Selective synthesis of 1-O-Alkyl(poly)glycerol ethers by catalytic reductive alkylation of carboxylic acids with a recyclable catalytic system

Article abstract of DOI:10.1002/cssc.201200447

(Poly)glycerol monoethers were synthesized in good yield and selectivity by the catalytic reductive alkylation of glycerol, diglycerol, and triglycerol with readily available, cheap and/or bio-sourced carboxylic acids. The reaction was catalyzed by 1 mol % of Pd/C under 50 bar H₂ using an acid ion-exchange resin as a recyclable cocatalyst. The catalytic system was recycled several times, and a mechanism is proposed for this transformation.

Full text of DOI:10.1002/cssc.201200447

DOI: 10.1002/cssc.201200447
Selective Synthesis of 1-O-Alkyl(poly)glycerol Ethers by
Catalytic Reductive Alkylation of Carboxylic Acids with
a Recyclable Catalytic System
Marc Sutter,[a] Wissam Dayoub,[a] Estelle Mꢀtay,[a] Yann Raoul,[b] and Marc Lemaire*[a]
(Poly)glycerol monoethers were synthesized in good yield and
selectivity by the catalytic reductive alkylation of glycerol, di-
glycerol, and triglycerol with readily available, cheap and/or
bio-sourced carboxylic acids. The reaction was catalyzed by
1 mol% of Pd/C under 50 bar H2 using an acid ion-exchange
resin as a recyclable cocatalyst. The catalytic system was recy-
cled several times, and a mechanism is proposed for this trans-
formation.
Introduction
Surfactants are one of the most important families of chemi-
cals with multiple applications that range from detergent and
cleaner formulations, personal care, and pharmaceuticals to
textile, chemical, and food industries.[1] The global surfactant
market volume is more than 12 million tonnes per year with
an expected annual growth of 3–4%. Consequently, it repre-
sents one of the most important markets for organic chemi-
cals.[1] As the use of agricultural resources for industrial purpos-
es will be one of the major challenges of this century with the
depletion of fossil carbon reserves, bio-based surfactants will
become increasingly important.[1,2]
results were recently obtained by Jꢀrꢁme et al., and monopen-
tylglycerol ether was prepared in a high yield of 45% by using
Amberlyst A70 at a high temperature (1608C) with a long reac-
tion time (96 h).[26]
More than 15 years ago, in the search for new catalytic path-
ways for the synthesis of ethers, we reported an eco-friendly
method starting from linear alcohols and carbonyl compounds
[27]
with Pd/C as the catalyst under H2.
This process was adapt-
ed to polyfunctional alcohols such as glycerol in some exam-
ples, but at high temperature and H2 pressure, which resulted
in a low selectivity for the corresponding 1-O-alkylglycerol
ethers.[28]
In the context of sustainable chemistry, the increased pro-
duction of biodiesel has led to a large availability of glycerol as
a coproduct in the transesterification reaction of vegetable oils
and animal fats with methanol.[3,4] Consequently, new and effi-
cient transformations of glycerol into higher value-added
chemicals are needed to support the viability of the biodiesel
activity.[4–12] Glycerol monoethers (GMEs) are one of the most
valuable derivatives of glycerol with many applications in di-
verse domains. These amphiphilic compounds are the subject
of a number of patents and publications[13] because of their
surfactant,[14] antimicrobial,[15] and antitumor properties,[16] and
because they are also intermediates for the production of
chemicals such as dioxolanes.[17] In this context, the develop-
ment of new processes for the direct and selective etherifica-
tion of glycerol with a compound that contains a long alkyl
chain is of considerable interest.
The only catalytic route that allows the successful synthesis
of GMEs by reductive alkylation was reported by our group.[29]
The synthesis of linear 1-O-alkylglycerol- and diglycerol mono-
ethers was achieved by a one-step catalytic reductive alkyla-
tion of glycerol and diglycerol with a long-chain aldehyde or
ketone in the presence of Pd/C as a catalyst and a Brønsted
acid as a cocatalyst. Thus, linear alkyl(di)glycerol monoethers
were obtained in both high yield and selectivity. Unfortunately,
there is no industrial access to aldehydes and ketones from re-
newable starting materials.
To prepare glycerol monoethers by an eco-efficient process,
we searched for bio-sourced, inexpensive, and readily available
compounds, that is, carboxylic acids. One part of this family
[a] M. Sutter, Dr. W. Dayoub, Dr. E. Mꢀtay, Prof. M. Lemaire
Laboratoire de Catalyse, Synthꢁse et Environnement (CASYEN)
Institut de Chimie et Biochimie Molꢀculaires et
Supramolꢀculaires (ICBMS), CNRS. UMR5246
Traditionally, alkylglycerol ethers are prepared by the Wil-
liamson ether synthesis, despite the need for a strong base
and the formation of a stoichiometric amount of salts as by-
products.[14a,18–20] The catalytic etherification of glycerol has
been achieved from alcohols or alkenes over acid cata-
lysts.[21–25] A study of these synthesis methods reveals a poor
selectivity of the reaction for the corresponding glycerol mon-
oethers. Starting from activated alcohols, GMEs were prepared
in good yield, but unfortunately this process was inefficient
with aliphatic alcohols.[24] The acid-catalyzed etherification of
glycerol with alcohols was improved with ethanol.[25] The best
Universitꢀ Lyon 1, Bꢂtiment Curien-CPE, 38 ꢀtage
43 Bd du 11 Novembre 1918, 69622, Villeurbanne Cedex (France)
Fax: (+33)472-431-408
E-mail: marc.lemaire.chimie@univ-lyon1.fr
[b] Dr. Y. Raoul
Sofiprotꢀol
11, rue de Monceau, CS 60003, 75378 Paris Cedex 08 (France)
Fax: (+33)147-230-288
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201200447.
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M. Lemaire et al.
comes from the biodiesel industry. Most are inexpensive and
available on a large scale.[30] Moreover, these starting materials
have never been used for the synthesis of GMEs.
As part of our continued interest in the reductive alkylation
of glycerol, diglycerol, and triglycerol, we performed an exten-
sive study of the reaction with linear and branched carboxylic
acids and the influence of all reaction parameters. This is the
first successful example of the direct etherification of glycerol
with these bio-sourced and/or readily available substrates by
using a recyclable catalytic system (Scheme 1).
Scheme 2. Reductive alkylation of a carboxylic acid 1 with glycerol under
optimized conditions.
GME 2a in 68% isolated yield (entry 1). Similarly, the reaction
of glycerol with carboxylic acids that contain a short alkyl
chain, valeric acid (1b) and hexanoic acid (1c), allowed the for-
mation of ethers 2b and 2c in 73 and 72% isolated yields, re-
spectively, with a total conversion of the starting material to
the expected GMEs (entries 2 and 3).
The reactivity of acids that contain a longer alkyl chain was
studied. The reaction of octanoic acid (1d) with glycerol afford-
ed GME 2d in 57% isolated yield (entry 4). In this case, the b re-
gioisomer 3d was isolated and characterized. With decanoic
acid (1e), dodecanoic acid (1 f), myristic acid (1g), palmitic
acid (1h), and stearic acid (1I), the etherification reaction af-
forded ethers 2e, 2 f, 2g, 2h, and 2i in 46, 42, 41, 28, and
29% isolated yields, respectively, with excellent selectivities for
the glycerol monoethers (entries 5–9). However, the yields of
the dialkylated glycerol ethers increased with the length of the
alkyl chain. These observations could be explained by the reac-
tion medium, which became biphasic in these cases. Indeed,
after the first etherification, the monoalkylated product, which
becomes insoluble in glycerol, probably migrates into the acid
phase where the second alkylation occurs. Consequently, the
yields for 1-O-alkylglycerol monoethers decreased. When start-
ing from branched acids such as isovaleric acid (1j), 2-methyl-
valeric acid (1k), and 2-ethylhexanoic acid (1l), the correspond-
ing GMEs 2j, 2k, and 2l were isolated in good yields of 72, 71,
and 47%, respectively (entries 10–12). 2-Ethylhexylglycerol
monoether (2l) is widely used as an additive in cosmetics and
sold as Sensiva SC 50.[31] In all these examples, the selectivity
between 1-O-alkylglycerol monoethers 2 and 2-O-alkylglycerol
monoethers 3 was approximately 4:1, independent of the alkyl
chain length and/or the presence of ramification.
Scheme 1. General scheme for the synthesis of glycerol, diglycerol, and tri-
glycerol monoethers directly from glycerol, diglycerol, or triglycerol and car-
boxylic acids with a recyclable catalytic system.
In this paper, we first describe the scope of this methodolo-
gy and experiments performed to propose a mechanism. Next,
to collect the results summarized in Table 1, the experimental
conditions were optimized by using valeric acid as a model
substrate and glycerol. Therefore, different reaction parameters
were studied for their influence on the progress of the reduc-
tive alkylation. Finally, the possibility to recycle the catalytic
system was demonstrated.
In the presence of cyclic substrates such as cyclobutanoic
acid (1m), cyclopentanoic acid (1n), and cyclohexanoic acid
(1o), the reductive alkylation reaction afforded the correspond-
ing GMEs 2m, 2n, and 2o in 74, 73, and 71%, respectively (en-
tries 13–15). The cyclohexylglycerol monoethers present an an-
timicrobial activity,[15a] whereas the cyclopentyl and cyclobutyl
ethers are new products.
