Production of Low-Freezing-Point Highly Branched Alkanes through Michael Addition

Article abstract of DOI:10.1002/cssc.201701789

A new approach for the production of low-freezing-point, high-quality fuels from lignocellulose-derived molecules was developed with Michael addition as the key step. Among the investigated catalysts, CoCl₂?6 H₂O was found most active for the Michael addition of 2,4-pentanedione with FA (single aldol adduct of furfural and acetone, 4-(2-furanyl)-3-butene-2-one). Over CoCl₂?6 H₂O, a high carbon yield of C₁₃ oxygenates (about 75 %) can be achieved under mild conditions (353 K, 20 h). After hydrodeoxygenation, low-freezing-point (<223 K) branched alkanes with 13 carbons within jet fuel ranges were obtained over a Pd/NbOPO₄ catalyst. Furthermore, C_18,23 fuel precursors could be easily synthesized through Michael addition of 2,4-pentanedione with DFA (double-condensation product of furfural and acetone) under mild conditions and the molar ratio of C₁₈/C₂₃ is dependent on the reaction conditions of Michael addition. After hydrodeoxygenation, high density (0.8415 g mL^?1) and low-freezing-point (<223 K) branched alkanes with 18, 23 carbons within lubricant range were also obtained over a Pd/NbOPO₄ catalyst. These highly branched alkanes can be directly used as transportation fuels or additives. This work opens a new strategy for the synthesis of highly branched alkanes with low freezing point from renewable biomass.

Full text of DOI:10.1002/cssc.201701789

Accepted Article
Title: Production of Low-Freezing-Point Highly Branched Alkanes via
Michael Addition
Authors: Yanqin Wang, Yaxuan Jing, Qineng Xia, and Xiaohui Liu
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ChemSusChem
10.1002/cssc.201701789
COMMUNICATION
Production of Low-Freezing-Point Highly Branched Alkanes via
Michael Addition
[a]
Yaxuan Jing, Qineng Xia, Xiaohui Liu and Yanqin Wang*
Abstract: A new approach for the production of low freezing point,
high-quality fuels from lignocellulose derived molecules was
developed with Michael addition as the key step. Among the
condensation, for example, the aldol condensation of furfural (or
5-hydroxymethylfurfural) with ketones containing α-H atoms to
[3]
obtain long-chain oxygenates. The second approach involves
hydroxyalkylation/alkylation (HAA) of 2-methylfuran (2-MF) and
lignocellulose-derived carbonyl compounds (furfural, 5-
hydroxymethylfurfural, 5-methylfurfural, acetone, hydroxyl-
acetone, etc.) to produce transportation fuel range oxy-
investigated catalysts, CoCl
Michael addition of 2,4-pentanedione with FA (single aldol adduct of
furfural and acetone, 4-(2-furanyl)-3-butene-2-one). Over
CoCl ·6H O, a high carbon yield of C13 oxygenates (about 75%) can
2 2
·6H O was found most active for the
2
2
[4]
be achieved under mild conditions (353 K, 20 h). After
hydrodeoxygenation, low freezing point (< 223 K) branched alkanes
with 13 carbons within jet fuel ranges were obtained over
compounds. The third strategy adopts benzoin coupling of
lignocellulose-derived platform molecules (furfural, 5-
hydroxymethylfurfural, aromatic aldehydes) to synthesize
[5]
Pd/NbOPO
4
catalyst. Furthermore, C18,23 fuel precursors could be
transportation fuel precursors.
easily synthesized through Michael addition of 2,4-pentanedione
with DFA (double-condensation product of furfural and acetone)
under mild conditions and the molar ratio of C18/C23 is dependent on
Inspired by all of the above routes, we are interested in the
exploration of potential C-C bond coupling reaction and a new
approach for converting lignocellulose-derived platform
chemicals into transportation fuel range branched alkanes. It is
well-known that Michael addition of β-dicarbonyl compounds to α,
β-unsaturated carbonyl compounds is one of the most important
C-C bond forming reactions in organic chemistry. However, the
Michael addition for converting lignocellulose-derived platform
compounds into transportation fuels is not reported. 2,4-
pentanedione, as a β-dicarbonyl compound, can be produced by
ring-opening and decarboxylation of biomass-derived chemicals
(4-hydroxy-6-methyl-2-pyrone) in the absence of a catalyst when
the
reaction
conditions
of
Michael
addition.
