Bio-based bisfuran: Synthesis, crystal structure, and low molecular weight amorphous polyester

Article abstract of DOI:10.1016/j.tetlet.2014.05.043

Discovery of renewable monomer feedstocks for fabrication of polymeric demand is critical in achieving sustainable materials. In the present work we have synthesized bisfuran diol (BFD) monomer from furfural, over four steps. BFD was examined via X-ray crystallography to understand the molecular arrangement in space, hydrogen bonding, and packing of the molecules. These data were further used to compare BFD with structurally related bisphenol A (BPA), and its known derivatives to predict the potential estrogenic or anti-estrogenic activities in BFD. Further, BFD was reacted with succinic acid to generate polyester material, bisfuran polyester (BFPE-1). MALDI characterization of BFPE-1 indicates low molecular weight polyester and thermal analysis reveals amorphous nature of the material.

Full text of DOI:10.1016/j.tetlet.2014.05.043

Tetrahedron Letters xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Bio-based bisfuran: synthesis, crystal structure, and low molecular
weight amorphous polyester
⇑
Vishwanath Gaitonde, Kyunghee Lee, Kristin Kirschbaum, Steven J. Sucheck
Department of Chemistry, School of Green Chemistry and Engineering, The University of Toledo, 2801 W. Bancroft Street, MS602, Toledo, OH 43606, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Discovery of renewable monomer feedstocks for fabrication of polymeric demand is critical in achieving
sustainable materials. In the present work we have synthesized bisfuran diol (BFD) monomer from
furfural, over four steps. BFD was examined via X-ray crystallography to understand the molecular
arrangement in space, hydrogen bonding, and packing of the molecules. These data were further used
to compare BFD with structurally related bisphenol A (BPA), and its known derivatives to predict the
potential estrogenic or anti-estrogenic activities in BFD. Further, BFD was reacted with succinic acid to
generate polyester material, bisfuran polyester (BFPE-1). MALDI characterization of BFPE-1 indicates
low molecular weight polyester and thermal analysis reveals amorphous nature of the material.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 9 April 2014
Revised 2 May 2014
Accepted 7 May 2014
Available online xxxx
Keywords:
Biomass
Furfural
Bisfuran diol (BFD)
Bisfuran polyester (BFPE-1)
Bisphenol A (BPA)
X-ray crystallography
The use of lignocellulose plays a central role in the potential of
renewable resources contributing to a self-sustained model, for
future polymer material demand.1,2 A significant percentage of bio-
mass consists of non-food-source materials like grass, wood, straw,
etc., which can be utilized for producing value-added chemicals
and polymers.3–5 Research in the extraction and the development
of raw materials from biomass for polymer synthesis is a field of
growing interest. Polymer industry is one of the ever growing
sectors, and biomass-derived polymers are attracting the attention
of academic and industrial researchers alike.5
The molecular framework of furan has been fascinating to
chemists. This is evident from the fact that some of the ground-
work involving the construction of furan-based compounds as
industrial commodities was envisaged as far back as the mid last
century.6 Alessandro Gandini explained the use of furan containing
moieties in the preparation of various polymers.7 The efforts of
Moore and Kelly, in producing furan polyesters are also recognized
as a significant contribution in the field.8–11 Furan-based com-
pounds have also been explored as monomeric units for creation
of polyamides, polyurethanes, polyesters, and polyethers by Gandini
and co-workers.7,12–30 Generation of furanic polyester material via,
polymerization of diacid chlorides, and diester derivatives with a
variety of diols has also been reported.10,21,29
Encouraged by these reports we designed an efficient gram
scale synthesis of bisfuran (BF) monomer, BFD, Scheme 1, com-
pound 5, from commercially available furfural, employing minimal
chemical transformations.31 The low melting BFD compound was
crystallized and examined via X-ray crystallography to understand
the molecular structure, hydrogen bonding, and packing of the
crystalline monomer. The crystal structure of BFD was compared
with BPA and its derivatives. BPA is a ubiquitous molecule in poly-
mer industry known to exhibit estrogenic activity.32–34 BFD was
further studied in a bench scale polyester polymerization using
classical step-growth polymerization which resulted in low molec-
ular weight linear polyester, BFPE-1, with average molecular
weight of 5 kDa, determined using MALDI-TOF/TOF analysis. TGA
and DSC experiments revealed amorphous nature of the polyester
material. IR, 1H and 13C NMR experiments were performed to
establish the identity of the synthesized polyester, BFPE-1.
