A Facile Solid-Phase Route to Renewable Aromatic Chemicals from Biobased Furanics

Article abstract of DOI:10.1002/anie.201509346

Renewable aromatics can be conveniently synthesized from furanics by introducing an intermediate hydrogenation step in the Diels-Alder (DA) aromatization route, to effectively block retro-DA activity. Aromatization of the hydrogenated DA adducts requires tandem catalysis, using a metal-based dehydrogenation catalyst and solid acid dehydration catalyst in toluene. Herein it is demonstrated that the hydrogenated DA adducts can instead be conveniently converted into renewable aromatics with up to 80 % selectivity in a solid-phase reaction with shorter reaction times using only an acidic zeolite, that is, without solvent or dehydrogenation catalyst. Hydrogenated adducts from diene/dienophile combinations of (methylated) furans with maleic anhydride are efficiently converted into renewable aromatics with this new route. The zeolite H-Y was found to perform the best and can be easily reused after calcination. Just heat and tumble: Furanics-derived hydrogenated Diels-Alder adducts can be conveniently converted, over acidic zeolites, into renewable aromatics using a solid-phase conversion strategy. The zeolite H-Y was found to perform the best and can be easily reused after calcination.

Full text of DOI:10.1002/anie.201509346

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International Edition: DOI: 10.1002/anie.201509346
German Edition: DOI: 10.1002/ange.201509346
Arenes
Hot Paper
A Facile Solid-Phase Route to Renewable Aromatic Chemicals from
Biobased Furanics
Shanmugam Thiyagarajan, Homer C. Genuino, Jan C. van der Waal, Ed de Jong,*
Bert M. Weckhuysen, Jacco van Haveren, Pieter C. A. Bruijnincx,* and Daan S. van Es*
Abstract: Renewable aromatics can be conveniently synthe-
sized from furanics by introducing an intermediate hydro-
genation step in the Diels–Alder (DA) aromatization route, to
effectively block retro-DA activity. Aromatization of the
hydrogenated DA adducts requires tandem catalysis, using
a metal-based dehydrogenation catalyst and solid acid dehy-
dration catalyst in toluene. Herein it is demonstrated that the
hydrogenated DA adducts can instead be conveniently con-
verted into renewable aromatics with up to 80% selectivity in
a solid-phase reaction with shorter reaction times using only an
acidic zeolite, that is, without solvent or dehydrogenation
catalyst. Hydrogenated adducts from diene/dienophile combi-
nations of (methylated) furans with maleic anhydride are
efficiently converted into renewable aromatics with this new
route. The zeolite H-Y was found to perform the best and can
be easily reused after calcination.
ing increased attention.[4–9] The DA aromatization strategy
typically involves two steps, that is, cycloaddition of a furanic
diene with an appropriate dienophile, followed by acid-
catalyzed dehydration of the intermediate DA adduct. A
prominent example of this approach is the reaction of 2,5-
dimethylfuran (DMF) and (excess of) ethylene over
Brønsted-acid-containing BEA- and FAU-type zeolites to
produce renewable p-xylene, a precursor to terephthalic acid
(TA) and polyethylene terephthalate (PET), with yields as
high as 90%.[4] Wang et al. showed that solid acid oxides, such
as WOx-ZrO2 and niobic acid, also demonstrate high catalytic
activities for this reaction.[5] Pacheco and Davis later explored
DA aromatization of various oxidized derivatives of 5-
hydroxymethylfurfural (HMF) with ethylene over Lewis-
acidic molecular sieves, Sn-Beta in particular.[6]
DA aromatization of 2-methylfuran (MF) and ethylene
proved less efficient over either H-Beta or Sn-Beta, with
toluene selectivities not exceeding 46%, because MF was
consumed by side reactions such as dimerization.[7] Indeed,
selectivity for aromatization typically decreases as the furan
ring becomes less substituted.[8] Related to the challenges
associated with controlling such furan-dependent side reac-
tions, careful control over the second catalytic aromatization
step is often critical as the intermediate DA adducts are
typically unstable and prone to retro-DA reaction, especially
at more elevated temperatures.[8,9] Consequently, one has to
run the aromatization reaction at either low temperature[10]
or, if ethylene is the dienophile, at high pressure.[4–6] Mah-
moud et al. addressed the issue of DA adduct instability and
furan reactivity by using a mixture of methanesulfonic acid
and acetic acid anhydride to synthesize (substituted) phthalic
anhydride with high selectivity at 808C.[8] In an alternative
approach, we recently reported on a new three-step strategy
