Pd-catalysed formation of ester products from cascade reaction of 5-hydroxymethylfurfural with 1-hexene

Article abstract of DOI:10.1016/j.apcata.2018.10.031

A cascade reaction involving decarbonylation of 5-hydroxymethylfurfural (HMF) followed by methoxycarbonylation of 1-hexene produces methyl heptanoate (MH) using a catalytic system composed of a Pd-phosphine complex and methanesulfonic acid (MSA) co-catalyst at moderate reaction temperature. Concomitant hydration of HMF followed by hydrogenation of methyl levulinate (ML) to γ-valerolactone (GVL) occurs with the catalytic system under the same reaction conditions using HMF and methanol as the source of CO and H₂, respectively. Under optimized reaction conditions, about 50% of MH along with 12% ML and 35% GVL is obtained from HMF using Pd-(1,2-bis(di-tert-butylphosphinomethyl)benzene) (DTBPMB), MSA and 1-hexene in methanol at 120 °C. Interestingly, sugars, such as glucose, fructose and xylose, are able to be converted to MH, ML and GVL as well. Isotopic labeling studies with ¹³C₁-fructose in methanol-d₄ and ¹³C-methanol-d₄ confirm that H₂ originates from methanol, while CO generates predominantly from the formyl group of the HMF formed by fructose dehydration.

Full text of DOI:10.1016/j.apcata.2018.10.031

Accepted Manuscript
Title: Pd-catalysed formation of ester products from cascade
reaction of 5-hydroxymethylfurfural with 1-hexene
Authors: Eduardo J. Garcia-Suarez, Dario Paolicchi, Hu Li,
Jian He, Song Yang, Anders Riisager, Shunmugavel
Saravanamurugan
PII:
S0926-860X(18)30540-4
DOI:
Reference:
https://doi.org/10.1016/j.apcata.2018.10.031
APCATA 16860
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
13-9-2018
24-10-2018
26-10-2018
Please cite this article as: Garcia-Suarez EJ, Paolicchi D, Li H, He J, Yang S, Riisager
A, Saravanamurugan S, Pd-catalysed formation of ester products from cascade reaction
of 5-hydroxymethylfurfural with 1-hexene, Applied Catalysis A, General (2018),
https://doi.org/10.1016/j.apcata.2018.10.031
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Pd-catalysed formation of ester products from cascade reaction of 5-
hydroxymethylfurfural with 1-hexene
Eduardo J. Garcia-Suareza,b,c, Dario Paolicchia#, Hu Lid#, Jian Hea,d#, Song Yangd, Anders
Riisagera*, Shunmugavel Saravanamurugana,e*
aCentre for Catalysis and Sustainable Chemistry, Department of Chemistry, Technical
University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
E-mail: ar@kemi.dtu.dk
bTecnalia, Energy and Environment Division, Parque Tecnológico de Álava, Leonardo Da
Vinci 11, 01510 Miñano, Spain
cIKERBASQUE, Basque Foundation for Science, Maria Díaz de Haro 3, 48013 Bilbao,
Spain.
dState-Local Joint Engineering Lab for Comprehensive Utilisation of Biomass, Center for
R&D of Fine Chemicals, Guizhou University, Guiyang, Guizhou 550025, China.
eLaboratory of Bioproduct Chemistry, Center of Innovative and Applied Bioprocessing
(CIAB), Mohali-140306, Punjab, India.
Email: saravana@ciab.res.in
# These authors equally contributed

Graphical abstract
Valorisation with in-situ CO/H2
Highlights
 Methoxycarbonylation of 1-hexene to methyl hepatanoate using HMF as CO
surrogate with Pd-complex is studied in methanol.
 Methyl levulinate and GVL are found to be other major ester products when
changing the concentration of acid additive.
 The influence of phosphine ligand and Pd source on the yield of ester products is
investigated.
 The direct conversion of sugars, such as glucose, fructose and xylose to ester
products is studied in methanol with Pd-complex in the presence of 1-hexene and
acid additive.
Abstract
A cascade reaction involving decarbonylation of 5-hydroxymethylfurfural
(HMF) followed by methoxycarbonylation of 1-hexene produces methyl heptanoate
(MH) using a catalytic system composed of a Pd-phosphine complex and
methanesulfonic acid (MSA) co-catalyst at moderate reaction temperature. Concomitant
hydration of HMF followed by hydrogenation of methyl levulinate (ML) to
-
valerolactone (GVL) occurs with the catalytic system under the same reaction

