4
mim]Br, the only two ILs that form ABS at pH 5. On the
toxic characteristics. Fig. 1 sketches the principle of the
reversible process under investigation, where the transitions
between the monophasic and the biphasic regimes could be
attained by the alternate addition of an acidic or an alkaline
species to the overall aqueous system. For mixture
compositions above each solubility curve there is the
4
C
1
4 1 1
other hand, ILs such as [C im]Cl and [C C C im]Cl, which are
amongst the most hydrophilic ILs investigated, do not form
ABS even at a pH of 6, being 7 the minimum pH value required
for ABS formation with these ILs. This pattern also mirrors the
5
-8
salting-out effect of the citrate-based salt over the IL.
A
2
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 6
Pleas Ge rdeo e nn o Ct ah de j mu si ts mt r ya rgins
View Article Online
DOI: 10.1039/C7GC00157F
Journal Name
COMMUNICATION
summary of the overall results according to the ability of each more specific equipment. Their reversibility is however a major
IL to form ABS at all studied pH values is given in the ESI†.
advantage in liquid-liquid extractions to attain selective
separations, and as demonstrated hereinafter.
We investigated the possibility of using the proposed systems
for the production of hydroxymethylfurfural (HMF) through
fructose dehydration at acidic pH, and then to proceed with an
integrated separation step of HMF from the unreacted
precursor by an increase in the pH and consequent formation
of two-phase systems. The dehydration of carbohydrates (e.g.
cellulose, glucose, fructose, sucrose, inulin, and cellobiose) to
produce HMF has attracted large attention in the past few
3
3, 34
years.
derived building block relevant in bio-based industries.
current applications of HMF are widespread and comprise the
In fact, HMF is nowadays considered a key biomass-
3
3, 35
The
3
6
37
production of solvents , biofuels (dimethylfuran), polymeric
materials (mainly based on its 2,5-furandicarboxylic acid
3
8
39
derivative), fine chemicals , among others. Recently, a
short-time synthesis of the active pharmaceutical ingredient
4
0
ranitidine (Zantac) also was reported making use of HMF.
Typically, HMF is produced from fructose via a dehydration
reaction, generally catalysed by acids (pH values ranging
4
1
between 1.5 and 3). However, high temperatures (>200 °C),
reduced pressure and long reaction times are usually
Fig. 2. Phase diagrams of ABS composed of [P4444]Cl + water + K
(▲), pH ≈ 8 (), pH ≈ 7 (ꢀ), pH ≈ 6 (ꢁ) and pH ≈ 5 (▬).
3 6 5 7 6 8 7
C H O /C H O at pH ≈
4
1
9
required. More recently, IL-acid mixtures or acidic ILs have
been used for sugars dehydration and production of HMF in
high yields, obtained at lower temperatures (<120 °C) and
After establishing the ternary phase diagrams, which describe
the mixture compositions and pH values for which the liquid-
liquid demixing occurs, the reversible IL-based ABS behaviour
was further appraised by the alternate addition of citric acid
and potassium hydroxide. For this purpose, an initial ternary
42
within short reaction times. Although good results using ILs
for the fructose dehydration have been described, the
development of
a cost-effective, integrated and more
sustainable production-separation process is still in crucial
demand. In this line, we propose herein the discussed
switchable ABS as an integrated and more benign platform for
the production and separation of HMF.
3 6 5 7
mixture at the biphasic region (IL at 25 wt% + K C H O at 35
wt% + water at 40 wt%) was prepared and allowed for phase
separation at 25 °C. At this initial mixture composition the pH
values of the aqueous media of all IL-containing systems are
ca. 9. An aqueous solution of citric acid at 50 wt% was added
dropwise, under constant agitation, until the mixture became
homogeneous (monophasic). Then, an aqueous solution of
potassium hydroxide at 50 wt% was added, under agitation, to
recover the initial pH value of 9 and the biphasic system.