Results and Discussion
To test the versatility of our approach, we finally applied
these optimized conditions to the reductive alkylation of digly-
cerol with 1c, 1d, and 1e, and the desired diglycerol mono-
ethers 8c, 8d, and 8e were obtained in 67, 65, and 38% isolat-
ed yields, respectively, with an excellent conversion of the
starting acids (entries 16–18). However, the selectivity between
the 1-O-alkyldiglycerol monoethers 8 and 2-O-alkyldiglycerol
monoethers could not be determined.
Optimized conditions were used for the synthesis of linear or
branched saturated 1-O-alkyl(di)glycerol monoethers by the
catalytic reductive alkylation of glycerol and diglycerol. Carbox-
ylic acid (Scheme 2, Table 1) was added to glycerol in a 1:40
molar ratio. The reaction was performed under 50 bar H2 in the
presence of 1 mol% of Pd/C and 10 wt% of an acid ion-ex-
change resin Amberlyst 35 cocatalyst with a stirring speed of
800 rpm (revolutions per minute).
Finally, the reaction with triglycerol and 1 f afforded the cor-
responding triglycerol monoether 13 f in 33% isolated yield
(entry 19). These results clearly demonstrate that the process
As can be seen from the results in Table 1, the etherification
of butyric acid (1a) with glycerol afforded the corresponding
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Catalytic Synthesis of 1-O-Alkyl(poly)glycerol Ethers
Table 1. Etherification of mono-, di-, and triglycerol with different carboxylic acids under optimized conditions.[a]
Entry
Substrate (1)
Alcohol/solvent
Product
Conversion
of 1 [%][b]
Selectivity[c]
Isolated yield of
1-O-alkylether [%]
1
2
3
1a
1b
1c
glycerol
glycerol
glycerol
2a
2b
2c
>99
>99
>99
82:18
81:19
83:17
68
73
72
4
1d
1e
1 f
1g
1h
1i
glycerol
glycerol
glycerol
glycerol
glycerol
glycerol
glycerol
glycerol
2d
2e
2 f
2g
2h
2i
>99
>99
>99
>99
>99
>99
>99
>99
80:20
81:19
82:18
80:20
80:20
81:19
83:17
84:16
57
46
42
41
28
29
72
71
5
6
7
8
9
10
11
1j
2j
1k
2k
12
13
14
1l
glycerol
glycerol
glycerol
2l
>99
>99
>99
84:16
86:14
88:12
47
74
73
1m
1n
2m
2n
15
1o
glycerol
2o
>99
84:16
71
16
17
1c
diglycerol
diglycerol
8c
>99
>99
nd[d]
nd[d]
67
65
1d
8d
18
19
1e
1 f
diglycerol
triglycerol
8e
>99
>99
nd[d]
nd[d]
38
33
13 f
[a] Experimental conditions: molar ratio substrate/(poly)glycerol 1:40, 1 mol% Pd/C, 10 wt% Amberlyst 35, 50 bar H2, 1208C, stirring speed=800 rpm, 16 h.
[b] Conversions were determined by GC–MS and 1H NMR spectroscopy. [c] Selectivity between 1-O- and 2-O-alkyl(poly)glycerol monoethers. [d] Selectivity
between 1-O- and 2-O-alkyl(poly)glycerol monoethers could not be determined.
opens a route to a wide range of nonionic surfactants, with dif-
ferent hydrophilic–lipophilic balances as well as biological
properties.
and 8:1. This difference may induce the formation of another
intermediate. Therefore, to understand the mechanism, glycer-
ol was replaced by other alcohols. All the experiments were
performed with 1b, as this results in a homogeneous reaction
medium that overcomes mass transfer problems (Scheme 3).
The experiments were performed with 1b and 1-propanol,
a linear, saturated alcohol. The first hypothesis was the possi-
ble formation of an enol ether by the dehydration of the corre-
sponding hemiacetal allowed by the reduction of the carboxyl-
ic acid in aldehyde. Thus, a propanol/valeric acid molar ratio of
40:1 was reacted with 1 mol% of Pd/C (5%) and 10 wt% of
Mechanistic considerations
The previous method performed with aldehydes reveals selec-
tivity towards 1-O-alkylglycerol monoethers 2 and 2-O-alkylgly-
cerol monoethers 3 up to 25:1,[29] and the mechanism pro-
posed in this case supposed the formation of an acetal as an
intermediate. In this study, the selectivities are between 4:1
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As expected, all the substrate
was converted to the corre-
sponding ethers 2r and 3r, and
only traces of esters 4r and 5r
were observed. As seen from
the results in Table 3, the lack
of selectivity between a and
b ethers with 1,2-propanediol
and 1,2-butanediol (entries 1
and 3) indicates that the third
hydroxyl group of the glycerol
plays a crucial role. Coordina-
tion to Pd could explain the
higher selectivity toward the
primary ether. Indeed, with glyc-
erol, the selectivity of the reac-
tion was clearly directed to the
Scheme 3. Etherification of glycerol with valeric acid with all identified products formed under nonoptimized
conditions.
camphorsulfonic acid (CSA) at 1408C for 16 h under 50 bar H2
without solvent.
corresponding monoether 1-O-pentylglycerol (2b), which was
observed in 80% GC yield, whereas the monoether 2-O-alkyl-
glycerol (3b) was observed with 18% GC yield (entry 4).
The proposed mechanism for this transformation is given in
Scheme 4. First, CSA catalyzes the addition of glycerol onto the
No H2 was consumed at the end of the reaction, and the
corresponding propyl ester 10b was obtained in 80% GC yield
(Table 2, entry 1). In this case, no propyl ether 9b was ob-
served. This indicated that the reductive alkylation of a primary
alcohol cannot occur under these conditions and that an enol
ether is not an intermediate in the reaction. It was therefore
necessary to have a cyclic intermediate, such as a hemi-ortho
ester.
Table 2. Etherification of 1b with 1-propanol and 1,3-propanediol.[a]
The reaction was repeated under the same conditions, but
propanol was replaced by 1,3-propanediol (entry 2). Even if all
the starting material was converted, the reductive alkylation af-
forded the desired ether 9c in a low 6% GC yield, whereas the
corresponding ester 10c was obtained in 94% GC yield
(entry 2). This indicated that the cyclic intermediate is not
a six-membered cyclic hemi-ortho ester, but rather a five-mem-
bered cyclic one.
Entry
Alcohol/solvent
Conversion
of 1b [%]
GC yield [%]
ether 9
ester 10
1
2
1-propanol
1,3-propanediol
80
>99
0 (9b)
6 (9c)
80 (10b)
94 (10c)
Based on this hypothesis, the etherification reaction was
then performed with 1,2-propanediol (Table 3, entry 1) under
the conditions described above. As expected, the reductive al-
kylation afforded a mixture of primary ether 2p and
secondary ether 3p, in 32 and 36% GC yield, respec-
[a] Experimental conditions: 1b/alcohol 1:40, 1 mol% Pd/C (5%), 10 wt%
CSA, 50 bar H2, 1408C, 16 h.
tively. However, 31% of esters 4p and 5p were still
detected. Thus, this result shows that the intermedi-
ate in the reaction seems to be a five-membered
cyclic hemi-ortho ester as 70% of ethers were detect-
ed. To confirm this, two new experiments were per-
formed with 1,2-diols. With ethylene glycol, the cor-
responding monoether 2q was obtained in a low GC
yield of 49% (entry 2). This reduced yield could be
explained by the lower nucleophilicity of the ethyl-
ene glycol hydroxyls compared to those of 1,2-pro-
panediol owing to the positive inductive effect of
the methyl group. Indeed, a more nucleophilic hy-
droxyl group coordinates with the Pd surface more
easily. Therefore, with the aim of increasing the ether
yield, 1,2-butanediol was chosen as the starting ma-
terial because of the higher positive inductive effect
of its ethyl group (entry 3).
Table 3. Etherification of 1b with diols and glycerol[a]
Entry Alcohol/solvent Conversion GC yield [%]
Selectivity
(2/3)
of 1b [%]
ether
ether
esters
4+5
2
3
1
2
3
4
1,2-propanediol >99
32 (2p) 36 (3p) 31 (4p+5p) 47:53
1,2-ethanediol
1,2-butanediol
glycerol
>99
>99
>99
49 (2q)
–
51 (4q)
1 (4r+5r)
–
52 (2r) 47 (3r)
80 (2b) 18 (3b)
52:48
2 (4b+5b) 81:19
[a] Experimental conditions: 1b/alcohol 1:40, 1 mol% Pd/C (5%), 10 wt% CSA, 50 bar
H2, 1408C, 16 h.
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Catalytic Synthesis of 1-O-Alkyl(poly)glycerol Ethers
Scheme 4. Proposed mechanism for the etherification reaction of glycerol with a carboxylic acid.
carbonyl group of the carboxylic acid 1. The resulting inter-
mediate 11 can be dehydrated to form monoglyceride 4. The
formation of this glycerol ester is reversible. Based on previous
observations, the selective cleavage of the primary or secon-
dary CÀO bond is probably promoted by Pd. More precisely,
a complex between Pd/C and a five-membered cyclic hemi-
ortho ester 12 could be formed after the dehydration of 11.
