Fluorous gallic acid derivatives as versatile gelators. Self-assembly into nanosized fibers or balls

Article abstract of DOI:10.1016/j.tet.2010.04.086

A new class of low molecular mass organogelators, the fluorous derivatives of gallic acid 13, is described. The gelation properties have been examined in a large variety of organic liquids. The corresponding analogs possessing alkyl instead of semiperuluoroalkyl chains (46) do not display any gelation properties, thus revealing the key role of perfluorinated chains in the aggregationgelation process. Gels have been studied by scanning electron microscopy, revealing the presence of three-dimensional networks of nanosized fibers. In the case of an instable gel, SEM images showed that these elongated fibers curl up into nanoballs, failing to create the entangled network responsible for solvent entrapment.

Full text of DOI:10.1016/j.tet.2010.04.086

Tetrahedron 66 (2010) 5190e5195
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Fluorous gallic acid derivatives as versatile gelators. Self-assembly
into nanosized fibers or balls
*
*
Enrico Faggi, Rosa María Sebastián , Adelina Vallribera
Departament de Química, Universitat Autònoma de Barcelona, Campus de la UAB, 08193 Cerdanyola del Vallès, Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
A new class of low molecular mass organogelators, the fluorous derivatives of gallic acid 1e3, is de-
scribed. The gelation properties have been examined in a large variety of organic liquids. The corre-
sponding analogs possessing alkyl instead of semiperfluoroalkyl chains (4e6) do not display any gelation
properties, thus revealing the key role of perfluorinated chains in the aggregation/gelation process. Gels
have been studied by scanning electron microscopy, revealing the presence of three-dimensional net-
works of nanosized fibers. In the case of an instable gel, SEM images showed that these elongated fibers
curl up into nanoballs, failing to create the entangled network responsible for solvent entrapment.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 24 March 2010
Received in revised form 16 April 2010
Accepted 21 April 2010
Available online 24 April 2010
Keywords:
Nanostructures
Supramolecular chemistry
Organogels
Fluorous compounds
1. Introduction
organizing forces based on repulsion by the solvent or by other
different parts of the same molecule.8c,d On the other hand, some
Low mass organogelators (LMOGs, molecules whose molecular
mass is <3000) are a growing class of compounds able to form gels
with organic solvents at low concentrations (typically 10e50 mg/
ml).1 Solvent entrapment is the result of the ability to self-assemble
into a wide variety of modes (rods, long fibers, tubules, strands,
spheres, etc.).2 Organogels have received increasing attention due
to their potential useful applications: oil recovery systems,3 toxicity
remediation devices,4 scaffolds for tissue repair,5 drug delivery
systems,6 or templates for inorganic superstructures.7 Less com-
mon are compounds able to gelate pure perfluorocarbons (PFCs);8
however PFC gels have received special attention due to their po-
tential use as delivery barrier creams.9
gallic acid derivatives possessing long alkyl chains were found to
gelate alcohols and water.15 Herein we report on the synthesis and
gelation abilities of three new structurally simple organogelators
1e3 (Scheme 1). They are based on the gallic acid skeleton and are
comprised by a polar group (ester, acid, or amide), an aromatic ring
and three long semiperfluorinated chains. In principle, each of
these elements may set up intermolecular interactions leading to
aggregation. By comparison with their analogs 4e6 (Scheme 1, all
fluorine atoms are replaced by hydrogens) that show no gelation
properties, we demonstrate that the presence of semi-
perfluorinated chains is essential for the aggregation/gelation
process.
