New organic-inorganic LDH composites: Synthesis, characterization and catalytic behavior in the green epoxidation of α, β-unsaturated esters

Article abstract of DOI:10.1016/j.ica.2017.07.027

New organic-inorganic based LDH composites have been prepared using different methodologies, ie the ion-exchange method (Org@LDH-exch), the reconstruction (Org@LDH-mem) and the direct intercalation (Org@LDH-inter) method, respectively. Irrespective of the procedure, the –C[dbnd]O group of levulinate moiety was envisaged as a potential active organocatalyst in the epoxidation of trans-methylcinnamate to methyl-phenyl-glycidate. The characterisation of these materials through adsorption-desorption isotherms of nitrogen at ?196 °C, XRD, TG-DTA and DRIFT confirmed a successful intercalation only for Org@LDH-inter. The reactions were carried out via in situ generated dioxiranes using levulinate as active organocatalyst and H₂O₂/acetonitrile mixture as oxidant. Intercalated levulinate in aminoterephthalate/LDH structure led to conversions up to 25% with a total selectivity to methyl-phenyl-glycidate. Besides this, the heterogeneous organocatalyst behave as a green system: the constitutive levulinic acid represents one of the most important renewable platform molecules, while replacing the Oxone reagent with the more benign hydrogen peroxide and the substitution of an inorganic soluble base with the basic function of the LDH-support afford a more benign system.

Full text of DOI:10.1016/j.ica.2017.07.027

Accepted Manuscript
Research paper
New organic-inorganic LDH composites: synthesis, characterization and cata-
lytic behavior in the green epoxidation of α, β-unsaturated esters
Natalia Candu, Diana Paul, Ioan-Cezar Marcu, Madalina Tudorache, Vasile I.
Parvulescu, Simona M. Coman
PII:
S0020-1693(17)30581-9
http://dx.doi.org/10.1016/j.ica.2017.07.027
ICA 17750
DOI:
Reference:
Inorganica Chimica Acta
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Received Date:
Revised Date:
Accepted Date:
15 April 2017
10 July 2017
12 July 2017
Please cite this article as: N. Candu, D. Paul, I-C. Marcu, M. Tudorache, V.I. Parvulescu, S.M. Coman, New organic-
inorganic LDH composites: synthesis, characterization and catalytic behavior in the green epoxidation of α, β-
unsaturated esters, Inorganica Chimica Acta (2017), doi: http://dx.doi.org/10.1016/j.ica.2017.07.027
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New organic-inorganic LDH composites: synthesis, characterization and
catalytic behavior in the green epoxidation of α, β-unsaturated esters
Natalia Candu, Diana Paul, Ioan-Cezar Marcu, Madalina Tudorache, Vasile I. Parvulescu,* Simona
M. Coman*
Department of Organic Chemistry, Biochemistry and Catalysis, Faculty of Chemistry, University of
Bucharest, Regina Elisabeta Blvd., no. 4-12, Bucharest 030016, Romania
*e-mail: vasile.parvulescu@chimie.unibuc.ro; simona.coman@chimie.unibuc.ro
Abstract
New organic-inorganic based LDH composites have been prepared using different methodologies,
ie the ion-exchange method (Org@LDH-exch), the reconstruction (Org@LDH-mem) and the direct
intercalation (Org@LDH-inter) method, respectively. Irrespective of the procedure, the –C=O
group of levulinate moiety was envisaged as a potential active organocatalyst in the epoxidation of
trans-methylcinnamate to methyl-phenyl-glycidate. The characterisation of these materials through
adsorption-desorption isotherms of nitrogen at -196 °C, XRD, TG-DTA and DRIFT confirmed a
successful intercalation only for Org@LDH-inter. The reactions were carried out via in situ
generated dioxiranes using levulinate as active organocatalyst and H2O2/acetonitrile mixture as
oxidant. Intercalated levulinate in aminoterephthalate/LDH structure led to conversions up to 25%
with a total selectivity to methyl-phenyl-glycidate. Besides this, the heterogeneous organocatalyst
behave as a green system: the constitutive levulinic acid represents one of the most important
renewable platform molecules, while replacing the Oxone reagent with the more benign hydrogen
peroxide and the substitution of an inorganic soluble base with the basic function of the LDH-
support afford a more benign system.
1

