Synthesis of bio-additives: Transesterification of ethyl acetate with glycerol using homogeneous or heterogeneous acid catalysts

Article abstract of DOI:10.1590/S0103-50532013000100004

A new catalytic route with potential practical interest to sustainable production of bioadditives from glycerol is described. Ethyl acetate was transesterified with glycerol, in the ratio glycerol:EtOAc 1:10, at 25 or 90 °C using 0.1 equiv. of H₂SO₄ or TsOH, as homogeneous catalysts. H₂SO₄ led to the total glycerol consumption in 2 h. In the equilibrium, attained in 9 h, 100percent yield of a diacetin:triacetin (55:45) mixture was formed. Using Amberlyst^? 15 dry and Amberlyst^? 16 wet in 1:30 glycerol:EtOAc ratio and reflux at 90 °C the total glycerol consumption was achieved in 2 and 10h, respectively. The lower reactivity of Amberlyst-16 wet was explained in terms of deactivation of acid sites and decrease in glycerol diffusion to the inner resin pores, both factors caused by adsorbed water. The kinetics of glycerol transformation and product distribution in the equilibrium in relation to the H₂SO ₄, Amberlyst-15 (dry) and Amberlyst-16 (wet) catalyzed reactions were measured.

Full text of DOI:10.1590/S0103-50532013000100004

J. Braz. Chem. Soc., Vol. 24, No. 1, 17-25, 2013.
Printed in Brazil - ©2013 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Article
A
Synthesis of Bio-Additives: Transesterification of Ethyl Acetate with Glycerol using
Homogeneous or Heterogeneous Acid Catalysts
Bruno A. Meireles and Vera Lúcia P. Pereira*
Núcleo de Pesquisas de Produtos Naturais, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro,
Bloco H, Cidade Universitária, 21941-902 Rio de Janeiro-RJ, Brazil
Uma nova rota catalítica, de potencial interesse prático para a produção sustentável de acetinas
a partir do glicerol, é descrita. Acetato de etila foi transesterificado com glicerol, numa razão
glicerol:EtOAc 1:10, a 25 ou 90 oC, usando 0,1 equivalente de H2SO4 ou TsOH como catalisadores
homogêneos. H2SO4 levou ao consumo total de glicerol, a 90 oC, em 2 h. No equilíbrio, atingido
em 9 h, 100% de uma mistura diacetina:triacetina (55:45) foi formada. Usando-seAmberlystTM 15
seca e AmberlystTM 16 úmida numa razão glicerol:EtOAc 1:30 sob refluxo a 90 ºC, obteve-se o
consumo total do glicerol em 2 e 10 h, respectivamente.A menor reatividade da resinaAmberlyst-16
úmida foi explicada pela desativação dos sítios ácidos e pela diminuição da difusão do glicerol
para o interior dos poros, causada pela água adsorvida. A cinética da transformação do glicerol e
a distribuição de produtos no equilíbrio para a reação catalisada por H2SO4, AmberlystTM 15 seca
e AmberlystTM 16 úmida foram medidas e racionalizadas.
A new catalytic route with potential practical interest to sustainable production of bio-
additives from glycerol is described. Ethyl acetate was transesterified with glycerol, in the ratio
glycerol:EtOAc 1:10, at 25 or 90 oC using 0.1 equiv. of H2SO4 or TsOH, as homogeneous catalysts.
H2SO4 led to the total glycerol consumption in 2 h. In the equilibrium, attained in 9 h, 100% yield
of a diacetin:triacetin (55:45) mixture was formed. UsingAmberlystTM 15 dry andAmberlystTM 16
wet in 1:30 glycerol:EtOAc ratio and reflux at 90 ºC the total glycerol consumption was achieved
in 2 and 10h, respectively. The lower reactivity of Amberlyst-16 wet was explained in terms of
deactivation of acid sites and decrease in glycerol diffusion to the inner resin pores, both factors
caused by adsorbed water. The kinetics of glycerol transformation and product distribution in
the equilibrium in relation to the H2SO4, Amberlyst-15 (dry) and Amberlyst-16 (wet) catalyzed
reactions were measured.
