T.S. Hansen et al. / Applied Catalysis A: General 456 (2013) 44–50
49
Table 3
catalyst system in MeCN showed a high selectivity to DFF (97%) at
moderate conversions (44%). Using dioxygen as the oxidant under
identical reaction conditions increased the HMF conversion and
DFF yield. Reactions proceeded generally poorly in other solvents
than MeCN. Nevertheless, an enhancement in both substrate con-
version and DFF selectivity was observed when several NCPs were
added. 90–95% DFF yields were obtained after 24 h in MeCN at RT
with O2 as the oxidant. The use of NCPs, bipy in particular, improved
considerably the catalytic activity in other solvents than MeCN,
allowing application of MIBK, for instance. MIBK is interesting since
it is commonly used as solvent to extract HMF from the aqueous
phase in the synthesis from fructose, thus it could prove particu-
lar interesting to develop an efficient oxidation protocol with this
solvent.
In addition to the synthesis of DFF by oxidation of HMF, we
have also demonstrated for the first time (as far as we are aware),
that oxidation of HMF into the renewable terephthalic acid sub-
stitute FDCA can be achieved in fair to good yields (50%) by using
the oxidation pair CuCl/t-BuOOH in MeCN. Since FDCA is scarcely
soluble in the reaction media, such an oxidation approach might
facilitate effective separation of the product by simple filtration.
This feature will most likely be of significant importance for future
implementation of a HMF oxidation protocol into an integrated pro-
cess, where carbohydrates (e.g. glucose) are converted via HMF into
the renewable plastic monomer FDCA.
Cu-catalyzed oxidation of HMF to FDCA with different solvents, co-catalysts and
stoichiometric oxidants.a
Entry
Time (h)
Solvent
Oxidant
Co-catalyst
FDCA
yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15h
24
48
24
48
48
48
48
48
48
4
Me2CO
Me2CO
EtOAc
EtOAc
H2O
t-BuOOH
t-BuOOH
t-BuOOH
t-BuOOH
t-BuOOH
t-BuOOH
t-BuOOH
t-BuOOH
t-BuOOH
t-BuOOH
H2O2
–
–
–
–
–
–
–
–
23
33
6
19
5
26
36
43
<1
1
H2O:MeCNc
H2O:MeCNd
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
Bipye
LiBrf
LiBrf
LiBrf
–
24
48
24
2g
mCPBA
t-BuOOH
–
–
48
45
a
Reaction conditions: HMF (1 mmol), CuCl (0.1 mmol), MeCN (2 mL), oxidant (3.6
eq) unless otherwise mentioned, RT.
b
No HMF was detected in the products, conversion was 100% in all the cases.
H2O:MeCN = 1:1.
H2O:MeCN = 1:3.
0.2 mmol.
ca. 5 mg, i.e. catalytic amounts.
Reaction time where the highest FDCA yield was observed. FDCA was degraded
c
d
e
f
g
at longer reaction times.
h
Reaction employing CuCl2 as catalyst.
Acknowledgements
hexoses to HMF if using salting-out systems [30,31]) were found to
Also LiCl, NaBr and CaCl2 were utilized and showed the same effect
on the oxidation reaction (results not shown). After 48 h the reac-
than those obtained without added salts (Table 3, entries 10–12).
This effect was found for both catalytic and stoichiometric amounts
of added salts. Other peroxides such as hydrogenperoxide (H2O2)
and m-chloroperoxybenzoic acid (mCPBA) were not found useful in
the CuCl-catalyzed oxidation of HMF to FDCA (Table 3, entries 13
and 14) as only traces of FDCA were formed. Increasing the reac-
tion temperature to 35 or 40 ◦C resulted in an increased reaction
rate, as expected, but did not result in improved reaction yields of
FDCA compared to the corresponding experiment performed at RT
The work was supported by the Danish National Advanced Tech-
nology Foundation and Novozymes A/S. T.S. Hansen thanks the
Oticon Foundation, Otto Mønsteds Foundation, Reinholdt W. Jorck
and Hustrus Foundation and the Danish Chemical Society for fund-
ing.
Appendix A. Supplementary data
Supplementary data associated with this article can be
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