and dealt with this general challenge in DA aromatization by
including a mild intermediate hydrogenation step of the
oxabicyclic adduct 1.[9]
T
he development of new routes for the production of ꢀdrop-
inꢁ aromatic chemicals from renewable resources is currently
receiving considerable attention because of the increased
demand, finite fossil resources, and the recognized need for
more sustainable production routes.[1] This attention is further
compounded by the challenges associated with the changes in
bulk aromatics supply caused by the increased use of shale-
gas-derived feeds in steam cracker facilities.[2] Of the various
potential routes to biobased aromatics, Diels–Alder (DA)
conversions of sugar-derived furanic compounds[3] are receiv-
[*] Dr. S. Thiyagarajan, Dr. H. C. Genuino, Prof. Dr. B. M. Weckhuysen,
Dr. P. C. A. Bruijnincx
Inorganic Chemistry and Catalysis
Debye Institute for Nanomaterials Science, Utrecht University
Universiteitsweg 99, 3584 CG Utrecht (The Netherlands)
E-mail: p.c.a.bruijnincx@uu.nl
Dr. S. Thiyagarajan, Dr. J. van Haveren, Dr. D. S. van Es
Food & Bio-based Research
Wageningen University and Research Centre
P.O. Box 17, 6700 AA Wageningen (The Netherlands)
E-mail: daan.vanes@wur.nl
This new route, which is run in the liquid phase, is shown
in Scheme 1.[9a] The hydrogenated DA adduct 2 is thermally
stable and efficiently aromatized in a tandem catalytic
reaction using a mixture of a solid acid dehydration catalyst
(e.g., zeolites or resins) and a dehydrogenation catalyst (e.g.,
metal on a carbon support). For example, catalytic aromati-
zation of 2 in toluene at 2008C with H-VUSY (SiO2:Al2O3 =
11.5) and Pd/C resulted in a combined yield of 84% for all
aromatics.[9a] Formal catalytic oxidation would then give the
desired aromatic di- and tricarboxylic acid end products.[11]
Notably, if this solution-phase reaction was run with only the
zeolite catalyst, very low aromatics yields were obtained, with
the g-lactone intermediate 3 being the major product
Dr. J. C. van der Waal, Dr. E. de Jong
Avantium Chemicals
Zekeringstraat 29, 1014 BV Amsterdam (The Netherlands)
E-mail: ed.dejong@avantium.com
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201509346.
ꢀ 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co.
KGaA. TThis is an open access article under the terms of the Creative
Commons Attribution-NonCommercial-NoDerivs License, which
permits use and distribution in any medium, provided the original
work is properly cited, the use is non-commercial and no modifica-
tions or adaptations are made.
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Scheme 1. Three-step catalytic route to renewable aromatic chemicals, exemplified for the synthesis of 4, and 5 and 6. Comparison of the
solution-[9a] and solid-phase (this work) conversion of the hydrogenated DA adduct.
instead.[9a] Surprisingly, we have now discovered that the
aromatization reaction also proceeds smoothly without any
solvent and dehydrogenation catalyst, by simply mixing the
solid reactant and the solid acid catalyst with heating in
a standard Kugelrohr oven (see Figure S1 in the Supporting
Information).
Al2O3 = 5.2) in a 1:1 w/w ratio in situ by rotating the reaction
vessel prior to insertion into the preheated oven. Intimate
ex situ mixing of the substrate and catalyst by grinding gave
the same catalytic result. Mixing during reaction facilitates
mass transfer as well as prevents the creation of hot spots.
Upon heating, the thermally stable substrate melts (melt-
ing point of 2 is ca. 98–1008C)[9a] and diffuses into the zeolite
pores, thus resulting in a dry, free flowing powder (see
Movie S1). Monitoring the reaction as a function of time at
2008C showed rapid, acid-catalyzed isomerization of 2 into
the g-lactone 3, with subsequent aromatization being more
difficult (Figure 1). Notably, the aromatization reactions are,
as expected, accompanied by H2 release (see Movie S2).
Various organic transformations have already been ac-
complished in the solid state, for example, by using the
mechanochemical approach.[12] Indeed, such solid-phase,
solventless chemical reactions are very attractive from the
point of view of green chemistry and practicality. The facile,
new approach reported here for the aromatization of hydro-
genated DA adducts furthermore reduces reaction time and
allows lower reaction temperatures by using a relatively
inexpensive catalyst (Scheme 1, solid-phase). The reaction
requires no input of mechanical energy for it to proceed,
except for tumbling the vessel to facilitate mixing. In addition,
the omission of the (noble) transition-metal dehydrogenation
catalyst greatly facilitates catalyst recovery and regeneration.
