Heterogeneous catalysis for the ketalisation of ethyl levulinate with 1,2-dodecanediol: Opening the way to a new class of bio-degradable surfactants

Article abstract of DOI:10.1016/j.catcom.2015.10.011

The acid-catalysed ketalisation between ethyl levulinate and two different alkyl 1,2-diols (ethylene glycol and 1,2-dodecanediol) was investigated using different acid catalysts, e.g. p-toluensolfonic acid, Amberlyst 70, zeolite H-ZSM-5, and niobium phosphate. Good activity and recyclability were achieved in the reaction with ethylene glycol catalysed by niobium phosphate. Very promising results (both in diol conversion and in selectivity towards the desired ketal) were ascertained in the reaction with the longer-chain 1,2-dodecanediol catalysed by heterogeneous catalysts. The alkaline hydrolysis of the synthetised long-chain ketal ester allowed us to obtain a new green surfactant, with surface tension values falling in the range of the commercial anionic ones.

Full text of DOI:10.1016/j.catcom.2015.10.011

Heterogeneous catalysis for the ketalization of ethyl levulinate with 1,2-
dodecanediol: Opening the way to a new class of bio-degradable surfactants
Fla´vio A. Freitas, Domenico Licursi, Elizabeth R. Lachter, Anna Maria
Raspolli Galletti, Claudia Antonetti, Thamires C. Brito, Regina Sandra V.
Nascimento
PII:
DOI:
Reference:
S1566-7367(15)30106-0
doi: 10.1016/j.catcom.2015.10.011
CATCOM 4469
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
13 August 2015
1 October 2015
5 October 2015
Please cite this article as: Fl´avio A. Freitas, Domenico Licursi, Elizabeth R. Lachter,
Anna Maria Raspolli Galletti, Claudia Antonetti, Thamires C. Brito, Regina Sandra
V. Nascimento, Heterogeneous catalysis for the ketalization of ethyl levulinate with 1,2-
dodecanediol: Opening the way to a new class of bio-degradable surfactants, Catalysis
Communications (2015), doi: 10.1016/j.catcom.2015.10.011
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ACCEPTED MANUSCRIPT
Heterogeneous catalysis for the ketalization of ethyl levulinate with 1,2-
dodecanediol: opening the way to a new class of bio-degradable surfactants
a
b
Flávio A. Freitas , Domenico Licursi , Elizabeth R. Lachter*a, Anna Maria Raspolli
Galletti b, Claudia Antonetti b, Thamires C. Brito a and Regina Sandra V. Nascimento a
a Universidade Federal do Rio de Janeiro, Instituto de Química, Rio de Janeiro, Brazil.
b Department of Chemistry and Industrial Chemistry, University of Pisa, Via G. Moruzzi
13, 56124, Pisa, Italy.
* Corresponding author. E-mail address: lachter@iq.ufrj.br
The acid-catalysed ketalization between ethyl levulinate and two different alkyl 1,2-
diols (ethylene glycol and 1,2-dodecanediol) was investigated using different acid
catalysts, e.g. p-toluensolfonic acid, Amberlyst 70, zeolite H-ZSM-5 and niobium
phosphate. Good activity and recyclability were achieved in the reaction with ethylene
glycol catalyzed by niobium phosphate. Very promising results (both in diol conversion
and in selectivity towards the desired ketal) were ascertained in the reaction with the
longer-chain 1,2-dodecanediol catalyzed by heterogeneous catalysts. The alkaline
hydrolysis of the synthetized long-chain ketal ester allowed us to obtain a new green
surfactant, with surface tension values falling in the range of the commercial anionic
ones.
Keywords: ethyl levulinate, ketalization, heterogeneous catalysis, niobium phosphate
1

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1. Introduction
Many chemical products such as surfactants, plasticizers, and polymers are
currently manufactured from non-renewable, expensive, petroleum-derived or
natural gas-derived feedstock compounds. High raw material costs and
uncertainty of future supplies impelled the discovery and development of
chemical products that can be made from inexpensive renewable biomasses [1].