After
hydrodeoxygenation, high density (0.8415 g/ml) and low freezing
point (< 223 K) branched alkanes with 18, 23 carbons within
4
lubricant range were also obtained over Pd/NbOPO catalyst. These
highly branched alkanes can be directly used as transportation fuels
or additives. This work opens a novel strategy for the synthesis of
highly branched alkanes with low-freezing-point from renewable
biomass.
With the diminishing of fossil resources and the growing of
environmental concerns, the conversion of biomass to chemicals
[6]
water is used as the solvent. Furfural-acetone [4-(2-furanyl)-3-
buten-2-one, FA], a C oxygenate, easily produced through the
aldol condensation of acetone and furfural, contains an enone
group in the middle position of the C oxygenate, which makes it
[1]
and fuels has received increasing attention.
Liquid
8
[3a]
transportation fuels are mainly obtained from petroleum
nowadays, while the increasing demand for transportation fuels
requires ideal substitutes of oil-based ways. This demand has
led to active research with the liquid fuels from lignocellulose,
8
an ideal acceptor of the Michael addition and an excellent
precursor to generate high branched alkanes. Therefore, we
developed a novel approach for the production of high branched
[2]
which accounts for more than 60% of the entire biomass. As
we know, straight alkanes have lower octane numbers for
gasoline, lower density and higher freezing points, and cannot
C13 alkanes from Michael addition of 2,4-pentanedione and the
aldol adducts of furfural, followed by the one-step HDO process
under mild conditions for the first time. This C13 branched
alkanes have low freezing points, high density and can be
blended into transportation fuels without hydroisomerization.
Furthermore, the highly branched C18-23 alkanes that can be
used as lubricant were also prepared.
be
directly
used
as
transportation
fuels
without
hydroisomerization. To meet the specification of transportation
fuels, high branched alkanes should be synthesized and added
to the transportation fuels to increase the density, octane
numbers and decrease the freezing point.
Generally, the process for producing gasoline, diesel, jet
fuel and so on from lignocellulose-derived platform chemicals
involves two steps, namely, the C-C bond coupling reaction and
the following hydrodeoxygenation (HDO). Currently, there are
three main routes for C-C bond coupling to convert
lignocellulose-derived platform molecules into transportation fuel
precursors (oxygenates). The first method is the aldol
The process for converting furfural into jet fuel range
branched alkanes (Scheme 1) consists of three steps: (1) the
aldol condensation of furfural and acetone to C
(2-furanyl)-3-butene-2-one, FA), (2) the Michael addition of FA
and 2,4-pentanedione to jet fuel range 13 intermediates
8
oxygenate (4-
C
(furfural-acetone-diketone, FAD) (structural analysis see Figure
S1-S4 in the Supporting Information), and (3) the one-step
hydrodeoxygenation of FAD to aviation fuel range branched
alkanes (structural analysis see Figure S5-S9 in the Supporting
Information). The targeted alkane has low freezing point and can
be added directly into jet fuel without hydroisomerization. The
core of this route is to increase the carbon chain length by
Michael addition. This new route not only supplies a fully
undeveloped C-C bond coupling reaction for biomass-derived
compounds, but also provides a new approach for converting
lignocellulose derived platform chemicals into jet fuel ranged
branched alkanes.
[a]
Y. X. Jing, Dr. Q.N. Xia, X.H. Liu, Prof. Y.Q. Wang
Shanghai Key Laboratory of Functional Materials Chemistry and
Research Institute of Industrial Catalysis
School of Chemistry and Molecular Engineering, East China
University of Science of Technology
No. 130 Meilong Road, Shanghai, 200237 (P.R. China)
E-mail: wangyanqin@ecust.edu.cn
Supporting information for this article is given via a link at the end of
the document.