The supramolecular self-assembly of gelators is achieved by
a combination of non-covalent interactions. For most known
gelators such as amides, ureas, carbamates, peptides or sugars, H-
bond is the driving force for molecular aggregation.10 Gelators that
are able to self-assemble without H-bonds and only via weaker
interactions are not common. Among them, alkoxyaromatics,11
azobenzene derivatives,12 semiperfluoroalkanes,13 and even sim-
ple alkanes14 should be mentioned. In particular, molecules con-
taining fluoroponytails display unusual chemical behavior due to
the geometrical characteristics and the extreme hydrophobic and
lipophobic nature of the fluorinated linkage, providing unique
2. Results and discussion
2.1. Synthesis
Esters 1 and 4 were easily prepared by alkylation of commercial
propyl gallate with 1H,1H,2H,2H,3H,3H-perfluoroundecyl iodide
(98% yield) and undecyl bromide (50% yield), respectively, in
refluxing acetone and in presence of potassium carbonate. Notably,
our initial attempts to react propyl gallate with 1H,1H,2H,2H-per-
fluoroundecyl iodide in a variety of conditions (solvents: acetone,
DMF; bases: K2CO3, Cs2CO3, NaH) were unsuccessful, probably due
to elimination side-reactions. The esters were hydrolized with
lithium hydroxide in aqueous ethanol, to afford in good yields (64%
and 76%, respectively) the corresponding free acids 2 and 5. The
* Corresponding authors. Tel.: þ34 9 35 813 045; fax: þ34 9 35 811 265; e-mail
address: adelina.vallribera@uab.es (A. Vallribera).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.04.086

E. Faggi et al. / Tetrahedron 66 (2010) 5190e5195
5191
Table 1
Gelation abilities of fluorous compounds 1e3 in different organic solventsa
Solvent
Gelator
1
2
3
Silicone oil
Cyclohexane
Mineral oil
Undecane
Hexane
CG (10; 78 ꢀC)
P
I
P
P
I
S
I
P
OG (10; 46 ꢀC)
OGb
P
OG (11; 79 ꢀC)
VS
VS
VS
S
OG (9; 41 ꢀC)
CFC113c
S
Perfluorooctane
CCl4
Toluene
VSd
OG (22; 55 ꢀC)
P
S
S
OG (13, 45 ꢀC)
OG (17; 63 ꢀC)
CG (20; 56 ꢀC)
OG (8; 54 ꢀC)
OG (19; 53 ꢀC)
S
OG (10; 57 ꢀC)
CG (10; 54 ꢀC)
CG (25; 44 ꢀC)
OG (20; 47 ꢀC)
S
Dioxane
CG (18; 56 ꢀC)
Chloroform
Dichloromethane
Acetone
S
S
S
DMF
VS
CG (10; 48 ꢀC)
OG (9; 42 ꢀC)
CG (20; 60 ꢀC)
I
CG (10; 48 ꢀC)
CG (15; 45 ꢀC)
CG (12; 46 ꢀC)
I
tert-Butanol
Propionitrile
DMSO
OG (10; 43 ꢀC)
OG (18; 58 ꢀC)
P
Acetonitrile
Isopropanol
Ethanol
P
P
P
OG (8; 49 ꢀC)
VS
OG (10; 47 ꢀC)
P
CG (20; 45 ꢀC)
CG (12; 44 ꢀC)
a
CG: clear gel, OG: opaque gel, VS: viscous solution, P: precipitate, S: solution, I:
insoluble even at boiling temperature. Parentheses contain the MGC at 25 ꢀC (in mg/
ml) and the Tgel
.
b
Separates quickly in a precipitate and a viscous solution.
1,1,2-Trichloro-1,2,2-trifluoroethane.
c
d
OG at 4 ꢀC. Solvents are ordered by increasing Reichardt’s normalized empirical
parameter of solvent polarity ðETNÞ;16 polyfluorinated solvents were considered as
CCl4.
Scheme 1. Structures of organogelators 1e3 and synthesis of compounds 1e6. Con-
ditions: (a) C8F17(CH2)3I, K2CO3, acetone, reflux, overnight. (b) C11H23Br, KI, K2CO3,
acetone, reflux, 3 days. (c) LiOH, EtOH/H2O, reflux, overnight. (d) carbonyldiimidazole,
dichloromethane, reflux, 2 h; then propylamine, reflux, overnight.