In this context, levulinic acid (or 4-oxopentanoic acid) (LA) and levulinic esters
represent important platform molecules, obtained from biomass, which can be
converted into valuable chemicals such as plasticizers, solvents and flavours [2-
10]. The reaction between levulinic acid esters and an alcohol leads to ketal
formation and the presence of an acid catalyst is necessary. Diols, triols and
polyols can be also used to form cyclic ketals [11]. Acetalization/ketalization
reactions are acid-catalyzed processes. In the field of homogeneous catalysis,
mineral acids are used. However, they present limitations due to corrosion,
toxicity and environmental pollution problems and need complex and expensive
downstream steps, such as their neutralization. On the other hand, heterogeneous
catalysis presents easy work-up and does not involve the use of dangerous
substances [12]. Many heterogeneous catalysts have been used in the
acetalization and ketalization reactions, including zeolites, clays, sulfonic resins,
mesoporous aluminosilicates, SBA-15 and niobium phosphate [13-20]. During
the acid-catalyzed ketalization reaction, the ketal-ester or the keto-ester can
undergo further competing transesterification with the alcohol [11] and, therefore,
some by-products can be obtained, decreasing the yield of the target valuable
ketal ester. Mullen et al. [11] investigated the reaction between different keto-
esters and diols/triols using a variety of catalyst types, catalyst concentrations,
and reaction conditions. Different acids were tested, such as hydrochloric acid,
sulphuric acid, sulfamic acid and Amberlyst 15 and high conversion and
selectivity to the ketal product were achieved by adopting a low concentration of
the acid catalyst. Ono et al. [21] investigated the reaction of ethyl levulinate (EL)
with various alkyl 1-O-alkyl glycerol, by using PTSA as catalyst and toluene as
solvent. The authors reached variable yields in the range 78-98 %. The ketal ester
obtained was hydrolysed to produce an anionic surfactant. Ketal surfactants are in
general more labile than the corresponding acetal surfactants [21,22]. Recently
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the synthesis of sulfonated surfactants starting from furfural and carboxylate
surfactants obtained from 5-HMF (5-hydroxymethyl furfural) is reported in the
literature [23,24].
In the first part of this work, the study of the model reaction between ethyl
levulinate (EL) and ethylene glycol (EG) will be reported, by using different acid
catalysts, including Amberlyst 70 (A-70), zeolite H-ZSM-5 and niobium
phosphate (NbP). p-toluensolfonic acid (PTSA) will be considered as standard
homogeneous acid catalyst for the ketalization reaction, in order to better
understand the improvement given by the heterogeneous catalysis. In this
perspective, reaction between EL and EG will be studied adopting homogenous
(PTSA) or heterogeneous (A-70, H-ZSM-5 and NbP) systems, starting from the
worst reaction conditions at very low EL/EG molar ratio. Then, a deeper
investigation of the reaction conditions will be tested, adopting different reaction
conditions, such as catalyst loading, EL/EG molar ratio and reaction time.
Furthermore, the recyclability of the most promising heterogeneous catalysts will
be studied.
Current research is focused on the use of longer-chain diol precursors, in order to
improve the surface tension properties of the synthetized surfactants. In this
sense, 1,2-dodecanediol may represent a good green solution, being currently
used in cosmetics formulations [25]. Therefore, in the second part of this work,
the acid-catalysed ketalization reaction between the longer chain 1,2-
dodecanediol and EL will be carried out, in the presence of homogeneous (PTSA)
or heterogeneous (A-70 and NbP) catalysts. Surface tension of the sodium salt of
the produced ketal will be evaluated, in order to verify their possible use as green
surfactants.
2. Experimental
2.1. Materials
Commercial materials were used as received. Details about the procedures of treatment
and properties of the catalysts A70, NbP and H-ZSM-5 are described in the
supplementary information.
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2.2. Typical procedure of ketalization reaction of ethyl levulinate with ethylene glycol
and 1,2-dodecanediol
Catalytic liquid phase ketalization reactions between ethyl levulinate and ethylene
glycol or 1,2-dodecanediol were carried out as described in the supplementary
information.
3. Results and discussion
3.1. Ketalization reaction of ethyl levulinate with ethylene glycol
In the first part of this work, the model reaction between ethyl levulinate (EL) and
ethylene glycol (EG) was considered in order to optimize the reaction conditions and
identify the best catalysts, in terms of conversion and selectivity. The possible
ketalization/transesterification reactions are depicted in Fig. 1.
