One-pot synthesis of amines from biomass resources catalyzed by HReO4

Article abstract of DOI:10.1039/c8gc00915e

This work describes the one-pot synthesis of furfurylamines from carbohydrates catalyzed by HReO₄. These one-pot three-reaction and four-reaction processes allow the conversion of xylose and xylan, respectively, into a large variety of secondary and tertiary amines with good overall yields and chemoselectivity.

Full text of DOI:10.1039/c8gc00915e

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Oneꢀpot synthesis of amines from biomass resources catalyzed by HReO4
João A. T. Caetano and Ana C. Fernandes*
Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av.
Rovisco Pais, 1049ꢀ001 Lisboa, Portugal, Tel: 351 218419264; Fax: 351 218464455,
anacristinafernandes@tecnico.ulisboa.pt
Abstract – This work describes the oneꢀpot synthesis of furfurylamines from
carbohydrates catalyzed by HReO4. These one-pot three-reaction and four-reaction
processes allow the conversion of xylose and xylan, respectively, into a large variety of
secondary and tertiary amines with good overall yields and chemoselectivity.
Keywords: Biomass, carbohydrates, reductive amination, furfurylamines, perrhenic
acid.
Introduction
Sustainable conversion of biomass into drugs, chemicals, biofuels, and various
materials is one of the most challenging tasks for the modern chemistry and industry. In
particular, the conversion of carbohydrates into valuable nitrogen compounds represents
an interesting possibility for the sustainable synthesis of biologically active amines.1ꢀ7
Amines derived from furfural (furfurylamines) have diverse applications,
including in the preparation of polymers, biologically active compounds and also as
intermediates in the synthesis of pharmaceuticals such as antiseptic agents,
antihypertensives and diuretics (e.g. Furosemide, Figure 1).
Figure 1 – Furosemide
Reductive amination, involving the reaction of carbonyl compounds with
amines, remains one of the most versatile and useful synthetic routes for the synthesis of
amines. The synthesis of furfurylamines has been investigated only from furfural and 5ꢀ
hydroxymethylfurfural by reductive amination using Au,8 Fe/Ni,9 Ru,10 Pt,11 Ir,11 Zn,12
1

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or enzymes13 as catalysts. To best of our knowlegde, the oneꢀpot synthesis of amines
from carbohydrates has never been reported.
Several years ago, our group has developed an efficient methodology for the
synthesis of secondary and tertiary amines by direct reductive amination of aldehydes
catalyzed by oxoꢀrhenium complexes using silanes as reducing agents.14 However, the
catalytic activity of HReO4 was not evaluated in this study.
In continuation of our work on the reduction and deoxygenation of several
organic compounds such as sulfoxides,15 Nꢀoxides,15a aromatic nitro compounds,16
esters,17 amides,18 imines,19 alkenes,20 nitriles,21 epoxides,22 carbonyl compounds,23 and
carbohydrates24 catalyzed by oxoꢀrhenium and oxoꢀmolybdenum complexes, here we
investigated the oneꢀpot conversion of xylose and xylan into several furfurylamines
catalyzed by HReO4 (Figure 2).
Figure 2 – Oneꢀpot conversion of xylose and xylan into furfurylamines.
Results and discussion
Initially, we investigated the conversion of xylose into furfural, which is an
important chemical that can be obtained from biomass, and it is currently used in the
production of various resins, pharmaceuticals, herbicides, stabilizers and fuel, such as
liquid hydrocarbons or 2ꢀmethyltetrahydrofuran.25 In order to find the best reaction
conditions, the conversion of xylose into furfural catalyzed by HReO4 in dioxane was
studied using different amounts of catalyst and temperatures. The best result (80%) was
obtained in the presence of 5 mol% of HReO4 at 140 ºC after 2h (Table 1, entry 1). At
120 ºC, the furfural yield decreased to 60% (Table 1, entry 2). The reaction performed
with 2.5 mol% of HReO4 gave the furfural with 70% yield (Table 1, entry 3). Increasing
the amount of HReO4 to 10 mol% at 140 ° C, led to a similar yield of furfural (80%) to
that obtained in the presence of 5 mol% of HReO4 (Table 1, entry 4). Finally, no
reaction was observed in the absence of catalyst (Table1, entry 5).
2