In this work we present three new simple compounds that are
able to gelate a wide range of solvents (see Table 1). Ester 1 is the
most convenient for gelating apolar solvents such as cyclohexane,
hexane and also silicone and mineral oil. Less general behavior was
observed with polar solvents; however, ester 1 could also gelate
dioxane, propionitrile, and alcohols, such as tert-butanol and iso-
propanol. For solvents with a normalized empirical parameter of
polarity higher than that of toluene ðETN ¼ 0:099Þ (dioxane, chlo-
roform, dichloromethane, and DMF), compounds 2 and 3, con-
taining acid and amide moieties in their structures, are more
suitable. For all three compounds, gelation was prevented in
amides 3 and 6 were obtained in 70% and 80% yields by activation of
the acids with carbonyldiimidazole followed by reaction with
propylamine (Scheme 1).
The three semiperfluorinated compounds 1e3 were solid and
their solubility in organic solvent was rather low at room temper-
ature; however it significantly increased at higher temperatures.
On the other hand, while the ester 4 was a liquid, acid 5 and amide
6 were both solids with a good solubility in organic solvents at
room temperature.
2.2. Gelation studies
The gelation abilities of fluorous compounds 1e3 were in-
vestigated in various organic solvents and the results are summa-
rized in Table 1. Gelation tests were carried out following
a previously reported procedure:17 25 mg of the compound were
weighted in a vial, then 1 ml of the chosen solvent was added and
the mixture warmed until a clear solution was obtained. Upon
cooling down to room temperature and inversion of the vial, if the
solution did not flow, the compound was judged to be a gelator of
the corresponding solvent (Fig. 1). If a gel was formed, it was
evaluated quantitatively by determining the minimum gelator
concentration (MGC, expressed in mg/ml) needed to fully gelate the
solvent at 25 ꢀC. The MGC varied in the range 8e25 mg/ml
(5e15 mM), depending on the solvent and the gelator.
Gel formation occurred typically in 5e20 min. However, some
exceptions were observed: acid 2 gelated chloroform almost in-
stantly while ester 1 needed at least 1 h to gelate mineral oil. Gel-
to-sol phase transition temperatures (Tgel) were determined by the
‘inverse-flow method’.18 A sealed vial containing the gel was im-
mersed upside-down in a thermostated water-bath. The tempera-
ture of the bath was raised at a rate of 2 ꢀC/min. Tgel was defined as
the temperature at which the gel started to flow.
Figure 1. Gel obtained from 1 in silicone oil (left) and from 3 in perfluorooctane
(right).

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E. Faggi et al. / Tetrahedron 66 (2010) 5190e5195
acetone (due to the high solubility) and in highly polar aprotic
solvents such as DMSO or acetonitrile (ETN ¼ 0:444 and 0:460,
respectively), due to lack of solubility. However, highly polar protic
solvents, able to set up hydrogen bonds with the polar moieties
contained in 1e3 molecules, could be gelated in some cases, being
amide 3 the best gelator. It is noteworthy that fluorous amide 3
gelates also neat perfluorooctane, as perfluorocarbons (PFCs) are
probably the most difficult solvents to gelate, due to their low
surface tension, and only a few compounds were shown to gelate
pure PFCs.8 Fluorocarbon gels could be of great interest for topical
use to protect the skin or a wound while keeping it permeable to
gases.9a
opposite bilayer structure could be proposed as illustrated in
Figure 3.8c
Solvophilic
part
All the obtained gels were thermally reversible and stable for
weeks when stored at room temperature in closed vials in contact
with air. They were also thermally stable up to 40 ꢀC, being their
gel-to-sol transition temperature comprised between 42 ꢀC and
63 ꢀC. Exceptions are represented by the mineral oil and silicone oil
gels of 1, which exhibit superior thermal stabilities (Tgel 79 ꢀC and
78 ꢀC, respectively).
