1-O-Alkyl (di)glycerol ethers synthesis from methyl esters and triglycerides by two pathways: Catalytic reductive alkylation and transesterification/reduction

Article abstract of DOI:10.1039/c3gc36907b

From available and bio-sourced methyl esters, monoglycerides or oleic sunflower refined oil, the corresponding 1-O-alkyl (di)glycerol ethers were obtained in both high yields and selectivity by two different pathways. With methyl esters, a reductive alkylation with (di)glycerol was realized under 50 bar hydrogen pressure in the presence of 1 mol% of Pd/C and an acid co-catalyst. A second two step procedure was evaluated from methyl esters or triolein and consisted of a first transesterification to the corresponding monoglyceride with a BaO/Al₂O₃ catalyst, then its reduction to the desired glycerol monoether with a recyclable heterogeneous catalytic system Pd/C and Amberlyst 35 under H₂ pressure. In addition, a mechanism for the reaction was also proposed.

Full text of DOI:10.1039/c3gc36907b

Green Chemistry
View Article Online
View Journal
PAPER
1-O-Alkyl (di)glycerol ethers synthesis from methyl
esters and triglycerides by two pathways: catalytic
reductive alkylation and transesterification/reduction†
Cite this: DOI: 10.1039/c3gc36907b
Marc Sutter,a Wissam Dayoub,a Estelle Métay,a Yann Raoulb and Marc Lemaire*a
From available and bio-sourced methyl esters, monoglycerides or oleic sunflower refined oil, the corres-
ponding 1-O-alkyl (di)glycerol ethers were obtained in both high yields and selectivity by two different
pathways. With methyl esters, a reductive alkylation with (di)glycerol was realized under 50 bar hydrogen
pressure in the presence of 1 mol% of Pd/C and an acid co-catalyst. A second two step procedure was
evaluated from methyl esters or triolein and consisted of a first transesterification to the corresponding
monoglyceride with a BaO/Al2O3 catalyst, then its reduction to the desired glycerol monoether with
a recyclable heterogeneous catalytic system Pd/C and Amberlyst 35 under H2 pressure. In addition, a
mechanism for the reaction was also proposed.
Received 28th November 2012,
Accepted 22nd January 2013
DOI: 10.1039/c3gc36907b
www.rsc.org/greenchem
or glycidol in order to improve the selectivity towards the three
hydroxyls.19,20 The catalytic etherification of glycerol has been
Introduction
Glycerol is widely used in various industrial applications achieved starting from alcohols with acid catalysts,21–23
ranging from food, personal care and solvents1–3 to the syn- alkenes under acidic conditions24,25 or by telomerization
thesis of alkyd resins and polyurethanes.4 This building block reaction.26–28 In most of these processes, glycerol monoethers
is the main co-product of the vegetable oil industry, and its have been prepared in good yields starting from activated alco-
global output is increasing with the acceleration of oleochem- hols like benzyl alcohol,22 but a low selectivity for monoalky-
ical production.5 In fact, the synthesis of fatty acid methyl lated glycerol products was often observed when starting with
esters (FAMEs), also known as “biodiesel”, led to a dramatic alkenes.24–28 From an economical point of view, the acid-
increase of the availability of glycerol, since 11 kg of the latter catalytic route is inefficient, particularly the conversion of
is produced for every 100 kg of ester.5,6 In order to increase the glycerol and the selectivity towards the corresponding GME are
glycerol demand, it is necessary to find new large-scale appli- too low.21–23 The best results were described by Jérôme et al.,
cations for this polyol. For these reasons, glycerol has attracted with a higher yield of 45% of monopentyl glycerol ether using
much attention for the synthesis of various products of high Amberlyst A70 at high temperature (160 °C) and with a long
industrial interest.6–11
reaction time (96 h).23
Glycerol monoethers (GMEs) are eco-friendly renewable
More than 15 years ago, our group described an alternative
compounds. They are used in many industrial applications and more eco-friendly method for the Williamson ether syn-
such as cosmetics,12 cleaning formulations,13,14 pharmaceuti- thesis by reductive alkylation of linear alcohols and carbonyl
cals15,16 or ink formulations17 and an important number of compounds with Pd/C as a catalyst under hydrogen pressure.29
publications mention the interesting physical and biological Recently, this transformation was adapted to polyfunctional
properties of such compounds.18–20 Traditionally, GMEs are alcohols under mild conditions for the synthesis of linear
synthesized via the Williamson etherification, starting from 1-O-alkyl (di)glycerol monoethers in both high yields and
toxic and expensive epichlorohydrin, 3-chloropropane-1,2-diol selectivity. The best conditions were found to be the utilization
of (di)glycerol as a solvent and a reagent, in the presence
of Pd/C as a catalyst and a Brønsted acid as a co-catalyst.30,31
Unfortunately, aldehydes are not accessible at industrial
aLaboratoire de Catalyse, Synthèse et Environnement, Institut de Chimie et
Biochimie Moléculaires et Supramoléculaires (ICBMS), CNRS. UMR5246, Université
scales from renewable starting material for the moment.
Consequently, more recently, we reported for the first time
the catalytic reductive alkylation of readily available and/or
Lyon 1, Bâtiment Curien-CPE, 3° étage, 43 Bd du 11 Novembre 1918, 69622
Villeurbanne Cedex, France. E-mail: marc.lemaire.chimie@univ-lyon1.fr;
Fax: +33 472 431 408; Tel: +33 472 431 409
bSofiprotéol, 11, rue de Monceau, CS 60003, 75378 Paris Cedex 08, France.
biosourced carboxylic acids with (poly)glycerol using
a
E-mail: y.raoul@prolea.com; Fax: +33 147 230 288; Tel: +33 140 694 800
recyclable catalytic system associating Pd/C and Amberlyst
35.32,33
†Electronic supplementary information (ESI)
available. See DOI:
10.1039/c3gc36907b
This journal is © The Royal Society of Chemistry 2013
Green Chem.

