Acid-catalyzed etherification of glycerol with long-alkyl-chain alcohols

Article abstract of DOI:10.1002/cssc.201100129

Rubbing the right way: The direct etherification of glycerol with long-chain alcohols typically suffers from poor contact between the reaction phases. A dodecylbenzene sulfonic acid catalyst enables a better contact between the glycerol and alcohol phases, enhancing the yield of monoalkyl glyceryl ethers and offering a direct route for the synthesis of these surfactants. Copyright

Full text of DOI:10.1002/cssc.201100129

DOI: 10.1002/cssc.201100129
Acid-Catalyzed Etherification of Glycerol with Long-Alkyl-Chain Alcohols
Pierrick Gaudin,[a] Roland Jacquot,[b] Philippe Marion,[b] Yannick Pouilloux,*[a] and FranÅois Jꢀrꢁme*[a]
Surfactants are of great interest to the chemical industry
owing to their numerous applications. In 2003 the worldwide
production volume was estimated at 12 million tonnes,
making surfactants one of organic chemistry’s most important
markets. The synthesis of biobased surfactants has emerged as
a challenging task mainly boosted by the predicted exhaustion
of fossil carbon reserves and growing concerns about global
warming. In this context, the rational design of catalytic pro-
cesses for the direct and selective etherification of glycerol (a
co-product of the vegetable oil industry) with long-alkyl-chain
alcohols is the subject of numerous investigations because the
resulting amphiphilic alkylglycerylethers (1) exhibit a greater
stability than the corresponding monoglycerides in the pres-
ence of water, and (2) can be used as green solvents for cataly-
sis.[1]
and 1-dodecene, showing that the etherification of glycerol
with a long alkyl chain is a very difficult task.
So far the only catalytic route allowing the successful syn-
thesis of monododecyl glyceryl ethers was reported by Lem-
aire and co-workers, who investigated the reductive etherifica-
tion of glycerol with long-alkyl-chain aldehydes under hydro-
gen.[6] Although a 75% yield of monododecyl glyceryl ethers
was obtained in the presence of Pd/C as catalyst and camphor-
sulfonic acid as a co-catalyst, the process is limited by the
price and the availability of decylaldehyde. The direct catalytic
etherification of glycerol with long-alkyl-chain alcohols would
be much more economical and environmentally friendly. So
far, all attempts to catalytically etherify glycerol with long-alkyl-
chain alcohols reported in the literature have failed.
To achieve the successful coupling of glycerol with fatty al-
cohols several issues need to be addressed: (1) The large differ-
ence in polarity between glycerol and fatty alcohols renders
the reaction medium biphasic. Therefore, the catalyst has to
be active at the glycerol/fatty alcohol interface in order to
overcome mass-transfer limitations. (2) The formation of un-
symmetrical ethers is thermodynamically unfavorable. (3) The
very high reactivity of glycerol (owing to the presence of a sec-
ondary hydroxyl group) in acidic conditions may lead to the
formation of a wide range of undesired products, especially in
a biphasic system where the contact with fatty alcohol is ex-
pected to be poor.
To date, the catalytic etherification of glycerol has been ach-
ieved starting from activated alcohols (e.g., tertiobutanol[2] or
benzyl alcohol[3]) catalyzed over different solid acids (e.g.,
cation exchange resins, zeolites, or sulfonated silica). In all of
these processes the corresponding glycerol ethers have been
produced in fair to good yields, but unfortunately they are in-
efficient when starting from a fatty alcohol such as 1-dodeca-
nol.[3a] Indeed, the catalytic etherification of glycerol with less-
activated alcohols, such as aliphatic alcohols, is thermodynami-
cally much more difficult. Fajula and co-workers reported the
catalytic etherification of glycerol with ethanol over various
solid acid catalysts in 2009.[4] A maximum yield of 40% of mon-
oethoxy glyceryl ethers was obtained at 433 K by using sulfo-
nated polystyrene resins and zeolites with a Si/Al ratio of ca.