conditions using HMF and methanol as the source of CO and H2, respectively. Under
optimized reaction conditions, about 50% of MH along with 12% ML and 35% GVL is
obtained from HMF using Pd(dba)2-(1,2-bis(di-tert-butylphosphinomethyl)benzene)
(DTBPMB), MSA and 1-hexene in methanol at 120 °C. Interestingly, sugars, such as
glucose, fructose and xylose, are able to be converted to MH, ML and GVL as well.
Isotopic labeling studies with 13C1-fructose in methanol-d4 and 13C-methanol-d4 confirm
that H2 originates from methanol, while CO generates predominantly from the formyl
group of the HMF formed by fructose dehydration.
Keywords: HMF • decarbonylation • alkoxycarbonylation • palladium/phosphine •
hydrogenation
1. Introduction
The projection of limited fossil resources in the future has strived research to implement
sustainable alternative feeds stocks, such as lignocellulosic biomass, in order to keep the value
chain of chemicals [1-3]. In this context, a wide range of single reactions including aldol/retro-
aldol, oxidation, reduction, hydrogenolysis, dehydration, decarbonylation, decarboxylation and
dehydrogenation have been extensively studied in the past decade to valorize biomass-based
substrates like glucose to added-value compounds that could potentially substitute the ones

derived from fossil resources [4-8]. Especially, the dehydration of glucose to
5-hydroxymethylfurfural (HMF) and its catalytic oxidation have been comprehensively
investigated [10-17]. In addition, decarbonylation of furanics, such as HMF and furfural to
furfural and furan, respectively, has also been thoroughly explored using metal-containing
catalysts [18,19]. However, to the best of our knowledge, no study has been reported about the
use of in-situ generated CO from furanics to generate other chemicals of potential interest in
cascade, e.g. via alkoxycarbonylation of olefins.
Alkoxycarbonylation of olefins is an atom-efficient and important transformation for
C-C bond formation in which alkenes are converted into esters/acids in the presence of CO,
alcohol, a strong acid (typically sulfuric acid or methanesulfonic acid, MSA), and a metal-
complex catalyst which usually is Pd-based. The reaction has already been widely studied to
improve the catalytic system in terms of yield, recycling and easy product recovery as the
products (esters/acids) have a wide spectrum of applications for production of fine and bulk
chemicals [20-32]. Normally, fossil-derived CO gas supply in the processes is from pressurized
external gas cylinders. Particularly, for smaller-scale applications this introduces some
challenges and limitations, since CO gas is dangerous to handle and store due to its high toxicity
and flammability and processing is not cost-efficient. To overcome these drawbacks, an
alternative approach is to use biomass-based substrates, such as HMF and furfural, as CO
surrogates. Regarding this, decarbonylation of furfural (FURAL) and HMF with Pd-based
catalysts have separately been reported to achieve near quantitative yield of the corresponding
products furan (98%) and furfuryl alcohol (96%), respectively [33, 34]. However, this study
did not disclose to make use of in-situ produced CO to other chemicals.
This work presents a proof-of-concept study on the use of biomass-derived CO to
produce methyl heptanoate (MH) with 1-hexene over a Pd-phosphine catalyst system in
methanol at moderate reaction temperature. The applied phosphine ligand is diphoshine
1,2-bis(di-tert-butylphosphinomethyl)benzene (DTBPMB), which previously has shown
excellent performance in Pd-catalyzed methoxycarbonylation [28,31,32]. Notably, the study
not only focuses on the reaction cascade of decarbonylation followed by
methoxycarbonylation, but also on the hydrogenation of methyl levulinate (ML) formed from
HMF, to -valerolactone (GVL) (Scheme 1). Formation of GVL from HMF/fructose/glucose
has previously been reported using various dual catalyst systems (acid plus metal catalyst) in