View Article Online
Paper
Green Chemistry
Based on the conditions that we developed for the reductive
alkylation of carboxylic acids with (poly)glycerol, methyl
valerate 1a was used as a model substrate.33
Optimization of the reaction parameters with methyl esters
As shown in Table 1, the conversion of the starting material
was not complete when the optimized conditions for the
reductive alkylation of carboxylic acids were applied on methyl
valerate 1a (entry 1).33 In this first try, glycerol was used as a
solvent and a reagent in a molar ratio of 1/40, 1 mol% Pd/C
(5%) was used as a catalyst and 10 wt% Amberlyst 35 as a
recyclable acid co-catalyst corresponding to 5 mol% H+. The
reaction was performed under 50 bar H2 pressure and 120 °C,
with a stirring speed of 800 rpm (revolutions per minute) for
16 h in a Paar steel autoclave. Under these conditions, 63% of
methyl valerate 1a were converted, with a good selectivity
towards GME 4a, detected at 50% yield (entry 1). As a conse-
quence, the influence of the different parameters was evalu-
ated. With 2 mol% of Pd/C, the conversion was improved, and
ether 4a was observed in 60% yield, ether 5a in 11% and esters
2a and 3a in 6% yield (entry 2). By increasing the amount of
Amberlyst 35 to 15 wt%, the conversion of the starting methyl
valerate 1a reached 83%, but the reaction afforded the corre-
sponding GMEs 4a and 5a with a lower selectivity (entry 3).
With 4 mol% Pd/C and 30 wt% Amberlyst 35, the conver-
sion of the starting material was complete, but the yield for
the expected glycerol monoether 4a decreased to 46%, whereas
the yield for monoglycerides 2a and 3a increased to 47%
(entry 4). In view of these results, the nature of the acid co-
catalyst was changed. In order to help the addition of glycerol
to the methyl ester, a more acidic ion exchange resin Amber-
lyst 36 was used in 10 wt% (5.5 mol% H+). In this case, the
conversion decreased to 80% and ether 4a was observed in
only 24% yield (entry 5). Amberlyst 15 is known for its
efficiency in transesterification reactions.34 In our case, when
starting the reaction with 15 wt% Amberlyst 15 and 2 mol%
Pd/C, the conversion of methyl valerate 1a was not complete
(81%) and the reaction afforded GMEs 4a and 5a in 60% yield.
Monoglycerides 2a and 3a were obtained in this case in 21%
overall yield (entry 6). By increasing the amount of Pd/C to
4 mol% as well as the Amberlyst 15 loading to 30 wt%, the con-
version of the substrate was complete, but the selectivity for
glycerol monoethers 4a and 5a remained unchanged with
a 74% overall yield (entry 7). Finally, the best results were
obtained when the solid acid co-catalyst was replaced by a
strong Brønsted acid soluble in the medium, i.e. camphor-
sulfonic acid (CSA) (4.5 mol% H+), with 1 mol% Pd/C (5%). Under
these conditions, the reaction afforded the 1-O-pentylglycerol
monoether 4a in 81% yield and the 2-O-pentylglycerol mono-
ether 5a in 17% yield. The selectivity for GMEs was excellent
(99%), and only traces of monoglycerides 2a and 3a were
detected (entry 8). These results could be explained by a lower
solubility of the methyl esters in the glycerol phase than the
corresponding carboxylic acids.33 Thus, the mass transfer
problems were fixed with a more homogeneous medium (acid
co-catalyst soluble). Besides, it was necessary to add an acid
Scheme 1 Synthesis of glycerol and diglycerol monoethers (a) by reductive
alkylation of glycerol or diglycerol and methyl esters 1 and (b) a two step pro-
cedure composed of a first transesterification step of triglyceride 12 or methyl
ester 1 followed by a reduction of monoglyceride 2 with a recyclable catalytic
system.
Based on our earlier results for the preparation of (poly)-
glycerol monoethers and in order to establish new and alternative
eco-efficient processes for the alkylation of glycerol, the cata-
lytic etherification with the available triglycerides 12, methyl
esters 1 and monoglycerides 2 is investigated in this report by
two different pathways (Scheme 1). Interestingly, triglycerides
are used as low-cost and biosourced substrates in large scale
by the vegetable oil industry. In addition, methyl esters are
obtained as products in the biodiesel manufacture, with a
good accessibility and often a less expensive cost than the
corresponding carboxylicacids.5,6 Herein, the reductive alkylation
of methyl esters with glycerol is reported (Scheme 1, path a).
Besides, an efficient two step procedure for the synthesis of
GMEs is also described (Scheme 1, path b). The transesterifica-
tion of triolein 12 or FAMEs 1 with (di)glycerol using a mixed
metal oxide as a new catalyst is followed by the reduction of
the obtained monoglyceride to its corresponding glycerol
monoether under H2 pressure. A mechanistic consideration of
the reaction with these substrates is also proposed.
Results and discussion
At the beginning of our study, we first prepared GMEs by
reductive alkylation of methyl esters with glycerol (Scheme 2).
Scheme 2 Reductive alkylation of a methyl ester 1 with glycerol to the corres-
ponding 1-O-alkylglycerol monoether 4 under optimized conditions.
Green Chem.
This journal is © The Royal Society of Chemistry 2013

View Article Online
Green Chemistry
Paper
co-catalyst in the reaction medium in order to achieve a good
In order to evaluate the scope of the method, these last
conversion and selectivity for GMEs (entry 9). The reaction optimized conditions were used for the reductive alkylation of
without a palladium catalyst afforded only monoglycerides 2a linear and saturated methyl esters with glycerol and diglycerol.
and 3a in 84% yield (entry 10). Finally, the H2 pressure
Reductive alkylation of methyl esters with (di)glycerol
(50 bar), the molar ratio methyl valerate 1a/glycerol (1/40) as
well as the temperature (120 °C) were necessary to have a com- As can be seen from the results in Table 2, these conditions
plete conversion of the starting material to the desired glycerol were applied for the synthesis of linear, saturated 1-O-alkyl
monoethers 4a and 5a. After screening Ru/C, Rh/C and Pt/C (di)glycerol monoethers by catalytic reductive alkylation of
supported metals, we found that Pd/C was the most effective glycerol and diglycerol under 50 bar hydrogen pressure in the
catalyst for the reductive alkylation reaction.
presence of 1 mol% of Pd/C, 10 wt% of CSA, starting from a
Table 1 Optimization experiments for the reductive alkylation of glycerol with methyl valerate 1aa
Yieldb (%)
Entry
Pd/C
Acid co-catalyst
Conversionb (1a, %)
Ether 4a
Ether 5a
Esters 2a + 3a
Selectivityb (ethers/esters)
1
2
3
4
5
6
7
8
9
1 mol%
2 mol%
2 mol%
4 mol%
1 mol%
2 mol%
4 mol%
1 mol%
1 mol%
—
Amberlyst 35 (10 wt%)
Amberlyst 35 (10 wt%)
Amberlyst 35 (15 wt%)
Amberlyst 35 (30 wt%)
Amberlyst 36 (10 wt%)
Amberlyst 15 (15 wt%)
Amberlyst 15 (30 wt%)
Camphorsulfonic acid (10 wt%)
—
63
77
83
>99
80
81
>99
>99
26
50
60
51
46
24
51
62
81
5
9
11
10
7
5
9
12
17
<1
0
4
6
94/6
92/8
22
47
51
21
26
1
73/27
53/47
36/44
74/26
74/26
99/1
20
84
23/77
0/100
10
Camphorsulfonic acid (10 wt%)
85
0
a Experimental conditions: molar ratio methyl valerate 1a/glycerol of 1/40, Pd/C (5%), 10 wt% acid co-catalyst, 120 °C, 50 bar H2, stirring speed =
800 rpm, 16 h. b Conversions, yields and selectivity were determined by GC/MS analysis and 1H NMR spectroscopy.
Table 2 Reductive alkylation of mono- and di-glycerol with different methyl esters 1a
Methyl ester
(1)
Alcohol/
solvent
Conversionb
(1, %)
Isolated yield
(1-O-alkylether, %)
Entry
1
Product
Selectivityc
85/15
1a
1b
1c
Glycerol
Glycerol
Glycerol
4a
4b
4c
>99
>99
>99
71
73
53
2
3
83/17
81/19
4
5
6
1d
1e
1f
Glycerol
Glycerol
Glycerol
4d
4e
4f
>99
>99
>99
80/20
83/17
82/18
43
41
26
7
8
1b
1d
Diglycerol
Diglycerol
6b
6d
>99
>99
ndd
ndd
62
41
a Experimental conditions: 1 mol% Pd/C (5%), 10 wt% CSA, 50 bar H2 pressure, 120 °C, stirring speed = 800 rpm, 16 h. b Conversions were
determined by GC/MS analysis and 1H NMR spectroscopy. c Selectivity between 1-O-alkyl and 2-O-alkyl (di)glycerol ethers determined by 1H NMR
spectroscopy. d Selectivity between 1-O-alkyl and 2-O-alkyl (poly)glycerol monoethers could not be determined.
This journal is © The Royal Society of Chemistry 2013
Green Chem.