25. Although this work was a significant step towards new cat-
alytic routes for the selective etherification of glycerol with ali-
phatic alcohols, it was hampered by the formation of very
large amounts of diethylether. In the same year Weckhuysen
and co-workers investigated the acid-catalyzed etherification
of various polyols, including glycerol, with fatty alkenes such
as 1-octene and 1-dodecene.[5] Although good yields were ob-
tained from propylene glycol and ethylene glycol, very low
yields were obtained when starting from 1-octene and glycerol
(<10%). In addition, there was no reaction between glycerol
Herein, we investigate the catalytic activity of various homo-
geneous and heterogeneous catalysts towards the etherifica-
tion of glycerol with long-alkyl-chain alcohols. Under optimized
conditions dodecylbenzene sulfonic acid, a so-called surfac-
tant-combined-catalyst, allowed a better contact between the
glycerol and fatty alcohol phases, resulting in a significant im-
provement of the yield of monododecyl glyceryl ethers. To the
best of our knowledge, this is the first successful example of
the direct etherification of glycerol with fatty alcohols, opening
a new route for the synthesis of biobased surfactants.
In a first set of experiments an equimolar mixture of glycerol
(99% purity) and 1-dodecanol was heated at 1308C for 24 h in
the presence of 10 wt% Amberlyst 70 (A70, corresponding to
1.1 mol% H+). During the reaction water was continuously re-
moved by distillation. Amberlyst 70 was chosen as a reference
solid acid catalyst because of its strong acidity, high thermal
stability (up to 1908C), and high proton exchange capacity
(2.5 mmolgÀ1). The results are summarized in Table 1. Under
these standard conditions, only glycerol was converted (57%,
entry 1) while 1-dodecanol did not react. Glycerol was only
converted to di- (20% yield, mixture of isomers) and triglycerol
(5% yield, mixture of isomers) and the carbon mass balance
(69%) also clearly showed the conversion of glycerol to un-
identified products (presumably acrolein and soluble poly-
mers). An increase of (1) the glycerol/1-dodecanol molar ratio
[a] Dr. P. Gaudin, Prof. Y. Pouilloux, Dr. F. Jꢀrꢁme
Laboratoire de Catalyse en Chimie Organique, Universitꢀ de Poitiers
ENSIP, 40 avenue du recteur Pineau, 86022 Poitiers (France)
Fax: (+33)549453349
E-mail: francois.jerome@univ-poitiers.fr
yannick.pouilloux@univ-poitiers.fr
[b] Dr. R. Jacquot, Dr. P. Marion
RHODIA, Centre de Recherches et Technologies de Lyon
85, rue des Frꢂres Perret. 69192 Saint Fons Cꢀdex (France)
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201100129.
ChemSusChem 2011, 4, 719 – 722
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
719

Table 1. Catalytic etherification of glycerol with 1-dodecanol over A70
Entry
Alcohol
Glycerol/alcohol Total glycerol Alcohol
Monoethers Diglycerol Triglycerol Glycerol carbon
Alkyl alcohol carbon
molar ratio
conv. [%]
conv. [%] yield [%]
yield [%]
yield [%]
mass balance [%] mass balance
[%]
1
2
3[b]
4[d]
5
1-dodecanol
1-dodecanol
1-dodecanol
1-dodecanol
1-butanol
1-pentanol
1-pentanol
1-hexanol
1
4
4
4
4
4
4
4
4
57
36
78
96
17
13
36
11
36
0
5
7
10
26
22
66
13
5
0
5
7
10
26
22
45
13
5
20
22
22
5
4
4
12
4
6
5
3
9
4
0
0
0
0
0
69
90
64[c]
43[c]
94
96
91
100
100
100
100
100
100
100
100
79
6
7[e]
8
100
100
9
1-octanol
[a] Glycerol and 1-dodecanol were heated at 1308C for 24 h in the presence of 10 wt% A70. Conversions and yields were determined by gas chromatogra-
phy using dodecane as internal standard. [b] Reaction performed at 1458C. [c] Tetra-, penta- and hexaglycerol were also detected as minor products. In-
soluble black materials were also produced in a larger extent. [d] Reaction performed at 1608C. [e] Results collected after 96 h.
from 1 to 4 (entry 2), and/or (2) the reaction temperature from
1308C to 1458C and 1608C only resulted in the formation of
monododecyl glyceryl ethers in very low yields (entries 3
and 4. When increasing the reaction temperature the carbon
mass balance was lowered and an insoluble black material was
formed. These results confirm that the etherification of glycerol
with 1-dodecanol is a highly complex reaction and that, in a bi-
phasic glycerol/1-dodecanol system, the A70 solid catalyst in-
teracts only with glycerol.
glycerol was produced as minor side product, in 4% yield.