Again, the g-lactone (e.g., 3) is observed as a primary
intermediate and found to be the precursor to all aromatics.
Indeed, with 2, 3-methylphthalic anhydride (4), and the
decarboxylation products m- and o-toluic acid (5 and 6) are
again obtained. To the best of our knowledge, this is the first
report of such a simple, solid-state approach for the synthesis
of biomass-derived aromatics.
We first explored the influence of selected process
parameters and choice of catalyst on the efficiency of this
new route, using 2 as the substrate. The large-pore FAU-type
zeolite Y, containing strong Brønsted acid sites and meso-
pores (see Table 1 and Figure S2, S3, and S4), proved to be
most efficient. The substrate is simply mixed with H-Y (SiO2/
Figure 1. Conversion of 2 and product yields as a function of time at
2008C over H-Y at 1:1 w/w ratio.
Table 1: Textural and acidic properties of the fresh zeolites and reused[a] H-Y catalysts.
Solid acid catalyst BET surface
(SiO2/Al2O3)
Single point
adsorption
t-plot micropore
Mesopore
BJH adsorption average
pore diameter [nm]
Total acid sites
[mmol NH3 gÀ1
]
area [m2 gÀ1
]
volume [cm3 gÀ1
]
volume [cm3 gÀ1
]
total pore
volume [cm3 gÀ1
]
H-Beta (25)
H-Y (5.2)
520
544
0.98
0.37
0.40
0.46
0.53
0.16
0.23
0.24
0.27
0.27
0.82
0.14
0.16
0.19
0.26
12.0
3.9
4.4
3.2
2.8
0.81
0.63
0.63
0.80
0.30
Reused H-Y (5.2)[a] 556
H-VUSY (11.5)
H-SDUSY (32.3)
696
799
[a] After third reuse and (re)calcination.
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A blank reaction, without catalyst, was performed at
2008C under N2 and did not result in conversion of either 2 or
3. Trace metal analyses for potential metal contaminants in
zeolite Y samples revealed negligibly low concentrations of
Cu, Fe, Ni, V, and Zn (see Table S1), which could potentially
catalyze the required dehydrogenation step. This finding
indicates that the H2-evolving step is most likely thermal and
noncatalytic. Full conversion of 2 was already seen after
5 minutes at 2008C, thus yielding 59% of 3, 16% of 4, and 9%
of 5, and 5% of 6. The g-lactone 3 is then subsequently
gradually aromatized and then not observed anymore after
120 minutes of reaction (see Table S3). At this point, 4 is
obtained in 61% yield, together with 19% decarboxylation
products (5 + 6). Notably, the increase in 4 observed between
30 and 120 minutes is higher than the amount of 3 left after
30 minutes, thus implying that there may be an intermediate
which is not observed, yet contributes to the formation of 4.
The yield of the transfer hydrogenation product 7 is as low as
6%, with 7 being formed mainly at short reaction times.[9a]
The aromatic product distribution shows that the selec-
tivity for 4 in terms of total aromatics does not change
significantly after 30 minutes (73%). This observation
strongly suggests that the rate of the transformation of 3 is
directly proportional to the rate of formation of 4. For
comparison, the previously reported reactions run with the
physical mixture of H-Yand Pd/C at 2008C in toluene showed
full conversion of 2 only after 24 h at 2008C, thus giving
a similar aromatic product distribution.[9a] That the extent of
decarboxylation is similar for the solid-phase and solution-
phase reactions, suggests that this selectivity is dictated by the
zeolite only.
Figure 2. Effect of temperature on the conversion of 2 and product
distribution in the aromatization of 2 with H-Y (1:1 w/w, 120 min). The
values within parentheses indicate the amount of 4 formed as
a percentage of the total yield of the aromatics (4+5+6).
can access the Brønsted acid sites more easily in H-Y. With
conversion of 2 into 3 being more facile, this step could also be
catalyzed by weaker acid sites at the external surface of H-
Beta or within its mesopores. Of the zeolite Y catalysts tested
(Table 2), H-Y proved most selective for aromatic product
formation. A comparison of the Si/Al ratio and catalyst
performance shows that production of the aromatics is not
solely related to zeolite acidity. Indeed, the least acidic H-
SDUSY (SiO2/Al2O3 = 32.3) is more selective than H-VUSY.