Keywords: LDH-based organic-inorganic composite; direct intercalation of levulinate species;
physical-chemical characterization; epoxidation; green catalytic system.
1. Introduction
Grafting the organic molecules into a layered double hydroxide (LDH) may generate new
interesting properties of these materials, such as changes in the hydrophobic nano-pockets within
the galleries of the inorganic solid [1] or enhancements in the catalytic behavior [2]. Related to this
second direction, the use of the organic-LDH composite materials is expected to increase merely the
selectivity.
In this respect, one of the most important targets is the identification of more efficient and
practical epoxidation methods of a wide variety of olefins. This is currently justified by the broad
utility of epoxides especially as intermediates for pharmaceutical industry [3, 4]. Thus, the
epoxidation of olefins in chlorinated solvents using peroxy acids [5] or, very often, m-
chloroperbenzoic acid (m-CPBA) as epoxidation agents [6, 7] has been intensively studied.
However, while the epoxidation with m-CPBA occurs efficiently on electron-rich substrates such as
simple alkenes or functionalised alkenes, for cinnamic esters the reaction is either extremely slow as
cinnamates possess electron withdrawing groups [8], or it takes place with the formation of diol
ester derivatives as the major product (the case of cinnamates having electron donating groups). By
replacing the primary oxidant from m-CPBA in CH2Cl2 to Oxone® (a triple salt with the formula
2KHSO5 x KHSO4 x K2SO4) in acetone, Curci et al. [9] reported the epoxidation of the (E)-
cinnamic acid with yields of 95%. Later, Shi et al. [10] showed that Oxone® in conjunction with
a
D-fructose-derived ketone, also known as Shi's ketone organocatalyst, is highly active in the
epoxidation of a wide variety of (E)-di- and tri-substituted alkenes. However, a disadvantage of
using Oxone® arises from its low stability under the basic reaction conditions required for the
epoxidation of this kind of substrates. A greener alternative to Oxone® might be the use of
hydrogen peroxide (H2O2) as primary oxidant, in combination with acetonitrile [11], able to
2

generate peroxyimidic acid species, the active oxidant for the formation of the dioxirane. Moreover,
making the organocatalysts insoluble and, consequently, easily recoverable and reusable, it may be
the way for a sustainable development in this field.
In this context, we recently explored the potential of the LDH-intercalated materials with
renewable derived levulinate as efficient solid catalysts for the epoxidation of trans-methyl
cinnamate to methyl-3-phenyl-glycidate by using H2O2/acetonitrile as oxidant [2]. The low toxicity
of sodium levulinate and the middle oxidation conditions obey the green chemistry requirements.
Besides this, its anchoring on the corners of the LDH layers through ion exchange method led to
solid catalysts able to convert trans-methylcinnamate into corresponding epoxides in an efficient
manner (Ccinnamate = 21.4%, Sglycidate = 100%). Encouraged by these results and with the aim to
improve the former results, here we report novel procedures for the synthesis of organic-inorganic
composites prepared from MgAl-LDH and structurally-modified levulinic acid as organocatalyst.
The epoxidation of trans-methylcinnamate to methyl-3-phenyl-glycidate using H2O2/acetonitrile as
oxidant has been considered as test reaction. The catalytic results are discussed by comparison with
the previously reported LDH-intercalated levulinate materials [2].
2. Experimental
2.1. Organic-inorganic composites preparation
2.1.1. Layered double hydroxides (LDH) synthesis
The layered double hydroxides (LDH) were prepared by co-precipitation at pH = 10, using
an aqueous solution of Mg(NO3)2·6H2O and Al(NO3)3·9H2O. The quantities of the Mg and Al salts
were calculated for a Mg /Al molar ratio of 3.0 in the final material. The preparation procedure
follows the reported method in Ref. [2]. Briefly, two solutions of a) 44.8 g of Mg(NO3)2·6H2O and
3