After 96 h, monopentyl glyceryl ethers were obtained with an
unprecedented maximum yield of 45% (entry 7). Unfortunately
the yield of monopentyl glyceryl ether dropped with pro-
longed reaction time due to (1) subsequent etherification to di-
pentyl glyceryl ethers, and (2) oligomerization of monopentyl
glyceryl ethers.
When starting from 1-hexanol the reaction medium became
turbid. The conversion rate of 1-hexanol was two times lower
than that of 1-butanol and 1-pentanol (Figure 1). After 24 h,
13% 1-hexanol was consumed compared to 25% when start-
ing from 1-butanol and 1-pentanol, indicating that the catalyst
activity dropped significantly with an increase of the alkyl alco-
hol chain length (Table 1, entry 8). The yield of monoalkyl glyc-
eryl ethers was also lowered: after 24 h a monohexyl glyceryl
ethers yield of 13% was achieved, showing that contact be-
tween the glycerol and 1-hexanol phases become more diffi-
cult. However, the yield of diglycerol still remained low (4%).
The reaction medium was biphasic when starting from 1-octa-
nol and 1-dodecanol. Conversion of the alkyl alcohol was very
low while the glycerol conversion was increased (Table 1, en-
tries 2 and 9). Indeed, after 24 h the conversion of 1-octanol
and 1-dodecanol and the yield to the corresponding monoalk-
yl glyceryl ethers remained below 5% while di- and triglycerol
were produced in higher yields (22% yield for 1-dodecanol).
Clearly, in a biphasic system the A70 catalyst interacts more
strongly with the glycerol phase than with the alkyl alcohol
phase, at the expense of the yield of monoalkyl glyceryl ethers.
Notably, no monoalkyl glyceryl ethers were formed when
using other well-known solid acid catalysts such as a sulfonat-
ed mesoporous silica (SBA-SO3H), K-10 montmorillonite, and H-
ZSM-5 zeolite (Si/Al ratio=1000), or homogeneous acid cata-
lysts such as para-toluene sulfonic acid (pTSA) and triflic acid,
further demonstrating the complexity of this reaction (see Sup-
porting Information Table S1).
To find a suitable method for the catalytic etherification of
glycerol with long-alkyl chain alcohols, we next investigated
the influence of the chain length on the yield of monoalkyl
glyceryl ethers (Figure 1). Mixtures of glycerol with either 1-bu-
tanol, 1-pentanol, 1-hexanol, 1-octanol, or 1-dodecanol (molar
ratio 4:1) were heated at 1308C for 24 h in the presence of
10 wt% A70. The reaction medium was monophasic in the
cases of butanol and pentanol, and as expected corresponding
monobutyl glyceryl and monopentyl glyceryl ethers were ob-
tained in yields of 26% and 22% (Table 1, entries 5 and 6). Di-
Figure 1. Catalytic etherification of glycerol with various alkyl alcohols over
A70 (10 wt%). Results are given after 24 h of reaction at 1308C and using a
glycerol/alkyl alcohol molar ratio of 4.
On the basis of this study one may conclude that monoalkyl
glyceryl ethers can be selectively produced over A70 from
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ChemSusChem 2011, 4, 719 – 722

glycerol and alkyl alcohols with a chain length shorter than six
carbon atoms. Contrary to what was observed by Fajula and
co-workers when using ethanol,[4] the starting alkyl alcohols in
this work were selectively converted to the corresponding
monoalkyl glyceryl ethers while dialkyl ethers where not
formed, facilitating the isolation of the corresponding mono-
glyceryl alkyl ethers. This result stems from (1) dilution of the
alkyl alcohol in the glycerol phase (in the case of monophasic
system), and (2) the high affinity of the A70 resin for the glyc-
erol phase.
