Anhydrous proton conduction in self-assembled and disassembled ionic molecules

Article abstract of DOI:10.1039/c8ta00390d

In polymer based ionic conductors, the conductivity is suppressed by a low degree of chain mobility, therefore it is imperative to design a molecular system in which ionic groups can be mobilized and immobilized as a function of temperature to allow ions

Full text of DOI:10.1039/c8ta00390d

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Materials Chemistry A
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Anhydrous proton conduction in self-assembled
and disassembled ionic molecules†‡
Cite this: DOI: 10.1039/c8ta00390d
a
bc
Christoph Sieber,b Markus Klapperb
*
Avneesh Kumar,
Wojciech Pisula,
and Klaus Mullenb
¨
In polymer based ionic conductors, the conductivity is suppressed by a low degree of chain mobility,
therefore it is imperative to design a molecular system in which ionic groups can be mobilized and
immobilized as a function of temperature to allow ions to move freely as well as in a controlled manner
with a low energy barrier. Herein, we report an innovative approach to combine both the concepts of
self-assembly and disassembly of the functionalized molecules to investigate anhydrous ionic (proton)
conduction and related activation energy (Ea). For this purpose, organic proton conductors are designed
in such a way that self-assembly of the molecules can occur via non-covalent interactions giving rise to
an organized solid state in which ionic groups are held together via a network of hydrogen bonds. A new
class of anhydrous ionic conductors with hydrophobic and hydrophilic counterparts namely alkyl chains
and a phosphonic acid group, respectively, are investigated for fuel cell applications. The highest
anhydrous proton conductivity of up to 10ꢀ2 S cmꢀ1 at 140 ꢁC is recorded for these ionic molecules.
Thermal gravimetric analysis of these materials demonstrates their stability up to 190 ꢁC and thereby
their ability to perform at high temperature.
Received 12th January 2018
Accepted 3rd March 2018
DOI: 10.1039/c8ta00390d
rsc.li/materials-a
100 ꢁC. Other proton conducting materials such as polymers
doped with H3PO4, NaH4BF4 and NH4SCN have been reported.5,6
Introduction
Recently, a system consisting phosphosilicate, alkoxysilane and
H3PO4 has been claimed to show higher proton conductivity even
at medium temperature and under low humidity. The major
drawback of these materials is that the electrolyte used for proton
conduction leaches out of the system and decreases the
conductivity drastically. Therefore, new water insoluble electro-
lytes5–7 with high proton conducting properties are highly
demanded for fuel cell applications. It has been studied that the
proton conductivity decreases when the protogenic (ionic) groups
are immobilised; however, the highest proton conductivity can
only be achieved when the protogenic groups remain in free and
dynamic states allowing a faster hopping of ions or protons.
Self-organization of organic molecules with ionic function-
alities6–8 can lead to a better understanding of the structure–
property relationship phenomenon, particularly with regard to
ionic conductivity. Recently, porous nano-bers with ionic
channels were fabricated by using an electrospinning method.8
Further in this direction, acid–base block copolymer graed
graphene oxide8 and related composites8 have also been re-
ported for fuel cell membranes. This complex system was based
on ionic liquids, graphene oxide, SPEEK and proton conductive
chitosan. The same group has further advanced the research
focusing on imidazole based microcapsules for loading phos-
phoric acid molecules, thereby having high acid retention
ability.8 For porous nano-bers, the emphasis was on small
ionic liquid-like molecules due to their uidity, chemical
For more than two decades, the development of new types of
proton conductors other than Naon has been a major focus of
research for fuel cell applications. Many proton conducting
materials have been reported ranging from polymeric1–3 to non-
polymeric. In polymeric proton conductors, the ionic groups are
linked to the polymer chain via covalent linkage and are
responsible for proton conduction. In polymers, the location of
protogenic groups, the mobility of polymer chains4 and the
interaction of the ionic groups with each other have to be taken
into consideration while designing an ideal polymeric proton
conductor. Inorganic acids1,2 such as H2SO4 and H3PO4 have
been used as proton conducting materials due to their capability
of producing protons. Per-uorinated Naon4 membranes have
also been used as polymer electrolyte materials in fuel cells. The
applications of Naon are limited due to the requirement of
humidication for operation and its tendency to degrade above
aInstitute of Organic Chemistry, TU Darmstadt, L2|02, Room No. 554
Alarich-Weiss-Str. 4, 64287, Darmstadt, Germany. E-mail: avneesh.kumar@chemie.