View Article Online
Paper
Green Chemistry
methyl ester 1 in a substrate/glycerol molar ratio of 1/40 for α-monoglycerides, but by replacing the expensive Brønsted
16 h. acid CSA by Amberlyst 35 as a co-catalyst, in order to use the
When starting from methyl valerate 1a and methyl hexano- same recyclable catalytic system developed for the reductive
ate 1b, the catalytic reductive alkylation of glycerol afforded alkylation of carboxylic acids.33 Etherification of glycerol with
GMEs 4a and 4b in 71% and 73% isolated yields, respectively monoglycerides containing a short alkyl chain (glycerol pen-
(entries 1 and 2). With esters bearing longer alkyl chain length tanoate 2a and glycerol hexanoate 2b) afforded ethers 4a and
like methyl octanoate 1c, methyl decanoate 1d and methyl 4b in 74% and 75% isolated yields, respectively (entries 1 and
dodecanoate 1e, the desired 1-O-alkylmonoethers 4c, 4d and 2). Thus, these results demonstrated that it was possible to
4e were isolated in moderate 53%, 43% and 41% yields reduce a monoglyceride to its corresponding glycerol mono-
(entries 3, 4 and 5). Finally, with methyl stearate 1f, the reac- ether under H2 pressure by using this catalytic system. Interest-
tion afforded the corresponding GME 4f in 26% isolated yield ingly, the selectivities between 1-O-alkylglycerol monoethers 4
(entry 6). These results could be explained by the formation of and 2-O-alkylglycerol monoethers 5 were similar to those
dialkylated glycerol products. Indeed, the reaction medium observed starting from carboxylic acids or methyl esters (4/1 to
became biphasic in these cases.
5/1), even if the reactions were started with 100% of α-mono-
Thus, after a first etherification, the monoalkylated product glycerides. These results suggested that monoglycerides may
migrated into the methyl ester phase where a second alkyl- not be a key intermediate in the reductive alkylation of glycerol
ation occurred. As a consequence, the yields for 1-O-alkyl gly- with methyl esters or carboxylic acids, but they are rather first
cerol monoethers decreased, whereas the yields for dialkylated dehydrated to form 5-membered cyclic hemi-ortho esters in the
glycerol ethers increased. As observed in the case of carboxylic glycerol media before being reduced to the corresponding
acids, the selectivity towards the formation of 1-O-alkyl glycerol primary and secondary GMEs as explained further in this
monoethers 4 and 2-O-alkyl glycerol monoethers 5 ranged paper. When starting from glycerol octanoate 2c, glycerol
from 4/1 to 5/1, independently of the alkyl chain’s length. It decanoate 2d, glycerol dodecanoate 2e, glycerol stearate 2f and
indicated similarities between both mechanisms as discussed glycerol oleate 2g the reaction afforded the corresponding
further in this report. Finally, when using diglycerol as a GMEs 4c, 4d, 4e and 4f in yields of 58%, 49%, 43%, 34% and
solvent and a reagent with methyl esters 1b and 1d, the 35% respectively (entries 3–7). By increasing the alkyl chain
expected 1-O-alkyl diglycerol monoethers 6b and 6d were iso- length, the selectivity between 1-O-alkylglycerol monoethers 4
lated in 62% and 41% yield, respectively, with a complete con- and 2-O-alkylglycerol monoethers 5 increased from 4/1 to 9/1.
version of the starting FAMEs (entries 7 and 8).
It is worth mentioning that the yields for GMEs were slightly
better than those observed when starting with the correspond-
ing FAMEs (Table 2). Surprisingly, the reductive alkylation of
diglycerol with diglycerol hexanoate 7b and diglycerol decano-
ate 7d afforded ethers 6b and 6d in lower yields of 35% and
26% without a complete conversion of the substrates (Table 3,
entries 8 and 9). These results may be explained by a steric
hindrance of the starting ester’s diglyceryl moiety.
Reductive alkylation of monoglycerides with (di)glycerol
From these results, six main reasons pushed us to apply this
reaction to α-monoglycerides (Scheme 3). (1) They can be an
intermediate in the reductive alkylation with methyl esters or
carboxylic acids; (2) they are more soluble in the glycerol phase
than the corresponding methyl esters, because of the presence
of the two hydroxyls, thus resolving the mass transfer pro-
blems; (3) they might afford the corresponding 1-O-alkyl-
glycerol monoethers with an excellent selectivity, since a first
transesterification in the glycerol phase is not necessary; (4)
like methyl esters, these compounds are biosourced and/or
easily available, which makes the process cheaper; (5) they rep-
resent an alternative way to form GMEs and can already be
valorized as surfactants; (6) to the best of our knowledge, there
is no example in the literature for the reduction of an ester
function to its corresponding ether by catalytic hydrogenation.
As can be seen in Table 3, optimized conditions developed
for the reductive alkylation of methyl esters were applied with
Mechanism
In this present study, the results confirm the mechanism pro-
posed for the reductive alkylation of carboxylic acids, in which
the key step of the reaction seems to be the formation of a
complex between the Pd/C surface and a 5-membered cyclic
hemi-ortho ester 9.33 The proposed mechanism of this
transformation is given in Fig. 1, and explains the 4/1 to 9/1
selectivity between 1-O-alkylglycerol monoethers 4 and 2-O-
alkylglycerol monoethers 5 obtained from methyl esters 1 or
α-monoglycerides 2.
In the case of methyl esters 1, the acid co-catalyst catalyzes
the addition of glycerol to the carbonyl of the substrate. As
seen from the result given in Table 1, without an acid co-
catalyst the reaction was not efficient enough. Monoglyceride 2
can be formed by dehydration of intermediate 8. The for-
mation of this glycerol ester is reversible, as indicated by the
experiments performed when using monoglycerides 2 as start-
ing material. Finally, the palladium probably promotes the
selective cleavage of the primary or secondary C–O bond. In
fact, a complex between a 5-membered cyclic hemi-ortho ester
Scheme 3 Reduction of an α-monoglyceride 2 in glycerol under optimized
conditions.
Green Chem.
This journal is © The Royal Society of Chemistry 2013

