Two-step one-pot reductive amination of furanic aldehydes using CuAlOx catalyst in a flow reactor

Article abstract of DOI:10.3390/molecules25204771

Aminomethylhydroxymethylfuran derivatives are well known compounds which are used in the pharmaceutical industry. Reductive amination of 5-hydroxymethylfurfural (HMF) derived from available non-edible lignocellulosic biomass is an attractive method for the synthesis of this class of compounds. In the present study, the synthesis of N-substituted 5-(hydroxymethyl)-2-furfuryl amines and 5-(acetoxymethyl)-2-furfuryl amines was performed by two-step process, which includes the condensation of furanic aldehydes (HMF and 5-acetoxymethylfurfural) with primary amines in methanol on the first step and the reduction of obtained imines with hydrogen in a flow reactor over CuAlO_x catalyst derived from layered double hydroxide on the second step. This process does not require isolation and purification of intermediate imines and can be used to synthesize a number of aminomethylhydroxymethylfurans in good to excellent yield.

Full text of DOI:10.3390/molecules25204771

molecules
Article
Two-Step One-Pot Reductive Amination of Furanic
Aldehydes Using CuAlO Catalyst in a Flow Reactor
x
Alexey L. Nuzhdin * , Marina V. Bukhtiyarova and Valerii I. Bukhtiyarov
Boreskov Institute of Catalysis SB RAS, 630090 Novosibirsk, Russia; mvb@catalysis.ru (M.V.B.);
vib@catalysis.ru (V.I.B.)
*
Correspondence: anuzhdin@catalysis.ru; Tel.: +7-383-3269-410
ꢀ
ꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀ
ꢁꢂꢃꢄꢅꢆ
Received: 26 September 2020; Accepted: 15 October 2020; Published: 17 October 2020
Abstract: Aminomethylhydroxymethylfuran derivatives are well known compounds which are used
in the pharmaceutical industry. Reductive amination of 5-hydroxymethylfurfural (HMF) derived
from available non-edible lignocellulosic biomass is an attractive method for the synthesis of this class
of compounds. In the present study, the synthesis of N-substituted 5-(hydroxymethyl)-2-furfuryl
amines and 5-(acetoxymethyl)-2-furfuryl amines was performed by two-step process, which includes
the condensation of furanic aldehydes (HMF and 5-acetoxymethylfurfural) with primary amines in
methanol on the first step and the reduction of obtained imines with hydrogen in a flow reactor over
CuAlO catalyst derived from layered double hydroxide on the second step. This process does not
x
require isolation and purification of intermediate imines and can be used to synthesize a number of
aminomethylhydroxymethylfurans in good to excellent yield.
Keywords: reductive amination; 5-hydroxymethylfurfural; 5-acetoxymethylfurfural; Cu-based
catalyst; Cu-Al mixed oxide; primary amines; imine hydrogenation; flow reactor
1
. Introduction
N-Substituted 5-(hydroxymethyl)-2-furfuryl amines are an important class of compounds due to
their usage in pharmaceutical industry for production of calcium antagonists, muscarinic agonists,
cholinergic agents, carcinogenesis inhibitors, etc. (for instance, anti-hepatitis B virus drug and
antihypertensives, Scheme 1) [
reaction starting from furfural alcohol (or furfural), formaldehyde, and primary amines. However,
harsh reaction conditions are usually required, that leads to a low yield of the target product [ ].
1–3]. Generally, these structures are prepared by a Mannich-type
4–6
Meanwhile, reductive amination of 5-hydroxymethylfurfural (HMF) derived from available non-edible
lignocellulosic biomass is an attractive method for the synthesis of this type of amines [3,7–11].
OH
O
O
R
2
O
HN
N
O
N R
3
O
O
R
1
N
H
Anti-hepatitisB
Anti-hypertensive
Scheme 1. Examples of N-substituted 5-(hydroxymethyl)-2-furfuryl amines with pharmaceutical activity.