the presence of formic acid or under H2 pressure in a two-step approach, affording overall yield
of GVL about 50% [35-37]. However, the present study focuses on one-pot, one-step
production of esters employing methanol as solvent as well as CO and H2 source in the absence
of external added H2. The influence of the palladium source, the amount of acid additive, and
various furanics such as, e.g. FURAL, furfuryl alcohol (FUROL), 5-methylfurfural and (5-
methyl-2-furyl)methanol as CO source, on the yield of MH, ML and GVL are investigated.
Scheme 1. Pd-phosphine catalyzed cascade transformation of HMF to ester products.
2. Experimental Section
All reactions were performed in 15 mL Ace pressure tubes with appropriate amounts
of 5-hydroxymethylfurfural, Pd(OAc)2, DTBPMB ligand, n-hexene, methanesulfonic acid, and
methanol, otherwise unless stated. The tube was inserted into a preheated oil bath and stirring
started when the temperature set point was reached. After a desired reaction time, the tube was
quenched in cold water, and aliquots of the reaction mixture withdrawn and analyzed in GC-
FID (Agilent 6890N instrument, HP-5MS capillary column) and GC-MS (Agilent 6850GC
system coupled with an Agilent 5975C mass detector) for quantification and identification of
products. Substrate conversion and product yield were calculated using series of individual
standards with naphthalene as internal standard. Yields of MH were calculated supposing that
each mole of HMF gave one mole of CO, which eventually converted into MH during the
methoxycarbonylation reaction. MH yield for the background experiment (Table 2, entry 7)
was calculated by assuming a maximum of one mole of methanol being converted to MH. For
1
13
the isotope labelling study, H and C{H1} NMR spectra of pure chemicals and mixtures

obtained from reactions performed under optimal conditions with isotope labeled 13C1-fructose
13
or normal fructose in MeOH-d4 or C-MeOH-d4 were recorded on a JEOL-ECX 500 NMR
spectrometer.
3. Results and Discussion
3.1 Influence of MSA
Initially, catalytic conversion of HMF with 1-hexene in methanol with Pd-DTBPMB
catalyst was examined to optimize the addition of acid (MSA) on the yield of MH, as acid is
required to form and stabilize catalytically active Pd species in the methoxycarbonylation
reaction [38-40]. As shown in Table 1, no MH formed in the absence of MSA in the reaction
mixture as expected (Table 1, entry 1). Upon addition of 15 µL of MSA, 29.3% of MH formed
with a fair yield of 52.4% of ML and 2.2% of GVL after 20 h of reaction (entry 2). Interestingly,
a further increase in acid amount (65 µL) enhanced the yield of MH to 41.2% along with 25.4
and 39.5% of ML and GVL, respectively (entry 4), whereas higher acid amount (80-100 µL)
decreased the MH yield presumably due to protonation of the phosphine ligand and following
lack of Pd complex stability. In contrast, both the yields of ML and GVL remained here largely
unchanged. These initial results clearly indicated that the Pd-phosphine systems not only
catalyzed the decarbonylation of HMF followed by methoxycarbonylation of 1-hexene with
methanol and the CO liberated from HMF, but also the hydrogenation of ML formed from the
hydration of HMF into GVL.
Table 1. Influence of MSA amount on product yields.a
Entry
MSA (µL)
HMF conv.
(%)
Yield (%)
ML
MH
0.0
GVL
0.0
1
0
50.1b
0.0