During these manipulations the pH of the aqueous solutions
was experimentally controlled. Fig. 1 depicts the procedure
carried out to attain the reversible process under
investigation. It should be remarked that the differences in the
phases’ compositions are indeed negligible since a small
amount of each aqueous solution (± 0.6 wt%) is enough to
trigger the phase transition. The pH-driven reversibility was
experimentally confirmed with all the ILs investigated, at least
The production of HMF was carried out through fructose
dehydration in acidic medium (pH ca. 1.5), at 80 °C for 80 min,
in the IL-based ABS monophasic regions. After reaction, an
aqueous solution of KOH was added to stop the reaction and
to move the system into the biphasic region by a pH increase –
Fig. 1. The creation of two-phase systems is intended for the
selective separation (migration for opposite phases) of HMF
and unreacted fructose. Further experimental details are given
in the ESI†.
Fig. 3 depicts the results on the production of HMF in citric
acid aqueous solutions at the monophasic region
(corresponding to a mixture composition of 40 wt% of IL + 30
wt% of citric acid). The respective reactions were also carried
out in the absence of ILs, as well as in the absence of citric
acid, for comparison purposes. As shown, the use of an acidic
medium is required for the production of HMF through the
dehydration of fructose – when no acid was used a maximum
3
times, with no significant changes in the phases’
composition.
In summary, it is possible to prepare reversible IL-based ABS
playing around with the speciation behaviour of the organic
salt. This phase reversibility takes place at room temperature
.
-1
yield of 0.00281 g L of HMF was obtained. On the other hand,
.
-1
without IL, a maximum yield of HMF of 2.28 g L was found.
However, when ILs are used in acidic medium, HMF yields
(25 °C) and is achieved with cheap compounds already present
in the original mixture and with no need of sophisticated
equipment. Hence, IL-based ABS can be envisaged as potential
alternatives to the more complex reversible systems that
require additional energy inputs or the addition of gases and
. -1
ranging between 4.61and 6.37 g L have been observed,
supporting the need of the presence of both the IL and the
acidic medium to maximise the HMF production yield. These
results are consistent with previous studies describing the
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 6
View Article Online
DOI: 10.1039/C7GC00157F
COMMUNICATION
Journal Name
4
4, 45
requirement of the addition of ILs and acid catalysts to obtain compared to those reported in the literature.
2, 43
Partition
4
high HMF yields.
coefficients of HMF ranging between 0.5 and 2.0 have been
reported, with biphasic systems composed of water and
butanol,
methyl-iso-butylketone
(MIBK),
toluene,
dichloromethane or other mixtures of organic volatile
45
4
4
solvents. More recently, Blumenthal et al. suggested
biphasic systems formed by water and -propylphenol or
o
o-
isopropylphenol for the separation of HMF from the aqueous
reaction medium, in which an increase up to five times in the
partition coefficients was reported when compared to the
4
4
previously applied solvents.
The partition coefficients
obtained in the current work range between 9 and 17 (cf. the
ESI† with detailed data). Our results on the separation of HMF
are thus better than the most promising ones reported
hitherto in the literature. Moreover, with IL-based ABS, the use
of volatile and often toxic organic solvents is avoided; instead,
aqueous-rich media are used. Additionally, an integrated
methodology is here proposed for the separation of HMF by
Fig. 3 Production of HMF through fructose dehydration in presence (or not) of citric the creation of two-phase systems only through a pH increase,
acid and ILs, at 80ºC for 80 min.
representing thus a step forward on the development of more
sustainable production-separation processes.
After the HMF production, the reaction was stopped and the
two-phase systems simultaneously formed by the addition of
aqueous KOH (up to pH 7). Fig. 4 depicts the results regarding
the selective separation of HMF from fructose using IL-based
ABS. The results are given in extraction efficiencies of both
HMF and fructose (EEHMF% and EEFructose%) for opposite phases.
The extraction efficiencies are defined as the percentage ratio
between the total weight of HMF or fructose in one of the
phases to that in the total mixture (detailed results are given in
the ESI†). The results in partition coefficients values, defined as
the concentration of HMF between the IL-rich phase and the
salt-rich phase, as well as selectivity of the systems to HMF,
also are provided in the ESI†.