In general, the reductive amination of HMF is realized in the presence of noble metal-based
catalysts such as dichlorobis(2,9-dimethyl-1,10-phenanthroline) ruthenium(II) complex [
7], Pd/C [8],
Au/TiO2 [ ], and Pd nanoparticles immobilized in a MOF/polymer composite [ ] using batch reactors.
3
9
Molecules 2020, 25, 4771; doi:10.3390/molecules25204771
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Molecules 2020, 25, 4771
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However, the high price and limited availability of precious metals are stimulated interest in catalysts
based on earth-abundant elements. Chieffi et al. studied the reductive amination of HMF over
carbon-supported Fe-Ni catalyst under flow conditions. However, the amines used were limited to
3
-aminopropanol and alanine sodium and the yield of the target aminomethylhydroxymethylfuran
(AMHMF) derivatives did not exceed 78% [11].
In our previous study [12], an environmentally friendly procedure has been developed for the
synthesis of secondary amines through a two-step one-pot reductive amination of aromatic aldehydes
with primary amines. The condensation of benzaldehyde derivatives (or furfural) with amines in
methanol at room temperature gives imines, which are then hydrogenated in a flow reactor using Cu-Al
mixed oxide (denoted hereafter as CuAlO
work, we investigated the efficiency of this procedure for reductive amination of furanic aldehydes
HMF and 5-acetoxymethylfurfural) with primary amines via hydrogenation of the intermediate imines
over CuAlOx catalyst in a flow reactor.
x
) derived from layered double hydroxide (LDH). In present
(
2
. Results and Discussion
Methanol is a suitable solvent for the synthesis of N-substituted 5-(hydroxymethyl)-2-furfuryl
amines, since it is a good solvent for both the condensation of aromatic aldehydes with primary amines
and hydrogenation of imines [10 12 13]. We found that the reaction of HMF with aniline in low water
,
,
methanol (0.02 wt% H O) occurs at room temperature with imine yield of 98% (Table 1, entry 1) and
2
time dependence of imine yield let us to see that equilibrium concentrations are reached within 2 h
(
Supplementary Materials, Figure S1). The use of ethanol instead of methanol leads to a decrease in the
yield of imine 1a to 70% (Table 1, entry 2). Simultaneously, the yield of 1a in isopropanol is only 31%
under the same reaction conditions (Table 1, entry 3).
Table 1. Condensation of 5-hydroxymethylfurfural (HMF) with aniline 1.
Entry
Solvent
Yield, % 2
1
2
3
Methanol
Ethanol
Isopropanol
98
70
31
1
◦
2
Reaction conditions: HMF (0.05 M), aniline (0.05 M), batch reactor, T = 25 C, 2 h. GC yields.
The reaction mixtures obtained by condensation of HMF with primary amines were further
◦
hydrogenated over CuAlO
catalytic run, the CuO phase of CuAlO
]. The average size of copper crystallites in the reduced sample was about 7 nm [14] that is much
smaller than in case of the supported Cu/Al O catalysts with high copper content. Thus, CuAlO
x
catalyst in a flow reactor at 100 C and H pressure of 10 bar. Before each
2
x
was reduced in situ by hydrogen to metallic copper particles [12,
1
4
2
3
x
material prepared by calcination of LDH precursor is a promising non-noble metal catalyst for
hydrogenation reactions [12,14,15].
The hydrogenation of imine 1a, which is obtained by condensation of HMF and aniline in methanol,
leads to the formation of AMHMF derivative 2a with the yield of 97% (Table 2, entry 1). In addition
to 2a, undesired bis-(hydroxymethyl)furan
ethanol or isopropanol instead of methanol leads to a strong drop in the yield of the target product
Table 2, entries 2 and 3) due to the much lower yield of imine in the first stage (Table 1). As a result,
a greater amount of HMF is hydrogenated to . Raising the concentration of reactants in methanol
to 0.2 M reduces the yield to 94% (Table 2, entry 4). However, an increase of reaction temperature
3 was observed among the reaction products. The use of
(
3

Molecules 2020, 25, 4771
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◦
to 120 C at high reactant concentration leads to rise of the imine hydrogenation rate and allows
synthesizing 2a with the yield of 98% (Table 2, entry 5).