21.75 g of Al(NO3)3 · 9H2O in 100 mL of deionized water and b) 8.3 wt% Na2CO3 · 10H2O in 100
mL solution of NaOH 2M were simultaneously added drop wise to 200 mL of deionized water, at
room temperature with controlled rate to maintain the pH ≅ 10. After complete precipitation, the
slurry was aged at 80°C overnight under vigorous stirring. After the suspension separation, the wet
precipitate was washed and dried at 80°C for 12 h. The obtained LDH material was denoted MgAl-
LDH.
2.1.2. Levulinate-based organic structure synthesis
The synthesis of the organic part of the composite is schematized in Scheme 1.
O
O
CH3
CH3
HO
A.
Cl
+ SOCl2
(2)
+ SO2 + HCl
O
O
(1)
(3)
O
O
OK
OH
NH2
NH2
+ 2 H2O + 2 CO2
B.
+ 2 KHCO3
O
KO
O
HO
(4)
(5)
O
O
OK
OK
O
CH3
NH2
NH
O
O
CH3
C.
+
Cl
+ HCl
O
O
KO
O
KO
(3)
(5)
(6)
Scheme 1. The synthesis of levulinate-based organocatalyst
4

A. In a 100 mL round-bottom flask equipped with a condenser and a magnetic stirrer bar, 30 mL
(49.14 g) of thionyl chloride (SOCl2) was drop wise added to 3.48 g (0.03 moles) of levulinic acid,
at such a rate (2 mL/min) that the temperature of the reaction mixture did not exceed 50°C. The
reaction mixture was then held at about 50°C under a reduced pressure of about 30 mmHg to
remove HCl, SO2 and excess SOCl2. Levulinoyl chloride was recovered with a yield of 95% (3.83g;
0.0285 moles). B. 6.5g (0.065 moles) of KHCO3 and 2.63g (0.015 moles) of 2-amino terephthalic
acid were dissolved in 100 ml water. The mixture was stirred for 1h, at 80°C and then the solvent
was removed in an oven at 80°C. The crude potassium amino-terephthalate was recovered as a
white solid, with a yield of 90% (3.45 g). C. To the levulinoyl chloride (3.83 g, 0.0285 moles), 50
mL of dimethyl-formamide (DMF) and the 3.45 g of potassium amino-terephthalate (0.0143 moles)
were added and heated at 80 °C, for 72 h. At the end of the reaction the solvent was removed in
vacuum at room temperature, then the crude product was dissolved in CH2Cl2 (50 mL), dried with
anhydrous MgSO4, and filtered. The final solid obtained after evaporating the CH2Cl2 was not
further purified.
2.1.3. LDH-based organic-inorganic composite synthesis
For the synthesis of the LDH-based organic-inorganic composites different methodologies
such as ion-exchange, reconstruction and co-precipitation were applied as detailed below:
i) Ion-exchange method (Org@LDH-exch): 2.5g of reference MgAl-LDH was mixed with 0.1 g
(0.3 mmoles) of organocatalyst (6) (Scheme 1) in 150 mL of deionized water. The slurry was stirred
at room temperature, for 18h, in nitrogen atmosphere. The product was then filtered, washed with
distilled water until a pH of 7 and finally dried in an oven at 80 oC, for 12 h.
ii) Reconstruction method (Org@LDH-mem): 2 g of the reference MgAl-LDH was calcined at
450°C to the corresponding layered mixed oxide. The product (1 g) was mixed with 0.1 g
5