We envisioned the synthesis of BFD, compound 5, Scheme 1, as
a potential monomer to undertake a polymerization study. Starting
with commercially available furfural, we protected the aldehyde
functionality to afford 1,3-dithiolane protected compound 2. Com-
pound 2, was subjected to Friedel–Crafts alkylation, to yield dimer-
ized product, compound 3. The dedithioacetalization of compound
3 led to the desired deprotected dialdehyde product, compound 4.
In the last step, reduction of dialdehyde to the diol was accom-
plished to yield target compound 5, BFD. We note that we did
attempt condensation of furfural 1 with acetone under acidic
⇑
Corresponding author. Tel.: +1 419 530 1504; fax: +1 419 530 1990.
E-mail address: steve.sucheck@utoledo.edu (S.J. Sucheck).
http://dx.doi.org/10.1016/j.tetlet.2014.05.043
0040-4039/Ó 2014 Elsevier Ltd. All rights reserved.
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V. Gaitonde et al. / Tetrahedron Letters xxx (2014) xxx–xxx
Scheme 1. Synthetic route to access BFD from furfural. Reagents and conditions: (a) 1,2-ethanedithiol, glycerol, overnight, 90 °C, 93%; (b) hydroquinone, acetone, aq 50%
H2SO4, overnight, 65 °C, 58%; (c) SeO2, AcOH, 24 h, rt, 90%; (d) NaBH4, MeOH, N2, 30–40 min, rt, 96%.
conditions. This reaction failed and rapidly produced red colored
side products which we did not characterize.
strated the binding of BPA to human estrogen-related receptor
c
(EERc
) and its activity as an endocrine disruptor.37 The study
The BFD compound was crystallized and examined via X-ray
crystallography to understand the molecular structure, hydrogen
bonding, and packing of the crystalline monomer. Further, we
compared the structure of BFD with BPA and its known derivatives
with estrogenic activities to understand the molecular features
that may be involved in possible estrogenic or anti-estrogenic
activities.
reported the anchoring of the terminal hydroxyl groups on the
two aromatic rings with (i) Glu275 and Arg316, (ii) Asn346, accom-
panied with hydrophobic interactions with Tyr326 to establish a
good binding with ERRc 37
It has been documented that the
.
estrogen receptor ligands possessing hydroxyl groups with O–O
distance ranging from 9.7 to 12.3 Å display a medium to strong
endocrine receptor ligand capacity, and O–O distances outside of
this range are expected to weakly interact with the receptor.38
The O–O distance between the oxygen atoms of BPA is 9.404 Å. It
has also been discussed that the planarity of the non-hydrogen
atoms of the hydroxyphenol moieties in BPA ( 0.03 Å) is advanta-
The title compound BFD, also referred to as 50-(propane-2,
2-diyl)bis(furan-2,5-diyl)dimethanol 5, crystallized in the space
group P21/c with one molecule in the asymmetric unit. As shown
in Figure 1A, the molecules exhibit an approximate non-crystallo-
graphic 2-fold symmetry through the central bridging C6 atom
with the oxygen-atoms O1, O10 and O2, O20 pointing in opposite
directions, respectively. The orientation of the two aromatic rings
toward each other can be described by the dihedral angle between
the mean planes of the two rings, which has a value of 80.15(5)°.