View Article Online
Green Chemistry
Paper
Table 3 Reductive alkylation of mono- and di-glycerol with different monoglycerides 2a
Alcohol/
solvent
Conversionb
(2, %)
Isolated yield
Entry Substrate (2)
Product
Selectivityc (1-O-alkylether, %)
1
2a Glycerol
4a >99
81/19
86/14
87/13
89/11
89/11
89/11
89/11
ndd
74
75
58
49
43
34
35
35
26
2
3
4
5
6
7
8
9
2b Glycerol
2c Glycerol
2d Glycerol
2e Glycerol
4b >99
4c >99
4d >99
4e >99
2f
Glycerol
4f
>99
>99
73
2g Glycerol
7b Diglycerol
7d Diglycerol
4f
6b
6d
61
ndd
a Experimental conditions: 1 mol% Pd/C (5%), 10 wt% Amberlyst 35, 50 bar H2 pressure, 120 °C, stirring speed = 800 rpm, 16 h. b Conversions
1
were determined by GC/MS analysis and 1H NMR spectroscopy. c Selectivity between 1-O-alkyl and 2-O-alkyl (di)glycerol ethers determined by H
NMR spectroscopy. d Selectivity between 1-O-alkyl and 2-O-alkyl (poly)glycerol monoethers could not be determined.
Fig. 1 Proposed mechanism for the reductive alkylation reaction of glycerol with a methyl ester 1 and an α-monoglyceride 2.
9 and Pd/C could be formed after dehydration of 8 or 8′. C–O bond is easier than the primary one. Finally, the 1-O-alkyl-
Because of the assistance from the free hydroxyl that coordi- glycerol monoether 4 is obtained by hydrogenolysis of 9.
nates the palladium surface, the cleavage of the secondary According to this mechanism, the selectivity between the
This journal is © The Royal Society of Chemistry 2013
Green Chem.

View Article Online
Paper
Green Chemistry
1-O-alkylglycerol monoether 4 and the 2-O-alkylglycerol mono-
ether 5 ranging from 4/1 to 9/1 is explained.
The transesterification reaction was first performed with
La2O3 and a supported La2O3/Al2O3 catalyst with a higher
surface area. In both cases, the conversion of the starting
methyl valerate 1a was low, and the expected α-monoglyceride
2a was obtained in 39% and 33% yield, respectively (entries 1
and 2). With CeO2, the conversion was very low (entry 3). This
result was already observed in the literature.35 With praseody-
mium oxide, the yield for product 2a increased to 60%
(entry 4). Experiments were performed with hydroxyapatite,
Amberlyst 15 and magnesium oxides. In the case of hydroxy-
apatite, only traces of monoglyceride 2a were observed (entry 5).
With Amberlyst 15, the conversion was around 74%, and ester
2a was obtained in 69% yield (entry 6). Next, two reactions
with magnesium oxides with high surface areas of 230 m2 g−1
and 600 m2 g−1 were performed. In fact, Barrault et al. have
shown that the increase of the catalytic activity of MgO was
linked to the specific area.35 In our case, the reaction afforded
the corresponding glycerol ester 2a in high 88% and 84%
yields, respectively (entries 7 and 8). With barium oxide, the
conversion of ester 1a was almost complete, and 91% of gly-
cerol ester 2a was obtained (entry 9). This result can be
explained by the presence of stronger basic sites on BaO than
MgO due to a lower electronegativity of barium (0.89) than
magnesium (1.31). Finally, the best result was obtained with
barium oxide on a basic γ-alumina [BaO (22%); Al2O3 (78%)].
The conversion of the starting material 1a was complete, with
an excellent regioselectivity towards the α-monoglyceride 2a,
obtained in 98% yield (entry 10). This mixed metal oxide, gen-
erally known for the treatment of NOx when combined with a
noble metal,42 showed excellent results for the heterogeneous
catalytic transesterification of methyl valerate 1a with glycerol.
The effect of the basic sites from both oxides BaO and Al2O3
may play an important role in the conversion and the regio-
selectivity of the reaction. The characterization of the catalyst
is in progress in order to understand its high efficiency.
Catalytic synthesis of primary glycerol mono-esters
Monoglycerides may represent an alternative route to glycerol
monoethers starting from methyl esters after a first transesteri-
fication step. As a consequence, it was interesting to develop
an alternative two step procedure, in which the intermediate
monoglyceride 2 was obtained by transesterification of a
methyl ester 1 in glycerol and then reduced to its correspond-
ing glycerol monoether (Scheme 4). The synthesis of primary
monoglycerides is well described in the literature.7 The trans-
esterification reaction of methyl esters with glycerol catalyzed
by heterogeneous catalysts in the absence of a solvent presents
environmental and practical advantages.35–41 In addition,
when using methyl esters as substrates instead of carboxylic
acids, no autocatalytic reaction occurs, thus making more
efficient the control of the selectivity between primary and sec-
ondary esters by the catalyst. Some metal oxides are known for
their efficiency in the transesterification of fatty methyl esters
with glycerol, like MgO based catalysts.7,35,37–41 As expected,
the most basic metal oxides were generally the most active cata-
lysts in these examples. In order to improve the yield as well as
the selectivity for α-monoglycerides 2, several metal oxide
catalysts, which can be removed from the medium by fil-
tration, were evaluated for the transesterification reaction
(Scheme 5). All the experiments were performed with methyl
valerate 1a, in order to have good solubility in glycerol. The
molar ratio substrate/glycerol was defined at 1/20, to be close
to the reductive alkylation optimized conditions. The reaction
was performed with 10 wt% of catalyst at 120 °C for 16 h. All
the results are summarized in Table 4.
In view of these results, the reaction conditions were opti-
mized with the mixed metal oxide BaO/Al2O3.
Effect of the reaction parameters on the transesterification
reaction
The influences of the temperature, the molar ratio methyl vale-
rate 1a/glycerol and the catalyst loading were evaluated in
order to determine the best conditions for a solvent free trans-
esterification reaction (Table 5). At 80 °C, the conversion of
methyl ester 1a was low and the corresponding monoglyceride
Scheme 4 Two step procedure for the synthesis of glycerol monoethers 4, was obtained in 26% yield (entry 1). When the temperature
starting from a methyl ester 1, including (a) a first transesterification step fol-
was increased to 100 °C, the conversion of the substrate was
complete, and the expected α-monoglyceride 2a was detected
lowed by (b) a reduction of monoglyceride 2.
in 99% yield (entry 2), as observed at 120 °C (entry 3). The
molar ratio methyl valerate 1a/glycerol was an important para-
meter for the selectivity between monoglycerides and diglycer-
ides. By concentrating the reaction medium in a molar ratio
methyl ester 1a/glycerol of 1/10, the conversion slightly
decreased to 88%, but the selectivity for the desired ester 2a
remained unchanged (entry 4). At higher concentrations of 1/5
Scheme 5 Transesterification of methyl valerate 1a with glycerol, catalyzed by
a metal oxide catalyst.
and 1/2, monoester 2a was obtained in 73% and 36% yields
Green Chem.
This journal is © The Royal Society of Chemistry 2013

