Upgrading biogenic furans: Blended C10-C12 platform chemicals via lyase-catalyzed carboligations and formation of novel C12 - Choline chloride-based deep-eutectic-solvents

Article abstract of DOI:10.1039/c5gc00342c

Benzaldehyde lyase (BAL) results in an efficient biocatalyst for the umpolung carboligation of furfural, HMF, and mixtures of them, leading to blended C₁₀-C₁₂ platform chemicals. Subsequently, the mixing and gentle heating (<100°C) of the formed hydroxy-ketone with choline chloride leads to the formation of a novel biomass-derived deep-eutectic-solvent.

Full text of DOI:10.1039/c5gc00342c

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Upgrading biogenic furans: blended C10–C12
platform chemicals via lyase-catalyzed
Cite this: DOI: 10.1039/c5gc00342c
carboligations and formation of novel C12 –
choline chloride-based deep-eutectic-solvents†
Received 11th February 2015,
Accepted 2nd March 2015
Joseph Donnelly,a,b Christoph R. Müller,a Lotte Wiermans,a Christopher J. Chuck*c
DOI: 10.1039/c5gc00342c
www.rsc.org/greenchem
and Pablo Domínguez de María*‡a
Benzaldehyde lyase (BAL) results in an efficient biocatalyst for the and diesel fuels, the carbon number must be increased to the
umpolung carboligation of furfural, HMF, and mixtures of them, C10–C18 range. This can be achieved chemically through HMF
leading to blended C10–C12 platform chemicals. Subsequently, the self-condensation – yielding a C12 derivative – or from aldol
mixing and gentle heating (<100 °C) of the formed hydroxy-ketone condensation with additional acetone to access higher carbon
with choline chloride leads to the formation of a novel biomass- range precursors.2–4 Moreover, starting with fractions contain-
derived deep-eutectic-solvent.
ing different proportions of furfural and HMF, blended mix-
tures (C10 to C12) may be achieved. All these compounds can
then be either partially hydrogenated to retain functionality
for additives or fully hydrogenated to yield hydrocarbon fuels.
In this area, a promising but not yet sufficiently explored
option for HMF valorization would be its self-condensation in
umpolung fashion to afford C12 platform chemicals, both
the formed hydroxy-ketone and the subsequently oxidized
diketone.
By looking at the high functionalization of those molecules,
from a chemical perspective a broad range of options can be
anticipated (Scheme 1). HMF is highly reactive, being prone to
self-oligomerization, by-product formation and undesired reac-
tions under severe process conditions. Thus, the set-up of
HMF-based derivatizations operating under mild and efficient
conditions at the same time would become of utmost impor-
tance. To this end, for the self-condensation of HMF, organo-
catalysis – based on NHC carbenes – has been proposed by
several research groups, as a mild technology avoiding product
degradation.5
In this communication, biocatalysis was successfully
assessed for the self-carboligation of HMF for the first time.
The use of enzymes (both free or immobilised) and whole-cells
has gained considerable interest over the past decades, with
an ample range of industrial processes already implemented.6
Compared to other catalytic technologies, apart from the well-
known high selectivities and mild reaction conditions inherent
to enzymes, another important asset is that biocatalysts can be
produced at large scale via fermentation of recombinant
microorganisms.