The effect of primary amine structure on the formation of AMHMF derivatives was investigated by
reductive amination of HMF with different aromatic and aliphatic amines over CuAlO
entries 1 and 6–16). Formation of 2b 2c, and 2e with the excellent yield (95–97%) is observed for
aromatic amines containing electron-donating substituent (CH and OCH ) in meta- and para-position
x
catalyst (Table 2,
,
3
3
(
Table 2, entries 6, 7, and 9). It means that the rates of imine formation in the condensation of HMF with
these compounds are similar to that in the reaction of HMF with aniline while using o-toluidine gives
lower rate of imine formation due to steric hindrance created by methyl group in ortho-position [12].
A much longer period of time (16 h) is needed for the condensation of HMF with o-toluidine at the
first stage to obtain 2d with the yield of 88% by imine hydrogenation over the CuAlO catalyst at the
x
second stage (Table 2, entry 8).
Introduction of F and Cl substituent in the para-position of aniline slightly decreases the yield of
compounds to 93–94% (Table 2, entries 10 and 11). At the same time, in the case of p-bromoaniline
2
the significant drop in the yield of the target product to 60% was observed while imine amount in the
final mixture was increased (Table 2, entry 12). It is worth to mention that reaction was performed at
◦
1
10 C that is higher than in case of other aromatic amines. This result can be explained by the steric
x
hindrance created by bulky Br substituent during the diffusion of imine to active sites of CuAlO [12].
It should be noted that hydrodehalogenated product practically did not form during the reaction.
Table 2. Two-step one-pot reductive amination of HMF with primary amines 1.
Yield, % 2
◦
Entry
R
Step 1, h
T, C
2
1
2
3
4
1
Ph
Ph
Ph
Ph
Ph
3
3
3
3
3
3
3
16
3
3
3
3
3
16
16
3
100
100
100
100
120
100
100
100
100
100
100
110
100
100
100
100
2a
2a
2a
2a
2a
2b
2c
2d
2e
2f
2g
2h
2i
2i
2j
n.d.
n.d.
n.d.
3
97
74
67
94
98
97
96
88
95
94
93
60
55
95
52
93
3
26
33
3
<1
3
4
12
5
n.d.
n.d.
n.d.
<0.5
0.5
n.d.
n.d.
<0.5
n.d.
n.d.
n.d.
1
3
2
3
4
5
4
5
5
1
6
7
8
9
p-CH C H
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
22
n.d.
n.d.
n.d.
n.d.
3
6
4
m-CH C H
3
6
4
o-CH C H
3
6
4
p-CH OC H
3
6
4
10
11
12
13
14
15
16
p-FC H
6
7
6
4
p-ClC H
6
4
4
p-BrC H
16
45
4
42
7
6
m-ClC H
m-ClC H
n.d.
1
6
6
4
6
4
o-ClC H
6
4
n-hexyl
2k
n.d.
1
Reaction conditions: HMF (0.05 M), primary amine (0.05 M), CuAlO
x
catalyst (165 mg), 10 bar H
2
, liquid flow rate
−1
−1
2
1
3
of 0.5 mL min , hydrogen flow rate of 30 mL min
was used as a solvent. Isopropanol was used as a solvent. Reactant concentrations were 0.2 M.
.
The product yields were determined by H-NMR. Ethanol
4
5
The position of electron-withdrawing substituent in aromatic amine has a strong effect on the
reaction. The imine formation rate in the condensation of HMF with m-chloroaniline is much lower
than with p-chloroaniline. As a result, the reaction of HMF with m-chloroaniline for 3 h on the first
stage leads to formation of 2i in a low yield (Table 2, entry 13). However, carrying out the condensation
of HMF and m-chloroaniline for 16 h allows obtaining 2i in 95% yield (Table 2, entry 14). At the same
time, o-chloroaniline gave a moderate yield of 2j (52%) after the reaction with HMF on the first stage for

Molecules 2020, 25, 4771
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1
6 h (Table 2, entry 15). These observations are explained by a decrease in the nucleophilic properties
of chloroanilines in the following order: p-chloroaniline > m-chloroaniline > o-chloroaniline.
