Efficient and sustainable transformation of gamma-valerolactone into nylon monomers

Article abstract of DOI:10.1039/c5gc01922b

Herein, we reported the facile synthesis of dicarboxylic esters from biomass derived gamma-valerolactone (GVL) aiming for nylon monomer preparation via a novel synthetic route which improved the efficiency and overcame the need for toxic carbon monoxide for the synthesis of dicarboxylic esters from GVL.

Full text of DOI:10.1039/c5gc01922b

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Efficient and sustainable transformation of gamma-valerolactone
into Nylon monomers
Received 00th January 20xx,
Accepted 00th January 20xx
a,b
a,b
a,b
a,c
Yong Yang, Xurui Wei, Fanxin Zeng, and Li Deng*
DOI: 10.1039/x0xx00000x
www.rsc.org/
2
0,21
Herein, we reported the facile synthesis of dicarboxylic esters well
.
However, the efficiency and selectivity of
from biomass derived gamma-valerolactone (GVL) aiming for isomerization and hydroformylation was not adequate and
Nylon monomers preparation via a novel synthetic route which toxic carbon monoxide had to be employed as reactant.
improved the efficiency and overcame the need of toxic carbon Therefore, we extended our presented approach to enable a
monoxide for the synthesis of dicarboxylic esters from GVL.
new route for adipic ester production (Scheme 1). Metathesis
of methyl pentenoates to unsaturated dicarboxylic esters was
carried out in the presence of a Grubbs catalyst and the
following hydrogenation could be conducted without using
additional catalyst. The metathesis is not only efficient to
convert pentenoates to unsaturated dicarboxylic esters
The production of liquid fuels and chemicals from biomass has
attracted growing interest due to the issues caused by the
1
-3
depletion of fossil resources. Various strategies have been
developed in recent years for the chemicals and materials
4
, 5
-1
production from biomass derived platform molecules. In this
context, gamma-valerolactone (GVL) is identified as
promising candidate to bridge biomass and petroleum based
(TOF=1380 h ) but also allows a carbon monoxide free
a
synthesis. Regarding the above mentioned virtues, the
presented protocols enable an efficient, benign and
sustainable synthesis of dicarboxylic esters.
6
-8
processes. GVL not only possesses a significantly reduced
oxygen content and polarity compared to carbohydrates but
also is capable to provide downstream products for the
We began our study with the continuous catalytic distillation
of GVL to provide the key intermediates for dicarboxylic esters.
9
-15
2
According to our previous study, the Brønsted acidic ionic
2
current chemical industry.
To this end, dicarboxylic esters,
especially adipate, which are important Nylon monomers were
targeted to extend the application of GVL.
liquid DIM-TFA(Figure 1) which is an non-volatile
Concerning the synthetic pathway of adipates from
carbohydrates derived compounds, several protocols have
been developed. For instance, the conversion of mucic acid
into adipic esters via the methyl trioxorhenium catalyzed
Previous work:
O
Zhang et al.17
OH OH
O
1) MTO, TsOH, 120 °C
2) Pt@C, 160 °C
RO
HO
OR
OH
1
6
O
R = 3-pentyl or H
9 mol%
deoxydehydration and subsequent Pt-catalyzed transfer
O
OH OH
9
1
7
hydrogenation was realized by Zhang et al.. Starting from
HO
OH
1
8
Heer et al.18
O
Rh-Re@SiO
2
HO
H
hydroxymethylfurfural, Heeres et al. reported the synthesis
of caprolactone via the 1, 6-hexandiol intermediate, which
could also be applied to synthesize adipic acid. As a GVL-based
route, dimethyl adipate could be prepared through catalytic
OH
1
20 °C, 8 MPa H2
8
6 mol%
[O]
Adipic acid
O
O
(
sixantphos)PtCl
2
Vogt et al.20
OH
O
80 °C, 0.5 MPa CO+H2
O
TOF: 13.3 h-1
1
9
distillation of GVL to form methyl pentenoates
and
This work:
O
O
subsequent isomerization and hydroformylation to linear 5-
formyl methyl pentenoate and branched by-product as
O
O
O
O
O
Methanol
1) Grubbs Cat., 100 °C
2) 90 °C, 4 MPa H2
+
n
O
Ionic liquid
O
n=1, 2 or 3
170 °C
without additional catalyst
O
99 mol%
CO-f ree
TOF: 1380 h-1 (Metathesis)
9
8 mol%
Vaccum distillation
KPa
Dimethyl adipate
+
Dimethyl pimelate
Nylon industry
5
Purity: 96 mol%
Purity: 95 mol%
Scheme 1. Catalytic transformation of carbohydrates derived compounds to
dicarboxylic acids/esters.