tu-darmstadt.de; Fax: +4961511623527; Tel: +4917664104085
bMax Planck Institute for Polymer Research, Ackermannweg 10, Mainz, 55128,
Germany
cDepartment of Molecular Physics, Faculty of Chemistry, Lodz University of
Technology, Zeromskiego 116, 90-924 Lodz, Poland
† This paper is dedicated to Prof. K. Mullen on his 70th birthday.
¨
‡ Electronic supplementary information (ESI) available: Table for relative proton
conductivity, activation energy (Ea) and DSC data. See DOI: 10.1039/c8ta00390d
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stability and tunable compatibility that enabled the formation polymer was achieved to suggest that the phenomenon of
of interconnected ionic channels. nanochannel formation is associated with proton conduction.
In this study, a new class of organic phosphonates bearing In our endeavour, we have excluded any usage of amphiphilic
an amphoteric ionic functional group and hydrocarbon chains polymers and wanted to translate the self-assembly effect into
to form water insoluble supramolecular assemblies8–12 are phosphonated small molecules avoiding any necessity of
described for their proton conducting properties. These organic a complex chemical system. Additionally, the prediction about
phosphonates consist of long alkyl chains and a phosphonic the morphology of small phosphonated molecules with
acid group accountable for self-assembly and proton conduc- lyophilic chains and hydrophilic counterparts was rather
tion. Molecular organization was assisted and induced by the straight forward which offered the possibility to design such
hydrogen bonds of the pendant phosphonic acid group. The a molecular system in a simple and precise way by considering
temperature dependent transition from the assembled state to all the factors such as alkyl chains, pi–pi and hydrogen bond
a disassembled one allows these conductors to function in the interactions. Typically, proton conductivity depends on various
dry state at low temperature and in a high temperature regime. factors such as the concentration of the protogenic groups,12–14
Our investigations show a state-of-the-art strategy for devel- water uptake, and temperature.
oping proton conductors by combining two concepts: (1)
The distance between two protogenic groups also plays a very
supramolecular self-assembly in which all the molecules are crucial role for the protons to hop from one group to another.
allowed to remain held to form the ionic channels and (2) Thus, it is very necessary to design a proton conductor that has
disassembly, where all the molecules are free and have higher a high local concentration of protogenic groups, is insoluble in
diffusion enabling protons to move at a faster rate and thereby water and shows temperature dependent proton conductivity in
can show a higher conductivity for practical applications. To
further understand the objective of this research, a diagram-
matic illustration of the self-assembly of the molecules in which
ionic groups are immobilized inside the columns via hydrogen
bonds and of the disassembly of molecules with a mobilized
ionic head is depicted in Fig. 1.
Results and discussion
Ionic conductivity and self-assembled microstructures
A polymeric approach to enhance anhydrous proton conduction
via supramolecular assembly was explored by Thayumanavan
et al.11 In this attempt, an amphoteric benzotriazole based comb
Scheme 1 Synthesis of organic phosphonic acids (OPA) with different
alkyl chains.
Fig. 1 Schematic representation of the (a) self-assembly of the molecules into columns in which aliphatic chains and the aromatic spine remain
outside, and the ionic groups are located in the centre; (b) disassembly of the molecules into an isotropic phase in which molecules can move
freely with more kinetic energy and hence allow higher conduction (proton conduction is shown by normal and dotted arrows).