Keywords: triacetin, diacetin, Amberlyst-16 wet, acidic ion-exchange resins, glycerol
acetylation
Introduction
the chemical industry.5-8 More recently it has been used
as a building block and solvent in organic synthesis.9-11
Biologically, it is currently used as a cryoprotectant of
different biological materials, in purification of proteins and
enzymes, in bacterial cultures, and in the production of bio-
plastics, among other uses.12 Despite its enormous industrial
applicability, the predictably increasing volumes of glycerol
generated from biodiesel production will create a glut in the
market in the short term. It is estimated that the worldwide
production of glycerol in 2012 will be around 1.2 million
tonnes.6 To make biodiesel economically viable, new and
efficient routes for transforming glycerol into higher value
products must be developed.5-8 Although most biodiesel
physico-chemical properties have close resemblance to petrol
diesel, freezing problems and increase in viscosity at low
Biodiesel is usually produced via base catalyzed
transesterification reaction between methanol or ethanol
and triacylglycerides. Glycerol is the main co-product
from this transformation. Its production is equivalent to
approximately 10 wt% of the total biodiesel production
(Figure 1).1-3
Glycerol offers a variety of applications in different areas.4
For example, it has been used as a humectant, emollient,
demulcent, solvent, and thickener in food and pharmaceutical
manufacturing. Other uses include production of explosives,
dyes, polymers, lubricants, printing ink and papers in
*e-mail: patrocinio@nppn.ufrj.br

18
Synthesis of Bio-Additives: Transesterification of Ethyl Acetate with Glycerol
J. Braz. Chem. Soc.
Figure 1. Glycerol production via triacylglyceride transesterification with methanol or ethanol.
temperatures, besides low resistance to oxidation, render it
inferior in comparison to petrol diesel. The addition of bio-
additives derived from glycerol could lead to an improvement
in biodiesel efficiency and glycerol valorization, thus
decreasing the total cost biodiesel production making it
an even more attractive fuel.13,14 Several additives such as
ethers,15,16 carbonates,17 acetals18,19 and esters of glycerol13
have already been synthesized. In this context, the
production of acetins is a chemically suitable application
for the excess glycerol from biodiesel production.20-30
Acetins are mono-, di-, and triacetate esters of glycerol.
Monoacetins and diacetins have wide applications as raw
materials for biodegradable polyesters, pharmaceuticals,
food and cosmetic industries.20,21 Triacetin occupies 10% of
the worldwide glycerol market as fuel additives, antiknock
additive for gasoline, additives in cosmetics, in foods, and
as solvents, among other uses.22,23 Conventionally, acetins
are synthesized via glycerol esterification with excess
acetic acid and/or acetic anhydride under mineral acid
catalysis.24 Currently, heterogeneous catalysts such as acidic
ion-exchange organic resins,20,21 zeolites,25 niobic acid,26
activated carbon-supported heteropolyacids,27 zirconia-based
catalysts,28 metal/SBA-15 catalyst29 among others are being
utilized in the synthesis of acetins. Despite being widely
used the acid catalyzed esterification process suffers from
drawbacks such as high costs, corrosive/toxic reagents’
use leading to environment problems and economical
inefficiency.30
We have investigated another possible route for acetin
production consisting of transesterification of ethyl acetate,
using homogeneous or heterogeneous acid catalysis.31,32 To
the best of our knowledge, no systematic study for glycerol
acetylation via transesterification of ethyl acetate or other
alkyl esters had been performed prior to ours. In the course
of the writing this work, Morales et al.33 described a second
study where the transesterification of methyl acetate with
glycerol catalyzed by different heterogeneous catalysts
was investigated.
We wish to report here our detailed results about
the production of acetins via the transesterification
reaction of ethyl acetate with glycerol using sulfuric acid
(H2SO4), p-toluenesulfonic acid (TsOH) or piridinium
p-toluenesulfonate (PPTS) as homogeneous catalysts and
Amberlyst-15 (dry) resin or Amberlyst-16 (wet) resin as
heterogeneous catalysts (Figure 2).