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a
Table 1 – Conversion of xylose into furfural catalyzed by HReO4
Entry
HReO4 (mol%)
Temp. (ºC)
140
Time (h)
Yield (%)b
1
2
3
4
5
5
2
80
5
120
2
60
2.5
10
−
140
3
70
140
2
80
140
24
No reaction
a The reactions were carried out with 1 mmol of xylose.
b Yields determined by 1H NMR spectroscopy using mesitylene as standard.
The direct synthesis of furfurylamines from xylose catalyzed by HReO4 was
investigated using different silanes. The best result (76%) was obtained employing
tertiary silane Me2PhSiH as reducing agent (Table 2, entry 1). The reaction with
primary silane PhSiH3, which is generally the most reactive silane, gave furfurylamine
in a slightly lower yield (70%), probably due to some polymerization of phenylsilane at
high temperature (Table 2, entry 2). The conversion of xylose was also tested using
polymethylhydrosiloxane (PMHS), a cheaper, easyꢀtoꢀhandle and environmentally
friendly silicone industry byproduct, however this reducing agent proved to be less
efficient, producing the amine in only 35% yield after 3 h (Table 2, entry 3). In contrast
to Me2PhSiH, the tertiary silanes Et3SiH and Pr3SiH were less effective. No
furfurylamine was formed using these silanes after 1h (Table 2, entries 4 and 6), but
after 18 h, the product was obtained in 54% and 19% yields, respectively (Table 2,
entries 5 and 7). Finally, the formation of furfurylamine was not observed using
triphenylsilane (Table 2, entry 8) or in the absence of silane (Table 2, entry 9).
Table 2 – Oneꢀpot synthesis of furfurylamine using different silanesa
Entry
Silane
Time (h)b
Yield (%)c
1
2
Me2PhSiH
PhSiH3
1
1
76
70
3

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3
4
5
6
7
8
9
PMHS
3
35
Pr3SiH
1
0
Pr3SiH
2.5
1
62
Et3SiH
0
Et3SiH
18
18
18
54
Ph3SiH
Without silane
No reaction
No reaction
a The reactions were carried out with 1 mmol of xylose and 1.2 mmol of silane.
b Reaction time after addition of the silane.
c Isolated yields.
To evaluate the general applicability of HReO4 as catalyst for the oneꢀpot
synthesis of furfurylamines from xylose, this reaction was explored with a variety of
anilines (Table 3). Initially, we tested the reaction of xylose using 4ꢀfluoroaniline
catalyzed by 2.5 mol% of HReO4, obtaining the amine in 65% yield (Table 3, entry 1).
This reaction was also explored with a higher amount of catalyst (5 mol%), leading to
the formation of product with a better yield of 76% (Table 3, entry 2). Then, we decided
to study the conversion of xylose into a wide range of furfurylamines using 5 mol% of
HReO4. Generally, moderate to good overall yields of the secondary amines were
obtained. The best yields were observed in the reactions with anilines containing
electronꢀwithdrawing groups, which promote the attack of the silane to the imine. In
contrast, no reaction was observed using benzylamine and cyclohexylamine. This
method was also tested with Nꢀmethylaniline in order to evaluate the efficiency of this
catalyst in the synthesis of a tertiary amine, giving the amine with an overall yield of
71% (Table 3, entry 14). This methodology is also chemoselective tolerating several
functional groups including ꢀCN, ꢀCO2Me, ꢀSO2Me, ꢀCF3, ꢀF, ꢀBr, ꢀCl, ꢀOMe.
a
Table 3 ꢀ Oneꢀpot synthesis of furfurylamines from xylose catalyzed by HReO4
Entry
Aniline
Product
Yield (%)b
4

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1
2
65c
76
3
80
4
75
5
6
71
71
7
65
8
9
60
59
10
73
67
11
12
55d
56d
13
14
75
5

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a The reactions were carried out with 1.0 mmol of xylose, 1.0 mmol of aniline
and 1.2 mmol of Me2PhSiH.
b Isolated yields.
c Using only 2.5 mol% of HReO4.
dYields determined 2h after the addition of silane.
To study the scope of this reaction, we also investigated the synthesis of
furfurylamines from other carbohydrates such as arabinose, ribose and the
polysaccharide xylan. These reactions were carried out with 4ꢀfluoroaniline using
dimethylphenylsilane as reducing agent in the presence of higher amount of HReO4 (10
mol%). The reaction of arabinose, the second most abundant pentose in biomass after
xylose, gave the furfurylamine in only 29% yield (Figure 3). Low yields for the
conversion of arabinose were also reported before by other authors. For example,
Gallo26 found that the furfural yield obtained from arabinose was approximately half of
that from xylose using H2SO4 solution. Garrett27 studied the kinetics of the conversion
of arabinose and xylose into furfural and observed that the reaction rate of xylose was
much higher than that of arabinose, proposing that the steric positioning of the
hydroxyls in the pentose is the controlling factor leading to different reactivities.
Dussan28 further suggested that the distribution of isomers of pentose is another factor
affecting the reactivity. In xylose, the βꢀpyranose form is the predominant form,
whereas the αꢀpyranose is the predominant for arabinose. As the αꢀpyranose tautomer is
more stable than βꢀpyranose, it is more difficult to dehydrate it to furfural. The reaction
of ribose catalyzed by HReO4 also gave furfural in only 36% yield (Figure 3). In
Figure 3 ꢀ Synthesis of furfurylamines from arabinose and ribose.
contrast, the reaction of xylan produced the furfurylamine with a better yield (57%)
(Table 4, entry 3). Then, we decided to explore the reaction of xylan with different
6