entry 2). This relatively large amount of DBSA is consistent
with existing literature related to catalysis in biphasic water/oil
mixtures. Interestingly, the formation of monododecyl glyceryl
ethers was favored when using 20 mol% of DBSA: a yield of
25% was achieved within 3 h. The emulsification of the reac-
tion medium also resulted in a decrease of the production of
side product (di-dodecylether), from 62% to 19%. As men-
tioned above, the monododecyl glyceryl ethers yields dropped
with prolonged reaction time due to oligomerization and/or
subsequent etherification with 1-dodecanol. This also applies
to 1-octanol, as in the presence of 20 mol% of DBSA the corre-
sponding monooctyl glyceryl ethers were isolated with a maxi-
mum yield of 24% yield (compared to 5% over A70), offering
the first route for the etherification of glycerol with long-alkyl-
chain alcohols.[10]
To overcome mass transfer problems particular attention has
to be paid to the design of the catalyst. Ideally, a catalyst
would have to exhibit some sulfonic sites and also be able to
operate at the glycerol/1-dodecanol interface. Kobayashi and
co-workers have extensively studied the performances of do-
decylbenzene sulfonic acid (DBSA) for catalysis in a biphasic
water/oil mixture.[7] A recent Review related to micellar cataly-
sis in organic reactions is available.[8] In these works, DBSA acts
not only as acid catalyst but also as emulsifier. We have recent-
ly reported that these surfactant-combined-catalysts can be
successfully employed when using glycerol, opening a new
strategy for our purpose.[9] Hence, we investigated the etherifi-
cation of glycerol with 1-dodecanol at 1308C in the presence
of DBSA. Using 2 mol% of DBSA, the reaction medium was still
biphasic. DBSA strongly interacts with the 1-dodecanol phase
in these conditions, leading to a significant enhancement of
the 1-dodecanol conversion, to 72% (Table 2, entry 1). On the
other hand, the glycerol conversion was lowered (26%). Impor-
tantly, compared to other acid catalysts tested the higher affin-
ity of DBSA for the 1-dodecanol phase unavoidably induces
the formation of didodecyl ether (62% yield). Nevertheless, uti-
lization of this Brønsted-acid surfactant-combined-catalyst con-
tributed to increase the monododecyl glyceryl ethers up to
10%.
Even though DBSA is a very cheap acid catalyst, the utiliza-
tion of 20 mol% of DBSA is a drawback. Therefore, with the
aim of decreasing the catalytic amount of DBSA to at most
10 mol%, while maintaining good interaction between the
glycerol and 1-dodecanol phases we studied the possible use
of an organic solvent. The choice of the organic solvent was
limited because the solvent should be able to dissolve glycerol
as well 1-dodecanol in reasonable amounts. We focused on
the use of dimethylsulfoxide (DMSO), diglyme, 1,4-dioxane,
and sulfolane. Unless noted otherwise all reactions were per-
formed in an autoclave (autogeneous pressure) at 1308C start-
ing from a glycerol/1-dodecanol molar ratio of 4, in the pres-
ence of 10 mol% of H+ and stopped after 24 h. To highlight
the effect of DBSA on the catalytic etherification of glycerol
with 1-dodecanol, we first used A70 as a reference acid cata-
lyst. In DMSO, diglyme, and 1,4-dioxane, 1-dodecanol mostly
remained unaltered and only glycerol was converted (20%,
65%, and 73%, respectively; Table 2, entries 4–6). Surprisingly,
neither di- nor triglycerol were detected in DMSO and diglyme,
and glycerol was only converted to unidentified products. In
1,4-dioxane, the formation of about 10% diglycerol was de-
tected (entry 6). The reaction was very slow in sulfolane: 60 h
were necessary (versus 24 h without organic solvent) for a
glycerol conversion of 38%
To further improve the contact between the glycerol and 1-
dodecanol phases, we increased the amount of DBSA until a
monophasic system was obtained. Up to 20 mol% of DBSA
was necessary to observe a monophasic system (Table 2,
(entry 7). This may be attributed
Table 2. Catalytic etherification of glycerol with 1-dodecanol in the presence of an organic solvent
to dilution of the reaction
medium. However, the reaction
selectivity was higher since the
corresponding
monododecyl
glyceryl ethers were produced
with 10% yield. Notably, the
yield of di-dodecylether re-
mained lower than 10%, indicat-
ing that in sulfolane the A70 cat-
alyst still reacts with difficulty
with 1-dodecanol. When the re-
action temperature was raised
from 1308C to 1608C in sulfo-
lane, the contact between glyc-
erol and 1-dodecanol was im-
proved and the yield of mono-
dodecyl glyceryl ethers increased
Entry
Catalyst
Solvent
Glycerol
conv. [%]
Dodecanol
conv. [%]
Monoether
yield [%]
Diglycerol
yield [%]
Didodecylether
yield [%]
1
2
3
4
5
6
7
8
9
DBSA
DBSA[c]
A70
A70
A70
–
–
–
26
59
36
20
65
73
38
78
72
72
50
5
0
0
<10
17
28
68
10
25
5
0
0
9
9
22
0
62
19
0
0
0
0
7
8
38
DMSO
diglyme
1,4-dioxane
sulfolane
Sulfolane
sulfolane
0
A70
0
10
11
11
14
A70[b]
A70[c]
DBSA
10
20
30
[a] Conversions and yields were determined by gas chromatography using dodecane as internal standard,
0.1 equiv of H+ was used for catalytic experiments. [b] Results collected after 60 h of stirring at 1308C. [c] Reac-
tion performed at 1608C.