View Article Online
Green Chemistry
Paper
Table 4 Catalyst screening for the transesterification reaction of methyl valerate 1a with glycerola
Yieldb (%)
Basic catalyst
(10 wt%)
Surface area
Conversionb
(1a, %)
Primary
monoglyceride 2a
Secondary
monoglyceride 3a
Selectivityb
2a/3a
Entry
(m2 g−1
)
1
2
3
4
5
6
7
8
9
La2O3
70
42
35
3
63
1
74
90
86
99
>99
39
33
3
60
1
69
88
84
91
98
3
2
0
3
0
5
2
2
8
2
93/7
94/6
100/0
95/5
—
93/7
98/2
97/3
92/8
98/2
La2O3 (4%)/Al2O3 (96%)
CeO2
Pr6O11
Hydroxyapatite
Amberlyst 15 dry
MgO(I)
MgO(II)
BaO
BaO (22%)/Al2O3 (78%)
190
113
3.3
9
45
230
600
—
10
103
a Experimental conditions: molar ratio methyl valerate/glycerol of 1/20, catalyst (10 wt%), 120 °C, 16 h. b Conversions, yields and selectivity were
determined by GC/MS analysis and 1H NMR spectroscopy.
quantitative yield (entries 7 and 8). However, by decreasing the
amount to 1 wt%, the conversion dropped to 57% (entry 9).
Finally, without catalyst BaO/Al2O3, no conversion was
observed, confirming that no autocatalytic reaction occurred
(entry 10).
Table 5 Influence of the temperature, the molar ratio and the catalyst loading
on the transesterification reaction of methyl valerate 1a with glycerola
Thus, the optimized conditions were found to be a reaction
temperature higher than 100 °C, a molar ratio methyl ester/
glycerol of 1/20 and a small amount of mixed metal oxide BaO/
Al2O3 catalyst (2.5–5 wt%) without any solvent.
Transesterification of methyl esters with glycerol
The optimized conditions were then applied to different
FAMEs with various alkyl chain lengths. The reactions were
performed with a molar ratio methyl ester/glycerol of 1/20,
with 5 wt% of BaO/Al2O3 and for 16 h. The reaction temp-
erature was increased with the alkyl chain length, in order to
improve the conversion after 16 h, as shown in Table 6.
Yieldb (%)
ratio 1a/ Catalyst Conv.b Ester
Diesters
Molar
Entry T (°C) glycerol (wt%) (1a, %) 2a (%) (10a + 11a, %)
1
2
3
4
5
6
7
8
9
10
80
1/20
1/20
1/20
1/10
1/5
10
10
10
10
10
10
5
2.5
1
0
26
>99
>99
88
93
52
>99
>99
57
26
>99
>99
88
73
36
>99
>99
57
0
0
0
100
120
120
120
120
120
120
120
120
The transesterification of methyl valerate 1a and methyl
hexanoate 1b with glycerol afforded the corresponding mono-
glycerides 2a and 2b in quantitative isolated yields (entries 1
and 2). This methodology was then applied to methyl esters
with longer alkyl chains at higher temperatures in order to
increase the solubility of glycerol in the FAME phase. Reaction
with methyl octanoate 1c afforded glycerol ester 2c in 96% iso-
lated yield (entry 3). In this case, 3% of diglycerides were
obtained. With methyl decanoate 1d, the conversion decreased
slightly to 91%, and the selectivity for the expected mono-
glyceride 2d was lower. Indeed, compound 2d was isolated in
79% yield, and 12% of diglycerides were obtained (entry 4).
When methyl dodecanoate 1e was used as a substrate, the con-
version decreased to 88%, and ester 2e was obtained in 71%
isolated yield (entry 5). In this example, the amount of digly-
cerides increased to 17%. Finally, with methyl stearate 1f the
reaction temperature had to be increased to 200 °C and the
0
13
12
0
0
0
1/2
1/20
1/20
1/20
1/20
0
0
0
a Reaction time = 16 h. b Conversions and yields were determined by
1H NMR spectroscopy.
whereas diesters 10a and 11a were obtained in 13% and 12%
yields (entries 5 and 6). In addition, the conversion of the
starting material decreased to 93% and 52%, respectively. The
ratio 1/20 was kept and the amount of BaO/Al2O3 was con-
sidered. By decreasing the quantity of the catalyst to 5 wt%
and 2.5 wt%, the reaction afforded monoglyceride 2a in
This journal is © The Royal Society of Chemistry 2013
Green Chem.

View Article Online
Paper
Green Chemistry
Table 6 Transesterification of methyl esters 1 with glycerol or diglycerola
Isolated yield (%)
Conv.b (1, %) α-Monoglyceride Diesters
Entry Substrate (1)
Alcohol/solvent Temp. (°C) Product
1a Glycerol
1
100
120
140
160
180
200
130
160
200
2a >99
99
99
96
79
71
55
83
54
53
0
2
1b Glycerol
1c Glycerol
1d Glycerol
1e Glycerol
2b >99
0
3
2c
2d
2e
2f
99
91
88
94
3
4
12
17
45
17
25
47
5
6c
7
1f
Glycerol
1b Diglycerol
1d Diglycerol
7b >99
8
7d
7f
79
96
9c
1f
Diglycerol
a Experimental conditions: molar ratio methyl ester/glycerol of 1/20, BaO/Al2O3 (5 wt%), 120 °C, 16 h. b Conversions were determined by GC/MS
analysis and 1H NMR spectroscopy. c Reaction time = 36 h.
corresponding monoester 2f was isolated in 55% yield (entry
6). This fall of conversion and growth of diglyceride yields were
explained by a lower solubility of the substrates with longer
alkyl chains in the glycerol phase, leading to a consecutive
reaction to form diglycerides. The reaction was finally per-
formed with diglycerol as a reagent and a solvent, in order to
synthesize diglycerol monoesters. Transesterification of methyl
hexanoate 1b with diglycerol afforded the corresponding digly-
cerol ester 7b in 83% isolated yield (entry 7). Similarly, reaction
of methyl decanoate 1d with diglycerol afforded ester 7d in
54% isolated yield (entry 8). Reaction with methyl stearate 1f at
200 °C gave monoester 7f in 53% isolated yield (entry 9).
All (di)glycerol monoesters were isolated before being used
as substrates in a reductive alkylation reaction with glycerol
under optimized conditions, as shown in Table 3.
Scheme 6 Two step procedure for the synthesis of 1-O-alkylglycerol mono-
ether 4f, starting from triolein 12, consisted of (a) a first transesterification step
followed by (b) a reduction of monoglyceride 2g.
by catalytic hydrogenation with Pd/C and Amberlyst 35
(Scheme 6).
The glycerolysis of triolein with glycerol to form monoolein
with BaO/Al2O3 was first performed at 120 °C without any
solvent in a sealed tube, using a molar ratio oleic oil/glycerol
of 1/20 and 10 wt% of catalyst. The results are shown in
Table 7.
Under these conditions, the conversion of triglyceride 12
was only around 5% after 24 h (entry 1). When using methyl-
THF as a co-solvent, the conversion of the substrate increased
slightly to 10% and the reaction gave the corresponding
α-monoglyceride 2g in 7% yield (entry 2). With a soluble
Transesterification tests of high oleic sunflower refined oil
with glycerol
The preparation of monoglycerides by direct transesterification
of oleic sunflower oil in the presence of heterogeneous basic
catalysts like MgO and MgO/Al2O3 was also reported in the
literature.43,44 It was then interesting to test the mixed metal
oxide catalyst BaO/Al2O3 in the glycerolysis of oleic refined oil
12 (≥90% of triolein), in order to obtain the corresponding
monoester 2g that will be reduced in a second step to GME 4f
Green Chem.
This journal is © The Royal Society of Chemistry 2013