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ChemSusChem
10.1002/cssc.201701789
COMMUNICATION
catalyzed, such as self condensations of FAD and the further
aldol condensation of FAD with 2,4-pentanedione. Transition
metal chlorides are also good catalysts for Michael addition,
because they have ability to form chelate complexes with β-
2 2
dicarbonyl compounds. CoCl ·6H O, an eco-friendly substitution
to classical basic catalyst, was used and exhibited the best
catalytic activity for Michael addition with 82.9% FA conversion
and 75.1% FAD yield. As chemically similar transition metal
chlorides, both FeCl
generate chelate compounds with β-dicarbonyl were also active
for this reaction, but did not perform as well as CoCl ·6H O. In
contrast, AlCl ·6H O was inert for this reaction. Therefore, highly
active and inexpensive CoCl ·6H O was employed as Michael
3 2 2 2
·6H O and NiCl ·6H O which have ability to
2
2
3
2
2
2
addition catalyst for further investigations.
Scheme 1. Reaction pathway for the production of jet fuel range branched
alkanes.
1
00
Conversion of FA
Yield of FAD
80
60
40
20
0
Scheme 2. Proposed reaction mechanism of the Co(II)-catalyzed Michael
addition of FA with 2,4-pentanedione.
O
O
O
O
B
T
H
H
H
H
6
·
H
O
6
6
·
6
K
·
·
K
l
l
iCl
lCl
C
C
e
o
C
F
N
A
[9]
Based on our results and previous reports, we proposed a
reaction mechanism for Co(II)-catalyzed Michael addition and
present in Scheme 2. Firstly, the chelate ligand 4 is formed by
the coordination of donor 1 to the metal center. The chelate
ligand 4 shows a planar configuration and it is commendably
stabilized by Π-delocalisation. Then the acceptor 2 of 1,4-
addition results in the formation of complex 5 by ligand
exchange. The metal center is not only to hold the acceptor 2 in
proximity to donor 1, but also activated acceptor 2 by its Lewis
acidity. Subsequently, the complex 5 undergoes the nucleophilic
conjugate addition to form new C-C bond, which affords the
intermediate 6. Finally, the target product 3 is liberated from the
intermediate 6 and the chelate ligand 4 is regenerated by
coordination with donor 1. Christoffers et al. performed quantum
chemical density functional calculations to prove the catalytic
Figure 1. Michael addition of FA with 2,4-pentanedione over various catalysts.
0
2
.2 g of FA, 5 g of 2,4-pentanedione, 0.05 g of catalyst, 0.1 g of CaCl
0h.
2
, 80 °C,
The aldol condensation of furfural with acetone can be
carried out with a liquid or solid base. NaOH was used here to
enable the complete conversion of furfural to synthesize FA (the
details of the aldol adduct preparation see the Supporting
[3a, 7]
Information).
FA, which contains an enone group, is an ideal
acceptor of Michael addition. Similarly, 2,4-pentanedione is
considered to be one of the typical β-dicarbonyl compounds.
2,4-pentanedione plays two key roles in the Michael addition
[9b]
process: one is the suitable solvent to dissolve FA; another is
the reactant involved in the conjugate addition.
cycle,
but direct support from experiment for the catalytic
cycle and the intermediates is still lacking so far. So, we tried to
characterize the intermediates in the catalytic reaction by ESI-
TOF MS and the result is present in Figure S10. An obvious
molecular ion peak at 258.0 [M+1] was detected, may be
attributed to intermediate 4 (the chelate ligand formed by the
coordination of donor to the metal center). To conform this, the
Generally, Michael addition can be catalyzed by alkaline
species. Figure 1 shows the conversions of FA and the yields of
FAD over various catalysts. The mechanism for base catalysis
involves the formation of an anion from the active methylene
compound, and the 1,4-addition of the anion to the α,β-
unsaturated carbonyl complex, followed by the acceptance of a
2
MS profile of the mixture of 2,4-pentanedione and CoCl was
[8]
proton. As typical alkaline species, potassium tert-butoxide
KTB) and KOH were used first, but demonstrated
also measured and a molecular ion peak at 258.0 [M+1] was
also found (Figure S11 in the Supporting Information), so we
believe that intermediate 4 does exist in the catalytic cycle. By
analyzing the molecular weight, we found the molecular ion peak
at 258.0 [M+1] was attributed to cobalt (II) acetylacetonate
(
a
relatively poor catalytic efficiency with 77.3% conversion of FA
and 46.6% yield of FAD, 70.1% conversion of FA and 46.6%
yield of FAD, respectively. This may be due to their strong basic
properties, where a lot of side and subsequent reactions are
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ChemSusChem
10.1002/cssc.201701789
COMMUNICATION
(
Co(C
5
H
7
2
O )
2
). To further prove this, we employed cobalt (II)
from 44.2 to 89.4% and the yield of FAD significantly increases
from 37.8 to 75.1% as the time prolongs from 4 to 20 h.