These differences in selectivity can be attributed to the degree
of mesoporosity, which may enhance mass transport.
The hydrogenated DA adducts of maleic anhydride (MA)
with furan or DMF were also investigated (Table 2). As seen
before for the liquid-phase experiments, the DMF-derived
adduct gave the highest cumulative selectivity towards
aromatics (90%). Full decarboxylation was seen to a limited
extent for this substrate, with p-xylene being obtained in 11%
yield. The decarboxylation selectivity for 2,5-dimethylbenzoic
acid is the same as previously seen in solution. Importantly,
the reactivity of the furan-derived adduct is significantly
improved in the solid phase (100% conversion and 57% total
aromatics selectivity), compared to only 24% conversion and
Variation of the reaction temperature showed that the
highest yield of 4 (61%) and the combined aromatics (80%)
are obtained at 2008C after 120 minutes (Figure 2). The
decarboxylation selectivity increases with temperature at the
expense of the formation of 4, with 5 + 6 making up 12 and
43% of the total yield of aromatics (4 + 5 + 6) at the lowest
and highest temperatures, respectively (Figure 2). The use of
H-Beta as the catalyst (SiO2/Al2O3 = 25) gave a higher yield
of 3 (30%) and a much lower yield of the aromatic products
(39%) under standard reaction conditions (Table 2). As
a result of the smaller dimensions of the BEA microstructure
compared to that of the FAU-type H-Y, not only 2 but also 3
Table 2: Catalytic aromatization of hydrogenated Diels–Alder adducts using the new solid-phase route developed in this work.[a]
Molar yield (mol%)[b]
Total
Solid acid
catalyst
(SiO2/Al2O3)
Conversion
(mol%)[b]
aromatics
Mole
yield [% ] balance [%][c]
(4+5+6)
H-Beta (25)
H-Y (5.2)
H-VUSY (11.5)
H-SDUSY (32.3) X=CH3; Y=H 100
H-Y (5.2)
H-Y (5.2)
X=CH3; Y=H
X=CH3; Y=H 100
X=CH3; Y=H 100
97
30
–
15
–
26
–
27
61
39
50
32
69
7
12
15
15
5
7
7
5
2
6
7
5
–
39
80
61
70
57
90
74
86
83
75
83
90
[d]
[d]
[d]
[d]
X=Y=H
X=Y=CH3
100
100
25[e]
11[f]
10[g]
–
[d]
[a] Reaction conditions: 0.1 g of hydrogenated adduct, 0.1 g solid-acid catalyst, 120 min, 2008C, catalyst is indicated in the Table. [b] Calculated by q-
NMR using 1,4-dinitrobenzene as the internal standard. [c] Mole balance determined from the total number of moles determined by 1H NMR analysis
of the crude reaction mixture. [d] Not observed. [e] Benzoic acid. [f] p-Xylene. [g] 2,5-Dimethylbenzoic acid.
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14% yield of the aromatics in solution,[9a] with activity
the Netherlands Organization for Scientific Research
presumably limited by the number of Brønsted acid sites
under the latter reaction conditions. Decarboxylation is more
severe for this substrate with benzoic acid being obtained in
25% yield.
(NWO). Guus Frissen is acknowledged for some of the
NMR analyses.
Keywords: arenes · biomass · cycloaddition · heterocycles ·
Facile catalyst reuse is key for the practical application of
such a solid-phase, zeolite-only synthesis route, which would
be expected to be applied in batch mode. Recovered H-Y
catalyst was therefore first reused directly, that is, after
applying only a washing and mild drying step. While activity
remained the same, selectivity towards aromatic products was
significantly decreased. This decrease was attributed to the
deposition of carbonaceous materials, as evidenced by the
coloration of the zeolite (see also TGA profiles in Figure S5).
Calcination of the recovered, spent H-Y catalyst at 5508C in
air before reuse proved effective for regeneration, as aro-
matics yields were fully restored. In fact, the yield of 4
remained almost unchanged after three runs (Figure 3).
zeolites
How to cite: Angew. Chem. Int. Ed. 2016, 55, 1368–1371
Angew. Chem. 2016, 128, 1390–1393
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Acknowledgments
This work is part of research program Technology Areas for
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Received: October 6, 2015
Published online: December 18, 2015
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