Methyl 4-methoxypentanoate: A novel and potential downstream chemical of biomass derived gamma-valerolactone

Article abstract of DOI:10.1039/c4ra13682a

Lignocellulosic derived gamma-valerolactone was effectively converted into methyl 4-methoxypentanoate, a potential liquid biofuel, solvent and fragrance, by the catalysis of a hydrogen exchanged ultra-stable Y zeolite (HUSY) and insoluble carbonates such as CaCO₃. The catalytic competing generation process between methyl 4-methoxypentanoate and pentenoate esters was also analysed.

Full text of DOI:10.1039/c4ra13682a

RSC Advances
View Article Online
View Journal | View Issue
COMMUNICATION
Methyl 4-methoxypentanoate: a novel and
potential downstream chemical of biomass derived
Cite this: RSC Adv., 2015, 5, 8297
gamma-valerolactone†
Received 3rd November 2014
Accepted 23rd December 2014
*
*
Zheng Li, Yetao Jiang, Xing Tang, Miao Zuo, Xianhai Zeng, Yong Sun and Lu Lin
DOI: 10.1039/c4ra13682a
www.rsc.org/advances
Lignocellulosic derived gamma-valerolactone was effectively methyl 4-methoxypentanoate (MMP), as concluded in Scheme
converted into methyl 4-methoxypentanoate, a potential liquid 1. MMP, which has been regarded as a by-product of the reac-
biofuel, solvent and fragrance, by the catalysis of a hydrogen tion, occupies a yield of 5–20%,6 has more potential to be
exchanged ultra-stable Y zeolite (HUSY) and insoluble carbonates applied as fuel additive, bio-oxygenated solvent,13 medical
such as CaCO3. The catalytic competing generation process intermediate and fragrance than GVL and pentenoate esters
between methyl 4-methoxypentanoate and pentenoate esters was owing to its advantageous properties such as water insolubility
also analysed.
and high heat-value. In this study, MMP was produced, for the
rst time as we know, in a rather high conversion and selectivity
in methanol with high GVL loadings in the presence of hydrogen
exchanged ultra-stable Y zeolite (HUSY) and CaCO3 (Scheme 1).
In our previous study on the liquefaction of biomass in
GVL–methanol solvent, we accidentally found that the ash
components in biomass could signally improve the yield of
MMP in GVL ring-opening reaction under 3 MPa nitrogen
(at RT) with the catalysis of HUSY. Aer a series of strict
experiments, CaCO3, a common insoluble carbonate, was
discovered to be the key compound in the ash content which
effectively promoted the generation of MMP, while other salts
and oxides in the ash, such as KCl, K2CO3, NaCl, SiO2, Al2O3,
were found to be ineffective.
The worldwide consumption in transportation and chemical
industry, which strongly depend on fossil resources, has given
rise to problems of resource shortage coupled with global
warming, environmental deterioration, serious political issues
and military crisis. Lignocellulosic biomass, as a sustainable
and renewable carbon source, is being studied for the produc-
tion of fuels and chemicals which are comparable with that
derived from oil and coal. The carbohydrates derived from
biomass can be converted into various platform molecules,
such as furfural, 5-hydroxymethylfurfural (5-HMF), levulinate
acid (LA) and levulinate esters.
In recent years, a lot of attention has been given to gamma-
valerolactone (GVL), a platform molecule which could be
synthesized from LA or ethyl levulinate using diverse hydrogen
sources,1–3 because it's recognized as a potential fuel additive,
green solvent and promising precursor for other downstream
chemicals, such as liquid hydrocarbons for fuel application.4,5
Simultaneously, a fair amount of previous reports have been
focused on the synthesis of pentanoate esters, pentenoate esters
and bio-based nylon monomers from GVL in the presence of
methanol (or ethanol) and acid catalysts.6–12 The main products
could be categorized into unsaturated fatty acid esters including
methyl 2-pentenoate (M2P), methyl 3-pentenoate (M3P) and
methyl 4-pentenoate (M4P) which could be hydrogenated to
methyl pentanoate (MP), and unexpected by-products such as
With the catalysis of several acidic zeolites and CaCO3, the
product distribution of the ring-opening reaction of GVL in
methanol with a quite high GVL–methanol ratio (1 : 2 v/v) were
classed into three categories: pentenoate esters, MP and MMP,
as summarized in Table 1 and Fig. S1.† It is noted that USY
zeolite showed higher activity in the conversion of GVL to form
MMP, among which hydrogen exchanged ultra-stable Y zeolite
(HUSY) was chosen as acid catalyst in this research because of
its relatively higher activity under given conditions. The
percentage conversion of GVL was 46.4%, which is rather high
in consideration of the enlarged amount of substrate under a
sealed condition in this research (1 : 2 v/v). There was only a
little M2P generated during the reaction, which was consistent
with the result given by Zeng,6 suggesting that the rearrange-
ment reaction rarely occurred among a-C, b-C and g-C. Besides,
two cis–trans-isomers of M3P, E-M3P and Z-M3P, with different
retention times and a relative amount of approximately 2 : 1,
were identied by GC-MS (Fig. S1†). Additionally, the ratio of
College of Energy, Xiamen University, Xiamen 361005, PR China. E-mail: xianhai.
zeng@xmu.edu.cn; lulin@xmu.edu.cn; Tel: +86-592-2880701
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra13682a
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 8297–8300 | 8297