However, further increase of time did not affect the yield of FAD,
implying 20 h is an applicable time for Michael addition.
To probe the influence of excessive reaction conditions, we
2 2
tested the Michael addition over CoCl ·6H O catalyst at 100 °C
2 2
acetylacetonate instead of CoCl ·6H O to catalyze the Michael
addition of 2,4-pentanedione with FA and found it really showed
good catalytic performance (74.4% yield), indicating cobalt (II)
acetylacetonate is indeed a stable form of intermediate 4.
However, due to poor stability and low degree of ionization,
other possible intermediates cannot be detected.
To optimize the reaction parameters, Michael addition
was conducted under various conditions (such as reaction
2 2
temperature and reaction time) over CoCl ·6H O catalyst and
the results are shown in Figure. 2. It is found that the increase
of reaction temperature from 60 to 80 °C observably
enhanced the conversion of FA from 47.2 to 82.9% and the
yield of FAD from 44.3 to 75.1%. Further increase the
reaction temperature to 100 °C, the conversion of FA also
increased, reached 97.6%, however, the yield of FAD
significantly decreased to 52.3%. We find that the subsequent
reactions, such as the self-aldol condensation of FAD
happened under higher temperature, resulted in the decrease
for 30h. The GC-MS trace reveals that the self-aldol
condensation of FAD was really happened under excessive
reaction conditions (Scheme S1, Figure S12-S14 in the
Supporting Information). Interestingly, C13 cycloalkanes were
seized by GC-MS after hydrodeoxygenation (Figure S15 and
Figure S16 in the Supporting Information). This result is in good
consistent with the above reduction of FAD yield with the
increase of reaction temperature from 80 to 100 °C. As we know,
cyclic hydrocarbons have relatively higher densities or
volumetric heating values than chain alkanes due to strong ring
strain and can be directly blended with conventional
transportation fuels. The unexpected finding provides extensive
insight in converting lignocellulose derived molecules to
transportation fuel range cycloalkanes with Michael addition and
aldol condensation for us.
of the yield of FAD. Therefore, 80 °C is
temperature for Michael addition.
a suitable
To eliminate the influence of water in non-pretreated 2,4-
pentanedione, we added anhydrous calcium chloride as
desiccant during reaction. Compared with the result without
Conversion of FA
Yield of FAD
1
00
CaCl
5.2% (shown in Figure S17 in the Supporting Information). This
result suggests that CaCl can absorb water in the reaction
2
, the yield of FAD significantly increases from 48.6 to
7
8
6
4
2
0
0
0
0
0
2
system to prevent the hydrolysis of 2,4-pentanedione (2,4-
pentanedione easily hydrolyzes to acetone and acetic acid), so
the side reaction was effectively prohibited. As comparison,
when soly CaCl
that CaCl does not have catalytic activity for Michael addition.
To see whether the interactions of CaCl with CoCl ·6H O exist
2
was involved, not FAD was obtained, indicating
2
2
2
2
and affect reaction, 2,4-pentanedione was pre-treated with
anhydrous calcium chloride to remove water, then the Michael
6
0
70
80
90
100
o
Reaction temperature ( C)
addition of pre-treated 2,4-pentanedione, FA and CoCl
was carried out and 72.0% FAD yield was achieved, a little bit
lower than that (75.2%) with CaCl co-added during reaction,
this may be comes from the influence of crystalline water in
CoCl ·6H O. These results indicate that CaCl just plays a
desiccant role and it is better to add during reaction.