Thus, the yield of is determined by the imine formation at the first stage. Higher yield of the
2
intermediate imine provides higher yield of AMHMF derivative. In the case of primary amines with
weak nucleophilic properties (o-toluidine, m-chloroaniline, o-chloroaniline), a longer condensation
time (16 h) is required to obtain compound 2 with a higher yield.
Using aliphatic hexylamine gave a slightly lower yield of AMHMF derivative than aniline (Table 2,
entries 1 and 16) that can be explained by instability of intermediate imines containing alkyl substituent [16].
The time-on-stream measurements for reductive amination of HMF with aniline over the CuAlO
x
catalyst were performed for~3 h (Supplementary Materials, Figure S3). The yield of 2a (97%) remained
unchanged meaning that the catalyst exhibits good stability during the reaction [12,14].
5
-Acetoxymethylfurfural (AMF), which can be prepared from carbohydrates without isolating
HMF, is less reactive, more stable and easily extracted from the aqueous reaction mixture. Therefore,
AMF represents a good substitute for HMF [17 19]. Similar to HMF, AMF reacts with aniline in methanol
to form imine with the yield of 98% (Supplementary Materials, Figure S2). The hydrogenation of
–
imines obtained by condensation of AMF with different amines was carried out on the CuAlO
x
catalyst
◦
at lower temperature of 80 C than in case of HMF in order to avoid the reduction of the acetoxymethyl
group. It was found that reductive amination of AMF with aniline and its derivatives containing CH3
group in para- and meta- positions leads to the formation of N-substituted 5-(acetoxymethyl)-2-furfuryl
amines 6a–c with the yields about 99% (Table 3, entries 1–3). Introduction of methyl substituent in
ortho-position of aniline decreases the yield of compound
6 to 96% (Table 3, entry 4). It is worth to
mention that condensation of AMF with o-toluidine was performed for 16 h while temperature of
◦
following hydrogenation of obtained imine was raised to 90 C. In the case of anilines with CH O,
3
F, and Cl substituents in para-position, AMHMF derivatives 6e, 6f, and 6g were obtained with the
yield of 99, >98 and 97%, respectively (Table 3, entries 5–7). Simultaneously, the reaction of AMF with
◦
m-chloroaniline for 16 h at the first stage, followed by imine hydrogenation at 80 C, allows synthesizing
6h with the yield of 96% (Table 3, entry 8). In contrast to aromatic amines, hexylamine gives only 82%
yield of the AMHMF derivative due to hydrogenation of acetyl group in 6i (Table 3, entry 9).
Table 3. Two-step one-pot reductive amination of 5-Acetoxymethylfurfural (AMF) with primary amines 1.
Yield, % 2
Entry
R
Step 1, h
6
5
6
7
8
9
1
2
3
Ph
3
3
3
16
3
3
3
16
3
6a
6b
6c
6d
6e
6f
6g
6h
6i
n.d.
n.d.
<0.5
n.d.
n.d.
<0.5
<0.5
n.d.
n.d.
99
>99
>98
96
99
>98
97
<0.5
n.d.
n.d.
1
0.5
<0.5
0.5
<1
<1
1
3
<0.5
1
2
2
n.d.
n.d.
n.d.
n.d.
n.d.
<0.5
n.d.
<0.5
2
p-CH C H
3
6
4
m-CH C H
3
6
4
3
4
o-CH
p-CH OC H
4
3
C
6
H
4
5
6
7
8
9
3
6
p-FC H
6
4
p-ClC H
6
4
m-ClC H
n-hexyl
96
<0.5
n.d.
6
4
4
82
n.d.