Solvophobic
part
Once we had determined the gelation properties of 1e3, in order
to get insight into the nature of the interactions involved in the
gelation process, we studied their anologues 4e6, in which the
fluoroponytails were replaced by aliphatic chains of the same
length. These new compounds were tested for gel formation in the
same solvents following the same procedure, but none displayed
gelation properties, not even with the concentration raised up to
50 mg/ml. This result clearly demonstrates that the semi-
perfluorinated chains play a key role in imparting the gelation
ability upon these molecules. In fact, organogelators 1e3 contains
two markedly different segments: a solvophilic polar head (ester,
acid, or amide group) and a solvophobic fluorous tail, joined by an
aromatic ring. In our case, it is probable that the organized mo-
lecular assembly is driven by the solvophobic property of the
semiperfluorinated chains that result in a molecular bilayer as the
fundamental building unit of the aggregate, as schematically il-
lustrated in Figure 2.
Solvophilic
part
Figure 3. Schematic illustration of the bilayer structure of 3 in fluorous media.
The presence of hydrogen-bonding interactions was in-
vestigated with NMR and IR studies. Among the three gelators,
secondary amide 3 was selected as its NH signal is easy to be
studied by both of these techniques and can provide useful in-
formation. Firstly, the IR peak characteristic of the amino moiety of
the chloroform xerogel of 3 (obtained by slow evaporation of the
solvent) falls within the expected ranges of H-bonded ones20
(3286 cmꢁ1 in chloroform and 3326 cmꢁ1 in perfluorooctane, NH
stretching band, see ESI). This observation suggests that hydrogen
bonding is involved in the organogel formation, as previously
described.8d Secondly, a variable temperature 1H NMR study of the
CDCl3 gel of 3 was carried out. At 60 ꢀC, when the system is a clear
solution, the signals are sharp (Fig. 4a), while when the tempera-
ture is lowered down, below the Tgel, the system gelates and a sig-
nificant line broadening of all the signals is observed (Fig. 4b). This
line broadening effect is common for gels and in some cases may
lead to unobservable (NMR silent) samples.21 All of the signals
present almost identical chemical shifts in both spectra and only
a small downfield shift (Dd¼0.07 ppm) for the signal of the NH
proton was observed. This result is similar to those found for other
Solvophilic
part
Solvophobic
part
Solvophilic
part
Figure 2. Schematic illustration of the bilayer structure of 1e3 in organic media.
In fact, ‘amphiphiles’ containing one or more perfluorinated
chains are known to self-assemble in microstructures in water or
organic media.19a,b Moreover, perfluoroalkyl fragments promote
the formation of fibers.19c Polar heads may interact further through
hydrogen bonding (in the case of 2 and 3) and/or dipolar in-
teractions; anyway, the fact that the non fluorous analogs 4e6 do
not display gelation abilities clearly shows that these interactions
represent a minor contribution. However, it is likely that in the
perfluorooctane gelation, the hydrogen-bond formation between
amide groups is an important driving force for aggregation, and an
Figure 4. 1H NMR spectra of 3 in CDCl3 at 60 ꢀC (a) and at room temperature (b); [3]¼
0.04 M.

E. Faggi et al. / Tetrahedron 66 (2010) 5190e5195
5193
amide-based organogelators 22 and confirms the presence of weak
hydrogen-bonding interactions.
2.3. Morphological characterization of the organogels
The morphologies of the obtained gels of 1e3 in various solvents
were determined by scanning electron microscopy (SEM). SEM im-
ages of the gels formed by compound 1 in hexane (Fig. 5) and in
isopropanol (see ESI) showed three-dimensional networks, con-
sisting of entangled bundles of fibers. These fibers were ribbon-
shaped and had an average width of 0.5 mm. In Figure 4 twists of
these ribbons and junction zones are clearly visible. This assembly is
closely packed and able to trap solvent molecules into its interstices.
Figure 7. SEM images of the viscous solution of 3 in cyclohexane.