Figure 1, near here
On the basis of the Fig. 1, ethylene glycol could react with the ketone group, thus giving
the target ketal product (2), or with the ester groups, thus producing a new ketal ester (3)
or a new ester (4), both representing by-products. Niobium phosphate (NbP), sulfonic
resin (A-70) and zeolite (H-ZSM-5) were tested as heterogeneous acid catalysts. These
systems have been selected because avoid the drawbacks of homogeneous catalysts,
such as waste generation, catalyst separation and neutralization [26]. However, PTSA
was also tested as reference homogeneous catalyst in order to compare homogeneous
versus heterogeneous systems. The ketalization is an equilibrium reaction and therefore
it is appropriate to use an organic solvent, such as toluene, in order to remove the
evolved water, thus increasing the yield in the desired ketal. The reaction was
performed at 110 °C, by adopting different EL/EG molar ratios, equal to 0.5, 1.2 and
2.5. Because the choice of an EL excess could represent an economic limit, the lowest
EL/EG molar ratio should be preferred. The results obtained by using EL/EG molar
ratio = 0.5 are reported in Table 1 both for homogeneous (PTSA) and heterogeneous
(A-70, H-ZSM-5 and NbP) catalytic systems.
Table 1, near here
This run shows that, despite the acceptable catalytic activity of PTSA, the selectivity
towards the desired ketalization product (2) is very low, due to the formation of the by-
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product (3) and, in lower amount, of the by-product (4). On the contrary, all the
investigated heterogeneous systems gave the almost complete selectivity towards the
desired ketalization product (2) (runs 2-8). On the other hand, the not complete
conversion was probably due to the too low EL/EG molar ratio. The comparison among
the catalytic performances obtained with heterogeneous catalysts immediately evidences
that EL conversion was higher for the A-70-catalysed reactions (runs 2-4) rather than
for the NbP- and H-ZSM-5-catalysed ones (runs 5-8). When A70 and H-ZSM-5 were
employed (runs 2-4 and 7-8 respectively), selectivity towards the ketal product (2) was
never complete, due to the formation of by-product (3). Instead, NbP evidenced a lower
activity in EL conversion, but the selectivity to the target product (2) was complete
(runs 5-6). Mullen et al. [11] evaluated the effect of H2SO4 catalyst concentration in the
ketalization reaction between EL and EG. The authors reported a higher selectivity
towards the product (2) when a lower catalyst concentration was used. In our case, the
lower concentration of NbP acidic sites may justify the complete selectivity of the
ketalization reaction towards the product (2). The results of the ketalization reaction
between ethyl levulinate (EL) and ethylene glycol (EG) at higher EL/EG molar ratios
adopting different catalytic systems PTSA, A-70, H-ZSM-5 and NbP are reported in
Table 2.
Table 2, near here
When harsher reaction conditions were employed, in terms of catalyst loading and time
(10 wt % and 24 h), all catalysts gave an incomplete selectivity toward the target
product (2) (runs 9, 10, 14 and 18 for PTSA, A70, H-ZSM-5 and NbP respectively,
Table 2). By decreasing the catalyst loading from 10 to 1 wt % but increasing the
EL/EG molar ratio from 1.2 to 2.5, it was possible to significantly reduce the reaction
time, achieving a complete selectivity towards the ketalization product (2) (runs 11, 15
and 19 for A70, H-ZSM-5 and NbP respectively, Table 2). Taking into account the
interesting result regarding the complete selectivity, the catalyst loading was further
decreased from 1 to 0.1 wt % in order to find more sustainable reaction conditions. The
catalytic runs carried out in the presence of the most active catalysts A70 and H-ZSM-5
(runs 12 and 16 respectively, Table 2) showed that the complete selectivity towards the
target product (2) was retained at the same low reaction time (1h), despite of the EG
conversion decrease. On the basis of these results, in order to improve the EG
conversion, a longer reaction time (4h) was employed for all the heterogeneous catalysts
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(runs 13, 17 and 21 for A70, H-ZSM-5, NbP respectively, Table 2). Remarkable
catalytic results were achieved with all the catalytic systems due to the almost complete
conversion together with the total selectivity towards the ketalization product (2). The
most promising catalytic results were obtained with zeolite H-ZSM-5 and thus this
system was further investigated for its recyclability. Anyway, the recycle of this catalyst
was not satisfactory, showing a decrease of its catalytic activity of about 30 % in the
first recycle, probably due to the inefficient mild adopted catalyst regeneration
procedure carried out simply by toluene washing.