compound (6) dissolved in 20 mL deionized water, under vigorous stirring at room temperature, for
10h. The precipitate was then filtered, washed until pH of 7 and dried at 80°C, for 12 h.
iii) Direct intercalation method (Org@LDH-inter): intercalated LDH structures were prepared by
Mg2+ and Al3+ ions hydrolysis in the presence of 2-aminoterephthalic acid. The mixed solution of
1M Mg(NO3)2·6H2O and Al(NO3)3·9H2O was drop-wise added to a 50mM aminoterephthalic acid
solution (Mg2+/Al3+/aminoterephthalic acid molar ratio = 2/1/1) under stirring and N2 atmosphere.
The pH of the reaction mixture was adjusted by drop-wise addition of 1M NaOH solution, and
temperature was kept at 40oC. The resulted precipitate was aged overnight, filtered, washed with
distilled deionized (DD) water and finally dried under vacuum, at 60oC [12]. The obtained solid
product was modified with levulinyl chloride following a similar procedure as described in the step
C, Scheme 1. However, in this step adapted amounts of levulinyl chloride to keep a 2/1 molar ratio
of levulinyl chloride/intercalated aminoterephthalic acid were used.
2.2. Catalysts characterization
The synthesized organic-inorganic composites were characterized using various techniques
such as adsorption-desorption isotherms of nitrogen at -196°C, powder X-ray diffraction (XRD),
differential thermal analysis and thermogravimetric analysis (TG-DTA), and diffuse reflectance
infrared Fourier transform spectroscopy (DRIFT). Textural characteristics (surface area, pore
volume and pore diameter) were determined from the adsorption-desorption isotherms of nitrogen
at -196 °C using a Micromeritics ASAP 2020 Surface Area and Porosity Analyzer. The XRD
patterns were recorded on a Shimadzu XRD-7000 diffractometer using Cu Kα radiation (λ = 1.5418
Å, 40 kV, 40 mA) at a step of 0.02o and a scanning speed of 2 degrees min-1 in the 5 – 90 degrees
2Θ range. The TG-DTA analyses were carried out using a Shimadzu DTG-60 Simultaneous DTA-
TG Apparatus, under air atmosphere, with a flow rate of 10 mL min-1 at a heating rate of 10°C min-
6

1, from RT to 700°C and using alpha-alumina as reference. The DRIFT spectra were collected with
a Thermo 4700 spectrometer (200 scans with a resolution of 4 cm−1) in the range of 600–4000 cm−1.
2.3. Catalytic tests
The LDH-based organic-inorganic composites were tested in the epoxidation of trans-
methylcinnamate (TMC) to methyl-3-phenyl glycidate (MPG). In brief, to a mixture of 0.162 g
TMC in 3.0 mL acetonitrile, 0.8-1.5 mL H2O2 and 0.05-0.10 g of catalyst were added. The reaction
mixture was stirred at 24-40°C for 18-24 h. After completion, the solid catalyst was separated by
filtration, the filtrate was concentrated under vacuum and the resulted reaction products were
analyzed by GC-FID chromatography (Shimadzu GC-2014 apparatus).
The retention times were 13.9 min and 14.5-14.9 min for trans-methyl cinnamate (TMC)
and methyl-3phenyl glycidate (MPG), respectively. The identification of the products was made
using a GC-MS apparatus (GC Trace 2000 DSQ system coupled with an MS detector, from Thermo
Electron Corporation) equipped with a Factor Four VF-5HT column with the following
characteristics: 0.32 mm x 0.1 µm x 15 m working with a temperature program at a pressure of 0.38
Torr with He as carrier gas.
3. Results and discussion
The XRD patterns of the reference MgAl-LDH and Org@LDH-exch and Org@LDH-mem
samples display sharp and symmetric diffraction lines at 2θ 11.4, 22.8 and 34.6° [13] indicating a
well-formed crystalline layered structure. No intercalation of the levulinate-based organocatalyst
occurred using these methods (Figure 1). In these cases only grafting onto the external surface of
the LDH was possible. In all cases the basal spacing distance d003 corresponds to carbonate as
7

compensating anion (7.77 Å). Since the thickness of the brucite-like layer is 4.8 Å, the height of the
gallery was calculated as being 2.97 Å [14].
Figure 1. The XRD diffraction patterns of the reference MgAl-LDH sample and Org@LDH-exch
and Org@LDH-mem intercalated samples
The IR spectrum and TG-DTA profile confirm the intercalation failure evidenced by the
XRD diffraction patterns for the Org@LDH-exch and Org@LDH-mem samples. The DRIFT
2-
spectra of both Org@LDH-exch and Org@LDH-mem samples show only the presence of the CO3
(1430 cm-1) anions in the LDH gallery together with the OH- (1647 cm-1) ones (Figure 2). The
broad shoulder present at ca. 3000 cm-1 is attributed to carbonate hydrogen-bonded to the LDH
hydroxides [15] while the broad band at 3588 cm-1 is assigned to the (-OH) hydroxyl stretching
vibration of the isolated and hydrogen bonded to the octahedral layer and water molecules [16].
8