2 2
·6H O
Figure 2. Michael addition of FA with 2,4-pentanedione with different reaction
temperature over CoCl ·6H O. 0.2 g of FA, 5 g of 2,4-pentanedione, 0.05 g of
CoCl ·6H O, 0.1 g of CaCl , 20h.
2
2
2
2
2
2
2
2
2
In order to get branched alkanes, the hydrodeoxygenation
(HDO) of FAD was investigated. Our previous studies showed
100
Conversion of FA
Yield of FAD
that Pd supported NbOPO
4
catalyst had excellent activity and
8
6
4
2
0
0
0
0
0
stability for the total HDO of biomass and biomass-derived
[10]
oxygenated chemicals.
indicated that Pd supported NbOPO
HDO, namely, the noble metal for H
Experimental and theoretical studies
plays three key roles for
activation and dissociation,
4
2
NbOx species for C-O bond activation and acid sites for
dehydration. Therefore, the HDO of Michael addition products
was carried out over Pd/NbOPO
long carbon chain alkanes was achieved. As comparison, H-
ZSM-5 and Al were also used as support and found that the
activity for the HDO of Michael addition products decreases as
follows: Pd/NbOPO > Pd/H-ZSM-5 > Pd/Al , indicating that
NbOPO is really the best support for HDO process. As
comparison, Rh, Pt and Ru supported NbOPO were also
4
catalyst and very high yield of
2
O
3
4
8
12
16
20
24
28
Reaction time (h)
4
2 3
O
4
Figure 3. Michael addition of FA with 2,4-pentanedione with different reaction
time over CoCl ·6H O. 0.2 g of FA, 5 g of 2,4-pentanedione, 0.05 g of
CoCl ·6H O, 0.1 g of CaCl , 80 °C.
4
2
2
involved as HDO catalysts, but only 54.0, 46.8 and 29.0 % yield
of C13 alkanes were obtained, respectively (Figure 4). Notably, a
large amount of C-C cleavage products was formed over Rh, Pt
2
2
2
and Ru supported NbOPO
catalyzed HDO, deep C-C cleavage products were obtained
mathane and ethane in gas phase). These results clearly
4
.
Especially for Ru/NbOPO
4
Figure 3 shows the conversion of FA and the yield of FAD
as a function of time. The conversion of FA markedly increases
(
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ChemSusChem
10.1002/cssc.201701789
COMMUNICATION
revealed that Pd/NbOPO
4
was a more suitable catalyst for the
produce C18,23 branched alkanes (Scheme 3), the molar ratio of
HDO of Michael addition products.
C18 to C23 is dependent on reaction conditions of Michael
addition (Figures S24-S26 in the Supporting Information). High
carbon length alkanes with a molecular weight of 230-500 (from
MSDS,(Material Safety Data Sheet)) are the main constituents
of lubricants and highly branched alkanes can be added to
lubricants to increase oxidation stability. Therefore, the highly
branched C18,23 alkanes can be used as the components of
lubricant. Generally, lubricant alkanes are mainly produced by
hydrocracking and hydroisomerization of long-chain paraffinic
and naphthenic compounds. However, similar to the process (C-
C bond coupling reaction and the following hydrodeoxygenation)
90
80
70
60
50
40
30
20
10
0
C alkane
8
C alkane
9
C11 alkane
C13 alkane
of
producing
conventional
transportation
fuels
from
lignocellulose-derived chemicals, the approach to convert
lignocellulose-derived platform compounds into lubricant alkanes
[3f,11]
5
-
was rarely developed.
Here we open a new strategy for the
O
M
P
O
O
P
O
O
P
l
S
P
O
b
O
O
O
b
/
A
Z
-
b
b
synthesis of high-quality lubricant-based oil components from
lignocellulose-derived chemicals.
d
d/N
/
N
t/N
P
P
d/H
P
u/N
h
P
R
R
Figure 4. Results of HDO of FAD over various catalysts. Reaction conditions:
FAD (0.2 g), cyclohexane (6.46 g), catalyst (0.1 g), 200 °C, 4 MPa H , 12 h.