2
3
4
5
6
15
30
>99
>99
>99
>99
>99
29.3
35.7
41.2
31.7
36.4
52.4
27.7
25.4
25.9
25.6
2.2
27.6
39.5
33.1
39.3
65
80
100
a Reaction conditions: Pd(OAc)2 (0.025 mmol); HMF (1 mmol); DTBPMB ligand (0.125
mmol); 1-hexene (1.8 mmol); MeOH (5 mL), 120 °C, 20 h. b Mainly aldolization product.
3.2 Influence of furanic and other substrates
In order to substantiate the origin of CO and H2 generated from the aldehyde and methyl
hydroxy moieties of HMF, reference compounds as well as alternative furanic substrates were
employed for the conversion to MH, ML and GVL (Table 2). Based on results from the
investigations a plausible reaction pathway is proposed in Scheme 2. A reference experiment
with ML in methanol under identical reaction conditions as the initial experiments, resulted in
49.6% conversion of ML into GVL, revealing that methanol was H-donor for the
hydrogenation (Table 2, entry 6). Moreover, an experiments with methyl formate (MF), which
formed along with ML from HMF during the reaction under similar conditions, yielded MH
(18.1%) but neither ML nor GVL formed, implying that the CO for the methoxycarbonylation
was partially generated from MF, possibly by decomposition of initially formed formaldehyde
(entry 5)[41]. Moreover, H2 might have generated from the decomposition of formate ions and
participated in the methoxycarbonylation reaction to slightly enhance the yield of MH, as there
was no transformation of ML to GVL. Other by-products, including methyl 2-methylhexanoate
(5-7%, IMH), isomer of MH, was further observed by GC-MS analysis confirming that
formation of the linear ester was predominant over the branched (Table S1). In addition, the
hydrogenated byproduct 2,5-hexadione (HD) was also found as also reported previously for
HMF hydrogenation [42] (Table S1).
Table 2. Influence of substrate on product yields.a
Entry
Substrate
Conv. (%)
Yield (%)

MH
19.3
25.0
16.6
17.6
ML
21.4
24.6
2.5
GVL
19.5
23.2
0.0
1
2
3
4
Furfuryl alcohol
Furfural
>99
>99
>99
>99
5-methylfurfural
5-methylfurfuryl
alcohol
0.0
0.0
5
6
7
Methyl formate
24.9
63.2
-
18.1
0.0
0.0
36.8b
0.0
0.0
49.6
0.0
Methyl levulinate
-
8.0
a Reaction conditions: Pd(OAc)2 (0.025 mmol); Substrate (1 mmol); MSA (65 µL; 1 mmol);
b
DTBPMB ligand (0.125 mmol); 1-hexene (1.8 mmol); MeOH (5 mL), 120 ° C, 20 h.
Unconverted ML.
The alternative furanic compound FUROL yielded 19.3% MH along with 21.4 and
19.5% of ML and GVL, respectively (Table 2, entry 1), inferring that FUROL could produce
ML but not formic acid/MF under the applied reaction conditions. This demonstrated that CO
and H2 originated from the decomposition of the methyl hydroxy moiety of FUROL, as also
suggested by the formation of formaldehyde dimethylacetal (found by GC-MS analysis). With
FURAL as substrate the MH yield was improved ca. 30% (from 19.3 to 25%), exhibiting
enhanced decarbonylation of FURAL followed by 1-hexene methoxycarbonylation (Table 2,

Scheme 2. Plausible reaction pathway for the formation MH, ML and GVL from furanic
compounds under the applied reaction conditions.
entry 2). Furthermore, yields of 16.6 and 17.6% of MH were found when 5-methylfurfural
(Me-FURAL) and 5-methylfurfuryl alcohol (Me-FUROL), respectively, were used as
substrates (Table 2, entries 3 and 4). Aliquots of the reaction mixtures were subjected to GC-
MS analysis and no decarbonylated product, i.e. 2-methylfuran, was found, implying that this
product was highly unstable under the reaction conditions (Figure S1). In line with this, no
unreacted furan or 2-methylfuran were found in the GC-MS chromatograms after reactions
where the substrates were employed separately, substantiating that these products were indeed
highly unstable during the reaction under this conditions (Figure S2). Notably, formation of
MH (8%) also occurred when using only 1-hexene as substrate in methanol, evidencing that
solvent reformed took place to a small extent (Table 2). Hence, overall the obtained results
substantiated that the CO source when using HMF as substrate were predominantly the
aldehyde and the methyl hydroxy moiety of HMF (product distributions from all experiments
are compiled in Table S2). However, it cannot be ruled out that CO was not also generated
from methanol and the generated CO might have partly reacted with n-hexene to form methyl
heptanoate.