Thus, the cleavage of the secondary CÀO bond is easier than
that of the primary one owing to assistance from the free hy-
droxyl group that coordinates the Pd. This type of assistance
was reported by Fan et al. for the isomerization of alkenes.[33]
Finally, the 1-O-alkylglycerol monoether 2 is obtained by the
hydrogenolysis of 12.
corresponding GMEs increased (entries 2–4). The best selectivi-
ty for glycerol monoethers was obtained with 50 bar H2 with
80 and 18% for the a-ether 2b and b-ether 3b, respectively.
Only traces of the glycerol monoesters and dialkylated glycerol
ethers 6b and 7b were observed (entry 4).
At a higher H2 pressure of 60 bar, the selectivity for the de-
sired GME 2b remained unchanged (entry 5). From an industri-
al point of view, 50 bar H2 is a relatively low pressure, which is
easy to apply.
Table 4. Etherification of 1b with glycerol at different H2 pressures.[a]
Effect of H2 pressure
Hydrogenation of carboxylic acids is usually performed under
high pressure. Therefore, the effect of H2 pressure was studied.
The etherification reaction of glycerol was realized in the pres-
ence of a small amount of Pd/C (1 mol%) with 10 wt% of CSA
in a molar ratio of acid/glycerol of 1:40 at 1408C for 16 h. The
results are given in Table 4. The first experiment was per-
formed at 20 bar H2. Under these conditions, a complete con-
version of the starting acid afforded the ethers 2b and 3b in
61% overall yield with a selectivity of 83:17 (entry 1). The acidi-
ty of the medium as well as an insufficient H2 pressure could
explain the formation of esters 4b and 5b in 38% overall
yield. At higher pressures, the selectivity of the reaction for the
Entry H2 pressure Conversion GC yield [%]
Selectivity
(ethers/
4b+5b esters)
[bar]
of 1b [%]
ether ether esters
2b
3b
1
2
3
4
5
20
30
40
50
60
>99
>99
>99
>99
>99
51
62
70
80
81
10
15
16
18
18
38
21
11
2
63:37
79:21
89:11
98:2
1
99:1
[a] Experimental conditions: valeric acid/glycerol 1:40, 1 mol% Pd/C (5%),
10 wt% CSA, 1408C, 16 h.
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Effect of temperature
Table 6. Etherification of 1b with glycerol at different 1b/glycerol molar
ratios.[a]
To design a process that is as competitive as possible while
using the optimum H2 pressure defined with the model sub-
strate, the effect of temperature was studied. Consequently,
the reductive alkylation reactions were performed with con-
stant Pd/C and acid cocatalyst amounts, H2 pressure, and glyc-
erol/1b ratio. The temperature was increased by increments of
208C. The results are given in Table 5, the best of which was
Table 5. Etherification of 1b with glycerol at different temperatures.[a]
Entry
Ratio
Conversion GC yield [%]
ether ether esters
1b/glycerol of 1b [%]
diethers
4b+5b 6b+7b
2b
3b
1
2
3
4
5
6
1:10
1:20
1:30
1:40
1:50
1:60
>99
>99
>99
>99
>99
>99
65
67
74
80
79
81
15
17
16
18
18
18
6
5
4
2
3
1
9
7
5
<1
<1
<1
Entry
T
[8C]
Conversion
of 1b [%]
GC yield [%]
Selectivity
(ethers/
esters)
ether
ether
esters
4b+5b
2b
3b
1
2
3
4
100
120
140
160
79
>99
>99
>99
52
81
80
50
14
19
18
12
10
0
2
87:13
100:0
98:2
[a] Experimental conditions: 1 mol% Pd/C (5%), 10 wt% CSA, 50 bar H2,
1408C,16 h.
29
68:32
[a] Experimental conditions: 1b/glycerol 1:40, 1 mol% Pd/C (5%), 10 wt%
1:60, the results remained unchanged, and the corresponding
alkylglycerol monoethers were obtained in excellent yields (en-
tries 5 and 6). Therefore, the substrate/glycerol ratio retained
for further experiments was 1:40.
CSA, 50 bar H2, 16 h.
obtained at 1208C with a total conversion of 1b to ethers 2b
and 3b and no production of esters 4b and 5b (entry 2). Simi-
lar ratios of the GMEs 2b and 3b were observed at 1408C
(entry 3). At a lower temperature (1008C), the conversion of
1b was incomplete, and the selectivity for the ethers was
lower (entry 1). At a higher temperature (1608C), the reaction
led to byproducts with a low selectivity for the glycerol mono-
ethers (entry 4). Therefore, 1208C was chosen for subsequent
experiments.
Catalyst screening and amount of catalyst
The cost of a process is often linked to the nature and quantity
of the catalyst used. Based on our previously optimized condi-
tions for the preparation of (di)glycerol monoethers, the nature
of the metal and its support was also investigated. In the previ-
ous publication dealing with the etherification of glycerol with
aldehydes and ketones, our group proposed that an additional
acid in the medium was responsible for the reduction of the
intermediates, that is, acetals.[29] This was also mentioned by
Kita et al., who reported that acidic treatment of Pd/C was re-
quired to promote the activity of the immobilized Pd catalyst
for the etherification of linear primary alcohols.[34] In addition,
Marecot et al. demonstrated that the support acidity of a Pd/C
catalyst allowed the formation of the intermediates in the re-
ductive alkylation of octanal with butanol.[35] We therefore first
thought that an acid cocatalyst in the medium would be un-
necessary because of the acidity of the starting valeric acid 1b.
The reductive alkylation of the model substrate 1b with glycer-
ol was performed firstly in a 1:40 ratio at 50 bar H2 and 1408C
for 16 h with a supported metal catalyst, but without an acid
cocatalyst (Table 7).
Effect of the substrate/glycerol ratio
After studying the effects of H2 pressure and temperature, the
1b/glycerol molar ratio was considered to determine the maxi-
mum concentration of substrate in the medium that mini-
mized the formation of byproducts, notably the quantity of di-
alkylglycerol ethers 6b and 7b (Scheme 3). After several ex-
periments at different concentrations, the best conditions were
defined with a low 1b/glycerol ratio (Table 6). At a 1:10 molar
ratio of 1b/glycerol, the reaction afforded the corresponding
monoether 2b in only 65% GC yield (entry 1). Several byprod-
ucts were identified, especially the dialkylated compounds 6b
and 7b, which were detected in 9% GC yield. As expected, the
quantity of byproducts decreased with lower 1b/glycerol
molar ratios (entries 2 and 3). Under dilute reaction conditions
(1:40) the amount of byproducts decreased and the reductive
alkylation reaction afforded the desired GMEs 2b and 3b in
98% overall GC yield. Only traces of dialkylated glycerol ethers
were detected (entry 4). With higher molar ratios of 1:50 and
From the results in Table 7, we see that with 1 mol% Pd/C
(5%), a small amount of GMEs was obtained (14%) with a con-
version of the starting material of 51% (entry 1). The main
products were the monoglycerides 4b and 5b, detected in
37% GC yield. The nature of the support was then changed.
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Catalytic Synthesis of 1-O-Alkyl(poly)glycerol Ethers
(entry 12). With 1 mol% of Rh/C and 10 wt% of CSA, the GC
yield of the desired product was 42% (entry 13), which slightly
improved to 58% when 1 mol% of Ru/C was used as catalyst
with 10 wt% of CSA as the cocatalyst (entry 14). Finally, the
best results were obtained with 1 mol% of Pd/C and 10 wt%
of CSA. The reductive alkylation of glycerol with 1b afforded
the desired GMEs 2b and 3b in an excellent overall GC yield
of 98%, and only traces of the undesired monoglycerides 4b
and 5b were detected (entry 15). Therefore, we chose 10 wt%
of acid cocatalyst in subsequent experiments.
Table 7. Catalyst screening.[a]
Entry Catalyst
CSA
Conversion GC yield [%]
ether ether esters
[wt%] of 1b [%]
2b
3b
4b+5b
1
2
3
4
5
6
7
8
1 mol% Pd/C (5%)
0
0
0
0
0
0
0
0
0
51
43
47
28
36
49
50
32
42
11
3
0
0
37
43
46
1 mol% Pd/Al2O3 (1%)
1 mol% Pd/SiO2 (5%)
1 mol% Ru/C (5%)
1 mol% Ru/Al2O3 (5%)
1 mol% Pt/C (5%)
1 mol% Pt/Al2O3 (5%)
1 mol% Pt/SiO2 (5%)
1 mol% Rh/C (5%)
1 mol% Ir/C (1%)
0
<1
3
0
4
0
0
2
<1
3
Acid cocatalyst screening
<1 24
36
<1 45
From both an economic and environmental point of view, the
use of CSA represents a serious limitation for this method.
Consequently, the nature of the acid cocatalyst was varied to
replace soluble CSA by an ion-exchange resin, which could be
recycled after the reductive alkylation reaction (Table 8).
0
0
0
50
32
9
<1 39
0
0
3
8
10
11
12
13
14
15
0
25
24
97
85
50
33
2
1 mol% Ir/C (1%)
10
10
10
10
10
>99
>99
>99
>99
>99
1 mol% Pt/C (5%)
1 mol% Rh/C (5%)
1 mol% Ru/C (5%)
1 mol% Pd/C (5%)
12
42
58
80
Table 8. Cocatalyst screening.[a]
9
18
[a] Experimental conditions: 1b/glycerol 1:40, catalyst (1 mol%), 50 bar
H2, 1408C, 16 h.
