P-Sulfonic acid calix[n]arenes as organocatalysts for the transesterification reaction of Passiflora seed oil

Article abstract of DOI:10.1007/s00706-015-1546-0

The catalytic activity of p-sulfonic acid calix[4]arene was studied in the transesterification reactions of Passiflora seed oil with methanol or ethanol. Calix[n]arenes are highly versatile organocatalysts and conversion rates >98 % were obtained for the transformation of Passiflora seed oil to its methyl or ethyl esters after 5 h of reaction in the presence of p-sulfonic acid calix[4]arene (3.52 mol % in ethanol; 5.28 mol % in methanol). Moreover, the organocatalyst was recovered and reused in two subsequent cycles without a significant decrease in the activity or selectivity. The use of a non-corrosive and reusable organocatalyst is the positive aspect of this process.

Full text of DOI:10.1007/s00706-015-1546-0

Monatsh Chem
DOI 10.1007/s00706-015-1546-0
ORIGINAL PAPER
p-Sulfonic acid calix[n]arenes as organocatalysts
for the transesterification reaction of Passiflora seed oil
2
Camila G. Almeida1 Isabella F. Souza1 Natalia A. Liberto
•
•
•
´
Marcio J. Da Silva Sergio A. Fernandes2 Mireille Le Hyaric1
2
•
•
´
Received: 16 April 2015 / Accepted: 30 July 2015
Ó Springer-Verlag Wien 2015
Abstract The catalytic activity of p-sulfonic acid
calix[4]arene was studied in the transesterification reactions
of Passiflora seed oil with methanol or ethanol.
Calix[n]arenes are highly versatile organocatalysts and
conversion rates [98 % were obtained for the transforma-
tion of Passiflora seed oil to its methyl or ethyl esters after
5 h of reaction in the presence of p-sulfonic acid calix[4]-
arene (3.52 mol % in ethanol; 5.28 mol % in methanol).
Moreover, the organocatalyst was recovered and reused in
two subsequent cycles without a significant decrease in the
activity or selectivity. The use of a non-corrosive and reu-
sable organocatalyst is the positive aspect of this process.
Graphical abstract
Keywords Seed oil Á Calix[n]arenes Á Catalysis Á
Biodiesel Á Fatty acids
Introduction
Recently, a tremendous interest in the utilization of
biomass as feedstock to produce renewable fuels and
chemicals has been observed worldwide. The biodiesel
production from biomass is usually carried out by the
esterification and transesterification of vegetable oils with
methanol or ethanol, producing glycerine and methyl or
ethyl esters (biodiesel). It is a highlighted industrial
process which has gained an increasing importance, since
vegetable oils are an interesting green energy resource as
a
renewable, biodegradable, and non-toxic material
[1–5].
The most common method used for the production of
biodiesel is the transesterification of vegetable oils with
methanol or ethanol under homogeneous alkaline catalysis
conditions, sodium and potassium hydroxides or methox-
ides being the most employed catalysts [6]. Despite of the
low cost of those chemicals and the high yields of ester
obtained, these processes have significant drawbacks [7].
Besides the high corrosion caused by the alkaline cata-
lysts, there are great difficulties in removing them from the
reaction medium. The necessity of neutralization at the end
of the reaction results in the production of a large amount
of effluents and residues, unfriendly to the environment.
The high cost of raw material has led to the search for
inexpensive feedstocks to produce biodiesel. However,
these raw materials frequently contain high levels of free
fatty acids (FFA) and their alkaline esterification leads to
the formation of soaps or emulsions, hampering even more
the recovery and purification of the esters.
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-015-1546-0) contains supplementary
material, which is available to authorized users.
& Mireille Le Hyaric
mireille.hyaric@ufjf.edu.br
1
´
Departamento de Quımica, Instituto de Ciencias Exatas,
Universidade Federal de Juiz de Fora, Campus Universitario,
ˆ
´
´
Rua Jose Lourenc¸o Kelmer, s/n, Juiz De Fora, MG
36036-900, Brazil
2
´
Grupo de Quımica Supramolecular e Biomimetica (GQSB),
Departamento de Quımica, CCE, Universidade Federal de
´
´
Vic¸osa, Vic¸osa, MG 36570-900, Brazil
123