View Article Online
RSC Advances
Communication
Scheme 1 The synthesis of pentenoate esters and MMP from GVL and alcohols.
a
Table 1 The product distruibution of ring-opening reaction of GVL catalyzed by solid acids and CaCO3
Selectivity to pentenoate esters (%)
Entry
Catalyst
Conversion (%)
M2P
M3P
M4P
MP (%)
MMP (%)
1
2
3
4
5
HY
HZSM-5
USY
32.6
14.4
20.8
46.4
40.1
—
—
—
—
4
12.3
38.2
6.9
8.5
35.5
5.9
11.7
5.7
5.2
12.9
6.9
10.2
11.5
7.3
74.8
39.8
75.9
78.9
37.6
HUSY
SO42À/USY
9.7
a
Reaction conditions: 10 mL GVL, 20 mL methanol, 0.5 g HUSY, 0.5 mmol CaCO3, 250 ꢀC, N2 (3 MPa, RT), 700 rpm, 4 h.
M3P and M4P in every experiment ranged between 2 : 1 and to 4 h and proper temperature beneted the conversion of GVL,
4 : 1, implying that the reaction obeyed Saytzeff rule. It was also while the selectivity to MMP was not changed much (Table 2,
determined that other zeolites with sufficient acidity might also entry 6 and 11–13). However, when the reaction time was pro-
be effective for the ring-opening reaction of GVL, such as HY longed to 12 h, the selectivity to MMP was dramatically reduced
(Table 1, entry 1).
from 78.9% to 45.7% (Table 2, entry 6 and 14). Simultaneously,
Detailed optimization has been conducted to achieve higher the conversion of GVL was a little higher, while the selectivity to
MMP yield, as shown in Table 2. Prolonged reaction time from 1 pentenoate esters was up to 49.9% probably as a result of
Table 2 Catalytic conversion of GVL to MMP under different reaction conditionsa
Selectivity (%)
Entry
Feed ratiob
Temperature (ꢀC)
Reaction time (h)
Conversion (%)
Pentenoate esters
MMP
6
7
8
9
10
11
12
13
14
1 : 2
1 : 5
1 : 2c
1 : 5d
1 : 5e
1 : 2
1 : 2
1 : 2
1 : 2
250
250
250
250
250
200
250
250
250
4
4
4
4
4
4
1
2
12
46.4
50.7
40.9
57.9
43.5
37.9
40.0
44.0
53.0
13.7
21.3
44.0
6.3
17.3
6.2
9.9
10.1
49.9
78.9
70.5
47.4
87.1
75.5
76.8
76.7
82.0
45.7
a
Reaction conditions: 0.5 g HUSY, 0.5 mmol CaCO3, N2 (with an initial pressure of 3 MPa, RT), 700 rpm. b The volume ratio of GVL and methanol.
c
The amount of HUSY was increased from 0.5 g to 0.8 g. d The amount of CaCO3 was increased from 0.5 mmol to 1 mmol. e The total amount of
GVL, methanol, HUSY and CaCO3 was 5 times of those in entry 9.
8298 | RSC Adv., 2015, 5, 8297–8300
This journal is © The Royal Society of Chemistry 2015