Figure 2. The IR spectra of the Org@LDH-exch (A) and Org@LDH-mem (B) samples
Moreover, the TG and DTA profiles show three main steps characteristic to LDH materials,
matching the literature reports: i) the loss of physically adsorbed and interlayer water molecules at
temperatures lower than 200°C; ii) the dehydroxylation of the double hydroxide layers, at 200-
400°C, and iii) the complete dehydroxylation together with the decomposition of the interlayer
carbonate anions with the formation of mixed oxides, at temperatures higher than 400°C [17, 18] in
good concordance to the XRD and IR results.
However, the co-precipitation route (direct intercalation) led to materials in which the
carbonate ions were replaced by 2-amino-terephthalate ones. The XRD pattern (Figure 3) clearly
confirmed the intercalation of 2-aminoterephthalate. It indicates the existence of two different
anions, with different sizes, well intercalated into the gallery of the LDH support. The two different
basal distances corresponding to the (003) and (006) diffraction planes account for this process.
Indeed, the intercalation of the 2-amino-terephthalate species into the LDH host structure agrees
with the shift towards lower 2θ angles of the (00l) reflections (#). However, the diffraction lines
corresponding to the interlayer (*) hydroxyl anions (d003 = 7.4 Å) can still be observed, revealing an
9

incomplete intercalation of 2-amino-terephthalate species into the LDH host structure. Assuming a
3R stacking for the hexagonal structure of the LDH, the position of the (003) reflection allowed to
calculate lattice c (c = 3 × d003) parameter of 33.5 Å in the intercalated LDH (d003 = 11.15 Å).
Accordingly, the thickness of the LDH layer was of 4.8 Å, while the interlayer space for the
intercalated LDH of 6.4 Å.
Figure 3. The XRD pattern of the intercalated 2-aminoterephthalate anion in the LDH structure
This sample was then subjected to the condensation of –COCl of the levulinyl chloride with
–NH2 groups from 2-aminoterephthalate, in accordance with the step C from Scheme 1.
Finally the XRD pattern of the Org@LDH-inter sample displays similar diffraction lines
with those of the intercalated 2-aminoterephthalate anion showing the presence of levulinate into
the LDH gallery without any further modification of the LDH structural characteristics.
The textural characterisation of the Org@LDH-inter sample also confirms the presence of
the amino-terephthalate-based entity in between the LDH sheets. The intercalated Org@LDH-inter
sample displays a higher BET surface than the corresponding MgAl-LDH (Table 1). Moreover, the
narrow mesopores of the bimodal MgAl-LDH sample disappear while the novel formed mezopores
10

of the mono-modal Org@LDH-inter sample are larger than those of the corresponding MgAl-LDH
(Figures 4 and 5). On this basis, the intercalation of the amino-terephthalate molecules in between
the LDH layers or/and inside the narrow mesopores of the LDH is well justified [2]. In both cases,
the hysteresis loops suggest mesopores with a regular geometry and uniform sizes, while no
microporosity has been detected.
Table 1. Textural properties of the MgAl-LDH and Org@LDH-inter samples
Sample
SBET, m2/g
42.0
Pore size (nm) Reference
MgAl-LDH
Org@LDH-inter
3.5 and 14.6
23.5
[2]
68.0
This work
Figure 4. Nitrogen adsorption-desorption isotherms and pore size distribution for the MgAl-LDH
sample [2]
11

