Acid Catalyzed Competitive Esterification and Ketalization of Levulinic Acid with 1,2 and 1,3-Diols: The Effect of Heterogeneous and Homogeneous Catalysts

Article abstract of DOI:10.1007/s10562-016-1812-8

Abstract: Condensation reactions of levulinic acid (LA) with 1,2-ethanediol (1,2-ED), 1,2-propanediol (1,2-PD), and 1,3-propanediol (1,3-PD) were studied using Amberlyst-15 as well as p-toluenesulfonic acid catalysts in benzene under Dean–Stark conditions. In Amberlyst-15 catalyzed reactions the products are ketals and ketal-esters, whereas p-toluenesulfonic acid catalyzed reactions produce esters and ketal-esters as products. In p-toluenesulfonic acid catalyzed reactions with 1,2-ED and 1,3-PD, LA monoester product is formed as the major product after 180?min in 75 and 97?% yields respectively. Unlike the previously reported acid catalyzed ketalization of ethyl levulinate with diols, combined ketalization–esterification of LA with diols is a complex process. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-016-1812-8

Catal Lett
DOI 10.1007/s10562-016-1812-8
Acid Catalyzed Competitive Esterification and Ketalization
of Levulinic Acid with 1,2 and 1,3-Diols: The Effect
of Heterogeneous and Homogeneous Catalysts
1
1
Ananda S. Amarasekara
•
Moriam A. Animashaun
Received: 25 April 2016 / Accepted: 7 July 2016
Ó Springer Science+Business Media New York 2016
Abstract Condensation reactions of levulinic acid (LA) with
,2-ethanediol (1,2-ED), 1,2-propanediol (1,2-PD), and 1,3-
1 Introduction
1
propanediol (1,3-PD) were studied using Amberlyst-15 as well
as p-toluenesulfonic acid catalysts in benzene under Dean–
Stark conditions. In Amberlyst-15 catalyzed reactions the
products are ketals and ketal-esters, whereas p-toluenesulfonic
acid catalyzed reactions produce esters and ketal-esters as
products. In p-toluenesulfonic acid catalyzed reactions with
Levulinic acid (LA) or 4-oxopentanoic acid is a key
renewable chemical since this C-5 feedstock can be pro-
duced from the most abundant biopolymer cellulose via a
series of acid catalyzed reactions [1]. This keto-acid was
listed as one of the top 12 most promising value added
chemicals from biomass by the Biomass Program of the US
Department of Energy in 2004 [2] and continues to rank
highly in more recent reviews of major biorefinery target
products [3]. Even though the current global LA con-
sumption is around 2600 tons/year, it is expected to
increase steadily in the coming years, especially due to the
introduction of the Biofine process, which has been pro-
1,2-ED and 1,3-PD, LA monoester product is formed as the
major product after 180 min in 75 and 97 % yields respec-
tively. Unlike the previously reported acid catalyzed ketaliza-
tion of ethyl levulinate with diols, combined ketalization–
esterification of LA with diols is a complex process.
Graphical Abstract
R
R
O
n
n
OH
OH
R
+
O
O
O
O
H
OH
O
OH
O
+
+
n
O
O
R
HO
R
O
n
O
OH
n
O
Keywords Levulinic acid Á 1,2-Ethanediol Á
,2-Propanediol Á 1,3-Propanediol Á Acid-catalysis
jected to lower LA costs to as low as 0.09–0.22 $/kg [4].
This versatile building block can be used in the synthesis of
various organic chemicals such as levulinate esters,
1
2
-methyl THF, c-valerolactone, acrylic acid, 1,4-pentane-
&
Ananda S. Amarasekara
asamarasekara@pvamu.edu
diol, b-acetylacrylic acid, a-angelica lactone, d-amino
levulinic acid, etc. [4, 5]. LA and its derivatives have been
used as building blocks for the preparation of polymers
1
Department of Chemistry, Prairie View A&M University,
Prairie View, TX 77446, USA
123