C. G. Almeida et al.
In the last years, a great number of studies have been
conducted to search for new efficient catalysts. Heteroge-
neous alkaline catalysts have been developed to answer this
demand [8, 9]. Nevertheless, they are unable to catalyze the
transesterification of raw materials such as non-edible oils
or industrial oil-chemistry residues. For these reasons, solid
acid catalysts have occupied a highlighted position and
their use for the biodiesel production from these feedstocks
has been intensively explored [10–12]. Although signifi-
cant advances have been achieved, the leaching of solid
catalysts caused by the highly polar medium results in their
deactivation and in the contamination of the products with
metal, remaining thus a challenge to be overcome [13, 14].
Recyclable organocatalysts are still little explored
alternatives and may promote the esterification and trans-
esterification reactions, with potential cost and energy
savings, operational simplicity, lower toxicity, and greater
water tolerance than conventional catalysts [15]. Recently,
the application of calix[n]arenes as organocatalysts in
several organic transformations has been described [16–
19]. Calix[n]arenes are macrocyclic compounds obtained
via the condensation of p-substituted phenols with
formaldehyde [20–22]. They are recyclable catalysts and
their main advantage is that they avoid the contamination
of the products with metal.
Table 1 Passiflora oil analysis [12, 13]
Physicochemical analysis
Density/
g cm-3
SV/mg
KOH/g
IV
(I2/100 g)
PV/meq/
1000 g
AV/meq/
1000 g
EV/
%
0.92
173.4
236.8
3.69
0.2
99.8
Fatty acid composition/%
C16:0
21.6
C18:1
21.9
C18:2
56.5
SV saponification value, IV iodine value, PV peroxide value, AV
acidity value, EV esterification value
(C18:2) was the major component (ca. 56.5 %). Although
the presence of C18:0 and C18:3 (2.2–3.1 and 0.3–0.4 %) has
been described in Passiflora species [29], they were not
detected in the present work.
p-Sulfonic acid calix[4]arene-catalyzed Passiflora oil
transesterification with methanol or ethanol:
1
conversion rate determination via H NMR
spectroscopy results
The triglycerides conversion rate of Passiflora oil to fatty
esters was calculated from the 1H NMR spectra [30]
obtained after the transesterification reactions with ethanol
or methanol compared to the one of the starting Passiflora
oil (Electronic Supplementary Material). No signals from
the four methylene hydrogens of the glycerol at 4.2 ppm
were observed after the completion of the transesterifica-
tion reaction indicating that the reaction was complete. The
remaining olefinic hydrogens of the unsaturated portions of
the aliphatic chains resulted in resonance signal at
5.35 ppm.
We previously reported excellent results for the esteri-
fication of carboxylic acids catalyzed by calix[n]arenes
[23–25]. The present work describes the first use of p-
sulfonic acid calix[4]arene as a reusable organocatalyst in a
simple and efficient method for the transesterification of a
vegetable oil with methanol or ethanol. Passiflora oil,
obtained by the extraction the fruit seeds, a juice process-
ing industry residue, was chosen as a potential feedstock
for the production of biodiesel [26].
To obtain the conversion rate, signal of the hydrogens at
2.28 ppm, corresponding to the two hydrogens of the a-
carbonyl moiety of the oil, were integrated (I1), and related
to the signal integration I2 of the hydrogens at 4.11 ppm
(ethyl esters) or 3.64 ppm (methyl esters). The conversion
rate C was obtained by the ratios between these areas
Eqs. (1) and (2), within 2 % error [31]:
Results and discussion
Characterization of the Passiflora oil
The content and the composition in terms of FFA and
triglycerides are key aspects of the transesterification
reactions because these compounds have different chemi-
cal reactivity caused by the presence of double bonds and
by the different carbon chain length of fatty acids. Passi-
flora oil was analyzed according to AOCS official methods
[27, 28] and the main results are summarized in Table 1.
The results show that the Passiflora oil sample used in
the transesterification reactions had only ca. 0.2 % of FFA
(acidity value) and consequently, a high triglycerides
amount (ca. 99.8 %, esterification value). Palmitic and
oleic acids (C16:0 and C18:1) were present in almost equal
amounts (ca. 21.6 and 21.9 %, respectively). Linoleic acid
Ethyl esters : C=% ¼ ðI2=I1Þ Â 100
Methyl esters : C=% ¼ ð2I2=3I1Þ Â 100
ð1Þ
ð2Þ
Reaction selectivity of p-sulfonic acid calix[4]arene-
catalyzed Passiflora oil transesterification
with methanol determined by GC analysis
The reaction selectivity was assessed by GC analysis of
samples collected at the end of the reaction, which were
compared with authentic standard samples. In general, after
123