ChemSusChem 2011, 4, 719 – 722
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721

medium in ethanol followed by a treatment with a A26 resin was
necessary prior to purification over silica gel. This procedure re-
moves the DBSA, which hinders the isolation of the monododecyl-
glyceryl ethers over silica gel.
from 10% to 20%, while the formation of diglycerol side prod-
uct remained similar (11%; entries 7–8). However, at 1608C the
carbon mass balance on glycerol is low (40%, see Table 1), in-
dicating the formation of unidentified glycerol-based products.
Inspired by the results described above, we investigated the
possible use of DBSA in sulfolane. As expected the reaction
rate was higher in the presence of DBSA; mostly 70% conver-
sion of glycerol and 1-dodecanol was observed after 24 h
(compared to 38% conversion of glycerol after 60 h of reaction
over A70; entry 9). Interestingly the use of DBSA increased the
yield of monododecyl glyceryl ethers to an unprecedented
30%, further demonstrating the great potential of surfactant-
combined-catalyst for the catalytic etherification of glycerol
with 1-dodecanol.
Acknowledgements
The authors are grateful to the French Ministry of Research, the
CNRS, and RHODIA for their financial supports. P.G. is also grate-
ful to ADEME, RHODIA and the Rꢀgion Poitou-Charentes for fund-
ing his Ph.D. grant.
Keywords: catalysis · etherification · fatty alcohols · glycerol ·
In conclusion, we show that over A70 aliphatic alcohols with
a chain length shorter than six carbon atoms are selectively
converted into the corresponding monoalkyl glyceryl ethers
with maximum yields of 45%. When starting from 1-octanol
and 1-dodecanol the reaction medium becomes biphasic, in-
ducing mass transfer problems. A surfactant combined-catalyst,
DBSA, allows emulsification of the reaction medium, resulting
in the formation of monododecyl glyceryl ethers with 30%
yield. This work is the first successful example of direct etherifi-
cation of glycerol with long-chain alcohols such as 1-octanol
and 1-dodecanol, thus providing a new and straightforward
route for the design of biobased surfactants.
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Experimental Section
In a typical procedure, glycerol (21 mmol) and the corresponding
alcohols (5.3 mmol) were mixed together and heated for 24 h at
1308C in the presence of the desired acid catalysts (0.1 equiv H+).
During the reaction water was continuously removed by distilla-
tion. The reaction progress was monitored by gas chromatography.
Prior to analysis, the sample was silylated as follows: to the sample
(30 mg) was added 410 mL of pyridine, 210 mL of hexamethyldisila-
zane, and 110 mL of trimethylchlorosilane, and the resulting mixture
was stirred at room temperature for 10 min. Then, the solution was
filtered in order to remove the pyridinium salts before injection.
At the end of the reaction, the crude was directly purified over
silica gel using heptane/ethylacetate (70:30) as eluent. As an alter-
native, products of the reaction could also be first extracted from
the glycerol phase by addition of ethyl acetate prior to purification
over silica gel. In the case of DBSA, dilution of the reaction
[10] Data on 1-octanol are not reported in Table 2 because of overlapping
peaks in the gas chromatogram. We prefer to provide the isolated
yields of monooctyl glyceryl ethers. See the Experimental Section for
more information on the purification of the glyceryl ethers.
Received: March 8, 2011
Revised: April 8, 2011
Published online on May 17, 2011
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ChemSusChem 2011, 4, 719 – 722