2
100
C8 alkane
C9 alkane
C11 alkane
C13 alkane
90
80
70
60
The influence of reaction temperature on the yields of
Michael addition products was investigated and shown in Figure
5. The increase of reaction temperature from 160 to 180 °C
observably enhanced the yield of C13 alkanes from 1.3 to 79.1%,
indicating that a reasonably high temperature is required to
overcome the energy barrier. We found that the yield of jet fuel
range branched alkanes (C13 alkanes) reached up to 79.1% with
50
40
30
2
0
0
0
a small amount of C-C cleavage products (C11, C
alkanes). The C11 and C branched alkanes were generated by
the hydrocracking of the branched C
alkanes were produced by the hydrocracking of the branched C
9 8
and C
1
9
2
alkyl groups and the C
8
5
160
170
180
190
200
o
Reaction temperature ( C)
alkyl groups (Scheme S2 in the Supporting Information),
respectively, the other portion is owing to incomplete reaction of
substrate, FA in Michael addition. Further increase of reaction
temperature to 200 °C slightly decreased the yield of C13
alkanes to 69.3%, with the increase of C-C cleavage products
Figure 5. Results of HDO of FAD under various reaction temperature over
Pd/NbOPO Reaction conditions: FAD (0.2 g), cyclohexane (6.46 g),
Pd/NbOPO (0.1 g), 4 MPa H , 12 h.
4
.
4
2
9
(C11 and C alkanes). These results indicate that excessive
temperature would promote C-C cleavage. Furthermore, none of
oxygenates were seized by GC-MS as the temperature
increased from 180 to 200 °C, however, a large amount of
oxygenates were seized by GC-MS from 160 to 170 °C (Figure
S18-S20 in the Supporting Information). Therefore, 180 °C is a
suitable temperature for the HDO of Michael addition products.
After five recycling experiments, Pd/NbOPO catalyst shows a
4
high reusability for the HDO of Michael addition products (Figure
S21 and Figure S22 in the Supporting Information).
Based on the above results, we can conclude that Michael
addition, just as the aldol condensation, alkylation reaction and
benzoin coupling, is also an appropriate C-C bond coupling
reaction for biomass-derived compounds. Similar to the FA, DFA
(
double-condensation products of furfural with acetone; see the
Supporting Information for details of the aldol adduct
preparation) also contains enone groups, which should be an
ideal acceptor of the Michael addition(Figure S23 in the
Supporting Information). Therefore, we utilized DFA and 2,4-
pentanedione as substitutes to synthesize C18 (molar ratio of
Scheme 3. Reaction pathway for the production of C18 and C23 branched
alkanes.
2
,4-pentanedione to DFA = 1) and C23 (molar ratio of 2,4-
2 2 4
Similarly, CoCl ·6H O and Pd/NbOPO were employed as
pentanedione to DFA 2) intermediates (double-furfural-
=
Michael addition and HDO catalysts for further investigations,
respectively. One intractable problem in this approach is that
DFAD has too higher molecular weight (molecular weight of C18
acetone-diketone, DFAD) through Michael addition. Then, the
one-step hydrodeoxygenation of DFAD was performed to
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ChemSusChem
10.1002/cssc.201701789
COMMUNICATION
intermediates = 314; molecular weight of C23 intermediates =
Table 1. Properties of C13 and C18,23 branched alkanes.
414) and boiling point to be analysized by GC; fortunately, the
a
13
b
Property
C
C
18-23
C
18 and C23 branched alkanes can be seized by GC. Hence, the
Density at 298 K(g/ml)
Freezing point(K)
0.8005
< 223
0.8415
< 223
product distributions of the C13, C18 and C23 branched alkanes
achieved under different reaction time of Michael addition are
analysized and shown in Figure 6.
[
a] C13 are composed of C13 alkane (79.1%) and other carbon numbers
alkanes.
b] 18,23 are composed of C18 alkane (39.5%), C23 alkane (49.9%) and
[
C
8
0
other carbon numbers alkanes.