Figure 5. Nitrogen adsorption-desorption isotherms and pore size distribution for the Org@LDH-
inter sample
The intercalation of the aminoterephthalate-based species is also confirmed by the TG
analysis, carried out in nitrogen atmosphere. The TG profile (Figure 6) of the Org@LDH-inter
sample shows an increased mass loss for the aminoterephthalate-intercalated sample (85.7% versus
46.7% [2]), accompanied by a maximum mass loss centered at 569°C (Figure 6). This peak is
associated to the vaporization of the aminoterephthalate-intercalated species and their degradation
product.
Figure 6. The TG-DTA profile of Org@LDH-inter sample
12

The IR spectra confirm through the presence of the secondary amide (bands at 3382 and
3488 cm-1, corresponding to the N-H stretching, and 1690 and 1510 cm-1, corresponding to N-H
bending trans to the carbonyl oxygen) and ketone (band at 1700 cm-1) groups the successful
covalent binding of the levulinic species on the amino-terephthalate moiety already present in the
LDH gallery (Figure 7).
Figure 7. The IR spectra of the 2-amino-terephthalic acid (A), reference MgAl-LDH (B)
and Org@LDH-inter sample (C).
The kinetic diameter of the organic molecules used for the Org@LDH-inter sample
preparation (ie, 2-amino-terephthalate and the coresponding levulinate-based terephtalate
compound (structure (6), Scheme 1) and of the reactant and reaction product of the epoxidation
reaction (ie, trans-methylcinammate and methyl-phenyl-glycidate, Scheme 2) has been estimated
from the molecular weight correlation (Table 2), using the equation:
1/ 3
)
σ =1.234(Mw
13

for aromatic hydrocarbons (Mw = molecular weight in g mol-1) [19], in accordance with the
approximation method for the kinetic diameters of oxygenated molecules reported by Huber et al.
[20].
O
O
O
OCH3
catalyst
OCH3
H2O2-AcCN
rac-methyl-phenyl-glycidate
trans-methylcinnamate
Scheme 2. Trans-methylcinnamate epoxidation to methyl-phenyl-glycidate
Table 2. The kinetic diameter of the organic molecules
O-
O-
O
O
Structure
O
O
O
O
CH3
OCH3
OCH3
NH
NH2
O
O-
O
O-
O
Mw
164
262
162
6.7
178
7.1
(g mol-1)
σ (Å)
6.7
7.9
Obviously, the presence of levulinate connected to –NH2 left unaffected the amino-
terephthalate intercalated LDH layers, these species being orientated in a parallel direction to the
LDH layers.
14

Scheme 3. Graphical illustration of the intercalated Org@LDH-inter sample
Due to its basic properties, the surfaces of the LDH-type materials efficiently afford the
transformation of hydrogen peroxide into a perhydroxyl anion [21]. Therefore, such surfaces can be
directly involved into the epoxidation of olefins and even of electron deficient olefins like 2-
cyclohexen-1-one. However, for the case of the trans-methylcinnamate, the MgAl-LDH does not
show any catalytic activity, as we recently reported [2]. Instead, the basicity of the LDH can obviate
the need for the presence of an inorganic soluble base (e.g., K2CO3) in the catalytic system whiles
the -C=O groups of the intercalated levulinate species may act as catalytic active sites for the
epoxidation reaction [2]. Table 3 compiles the most representative catalytic results with this catalyst
and a comparison with those previously obtained using LEV@LDH-N2, and LEV@LDH-pp,
prepared by the intercalation of levulinate species via ionic exchange and precipitation routes [2].
Table 3. Catalytic performances of the LEV-intercalated LDH materials
Entry Catalyst
Reaction time, h
CTMC, %
SMPG, %
Reference
1
MgAl-LDH
18
18
0
-
2
2
2
LEV@LDH-N2
3.1
86.7
15