Entry Acid cocatalyst Conversion GC yield [%]
Selectivity
(ethers/
4b+5b esters)
When 1 mol% Pd/Al2O3 and 1 mol% Pd/SiO2 were used, only
traces of the expected GMEs were detected, but the conver-
sion to the corresponding glycerol esters 4b and 5b increased
to 43 and 46%, respectively (entries 2 and 3). Even by chang-
ing the nature of the catalyst, similar results were obtained:
with Ru/C, the reaction afforded mainly esters 4b and 5b in
24% GC yield with a low conversion of the starting material
(entry 4). As observed with Pd, when Ru/Al2O3 was used in the
reaction, the quantity of esters increased to 36% GC yield, but
no traces of the desired GMEs 2b and 3b were detected
(entry 5). With Pt catalysts, the results remained unchanged:
the conversion of 1b was low, and the reaction afforded the
GMEs only when Pt/C was used (entry 6). No traces of GMEs
were detected in the presence of Pt/Al2O3 (entry 7) or Pt/SiO2
(entry 8). Finally, with Rh/C, only traces of GMEs were detected
(entry 9), and with Ir/C, the reaction afforded mainly monogly-
cerides 4b and 5b (entry 10).
[10 wt%]
of 1b [%]
ether ether esters
2b
3b
1
2
3
4
Nafion NR50
Amberlyst 36
Zeolite H-ZSM-5 >99
Amberlyst 35 >99
74
>99
18
50
67
80
4
13
12
18
52
37
21
2
30:70
63:37
79:21
98:2
[a] Experimental conditions: 1b/glycerol 1:40, 1 mol% Pd/C (5%), 10 wt%
acid cocatalyst, 50 bar H2, 1208C, 16 h.
The reductive alkylation reaction with 1b was carried out
under the optimized conditions with 1 mol% of Pd/C (5%), at
1208C, under 50 bar H2, a 1:40 substrate/glycerol ratio, and
10 wt% of acid cocatalyst. From the results in Table 8, we can
see that 18% of the desired GME 2b was obtained in the pres-
ence of Nafion NR50 (entry 1). The yield was improved to 50%
by using a sulfonic acid resin (Amberlyst 36) with complete
conversion of the starting material (entry 2). A yield of 67% of
monoether 2b was obtained by using a strong acidic zeolite
H-ZSM-5 (Si/Al ratio=23) previously calcined at 6508C for 3 h
(entry 3). The best result was that obtained with Amberlyst 35.
In this case, the corresponding GME 2b was obtained in 80%
GC yield with an excellent selectivity of 98% for the glycerol
monoethers (entry 4). This result is comparable to that ob-
served with CSA. The selectivity between the monoethers 2b
and 3b was unchanged at about 4:1, and only traces of by-
products were detected. This result can be explained by the
surface area and the pore volume of Amberlyst 35, which are
larger than those of Amberlyst 36. Thus, it permits ready
These results show the importance of the presence of
a strong acid cocatalyst in the medium for the reductive alkyla-
tion of a carboxylic acid with glycerol as the acidity of the
starting substrate and the catalyst support is clearly insuffi-
cient. The acid cocatalyst activates the carboxylic acid function-
ality as proposed in the mechanism.
As expected, the results improved when the strong Brønsted
acid CSA was added. Only catalysts that allowed the formation
of GMEs 2b and 3b were considered. When 1 mol% Ir/C and
10 wt% CSA were used in the reaction, 3% of the desired
product 2b was obtained and all 1b was converted essentially
to esters (entry 11). The GC yield of the monoether 2b in-
creased to 12% with 1 mol% of Pt/C and 10 wt% of CSA
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M. Lemaire et al.
access of the reactants to the acid sites located throughout
the bead.
Table 9. Reductive alkylation at different stirring speeds.[a]
A GC–MS spectrum of the crude product after extraction
(Figure 1) demonstrated the good selectivity of the process for
the synthesis of glycerol ethers with 1b (entry 4). Indeed,
under the conditions used, the conversion of the starting ma-
terial was complete, and the major product was the expected
glycerol monoether 2b with 18% of monoether 3b and dialky-
lated glycerol ethers. In addition, only traces of monoglycer-
ides 4b or 5b were observed.
Entry Stirring speed Conversion GC yield [%]
Selectivity
(ethers/
4b+5b esters)
[rpm]
of 1b [%]
ether ether esters
2b
3b
1
2
3
4
5
200
400
600
700
800
>99
>99
>99
>99
>99
41
60
75
77
80
6
11
13
15
18
53
29
12
8
47:53
71:29
88:12
92:8
2
98:2
[a] Experimental conditions: 1b/glycerol 1:40, 1 mol% Pd/C (5%), 10 wt%
Amberlyst 35, 50 bar H2, 1208C, 16 h.
Figure 1. GC–MS chromatogram of the crude product obtained from the
etherification of glycerol with valeric acid under optimized conditions after
extraction (Table 8, entry 4).
Figure 2. Effect of stirring speed on the GC yield of the desired monoether
2b after reductive alkylation with glycerol.
Effect of stirring
In this heterogeneous system, mechanical stirring is also a key
parameter as good stirring allows better mixing of the different
reagents: H2, glycerol, carboxylic acid, and the catalysts, that is,
Pd/C and Amberlyst 35. Therefore, we explored the influence
of the stirring speed on the progress of the etherification reac-
tion of glycerol with 1b. Thus, these reactions were performed
under our optimized conditions but at different stirring speeds
(Table 9 and Figure 2).
As can be seen from the graph in Figure 2, the etherification
reaction afforded the desired GMEs in high yields at a stirring
speed above 600 rpm. Consequently, all reductive alkylation re-
actions were then performed at 800 rpm.
Taking into account all these studies with the model sub-
strate 1b, the optimized reductive alkylation conditions
[1 mol% Pd/C (5%), 10 wt% Amberlyst 35, 1208C, 50 bar H2,
40:1 glycerol/carboxylic acid ratio, stirring speed of 800 rpm]
were used for the synthesis of saturated 1-O-alkylglycerol, di-
glycerol, and triglycerol monoethers from carboxylic acids
(Table 1).
We found that at low stirring speeds (200 rpm), the conver-
sion of 1b was incomplete, and a low selectivity for GME 2b
was observed, with only 41% GC yield (entry 1). By increasing
the stirring speed to 400 rpm, conversion was complete and
2b was obtained in a good 60% GC yield. In this case, the se-
lectivity between ethers 2b and 3b and esters 4b and 5b was
close to 71:29 (entry 2). As expected, the GC yield of the glyc-
erol monoether 2b increased to 75% at 600 rpm and 77% at
700 rpm (entries 3 and 4). The best yield and selectivity for
GMEs was observed at 800 rpm. Ether 2b was obtained in an
excellent 80% GC yield, and the selectivity between ethers and
esters was better than 98:2 (entry 5).
Catalytic system and glycerol recycling
The main advantage of using a heterogeneous system is the
potential for recycling the catalysts. Therefore, we report
a simple procedure for the recycling of the catalysts after reac-
tion. After each run, the solution was filtered and extracted
three times with toluene. The mixture of the Amberlyst 35 and
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Catalytic Synthesis of 1-O-Alkyl(poly)glycerol Ethers
Pd/C catalysts was transferred to an autoclave in 5 mL of meth-
anol and left under an Ar flow for 2 h at room temperature.
After the total evaporation of the solvent, the catalysts were
used in a new run once the substrates were added, that is, 1b
and glycerol.
resin, Amberlyst 35, as the cocatalyst. This catalytic system was
recycled three times with no loss of glycerol monoether yield
and selectivity.
A mechanistic proposal for the reductive alkylation reaction
with these carbonyl compounds was made by changing the
nature of the alcohol. The key to the reaction seems to be the
formation of a complex between the Pd/C surface and a five-
membered cyclic hemi-ortho ester.
In our case, the catalysts were recycled three times after re-
action with the model substrate under the optimized condi-
tions with no decrease in the yield of the desired GME 2b
(Table 10).
To the best of our knowledge, this is the first successful cata-
lytic route for the straightforward, direct, heterogeneously cat-
alyzed reductive alkylation of glycerol with carboxylic acids to
afford ethers. This process opens the way to the possible pro-
duction of a wide range of bio-based surfactants with different
physical and chemical properties, which are of considerable in-
terest in many research fields.
Table 10. Catalyst recycling experiments.[a]
Entry
Run
Conversion
of 1b [%]
GC yield [%]
Selectivity
(ethers/
esters)
Experimental Section
ether
ether
esters
4b+5b
2b
3b
General
1
2
3
4
1
2
3
4
>99
>99
>99
>99
79
80
75
79
18
17
16
18
2
1
4
1
98:2
99:1
96:4
99:1
Glycerol (99%, Reagentplus) was purchased from Sigma–Aldrich,
diglycerol (80%) from TCI, triglycerol (80%) from Sigma–Aldrich,
and Pd/C [5%, Pd on activated carbon, reduced and dry (Escat
1431)] from Strem Chemicals. Dry Amberlyst 35 was bought from
Rohm and Haas, and the carboxylic acids were supplied by Acros,
Sigma–Aldrich, Alfa Aesar, and TCI. All reagents and reactants were
used as received without further purification. All reductive alkyla-
tion reactions were performed in a 300 mL steel Parr autoclave
equipped with a mechanical stirrer.
[a] Experimental conditions: 1b/glycerol 1:40, 1 mol% Pd/C (5%), 10 wt%
Amberlyst 35, 50 bar H2, 1208C, 16 h.