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homogeneous acidic catalyst enables the ring-opening another 12 h run (Figure S1b) and delivered almost the same
esterification of GVL at 170 °C. Considering a potential scale-up TOFs with the fresh one (Figure S2), revealing the robustness
and continuous operation, we conducted this transformation of DIM-TFA for this reaction and the viscous by-product
in a continuous flow mode. A solution of 20 wt% GVL in (Figure S5 and S6) separated from the reaction system might
-1
methanol was pumped at a flow rate of 15 mL h into a flask be a possible reason for the gradual decrease in TOF.
containing 1.1 g DIM-TFA and 5 g GVL. As a result, most GVL Following this continuous catalytic distillation, we prepared 1
was converted to methyl 3-pentenoate (M3P) and methyl 4- liter of pentenoates solution. Subsequently, the methanol
pentenoate (M4P) and less than 1 mol% of GVL was found in could be removed by distillation and then the water layer was
the distillate by gas chromatography (GC) analysis (Figure S1a). formed and separated directly from the methyl pentenoates
The concentration of the two isomers in the distillate reached owing to their hydrophobicity. The resulting organic layer
2
8 wt% and the overall yield of them was over 98 mol%.
contained M3P and M4P with a molar ratio of 5:1, as well as
-1
In the continuous mode, TOFs of 23~25 h could be achieved small amount of methanol and water. With the pentenoates
in the initial 6 h (Figure 1). Then a gradual decrease in TOF was mixture in hand, the metathesis of methyl pentenoates was
observed. The decrease should be attributed to two reasons: 1) investigated with Ru-based catalysts, which had been
the consumption of the initially added 5 g GVL since the max successfully applied in the conversion of natural oils to useful
-
1
23-27
TOF was 18.5 h on the basis of GVL supply per hour; 2) the chemicals.
As shown in Scheme 2, the self-metathesis of
formation of viscous by-product. To prove this assumption, M3P and M4P is expected to afford unsaturated dicarboxylic
different amount of initial GVL was loaded and the results esters C6 and C8, respectively. Meanwhile, the cross-
showed that the less GVL caused the earlier decrease in TOF metathesis of them may give C7 as product. In principle, the
(Figure 1). Moreover, these results can also exclude the atom efficiency of this step is between 76 % (C6) and 89 % (C8).
solvent effects of GVL on this transformation because the TOFs Despite this, the by-products ethene, propene and butene
in the first 3 h were not influenced by the concentration of could also be utilized to produce fuels and chemicals. Before
GVL. Additionally, we observed that the reaction mixture’s we used the prepared pentenoates mixture as substrates, the
color changed from light yellow to dark brown after several major isomer M3P was solely subjected to self-metathesis in
hours run. Thus extraction of the resulting mixture with water sealed tubes to examine different catalysts and solvents. As
and chloroform was performed to recover DIM-TFA
.
aresult, Grubbs catalyst G2 exhibited superior activity
Consequently, 95 % of transparent ionic liquid were obtained compared to the other three catalysts for the reaction at 55 °C
1
from water phase. Comparison of the H NMR spectra of the (Table 1, entry 1~4). Moreover, G2 allowed the reaction to
fresh and recovered DIM-TFA (Figure S3 and S4) showed no proceed even at 35 °C. The results suggested the chlorinated
structural change of the ionic liquid. This consisted with the solvents 1, 2-dichloroethane (DCE) and dichloromethane (DCM)
previous thermal gravity results which indicated the ionic were favorable in terms of conversion and selectivity (entry
2
2
liquid was stable below 350 °C. Moreover, the recovered 5~11). However, the yield of C6 couldn’t be improved
ionic liquid was able to convert most GVL to pentenoates in effectively by adding more catalyst or increasing reaction time
(entry 12, 13). We reckoned that the generated 2-butene
presumably inhibited the reaction due to the reversibility of
the metathesis reaction between C6 and 2-butene. Thus
butene was removed from the reaction system by refluxing
DCM under argon in a flask with a condenser connected to
Schlenk line. As a result, the yield of C6 was improved to 59
mol% (entry 14) and further improvement could be achieved
under solvent-free conditions (72 mol%, entry 15). Using a
pentenoates mixture as substrate, 18 mol% of C6 and 28 mol%
2
2
2
2
2
1
1
1
1
1
8
6
4
2
0
8
6
4
2
0
Initial GVL:
2.5 g
.0 g
5
7
.5 g
1
0.0 g
O
Self-metathesis
O
O
O
O
O
O
O
O
O
DIM-TFA
170 ℃
MeOH
+
O
+
O
O
O
O
O
C6
C7
M3P
M4P
M3P
Ru-based Catalyst Cross-metathesis
Solvent-free
O
O
+
HO
3
S
N
N
4
N
3
SO H
3
O
DIM-TFA :
3N
2
[CF
3
3
SO ]
M4P
Self-metathesis
O
0
2
4
6
8
10
12
14
16
O
M3P : M4P = 5 : 1
Time (h)
Fig.1 Catalytic distillation of GVL with different amount of initial GVL loading.