On the other hand, NbP is well-known as a water-tolerant catalyst [27]. The acidic,
textural, and catalytic properties of NbP are preserved in aqueous systems under harsher
reaction conditions of temperature [28, 29] than those employed in the current research.
Moreover, niobium is the 33rd most abundant element in the Earth’s crust, so it is a
plentiful resource and at the same time it is also nontoxic and physiologically inert [30].
Therefore, it was selected for the subsequent recyclability investigation. Five recycling
tests were carried out on NbP. After each catalytic run, also in this case, the catalyst was
simply washed with toluene and reused. After five cycles, catalyst has retained a high
activity and selectivity to the desired ketal, as shown in Fig. 2.
Figure 2, near here
The above catalytic runs show that NbP recycle has not significantly modified its acidic
properties, and the ascertained surface area of the recovered catalyst remained almost
unchanged (120 m2 g-1 versus 138 m2 g-1), thus confirming that our heterogeneous
catalysis approach can be applied to the eco-friendly synthesis of these ketals.
3.2. Ketalization reaction of ethyl levulinate with 1,2-dodecanediol
After having investigated the chemical behaviour of EL and EG towards ketalization by
means of heterogeneous catalysis, new ketalization reactions were performed by using a
more long-chain vicinal diol, that is 1,2-dodecanediol, in order to evaluate the
possibility of synthesizing a new class of efficient bio-surfactants.
Also in this case, an EL excess was adopted, e.g. a molar ratio EL/1,2-dodecanediol =
2.5, with PTSA, A-70, NbP and H-ZSM-5 as acid catalysts. Many different reaction
conditions were tested and it was found that, differently from ethylene glycol, the high
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conversion of 1,2-dodecanediol has required a longer reaction time, that is 24 hours, by
adopting the lowest catalyst loading. Best-obtained results are reported in Table 3.
Table 3, near here
When PTSA, A70 and NbP catalysts were employed (runs 22-24, respectively),
selectivities towards ketalization product (2) were complete and therefore no
13
transesterification by-products were obtained, as confirmed by C-NMR and HPLC
analysis of the reaction mixture. Only in the case of the homogeneous PTSA it is
possible to reach the total 1,2-dodecanediol conversion, whereas for the other
heterogeneous systems (A70 and NbP), promising values about 80-85 % were
ascertained. On the other hand, when the reaction was carried out in the presence of H-
ZSM-5, the selectivity towards the target product (2) was slightly lower than that of the
other heterogeneous systems, under the same reaction conditions. On the basis of these
results, ketal ester coming from A-70 and NbP catalyzed reactions was selected for its
further purification, due to the incomplete conversion of the diol. Then, the obtained
ketals were hydrolysed by NaOH/EtOH treatment and surface tensions of all the
synthesized sodium carboxylate surfactants were analogous. The surface tension of H2O
is 72.2 mN m-1 and in the presence of the new surfactant this value decreases to 33.5
mN m-1 (supplementary information).
4. Conclusions
In this investigation, a green bio-surfactant was prepared by using renewable and cheap
reagents. Heterogeneous catalysts, Amberlyst A70, zeolite H-ZSM-5 and niobium
phosphate, were tested in the model ketalization reaction between ethyl levulinate and
ethylene glycol. In fact, high yields and selectivities towards the target ketalization
product were ascertained. On the contrary, when the homogeneous PTSA system was
adopted, a big amount of by-products was obtained. In the presence of heterogeneous
systems, the results were improved by the optimization of the main reaction parameters,
catalyst loading, EL/EG molar ratio and reaction time. NbP resulted a very promising
system, due to its complete recyclability and good performances also at low catalyst
loading, taking also into account that, up to now, this catalytic system has not been
proposed for the ketalization reaction. A new kind of bio-surfactant was synthesized
starting from ethyl levulinate and 1,2-dodecanediol, in the presence of the same
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heterogeneous catalysts. The surface tension of this bio-derivative was similar to that of
the commercial sodium dodecyl sulphate (SDS) surfactant.
Acknowledgements
F.A. Freitas wishes to acknowledge Conselho de Aperfeiçoamento de Ensino Superior –
CAPES of Brazil for a Doctoral Grant. The authors thank Dr. Bianca Peres Pinto for the
GC-MS analysis. The authors also thank CBMM (Companhia Brasileira de Metalurgia
e Mineação) and Rhom & Haas for kindly providing niobium phosphate and Amberlyst
70, respectively.