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conductivity of compound 6a begins to increase slightly as the
temperature rises above the melting point. Above 90 ꢁC,
the conductivity of compound 6a remains still low up to
10ꢀ9 S cmꢀ1. The low proton conductivity of 6a can be related to
its insulating segment (alkyl chains) and the random orienta-
tion of assembled molecular columns on the top of the elec-
trodes which in turn reduces the contact of ionic groups with
the electrode surface during measurements. As a result, real
intrinsic conductivity could not be measured. It can further be
concluded that when the protogenic groups are immobilized
inside the molecular columns, the conductivity remains low,
whereas aer heating and supplying energy to the system it
increases as the individual molecules turn more dynamic21–24
and mobile in order to facilitate a faster proton hopping. As
displayed in Fig. 3, compound 6d also forms a columnar type of
molecular architecture in the range of 85–130 ꢁC. These
columns were found to be disrupted as a result of high
temperature and melting, and therefore, no X-ray scattering
patterns were seen in melting phase or rather the liquid state
which is obvious as the molecular assembly was disintegrated at
high temperature. For example, compound 6d has shown major
scattering peaks for its hexagonally packed molecules as
depicted in Fig. 3b. These scattering patterns disappeared or
reduced signicantly when the temperature was raised to 120 ꢁC
Scheme 2 Synthesis of organic phosphonic acid with two arms of
alkyl chains at the 2 and 4 positions of the benzene ring.
the dry state. Organic phosphonic acid derivatives (6a–e, Scheme
1 and 2) were designed to fulll the above requirements. The
alkoxybenzyl phosphonic acid derivatives (6a–e) consist of
a hydrophobic segment represented by alkyl chains and an
aromatic ring, and a protogenic head represented by a phos-
phonic acid group. The hydrophobic segment is responsible for
inducing the self-organization12–15 and insolubility of these
materials in water thereby reducing water absorbance signi-
cantly.17–20 Recently, organic proton conducting crystals14–17 with
a columnar morphology induced via hydrogen bonds and pi–pi
stacking were reported. In these crystals, the proton conduction
was credited to the interconnected phosphonic groups. The
conductivity (s) of all compounds was measured as a function of
temperature. Compound 3,4,5-tris(dodecyloxy)benzyl phos-
phonic acid 6a has shown very low proton conductivity below its
melting temperature (Fig. 2). As observed in X-ray studies of the
columnar morphology (Fig. 3) of compound 6a, the protogenic
groups remain inside the axis of these columns whereas alkyl
chains were facing outward, and therefore three dimensional
interconnected ionic channels could not form in it.
ꢁ
(Fig. 1, ESI‡). Above 130 C compound 6d existed as a viscous
phase in which the molecular order was disrupted tremen-
dously. Obviously, molecular packing via non covalent interac-
tions disappeared in the melting or isotropic phase that
originated via disassembly of molecules.
Although both compound 6a and 6d have similar architec-
tures as estimated from X-ray experiments, but the compara-
tively higher conduction for 6d can be associated with its
relatively lower fraction of aliphatic chains.
A schematic illustration of molecular organization into
hexagonally packed columns and molecules in the dis-
assembled phase is shown in Fig. 1.
From Fig. 2, it should be noted that the conductivity of
ꢁ
compound 6d at 130 C increases by a magnitude of three as
Since alkyl chains and the aromatic spine act as an insulator
and do not play any role in proton conduction and due to their
higher fraction, 3,4,5-tris(dodecyloxy)benzyl phosphonic acid
(6a) and 3,4-bis(dodecyloxy)benzyl phosphonic acid (6d) exhibit
very low proton conductivity (Fig. 2). However, the proton
compared to the conductivity of compound 6a. Compound 6d
undergoes a Colh–Iso transition at 130 C as measured by DSC
ꢁ
(Table 1, ESI‡). From 85 ꢁC to 130 ꢁC, the conductivity remained
almost constant regardless of variation in temperature. Based
on these observations, it is suggested that the proton conduc-
ꢁ
tivity of compound 6d at above 130 C approaches its highest
value due to a phase transition offering extra kinetic energy and
mobility to the molecules in the molten state.
In contrast, compounds 6b-c with shorter and branched
alkyl chains did not show any columnar morphology and
appeared to be viscous under ambient conditions. It can thus be
concluded that a certain fraction of aliphatic chains is required
for the formation of a columnar architecture via the process of
self-assembly. However, the highest proton conductivity 5.5 ꢂ
10ꢀ3 S cmꢀ1 for compound 6b can be attributed to higher
diffusion and improved molecular mobility. The X-ray results in
Fig. 3a and b show a characteristic pattern for compounds 6a
and 6d respectively at 30 ꢁC. The large number of reections in
the pattern indicates a highly crystalline order. The scattering
intensities in the equatorial plane of the pattern are typical for
columnar structures which are aligned along the extrusion
Fig. 2 Anhydrous proton conductivity (s) of organic phosphonic acids
(6a–d) with different alkyl chain lengths, as a function of temperature. direction of the lament. The unit cell can be derived from the
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Fig. 3 Two dimensional (2D) WAXS diffractograms of (a) compound 6a and (b) compound 6d as an extruded filament at 30 ꢁC (above) and
scattering intensity distribution as a function of the scattering vector (below), and (c) a schematic illustration of self-assembled molecules (left
bottom) into hexagonally packed columns in which ionic groups are located in the center of the columns.