C23
C18
70
In summary, we have presented a novel process for
converting furfural into liquid transportation fuels through three
consecutive catalytic steps that involve aldol condensation,
Michael addition and hydrodeoxygenation. It has been
demonstrated that the Michael addition of 2,4-pentanedione with
FA (single aldol adduct of furfural and acetone) can be carried
out conveniently with cheap transition metal chloride to obtain jet
fuel range (C13) oxygenates with 75.1% yield with reaction at
6
0
C13
50
40
30
20
10
3
53 K for 20 h. 79.1% yield of high branched C13 alkanes was
achieved from C13 oxygenates by the total hydrodeoxygenation
over Pd/NbOPO at 453 K, MPa for 12 h. With
the successful expansion of the substrate, lubricant range
18,23) oxygenates were achieved from Michael addition of 2,4-
0
0
4
8
12
16
20
24
28
32
4
4
H
2
Reaction time/h
(
C
Figure 6. The product distribution of the C13, C18 and C23 branched alkanes
under different reaction time of Michael addition. Reaction conditions of
pentanedione with DFA (double-condensation product of furfural
and acetone) and the product distribution of C18 and C23
branched alkanes is dependent on the reaction time of Michael
Michael addition: 0.5 g of DFA, 5 g of 2,4-pentanedione, 0.1 g of CoCl
.1 g of CaCl , 80 °C. Reaction conditions of HDO: DFAD (0.2 g), cyclohexane
6.46 g), Pd/NbOPO (0.1 g), 4 MPa H , 12 h, 190 °C.
2 2
·6H O,
0
(
2
4
2
addition. Specifically, the
C13 and C18,23 branched alkanes
possess low freezing point, high density, excellent branched
chain structure and can be directly blended with conventional
transportation fuels or as the component of lubricant. This work
opens a novel strategy for the synthesis of low-freezing-point
and high branched alkanes from renewable biomass.
It can be seen from Figure 6 that the portion of C23 and C18
were 5.9 and 76.3% at the time of 4 h, suggesting that the
Michael addition of C13 intermediates with 2,4-pentanedione is
easily happened. The selectivity to C23 markedly increased from
5.9 to 49.9% as the time prolonged from 4 to 20 h, with the
selectivity to C18 significantly decreased from 76.3 to 39.5%,
implying that Michael addition of C18 intermediates and 2,4-
pentanedione is really involved. Further increase the reaction
time to 28 h, the selectivity to C23 slowly increased from 49.9 to
Experimental Section
The Michael addition of FA and 2,4-pentanedione was performed in
50ml round-bottom flask. Typically, 2,4-pentanedione (5g), FA (0.2g),
5
3
C
3.8% and the selectivity to C18 slightly decreased from 39.5 to
5.6%, which may be caused by the self-aldol condensation of
18 intermediates under excessive reaction time because C18
CoCl ·6H O (0.05g) and CaCl (0.1g) were transferred into the flask,
2
2
2
which was then heated to a certain temperature (60 to 100 °C) and
allowed to react for a certain time (4–28 h). The reactor was quenched in
an ice-water bath to stop the reaction immediately. The liquid solution
was separated from the solid catalyst by centrifugation and analyzed
qualitatively by GC-MS (Agilent 7890A-5975C) and quantitatively by GC-
FID (Agilent 7890) using tridecane as the internal standard. Conversion
of FA and yield of FAD were calculated by using the equation: FA
conversion [%] = (moles of FA reacted) / (moles of starting FA) × 100%,
FAD yield [%] = (moles of FAD produced) / (moles of starting FA) × 100%.
For the separation of product (FAD) and recovery of un-reacted
substitutes, 10ml of deionized water were put into the flask after Michael
reaction. Then, FAD, FA and 2,4-pentanedione were extracted from the
flask by 3 * 20 ml of dichloromethane. Finally the mixture of FAD and FA
were directly obtained by removing dichloromethane with rotary
evaporation at 40 C and 2,4-pentanedione with rotary evaporation at 75
cycloalkanes were seized by GC-MS (Scheme S3, Figure S27
and Figure S28 in the Supporting Information). Therefore, we
could control the product distribution of C18 and C23 branched
alkanes by adjusting the reaction time of Michael addition.