In all investigated systems, HMF preferentially migrates to the
IL-rich phase while fructose is enriched in the opposite layer,
allowing thus the separation of the two compounds.
Remarkable extraction efficiencies of HMF to the IL-rich phase
ranging between 92 and 96%, and of fructose to the salt-rich
phase ranging between 45 and 59%, were obtained in a single-
step. This migration for opposite phases and selective
separation results from the higher affinity of HMF to more
Fig. 4 Selective separation of HMF from fructose that did not react through the addition
of KOH and formation of ABS.
hydrophobic (IL-rich) phases in contrast to the higher affinity In summary, the results here reported demonstrate that pH-
of fructose to more hydrophilic (salt-rich) phases, as reflected driven reversible ABS composed of ILs can be easily prepared
by their octanol-water partition coefficients (Kow) (log(Kow) of by playing around with the speciation of at least one of the
2
6
HMF = -0.10; log(Kow) of fructose = -2.76). Although the phase-forming components. Furthermore, these systems show
almost complete extraction of HMF to the IL-rich phase was potential to become remarkable integrated platforms, in which
achieved in a single-step in all studied systems, the extraction reaction and separation steps can be carried out sequentially
of fructose to the opposite phase seems to be more by taking advantage of their switchable behaviour, as
dependent on the nature of the IL employed; the selective demonstrated here with the HMF production and separation
separation of HMF and fructose increases in the following from fructose as the reaction precursor. In addition to the
order: [C
the IL hydrophobic nature as described by their ternary phase certainly tailored to fit the requirements of other separation
diagrams at a fixed pH shown in the ESI†.
processes. Additional reactions or separation processes that
4 4 4
mim]Cl < [C mpy]Cl < [C mpip]Cl. This trend follows example shown herein, reversible IL-based ABS can be
In what concerns the extraction performance and selectivity of occur at other pH values can indeed be carried out with the
the systems to HMF (ranging between 14 and 48; detailed data proposed systems. They are only constrained by the minimum
shown in the ESI†), our results are quite promising when pH value at which they are able to form two phases to proceed
4
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 6
Pleas Ge rdeo e nn o Ct ah de j mu si ts mt r ya rgins
View Article Online
DOI: 10.1039/C7GC00157F
Journal Name
COMMUNICATION
with the separation step (the pH range in which all systems are 17. M. G. Freire, C. M. S. S. Neves, K. Shimizu, C. E. S. Bernardes,
I. M. Marrucho, J. A. P. Coutinho, J. N. C. Lopes and L. P. N.
able to form ABS is shown in the ESI†). To this end, it is only
Rebelo, J. Phys. Chem. B, 2010, 114, 15925-15934.
1
required to choose an appropriate mixture point in each phase
8. P. Nockemann, B. Thijs, S. Pittois, J. Thoen, C. Glorieux, K.
Van Hecke, L. Van Meervelt, B. Kirchner and K. Binnemans, J.
Phys. Chem. B, 2006, 110, 20978-20992.
diagram to move between the monophasic and biphasic
regimes.
19. Y. Lu, G. Yu, W.-J. Wang, Q. Ren, B.-G. Li and S. Zhu,
Macromolecules, 2015, 48, 915-924.
This work was developed in the scope of the project CICECO-
Aveiro Institute of Materials (Ref. FCT UID /CTM /50011/2013)
and QOPNA research unit (FCT UID/QUI/00062/2013),
2
9
2
0. S. Saita, Y. Kohno and H. Ohno, Chem. Commun., 2013, 49,
3-95.
1. J. Lachwa, J. Szydlowski, A. Makowska, K. R. Seddon, J. M. S.
financed by national funds through the FCT/MEC and when S. Esperanca, H. J. R. Guedes and L. P. N. Rebelo, Green Chem.,
applicable co-financed by FEDER under the PT2020 Partnership 2006, , 262-267.