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Table 1 Results of the ketalization reaction between ethyl levulinate (EL) and an excess
of ethylene glycol (EG), in the presence of different heterogeneous acid catalysts.
Reaction conditions: Catalyst loading = 3 wt%, EL/EG molar ratio = 0.5, Temperature =
110°C.
Run Catalyst
Time (h)
EL
Selectivity to Selectivity to product
Conversion
product (2)
(3) (mol%)
(mol%)
78
(mol%)
18
1
2
3
4
5
6
7
8
PTSA
A70
A70
A70
NbP
NbP
H-ZSM-5
H-ZSM-5
1
0.5
1
4
1
4
1
4
41 a
6
6
4
-
-
3
4
58
82
87
50
54
65
68
94
94
96
100
100
97
96
a 7 mol % of product (4) together with other by-products were produced.
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Table 2 Results of the ketalization reaction between ethyl levulinate (EL) and ethylene
glycol (EG). Reaction conditions: Temperature = 110°C.
Run
Catalyst Catalyst EL/EG Time
EG
Conversion
(mol %)
96
Selectivity to Selectivity to
loading
(wt %)
10
molar
ratio
1.2
1.2
2.5
(h)
product (2)
(mol %)
20.1
86.3
100
product (3)
(mol %)
9
PTSA
A70
A70
24
24
1
33 a
10
11
12
13
14
15
16
17
18
19
20
21
10
1
100
96.8
85
99
100
98
85.5
100
100
82
6.6 b
-
A70
A70
0.1
0.1
10
2.5
2.5
1.2
2.5
2.5
2.5
1.2
2.5
1
4
24
1
1
4
24
1
100
-
100
90.2
100
-
9.8
-
H-ZSM-5
H-ZSM-5
H-ZSM-5
H-ZSM-5
NbP
1
0.1
0.1
10
100
-
100
-
98.5
100
1.5
-
NbP
1
NbP
NbP
0.1
0.1
2.5
2.5
1
4
80.3
96
100
-
100
-
a 8.5 mol % of product (4) together with other by-products were produced.
b 3.9 mol % of product (4) together with other by-products were produced.
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Table 3 Results of the ketalization reaction between ethyl levulinate (EL) and 1,2-
dodecanediol, in excess of ethyl levulinate.
O
O
OH
EtO
O
O
EtO
HO
O
Run Catalyst
1,2-dodecanediol
Selectivity to product (2) (mol%)
Conversion (mol%)
22
23
24
PTSA
A70
NbP
100
85
81
100
100
100
98
25 H-ZSM-5
82
Reaction conditions: EL/1,2-dodecanediol = 2.5 mol/mol; catalyst loading = 1 wt %;
reaction time = 24 hours; Temperature = 130 °C.
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Captions for figures and schemes
Fig. 1. Ketalization reaction between ethyl levulinate (EL) and ethylene glycol (EG).
Fig. 2. Catalytic performances (conversion and selectivity) of NbP to ketal, after five
catalytic cycles (run 21 and successive recycles of the solid catalyst). Reaction
conditions: Catalyst loading = 0.1 wt%, EL/EG molar ratio = 2.5, reaction time = 4
hours, Temperature = 110°C.
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O
O
H2O
O
2
3
O
O
O
OH
O
O
HO
O
OH
1
OH
OH
O
O
O
O
OH
4
O
Fig. 1. Ketalization reaction between ethyl levulinate (EL) and ethylene glycol (EG).
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Selectivity (mol%)
Conversion (mol%)
100
80
60
40
20
0
1
2
3
4
5
Catalytic cycles
Fig. 2. Catalytic performances (conversion and selectivity) of NbP to ketal, after five
catalytic cycles (run 21 and successive recycles of the solid catalyst). Reaction
conditions: Catalyst loading = 0.1 wt%, EL/EG molar ratio = 2.5, reaction time = 4
hours, Temperature = 110°C.
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Highligths
 Ketalization reaction between ethyl levulinate and alkyl 1,2-diols was evaluated.
 Different heterogeneous catalysts have showed good catalytic performances.
 Niobium phosphate was preferred for its easier and better recyclability.
 A surfactant was synthetized by alkaline hydrolysis of the ketal with longer
chain.
 The new green bio-surfactant showing good surface tension properties.
17