HMF Conv
MH
ML
GVL
100
80
60
40
20
0
Pd(OAc)2
Pd2(dba)3
Pd(dba)2
Figure 1. The influence of Pd source on the yield of MH. Reaction conditions: Pd (0.025
mmol); HMF (1 mmol); MSA (65 µL; 1 mmol); DTBPMB ligand (0.125 mmol); 1-hexene (1.8
mmol); MeOH (5 mL), 120 °C, 20 h.
3.3 Influence of Pd precursor and ligand
The influence of the Pd precursor on the MH formation from HMF was investigated
after optimizing the reaction time and temperature (Table S3) under identical reaction
conditions as previous experiments (Figure 1). The yield of MH improved to 48-50% from
41% with significant amount of GVL (30-35%) when changing Pd(OAc)2 to Pd2(dba)3 or
Pd(dba)2, (dba: dibenzylideneacetone), signifying that the Pd source was indeed important for
the reaction (Table S4). Similar enhancement in MH yield was also obtained with half or twice
of Pd loading, whereas only ML (87%) and no GVL or MH formed in absence of Pd (Figure
S3). Furthermore, to shed light on the role of the ligand the monophosphine ligand
triphenylphosphine (TPP) was used instead of DTBPMB along with Pd(OAc)2 but here no MH
formed (Figure 2). Instead, the Pd(OAc)2-TPP system rendered a fair yield of ML (61%) which
was similar to the ML yield (77%) obtained without added ligand. Importantly, no MH nor
GVL formed in these latter systems, clearly showing that the presence of DTBPMB ligand in
the Pd catalyst system was indispensable to form MH and GVL by methoxycarbonylation and
hydrogenation/cyclisation, respectively.

HMF Conv.
MH
ML
GVL
100
80
60
40
20
0
DTBPMB
None
TPP
Figure 2. The influence of phosphine ligand on the yield of MH, ML and GVL. Reaction
conditions: Pd (0.025 mmol); HMF (1 mmol); MSA (65 µL; 1mmol); ligand (0.125 mmol); 1-
hexene (1.8 mmol); MeOH (5 mL); 120 °C, 20 h.
3.4 Influence of sugars as substrate
Attempts was also made to extend the reaction protocol with the Pd(OAc)2-phosphine
system to C6 and C5 sugars, such as glucose, fructose and xylose. Here, fructose and xylose
yielded about 18% of MH along with significant amount of ML and GVL, whereas glucose
yielded only 8.8% of MH under identical reaction conditions (Table 3). This suggested that
fructose dehydrated in the presence of the strong mineral acid MSA to HMF followed by
decarbonylation and/or rehydration to form ML and formic acid/MF as well as MH.
Table 3. Conversion of sugars to MH, ML and GVL.a
Entry
Substrate
Conv. (%)
Yield (%)
ML
MH
8.8
GVL
1.7
1
2
3
Glucose
Fructose
Xylose
>99
>99
>99
24.1
17.8
17.5
30.1
19.1
19.0
24.6
a Reaction conditions: Pd(OAc)2 (0.025 mmol); substrate (1 mmol); MSA (65 µL; 1 mmol);
DTBPMB (0.125 mmol); 1-hexene (1.8 mmol), MeOH (5 ml); 120 °C, 20 h.