p-Sulfonic acid calix[n]arenes as organocatalysts for the…
p-sulfonic acid calix[4]arene-catalyzed transesterification
reactions only monoalkyl esters (i.e., FAMEs or FAEEs
when methanol or ethanol was used, respectively) were
formed. However, the reaction selectivity was almost
equal, regardless of the alcohol employed. The transester-
ification of Passiflora oil gave alkyl palmitate (ca. 22 %),
alkyl myristate (ca. 6 %), alky oleate (ca. 20 %), alkyl
linoleate (ca. 31 %), and non-identified alkyl ester (ca.
21 %).
This fact may be also explained by the higher temperature
(ca. 180 °C against 78 °C), besides the high internal
pressure reached in the autoclave, that increases the ethanol
concentration in the liquid phase.
Noticeably, the heating procedure had a crucial role on
p-sulfonic acid calix[4]arene-catalyzed transesterification
reaction. At the same temperature (ca. 78 °C, reflux tem-
perature of ethanol), the conversion rise from 5 to 98 %,
when the microwave heating was replaced by conventional
heating or autoclave heating. An increase of the tempera-
ture (78–180 °C) resulted in the reduction of the time to
complete reaction, from 28 to 5 h. It is important to note
that in the absence of catalyst the reaction conversion was
lower than 5 %.
Influence of the heating method
Three different methods to heat the reaction were used (i.e.,
conventional, microwave radiation, and Teflon autoclave
heating). All the reactions were carried out with p-sulfonic
acid calix[4]arene catalyst (ca. 20 % w/w; 23.5 mol %) in
an excess of ethanol (5 cm3). The results are detailed in
Table 2.
Effect of the catalyst concentration
in the transesterification of Passiflora oil
with methanol or ethanol
No reaction progress was observed performing the
reactions in a microwave reactor during 8 h. Conversely,
by the use of conventional heating (ca. reflux temperature)
or of an autoclave working under autogenic pressure the
reactions reached an almost total conversion. However, the
required time was noticeably dependent on the heating
process. When carried out during an equal time interval
(ca. 8 h), the reaction performed in an autoclave reactor
proceeded faster than that performed under reflux condi-
tions. This different behavior may be related to the phase
equilibrium established inside the reactor, affecting the
methanol concentration in the reaction solution [32].
Meneghetti et al. have estimated that heating to high
temperatures (ca. 150 °C), the alcohol concentration at
liquid phase is, in average, threefold higher than those
observed using reflux reactor [33]. Since an excess of
alcohol is desirable to shift the equilibrium towards prod-
ucts, the reaction carried out under autogenic pressure
achieved higher conversion.
Since the reactions reached high conversions when per-
formed in an autoclave reactor, this methodology was
selected to carry out the other investigations with ethanol
or methanol, in order to evaluate the effects of p-sulfonic
acid calix[4]arene concentration (Fig. 1). The catalyst load
varied from 0 to 4.5 % w/w (5.28 mol %) in relation to the
oil weight, keeping the time and the reaction temperature
constant (ca. 5 h and 180 °C).
The p-sulfonic acid calix[4]arene catalyst load was a
crucial aspect and remarkably affected the conversion rates
obtained in the transesterification reactions. The reactions
only proceeded significantly when the catalyst concentra-
tions were equal or higher than 3.0 % w/w; 3.52 mol %).
Remarkably, the transesterification of Passiflora oil with
ethanol was more effective than that with methanol [34,
35]. Increasing the catalyst amount to 4.5 % w/w
(5.28 mol %), conversions of Passiflora oil to ethyl or
methyl esters above 98 % was observed.
The reactions proceeded more slowly under conven-
tional heating (ca. 28 h) than the ones carried out in an
autoclave reactor, where triglycerides were completely
converted to fatty ethyl esters (FAEE) after 5 h of reaction.
We find out that employing the catalyst at low con-
centrations (i.e., 0.5–1.5 wt%), the methanol is more
reactive than ethanol. Nevertheless, using catalyst con-
centrations higher than 1.5 wt% (ca. 1.5–3 wt%), the
Table 2 Effects of the heating method on the p-sulfonic acid calix[4]arene-catalyzed Passiflora oil transesterification with ethanol (catalyst
20 % w/w) 23.5 mol % molar ratio
Run
Ethanol/cm3; mmol
Oil/g
Time/h
Temp./°C
Heating mode
Conv./%
1
2
3
4
5
a
4.0; 70
4.0; 70
4.0; 70
4.0; 70
4.0; 70
0.5
0.5
0.5
0.5
0.5
8
8
78
78
Microwave radiationa
Conventional
\5
25
28
8
78
Conventional
[98
55
78
Teflon autoclave reactor
Teflon autoclave reactor
5
180
[98
P = 150 Watt
123