3a
4
LEV@LDH-pp
24
24
24
24
24
24
0.7
1.5
100
100
100
100
100
100
2
2
5b
6a
7
21.4
10.2
16.5
25.6
2
Org@LDH-inter
This work
This work
8b
This work
a
Reaction conditions: 0.05 g catalyst, 0.162g TMC, 3mL AcCN, 0.8mL H2O2, 40°C;
temperature; b - 0.1 g catalyst and 1.5 mL H2O2
- room
As Table 3 shows, the catalytic results in the presence of the Org@LDH-inter are slightly
superior to those obtained in the presence of the previously reported LEV@LDH samples [2].
While the selectivity to methyl-phenyl-glycidate has been preserved at 100%, irrespective of the
catalyst structure, the conversion of the trans-methylcinnamate is improved with several
percentages by changing the catalyst from LEV@LDH to Org@LDH-inter (from 21.4% to 25.6,
entries 5 and 8, Table 3). Obviously, this enhancement is attributed both to the different location
and to the different structural orientations of the catalytic active species (ie, -C=O group of the
levulinate moiety). As we already shown, when the environment is not large enough to allow the
diffusion of the reactant molecules (ie, trans-methylcinnamate) and the formation of the spiro
transition state, in which the plane of the oxirane is perpendicular to the plane of the C=C π-system
[22, 23] the oxygen transfer takes place in a restrictive way. However, the increased activity of
Org@LDH-inter catalysts can not be explained strictly only on the basis of the steric hindrance
effect. Different electronic effects induced by replacing carboxylic (levulinic acid) with amide
16

(levulinate-terephthalate compound) groups in the γ-position of the organocatalyst should also be
taken into consideration.
It is also important to notice another achievement from the standpoint of the environmental
concern. It arises from the fact that the basicity of the LDH can obviate the need for the presence of
an inorganic soluble base (e.g., K2CO3) in the catalytic system. Moreover, the total selectivity in
methyl-phenyl-glycidate and the use of hydrogen peroxide/acetonitrile as a benign oxidation agent
bring high advantages from the green chemistry point of view, avoiding the generation of wastes.
Conclusions
Different methodologies for the synthesis of organic-inorganic based LDH composites were
investigated. Irrespective of the procedure, the –C=O group of levulinate moiety was envisaged as
potential active organocatalyst in the epoxidation of trans-methylcinnamate to methyl-phenyl-
glycidate. The characterisation methods showed that the direct intercalation through the co-
precipitation of the amino-terephthalate with Al and Mg salts constituted the only procedure able to
intercalate the organic aggregate. This was followed by the levulinyl chloride covalent binding on
the –NH2 bond of the intercalated aminoterephthalate. The reactions were carried out via in situ
generated dioxiranes using levulinate as active organocatalyst and H2O2/acetonitrile mixture as
oxidant. Intercalated levulinate in aminoterephthalate/LDH structure led to conversions up to 25%
with total selectivity to methyl-phenyl-glycidate. These results are slightly superior to the
previously levulinate-intercalated MgAl-LDH (C =21%, S = 100%) catalysts, this enhancement
being likely induced by both steric and electronic effects.
The use of the “heterogeneous organocatalyst” based on levulinic acid, one of the most
important renewable platform molecules, the replacing the Oxone reagent with more benign
hydrogen peroxide as primary oxidant and the homogeneous inorganic base substitution by the
17

basic function of the catalytic LDH-support may recommend this catalytic system as a valuable
green candidate for the selective epoxidation of α, β-unsaturated esters.
Acknowledgment:
Prof. Simona M. Coman kindly acknowledges UEFISCDI for the financial support (project PN-II-
ID-PCE-2011-3-0041, Nr. 321/2011).
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New organic-inorganic LDH composites: synthesis, characterization and
catalytic behavior in the green epoxidation of α, β-unsaturated esters
Natalia Candu, Diana Paul, Ioan-Cezar Marcu, Madalina Tudorache, Vasile I. Parvulescu,
Simona M. Coman
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Highlights
•
•
•
•
Levulinic acid is used for the synthesis of novel organic-inorganic LDH composites.
Levulinate was successfully grafted in aminoterephthalate/LDH through covalent bonds.
The heterogeneous organocatalyst exhibits catalytic potential in epoxidation reactions.
The heterogeneous organocatalyst behave as a green system.
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