View Article Online
Green Chemistry
Paper
Table 7 Transesterification of refined triolein with glycerol and diglycerola
Isolated yields (%)
Entry
Alcohol/solvent
Co-solvent
Temp. (°C)
Catalyst
Conversionb (10, %)
α-Monoester
Diesters
1
2
3
Glycerol
Glycerol
Glycerol
Glycerol
Glycerol
Glycerol
Diglycerol
Diglycerol
—
120
120
200
200
200
200
200
200
BaO (22%)/Al2O3 (78%)
BaO (22%)/Al2O3 (78%)
K2CO3
<5
10
95
4
7
1
3
Methyl THF (15 eq.)
—
—
—
1,2,3-TMP (15 eq.)
—
1,2,3-TMP (15 eq.)
68
66
51
88
41
63
25
24
49
12
50
22
4
CaO
90
5c
6c
7c
8c
BaO (22%)/Al2O3 (78%)
BaO (22%)/Al2O3 (78%)
BaO (22%)/Al2O3 (78%)
BaO (22%)/Al2O3 (78%)
>99
>99
>99
>99
a Experimental conditions: molar ratio oleic sunflower oil/glycerol of 1/20, catalyst (10 wt%), 24 h. b Conversions were determined by 1H NMR
spectroscopy. c Reaction time = 48 h.
catalyst K2CO3 and at higher temperature (200 °C), the conver- Table 8 Transesterificationa of methyl esters 1a and 1b with glycerol followed
by reduction under H2 b with no intermediate purification
sion of triolein reached 95%, and 68% of the corresponding
monoester 2g was isolated, in agreement with literature data
concerning soluble base catalysts45 (entry 3). With 10 wt%
CaO, previously calcinated for 3 h at 600 °C, the transesterifica-
tion reaction afforded monoglyceride 2g in 66% isolated yield
(entry 4). In this case, the catalyst was slightly soluble in the
medium. Finally, with BaO/Al2O3, the conversion was complete
after 48 h at 200 °C, and 51% of monoolein 2g could be iso-
lated (entry 5). When 1,2,3-trimethoxypropane (1,2,3-TMP) as a
co-solvent was added in 15 equivalents, monoolein (2g) was
isolated in 88% yield (entry 6). This solvent allowed better
solubility of the oleic refined oil 12 in the glycerol phase, and
its high boiling point allowed us to perform the reaction in a
sealed reactor at higher temperature (200 °C). In addition,
1,2,3-TMP was recycled after the reaction by evaporation of the
crude under reduced pressure. Finally, with diglycerol as a
solvent and a reactant, the corresponding monoester of digly-
cerol 7g was isolated in 41% yield (entry 7). By performing the
same reaction in 1,2,3-trimethoxypropane, the desired mono-
ester of diglycerol 7g was isolated in 63% yield (entry 8).
Transesterificationa
Conversionc Yieldc
Reductionb
Conversionc Yieldc
(2, %)
Overall isolated
yield (4, %)
Entry (1, %)
(2, %)
(4, %)
1
2
>99 (1a)
>99 (1b)
99 (2a) >99 (2a)
98 (2b) >99 (2b)
82 (4a) 81 (4a)
82 (4b) 80 (4b)
a Experimental conditions: molar ratio methyl valerate/glycerol of 1/40,
BaO/Al2O3 (5 wt%), 100 °C, 16 h. b Experimental conditions: crude
monoglyceride 2 + glycerol, 1 mol% Pd/C (5%), 10 wt% Amberlyst 35,
50 bar H2 pressure, 120 °C, 16 h. c Conversions and yields were
determined by GC/MS analysis and 1H NMR spectroscopy.
Transesterification and reductive alkylation with no
intermediate purification
on a Millipore filter. The crude was then engaged in a steel
autoclave, and the reductive alkylation was performed by
In order to have a process as cheap and environmentally adding 1 mol% Pd/C (5%), 10 wt% Amberlyst 35, under 50 bar
friendly as possible and considering the best conditions found H2 pressure for 16 h. After the reaction, the glycerol monoether
for the transesterification reaction as well as the reductive 4a was obtained in 81% overall yield after the two steps
alkylation reaction with methyl valerate 1a, a short procedure (Table 8, entry 1). This result can be compared to the direct
for the synthesis of the desired 1-O-pentylglycerol ether 4a in etherification of methyl valerate 1a under the same conditions,
two steps with no intermediate purification of monoglyceride in which the corresponding ether was detected in 50% yield
2a was realized. After a first transesterification step catalyzed (Table 1, entry 1). This result was similar to those observed
by 5 wt% of BaO/Al2O3, a molar ratio methyl valerate 1a/gly- when using the CSA as a co-catalyst in the direct etherification
cerol of 1/40, at 100 °C for 16 h, the medium was filtered off reaction of methyl valerate 1a with glycerol, in which the
This journal is © The Royal Society of Chemistry 2013
Green Chem.