8
2
1
2
2. K. Fukumoto and H. Ohno, Angew. Chem. Int. Ed., 2007, 46
852-1855.
3. Y. Kohno, S. Saita, K. Murata, N. Nakamura and H. Ohno,
,
Agreement. A. M. Ferreira acknowledges FCT for the PhD grant
SFRH/BD/92200/2013. This research was undertaken, in part,
thanks to funding from the Canada Excellence Research Chairs
Polym. Chem., 2011, 2, 862-867.
Program. The research leading to reported results has received 24. Z.-L. Xie and A. Taubert, ChemPhysChem, 2011, 12, 364-368.
funding from the European Research Council under the 25. H. Passos, A. Luis, J. A. P. Coutinho and M. G. Freire, Sci. Rep.,
2
2
016,
6. Chemspider, The free chemical database,
6, 7.
European Union’s Seventh Framework Programme (FP7/2007-
013)/ERC grant agreement no. 337753.
2
http://www.chemspider.com, (accessed October 2016).
7. M. T. Zafarani-Moattar and S. Hamzehzadeh, Fluid Phase
Equilib., 2011, 304, 110-120.
2
Notes and references
28. S. Li, C. He, H. Liu, K. Li and F. Liu, J. Chromatogr. B, 2005,
8
26, 58-62.
‡
ILs used: 1-butyl-3-methylimidazolium chloride, [C
dimethylimidazolium chloride, [C im]Cl; 1-butyl-1-methylpiperidinium chloride,
pip]Cl; 1-butyl-1-methylpyridinium chloride, [C
methylimidazolium bromide, [C
im]Br; tetrabutylphosphonium chloride, [P4444]Cl. 30. J. S. L. Hong-Shum, in Food Additives Data Book, ed. B. S. Ltd,
4 1
C im]Cl; 1-butyl-2,3-
2
9. K. A. Kurnia, M. G. Freire and J. A. P. Coutinho, J. Phys. Chem.
4 1 1
C C
[C
4
C
1
4 1
C
py]Cl; 1-butyl-3- B, 2014, 118, 297-308.
4 1
C
Blackwell Science Ltd, Wiley-Blackwell, 2003, DOI:
10.1002/9780470995327.fmatter, pp. i-xix.
31. A. F. M. Cláudio, A. M. Ferreira, S. Shahriari, M. G. Freire and
J. A. P. Coutinho, J. Phys. Chem. B, 2011, 115, 11145-11153.
32. A. F. M. Cláudio, L. Swift, J. P. Hallett, T. Welton, J. A. P.
Coutinho and M. G. Freire, Phys. Chem. Chem. Phys., 2014, 16
6593-6601.
33. A. A. Rosatella, S. P. Simeonov, R. F. M. Frade and C. A. M.
Afonso, Green Chem., 2011, 13, 754-793.
34. J. Song, B. Zhang, J. Shi, H. Fan, J. Ma, Y. Yang and B. Han,
1
. F. W. Fifield and D. Kealey, Principles and Practice of
Analytical Chemistry, 5th edn., 2000.
. J. Rydberg, M. Cox, C. Musikas and G. R. Choppin, Principles
2
and practices of solvent extraction. Second Edition, Revised and
Expanded, 2nd edn., 2004.
3
2
4
Lopes, L. P. N. Rebelo, J. W. Magee, K. R. Seddon and J. A.
Widegren, Nature, 2006, 439, 831-834.
5
R. P. Swatloski, J. D. Holbrey and R. D. Rogers, J. Am. Chem. Soc.,
,
. R. D. Rogers and K. R. Seddon, Science (New York, N.Y.),
003, 302, 792-793.
. M. J. Earle, J. M. S. S. Esperanca, M. A. Gilea, J. N. Canongia
RSC Adv., 2013, 3, 20085-20090.
35. R.-J. van Putten, J. C. van der Waal, E. de Jong, C. B.
. K. E. Gutowski, G. A. Broker, H. D. Willauer, J. G. Huddleston,
Rasrendra, H. J. Heeres and J. G. de Vries, Chem. Rev., 2013, 113
1499-1597.