From these results, we observe that after the first run, the
reaction afforded the desired monoethers 2b and 3b in 79
and 18% GC yield, respectively (entry 1). When the catalysts
were recycled for the first time, the GMEs 2b and 3b were ob-
tained in 80 and 17% GC yield, respectively (entry 2). After the
third run, the yields decreased slightly to 75 and 16% for mo-
noethers 2b and 3b, respectively (entry 3). Lastly, after the
fourth and final run, the reaction afforded the desired GMEs in
an excellent 79% GC yield for 2b and 18% GC yield for 3b
(entry 4). Thus, after four reactions with the same recycled cat-
alytic system, the yield for the desired GMEs remained good
and almost unchanged (Table 10). It was also possible to recy-
cle the glycerol at the end of the reaction by decantation
when the carboxylic acids contained an alkyl chain with at
least eight carbon atoms. When the length of the chain is
shorter, the separation can be performed by extraction or dis-
tillation under reduced pressure. Glycerol was then engaged in
a new run. The excess glycerol could be recycled three times
with no loss of GME yield and selectivity.
1H and 13C NMR spectra were recorded by using Bruker DRX 300 or
ALS 300 spectrometers (1H 300 MHz, 13C 75 MHz) in CDCl3 (except
when mentioned otherwise). The chemical shifts are given in ppm
and the J values are given in Hz. Abbreviations were defined as fol-
lows: br=broad singlet, s=singlet, d=doublet, dd=doublet of
doublets, t=triplet, q=quadruplet, Q=quintet, sex=sextuplet,
hept=heptuplet.
IR spectra were recorded by using a Spectro Nicolet IS10 Smart ITR
instrument with an attenuated total reflectance (ATR) diamond.
ESI HRMS mass spectra were recorded in positive-ion mode by
using a hybrid quadrupole time-of-flight mass spectrometer (Micro-
TOFQ-II, Bruker Daltonics, Bremen) with an ESI ion source. The flow
of spray gas was 0.6 bar, and the capillary voltage was 4.5 kV. The
solutions were infused at 180 mLhÀ1 in a mixture of solvents (meth-
anol/dichloromethane/water=45:40:15). The mass range of the
analysis was m/z=50–1000, and the calibration was performed
with sodium formate. HRMS–chemical ionization (CI) mass spectra
were recorded on a double-focusing mass spectrometer (Thermo-
Finnigan MAT95XL, Bremen, Germany) equipped with a CI source.
The reagent gas was isobutene, and the calibrations for HRMS
were performed with perfluorotrybutylamine (FC43).
The GC–MS analyses were performed by using a Focus GC instru-
ment (Thermo Electron Corporation, Bremen, Germany) equipped
with a DB-5 MS capillary column (30 m, 0.25 mm inner diameter,
0.25 mm film thickness) and a DSQ mass spectrometer as a detector
(Thermo Electron corporation, Bremen, Germany). The carrier gas
was He with a flow rate of 1 mLminÀ1. The column temperature
was initially 708C for 2 min, which gradually increased to 3108C at
158CminÀ1 and was finally kept at 3108C for 10 min. The injector
temperature was 2208C, and the transfer line temperature was
2808C. For GC–MS detection, an electron ionization system was
Conclusions
A new pathway for an easy, inexpensive, and environmentally
friendly access to glycerol monoethers is reported. The direct
etherification of glycerol, diglycerol, and triglycerol with readily
available and/or bio-sourced substrates and carboxylic acids
was performed under mild conditions with a low E-factor[36]
with glycerol as the solvent and a reagent together with
a small amount of Pd/C catalyst and an acidic ion-exchange
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M. Lemaire et al.
used with an electron energy of 70 eV, and the mass analyzer was
a simple quadrupole.
14.14 (CH3), 22.70 (CH2), 26.10 (CH2), 29.32 (CH2), 29.50 (CH2), 30.06
(CH2), 31.87 (CH2), 61.79 (CH2), 70.29 (CH2), 79.73 ppm (CHOH); IR
(ATR): n˜max =3373, 2924, 2855, 1466, 1378, 1109, 1046, 973,
722 cmÀ1; HRMS (ESI): m/z calcd for C11H24NaO3: 227.1618 [M+
Na+]; found: 227.1621.
Procedure for the reductive etherification of glycerol
Glycerol (713 mmol, 40 equiv.) and carboxylic acid (17.6 mmol,
1 equiv.) were mixed in a 300 mL steel autoclave at room tempera-
ture. Amberlyst 35 (10 wt%) and Pd/C (1 mol% Pd) were then
added. The autoclave was flushed with Ar then with H2 four times.
The solution was stirred (800 rpm) at 1208C under 50 bar H2 for
16 h. After the reaction, the medium was dissolved in absolute eth-
anol and filtered (Millipore Durapore filter 0.01 mm). The solvents
were evaporated under reduced pressure, and the organic prod-
ucts were extracted four times with dichloromethane or toluene.
The crude products were finally purified by silica column chroma-
tography (eluent: cyclohexane/ethyl acetate=4:1~1:0 for short
alkyl chains, cyclohexane/ethyl acetate=95:5~1:1 for long alkyl
chains; dichloromethane/methanol=99:1~9:1 for triglycerol mo-
noethers).
3-(Decyloxy)propane-1,2-diol [10430-97-4] (2e): White crystalline
solid; m.p.= <448C; H NMR: d=0.87 (t, J=7 Hz, 3H; CH3), 1.24–
1
1.36 (m, 14H; CH2), 1.54–1.60 (m, 2H; CH2), 2.34 (br, 2H; OH), 3.44–
3.55 (m, 4H; CH2), 3.61–3.74 (m, 2H; CH2), 3.82–3.87 ppm (m, 1H;
CHOH); 13C NMR: d=14.17 (CH3), 22.75 (CH2), 26.13 (CH2), 29.40
(CH2), 29.56 (CH2), 29.62 (CH2), 29.65 (CH2), 29.68 (CH2), 31.97 (CH2),
64.19 (CH2), 70.82 (CHOH), 71.90 (CH2), 72.32 ppm (CH2); IR (ATR):
n˜max =3347, 2954, 2917, 2850, 1467, 1459, 1325, 1254, 1237, 1121,
1111, 1060, 1018, 936, 864, 721, 680 cmÀ1; HRMS (ESI): m/z calcd for
C13H28NaO3: 255.1931 [M+Na+]; found: 255.1925.
3-(Dodecyloxy)propane-1,2-diol [1561-07-5] (2 f): White crystalline
1
solid; m.p.=468C; H NMR: d=0.88 (t, J=6.7 Hz, 3H; CH3), 1.21–
1.36 (m, 18H; CH2), 1.54–1.60 (m, 2H; CH2), 2.30 (br, 2H; OH), 3.44–
3.56 (m, 4H; CH2), 3.62–3.75 (m, 2H; CH2), 3.83–3.89 ppm (m, 1H;
CHOH); 13C NMR: d=14.21 (CH3), 22.79 (CH2), 26.17 (CH2), 29.46
(CH2), 29.58 (CH2), 29.67 (CH2), 29.70 (CH2), 29.72 (CH2), 29.74 (CH2),
29.77 (CH2), 32.02 (CH2), 64.29 (CH2), 70.72 (CHOH), 71.95 (CH2),
72.48 ppm (CH2); IR (ATR): n˜max =3351, 2954, 2917, 2850, 1469,
1325, 1253, 1239, 1122, 1094, 1060, 936, 864, 720, 680 cmÀ1; HRMS
(ESI): m/z calcd for C15H32NaO3: 283.2244 [M+Na+]; found:
283.2241.
Characterization of the synthesized compounds
1
3-(Butyloxy)propane-1,2-diol [624-52-2] (2a): Colorless oil; H NMR:
d=0.92 (t, J=7.1 Hz, 3H; CH3), 1.30–1.42 (m, 2H; CH2), 1.51–1.76
(m, 2H; CH2), 2.36 (br, 2H; OH), 3.44–3.52 (m, 4H; CH2), 3.64–3.71
(m, 2H; CH2), 3.83–3.86 ppm (m, 1H; CHOH); 13C NMR: d=13.93
(CH3), 19.26 (CH2), 31.63 (CH2), 64.16 (CH2), 70.81 (CHOH), 71.51
(CH2), 72.27 ppm (CH2); IR (ATR): n˜max =3372, 2958, 2932, 2869,
1459, 1379, 1233, 1109, 1042, 927, 844 cmÀ1; HRMS (ESI): m/z calcd
for C7H16NaO3: 171.0992 [M+Na+]; found: 171.0986.
3-(Tetradecyloxy)propane-1,2-diol [1561-06-4] (2g): White crystal-
line solid; m.p.=558C; 1H NMR: d=0.88 (t, J=6.7 Hz, 3H; CH3),
1.21–1.37 (m, 22H; CH2), 1.54–1.60 (m, 2H; CH2), 2.10 (br, 2H; OH),
3.44–3.56 (m, 4H; CH2), 3.62–3.75 (m, 2H; CH2), 3.83–3.89 ppm (m,
1H; CHOH); 13C NMR: d=14.22 (CH3), 22.80 (CH2), 26.17 (CH2),
29.46 (CH2), 29.58 (CH2), 29.67 (CH2), 29.71 (CH2), 29.72 (CH2), 29.76
(CH2), 29.78 (CH2), 29.79 (CH2), 32.03 (CH2), 64.29 (CH2), 70.72
(CHOH), 71.95 (CH2), 72.47 ppm (CH2); IR (ATR): n˜max =3349, 2954,
2916, 2850, 1470, 1326, 1254, 1238, 1117, 1099, 1061, 936, 863,
719, 680 cmÀ1; HRMS (ESI): m/z calcd for C17H36NaO3: 311.2557
[M+Na+]: found: 311.2550.