A. S. Amarasekara, M. A. Animashaun
[
6–8]. For example, 5-hydroxylevulinic acid derived from
the competing ketalization and esterification processes are
not reported in the literature. In continuing our efforts in
developing catalytic methods for the production of LA
derived new feedstock materials, we have studied the solid
acid Amberlyst-15 as well as p-toluenesulfonic acid cat-
alyzed condensations of LA with 1,2-ethanediol (1,2-ED),
1,2-propanediol (1,2-PD), and 1,3-propanediol (1,3-PD), as
shown in Fig. 1 [14–18].
LA has been used as the monomer for the preparation of
poly(5-hydroxylevulinic acid) and biodegradable poly(5-
hydroxylevulinic acid-co-L-lactic acid) [7, 8].
Bifunctional LA can undergo ketalization as well as
esterification with polyhydric alcohols like 1,2 and 1,3-
diols. We have recently explored this behavior in the
synthesis of a polymeric product by the condensation of
LA with another renewable resources based material
glycerol to give an oligomer of DP *10 [6]. The
ketalization of levulinate esters is also a current topic as
trans-esterification was not observed in the ketalization
of ethyl levulinate with polyols 1,2-ethanediol,
trimethylol propane and glycerol under low acid con-
centration conditions [9]. In a similar study, Freitas et al.
recently reported the acid-catalyzed ketalization of ethyl
levulinate with 1,2-dodecanediol using different acid
catalysts such as; p-toluenesulfonic acid, Amberlyst-70,
zeolite H-ZSM-5, and niobium phosphate. Good activity
and recyclability of the heterogeneous catalysts were
ascertained in the reaction with longer-chain 1,2-dode-
canediol [10]. In addition, levulinate ketal-esters can be
prepared directly by acid catalyzed degradation of glu-
cose or cellulose in a aqueous diol medium as well
2
Experimental
2.1 Materials and Instrumentation
LA, 1,2-ED (99 %), 1,2-PD ([99 %), 1,3-PD ([99 %),
Amberlyst-15 hydrogen form (4.7 meq/g by dry weight), p-
toluenesulfonic acid monohydrate (99 %) and anhydrous
1
benzene were purchased from Aldrich Chemical Co. H
NMR Spectra were recorded in CDCl on a Varian Mer-
3
cury plus spectrometer operating at 400 MHz and chemical
shifts are given in ppm downfield from TMS (d = 0.00).
1
3
C NMR were recorded in the same spectrometer at
00 MHz, and chemical shifts were measured relative to
1
CDCl3 and converted to d (TMS) using d (CDCl ) =
3
[
11–13]. For example, we have recently shown that a
77.00.
mixture of 2-hydroxyethyl levulinate, 2-hydroxyethyl
levulinate ethylene ketal, and 2,3,6,7-tetrahydro-cy-
clopenta[1,4]dioxin-5-one are formed during the lique-
faction of cellulose in ethylene glycol at 180 °C, using
2.2 General Procedure for Acid Catalyzed
Esterification and Ketalization of LA with 1,2
and 1,3-diols
1
-(1-alkylsulfonic)-3-methylimidazolium chloride ionic
liquids as catalysts.
In recent years, LA ketals and esters have attracted
attention as biodegradable surfactants [10] as well as
polymer additives [9]. However, the direct condensation of
LA with polyols and the effect of type of acid catalyst on
LA (116 mg, 1.00 mmol), diol (10 mmol), Amberlyst-15
?
hydrogen form or p-toluenesulfonic acid (0.047 mmol H )
were added to 20.0 mL of benzene in a Dean–Stark
apparatus and heated under reflux. Then 1.00 mL samples
R
n
O
O
+
O
+
OH
H
H
R
OH
O
K (3a-c)
n
O
R
LA (1)
+
+
O
O
H
O
OH
R
n
O
HO
OH
O
R
+
KE (5a-c)
n
+
H
H
2
a-c
O
OH
a, R = H, n = 0
n
O
b, R = CH , n = 0
3
E (4a-c)
c, R = H, n = 1
Fig. 1 Acid catalyzed condensation of levulinic acid (LA, 1) with diols (2a–c) to give ketal (K, 3a–c), ester (E, 4a–c), and ketal-ester (KE, 5a–
c) products
1
23

Acid catalyzed competitive esterification and ketalization of levulinic acid…
were withdrawn at t = 10, 20, 40, 80, 180 and 360 min
Similar equations were used in the calculation of pro-
into vials and solvent was evaporated under reduced
pressure. The residue was analyzed by recording NMR
duct mol% compositions and unreacted mol% of LA in the
reactions carried out with 1,2-ED, 1,2-PD and 1,3-PD using
two acid catalysts. The results showing the changes in
product mol% composition and unreacted mol% LA in six
experiments are shown in Fig. 3, plots a–f.
spectra in CDCl . The percent compositions of the samples
3
withdrawn were calculated by manual integration of
1
methyl and methylene H NMR peaks of unreacted LA,
ketal (K), ester (E), and ketal-ester (KE). A representative
1
H NMR spectrum of the sample withdrawn after 20 min
from the Amberlyst-15 catalyzed reaction of LA, with 1,2-
ED is shown in Fig. 2. This spectrum shows unreacted LA
as well as the formation of K and KE products.
3 Results and Discussion
The acid catalyzed condensation reaction of LA, with three
diols: 1,2-ED, 1,2-PD and 1,3-PD were studied as shown in
Fig. 1. Two sets of reactions were carried out using
Amberlyst-15 and p-toluenesulfonic acid as catalysts with
The mol% of unreacted LA in the sample was calculated
using peak areas corresponding to 2H’s and the formula:
mol% levulinic acid ðLAÞ
peak area at 2:76 ppm
?
the same H loading under identical conditions, in order to
¼
 100%
compare the effect of heterogeneous and homogeneous
catalysts on the condensation reactions. An excess of diol
peak area at 2:76 ppm þ peak area at 2:43 ppm
(
LA: diol 1:10 mol ratio) was used in all experiments to
The mol% of KE in the sample was calculated using the
formula:
minimize the formation of di-ester type products. The
changes in mol% composition with time was analyzed by
withdrawing small samples from the reaction mixture at
t = 10, 20, 40, 80, 180 and 360 min and recording NMR
mol% ketal-ester ðKEÞ
peak area at 4:24 ppm
¼
 100%
spectra in CDCl after removal of benzene. The products
3
peak area at 2:76 ppm þ peak area at 2:43 ppm
formed in the reactions and unreacted levulinic acid in
1
analyzed samples were identified by comparison of H and
The mol% of K in the sample was calculated using the
formula:
1
3
C NMR data with published data of these compounds
1
19, 20]. A representative H NMR spectrum of a sample
[
mol% ketal ðKÞ ¼ 100 À ½% levulinic acid ðLAÞ
þ % ketal-ester ðKEފ
withdrawn after 20 min from Amberlyst-15 catalyzed
condensation of levulinic acid (LA, 1) with 1,2-ethanediol
1
Fig. 2 Representative H NMR
spectrum of a sample of
Amberlyst-15 catalyzed
condensation of levulinic acid
(
(
LA, 1) with 1,2-ethanediol
1,2-ED) to give ketal (K), and
ketal-ester (KE) products.
Solvent: Benzene, reflux in
Dean–Stark water separator, 20
min
123