As shown in Table 1, amide 3 formed stable gels in chloroform
and propionitrile, and the SEM images for these gels revealed the
already seen fibrillar structures (see ESI). On the other hand, 3
formed a very instable gel in cyclohexane, that separated quickly
in a colloidal precipitate and a viscous solution. SEM images of
the viscous solution revealed compact, globular aggregates of fi-
bers, resembling balls of wool. At the best of our knowledge, this
kind of assembly has never been reported before. The balls have
Figure 5. SEM image of the gel formed by compound 1 in hexane.
SEM images of the gel of compound 2 in chloroform (see ESI)
showed the same structures observed in the case of ester 1: long,
ribbon-like fibers of about 1e1.5 mm width and more than 100 mm
an average diameter of 2e3
fibers with an average diameter of 200e300 nm. As we can see in
Figure 6A, these globular assemblies co-exist with small
mm and are made of long, cylindrical
a
length. Zoom images (Fig. 6) showed that these ribbon-like fibers
are made of tinier fibers of about 100 nm width, thus revealing
a hierarchically organized assembly.
amount of elongated fibers. The analysis of these images
prompted us to propose a pathway for different evolution of the
assemblies formed. As presented schematically in Figure 8,
Figure 8. Schematic representation of the possible evolution pathways of the orga-
nogelator assemblies. (a) Common gel formation. (b) Behavior of 3 in cyclohexane.
Figure 6. SEM image of chloroform gel of 2.

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E. Faggi et al. / Tetrahedron 66 (2010) 5190e5195
polyfluorinated molecules promote the formation of loose fibers
that can assemble in three-dimensional networks, trapping sol-
vent molecules and allowing the formation of a stable gel (as
observed in Figs. 5 and 6). However, in the case of amide 3 in
cyclohexane, this network does not form, and the fibers start to
curl up (See Fig. 7C; a globular aggregate, that is, almost fully
formed, but still presents an elongated tail) and this process lead
to nanosized balls of wool (Fig. 7A,B). These aggregates are un-
able to entrap the solvent and result in a viscous solution that
evolves into a colloidal precipitate.
3.2. Materials
All reagents were obtained from commercial suppliers and used
without further purification. Acetone was distilled under nitrogen
from calcium chloride prior to use.
3.3. Synthesis
3.3.1. Propyl
yloxy)benzoate (1). To
3,4,5-tris(1H,1H,2H,2H,3H,3H-perfluoroundecan-1-
solution of propyl gallate (60 mg,
a
A tentative explanation for the formation of globular aggregates
is proposed: in a very apolar solvent such as cyclohexane, H-bonds
are strong enough to become the main driving force for the su-
pramolecular assembly. So in the case of amide 3 in cyclohexane,
probably the organization of gelator molecules is the same as in
perfluorooctane (amide groups in the inner part and perfluorinated
tails in the outer part of the bilayer). However in the case of cy-
clohexane the tails are solvophobic, and the fibers would be forced
to curl up in order to minimize the contact surface with the solvent.
0.28 mmol) in dry acetone (5 ml) were added 1H,1H,2H,2H,3H,3H-
perfluoroundecyl iodide (600 mg, 1.02 mmol) and K2CO3 (464 mg,
3.36 mmol) and the reaction mixture was stirred under nitrogen at
reflux overnight. Reaction was monitored via TLC (SiO2, hexane/
AcOEt 2:1) and then stopped. The reaction mixture was filtered on
Celite and the solid washed several times with acetone. The solu-
tion was concentrated to dryness, and the crude product was
digested in tetrahydrofuran. The solid filtered off and the filtrate
concentrated in vacuo, affording the desired product as a white
solid (500 mg, 98% yield). 1H NMR (400 MHz, CDCl3)
d 7.32 (s, 2H),
4.30 (t, J¼6.7 Hz, 2H), 4.15 (t, J¼5.8 Hz, 4H), 4.09 (t, J¼5.8 Hz, 2H),
2.50e2.25 (m, 6H), 2.21e2.13 (m, 4H), 2.11e2.00 (m, 2H), 1.82 (sext,
J¼7.3 Hz, 2H), 1.05 (t, J¼7.4 Hz, 3H). 13C{1H}-NMR (100.6 MHz,
2.4. Concluding remarks
The fluorous gallic acid derivatives 1e3, a new class of struc-
turally simple LMOGs, have been synthesized. These molecules
have shown the ability to gelate a wide range of different organic
solvents, from alkanes to alcohols, in 8e25 mg/ml concentration.