C. G. Almeida et al.
Fig. 1 Effect of the p-sulfonic
acid calix[4]arene catalyst
concentration on the
transesterification of Passiflora
oil. Reactions were carried out
in an autoclave reactor under
autogenic pressure (reaction
conditions: 0.1 g oil, 5 cm3
alcohol, 180 °C, 5 h)
Fig. 2 Effect of temperature on
the p-sulfonic acid
calix[4]arene-catalyzed
Passiflora oil transesterification
reaction. Reactions carried out
in an autoclave reactor under
autogenic pressure (reaction
conditions: 0.1 g oil, 5 cm3
alcohol, catalyst (4.5 % w/w;
5.25 mol %), 5 h)
reactions with ethanol achieved higher conversion than that
with methanol. This fact reinforces the hypothesis that the
interactions (i.e., type van der Waals) between ethanol and
the catalyst molecules are more favored when these species
are in higher concentrations.
8.2 % conversion, respectively). A lower conversion rate
was achieved, similar to the described in the previous
section [34, 35]. These results suggest that when p-sulfonic
acid calix[4]arene is used, an increase of the alcohol carbon
chain may favor the reaction.
Effects of temperature in the p-sulfonic acid
calix[4]arene-catalyzed Passiflora oil
transesterification reaction
Effect of the catalyst nature
on the transesterification of Passiflora oil
with methanol or ethanol
Regardless of the kind of alcohol, the conversion rate of the
transesterification reactions increased with the temperature,
reaching almost 100 % after a 5-h reaction when heated to
180 °C (Fig. 2).
However, the alcohols reactivity was notably different.
When the reactions were carried out at 150 °C, the ethanol
was much more reactive than methanol (ca. 62.0 % against
For comparison, the transesterification of Passiflora oil
with methanol or ethanol were performed using the
monomer p-hydroxybenzenesulfonic acid of the
calix[n]arenes the same hydrogenionic concentration
(3.0 % w/w; 3.52 mol % or 4.5 % w/w; 5.28 mol %) of
p-sulfonic acid calix[4]arene and p-hydroxybenzenesul-
fonic acid at 12.0 or 18.0 % w/w, respectively.
123

p-Sulfonic acid calix[n]arenes as organocatalysts for the…
Remarkably, even when the catalyst was employed at
the same hydrogenionic concentration, the conversions
were significantly different, suggesting that other aspects
may be involved in these reactions [24, 25].
After 5 h of reaction in an autoclave reactor, the reaction
mixture with the fresh organocatalyst was cooled to
ambient temperature, and dichloromethane was added to
the mixture. The solid catalyst was removed by filtration,
dried, and reused in the same conditions of reaction. The
operation was repeated for two cycles (Fig. 3).
Acid-catalyzed transesterification reactions:
a comparison with results of the calix[4]arene-
catalyzed reactions
The relative amount of organocatalyst recovered in the
two cycles was similar (54 %). The conversion rate of
triglycerides to methyl esters remained almost unchanged
in the first cycle (96 %), but a decay was observed in the
The following section describes various Brønsted acid
catalysts based methods for the transesterification reaction,
which normally requires long reaction times. For instance,
Pryde et al. showed that the H2SO4-catalyzed methanolysis
of soybean oil, in the presence of 1 mol % of catalyst, with
an alcohol/oil molar ratio of 30:1 at 65 °C, takes 50 h to
reach complete conversion of the vegetable oil ([99 %)
[36]. The effects of reaction conditions such as tempera-
ture, alcohol-to-oil molar ratio, catalyst load, and type of
oil should be taken in account when a comparison is carried
out [37].
1
second one (76 %). However, the H NMR and IR spectra
of the organocatalyst after the third cycle did not show
evidences of drastic chemical decomposition of the struc-
ture (Electronic Supplementary Material).
We would point that when the effect of the catalyst
concentration was studied it was verified that when 3 wt%
the ethanol was used the conversion was almost complete
(see Fig. 3). It is corresponding to nearly 35 % of the
concentration initially used in the recycle reactions. In the
Table 3 summarizes some results that allow compare
calix[4]arene activity and other acid catalysts. As can be
seen, the reaction conditions affect the catalytic perfor-
mance of the transesterification process. However,
calix[4]arene was more active than sulfuric acid even when
employed at lower load.
Organocatalyst reusability and leaching tests
An important characteristic of the organocatalysts is their
reusability in successive reaction cycles, and a high level of
catalyst recovery, retaining its activity without further
treatment is highly desired.
The solubility of the p-sulfonic acid calix[4]arene was
observed in the mixture of ethanol and fatty ethyl esters
than in the analogues methyl esters, hampering the recov-
ery of the organocatalyst in ethanol. Thus, the recovery and
reuse of p-sulfonic acid calix[4]arene were only studied for
the reactions in methanol.
Fig. 3 Conversion rates obtained in the p-sulfonic acid calix[4]arene-
catalyzed transesterification reactions of Passiflora oil with methanol
after successive cycles of catalyst recovery/reuse (reaction conditions:
autoclave reactor under autogenic pressure; 0.1 g oil, 5 cm3 alcohol,
catalyst (3.0 % w/w; 3.52 mol % or 4.5 % w/w; 5.28 mol % in
ethanol, respectively), 180 °C; 5 h)
Table 3 Reaction of transesterification with methanol in presence of different Brønsted acid catalystsa
Exp
Catalyst, load/wt%
Methanol-to-oil molar ratio
Time/h
Temp./°C
Conversion/%
References
1
2
5
6
2
5
3
7
8
H2SO4, 1.3
6:1
3
48
20
4
85
60
95
70
85
65
85
85
78
1.5
90
[38]
H2SO4, 3.0
6:1
[39]
H2SO4, 4.0
20:1
90
[40]
H2SO4, 41.8
245:1
99
[41]
H3PO4, 1.0
6:1
3
\5
88
[38]
H3PW12O40, 3.75
Dehydrated H3PW12O40, 1.6
H3PO4, 1.0
70:1 (15 % FFA)
14
3
[42]
6:1
45
[38]
6:1
3
\5
99
[38]
Calix[4]arene, 4.5
220:1
5
[This work]
123