A. S. Amarasekara, M. A. Animashaun
a LA + 1,2-ED (Amberlyst-15)
d LA + 1,2-ED (p-TsOH)
100
100
LA
K
80
60
40
20
0
KE
8
6
4
0
0
0
LA
E
KE
20
0
0
100
200
300
400
0
100
200
300
400
Time (min.)
Time (min.)
b LA + 1,2-PD (Amberlyst-15)
e LA + 1,2-PD ( p-TsOH)
1
00
1
00
80
60
40
20
0
LA
K
KE
8
6
4
2
0
0
0
0
0
LA
E
KE
0
100
200
300
400
0
100
200
300
400
Time (min.)
Time (min.)
c LA + 1,3-PD (Amberlyst-15)
f LA + 1,3-PD (p-TsOH)
100
100
LA
K
KE
80
60
40
20
0
80
60
40
20
0
LA
E
KE
0
100
200
300
400
0
100
200
300
400
Time (min.)
Time (min.)
1
23

Acid catalyzed competitive esterification and ketalization of levulinic acid…
bFig. 3 The changes in mol% composition with time in Amberlyst-15
and p-toluenesulfonic acid catalyzed condensation reactions of
levulinic acid (LA) with 1,2-ethanediol (1,2-ED) 1,2-propanediol
(1,2-PD) and 1,3-propanediol (1,3-PD). Solvent: Benzene, reflux in
Dean–Stark water separator
180 min. This may be due to a slowdown in the esterifi-
cation due to steric hindrance in branched diol 1,2-PD and
at the same time competitive ketalization promotes the
formation of KE as the major product in 88 % yield after
180 min.
(1,2-ED, 2a) to give ketal (K, 3a), and ketal-ester (KE, 5a)
products is shown in Fig. 2. In the proton NMR spectrum
4
Conclusion
the CH group of unreacted LA can be observed as a sin-
3
Ketalization and esterification are competing processes in
acid catalyzed condensation of LA with 1,2 and 1,3-diols.
In Amberlyst-15 catalyzed reactions the products are K and
KE, whereas p-toluenesulfonic acid catalyzed reactions
produced E and KE. Unlike the previously reported acid
catalyzed ketalization of ethyl levulinate with diols, one-
pot combined ketalization–esterification of LA with diols is
a complex process. The highest K yield of 88 % was
obtained in a experiment with 1,2-ED using Amberlyst-15
catalyst. The highest KE (88 %) and E (97 %) yields were
obtained in experiments with 1,2-PD and 1,3-PD respec-
tively, using p-toluenesulfonic acid catalyst.
glet at 2.20 ppm, whereas two small triplets at 2.62 and
2
.76 ppm corresponds to the methylene protons of LA. The
ketal (K, 3a) and ketal-ester (KE, 5a) are the only products
formed in this reaction and the strong absorption from two
overlapped triplets at 2.43 ppm can be assigned to a set of
–
CH – groups from ketal (K, 3a), and ketal-ester (KE, 5a).
2
The other –CH – signals from these two products are
2
observed as a pair of close triplets at 2.09 and 2.04 ppm.
The two triplets at 3.80 and 4.23 ppm can be assigned to
–
CH –OH and –CH –OCO methylene groups of the ketal-
2 2
ester.
The mol% of unreacted LA, as well as KE and K in the
1
sample were calculated using H NMR peak areas and
Acknowledgments The authors would like to thank the National
Science Foundation (NSF) (through Grant Nos. CBET-0929970,
CBET-1336469, HRD-1036593), and the U.S. Department of Agri-
culture (USDA) (through Grant No. CBG-2010-38821-21569) for
financial support.
formulas as shown in section ‘‘General procedure for acid
catalyzed esterification and ketalization of levulinic acid
with 1,2 and 1,3-diols’’. Similar equations were used in
calculation of product mol% compositions and unreacted
mol% of LA in the reactions carried out with 1,2- 1,2-ED,
1
,2-PD and 1,3-PD using two acid catalysts. The results
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