A key challenge in the production of cellulose-based chemical
intermediates, fuels and novel solvents is the cost-effective
transformation of highly functionalized carbohydrate moieties
into value-added chemicals. One highly promising route is the
production of furan derivatives, such as furfural or 5-hydroxy-
methylfurfural (HMF), from the acid-catalyzed dehydration of
hexoses and pentoses. In particular, HMF is extremely versatile
and has the potential to become a key precursor to produce a
range of chemicals and fuels in a sustainable biorefinery.1 For
example, HMF can be converted into a range of C4 organic
acids suitable for the production of biopolymers by selective
oxidation reactions, whereas stable gasoline blending agents
(such as dimethyl furan) or solvents (THF) can be produced
from decarbonylation and hydrogenation. Moreover, key
pharmaceutical precursors can also be produced by amidation
or esterification reactions, e.g. the etherification of HMF to
yield larger intermediates suitable for retroviral drugs or
polymer precursors. However, to further broaden the appli-
cations, e.g. to access suitable surfactants or precursors to jet
aInstitut für Technische und Makromolekulare Chemie (ITMC), RWTH Aachen
University, Worringerweg 1, 52074 Aachen, Germany
bDoctoral Training Centre in Sustainable Chemical Technologies, Dept. of Chemical
Engineering, University of Bath, Bath, BA2 7AY, UK
cCentre for Sustainable Chemical Technologies, Dept. of Chemical Engineering,
University of Bath, Bath, BA2 7AY, UK. E-mail: c.chuck@bath.ac.uk;
Tel: +44 (0)1225383537
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
c5gc00342c
Thus, once (bio)catalyst design is performed (e.g. via
directed evolution), the requested quantities of the enzyme
can be straightforwardly produced under environmental con-
‡Present address: Sustainable Momentum, SL. Ap. Correos 3517. 35004, Las
Palmas de Gran Canaria, Canary Islands, Spain. Tel.: +34 609565237; E-mail:
dominguez@itmc.rwth-aachen.de, dominguez@sustainable-momentum.net
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Scheme 1 Self-carboligation of HMF in umpolung fashion, produced molecules and some applications thereof.
ditions. Last but not least, once the most appropriate biocata-
lyst has been designed, the use of (immobilized) biocatalysts –
either free enzymes or whole-cells – may decrease process
costs considerably,7 an aspect that will become obviously
crucial in the production of low-added value (bio)commod-
ities, e.g. the aforementioned HMF-based ones.
For the condensation of HMF the use of lyases,8 specifically
thiamine-diphosphate dependent lyases (ThDP-lyases), was
considered. ThDP-Lyases represent a useful group of enzymes
delivering α-hydroxy-ketones by the carboligation of two alde-
hydes. In this group, Benzaldehyde Lyase (BAL) from Pseudo-
monas fluorescens is a remarkable case, from which many
enantio- and diastereo-selective applications including aro-
matic and aliphatic aldehydes as substrates have been reported
over the last few years.8,9 Furthermore, there are some out-
standing examples of lyases in general, and BAL in particular,
catalyzing highly efficient processes with excellent productiv-
ities by means of whole-cell overexpressing systems.10 Thus,
once the proof-of-concept is shown, a subsequent optimization
Fig. 1 BAL-catalyzed condensation of HMF. Conditions: 20 mM HMF,
1 mg mL−1 BAL, 40 mM ThDP, potassium phosphate buffer (pH 8) with
20 vol% DMSO co-solvent at room temperature.
would allow the set-up of a robust biocatalytic process for within a whole cell or when immobilized) – becomes deacti-
HMF condensation.
vated at that time. Furthermore, the oxidized diketone 3 is also
While BAL-catalyzed furoin production (condensation of observed after some time, formed at the cost of 2. This spon-
furfural to afford C10 derivatives) was described years ago,8,9 to taneous oxidation is not observed in the carbene catalysed pro-
our knowledge the use of lyases for (the more challenging) cesses.5 From
a
process development viewpoint, the
HMF condensation has not been assessed to date. In our establishment of immobilized BAL-containing whole-cells
concept, BAL would operate under mild aqueous conditions – should enable the stable production of 2 under continuous
using a cosolvent for substrate solubility – at room temperature processing, thus performing rapidly the downstream proces-
leading to the formation of the hydroxy-ketone 2.§ It may be sing and avoiding further oxidation to the diketone. Neverthe-
expected that some spontaneous oxidation of 2 to afford the less, it must be noted that both products, 2 and 3, may
diketone 3 will be observed. Kinetic results of the BAL-cata- encounter potential applications in many fields.