positions from the reections; however, in this case it was not
possible to nd an appropriate lattice. The meridional and off-
meridional reections represent correlations within the
columnar structures. Thereby, the individual building blocks
are tilted by ca. 40ꢁ towards the columnar axis. Recently, the
authors have reported a protogenic molecular wire with phos-
phonic acid groups facing externally, thereby causing an
increment in proton conductivity.17–20 In contrast, in our system,
the phosphonic acid groups are located in the centre of the
columns and hence are not involved in building up a contin-
uous ionic channels or pathway. Our studies further conclude
that the location of phosphonic acid groups in an ordered phase
plays a crucial role in the formation of interconnected nano-
channels and in determining the proton conduction. However,
Fig. 4 Anhydrous proton conductivity (s) of compound 6e with two
branched alkyl chains (C-8), as a function of temperature.
an accurate orientation of molecular columns with ionic
channels on an electrode surface should also be considered an
important factor while measuring the conductivity. In the
ordered phase of the molecules described above, an intra-
columnar period of 0.54 nm with a p-stacking distance of 0.41
nm was determined. The organization of the molecules into
these columnar superstructures can be regarded in two steps.
Firstly, the molecules form disc-like assemblies via hydrogen
bonds, which in the second step arrange via p-stacking inter-
actions, and local phase separation into columns occurs
between the aromatic part and aliphatic constituents.
for higher conduction can be linked with the faster ionic diffu-
sion19,20 and a low fraction of non-conducting alkyl chains
(insulator).
The linear sharp increment in the conductivity of 6e up to
60 ꢁC indicated that the mechanism for conduction was driven
by structural diffusion. The temperature dependent conduc-
tivity of compound 6e followed a linear curve below 110 ꢁC
(Fig. 4) which is in agreement with the Grotthuss mecha-
nism.18–20 At above 140 C, the decreased conductivity can be
ꢁ
In a separate study, for molecule 6e with two arms of branched
alkyl chains (C-8), the highest conductivity 2 ꢂ 10ꢀ2 S cmꢀ1 was
recorded at 120 ꢁC (Fig. 4). This peculiar and interesting behavior
correlated with the formation of an anhydride from the
condensation of two phosphonic acid groups.18–22 In the past,
some research groups18 have proposed that since phosphonic
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acid groups are hygroscopic, it may be difficult to remove water compounds 6a–e, the activation energies (Ea) were also esti-
or moisture completely from phosphonated polyelectrolytes. mated in order to study the proton conduction mechanism.31
Additionally, the release of water from P–O–P anhydride
The evaluation of activation energies (Ea) was done by
formation18 can inuence the conductivity. However, mate- considering the slope of the Arrhenius plots of relevant proton
rials with phosphonic acid groups are said to absorb a negli- conductivity. All values of activation energies (Ea) were obtained
gible amount of water as compared to their sulfonated by employing the Arrhenius equation19–22 according to
counterparts.18 It may be difficult to remove water from these
phosphonic acid groups if they are embedded deeply in the
microstructure of polymers. But for small molecules, elimi-
nation of water through a drying method seems not to be
a problem. Nevertheless, to prevent atmospheric moisture
from affecting the conductivity; the samples were dried at
60 ꢁC prior to the measurements. The samples for testing were
transferred into a closed chamber whose inner atmosphere
was maintained with N2 excluding further possibility of any
moisture. It should be noted that all the conductivity data
reported here were taken from the second heating cycle.