Compound 1 is the best gelator for apolar solvents, while 2 and 3
are more suitable to gelate polar protic and aprotic solvents. No-
tably, compound 3 is one of the few known molecules able to gelate
neat perfluorooctane. The analog compounds 4e6, in which all
fluorine atoms are replaced by hydrogens, were tested for gelation,
giving negative results and revealing that the driving force for the
aggregation/gelification process is the solvophobic effect displayed
by semiperfluorinated chains. Gelation process is likely to be an
equilibrium between the solubility of compounds and their ability
to organize themselves in different media.
Scanning electron microscopy showed that in all cases the
aggregates that lead to gelification have a fibrillar nature. The
SEM study of the 3/cyclohexane system revealed that the long
fibers curl up into globular assemblies resembling balls of wool,
instead of forming the entangled network responsible for gel-
ification. As the best of our knowledge, it is the first time that this
kind of structure has been described. Further studies will be
performed to establish if this behavior is observed in other cases.
A bilayer structure was proposed for the organization of gelator
molecules in fibers: semiperfluorinated chains are oriented in-
ward or outward the bilayer depending on the polarity of sol-
vents and the force of the intermolecular hydrogen bonds
formed.
CDCl3) d 166.0, 152.6, 141.9, 126.2, 108.9, 71.9, 67.9, 66.5, 28.0, 22.2,
20.7, 10.2. Mp¼92e94 ꢀC. IR (ATR): 2966, 1711, 1588, 1430, 1371,
1197, 1145, 1113, 687. HR-ESI-MS: 1615.0890 (MþNa)þ; calcd for
C43H27F51O5Na 1615.0936.
3.3.2. 3,4,5-Tris(1H,1H,2H,2H,3H,3H-perfluoroundecan-1-yloxy)ben-
zoic acid (2). To a suspension of the ester 2 (1.7 g, 1.1 mmol) in
ethanol (45 ml) was added a solution of LiOH$H2O (260 mg,
6.2 mmol) in water (5 ml) and the reaction mixture stirred at reflux
overnight. Reaction mixture was cooled down to room tempera-
ture, diluted HCl was added until pH 2 was reached and a white
solid formed. Additional 20 ml of water were added and more solid
formed. This was filtered, washed with more water and dried,
affording the desired product as a white powder (1.06 g, 64% yield).
1H NMR (400 MHz, acetone-d6, 40 ꢀC)
J¼5.8 Hz, 4H), 4.21 (t, J¼5.8 Hz, 2H), 2.62e2.48 (m, 6H), 2.21e2.17
d 7.40 (s, 2H), 4.28 (t,
(m, 6H). 13C{1H}-NMR (100.6 MHz, acetone-d6, 40 ꢀC)
d 166.9, 152.9,
142.4, 126.4, 109.1, 72.1, 68.1, 28.0, 21.8, 20.9. Mp¼128e130 ꢀC. IR
(ATR): 2960, 2360, 1686, 1588, 1434, 1371, 1196, 1145, 703. HR-ESI-
MS: 1573.0426 (MþNa)þ; calcd for C40H21F51O5Na 1573.0467.