3-(Pentyloxy)propane-1,2-diol [22636-32-4] (2b): Colorless oil;
1H NMR: d=0.88 (t, J=7 Hz, 3H; CH3), 1.29–1.32 (m, 4H; CH2),
1.54–1.59 (m, 2H; CH2), 2.65 (br, 2H; OH), 3.44–3.50 (m, 4H; CH2),
3.59–3.71 (m, 2H; CH2), 3.82–3.86 ppm (m, 1H; CHOH); 13C NMR:
d=14.11 (CH3), 22.60 (CH2), 28.34 (CH2), 29.35 (CH2), 64.33 (CH2),
70.69 (CHOH), 71.94 (CH2), 72.52 ppm (CH2); IR (ATR): n˜max =3373,
2959, 2931, 2861, 1458, 1379, 1216, 1110, 1041, 927, 851 cmÀ1
;
HRMS (ESI): m/z calcd for C8H18NaO3: 185.1148 [M+Na+]; found:
185.1147.
3-(Hexadecyloxy)propane-1,2-diol [6145-69-3] (2h): White crystal-
line solid; m.p.=678C; 1H NMR: d=0.88 (t, J=6.7 Hz, 3H; CH3),
1.20–1.37 (m, 26H; CH2), 1.54–1.60 (m, 2H; CH2), 2.17 (br, 1H; OH),
2.59 (br, 1H; OH), 3.43–3.57 (m, 4H; CH2), 3.62–3.75 (m, 2H; CH2),
3.83–3.89 ppm (m, 1H; CHOH); 13C NMR: d=14.23 (CH3), 22.81
(CH2), 26.19 (CH2), 29.48 (CH2), 29.60 (CH2), 29.69 (CH2), 29.72 (CH2),
29.74 (CH2), 29.82 (CH2), 32.05 (CH2), 64.31 (CH2), 70.71 (CHOH),
71.96 (CH2), 72.50 ppm (CH2); IR (ATR): n˜max =3355, 2954, 2916,
3-(Hexyloxy)propane-1,2-diol [10305-38-1] (2c): Colorless oil;
1H NMR: d=0.88 (t, J=6.8 Hz, 3H; CH3), 1.26–1.35 (m, 6H; CH2),
1.55–1.60 (m, 2H; CH2), 2.29 (br, 2H; OH), 3.44–3.52 (m, 4H; CH2),
3.61–3.74 (m, 2H; CH2), 3.82–3.88 ppm (m, 1H; CHOH); 13C NMR:
d=14.05 (CH3), 22.63 (CH2), 25.73 (CH2), 29.52 (CH2), 31.69 (CH2),
64.12 (CH2), 70.82 (CHOH), 71.83 (CH2), 72.23 ppm (CH2); IR (ATR):
n˜max =3374, 2928, 2859, 1458, 1378, 1111, 1041, 926, 853, 725 cmÀ1
HRMS (ESI): m/z calcd for C9H20NaO3: 199.1305 [M+Na+]; found:
;
2849, 1471, 1327, 1254, 1120, 1105, 1060, 936, 863, 718, 680 cmÀ1
;
HRMS (ESI): m/z calcd for C19H40NaO3: 339.2870 [M+Na+]; found:
199.1307.
339.2859.
3-(Octyloxy)propane-1,2-diol [10438-94-5] (2d): Colorless oil;
1H NMR: d=0.88 (t, J=6.7 Hz, 3H; CH3), 1.25–1.35 (m, 10H; CH2),
1.54–1.60 (m, 2H; CH2), 2.51 (br, 2H; OH), 3.44–3.56 (m, 4H; CH2),
3.61–3.74 (m, 2H; CH2), 3.83–3.89 ppm (m, 1H; CHOH); 13C NMR:
d=14.14 (CH3), 22.71 (CH2), 26.11 (CH2), 29.32 (CH2), 29.49 (CH2),
29.60 (CH2), 31.88 (CH2), 64.19 (CH2), 70.80 (CHOH), 71.88 (CH2),
72.32 ppm (CH2); IR (ATR): n˜max =3378, 2924, 2855, 1458, 1378,
3-(Octadecyloxy)propane-1,2-diol [544-62-7] (2i): White crystalline
solid; m.p.=738C; H NMR: d=0.88 (t, J=6.6 Hz, 3H; CH3), 1.20–
1
1.38 (m, 30H; CH2), 1.55–1.60 (m, 2H; CH2), 2.15 (br, 2H; OH), 3.44–
3.56 (m, 4H; CH2), 3.62–3.75 (m, 2H; CH2), 3.83–3.88 ppm (m, 1H;
CHOH); 13C NMR: d=14.24 (CH3), 22.82 (CH2), 26.20 (CH2), 29.50
(CH2), 29.60 (CH2), 29.69 (CH2), 29.73 (CH2), 29.75 (CH2), 29.79 (CH2),
29.83 (CH2), 32.05 (CH2), 64.35 (CH2), 70.68 (CHOH), 71.97 (CH2),
72.54 ppm (CH2); IR (ATR): n˜max =3358, 2954, 2916, 2849, 1471,
1327, 1254, 1120, 1104, 1060, 936, 863, 718, 680 cmÀ1; HRMS (ESI):
m/z calcd for C21H44NaO3: 367.3183 [M+Na+]; found: 367.3165.
1112, 1042, 926, 852, 735 cmÀ1
; HRMS (ESI): m/z calcd for
C11H24NaO3: 227.1618 [M+Na+]; found: 227.1624.
2-(Octyloxy)propane-1,3-diol [35396-30-6] (3d): Colorless oil;
1H NMR: d=0.88 (t, J=6.7 Hz, 3H; CH3), 1.25–1.35 (m, 10H; CH2),
1.54–1.60 (m, 2H; CH2), 1.93 (br, 2H; OH), 3.44–3.49 (m, 1H; CH),
3.56 (t, J=6.5 Hz, 2H; CH2), 3.72 ppm (m, 2H; CH2); 13C NMR: d=
3-(Isopentyloxy)propane-1,2-diol [627-92-9] (2j): Colorless oil;
1H NMR: d=0.90 (d, J=6.6 Hz, 6H; CH3), 1.47 (q, J=6.8 Hz, 2H;
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Catalytic Synthesis of 1-O-Alkyl(poly)glycerol Ethers
CH2), 1.48 (Q, J=6.7 Hz, 1H; CH), 2.30 (br, 2H; OH), 3.46–3.54 (m,
4H; CH2), 3.61–3.74 (m, 2H; CH2), 3.83–3.87 ppm (m, 1H; CHOH);
13C NMR: d=22.65 (CH3), 25.09 (CH), 38.33 (CH2), 64.14 (CH2), 70.18
(CH2), 70.81 (CHOH), 72.29 ppm (CH2); IR (ATR): n˜max =3373, 2955,
2927, 2869, 1467, 1385, 1367, 1111, 1040, 924, 864, 828 cmÀ1; HRMS
(ESI): m/z calcd for C8H18NaO3: 185.1148 [M+Na+]; found: 185.1142.
(CH2), 71.80 (CH2), 72.79 (CH2), 72.90 (CH2), 73.09 (CH2), 73.20 ppm
(CH2); IR (ATR): n˜max =3363, 2928, 2860, 1457, 1378, 1109, 1040, 930,
869 cmÀ1; HRMS (ESI): m/z calcd for C12H26NaO5: 273.1672 [M+
Na+]; found: 273.1668.
3-[3-(Octyloxy)-2-hydroxypropoxy]propane-1,2-diol
[85590-50-7]
1
(8d): Colorless oil; (mixture of optical isomers); H NMR: d=0.88 (t,
J=6.7 Hz, 3H; CH3), 1.22–1.37 (m, 10H; CH2), 1.52–1.61 (m, 2H;
CH2), 2.63 (br, 3H; OH), 3.43–3.77 (m, 10H; CH2), 3.85–3.90 (m, 1H;
CHOH), 3.93–3.99 ppm (m, 1H; CHOH); 13C NMR: d=14.17 (CH3),
22.71 (CH2), 26.11 (CH2), 29.33 (CH2), 29.51 (CH2), 29.62 (CH2), 31.89
(CH2), 63.81 (CH2), 69.47 (C*HOH), 69.57 (C*HOH), 70.95 (C*HOH),
71.08 (C*HOH), 71.79 (CH2), 71.84 (CH2), 72.84 (CH2), 72.95 (CH2),
73.11 (CH2), 73.23 ppm (CH2); IR (ATR): n˜max =3363, 2923, 2855,
1457, 1327, 1110, 1042, 870 cmÀ1; HRMS (ESI): m/z calcd for
C14H30NaO5: 301.1985 [M+Na+]; found: 301.1989.