C. G. Almeida et al.
first step, the recovery percentage of the catalyst was
slightly higher than 60 %.
Conclusions
To justify the low rate of recovery of the catalyst, an
experiment where Passiflora oil, methanol, and catalyst
were heated in an autoclave at 180 °C for 1 h was con-
ducted. After this period, the catalyst was removed from
the reaction and the mixture was heated during 4 h. The 1H
NMR spectra of the reaction mixture were obtained for the
samples after 1 and 5 h of reaction, where conversions of
20 and 90 % were obtained, respectively. These results
show that the catalyst is soluble in the methyl esters and
glycerol mixture thus hindering their recovery.
In this work, a novel and efficient process based on p-
sulfonic acid calix[4]arene as a homogeneous and recy-
clable organocatalyst was developed for the synthesis of
esters, which make it a potential catalyst for the production
of biodiesel. The p-sulfonic acid calix[4]arene catalyst used
in this work was able to promote the transesterification of a
vegetable oil in high yields of conversion in a short time
and free metal conditions.
Experimental
Proposed mechanism for transesterification
Refined passion fruit oil was purchased from Emfal
´
Empresa Fornecedora de Alcool Ltda (Betim, Minas Ger-
Based on the reports documented in literature and on our
observation in the present protocol, a plausible reaction
mechanism has been proposed (Scheme 1). The sulfonic
groups of the catalyst are completely dissociated in
methanol or ethanol [43, 44]. The esterification reaction
catalyzed by homogeneous acids proceeds through the
following mechanism: in a first step, the carbonyl oxygen is
attacked by the acid proton that increases the elec-
trophilicity of the carbon atom. This carbon atom is then
more susceptible to the nucleophilic attack of the hydroxyl
group of the alcohol, which is the rate determining step.
The following steps are the dehydration and deprotonation
(transesterification) of the intermediate with the corre-
sponding formation of the new ester and the recovery of the
catalyst [45, 46].
ais, Brazil) and analyzed before used. Methanol and
´
ethanol were purchased from VETEC Quımica Ltda (Rio
de Janeiro, Brazil) and used without further purification.
Characterization of the Passiflora oil
Passiflora oil physicochemical properties were determined
in agreement with AOCS rules [27]. The fatty acid profile
was determined as fatty acid methyl esters by gas chro-
matography–mass spectroscopy [28]. Separation of fatty
acid esters was performed on a Shimadzu GC-2010 Gas
Chromatograph equipped with a Restek RTX-2330 capil-
lary column (60 m 9 0.25 mm 9 0.2 mm). The column
temperature was programmed at 130 °C for 10 min, then
Scheme 1
SO3
OH
SO3
OH
H
SO3
OH
H
SO3
OH
SO3
H
SO3
O3S
H
SO3
+
4 H
HO
OH
R'
HO
R'
OH
O
OH
OH
OH
R'
H
R'
OR"
OR"
OR"
OR"
R'
OR"
OH
H
OH
O
R'
HO
R'
HO
OR
OR
-H+
-R"OH
+
ROH
R'
OR
R'
OR
OR"
OR"
H
;
O
=
R"
glyceride
HO
OH
= carbon chain of the acid
alkyl group of the alcohol
R'
R
=
123