1
◦
Reaction conditions: AMF (0.05 M), primary amine (0.05 M), CuAlO
x
catalyst (165 mg), 80 C, 10 bar H
2
, liquid flow
−1
−1
2
1
rate of 0.5 mL min , hydrogen flow rate of 30 mL min
.
The product yields were determined by H-NMR.
3
◦
4
T = 90 C. Compound 2k was also formed.

Molecules 2020, 25, 4771
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3
. Materials and Methods
3
.1. Chemicals
Aniline (99.8%), o-toluidine (99%), m-toluidine (99%), p-toluidine (99%), p-anisidine (99%),
o-chloroaniline (>98%), m-chloroaniline (99%), p-chloroaniline (98%), p-fluoroaniline (98%),
p-bromoaniline (>99%), n-hexylamine (99%), and 5-(acetoxymethyl)-2-furaldehyde (97%) from Acros
Organics (Geel, Belgium), as well as 5-hydroxymethylfurfural (99%) from Sigma-Aldrich (St Louis, MO,
USA), were used without additional purification. Methanol (99.8%) from J.T. Baker (Phillipsburg, NJ,
USA), ethanol (99.9%) from J.T. Baker and isopropanol (99.5%) from Acros Organics were employed as
a solvent.
3
.2. Catalyst Preparation
Cu-Al layered double hydroxide was prepared by co-precipitation method at pH 9.0 and
◦
temperature of 70 C using the mixture of copper (II) nitrate and aluminum nitrate as starting material
2
−
3+
−
3+
2+
and solution containing NaOH and Na CO ([CO ]/[Al ] = 0.86, [OH ] = 1.6([Al ] + [Cu ]) as
precipitant agent. The aging of the obtained suspension was performed at 70 C for 4 h. Afterwards,
the precipitate was filtered, washed with hot water and dried at 110 C for 14 h. The as-prepared LDH
was calcined at 650 C for 4 h to obtain desired CuAlO
2
3
3
◦
◦
◦
x
catalyst [11
,13] containing 47.2 wt% of Cu and
1
9.9 wt% of Al. The texture properties of CuAlO
x
were found to be as follows: BET specific surface
2
−1
3
−1
area—68 m g and total pore volume—0.15 cm g
.
3
.3. Characterization Techniques
The Cu and Al content was measured by atomic absorption spectroscopy on an Optima 4300 DV
instrument (Perkin Elmer, Waltham, MA, USA). Textural characteristics were determined from
nitrogen adsorption–desorption isotherms (77 K) obtained on a Micromeritics ASAP 2400 analyzer
(Micromeritics, Norcross, GA, USA).
3
.4. General Procedure for Reductive Amination of Furanic Aldehydes with Primary Amines
Depending on the nucleophilic properties of the amine, the solution of furanic aldehyde (0.05 M)
◦
and primary amine (0.05 M) in methanol was kept at 25 C for 3 or 16 h. Then, the reaction
x
mixture was mixed with H and pumped through the flow reactor packed with the CuAlO material.
2
Catalytic experiments were performed in H-Cube Pro setup (Thalesnano, Budapest, Hungary) equipped
®
with a 30 mm CatCart cartridge (CatCart 30, 0.30 mL empty volume) [11
,
13]. Before the catalytic run,
the catalyst (0.165 g of 250–500
µ
m particles) was reduced by a mixture of hydrogen with methanol at
◦
−1
1
20 C for 1 h (pressure of 10 bar, flow rates of methanol and H were 0.5 and 30 mL min , respectively).
2
Afterwards, the reaction mixture was pumped through the reactor instead of pure solvent, and this
point in time was chosen as the starting point of the experiment.
◦
The reaction was carried out at temperature of 80–120 C, H pressure of 10 bar, liquid feed rate of
2
−
1
−1
0
.5 mL min and hydrogen flow rate of 30 mL min (inlet H /substrate molar ratio was 54). The use
2
of a large excess of H in the reaction medium is necessary to avoid the influence of external mass
2
transfer on the reaction progress [13]. The performance of the catalyst was evaluated by analysis of the
samples taken in the interval of 30–33 min from the beginning of the experiment. The composition of
1
the reaction products was determined using H NMR spectroscopy in CDCl . The error in determining
3
the yield is ±1%.