This is within the broad range of equivalent angles in the solid
state structures of BPA and its derivatives (71.43–89.62°). Specifi-
cally, the three crystallographically independent molecules in the
crystal structure of BPA possess dihedral angles of 79.7(2),
83.6(2), and 86.9(2)°.35,36
geous for its locking into the estrogen acceptor pocket of ERRc. By
replacing the hydroxyl group with a CH2OH-group in BFD, the
geometry of the substituent is distinctively non-planar with O2
and O20 being 1.050(3) and 1.210(3) Å above the respective
aromatic ring moiety potentially hindering the binding of BFD, to
the receptor. Also, the O–O distance between terminal hydroxy
groups of BFD is 8.215(2) Å, which is substantially outside the
range to be a xenoestrogen.
Further, the conformation of BFD in the solid state comes from
steric hindrance of the two methyl groups (C7 and C70) and packing
effects, especially hydrogen bonds. Although on initial inspection,
molecules of BFD seem to exhibit a non-crystallographic 2-fold
axis, closer examination reveals a quite different secondary coordi-
nation sphere for O1 and O10 as well as O2 and O20. While the furan
oxygen O1 is not involved in any hydrogen bonds, the other furan
oxygen O10 acts as an acceptor with O10ꢀ ꢀ ꢀH2_C–O2_C (x, 0.5 ꢁ y,
0.5 + z) = 2.05(3) Å. Concomitantly, the C2–O1 and C5–O1 bonds
are with 1.380(2) and 1.378(2) Å shorter than the comparable
C20–O10 and C50–O10 bonds of 1.386(2), respectively. In a similar
way, the hydroxyl group O20–H20 is acting as a hydrogen bond
There is a significant difference in the conformation of the BPA
and the currently discussed structure of BFD with respect to the
propeller-like arrangement of the aromatic rings. A pitch angle,
w
, can be used to describe the amount of rotation around the
C6–C5 or C6–C50 bond, turning the respective aromatic ring in
= 0°) and out of the central C5–C6–C50 plane.36 The two rings
(w
in BFD are with pitch angles of 74.98(8) and 66.04(7)° significantly
more twisted toward a perpendicular arrangement than the ones
in all three BPA molecules, whose pitch angles range from only
45.59(6) to 59.62(7)°. In 2007, Matsushima et al. have demon-
Figure 1. (A) ORTEP drawing of BFD with 50% probability ellipsoids and labeling scheme, and (B) dimer of BFD created by strong H-bonds in the solid state.
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V. Gaitonde et al. / Tetrahedron Letters xxx (2014) xxx–xxx
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Scheme 2. Synthesis of BFPE-1 from BFD. Reagents and conditions: (a) succinic acid, N,N-dimethyl-4-aminopyridine, N,N0-diisopropylcarbodiimide, 1,2-dichloroethane, N2,
15 h, rt.
Figure 2. MALDI-TOF/TOF mass spectrum of BFPE-1 with DHB matrix in range of 3–7.5 kDa. Inset shows an expanded region between 0.5 and 3 kDa. Structures of 318 mass
units and 276 mass units of the BFPE-1 shown in inset picture.