View Article Online
Paper
Green Chemistry
To the best of our knowledge, with the reductive alkylation
of carboxylic acids and glycerol that we reported recently, this
is the first catalytic route describing the straightforward direct
etherification of glycerol with these substrates. These two pro-
cesses open an alternative route at industrial scales for the pro-
duction of bio-based surfactants.
Experimental
General
Scheme 7 Transesterification of triolein 12 with glycerol followed by reduction
under H2 pressure with no intermediate purification.
All reagents were used as received from the chemical company.
Glycerol, 99%, Reagentplus® was purchased from Sigma-
Aldrich, diglycerol 80% from TCI, Pd/C (5%) on activated
carbon, reduced and dried (Escat 1431) from Strem Chemicals.
Oleic sunflower refined oil (≥90%) was provided by our indus-
trial partner and was used without further purification. Amber-
lyst 15 dry, Amberlyst 36 dry, Amberlyst 35 dry were bought
from Rohm and Haas and the methyl esters were supplied by
Acros, Sigma-Aldrich, Alfa Aesar and TCI. The BaO/Al2O3 cata-
lyst was prepared by an incipient-wetness impregnation
method.46 Reductive alkylation reactions were performed in a
300 ml steel Parr autoclave equipped with a mechanical stirrer.
1-O-pentylglycerol ether 4a was obtained in 81% yield (Table 1,
entry 8). The same methodology was performed with methyl
hexanoate 1b: after the transesterification step followed by the
reductive alkylation, the 1-O-hexylglycerol monoether 4b was
obtained in 80% yield after the two steps (Table 8, entry 2).
Finally, the two step procedure with no intermediate purifi-
cation was applied on sunflower oleic refined oil 12
(Scheme 7). The best conditions found for the transesterifica-
tion of the starting triglyceride without a co-solvent (Table 7,
entry 5) and the reductive alkylation of monoolein 2g (Table 3,
entry 7) were used in that case. The corresponding 1-O-stearyl-
glycerol monoether 4f was isolated in 34% overall yield after
the two steps.
General procedure for reductive alkylation of glycerol with a
methyl ester or a monoglyceride using H2 as a reducing agent
Thus, the process in two steps could be very interesting
from both environmental and industrial points of view, with
the use of two heterogeneous catalytic systems.
Glycerol (713 mmol, 40 eq.) and methyl ester or α-monoglycer-
ide (17.6 mmol, 1 eq.) were mixed in a 300 ml steel autoclave
at room temperature. CSA or Amberlyst 35 (10 wt%) and Pd/C
(1 mol% Pd) were then added. The autoclave was first flushed
with argon then with hydrogen four times. The solution was
stirred (800 rpm) at 120 °C under 50 bar hydrogen for 16 h.
The reaction mixture was then dissolved in absolute ethanol
and filtered (Millipore Durapore filter 0.01 μm). The solvents
were concentrated under reduced pressure and the organic
products were extracted four times with dichloromethane or
toluene. The crude products were finally purified by silica
column chromatography (eluent: cyclohexane–ethyl acetate =
4 : 1 ∼ 1 : 0 for short alkyl chain lengths; cyclohexane–ethyl
acetate = 9 : 1 ∼ 1 : 2 for long alkyl chain length).
Conclusion
Two new pathways for an easy, cheap and environmentally
friendly route to glycerol monoethers were reported in this
paper. The direct etherification of glycerol with methyl esters
and α-monoglycerides was performed under mild conditions,
without any solvent, a small amount of Pd/C catalyst and a
strong Brønsted acid as a co-catalyst in the case of methyl
esters and an acid ion exchange resin Amberlyst 35 as a co-
catalyst in the case of α-monoglycerides. With methyl esters, an
alternative procedure in two steps was developed: a transesteri-
fication step with glycerol catalyzed by a small amount of a
mixed metal oxide BaO/Al2O3 followed by the reduction of the
General procedure for transesterification of glycerol with
methyl ester or triolein
corresponding α-monoglyceride under optimized conditions. Glycerol (350 mmol, 20 eq.) and methyl ester (17.5 mmol,
The same procedure was successfully applied when oleic sun- 1 eq.) were added in a round bottom flask under an inert
flower refined oil was used as a substrate.
atmosphere (argon). The mixture was heated to temperature
A mechanistic consideration of the reductive alkylation and the mixed metal oxide BaO/Al2O3 was added (5 wt%). After
reaction with methyl esters and the catalytic reduction under 16 h, the reaction mixture was diluted in a minimum of absol-
H2 pressure with monoglycerides was proposed. The results ute ethanol and filtered off (Millipore Durapore filter 0.01 μm).
led us to conclude that the key point in both mechanisms was The solvents were concentrated under reduced pressure and
the formation of a heterogeneous complex between the Pd/C the organic products were extracted three times with dichloro-
surface and a 5-membered cyclic hemi-ortho ester, which methane or toluene. The crude was finally purified by silica
explained the selectivity towards the 1-O-alkylglycerol ether. column chromatography to afford the desired monoglyceride
The catalytic reduction of α-monoglycerides is then certainly (eluent: cyclohexane–ethyl acetate = 4 : 1 ∼ 1 : 0 for short alkyl
the first example of an ester function reduction to its corre- chain length; cyclohexane–ethyl acetate = 5 : 1 ∼ 1 : 2 for long
sponding ether under H2 pressure.
alkyl chain length).
Green Chem.
This journal is © The Royal Society of Chemistry 2013