4
. Conclusions
The two-step one-pot reductive amination of furanic aldehydes, including non-catalytic
condensation of HMF (or AMF) with primary amines and the subsequent flow hydrogenation
of the obtained imine over Cu-based catalyst derived from layered double hydroxide, was successfully

Molecules 2020, 25, 4771
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performed using methanol as a solvent. This inexpensive and environmentally friendly process
can be utilized to obtain a wide range of N-substituted 5-(hydroxymethyl)-2-furfuryl amines and
5-(acetoxymethyl)-2-furfuryl amines in good to excellent yields (up to 98 and 99%, respectively).
The proposed approach is a new method for the synthesis of aminomethylhydroxymethylfuran
derivatives which can be used as pharmaceuticals or their precursors.
Supplementary Materials: The following are available online, Figure S1: The time dependence of imine yield in
the condensation of HMF (0.05 M) and aniline (0.05 M) at room temperature; Figure S2: The time dependence of
imine yield in the reaction between AMF (0.05 M) and aniline (0.05 M) in methanol at room temperature; Figure S3:
Time dependence of 2a yield in the two-step one-pot reductive amination of HMF (0.05 M) with aniline (0.05 M) at
◦
1
1
00 C; H-NMR spectra of the final reaction mixtures.
Author Contributions: A.L.N. planned and designed the experiments, performed the catalytic activity tests,
and wrote the manuscript. M.V.B. performed the catalyst synthesis and revised the manuscript. V.I.B. supervised
the project. All authors discussed the results and approved the final version of the manuscript.
Funding: The work was supported by the Russian Science Foundation (grant no. 20-43-05002).
Conflicts of Interest: The authors declare no conflict of interest.
References
1
.
Feriani, A.; Gaviraghi, G.; Toson, G.; Mor, M.; Barbieri, A.; Grana, E.; Boselli, C.; Guarneri, M.; Simoni, D.;
Manfredini, S. Cholinergic Agents Structurally Related to Furtrethonium. 2. Synthesis and Antimuscarinic
0
Activity of a Series of N-[5-[(1 -Substituted-acetoxy)methyl]-2-furfuryl]dialkylamines. J. Med. Chem. 1994
,
3
7, 4278–4287. [CrossRef] [PubMed]
2
3
.
.
Caetano, J.A.T.; Fernandes, A.C.; Catano, J.A.T. One-pot synthesis of amines from biomass resources catalyzed
by HReO4. Green Chem. 2018, 20, 2494–2498. [CrossRef]
Zhu, M.-M.; Tao, L.; Zhang, Q.; Dong, J.; Liu, Y.-M.; He, H.-Y.; Cao, Y. Versatile CO-assisted direct reductive
amination of 5-hydroxymethylfurfural catalyzed by a supported gold catalyst. Green Chem. 2017, 19,
3
880–3887. [CrossRef]
4
5
.
.
Li, X.; Xu, R.; Yang, J.; Nie, S.; Liu, D.; Liu, Y.; Si, C. Production of 5-hydroxymethylfurfural and levulinic
acid from lignocellulosic biomass and catalytic upgradation. Ind. Crop. Prod. 2019, 130, 184–197. [CrossRef]
Hu, L.; Lin, L.; Wu, Z.; Zhou, S.; Liu, S. Recent advances in catalytic transformation of biomass-derived
5
2
-hydroxymethylfurfural into the innovative fuels and chemicals. Renew. Sustain. Energy Rev. 2017, 74,
30–257. [CrossRef]
6
.
.
Froidevaux, V.; Negrell, C.; Caillol, S.; Pascault, J.-P.; Boutevin, B. Biobased Amines: From Synthesis to
Polymers; Present and Future. Chem. Rev. 2016, 116, 14181–14224. [CrossRef] [PubMed]
Xu, Z.; Yan, P.; Xu, W.; Jia, S.; Xia, Z.; Chung, B.; Hou, G. Direct reductive amination of 5-hydroxymethylfurfural
with primary/secondary amines via Ru-complex catalyzed hydrogenation. RSC Adv. 2014, 4, 59083–59087.