A study on the influence of parameters such as
temperature effect, molar ratio of glycerol:ethyl acetate
and catalyst loading was accomplished. In addition,
the equilibrium selectivity was determined for the most
efficient catalysts.
O
O
O
O
O
O
triacetin
O
O
O
OH
acid catalysts
+
3 CH3CH2OH
HO
OH
+ 3
ethyl acetate
O
O
O
OH
glycerol
diacetins (1,2 and 1,3-isomer mixture)
O
Acid catalysts: H2SO4, TsOH, PPTS,
AmberlystTM 15 dry or AmberlystTM 16 wet
HO
O
OH
monoacetins (1 and 2-isomer mixture)
Figure 2. Acetin production via transesterification of ethyl acetate with glycerol in the presence of acid catalysts.

Vol. 24, No. 1, 2013
Meireles and Pereira
19
Experimental
liquid consisting of an acetin mixture (100% conversion,
10.1 g of acetins). Acetins separation could be done by
column chromatography on silica gel (hexane/EtOAc 4:1)
or more easily by counter current chromatograph resulting
in colorless liquids.32
Materials
Glycerol (99.5%) and ethyl acetate (99.5%) both
p.a.-ACS were used as well as sulfuric acid, 96%
(H2SO4), p-toluenesulfonic acid (PTSA) and pyridinium
p-toluenesulfonate (PPTS), all purchased from Vetec
Química Fina Ltda and used as provided. AmberlystTM 15
dry and AmberlystTM 16 wet were purchased from Sigma-
Aldrich® and readily utilized. The catalyst properties were
considered as informed in the specifications provided by
the manufacturer (Rohm and Haas Company).
Spectroscopy data for monoacetin (mixture of
1
1:2-regioisomers): H NMR (400 MHz, CDCl3) d 2.10
(m, 6H), 3.67 (brs, 2H), 3.11(brs, 1H), 3.00 (brs, 1H),
4.14-4.02 (m, 8H), 4.25 (m, 1H), 5.01 (m, 1H); 13C NMR
(101 MHz, CDCl3) d ppm 20.6, 20.9, 61.1, 62.3, 65.1, 67.8,
72.2, 170.6, 171.1; GC-MS (70 eV) m/z 43, 103, 73; IR
(film) nmax/cm-1: 1743, 1367, 1240, 1050.
Spectroscopy data for diacetin (2.8:1 mixture of
1,3:1,2-regioisomers): 1H NMR (400 MHz, CDCl3) d 2.08
(m,12H), 4.36-4.01 (m, 5H), 4.67 (brs,1H), 5.07 (m,1H);
13C NMR (100 MHz, CDCl3) d 19.9, 20.1, 59.9, 61.7, 62.2,
66.6, 71.4, 170.0, 170.4; GC-MS (70 eV) m/z 43, 103, 73;
IR (film) nmax/cm-1: 1740, 1373, 1233.
Methods
Gas chromatography analyses were performed every
60 min, using a GC-FID (Shimadzu GC-FID 2010;
DB-1MS (100% polydimethylsiloxane) fused silica
capillary column (30 m × 0.25 mm, film thickness
0.25 μm); carrier gas H2 (1.0 mL min-1); temperature:
injector 290 ºC, column oven 60-290 ºC at 10 ºC min-1,
FID 290 ºC). Acetins were the only detected products
exhibiting the retention times of 6.16 min (monoacetin);
8.13 min (diacetin); 9.51 min (triacetin). These times were
obtained by GC from isolated and characterized samples.32
Acetin conversion was measured relative to glycerol
1
Spectroscopy data for triacetin: H NMR (400 MHz,
CDCl3) d 2.03 (d, 9 H, J 8Hz), 4.1 (dd, 2H, J 4.0, 8.0 Hz),
4.2 (dd, 2H, J 8.0, 8.0 Hz), 5.2 (m, 1H), 4.2 (dd, 2H, J 8.0,
8.0 Hz), 5.2 (m,1H); 13C NMR (101 MHz, CDCl3) d 20.5,
20.6, 62.1, 68.9, 169.9, 170.3; CG/MS (70 eV) m/z 43,
145, 103, 73; IR (film) nmax/cm-1: 1747, 1372, 1225, 1501.