Reaction Conditions: 1.1 g (1.35 mmol) DIM-TFA, 20 wt% GVL in methanol with a
O
C8
PCy
Ru
O
Catalyst :
Cl
PCy
3
N
N
Mes
N
N
Cl
Cl
Mes
Mes
Mes
Ph
Cl
Cl
Ru
Cl
Cl
Ru
O
-
1
-1
Cl
Ph
Ru
flow rate of 15 mL h (Density: 0.83 Kg L ), 170 °C. The TOFs were calculated
based on the molar amount of pentenoates generated per mole of catalyst per
hour.
PCy
3
PCy
3
G1
G2
HG1
HG2
Scheme 2 Ru-catalyzed metathesis of methyl pentenoates.
2
| J. Name., 2012, 00, 1-3
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Table 1 Self-metathesis of M3P into C6 under various conditions
Table 2 Synthesis of unsaturated dicarboxylic esters from the mixture of M3P
and M4P (5:1) through metathesis reaction
[
a]
T
Yield of C6
Conversion of M3P
Entry
Catalyst
Solvent
(
°C)
(mol%)
(mol%)
Yields of dicarboxylic
esters (mol%)
Conversion
(mol%)
[
a]
T
Reaction Time
(h)
Entry
1
2
3
4
5
6
7
8
9
G1
G2
HG1
HG2
G2
G2
G2
G2
G2
G2
G2
G2
G2
G2
G2
55
55
55
55
35
35
35
35
35
35
35
35
35
Methanol
Methanol
Methanol
Methanol
Methanol
Toluene
THF
17
32
8
19
34
9
(°C)
C6
C7
28
28
28
29
31
28
30
30
32
32
26
32
32
C8
M3P
43
M4P
1
2
3
4
5
6
7
8
9
80
80
1
2
18
18
43
47
49
44
49
48
57
59
41
64
64
2
2
3
3
3
3
3
3
3
3
2
3
3
86
86
43
24
10
20
11
25
2
26
13
33
12
27
3
80
0.5
1
70
96
80
76
97
80
2
82
99
60
1
71
97
Cyclohexane
Acetonitrile
DCE
100
120
100
100
100
100
100
1
78
98
1
79
98
1
1
0
1
34
34
38
40
59
72
34
36
41
42
62
73
4
92
100
100
91
DCM
1
0
12
1
95
[
b]
1
2
3
DCM
[
b]
1
1
65
[
c]
1
1
1
DCM
[
c]
1
2
1
100
100
100
100
[
d]
[e]
4
5
50
50
DCM
[
d]
1
3
1
[
d]
Solvent-free
[
a] Reaction conditions: 1 g methyl pentenoates (M3P:M4P=5:1) and 0.1 mol%
a] Reaction conditions: 0.21 g M3P, 1 mol% catalyst and 1.6 mL solvent were G2 were added to a flask equipped with a condenser connected to Schlenk line.
added to a sealed glass tube under argon and reacted for 6 h. [b] 3 mol% catalyst. For entry 3~12, the methyl pentenoates were dried with anhydrous Na SO4
[
2
[c] 3 mol% catalyst and reaction time of 24 h. [d] Reaction was conducted in a before reactions. [b] 0.05 mol% G2. [c] 0.2 mol% G2. [d] 20 g methyl pentenoates
flask equipped with a condenser connected to a Schlenk line. [e] Temperature of and 0.2 mol% G2.
oil bath.
presence of 0.2 mol% G2 (entry 12). Scale-up experiments
of C7 were obtained in the presence of 0.1 mol% G2 at 80 °C in
h (Table 2, entry 1). The cross-metathesis product C7 became
using 20 g of substrates gave the identical results, affording
ca.16 g unsaturated dicarboxylic esters (entry 13).
1
the major one because M4P containing terminal double bond
was more reactive than M3P. Accordingly, the conversion of
M3P and M4P were 43 mol% and 86 mol%, respectively.
Nevertheless, the reaction didn’t continue in the extended
reaction time, indicating that the catalyst was decomposed or
deactivated in the first hour (entry 2). The probable reason for
this inhibition could be attributed to the residual water in
pentenoates mixture. To our delight, after removal of water in
The subsequent hydrogenation of the unsaturated dicarboxylic
esters into the corresponding final products, namely dimethyl
adipic, pimelic and subericester, was performed without an
additional catalyst. The resulting mixture of scale-up
experiments (entry 13) was directly transferred into an
autoclave, followed by charging 4 MPa H . The G2 in the
2
metathesis mixture was able to act as catalyst for the
subsequent hydrogenation. Consequently, a quantitative yield
of saturated dicarboxylic esters was achieved at 90 °C within 5
h. The products distribution were the same with that of their
unsaturated precursors (adipate : pimelate : suberate = 64 :
pentenoates simply using anhydrous Na SO4, the conversion
2
of M3P went up to 70 mol% in 0.5 hour and 43 mol% C6 could
be produced. The conversion of M3P increased with the
reaction time and the yield of C6 reached 49 mol% in 2 h
3
2 : 3).