3.3.3. 3,4,5-Tris(1H,1H,2H,2H,3H,3H
-perfluoroundecan-1-yloxy)
benzoic acid propyl amide (3). To a solution of the acid 2 (600 mg,
0.39 mmol) in dichloromethane (12 ml) and CFC113 (8 ml) was
added carbonyldiimidazole (75 mg, 0.46 mmol) and the mixture
was stirred under reflux for 2 h. Propylamine (42 ml, 0.51 mmol)
was added and the reaction mixture stirred at reflux overnight
under nitrogen. The reaction mixture was cooled down to room
temperature and washed three times with a diluted solution of HCl
(pH 2); the organic fraction was dried over Na2SO4 and concen-
trated to dryness. The crude product was washed with ethanol and
dried in vacuo, affording the desired product as a white powder
(437 mg, 70% yield). 1H NMR (400 MHz, CDCl3 and CFC113, 40 ꢀC)
3. Experimental
3.1. Apparatus
Scanning electron microscopy (SEM) observations were car-
ried out on an Hitachi S-570 electron microscope. The samples
for these measurements were prepared as follows: 1 mM solu-
tions of the organogelators were casted on silicon wafers, dried at
room temperature and finally coated with gold vapor. FT-IR
spectra were recorded on a Bruker Tensor 27 instrument. 1H NMR
and 13C NMR spectra were recorded on a Bruker AV400 spec-
trometer. High resolution mass spectra (HR-ESI-MS) were recor-
ded on a Bruker Daltonics microTOF instrument, equipped with
an electrospray source.
d
7.05 (s, 2H), 6.11 (t, J¼5.3 Hz, 1H), 4.15 (t, J¼5.8 Hz, 4H), 4.09 (t,
J¼5.8 Hz, 2H), 3.46 (m, 2H), 2.52e2.25 (m, 6H), 2.22e2.02 (m, 6H),
1.70 (sext, J¼7.3 Hz, 2H), 1.03 (t, J¼7.4 Hz, 3H). 13C{1H}-NMR
(100.6 MHz, CDCl3, 40 ꢀC)
d 167.8, 153.2, 141.7, 131.3, 107.0, 72.5,
68.8, 42.7, 30.0, 28.3, 23.3, 21.9, 21.1,11.6. IR (ATR): 3318, 2962, 2875,
1687, 1629, 1578, 1550, 1497, 1438. Mp¼100e102 ꢀC. HR-ESI-MS:
1614.1060 (MþNa)þ; calcd for C43H28F51O4NNa 1614.1096.
3.3.4. Propyl 3,4,5-tris(undecyloxy)benzoate (4). To a solution of
propyl gallate (2.6 g, 12.4 mmol) in dry acetone (140 ml) were

E. Faggi et al. / Tetrahedron 66 (2010) 5190e5195
5195
added undecyl bromide (10.0 ml, 44.6 mmol), K2CO3 (15.4 g,
111 mmol), and KI (920 mg, 5.6 mmol) and the reaction mixture
was stirred under nitrogen at reflux for 3 days. Reaction was
monitored via TLC (SiO2, hexane/AcOEt 5:1) and then stopped. The
reaction mixture was filtered on Celite and the solid washed several
times with acetone. The filtrate was concentrated to dryness, and
the crude product was purified via column flash chromathography
(SiO2, hexane/AcOEt, 15:1), affording the desired product as a pale
(Servei de Microscòpia-UAB) for his technical assistance in SEM
experiments.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tet.2010.04.086.
yellow liquid (4.2 g, 50% yield). 1H NMR (400 MHz, CDCl3)
d 7.29 (s,
2H), 4.28 (t, J¼6.7 Hz, 2H), 4.04 (t, J¼6.5 Hz, 6H), 1.89e1.71 (m, 6H),
References and notes
1.55e1.44 (m, 2H), 1.29 (m, 48H), 1.04 (t, J¼7.4 Hz, 3H), 0.91 (t,
J¼6.5 Hz, 9H). 13C{1H}-NMR (100.6 MHz, CDCl3)
d
166.9, 153.4,
1. (a) Terech, P.; Weiss, R. G. Chem. Rev. 1997, 97, 3133e3159; (b) Weiss, R. G.;
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Springer: Dordrecht, The Netherlands, 2006; (c) George, M.; Weiss, R. G. Acc.