Scanning the sample for the second heating cycle provided an
accurate and intrinsic conductivity regardless of P–O–P anhy-
dride formation. From the X-ray results as well, it can be
interpreted that the formation of a columnar architecture via
self-assembly occurred only in the pristine form of material,
otherwise the presence of water molecules could have dis-
rupted the stacking of molecules and thus no columns with
pi–pi interactions would have formed. It should be empha-
sized that the samples for X-ray (2DWAXS) analysis were
prepared by an extrusion method in which the corresponding
material was heated to its deformable state suggesting the
absence of any water or moisture. The extent of anhydride
formation was not estimated experimentally due to the fact
that the conditions particularly humidity and temperature for
NMR and proton conductivity measurements will always
remain different and therefore will yield unmatched data. It is
further observed that compounds 6b and 6e display a higher
conduction during which less apparent activation energy
(Table 2, ESI‡) is required for proton hopping. In contrast,
compound 6c with a similar aliphatic chain length i.e. C-8 but
with a branched side chain i.e. C-2 demonstrates lower
conduction and needs relatively higher apparent activation
energy for the proton dynamic process. The side chains are
supposed to promote steric hindrance and reduce the mobility
of the molecule, thereby causing a slow proton diffusion which
in turn lowers the conduction of protons.19 It is to be noted
that the molecules of compounds 6a and 6d with two aliphatic
chains of C-11 self-assemble into a columnar morphology
(Fig. 3) despite the position of chains on the aromatic ring.
However, the packing of the molecules is found to be weaker
for compound 6d, evidenced by weaker intensity in the X-ray
diffractogram. A weak packing of the molecules (Fig. 3b) for 6d
is the possible reason for its higher conductivity as compared
6a. It is well known that the proton conduction in phospho-
nated proton exchange materials occurs via a hopping mech-
anism in which the protons move from one donor site to an
acceptor across a dynamic hydrogen bonded network. In this
process, the apparent activation energy (Ea) required for
proton transport must be 0.10–1.6 eV.22–24 In the case of
ꢀ
ꢁ
Ea
s ¼ s0 exp ꢀ
RT
The values for all apparent activation energies (Ea) estimated
are given in Table 2 (ESI‡). The values obtained were in the
range of 0.90–2.11 eV suggesting the involvement of a Grotthuss
type mechanism for proton transportation.19–25 The estimated
values of activation energies (Ea) have clearly suggested that the
mechanism did not involve any vehicle molecules such as
hydronium ions and was similar to that of the hopping process.
The linear plots of proton conductivity for compounds 6a–c at
90–180 ꢁC and for compound 6d at 90–130 ꢁC were ascribed to
the dominance of only one kind of mechanism for proton
conduction in the anhydrous state. The activation energies (Ea)
have also supported that the conduction was mediated by only
one type of mechanism both at lower and higher temperature. It
is also evidenced that the length and number of alkyl chains
play a signicant role in forming hexagonal columns of the
molecules22–32 for higher conduction. The factors such as
number and length of alkyl chains are found directly related to
the phenomenon of ionic channels and proton conduction in
general.
Thermal stability of ionic conductors
For fuel cell applications, high thermal stability is a very
essential criterion in order to prevent the material from degra-
dation at high temperature.18 The decomposition temperatures
of organic phosphonates are recorded by TGA, in which the
temperature dependent weight loss of the material can be
monitored. Fig. 5 shows the TGA curves of all organic phos-
phonic acid derivatives 6a–d.
All experiments were carried out under a N2 atmosphere at
a 10 ꢁC minꢀ1 heating rate. All derivatives (6a–e) were stable up
to 150 ꢁC. Compound 6a showed the rst decomposition at
Fig. 5 Thermal gravimetric analysis (TGA) of organic phosphonic acid
ion conductors.