3.5 Validating origin of CO and H2 with NMR studies
In order to corroborate the origin of CO and H2 from the employed sugar substrates
leading to the formation of MH and GVL, respectively, NMR studies were performed with
normal and 13C1-fructose in deuterated methanol-d4. In the 1H NMR spectrum of the reaction
mixture (Figure S4), the c3 (2.3 ppm) and b3 (4.6 ppm) GVL protons were absent probably
due to the incorporation of deuterium. Especially, the formation of deuterium-labelled b3
suggested that methanol was the source for H2 during the reaction. This was further
13
substantiated by performing the experiment with C1-fructose in normal methanol, where a
peak appeared for the respective proton in GVL ( 4.5 ppm, b3 proton of GVL) which
originated from methanol as H2-donor. (Figure S5) On the other hand, the protons in e2 (1.6
ppm), f2 (2.3 ppm), and g2 (3.6 ppm) positions of the formed MH disappeared due to either
introduction of – OCD3 by reaction with methanol (for g2), or fast ion exchange between
hydrogens in the double bond of 1-hexene and deuterium in the hydroxyl group of methanol-
d4 (for e2 and f2). The appearance of the g2 peak (Figure S5) of MH from the experiment with
normal methanol confirmed that -OCH3 was generated from methanol. The absence of proton
signals from e1 (5.8 ppm) and f1 (5.0 ppm, partially overlapped with the solvent methanol-d4)
of 1-hexene supported the occurrence of H/D exchange. In case of ML, the addition of -OCD3
from methanol-d4 cause disappearance of the d4 (3.6 ppm) protons, and the incorporation of
deuterium in the b4 (2.7 ppm) position of ML resulted possibly due to H/D exchange between
the furan-ring of the upstream intermediate (e.g., HMF) and deuterium in the –OD group of
methanol-d4. Figure S5 revealed the d4 peak of ML due to the introduction of -OCH3 from
methanol, evidencing the role of the methanol. It is worth noting that a small singlet resonance
at 4.5 ppm in the spectrum of reaction mixture indicated presence of H species assigned to H2,
thus implying formation of Pd hydride species during the reaction [43].
13
13
Comparison of the C NMR spectra of C1-fructose with the reaction mixture with
13
13C1-fructose in methanol-d4 (Figure S6) and normal fructose in C-methanol-d4 (Figure S7)
13
indicated almost complete conversion of C1-fructose. Moreover, a new peak appeared at
around 173.1 ppm (Figure S6) assigned to 13C=O in the ester of MH, while no corresponding
peak was found when using normal fructose as substrate even in the presence of 13C-methanol-
d4 (Figure S7). However, MH was formed as confirmed by GC-MS (vide supra) when the
experiment was performed with 1-hexene as substrate (Table S2). Combined, the NMR results
corroborate that the formyl group of HMF, which formed in-situ from fructose by dehydration

during the reaction, was the predominant source for CO species for the methoxycarbonylation
of 1-hexene.
4. Conclusions
In summary, this work demonstrates a novel and alternative approach where furanic
compounds, such as HMF and furfural, are CO surrogates for the conversion of 1-hexene to
MH by methoxycarbonylation with a Pd-catalyst system based on the diphosphine DTBPMB
and MSA. The catalytic system yielded not only the methoxycarbonylated product MH (up to
50%) but also ML and its hydrogenated product GVL, revealing that methanol acted as source
of H2 in the system. This was confirmed by complementary experiments with ML in methanol,
where up to 50% GVL formed. Supporting experiments with other furanic and reference
compounds as substrates revealed that both aldehyde and methyl hydroxy moieties were
potential sources of CO in the reaction system. Isotopic labeling studies with normal fructose
or 13C1-fructose in methanol-d4 or 13C-methanol-d4 further corroborated that H2 and CO
originated from methanol and the formyl group of HMF formed by fructose dehydration,
respectively. However, CO might also have originated from formaldehyde derived from
methanol and reacted partly with n-hexene to form methyl heptanoate. Finally, the substrate
scope of the reaction protocol was extended to the direct transformation of C5 and C6 sugars.
Here, results clearly showed that the catalyst system was indeed able to convert the sugars into
high valuable products such as MH, ML and GVL in significant amounts paving the way for
upgrading biomass-containing hexoses and pentoses. However, further improvement to the
catalytic system is required to enhance the yields of the respective products to close the carbon
balance.
Acknowledgements
The Danish Council for Independent Research-Technology and Production Sciences
(project no. 10-081991) and the National Natural Science Foundation of China (project no.
21576059 and 21666008) are thanked for financial support of the work. SS gratefully
acknowledge Department of Biotechnology (Govt. of India), New Delhi, India for support.
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