lyzed process using HMF (20 mM) for proof-of-principle experi-
Once BAL-catalyzed proof-of-concept was successfully
ments are depicted in Fig. 1. Gratifyingly, BAL is able to shown, further experiments with regard to HMF concentration
accept HMF as substrate to afford the hydroxy-ketone 1. More- (20–250 mM) and oxidation patterns were conducted. Reac-
over, under these proof-of-concept and non-optimized con- tions were run for 18 h, and then analyzed (Fig. 2). Interest-
ditions an initial rate of ∼7 g L−1 h−1 of hydroxy-ketone 2 was ingly, BAL is able to perform the carboligation even at higher
observed. The reaction proceeded until a conversion of around HMF loadings of up to 250 mM, leading to a remarkable
70% was reached. This is a slightly reduced yield in compari- accumulation of ∼35 g L−1 of hydroxy-ketone 2, though the
son to the NHC carbene catalysts that have been reported to conversion of HMF was reduced slightly from 75% to 63%.
produce yields in excess of 90% on heating over an hour.5 Pre- The presence of the oxidized diketone 3 is detected at the
sumably BAL – herein used as free enzyme (less stable than higher loadings of HMF yet at significantly lower proportions
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to also form mixtures of furfural-HMF, thus leading to C11
derivatives. Depending on the initial concentration of the
furans, mixtures with Cx averages from C10 to C12 were
achieved.
This was achieved with the BAL retaining higher activity
than on conversion of the HMF alone. Given the broad sub-
strate range acceptance of BAL – also using aliphatic aldehydes
such as acetaldehyde or butyraldehyde, among others, with
the concept herein provided, numerous possibilities for bio-
based product upgrading can be envisaged.
Apart from HMF upgrading to C12 derivatives, within bio-
refineries another important trend is the identification of novel
biomass-derived neoteric solvents that may be further used for
varied applications. For instance, several deep-eutectic-solvents
(DES) formed by the combination of a hydrogen-bond donor
(HBDs, e.g. alcohols, carboxylic acids) and quaternary
ammonium salts, such as choline chloride, have been recently
reported.11 Herein, the obtained HMF-based hydroxy-ketone 2
resulted to be a yellowish solid powder. However, bearing three
–OH groups in its structure, it might become a promising HBD
to form DES. If successful, this approach might lead to the
provision of a series of novel neoteric solvents based on
HMF-C12 derivatives. Thus, the formation of a deep-eutectic-
Fig. 2 Ratio of substrate (HMF), hydroxy-ketone and diketone at 18 h
and at different HMF concentrations. Conditions: variable 20–250 mM
HMF, 1 mg mL−1 BAL, 40 mM ThDP, potassium phosphate buffer (pH 8)
with 20 vol% DMSO co-solvent at room temperature, 18 h.
than in the previous experiment. For example, the diketone
made up only 18% of the product mixture at an HMF loading
of 250 mM compared with near 60% at 30 mM HMF loading.
Presumably, the spontaneous (non-enzymatic) oxidation rate
remains constant in all reaction conditions, whereas the enzy-
matic process undergoes faster at higher concentrations
(before the free enzyme gets deactivated), thus accumulating 2
in the reaction system.
Encouraged by these results, subsequent alternative
aqueous mixtures of furfural and HMF were assessed (as
would be produced from actual biorefineries whereby pretreat-
ment has been conducted). Depending on the initial pro-
portion of both furans, different blended mixtures C10–C12
may be expected. This may open a novel way of valorizing such
mixtures, especially when mixtures with a Cx average range are
needed. Results are depicted in Fig. 3. Gratifyingly, BAL is able
solvent (DES) between
2 as HBD and choline chloride
(1 : 1 mol : mol) was assessed. Successful results are depicted in
Fig. 4, where it is seen that the combination and gentle mixing
(<100 °C) of two solids leads to the formation of a stable
viscous liquid at room temperature.
Fig. 3 BAL-catalyzed carboligation of aqueous mixtures of furfural and
HMF in different proportions, leading to blended C10–C12 compounds.
Conditions: 20 mM total substrate consisting of varying proportions of
HMF and furfural, 1 mg mL−1 BAL, 40 mM ThDP, potassium phosphate
buffer (pH 8) with 20 vol% DMSO co-solvent at room temperature
over 18 h.