(entry 3~5). Moreover, elevated temperatures facilitate the
Concerning the products purification, we tried two methods to
isolate pure dicarboxylic esters, especially adipate. First, to
limit the formation of C7 and C8 products, the pentenoates
mixture was distilled under vacuum (5 KPa) to increase the
M3P content. However, only slight improvement was achieved
transformation of M3P to C6 (entry 6~8). At 100 °C, the
conversion of M3P was 92 mol% and 95 mol% after 4 h and 12
h and the overall yield of C6
entry 9, 10). With a lower catalyst loading of 0.05 mol%, 69
mol% of dicarboxylic esters were produced and the TOF was as
, C7 and C8 exceeded 90 mol%
(
(from 82 wt% to 85 wt%) due to the close vapor pressure of
-1
high as 1380 h (based on the converted methyl pentenoates,
entry 11). Note that a full conversion of the two pentenoates
into unsaturated dicarboxylic esters could be achieved in the
these methyl pentenoates. Another attempt was the vaccum
distillation of the hydrogenated dicarboxylic esters. To our
delight, distillates collected at 111 °C and 125 °C were 9.1 g
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and 5.4 g containing 96 mol% dimethyl adipate (Figure S7a, Palkovits of RWTH Aachen for helpful suggestions. Dr. L. Deng
S8a) and 95 mol% dimethyl pimelate (Figure S7b, S8b), would like to thank Alexander von Humboldt Foundation.
respectively. The later product could also find application in
2
8
29, 30
Nylon production and pharmaceutical synthesis
. Further
References
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3
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502.
In summary, we developed a novel synthetic strategy for the
efficient production of bio-Nylon monomers. Relatively pure
dimethyl adipate and pimelate were prepared efficiently from
GVL under CO-free conditions. We demonstrated that the key
intermediates M3P and M4P could be prepared with high yield
in a continuous flow mode using the recyclable Brønsted acidic
ionic liquid DIM-TFA as catalyst. A full conversion of the
intermediates to Nylon monomers was achieved via a Ru-
catalyzed metathesis followed by hydrogenation without any
additional catalyst. Finally, purification of dimethyl adipate was
achieved with a purity of 96 mol%. In order to make this route
economically feasible, further study should improve the
efficiency and stability of the catalytic systems and lower the
cost of catalysts, especially for metathesis step. Despite these,
the presented study could enhance the role of GVL as a
2
4
5
6
7
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Experimental Section
All reagents were obtained from commercial supplier and used
without further purification. The ionic liquid DIM-TFA was
synthesized according to our previously reported
2
011, 50, 7083-7087.
2
2
procedure. To prepare methyl pentenoates, 1.1 g DIM-TFA 19 J. P. Lange, J. Z. Vestering and R. J. Haan, Chemical
Communications, 2007, 43, 3488-3490.
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and E. Bouwman, Chemsuschem, 2014, 7, 1984-1990.
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to 170 °C. Then a methanol solution containing 20 wt% GVL
was injected by a syringe pump at a flow rate of 15 mL h-1.
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2
2
0
1
containing M3P and M4P could be separated directly from the 22 F. X. Zeng, H. F. Liu, L. Deng, B. Liao, H. Pang and Q. X. Guo,
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carried out in a 100 mL stainless steel autoclave using
methanol as solvent. As a typical procedure of metathesis
reactions, 1 g substrates and desired amount of catalyst were
2
2
3
4
1
55.
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technique. To hydrogenate the unsaturated dicarboxylic esters,
the mixture from metathesis reaction was diluted with 20 mL
methanol and transferred to an autoclave. The hydrogenation
2
2
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2
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Acknowledgements
The authors are grateful to Natural Science Foundation of
China (21302230) and Youth Innovation Promotion Association,
CAS for the financial support. The authors thank Prof. Regina
4
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DOI: 10.1039/C5GC01922B
O
O
O
O
O
Methanol
1) Grubbs Cat., 100 °C
O
+
O
Ionic liquid
O
n
2) 90 °C, 4 MPa H
2
170 °C
without additional catalyst
O
n=1, 2 or 3
O
9
9 mol%
-1
9
8 mol%
CO-free
TOF: 1380 h (Metathesis)
Vaccum distillation
KPa
Dimethyl adipate
+
Dimethyl pimelate
Nylon industry
5
Purity: 96 mol%
Purity: 95 mol%
A route for efficient synthesis of bio-Nylon monomers from gamma-valerolactone has been developed.