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anilines obtaining the corresponding furfurylamines in 62ꢀ58% yields (Table 4). These
results demonstrate that HReO4 also catalyzes the hydrolyse of the glycosidic bonds of
xylan.
a
Table 4 – Oneꢀpot synthesis of furfurylamines from xylan catalyzed by HReO4
R1
R2
N
O
O
1) HReO4 (10 mol%), dioxane, 140 ºC, 2 h
2) Aniline, Me2PhSiH, 1h
O
OH
HO
O
HO
HO
OH
OH
n
Xylan
Entry
Aniline
Furfurylamine (%)
Yield (%)b
62
c
1
2
60
3
4
58
57
5
6
57
56
7
9
56
53
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53
10
a The reactions were carried out with 1.0 mmol of xylan, 1.0 mmol of aniline and
1.2 mmol of Me2PhSiH.
b Isolated yields.
The catalytic activity of HReO4 on the conversion of xylose was also tested in
gram scale. The reaction carried out from 10 mmol (1,5 g) of xylose with 4ꢀ
flouroaniline using dimethylphenylsilane as reducing agent in the presence of 5 mol%
of HReO4 gave the corresponding furfurylamine with 43% yield. Using a higher amount
of HReO4 (10 mol%), the furfurylamine was obtained with 58% yield.
Conclusion
This work describes the first methodology for the oneꢀpot conversion of monoꢀ
and polysaccharides into amines catalyzed by an oxoꢀrhenium complex. This
methodology is chemoselective and produces a large variety of secondary and tertiary
amines with good overall yields. This oneꢀpot multiꢀreaction process has also the
advantage of minimize chemical wastes, reduce cost, time and the separation of
intermediate compounds.
HReO4 also efficiently catalyzed the conversion of xylose into furfural, which
has been identified as one of the most promising chemical platforms for the synthesis of
valueꢀadded chemicals and fuels. These results extend the scope of the use of oxoꢀ
rhenium complexes as efficient catalysts for the synthesis of valuable amines from
renewable resources and open a new area of research for these complexes.
Experimental Section
General information
Carbohydrates, anilines, silanes and the catalyst HReO4 (75ꢀ80% aqueous solution)
were obtained from commercial suppliers and were used without further purification.
1
Flash chromatography was performed on MN Kieselgel 60M 230ꢀ400 mesh. H NMR,
13C NMR and 31P NMR spectra were measured on a Bruker Avance II+ 400 MHz and
8

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300 MHz spectrometers. Chemical shifts are reported in parts per million (ppm)
downfield from an internal standard.
General procedure for the conversion of xylose into furfural catalyzed by HReO4
To a Schlenk flask equipped with a J. Young tap containing a solution of xylose (1.0
mmol) in 1,4ꢀdioxane (10 mL) was added HReO4 (5 mol%). The reaction mixture was
stirred in a closed Schlenk at 140 °C during 2 h. The yield of furfural was determined
by spectroscopy 1H NMR using mesitylene as internal standard.
General procedure for the one-pot synthesis of furfurylamines
To a Schlenk flask equipped with a J. Young tap containing a solution of carbohydrate
(1.0 mmol of pentose) in 1,4ꢀdioxane (10 mL) was added HReO4 (5 mol%). The
reaction mixture was stirred in a closed Schlenk at 140 °C during 2 h. Then, the reaction
mixture was cooled at room temperature and aniline (1.0 mmol) and
dimethylphenylsilane (1.2 mmol) was added. After 1h at 140ºC, the reaction mixture
was evaporated and the residue was purified by flash chromatography with appropriate
mixtures of nꢀhexane:ethyl acetate, affording the furfurylamines.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This research was supported by Fundação para a Ciência e Tecnologia through project
UID/QUI/00100/2013. Ana Fernandes (IF/00849/2012) acknowledges FCT for the
“Investigador FCT” Program. Authors also thank the Portuguese NMR Network (ISTꢀ
UTL Center) for providing access to the NMR facilities.
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Graphical abstract
O
HO
HO
OH
OH
One-pot
Xylose
synthesis of
fur furylamines
catalyzed
R1
R2
N
O
by HReO4
O
Furfurylamines
O
O
HO
OH
HO
HO
OH
OH
Biomass
Resources
n
Xylan
HReO4 as an efficient catalyst for one-pot conversion of xylose and xylan into a large
variety of amines with good overall yields.