36. S. K. M. Konduri, S. K. Thoota, C. Javvadi, P. R. Muddasani, K.
S. B. R. Adibhatla and V. C. Nannapaneni, WO/2015/155784,
2015.
,
2
6
003, 125, 6632-6633.
. M. G. Freire, A. F. M. Cláudio, J. M. M. Araújo, J. A. P.
Coutinho, I. M. Marrucho, J. N. C. Lopes and L. P. N. Rebelo,
Chem. Soc. Rev., 2012, 41, 4966-4995.
7. M. G. Freire, C. L. S. Louros, L. P. N. Rebelo and J. A. P.
Coutinho, Green Chem., 2011, 13, 1536-1545.
37. Y. Roman-Leshkov, C. J. Barrett, Z. Y. Liu and J. A. Dumesic,
Nature, 2007, 447, 982-985.
8
. M. G. Freire, C. M. S. S. Neves, I. M. Marrucho, J. N. Canongia 38. A. F. Sousa, C. Vilela, A. C. Fonseca, M. Matos, C. S. R. Freire,
Lopes, L. P. N. Rebelo and J. A. P. Coutinho, Green Chem., 2010,
G.-J. M. Gruter, J. F. J. Coelho and A. J. D. Silvestre, Polym.
Chem., 2015, , 5961-5983.
1
9
7
1
2, 1715-1718.
6
. Y. Kohno and H. Ohno, Chem. Commun., 2012, 48, 7119-
130.
0. P. G. Jessop, S. M. Mercer and D. J. Heldebrant, Energy
39. P. Gupta, S. K. Singh, A. Pathak and B. Kundu, Tetrahedron,
2002, 58, 10469-10474.
40. M. Mascal and S. Dutta, Green Chem., 2011, 13, 3101-3102.
41. F. Salak Asghari and H. Yoshida, Ind. Eng. Chem. Res., 2006,
45, 2163-2173.
42. S. P. Teong, G. Yi and Y. Zhang, Green Chem., 2014, 16, 2015-
2026.
43. C. Sievers, I. Musin, T. Marzialetti, M. B. Olarte, P. K. Agrawal
Environ. Sci., 2012,
1
1
5
, 7240-7253.
1. J. Luo, T. Xin and Y. Wang, New J. Chem., 2013, 37, 269-273.
2. S. Saita, Y. Kohno, N. Nakamura and H. Ohno, Chem.
Commun., 2013, 49, 8988-8990.
1
4
1
2
1
3. Y. Kohno, H. Arai and H. Ohno, Chem. Commun., 2011, 47
772-4774.
,
and C. W. Jones, ChemSusChem, 2009, 2, 665-671.
4. D. Xiong, H. Wang, Z. Li and J. Wang, ChemSusChem, 2012,
255-2261.
5. D. Z. Xiong, G. K. Cui, J. J. Wang, H. Y. Wang, Z. Y. Li, K. S. Yao
5
,
44. C. Fan, H. Guan, H. Zhang, J. Wang, S. Wang and X. Wang,
Biomass Bioenergy, 2011, 35, 2659-2665.
45. L. C. Blumenthal, C. M. Jens, J. Ulbrich, F. Schwering, V.
and S. J. Zhang, Angew. Chem. Int. Ed., 2015, 54, 7265-7269.
Langrehr, T. Turek, U. Kunz, K. Leonhard and R. Palkovits, ACS
16. G. Yu, Y. Lu, X. Liu, W.-J. Wang, Q. Yang, H. Xing, Q. Ren, B.-G. Sustain. Chem. Eng., 2016,
4, 228-235.
Li and S. Zhu, Ind. Eng. Chem. Res., 2014, 53, 16025-16032.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Green Chemistry
Page 6 of 6
View Article Online
DOI: 10.1039/C7GC00157F
pH-driven reversible aqueous biphasic systems are remarkable production-separation platforms and can
be easily prepared by playing around with the speciation of at least one of the phase-forming
components