p-Sulfonic acid calix[n]arenes as organocatalysts for the…
Catalytic tests
increased to 230 °C at 5 °C/min with a final isothermal
period of 13 min. Hydrogen was used as carrier gas with
constant linear velocity of 25 cm/s. The injector temper-
ature was set at 250 °C, with a split ratio of 1:10. The
flame ionization detector temperature was 250 °C. Fatty
acid methyl esters (FAMEs) were identified by compar-
ison of retention times with authentic standards (Supelco
37 comp. FAME mix 10 mg/cm3 in CH2Cl2), and quan-
tification was performed by the internal normalization
method.
The catalytic reactions were carried out in a Teflon-lined
stainless steel autoclave of 20 cm3 capacity placed in a
digital oven (M.S. Mistura Equipamentos Para Labo-
´
ratorios, Rio de Janeiro, Brazil) or in a CEM Discover
microwave reactor (CEM Corporation, Matthews, NC,
USA) or under conventional heating (glass reflux apparatus
heated with an oil bath on a magnetic stirrer hotplate).
Typically, a mixture of 0.05–0.34 g oil, 5 cm3 methanol
or ethanol, and p-sulfonic acid calix[4]arene (2.15–21.5 %
w/w; 23.5 mol %) were heated at 78–180 °C for 3–36 h.
All experiments were performed in triplicate.
Catalyst synthesis
The p-sulfonic acid calix[4]arene was synthesized in our
laboratory according to literature procedures [20–22], as
described in Scheme 2.
Separation and quantification of the reaction
products
The synthesis of the p-tert-butylcalix[4]arene (20.8 g,
77 % yield) was prepared by the condensation of 25.0 g p-
tert-butylphenol and 16.0 cm3 formaldehyde solution in a
basic medium (NaOH, 0.6 g) and under heating. The pro-
duct was obtained as a white solid in 77 % yield. The
synthesis of calix[4]arene (10.6 g) was carried out using
20.0 g p-tert-butilcalix[4]arene, 13.5 g phenol, and 23.0 g
anhydrous aluminum chloride in toluene [20]. The system
was kept under stirring and nitrogen atmosphere at room
temperature for 1 h. The desired product was obtained as a
white solid in 81 % yield after recrystallization in metha-
nol–chloroform. The synthesis of p-sulfonic acid
calix[4]arene (16.0 g) was conducted from 10.0 g
calix[4]arene in the presence of 100 cm3 concentrated
sulfuric acid and heated for 4 h [22]. The product was
obtained in 75 % yield as a white solid.
The reaction mixtures were cooled to room temperature
and dichloromethane was added. The precipitated
organocatalyst was then removed by filtration and washed
with brine and dichloromethane. The concentrated organic
1
phase was analyzed by H NMR spectroscopy to calculate
the conversion rate of triglycerides to methyl or ethyl
esters. NMR spectra were recorded on a Bruker AVANCE
DRX 300 MHz, in deuterated dichloromethane and
trimethylsilane as internal reference.
Recovery and reuse of catalyst
The precipitated organocatalyst recovered from the reac-
1
tion was dried at 50–60 °C, analyzed by H NMR, and
reused in another catalytic run.
Scheme 2
6
5
4
3
NaOH, 110 oC, 2 h
i)
+
4
HCHO
2
Hb
ii) diphenyl ether, reflux, 2 h
HO 1
OH
OH
OH
OH
Ha
AlCl3 phenol,
,
toluene,
h
1
H
SO3
H
H
SO3
OH
SO3
OH
H
SO3
H
100 o 4 h
C,
2SO4
,
Hb
Ha
HO
OH
HO
OH
OH
OH
123

C. G. Almeida et al.
Acknowledgments The authors acknowledge the Brazilian agen-
cies CNPq for research fellowships (MJS and SAF), FAPEMIG, and
CAPES for financial support.
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