3-[(2-Methylpentyl)oxy]propane-1,2-diol [no CAS number] (2k): Col-
orless oil; 1H NMR: d=0.86–0.91 (m, 6H; CH3), 1.06–1.11 (m, 1H;
CH2), 1.25–1.37 (m, 3H; CH2), 1.36–1.77 (m, 1H; CH), 2.33 (br, 2H;
OH), 3.19–3.36 (m, 2H; CH2), 3.49–3.53 (m, 2H; CH2), 3.62–3.75 (m,
2H; CH2), 3.84–3.87 ppm (m, 1H; CHOH); 13C NMR: d=14.18 (CH3),
16.82 (CH3), 19.86 (CH2), 32.83 (CH), 35.66 (CH2), 64.05 (CH2), 70.58
(CHOH), 72.30 (CH2), 76.54 ppm (CH2); IR (ATR): n˜max =3374, 2956,
2928, 2872, 1457, 1379, 1108, 1042, 928, 856, 739 cmÀ1; HRMS (ESI):
m/z calcd for C9H20NaO3: 199.1305 [M+Na+]; found: 199.1301.
3-[(2-Ethylhexyl)oxy]propane-1,2-diol [70445-33-9] (2l): Colorless
oil; 1H NMR: d=0.85–0.90 (m, 6H; CH3), 1.25–1.36 (m, 8H; CH2),
1.47–1.52 (m, 1H; CH), 2.31 (br, 2H; OH), 3.31–3.39 (m, 2H; CH2),
3.46–3.54 (m, 2H; CH2), 3.63–3.73 (m, 2H; CH2), 3.73–3.88 ppm (m,
1H; CHOH); 13C NMR: d=11.21 (CH3): d=14.23 (CH3), 23.19 (CH2),
24.00 (CH2), 29.22 (CH2), 30.68 (CH2), 39.70 (CH), 64.52 (CH2), 70.54
(CHOH), 72.98 (CH2), 74.69 ppm (CH2); IR (ATR): n˜max =3378, 2958,
2927, 2859, 1459, 1379, 1108, 1043, 925, 853, 768, 727 cmÀ1; HRMS
(ESI): m/z calcd for C11H24NaO3: 227.1618 [M+Na+]; found:
227.1621.
3-[3-(Decyloxy)-2-hydroxypropoxy]propane-1,2-diol
[88456-94-4]
1
(8e): Colorless oil; (Mixture of optical isomers); H NMR: d=0.88 (t,
J=6.7 Hz, 3H; CH3), 1.20–1.39 (m, 14H; CH2), 1.54–1.59 (m, 2H;
CH2), 2.42 (br, 1H; OH), 2.91 (br, 1H; OH), 3.25 (br, 1H; OH), 3.42–
3.75 (m, 10H; CH2), 3.85–3.92 (m, 1H; CHOH), 3.94–3.99 ppm (m,
1H; CHOH); 13C NMR: d=14.16 (CH3), 22.72 (CH2), 26.10 (CH2),
29.38 (CH2), 29.54 (CH2), 29.60 (CH2), 29.64 (CH2), 29.67 (CH2), 31.94
(CH2), 63.77 (CH2), 69.44 (C*HOH), 69.55 (C*HOH), 70.95 (C*HOH),
71.08 (C*HOH), 71.79 (CH2), 71.81 (CH2), 72.80 (CH2), 72.91 (CH2),
73.10 (CH2), 73.22 ppm (CH2); IR (ATR): n˜max =3363, 2922, 2853,
1458, 1378, 1110, 1043, 932, 871, 721 cmÀ1; HRMS (ESI): m/z calcd
for C16H34NaO5: 329.2298 [M+Na+]; found: 329.2288.
3-(Cyclobutylmethoxy)propane-1,2-diol [no CAS number] (2m): Col-
orless oil; 1H NMR: d=1.67–1.78 (m, 2H; CH2), 1.81–1.97 (m, 2H;
CH2), 2.00–2.10 (m, 2H; CH2), 2.37 (br, 2H; OH), 2.57 (Q, J=7.3 Hz),
3.45 (dd, J=1.9 Hz, J=7 Hz, 2H; CH2), 3.49–3.54 (m, 2H; CH2),
3.61–3.74 (m, 2H; CH2) 3.82–3.89 ppm (m, 1H; CHOH); 13C NMR:
d=18.65 (CH2), 25.10 (CH2), 34.99 (CH), 64.19 (CH2), 70.76 (CHOH),
72.49 (CH2), 76.26 ppm (CH2); IR (ATR): n˜max =3373, 2933, 2861,
1325, 1242, 1040, 979, 925, 854, 734 cmÀ1; HRMS (ESI): m/z calcd
for C8H16NaO3: 183.0992 [M+Na+]; found: 183.0988.
3-{3-[3-(Dodecyloxy)-2-hydroxypropoxy]-2-hydroxypropoxy}pro-
pane-1,2-diol [123541-03-7] (13 f): White wax (mixture of optical
isomers); 1H NMR: d=0.88 (t, J=6.8 Hz, 3H; CH3), 1.20–1.35 (m,
18H; CH2), 1.52–1.59 (m, 2H; CH2), 3.33 (br, 4H; OH), 3.32–3.73 (m,
15H; CH2), 3.82–3.90 (m, 1H; CHOH), 3.91–4.01 ppm (m, 1H;
CHOH); 13C NMR: d=14.27 (CH3), 22.83 (CH2), 26.20 (CH2), 29.50
(CH2), 29.63 (CH2), 29.71 (CH2), 29.77 (CH2), 29.78 (CH2), 29.81 (CH2),
32.06 (CH2), 63.90 (CH2), 63.93 (CH2), 69.59 (C*HOH), 69.71 (C*HOH),
69.79 (C*HOH), 69.91 (C*HOH), 70.91 (C*HOH), 71.02 (C*HOH),
71.79 (CH2), 71.91 (CH2), 72.76 (CH2), 72.81 (CH2), 72.87 (CH2), 73.10
3-(Cyclopentylmethoxy)propane-1,2-diol [no CAS number] (2n):
Colorless oil; 1H NMR: d=1.17–1.24 (m, 2H; CH2), 1.50–1.61 (m,
4H; CH2), 1.67–1.76 (m, 2H; CH2), 2.11–2.31 (Q, 1H; CH), 2.31 (br,
2H; OH), 3.34 (dd, J=1.9 Hz, J=12.2 Hz, 2H; CH2), 3.48–3.58 (m,
2H; CH2), 3.62–3.75 (m, 2H; CH2) 3.82–3.87 ppm (m, 1H; CHOH);
13C NMR: d=25.43 (CH2), 29.53 (CH2), 39.30 (CH), 64.23 (CH2), 70.74
(CHOH), 72.48 (CH2), 76.34 ppm (CH2); IR (ATR): n˜max =3372, 2948,
2864, 1453, 1110, 1040, 927, 854 cmÀ1; HRMS (ESI): m/z calcd for
C9H18NaO3: 197.1148 [M+Na+]; found: 197.1142.
(CH2), 73.12 (CH2), 73.22 (CH2), 73.24 ppm (CH2); IR (ATR): n˜max
=
;
3355, 2921, 2852, 1456, 1333, 1112, 1040, 932, 891, 717 cmÀ1
HRMS (ESI): m/z calcd for C21H44NaO7: 431.2979 [M+Na+]; found:
431.2976.
1
Propyl pentanoate [141-06-0] (10b): Colorless oil; H NMR: d=0.91
(t, J=7.1 Hz, 6H; CH3), d=0.94 (t, J=7.3 Hz, 3H; CH3), 1.34 (sex,
J=7.4 Hz, 2H; CH2), 1.63 (hept, J=7.1 Hz, 4H; CH2), 2.30 (t, J=
7.5 Hz, 2H; CH2), 4.02 ppm (t, J=6.7 Hz, 2H; CH2); 13C NMR: d=
10.38 (CH3), d=13.69 (CH3), 22.04 (CH2), 22.30 (CH2), 27.13 (CH2),
34.08 (CH2), 65.78 (CH2), 173.90 ppm (Cq); IR (ATR): n˜max =2960,
2928, 2875, 1736, 1465, 1380, 1340, 1244, 1174, 1093, 1061, 952,
756 cmÀ1; HRMS (CI): m/z calcd for C8H17O2: 145.1223 [M+H+];
found: 145.1222.
3-(Cyclohexylmethoxy)propane-1,2-diol [147526-34-9] (2o): Color-
less oil; H NMR: d=0.90–0.97 (m, 2H; CH2), 1.16–1.26 (m, 3H; CH,
1
CH2), 1.57–1.74 (m, 6H; CH2), 2.23 (br, 2H; OH), 3.27 (dd, J=2 Hz,
J=6.4 Hz, 2H; CH2), 3.51 Hz (dd, J=1.6 Hz, J=6.4 Hz, 2H; CH2),
3.69 (qd, J=5.4 Hz, J=10 Hz, 2H; CH2) 3.82–3.87 ppm (m, 1H;
CHOH); 13C NMR: d=25.85 (CH2), 26.61 (CH2), 30.02 (CH2), 37.90
(CH), 64.23 (CH2), 70.76 (CHOH), 72.53 (CH2), 77.57 ppm (CH2); IR
(ATR): n˜max =3373, 2920, 2850, 1449, 1120, 1040, 924, 889,
843 cmÀ1; HRMS (ESI): m/z calcd for C10H20NaO3: 211.1305 [M+
Na+]; found: 211.1307.