Acetylation reactions in heterogeneous media
1
absolute conversion (retention time 4.92 min); H NMR
and 13C NMR spectra were recorded on Varian MR-400
(400 MHz) with TMS as internal reference. The coupling
constant (J) is in hertz (Hz). IR spectra were recorded on
a Shimadzu IR-Prestige-21 (FTIR) spectrophotometer as
a film on NaCl plate.Analyses by GC-MS were performed
on a Shimadzu GC/MS-QP 500.
All reactions were carried out in batch mode. Glycerol
(1.0 g, 10.9 mmol, 1.0 equiv.), ethyl acetate (327 mmol,
28.8 g, 36.5 mL, 30 equiv.) and an acid catalyst (1.09
mmol, 0.1 equiv., 0.23 g ofAmberlystTM 15 dry) were added
to a round bottom flask. Next, a Liebig condenser and a
pressure equalizer were adapted to the reaction system and
the resulting triphasic mixture was magnetically stirred at
room temperature for 24 h or at 90 oC for 18 h. After 1.5 h
it was possible to observe a biphasic mixture. Complete
glycerol consumption was reached in 2 and 10 h when
Amberlyst-15 (dry) and Amberlyst-16 (wet) acid resins
were used, respectively. Simple filtration, washing with
ethyl acetate (twice the reaction volume) and removal of
volatile portions under reduced pressure led to a colorless
liquid of low viscosity comprising a mixture of acetins
(1.9 g).
Acetylation reactions in homogeneous media
All reactions were carried out in batch mode. Glycerol
(5.0 g, 54.3 mmol, 1.0 equiv.), ethyl acetate (47.8 g,
60.6 mL, 543 mmol, 10 equiv.) and an acid catalyst
(5.43 mmol, 0.1 equiv.) were added to a round bottom flask.
Next, a Liebig condenser and a pressure equalizer were
adapted to the system and the reaction medium was kept
under strong magnetic stirring at room temperature or 90 oC
for 24 h. Initially, two phases were formed but at 45 min
o
(90 C) and 180 min (room temperature) only one phase
Results and Discussion
could be observed. Next, the reaction medium was diluted
with ethyl acetate (500 mL) washed with saturated NaHCO3
(3 × 20.0 mL) and brine (1 × 15 mL). The organic phase
was dried over Na2SO4 and the solvent removed in vacuum.
The residue was constituted of a low viscosity yellow
After several trials it was discovered that the 1:10
glycerol:EtOAc ratio, under strong magnetic stirring,
using 0.1 equiv. of homogeneous catalyst, and at room
temperature allows an adequate fluidity of the reaction

20
Synthesis of Bio-Additives: Transesterification of Ethyl Acetate with Glycerol
J. Braz. Chem. Soc.
medium, with one phase being observed after 3 h of
reaction. Thus, this ratio was utilized in the experiments
that employed homogeneous catalysts. On the other hand,
the use of a stoichiometric 1:3 glycerol:EtOAc ratio
produced an extremely viscous medium and a low glycerol
conversion (ca. 20%) was obtained. Contrarily for the
heterogeneous catalysts (0.1 equiv.) the use of a higher
glycerol:EtOAc ratio (1:30) was necessary. In both cases,
it was observed that as the reaction progresses the media
becomes more fluid due to the formation of the less viscous
acetins and mainly ethanol production.
(dry) and -16 (wet) ion exchange resins compared to
homogeneous catalysts. Aiming to increase glycerol
conversion for the reactions catalyzed by solid resins and
PPTS besides increasing the overall triacetin production,
the reactions were carried out at 90 C under the same
reaction conditions, as shown in Figure 4.
o
From the trial results, acetin formation was investigated
by reacting 1 equiv. glycerol with 10 equiv. of ethyl
acetate, at room temperature, for 24 h using 0.1 equiv. of
H2SO4, TsOH (p-toluenesulfonic acid), PPTs (piridinium
p-toluenesulfonate),Amberlyst-15 (dry) andAmberlyst-16
(wet) acid resin as catalysts, as shown in Figure 3.