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143.1, 125.7, 108.7, 73.9, 69.6, 66.8, 32.3, 30.7, 30.1, 30.0, 29.8, 26.5,
23.1, 22.6, 14.4, 10.9. IR: 2921, 2852, 2361, 1716, 1585, 1331, 1210,
1111. HR-ESI-MS: 697.5719 (MþNa)þ; calcd for C43H78O5Na
697.5741.
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3.3.5. 3,4,5-Tris(undecyloxy)benzoic acid (5). To a solution of the
ester 4 (3.0 g, 4.44 mmol) in ethanol (95 ml) was added a solution
of LiOH$H2O (1.12 g, 26.6 mmol) in water (5 ml) and the reaction
mixture stirred at reflux overnight. Reaction mixture was cooled
down to room temperature, diluted HCl was added until pH 2 was
reached and a white solid formed. Additional 50 ml of water were
added and more solid formed. This was filtered and dried. The
crude product was recrystallized from ethanol, affording the de-
sired product as a white powder (2.15 g, 76% yield). 1H NMR
(400 MHz, CDCl3)
6H), 1.56e1.45 (m, 6H), 1.40e1.25 (m, 42H), 0.90 (t, J¼7.1 Hz, 9H).
13C{1H}-NMR (100.6 MHz, CDCl3)
172.2, 153.0, 143.4, 123.8, 108.8,
d 7.35 (s, 2H), 4.09e4.02 (m, 6H), 1.90e1.72 (m,
d
73.7, 69.4, 32.1, 30.5, 29.9, 29.8, 29.7, 29.5, 26.2, 22.8, 14.2.
Mp¼53e54 ꢀC. IR (ATR): 2918, 2849, 1681, 1585, 1430, 1331, 1225,
1118. HR-ESI-MS: 655.5247 (MþNa)þ; calcd for C40H72O5Na
655.5272.
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ture was stirred at reflux for 2 h. Propylamine (160 ml, 1.9 mmol)
was added and the reaction mixture stirred at reflux overnight
under nitrogen. The reaction mixture was cooled down to room
temperature and washed three times with a diluted solution of HCl
(pH 2); the organic fraction was dried over Na2SO4 and concen-
trated to dryness. The crude product was washed with a little
amount of acetone and dried in vacuo, affording the desired
product as a white powder (852 mg, 80% yield). 1H NMR (400 MHz,
CDCl3)
d
6.98 (s, 2H), 6.26 (t, J¼5.6 Hz, 1H), 3.99 (t, J¼6.4 Hz, 6H),
3.39 (q, J¼6.7 Hz, 2H), 1.83e1.72 (m, 6H), 1.63 (sext, J¼7.3 Hz, 2H),
14. Abdallah, D. J.; Weiss, R. G. Langmuir 2000, 16, 352e355.
1.50e1.42 (m, 6H),1.38e1.20 (m, 42H), 0.97 (t, J¼7.4 Hz, 3H), 0.89 (t,
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J¼6.9 Hz, 9H). 13C{1H}-NMR (100.6 MHz, CDCl3)
d 167.5, 153.0, 141.1,
129.8, 105.8, 73.5, 69.4, 41.8, 31.9, 30.3, 29.7, 29.6, 29.3, 26.1, 22.7,
14.0, 11.4. Mp¼52e53 ꢀC. IR (ATR): 3270. 2918, 2850, 1629, 1580,
1550, 1499, 1335, 1112. HR-ESI-MS: 696.5878 (MþNa)þ; calcd for
C43H79O4NNa 696.5901.
Acknowledgements
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Financial support from Ministerio de Ciencia e Innovación of
Spain (Projects CTQ2008-05409-C02-01 and Consolider Ingenio
2010 (CSD2007-00006)) and DURSI-Generalitat de Catalunya (SGR
2009e1441) are gratefully acknowledged. We thank M. Rosado