The transportation fuel-related properties including density
and freezing point were measured to evaluate the potential as
aviation fuel and lubricant and shown Table 1. Freezing point
was measured according to GB/T 510 standard test method by
BF-13C Freezing Point Apparatus. Density was measured by
DMA 4500M Density Meter of Anton Paar. The C13 branched
alkane has a density of 0.8005 g/ml at 298 K and a freezing
point of lower than 223 K (equipment measurement limitation).
In contrast, the density and the freezing point of n-tridecane are
C. Dichloromethane and 2,4-pentanedione can be reused without further
purification. The relatively pure FAD was purified by silica gel column
chromatography and used as standard, the structure and purity were
0.7650 g/ml at 298 K and about 268 K, respectively. Therefore,
1
13
the C13 targeted alkanes have three satisfactory advantages,
namely, low freezing point, high density and excellent branched
chain structure. These superiorities are ideal for the widely used
aviation aircraft, suggesting the branched liquid alkane is
suitable for jet fuel. The C18,23 branched alkane has a density of
confirmed by H NMR, C NMR spectroscopy and mass spectrometry.
The HDO of as-prepared products and FA mixture was conducted in a
5
0 mL Teflon-lined stainless-steel autoclave. Typically, mixture (0.2 g),
Pd/NbOPO (0.1 g), and cyclohexane (6.46 g) were transferred into the
autoclave. The reactor was then sealed, purged with H for three times
and charged to 4MPa H pressure. The reaction was then carried out at
60 to 200 °C and 4 MPa under magnetic stirring for 12 h. After the
4
2
2
0.8415 g/ml at 298 K and a freezing point of lower than 223 K,
1
may be a good component of lubricant. Therefore, The C13
branched alkane and the C18,23 branched alkanes are desirable
candidates for transportation fuels.
reaction, the autoclave was quenched in an ice–water bath to room
temperature. The liquid solution was separated from the solid catalyst by
centrifugation and analyzed qualitatively by GC-MS (Agilent 7890A-
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ChemSusChem
10.1002/cssc.201701789
COMMUNICATION
5
975C) and quantitatively by GC-FID (Agilent 7890) using pentadecane
[7]
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9
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[
%] = (moles of carbon in product)/ (moles of carbon in 1a) ×100%.
Similarly, the Michael addition of DFA and 2,4-pentanedione was
performed in 50ml round-bottom flask. Typically, 2,4-pentanedione (5g),
DFA (0.5g), CoCl ·6H O (0.1g) and CaCl (0.1g) were transferred into
2
2
2
the flask, which was then heated to a certain temperature (60 to 100 °C)
and allowed to react for a certain time (4-28 h). After the reaction, the
reactor was quenched in an ice–water bath to room temperature and the
products were separated as FAD did above. The HDO of as-prepared
DFAD was also conducted in a 50 mL Teflon-lined stainless-steel
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autoclave. Typically, DFAD (0.2 g), Pd/NbOPO
4
(0.1 g), and cyclohexane
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(6.46 g) were transferred into the autoclave. The reactor was then sealed,
2 2
purged with H for three times and charged to 4MPa H pressure. The
reaction was then carried out at 190 °C and 4 MPa for 12 h. After the
reaction, the autoclave was quenched in an ice-water bath to room
temperature. The liquid solution was separated from the solid catalyst by
centrifugation and analyzed qualitatively by GC-MS (Agilent 7890A-
5975C) and quantitatively by GC (Agilent 7890) equipped with an HP-5
column and flame ionization detector (FID) using
a
area normalization method. The product distribution was calculated by
using the equation: The product seclectivity [%] = (product peak area)/
(total peak area) ×100%.
Acknowledgements
This work was supported financially by the NSFC of China (No.
9
1545103, 21603072 and 21403065), the Science and
Technology Commission of Shanghai Municipality
10dz2220500), China Postdoctoral Science Foundation
2016M590328), and the Fundamental Research Funds for the
(
(
Central Universities (222201714010, 222201718003).
Keywords: Michael addition • biomass • furfural• branched
alkanes• low freezing point
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Yaxuan Jing, Qineng Xia, Xiaohui Liu
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Production of Low-Freezing-Point
Highly Branched Alkanes via Michael
Addition
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