Fig. 4 Formation of a DES composed of hydroxy-ketone 2 (1 mol) and
choline chloride (1 mol), to afford a liquid viscous solution at room
temperature.
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1 Biorefineries – Industrial processes and products. Status quo
and future directions, ed. B. Kamm, P. R. Gruber and M.
Kamm, Wiley-VCH, Weinheim, 2010.
Conclusions
In summary, this communication reports successfully for the
first time the use of lyases as biocatalysts for the umpolung
carboligation to upgrade HMF to C12 platform chemicals.
Under non-optimized conditions initial rates of ∼7 g hydroxy-
ketone 2 L−1 h−1 have been observed, with accumulation of the
product up to 35 g L−1. Moreover, aqueous mixtures of furfural
and HMF can be valorized, leading to blended C10–C12 compo-
sition, promising for further hydrogenation to deliver tailored
blends. For these synthetic approaches, the further choice of a
better cosolvent – rather than challenging DMSO –, together
with biocatalyst design and process set-up (e.g. use of immobi-
lized BAL or immobilised whole-cells overexpressing BAL) may
certainly deliver robust reaction conditions for the valorization
of biogenic furans, furfural and HMF. The intrinsic reactivity
makes the biocatalytic approach highly appealing for further
research and development. Furthermore, the formation of
novel DES may lead to novel exciting applications of them as
biomaterials and/or solvents.
We would like to thank Dr Catherine Lyall (Bath, UK) for
her outstanding assistance in the NMR analysis, and grate-
fully acknowledge financial support from DFG training group
1166 “BioNoCo” (“Biocatalysis in Non-conventional Media”).
The authors would also like to extend their thanks to the
EPSRC for partially funding this work through the Doctoral
Training Centre in Sustainable Chemical Technologies (EP/
G03768X/1) and to Roger and Sue Whorrod for their kind
endowment to the University resulting in the Whorrod
Fellowship in Sustainable Chemical Technologies held by
Dr C. Chuck.
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Notes and references
§Benzaldehyde lyase from Pseudomonas fluorescens was cloned and overex-
pressed in E. coli cells, and produced by fermentation.9 After fermentation,
BAL was lyophilized and stored at −20 °C until use. BAL characterization was
performed using benzaldehyde as substrate, and benzoin formation as reaction
test, as reported elsewhere.9 Standard reaction with BAL for HMF carboligation.
To a mixture of 40 mL potassium phosphate buffer (pH 8) with DMSO (20 vol%)
was added ThDP (2 mg, 4.03
×
10−3 mmol) and BAL (40 mg). HMF
(100.89 mg, 0.8 mmol) was then added to the reaction and the vessel stop-
pered. The reaction was allowed to stir for 18 h at room temperature. The reac-
tion was quenched by addition of 80 mL EtOAc and the product extracted into
the same. EtOAc was removed under reduced pressure and the product dried
under high vacuum. Characterisation was effected through NMR spectroscopy.
Standard reaction with BAL with aqueous mixtures of furfural and HMF. To mix-
tures of 20 mL potassium phosphate buffer (pH 8) with DMSO (20 vol%) was
added ThDP (1 mg, 2.02 × 10−3 mmol) and BAL (20 mg). HMF and furfural
were then added in varying molar proportions (75/25, 50/50, 25/75) to make up
0.4 mmol total substrate and the reaction vessels stoppered. The reactions were
allowed to stir for 18 h at room temperature. The reactions were quenched by
addition of 40 mL EtOAc and the products extracted into the same. EtOAc was
removed under reduced pressure and the products dried under high vacuum.
Characterisation was effected through NMR spectroscopy and mass spec-
trometry. DES formation. 100 mg (0.41 mmol) HMF hydroxyl-ketone 2 and
59.0 mg choline chloride (0.41 mmol) (both solids) were stirred in a GC vial in
a molar ratio of 1 : 1 at 60–70 °C for ∼1 hour. When cooled down, the viscous
liquid remained.
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