Figure 4.Yield of acetins produced via transesterification of ethyl acetate
(10 equiv.) with glycerol (1.0 equiv.) at 90 oC for 24 h using 0.1 equiv.
of H2SO4, TsOH, Amberlyst-15 (dry), Amberlyst-16 (wet) or PPTS, as
catalysts.
This temperature was employed because it could lead
to a lowering of the viscosity of the reaction medium and
inhibits the formation of unidentified by-products which
were observed when the reaction was done at 120 oC. As
expected, an increase in the temperature improved the
glycerol conversion in the reactions catalyzed by PPTS,
Amberlyst-16 (wet) andAmberlyst-15 (dry)34 and a general
increase in the triacetin production. A mechanism based
on the literature30 was proposed for homogeneous acid-
catalyzed transesterification of ethyl acetate with glycerol
and may explain these results, as shown in Figure 5.
The transesterification reaction involves several
reversible successive steps that convert ethyl acetate into
monoacetin, diacetin and triacetin, producing 1 mol of
ethanol for each mol of acetin formed. The initial step
is the fast protonation of the carbonyl group from ethyl
acetate leading to the formation of a more electrophilic
species (I). The second step, which is rate determining,
consists of a nucleophilic attack of the glycerol primary
hydroxyl to the activated ethoxycarbonyl group affording
a tetrahedral intermediate (II) which undergoes a quick
ethanol elimination to form monoacetin and regenerate the
catalyst. The di and triacetin formation follows a similar
process. In 2009, Granados et al.36 suggested that an
analogous transesterification mechanism can also occur on
a resin surface. It is worth mentioning that both monoacetin
Figure 3.Yield of acetins produced via transesterification of ethyl acetate
(10 equiv.) with glycerol (1.0 equiv.), for 24 h at room temperature, using
0.1 equiv. of H2SO4, TsOH, Amberlyst-15 (dry) Amberlyst-16 (wet) or
PPTS, as catalysts.
Under these conditions, it was observed that the use
of H2SO4 and TsOH led to total glycerol conversion into
an acetin mixture. PPTS was not reactive. Contrarily, the
use of the heterogeneous catalysts Amberlyst-16 (wet)
and Amberlyst-15 (dry) was less effective since 23 and
38% of glycerol, respectively, remained unreacted without
observable formation of triacetin. The lower activity in
solid catalysts is often related to other factors, among
them external/internal diffusion that hindered the access of
reagents to the active acid sites of the catalysts.34 Indeed, in
the 1:10 glycerol/EtOAc ratio and at room temperature it
is difficult for the reagents to access the active sites of the
outer and inner surface resins because of the viscosity of
the reaction medium. This mass transfer resistance is the
main reason for the lower performance of theAmberlyst-15

Vol. 24, No. 1, 2013
Meireles and Pereira
21
H
OEt
O
H
HO
O
O
O
HO
H
−H
+
HO
OH
OH
O
−EtOH
OEt
OEt
OH
H
I
II
OH
AcO
H
H
OH
AcO
OAc
O
O
OAc
HO
III
OAc
+ EtOH
AcO
+ EtOH
V
OEt
OEt
OAc
OH
+ EtOH
H
HO
OH
−H / −EtOH
AcO
OAc
−H / −EtOH
IV
VI
Figure 5. Homogeneous acid-catalyzed reaction mechanism for the transesterification of ethyl acetate with glycerol.
and diacetin consist of an inseparable regioisomer mixture
(III + IV) and (V + VI), respectively. These regioisomers
are in a dynamic equilibrium and interconvert rapidly
through an internal migration of the acetyl group to the
vicinal hydroxyl group and thus individual isomers cannot
be isolated.32,35 In our studies it was observed that the
homogeneous acidic catalysts H2SO4 and TsOH favored
a higher triacetin proportion in comparison with solid
acid resins Amberlyst-15 (dry) and -16 (wet), which in
turn favored a higher diacetin concentration, as shown in
Figures 3 and 4. This behavior is due to the influence of the
acid strength on the reaction rate-determining step. Thus,
H2SO4 (pka = -2) yielded a greater triacetin concentration
compared to TsOH (pka = 2). PPTS (pka = 5.5), a very weak
organic acid was either unreactive or poorly reactive at 90 oC.