View Article Online
Communication
RSC Advances
Table 3 The effects of carbonates and calcium salts in the synthesis of MMPa
Selectivity (%)
Entry
Catalyst
Conversion (%)
Pentenoate esters
MP
MMP
15
16
17
18
19
20
21
22
23
24
25
26
27
—
HUSY
CaCO3
14.6
44.8
14.8
17.8
15.0
12.0
46.4
40.1
46.4
35.7
8.4
—
75.2
—
—
—
94.5
4.2
1.6
19.0
4.3
95.7
92.3
88.1
27.7
7.3
18.3
16.9
4.2
HUSY + K2CO3
HUSY + Na2CO3
HUSY + CaO
HUSY + CaCO3
HUSY + BaCO3
HUSY + MnCO3
HUSY + CaSO4
HUSY + CaCl2
HUSY + CH3ONab
7.7
11.8
72.3
78.9
77.0
79.1
10.4
57.8
82.1
60.0
—
13.7
4.7
3.4
83.4
—
42.2
8.1
3.6
52.2
43.1
9.3
36.4
c
HUSY + CO2
a
Reaction conditions: 10 mL GVL, 20 mL methanol, 0.5 g HUSY, 0.5 mmol carbonates, oxide or salts, 250 ꢀC, N2 (with an initial pressure of 3 MPa,
RT), 700 rpm, 4 h. 60 mL of CH3ONa solvent (in methanol, 5 mol LÀ1) was added. CO2 (about 80 mL, 1 bar, RT) was purged into the reactor
b
c
followed by pressurizing to 3 MPa by N2. The solvent was 19 mL methanol and 1 mL H2O.
chemical equilibrium which will be discussed later. Moreover, properties of MMP were studied and presented in Table S2,†
no obvious effect has been observed by enlarging the add which provide considerable potential of MMP as a fuel additive
amount of methanol or HUSY (Table 2, entry 7 and 8). As entry 9 and solvent.
showed, when the dosage of CaCO3 was double, the conversion
It is quite interesting why CaCO3 showed such excellent
percentage of GVL and selectivity to MMP were increased to catalytic activity in the generation of MMP. In order to study the
nearly 60% and 90%, observably more than those of entry 7 and mechanism, various carbonates and calcium salts were
10. Otherwise, the recycle performances of catalyst have also employed to verify the effective ingredient (Ca2+ or CO32À). As
been tested. As shown in Table S1,† the catalytic activity of used entry 16 in Table 3, GVL conversion of 44.8% was reached when
catalyst could be recovered by calcining.
HUSY was applied alone, but only 19.0% of which contributed
MMP produced in the enlargement experiment of entry 10 to MMP while 75.2% to pentenoate esters. Compared with that
was separated by vacuum distillation and characterized by proceeded with no catalyst in entry 15 or with CaCO3 alone in
GC-MS and 13C-NMR (Fig. S2 and S3†). Physical and chemical entry 17, less than 15% GVL was consumed, mainly alcoholyzed
Scheme 2 (a) A model reaction conducted with GBL as reactant; (b) the competing reactions in the formation of MMP from GVL.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 8297–8300 | 8299