View Article Online
Green Chemistry
Paper
For the transesterification reactions of triolein with glycerol 19 S. Queste, Y. Michina, A. Dewilde, R. Neueder,
and diglycerol, the reaction was performed in sealed tubes,
W. Kunz and J.-M. Aubry, Green Chem., 2007, 9, 491–
under an inert atmosphere of argon. Monoolein 2g was puri-
499.
fied by column chromatography (silica gel; eluent: cyclo- 20 J. L. García, H. García-Marín, J. A. Mayoral and P. Pérez,
hexane–ethyl acetate = 5 : 1 ∼ 1 : 2) and for the monoester Green Chem., 2010, 12, 426–434.
of diglycerol 7g, eluent was dichloromethane–methanol 99/1 21 S. Pariente, N. Tanchoux and F. Fajula, Green Chem., 2009,
∼ 9/1. 11, 1256–1261.
All the product characterizations (1H NMR, 13C NMR, IR, 22 Y. Gu, A. Azzouzi, Y. Pouilloux, F. Jérôme and J. Barrault,
HRMS) are disclosed in the ESI.†
Green Chem., 2008, 10, 164–167.
23 P. Gaudin, R. Jacquot, P. Marion, Y. Pouilloux and
F. Jérôme, ChemSusChem, 2011, 4, 719–722.
24 J. A. Melero, G. Vicente, G. Morales, M. Paniagua,
J. M. Moreno, R. Roldán, A. Ezquerro and C. Pérez, Appl.
Catal., A, 2008, 346, 44–51.
25 A. M. Ruppert, A. N. Parvulescu, M. Arias, P. J. C. Hausoul,
P. C. A. Bruijnincx, R. J. M. Klein Gebbink and
B. M. Weckhuysen, J. Catal., 2009, 268, 251–259.
26 R. Palkovits, I. Nieddu, C. A. Kruithof, R. J. M. Klein
Gebbink and B. M. Weckhuysen, Chem.–Eur. J., 2008, 14,
8995–9005.
Acknowledgements
The authors warmly thank Sofiprotéol for their financial
support and are grateful for the access to the GC-MS analysis
at the Centre Commun de Spectroscopie de Masse (F. Albrieux,
C. Duchamp and N. Henriques) and NMR facilities at the
Université Lyon 1.
Notes and references
1 G. Cravotto, L. Orio, E. C. Gaudino, K. Martina, D. Tavor 27 S. Bigot, H. Bricout, I. Suisse, A. Mortreux and Y. Castanet,
and A. Wolfson, ChemSusChem, 2011, 4, 1130–1134.
2 Y. Gu and F. Jérôme, Green Chem., 2010, 12, 1127–1138.
3 A. P. Abbott, R. C. Harris, K. S. Ryder, C. D’Agostino,
Ind. Eng. Chem. Res., 2011, 50, 9870–9875.
28 J. M. Lopes, Z. Petrovski, R. Bogel-Lukasik and E. Bogel-
Lukasik, Green Chem., 2011, 13, 2013–2016.
L. F. Gladden and M. D. Mantle, Green Chem., 2011, 13, 29 V. Bethmont, F. Fache and M. Lemaire, Tetrahedron Lett.,
82–90. 1995, 36, 4235–4236.
4 B. Katrynlok, S. Paul, V. Bellière-Baca, P. Rey and 30 Y. Shi, W. Dayoub, G. R. Chen and M. Lemaire, Green
F. Dumeignil, Green Chem., 2010, 12, 2079–2098. Chem., 2010, 12, 2189–2195.
5 M. Pagliaro and M. Rossi, in The Future of Glycerol, 2nd 31 Y. Shi, W. Dayoub, G. R. Chen and M. Lemaire, Tetrahedron
edn, RSC Green Chemistry Book Series, 2010. Lett., 2009, 50, 6891–6893.
6 M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi and 32 (a) M. Sutter, W. Dayoub, Y. Raoul and M. Lemaire, FR Pat.,
C. Della Pina, Angew. Chem., Int. Ed., 2007, 46, 4434–4440.
7 F. Jérôme, Y. Pouilloux and J. Barrault, ChemSusChem,
2008, 1, 586–613.
8 C.-H. Zhou, J. N. Beltramini, Y.-X. Fan and G. Q. Lu, Chem.
Soc. Rev., 2008, 37, 527–549.
2969146, 2012; (b) M. Sutter, W. Dayoub, Y. Raoul and
M. Lemaire, WO 2012080682, 2012.
33 M. Sutter, W. Dayoub, E. Metay, Y. Raoul and M. Lemaire,
ChemSusChem, 2012, 5, 2397–2409.
34 D. E. López, J. G. Goodwin Jr., D. A. Bruce and E. Lotero,
Appl. Catal., A, 2005, 295, 97–105.
9 M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi and
C. Della Pina, Eur. J. Lipid Sci. Technol., 2009, 111, 788–799. 35 S. Banquart, C. Vanhove, Y. Pouilloux and J. Barrault, Appl.
10 A. Behr, J. Eilting, K. Irawadi, J. Leschinski and F. Lindner,
Green Chem., 2008, 10, 13–30.
Catal., A, 2001, 218, 1–11.
36 F. Jérôme, G. Kharchafi, I. Adam and J. Barrault, Green
Chem., 2004, 6, 72–74.
37 A. Corma, S. B. A. Hamid, S. Iborra and A. Velty, J. Catal.,
2005, 234, 340–347.
38 C. A. Ferretti, A. Soldano, C. R. Apesteguía and J. I. Di
Cosimo, Chem. Eng. J., 2010, 161, 346–354.
39 V. K. Díez, C. A. Ferretti, P. A. Torresi, C. R. Apesteguía and
J. I. Di Cosimo, Catal. Today, 2011, 173, 21–27.
11 A. E. Díaz-Álvarez, J. Francos, B. Lastra-Barreira, P. Crochet
and V. Cadierno, Chem. Commun., 2011, 47, 6208–6227.
12 M. Neuss, T. Albers, S. Bruening, A. Ansmann, H. Gondek
and K.-H. Schmid, US Patent 20100261798A1, 2010.
13 N. Shoji and Y. Yuikinaga, EP N° 0624563, Kao corporation,
1994.
14 K. Kozo and N. Shoji, JP 06346092, Kao corporation, 1994.
15 V. M. Arredondo, D. J. Back, P. J. Corrigan, D. P. Kreuzer 40 C. A. Ferretti, C. R. Apesteguía and J. I. Di Cosimo, Appl.
and A. C. Cearley, WO 2007/113776, The Procter & Gamble
Catal., A, 2011, 399, 146–153.
Company, 2007.
16 A. G. Hazra and P. Chatterjee, Ind. Crops Prod., 2008, 27,
39–43.
41 C. A. Ferretti, S. Fuente, R. Ferullo, N. Castellani,
C. R. Apesteguía and J. I. Di Cosimo, Appl. Catal., A, 2012,
413–414, 322–331.
17 I. Katsuhiko and T. Takehiro, JP 2006176692, Kao corpor- 42 Recent, selected articles: (a) C. Shi, Y. Ji, U. M. Graham,
ation, 2006.
G. Jacobs, M. Crocker, Z. Zhang, Y. Wang and T. J. Toops,
Appl. Catal., B, 2012, 119–120, 183–196; (b) C. D. DiGiulio,
V. G. Komvokis and M. D. Amiridis, Catal. Today, 2012,
18 S. Queste, P. Baudin, D. Touraud, W. Kunz and J.-M. Aubry,
Green Chem., 2006, 8, 822–830.
This journal is © The Royal Society of Chemistry 2013
Green Chem.

View Article Online
Paper
Green Chemistry
184, 8–19; (c) B. M. Shakya, M. P. Harold and 43 A. Corma, S. Iborra, S. Miquel and J. Primo, J. Catal., 1998,
V. Balakotaiah, Catal. Today, 2012, 184, 27–42; (d) N. Le 173, 315–321.
Phuc, X. Courtois, F. Can, S. Berland, S. Royer, P. Marecot 44 T. Ebiura, T. Echizen, A. Ishikawa, K. Murai and T. Baba,
and D. Duprez, Catal. Today, 2011, 176, 424–428; Appl. Catal., A, 2005, 283, 111–116.
(e) A. Kumar, M. P. Harold and V. Balakotaiah, J. Catal., 45 N. O. V. Sonntag, J. Am. Oil Chem. Soc., 1982, 59, 795A–
2010, 270, 214–223; (f) C.-W. Yi, J. H. Kwak, C. H. F. Peden, 802A.
C. Wang and J. Szanyi, J. Phys. Chem. C, 2007, 111, 14942– 46 E. Rohart, V. Belliere-Baca, K. Yokota and C. Pitois, Top.
14944.
Catal., 2007, 42–43, 71–75.
Green Chem.
This journal is © The Royal Society of Chemistry 2013