Considering the mechanism proposed in Figure 5, triacetin
production is less favored because the nucleophilic attack
of the voluminous diacetin on the activated ethoxycarbonyl
is more sterically hindered, resulting in a lower triacetin
concentration. The use of stronger acids leads to greater
concentration of H+ ions in solution and consequently, a
greater concentration of electrophilic species. In turn, this
greater concentration of electrophilic species favors the
determining step of the reaction, increasing the overall rate
at equilibrium and in consequence the triacetin concentration.
Assuming that heterogeneous transesterification proceeded
through a mechanism similar to the homogeneous one,36
the acid strength and/or the number of active sites on
Amberlyst TM 15 dry (4.8 mmol g-1) and AmberlystTM 16
wet (4.7 mmol g-1) were not sufficient to catalyze triacetin
formation and thus greater diacetin concentration was
obtained. These results will be discussed ahead.
Next, the kinetics of glycerol transformation and
product distribution for the reaction catalyzed by H2SO4
was investigated as shown in Figure 6.
Figure 6. Kinetic of acetins production via transesterification of ethyl
acetate (10 equiv.) with glycerol (0.1 equiv.), catalyzed by H2SO4 0.1
equiv. at 90 oC.

22
Synthesis of Bio-Additives: Transesterification of Ethyl Acetate with Glycerol
J. Braz. Chem. Soc.
Total glycerol consumption occurred within 2 h and
the equilibrium, which consisted of a 55:45 di:triacetin
ratio was reached within 9 h. In general, acid catalyzed
transesterification reactions are slower than esterification
reactions and perhaps this is the reason why acetins have
been produced almost exclusively via glycerol esterification
reactions with acetic acid and/or acetic anhydride using
homogeneous and heterogeneous acid catalysts.24,25,33
Recently, Mota et al.24 performed a very efficient glycerol
acetylation via an esterification process employing a 4:1
acetic anhydride:glycerol ratio and different catalysts.
Triacetin was produced with 100% selectivity and total
glycerol conversion, at 60 oC, in 20 min, when zeolite Beta
or K-10 Montmorillonite were used as catalysts. Reactions
with acetic acid as acylating reagent (AcOH:glicerol, 4:1)
under the same catalysts were also carried out. In this case,
a mixture of mono, di and triacetins was obtained, in 2 h,
Figure 7. Kinetics of acetin production via transesterification of ethyl
acetate with glycerol catalyzed byAmberlyst-15 (dry) 0.1 equiv., at 90 oC
using a 1:30 glycerol:EtOAc ratio.
o
at 120 C with yields over 90%. Acetin production via
esterification process demands shorter reaction times and
takes advantage of the use of heterogeneous catalysts.30 On
the other hand, the transesterification route employs EtOAc,
a reagent of lower cost and toxicity and produces EtOH as
a low toxicity waste. These advantages can compensate the
problems arising by homogeneous Brönsted acid catalysts
in industrial transesterification processes.37
Interestingly, catalyses promoted byAmberlyst-15 (dry)
and -16 (wet) acid resins (Figure 4) were quite similar to
each other and led to a mixture of mono, di and triacetins
with a large predominance of diacetin. Aiming to attain
total glycerol conversion and the equilibrium selectivity for
both resins, the reaction was carried out on Amberlyst-15
(dry) and Amberlyst-16 (wet), under the same conditions
showed in Figure 4, except for the glycerol:EtOAc ratio.