View Article Online
RSC Advances
Communication
to form MP and gave only a small amount of MMP. As such, it (Table 3, entry 26–27, and Table S3†). Satisfying GVL conversion
could be deduced that the formation of pentenoate esters and MMP selectivity were obtained, proving the importance of
2À
strongly depended on HUSY, which effectively catalyzed the CO3 and methoxy anion.
ring-opening reaction and dehydration process of GVL. Simi-
However, it was remarkable that there existed a dynamic
larly, no pentenoate ester was detected when soluble alkalis equilibrium between GVL and MMP, because the GVL conver-
such as Na2CO3, K2CO3 and CaO (Table 3, entry 18–20) were sion could hardly be improved much by prolonging the reaction
adopted, indicating that HUSY was totally disabled by the time in a sealed reactor (Table 2, entry 14). The reason of the
alkalis as the mechanism given in Scheme S1.† The addition of selectivity to pentenoate esters could be increased obviously was
insoluble carbonates, such as BaCO3 and MnCO3 (Table 3, entry that the E1 elimination reaction of HP was irreversible, which
22 and 23) showed no harm for HUSY, thus leading to similar was in accordance with that Zeng has proved.1
GVL conversion and selectivity to MMP as compared with that
of in the presence of CaCO3. On the contrary, experiments
conducted with calcium oxide and salts (Table 3, entry 20, 24
Conclusions
and 25) didn't give high yields of MMP, suggesting that Ca2+ was
In summary, the selectivity of GVL ring-opening reaction to
not the key factor for the reaction. In conclusion, insoluble
MMP could be greatly improved from less than 20% up to nearly
carbonates, as trace CO32À donors, played an important role in
90% by the addition of CaCO3 or other insoluble carbonates.
the synthesis of MMP in the premise that HUSY existed.
The anion, CO32À, was proved as the active species to promote
Although CaCO3 showed signicant effect on the generation
the generation of CH3OÀ which acted as nucleophile to attack
of MMP from GVL, it was still confused that there was an inverse
HP derived from the ring-opening reaction of GVL to produce
correlation between the amount of MMP and pentenoate esters,
MMP by SN1 or SN2 procedure in competition with pentenoate
which suggested that pentenoate esters or MMP might be
esters. Meanwhile, a supposed mechanism of the competing
generated successively or competitively. To investigate this
reaction was also provided. Ongoing work will be focused on the
issue, gamma-butyrolactone (GBL) was chosen to conduct a
downstream application of MMP for value added molecule
model reaction under the same conditions. Interestingly,
production.
although 56.8% GBL was converted in the presence of HUSY
and CaCO3 to form methyl 4-methoxybutyrate (MMB, major
product), a little 4-methoxybutyric acid and 4-hydroxybutyrate,
no butenoate esters was detected in the product (see the GC
Notes and references
spectra in Fig. S4†), which indicated that there was no carbo-
cation generated. Hence, the formation of MMB from GBL was
subjected to a SN2 process (Scheme 2a), implying that the
methoxy group was not from the addition reaction on the
double-bonds of butenoate esters, which was also applicable to
that of GVL.
With respect to 4-hydroxypentanoate (HP, which can be
considered as a secondary alcohol), the ring-opening interme-
diate of GVL, it was feasible for the hydroxyl group to be
protonized and then dehydrated under the catalysis of HUSY to
form secondary carbocation followed by E1 elimination
pathway to generate pentenoate esters, as shown in Scheme 2b.
Meanwhile, a little MMP might be produced with the presence
of methoxy anion from the self-ionization of methanol.
However, HP could not be detected by GC-MS as a thermal
instable intermediate, which was quickly converted into GVL or
other products at high temperature.14 When CaCO3 was intro-
1 X. Tang, H. Chen, L. Hu, W. Hao, Y. Sun, X. Zeng, L. Lin and
S. Liu, Appl. Catal., B, 2014, 147, 827–834.
2 Z. Yan, L. Lin and S. Liu, Energy Fuels, 2009, 23, 3853–3858.
3 X. Du, L. He, S. Zhao, Y. Liu, Y. Cao, H. He and K. Fan, Angew.
Chem., Int. Ed., 2011, 50, 7815–7819.
4 D. M. Alonso, J. Q. Bond, J. C. Serrano-Ruiz and
J. A. Dumesic, Green Chem., 2010, 12, 992–999.
5 X. Tang, X. Zeng, Z. Li, L. Hu, Y. Sun, S. Liu, T. Lei and L. Lin,
Renewable Sustainable Energy Rev., 2014, 40, 608–620.
6 F. Zeng, H. Liu, L. Deng, B. Liao, H. Pang and Q. X. Guo,
ChemSusChem, 2013, 6, 600–603.
7 T. Pan, J. Deng, Q. Xu, Y. Xu, Q. Guo and Y. Fu, Green Chem.,
2013, 15, 2967–2974.
8 C. E. Chan-Thaw, M. Marelli, R. Psaro, N. Ravasio and
F. Zaccheria, RSC Adv., 2013, 3, 1302.
9 J. P. Lange, J. Z. Vestering and R. J. Haan, Chem. Commun.,
2007, 3488–3490.
duced, it was supposed that the generation of methoxy anion (as 10 J. P. Lange, R. Price, P. M. Ayoub, J. Louis, L. Petrus, L. Clarke
the dotted box in Scheme 2b), a strong nucleophile, was thus
promoted, and then induced the addition reaction of carboca-
and H. Gosselink, Angew. Chem., Int. Ed., 2010, 49, 4479–
4483.
tion to form MMP. Furthermore, enriched methoxy anions 11 R. Palkovits, Angew. Chem., Int. Ed., 2010, 49, 4336–4338.
could also greatly enhance the SN2 substitution process of HP, 12 L. Dong, L. He, G. Tao and C. Hu, RSC Adv., 2013, 3, 4806–
which led to a signicant increase of selectivity to MMP from
less than 20% to nearly 80% (Table 3, entry 16 and 21). Mean- 13 D. Fegyverneki, L. Orha, G. Lang and I. T. Horvath,
while, a slight increase of GVL conversion was also observed Tetrahedron, 2010, 66, 1078–1081.
(Table 3, entry 14 and 19–21). The assumption was further 14 X. Tang, L. Hu, Y. Sun, G. Zhao, W. Hao and L. Lin, RSC Adv.,
veried by introducing CH3ONa or CO2 in place of CaCO3 2013, 3, 10277–10284.
4813.
´
´
8300 | RSC Adv., 2015, 5, 8297–8300
This journal is © The Royal Society of Chemistry 2015