donor O20–H20ꢀ ꢀ ꢀO2_A(ꢁx, 2 ꢁ y, 1 ꢁ z) = 1.90(3) Å, while the other
hydroxyl group O2–H2 acts simultaneously as a hydrogen-bond
acceptor (O2ꢀ ꢀ ꢀH20_A-O20_A(ꢁx, 2 ꢁ y, 1 ꢁ z) = 1.90(3) Å) and as
Thermal analysis of the synthesized BFPE-1 material was stud-
ied via TGA and DSC experiments. At 100 °C the material shows a
weight loss of ꢃ2% which could be accounted for the loss of resid-
hydrogen-bond donor to
a
furan oxygen (O2–H2ꢀ ꢀ ꢀO10_B(x,
ual water, Figure 3. The start of thermal decomposition (Tstart)
1.5 ꢁ y, ꢁ0.5 + z) = 2.05(3) Å). Figure 1B shows how hydrogen
bonds between two molecules of BFD with O20 as a hydrogen bond
donor and O2 as the acceptor form a rectangular dimer of approx-
imate dimensions 8 ꢂ 12 Å.2 The structure resembles the cova-
lently bonded cyclic BPA-carbonate dimer, which shows a similar
small ring structure with dimensions 9 ꢂ 10 Å.39,40
between 100 and 225 °C, displays a weight loss of ꢃ5%. A plot of
derivative weight (%/°C) versus temperature (°C) reveals two stage
degradation of the BFPE-1 material with two maximum (Tmax),
inset Figure 3. The Tmax for first stage of degradation exhibits a
value of 266 °C, and for the second stage 329 °C. The corresponding
weight losses at the end (Tend) of the two degradation stage
temperatures are ꢃ52% and ꢃ80%, respectively.
BFD was further utilized to develop a linear polyester material
employing a classical step-growth polymerization via alcohol
esterification, Scheme 2. Two co-monomeric units, diol 5 and suc-
cinic acid were used to generate poly (furan succinate) copolyester,
BFPE-1, and compound 6. Succinic acid is a well established
industrial commodity and identified as one of the top value added
chemicals accessible from fermentable sugars, via biomass.41,42
The molar mass distribution of the synthesized BFPE-1 was
determined using MALDI-TOF/TOF analysis. The spectrum of
BFPE-1 illustrates mass distribution in the range of 3–7.5 kDa Fig-
ure 2 and 05–3.0 kDa, inset Figure 2. A repeat of 318 mass units
and residue of 276 mass units was identified from the MALDI
spectrum.
DSC analysis of BFPE-1 was performed to observe glass transi-
tion (Tg) between 15 and 25 °C and degradation temperature (Td)
of 260 °C. Absence of melt crystallization (Tc) and melting (Tm)
suggests the amorphous nature of BFPE-1. The BFPE-1 sample
was subjected to a heat-cool-reheat cycle from ꢁ10 to 150 °C,
Figure 4, to record Tg = 20 °C, and
D
Cp of 0.676 J/g⁄°C.
At present polyethers, polyesters, polycarbonates, and epoxy
resins of significant commercial value are derived from non-
renewable feedstock. Furfural can be readily accessed from renew-
able and non-food-source biomass. The use of renewable furfural
to access furan based polymer, would aid in generating next-gen-
eration bio-based materials. We have demonstrated the gram-scale
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V. Gaitonde et al. / Tetrahedron Letters xxx (2014) xxx–xxx
Figure 3. TGA thermograms of BFPE-1 weight loss (%) versus temperature (°C). Inset shows TGA thermograms of BFPE-1 derivative weight (%/°C) versus temperature (°C).
Figure 4. DSC thermograms of BFPE-1 obtained during heat-cool-reheat cycle from ꢁ10 to 150 °C. Inset shows expanded glass transition (Tg) region from 2nd heat (reheat)
curve.
conversion of furfural to BFD, and an exploratory example as feed-
stock for polymer generation, accessing the BFPE-1 material. Char-
acterization of BFPE-1 has displayed encouraging results for the
application of BFD as monomeric unit in polymer synthesis. Based
on this preliminary investigation we anticipate employing BFD in
generating other classes of BF-based polymers. The X-ray crystallo-
graphic study provides an insight to the molecular structure of
BFD, which will be useful in future, polymerization studies. These
data would also provide the basis for understanding the potential
self-healing properties based on H-bonding and
the monomeric BFD molecules.
p–p stacking of
Acknowledgements
We are grateful in part to the University of Toledo for an
Interdisciplinary Research Initiation Award and to the National
Institutes of Health (Grant numbers GM094734 and AI105084) to
Professor S.J.S. for the financial support. We thank Professor Maria
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V. Gaitonde et al. / Tetrahedron Letters xxx (2014) xxx–xxx
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