A dilute medium (glycerol:EtOAc, 1:30) was used to
enhance stirring and total glycerol consumption and
favor equilibrium. Both resins were used without any
prior treatment. Figure 7 shows that Amberlyst-15 (dry)
promoted total glycerol consumption in 2 h and the
equilibrium was reached in approximately 20 h with a
greater predominance of diacetin.
On the other hand, Amberlyst-16 (wet) led to similar
products distribution in 20 h, but the total consumption of
glycerol was observed in 10 h, as show in Figure 8.
Amberlyst-15 (dry) has been widely used both in
industry and in academia for converting glycerol and other
alcohols into high value-added products via esterification,
transesterification, etherification and acetalization
reactions.5,16,19 Contrarily, Amberlyst-16 (wet) has been
less utilized. Usually, academic studies on its catalytic
activity do not employ the resin in its wet form and water
removal before using is performed.16,38,39 Amberlyst-15
Figure 8. Kinetics of acetin production via transesterification of ethyl
acetate with glycerol catalyzed byAmberlyst-16 (wet) 0.1 equiv., at 90 oC
using a 1:30 glycerol:EtOAc ratio.
(dry) and -16 (wet) are strongly acidic, macroreticular
divinylbenzene copolymer matrix-based sulfonic acid
resins whose main physical and structural properties are
shown in Table 1.
One could expect a poor performance withAmberlyst-16
(wet) compared to Amberlyst-15 (dry) due to a higher
moisture content, to an average crosslinked structure, to a
smaller surface area and to a smaller macropore diameter.
However, in the catalysis promoted by Amberlyst-16
(wet), total glycerol consumption was observed resulting
in a product distribution very similar to that obtained
with Amberlyst-15 (dry), although a longer reaction time
was necessary, as shown in Figures 7 and 8. It is well
documented that water reduces considerably the catalytic

Vol. 24, No. 1, 2013
Meireles and Pereira
23
Table 1. Physical and structural properties of sulfonic macroreticular ion exchange resins
Acidity /
(mmol g-1)
Average pore
Diameter / nm
SBET
/
Particle size /
mm
Moisture
Content / %
Tmax
oC
/
Catalyst
% Cross-linking
(m2 g-1)
Amberlyst-15(dry)
Amberlyst-16(wet)
High
≥ 4.7
≤ 4.8
30
25
53
0.74
0.7
≤ 1.3
120
130
Medium
30
52-58
activity of resins and other solid acid catalysts since it is
strongly adsorbed on the active catalytic sites, inactivating
them.16 In fact, water adsorbed on Amberlyst-16 (wet)
causes a decrease in the concentration of acid sites as well
as an increase in the diffusion resistance, hindering the
entry of the glycerol molecule in the inner resin surface.34
These are the main factors that decrease the catalytic
activity of Amberlyst-16 (wet) resulting in a lag-period
in glycerol conversion in comparison to Amberlyst-15
(dry). In this manner, it is reasonable to suggest that the
catalysis promoted by Amberlyst-16 (wet) occurs initially
in the more accessible active sites on the outer polymer
surface since few active sites of the inner resin surface are
available. Glycerol diffusion resistance decreases in the
course of reaction as the fluidity of the reaction medium
increases with the formation of the acetins and ethanol.
At this moment, it can be suggested that the active sites
of the inner surface resin are now more accessible and
participating in the reaction rate. Thus, as Amberlyst-16
(wet) is nearly as acid as Amberlyst-15 (dry), the results
of glycerol conversion and acetin distribution in the
equilibrium are similar. On the other hand, Amberlyst-15
(dry) has a greater crosslinked structure, larger pore
diameter and only 1.6% of water. These features minimize
the internal glycerol diffusion resistance and exclude the
decrease in the concentration of active acid sites compared
to Amberlyst-16 (wet) and as a result, the total glycerol
consumption is achieved in 2 h only.
as show in Figure 9. Evaporation of the residual ethyl
acetate, for 24 h, at normal pressure and room temperature
was sufficient to activate it.
Figure 9. Graphical representations of recycle data for the reaction of
transesterification of ethyl acetate (30 equiv.) with glycerol (1.0 equiv.)
at 90 oC for 24 h using 0.1 equiv. AmberlystTM 15 dry.