7
[CrossRef]
8
.
.
Garc a-Ortiz, A.; Vidal, J.D.; Climent, M.J.; Concepción, P.; Corma, A.; Iborra, S. Chemicals from Biomass:
Selective Synthesis of N-Substituted Furfuryl Amines by the One-Pot Direct Reductive Amination of Furanic
Aldehydes. ACS Sustain. Chem. Eng. 2019, 7, 6243–6250. [CrossRef]
Karve, V.V.; Sun, D.T.; Trukhina, O.; Yang, S.; Oveisi, E.; Luterbacher, J.S.; Queen, W.L. Efficient reductive
amination of HMF with well dispersed Pd nanoparticles immobilized in a porous MOF/polymer composite.
Green Chem. 2020, 22, 368–378. [CrossRef]
í
9
1
1
1
0. Cukalovic, A.; Stevens, C.V. Production of biobased HMF derivatives by reductive amination. Green Chem.
2
010, 12, 1201–1206. [CrossRef]
1. Chieffi, G.; Braun, M.; Esposito, D. Continuous Reductive Amination of Biomass-Derived Molecules over
Carbonized Filter Paper-Supported FeNi Alloy. ChemSusChem 2015, 8, 3590–3594. [CrossRef] [PubMed]
2. Nuzhdin, A.L.; Bukhtiyarova, M.V.; Bukhtiyarova, G.A. Cu-Al mixed oxide derived from layered double
hydroxide as an efficient catalyst for continuous-flow reductive amination of aromatic aldehydes. J. Chem.
Technol. Biotechnol. 2020. [CrossRef]
1
3. Hizartzidis, L.; Cossar, P.J.; Robertson, M.J.; Simone, M.I.; Young, K.A.; McCluskey, A.; Gordon, C.P.
Expanding the utility of flow hydrogenation—A robust protocol restricting hydrodehalogenation. RSC Adv.
2
014, 4, 56743–56748. [CrossRef]

Molecules 2020, 25, 4771
7 of 7
1
4. Nuzhdin, A.L.; Bukhtiyarova, M.V.; Bulavchenko, O.A.; Bukhtiyarova, G.A. Flow hydrogenation of
-acetoxymethylfurfural over Cu-based catalysts. Mol. Catal. 2020, 494, 111132. [CrossRef]
5
1
5. Kumalaputri, A.J.; Bottari, G.; Erne, P.M.; Heeres, H.; Barta, K. Tunable and Selective Conversion of 5-HMF
to 2,5-Furandimethanol and 2,5-Dimethylfuran over Copper-Doped Porous Metal Oxides. ChemSusChem
2
014, 7, 2266–2275. [CrossRef] [PubMed]
1
6. Layer, R.W. The Chemistry of Imines. Chem. Rev. 1963, 63, 489–510. [CrossRef]
1
7. Kang, E.-S.; Hong, Y.-W.; Chae, D.W.; Kim, B.; Kim, B.; Kim, Y.J.; Cho, J.K.; Kim, Y.G. From Lignocellulosic
Biomass to Furans via 5-Acetoxymethylfurfural as an Alternative to 5-Hydroxymethylfurfural. ChemSusChem
2
015, 8, 1179–1188. [CrossRef] [PubMed]
8. Gavil , L.; Esposito, D. Cellulose acetate as a convenient intermediate for the preparation of
-acetoxymethylfurfural from biomass. Green Chem. 2017, 19, 2496–2500. [CrossRef]
1
1
à
5
9. Shinde, S.; Deval, K.; Chikate, R.; Rode, C.V. Cascade Synthesis of 5-(Acetoxymethyl)furfural from
Carbohydrates over Sn-Mont Catalyst. ChemistrySelect 2018, 3, 8770–8778. [CrossRef]
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