3-Hydroxypropyl pentanoate [35019-17-1] (10c): Colorless oil;
1H NMR: d=0.91 (t, J=7.2 Hz, 3H; CH3), d=1.36 (sex, J=7.3 Hz,
2H; CH2), 1.62 (Q, J=7.5 Hz, 2H; CH2), 1.81 (br, 1H; OH), 1.87 (Q,
J=7.2 Hz, 2H; CH2), 2.31 (t, J=7.5 Hz, 2H; CH2), 3.69 (t, J=6 Hz,
2H; CH2), 4.23 ppm (t, J=6.2 Hz, 2H; CH2); 13C NMR: d=13.72
(CH3), 22.27 (CH2), 27.06 (CH2), 31.75 (CH2), 34.06 (CH2), 59.06 (CH2),
61.30 (CH2), 174.47 ppm (Cq); IR (ATR): n˜max =3400, 2959, 2933,
3-[3-(Hexyloxy)-2-hydroxypropoxy]propane-1,2-diol [146490-38-2]
1
(8c): Colorless oil (mixture of optical isomers); H NMR: d=0.89 (t,
J=6.9 Hz, 3H; CH3), 1.20–1.39 (m, 6H; CH2), 1.57 (m, 2H; CH2), 2.85
(br, 3H; OH), 3.43–3.80 (m, 10H; CH2), 3.82–3.92 (m, 1H; CHOH),
3.94–4.00 ppm (m, 1H; CHOH); 13C NMR: d=14.09 (CH3), 22.65
(CH2), 25.75 (CH2), 29.54 (CH2), 31.70 (CH2), 63.78 (CH2), 69.44
(C*HOH), 69.55 (C*HOH), 70.94 (C*HOH), 71.07 (C*HOH), 71.77
2874, 1734, 1716, 1467, 1261, 1175, 1094, 1052, 977, 938 cmÀ1
;
HRMS (ESI): m/z calcd for C8H16NaO3: 183.0992 [M+Na+]; found:
183.0991.
ChemSusChem 0000, 00, 1 – 14
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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M. Lemaire et al.
1-(Pentyloxy)propan-2-ol [55546-15-1] (2p): Colorless oil; 1H NMR:
d=0.90 (t, J=6.9 Hz, 3H; CH3), 1.13 (d, J=6.6 Hz, 3H; CH3), 1.30–
1.36 (m, 4H; CH2), 1.56–1.60 (m, 2H; CH2), 2.23 (br, 1H; OH), 3.19
(dd, J=8.3 Hz, J=9.3 Hz, 1H; CH2), 3.39–3.50 (m, 3H; CH2), 3.93–
3.98 ppm (m, 1H; CHOH); 13C NMR: d=14.19 (CH3), 18.70 (CH3),
22.67 (CH2), 28.43 (CH2), 29.48 (CH2), 66.56 (CHOH), 71.61 (CH2),
76.39 ppm (CH2); IR (ATR): n˜max =3417, 2957, 2930, 2859, 1458,
1376, 1324, 1258, 1110, 982, 850, 729 cmÀ1; HRMS (ESI): m/z calcd
for C8H18NaO2: 169.1199 [M+Na+]; found: 169.1196.
Keywords: alkylation
catalysis · palladium · reduction
·
carboxylic acids
·
heterogeneous
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2-(Pentyloxy)propan-1-ol [55546-41-3] (3p): Colorless oil; 1H NMR:
d=0.89 (t, J=7 Hz, 3H; CH3), 1.10 (d, J=6.3 Hz, 3H; CH3), 1.30–
1.34 (m, 4H; CH2), 1.56–1.60 (m, 2H; CH2), 2.12 (br, 1H; OH), 3.34–
3.60 ppm (m, 5H; CH2, CHOH); 13C NMR: d=14.19 (CH3), 15.99
(CH3), 22.68 (CH2), 28.52 (CH2), 29.91 (CH2), 66.51 (CH2), 69.05 (CH2),
75.84 ppm (CH); IR (ATR): n˜max =3410, 2957, 2931, 2861, 1457, 1375,
1342, 1242, 1091, 1045, 988, 914, 837, 729 cmÀ1; HRMS (ESI): m/z
calcd for C8H18NaO2: 169.1199 [M+Na+]; found: 169.1195.
2-(Pentyloxy)ethanol [6196-58-3] (2q): Colorless oil; 1H NMR: d=
0.90 (t, J=7 Hz, 3H; CH3), 1.29–1.35 (m, 4H; CH2), 1.55–1.62 (m,
2H; CH2), 2.04 (br, 1H; OH), 3.47 (t, J=6.7 Hz, 2H; CH2), 3.52–3.55
(m, 2H; CH2), 3.71–3.74 ppm (m, 2H; CH2); 13C NMR: d=14.02
(CH3), 22.54 (CH2), 28.26 (CH2), 29.32 (CH2), 61.72 (CH2), 71.46 (CH2),
71.93 ppm (CH2); IR (ATR): n˜max =3404, 2931, 2860, 1458, 1379,
1357, 1217, 1117, 1063, 992, 888, 729 cmÀ1; HRMS (ESI): m/z calcd
for C7H16NaO2: 155.1043 [M+Na+]; found: 155.1038.
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Chem. 2007, 119, 4516–4522; Angew. Chem. Int. Ed. 2007, 46, 4434–
4440.
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Chem. Commun. 2011, 47, 6208–6227.
2-Hydroxyethyl pentanoate [16179-36-5] (4q): Colorless oil;
1H NMR: d=0.92 (t, J=7.4 Hz, 3H; CH3), 1.29–1.42 (m, 2H; CH2),
1.57–1.67 (m, 2H; CH2), 1.95 (br, 1H; OH), 2.36 (t, J=7.5 Hz, 2H;
CH2), 3.82 (m, 2H; CH2), 4.21 ppm (m, 2H; CH2); 13C NMR: d=13.66
(CH3), 22.20 (CH2), 26.93 (CH2), 33.87 (CH2), 60.90 (CH2), 65.81 (CH2),
174.36 ppm (Cq); IR (ATR): n˜max =3435, 2959, 2874, 1733, 1456,
1419, 1381, 1260, 1173, 1079, 1031, 940, 886, 734 cmÀ1; HRMS (ESI):
m/z calcd for C7H14NaO3: 169.0835 [M+Na+]; found: 169.0831.
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2008, 6011–6012; b) J. Barrault, F. Jꢀrꢁme, Eur. J. Lipid Sci. Technol.
2008, 110, 825–830.
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1-(Pentyloxy)butan-2-ol [131247-93-3] (2r): Colorless oil; 1H NMR:
d=0.90 (t, J=6.8 Hz, 3H; CH3), 0.92 (t, J=7.5 Hz, 3H; CH3), 1.29–
1.36 (m, 4H; CH2), 1.42–1.52 (m, 2H; CH2), 1.54–1.63 (m, 2H; CH2),
2.30 (br, 1H; OH), 3.24 (dd, J=8.1 Hz, J=9.6 Hz, 1H; CH2), 3.38–
3.50 (m, 3H; CH2), 3.65–3.75 ppm (m, 1H; CHOH); 13C NMR: d=
9.98 (CH3), 14.10 (CH3), 22.60 (CH2), 26.19 (CH2), 28.37 (CH2), 29.41
(CH2), 71.56 (CH2), 71.72 (CHOH), 74.86 ppm (CH2); IR (ATR): n˜max
=
[19] P. A. van Elburg, O. A. Ormskerk, K. P. de Kloe, P. J. Boogaard, J. Labelled
Compd. Radiopharm. 2000, 43, 147–167.
3448, 2958, 2930, 2860, 1460, 1379, 1232, 1110, 1030, 989, 921,
777, 729 cmÀ1; HRMS (ESI): m/z calcd for C9H20NaO2: 183.1356
[M+Na+]; found: 183.1350.
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2-(Pentyloxy)butan-1-ol [131247-96-6] (3r): Colorless oil; 1H NMR:
d=0.90 (t, J=7 Hz, 3H; CH3), 0.91 (t, J=7.4 Hz, 3H; CH3), 1.30–1.37
(m, 4H; CH2), 1.43–1.53 (m, 2H; CH2), 1.54–1.63 (m, 2H; CH2), 1.96
(br, 1H; OH), 3.24–3.32 (m, 1H; CHOH), 3.40–3.68 ppm (m, 4H;
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28.40 (CH2), 29.89 (CH2), 63.89 (CH2), 69.71 (CH2), 81.32 ppm
(CHOH); IR (ATR): n˜max =3412, 2958, 2931, 2873, 1464, 1379, 1348,
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Acknowledgements
The authors warmly thank Sofiprotꢀol for financial support and
are grateful for access to the GC–MS and NMR spectroscopic fa-
cilities at the Universitꢀ Lyon 1.
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Catalytic Synthesis of 1-O-Alkyl(poly)glycerol Ethers
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Received: June 28, 2012
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Published online on && &&, 0000
ChemSusChem 0000, 00, 1 – 14
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
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These are not the final page numbers!

FULL PAPERS
M. Sutter, W. Dayoub, E. Mꢀtay, Y. Raoul,
M. Lemaire*
&& – &&
Selective Synthesis of 1-O-
Alkyl(poly)glycerol Ethers by Catalytic
Reductive Alkylation of Carboxylic
Acids with a Recyclable Catalytic
System
Reductive alkylation, a new sensation:
Reductive alkylation of (poly)glycerol is
realized for the first time with bio-
ing 1-O-alkyl(poly)glycerol monoethers
are obtained in good yield and selectivi-
ty, and the catalysts can be recycled
three times with no loss of activity,
opening a new access to glycerol ethers
on a large scale.
sourced and/or cheap carboxylic acids
under mild conditions by using a recy-
clable catalytic system. The correspond-
&14
&
www.chemsuschem.org
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 0000, 00, 1 – 14
ÝÝ
These are not the final page numbers!