It is worth mentioning that the ethyl acetate used in the
reaction (as reagent or extraction solvent) can be salvaged
for reuse while the ethanol by-product, a low toxicity
substance, can be theoretically directly transformed into
ethyl acetate by oxidative and dehydrogenating routes40
and fed to the process thereby increasing its efficiency.
A similar and extensive study on the water influence
on glycerol tert-butylation with isobutylene employing
different macroreticular and gelularAmberlystA-15,A-35,
A-36, A-39, A-31 and A-119 acid resins in their wet and
dry forms was described by Mravec and co-workers.16
Their studies showed that the highest conversion and
selectivity to the desired di- and tri-ethers was obtained
with all Amberlysts with macroreticular structure in dry
form (A-15, A-35, A-36, A-39). Only catalysts A-15 and
A-35 with very high degree of crosslinking were active
and selective in dry and wet forms. The authors explained
their results based mainly on the diameter of the resin pore.
Finally, thereusabilityandefficiencyoftheAmberlyst-15
(dry) resin was investigated. Thus,Amberlyst-15 (dry) was
separated from the reaction mixture by filtration and reused
at least thrice without significant loss of glycerol conversion
Conclusions
We have discovered a cost-effective environmentally
friendly process of producing diacetins and triacetins
through acid catalyzed transesterification of glycerol with
ethyl acetate, a clean alternative to the traditional methods
which employ acetic anhydride and/or acetic acid. Both
homogeneous (H2SO4, TsOH) and heterogeneous catalysts
(Amberlyst-15TM dry,Amberlyst-16TM wet) led to an acetin
mixture with 100% yield. With respect to the selectivity
results, after 24 h of reaction and at 90oC, the homogeneous
catalysts showed higher selectivity toward triacetin than
the Amberlyst acid resins. This result may be explained
by the greater acid strength influencing the reaction rate-
determining step. H2SO4 andAmberlystTM 15 dry acid resin
(10% mol) proved to be the most efficient catalysts for the

24
Synthesis of Bio-Additives: Transesterification of Ethyl Acetate with Glycerol
J. Braz. Chem. Soc.
process since both promoted total glycerol consumption
in 2.0 h at 90 oC, with the equilibrium being established in
9 and 20 h, respectively. On the other hand, Amberlyst-16
(wet) produced similar results toAmberlyst-15 (dry) and a
mixture of mono, di and triacetin with a large predominance
of diacetins was obtained, however, 10 h were necessary
for total glycerol consumption. A possible explanation for
the longer time required is that the water adsorbed on the
surface of Amberlyst-16 (wet) causes a deactivation of the
acid sites and leads to an increase in the glycerol diffusion
resistance, hindering the entry of the glycerol molecule in
the inner resin macropore.
13. Rahmat, N.;Abdullah, A. Z.; Mohamed, A. R.; Renew Sustain.
Energ. Rev. 2010, 14, 987; Khayoon, M. S; Hameed, B. H.;
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14. Melero, J. A.; Vicente, G.; Morales, G.; Paniagua, M.;
Bustamante, J.; Fuel 2010, 89, 2011; Yang, F.; Hanna, M. A.;
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24, 4668.
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Tost, R.; Merida-Robles, J. M.; Santamaria-Gonzalez, J.;
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Supplementary Information
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Chem. 2010, 12, 578.
Supplementary data are available free of charge at
http://jbcs.sbq.org.br as PDF file.
18. Vicente, G.; Melero, J.A.; Morales, G.; Paniagua, M.; Martín, E.;
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Acknowledgments
19. Silva P. H. R.; Gonçalves, V. L. C.; Mota, C. J. A.; Bioresour.
Technol. 2010, 101, 6225.
We thank CAPES and CNPq for fellowships to B. A.
Meireles andV. L. P. Pereira, respectively, and FAPERJ for
the financial support. We also thank Dr C. B. Barreto-Jr for
graphic layout assistance.
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Published online: February 7, 2013