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above 250 ꢁC which was attributed to the hydrocarbon content. the die. The inner diameters of the cylinder and the orice were
Decomposition via the C–P bond was not observed below 2.0 mm and 0.7 mm, respectively. The thickness of the la-
250 ꢁC. A slight weight loss was noticed at 100–150 ꢁC that can ments prepared by this method was about 0.7 mm. The move-
be associated with moisture since the phosphonic acid group ment of the pistol was controlled at the rate of 5 mm sꢀ1 in
may absorb some water from the atmosphere. Similar decom- order to have a high drawing rate of dl/dt ¼ 20 sꢀ1. All X-ray
position results were obtained for compounds 6d-e and 6b-c. diffraction measurements have shown no effect of drawing rate
Organophosphꢁonates (6a–d) underwent actual decomposition on the columns that were oriented in the direction of the
at around 290 C, indicating their higher temperature stability extrusion. A 2D wide-angle X-ray scattering (WAXS) setup was
(Fig. 5). The possible reason for the higher stability can be used to perform structure and self-assembly investigations. In
linked with the higher concentration of the alkyl chains.18 The all cases, the position of the samples was maintained perpen-
ꢁ
range of thermal stability (150–290 C) for these organic phos- dicular to the incident X-ray beam. The reection positions
phonated molecules has further suggested their capacity to be obtained in the 2D WAXS pattern can provide information
heat resistant without any degradation.
about the intra- and inter-columnar supramolecular organiza-
tion of the desired sample.
Experimental section
Materials
Anhydrous proton conductivity
The temperature dependent proton conductivity under dry
conditions was investigated by using a Schlumberger SI 1260
impedance/gain phase analyzer with a dielectric interface in the
frequency range from 10ꢀ1 to 106 Hz with the temperature
ranging from 20 ꢁC to 160 ꢁC with increments of 10 ꢁC. The
measurements were carried out on a Novocontrol cryostat
(Novocontrol, Hundsangen, Germany) in which the sample was
sandwiched between two Pt electrodes under a nitrogen gas
atmosphere. All samples were pressed in the form of pellets
using a pellet making instrument and dried in a vacuum oven at
60 ꢁC for 24 h prior to carrying out the proton conductivity
experiments.
All chemicals required for synthesis were purchased from
Aldrich and used without further purication. 1-Bromodode-
cane (Fluka; >99.5%), lithium aluminium hydride (95%,
Aldrich), sodium borohydride (98%, Aldrich), thionyl chloride
(99%, Aldrich), triethylphosphite (95%, Fluka), triethyl silyl
bromide (98%, Aldrich), triethyl amine (Fluka; p.a. > 99.5%),
methanol (Fisher Scientic; HPLC, 99.8%), toluene (Sigma
Aldrich; 99.8%), aqueous HCl (Prolabo; p.a. 37%), and NaOH
(Sigma Aldrich; 98%) were used as received.
Characterization
1H NMR and 13C NMR spectra were recorded on 250 MHz
1
Bruker spectrometers. H NMR chemical shis are reported in
General synthesis of compounds 6a–e (Scheme 1 and 2)
ppm vs. residual protons in deuterated solvents as follows: d ¼
3,4,5-Tris(dodecyloxy)benzyl phosphonic acid (6a)
7.27; CDCl3 and d ¼ 2.50; (CD3)2SO. Solvent proton or carbon
3,4,5-Tris(dodecyloxy)benzoate (6a). To a solution of 3,4,5-
trihydroxy benzoate (3.30 g, 17.92 mmol) in DMF (25 mL) in
a round bottom ask, 250 mL was added 1-bromododecane
(14.9 g, 59.78 mmol) and K2CO3 (9.9 g, 71.63 mmol). The reac-
signals were used as the internal standard for 1H NMR and 13
C
NMR measurements, respectively, while triphenylphosphine
(TPP) was applied for the calibration of the 31P NMR
measurements.
ꢁ
tion mixture was reuxed at 70 C under argon for 15 h. The
Thermal stability of all block copolymers was evaluated by
thermogravimetric analysis (TGA) on a Perkin Elmer TGA 7
thermogravimetric analyzer (10 K minꢀ1 heating rate in
a nitrogen atmosphere). All TGA trace data were obtained from
crude mixture was extracted with EtOAc. The organic layer was
washed with water, saturated aqueous NH4Cl and saturated
aqueous NaCl successively. Aer this, the organic phase was
dried over MgSO4 and ltered. All solvents were removed under
vacuum. A brownish crude mixture was obtained which was
further puried by crystallization.
ꢁ
ꢁ
30 C to 500 C.
Wide angle X-ray (WAX) measurements
Yield: 8.2 g, 94%.
The samples for 2D wide angle X-ray experiments were prepared
1H NMR (250 MHz, CD2Cl2, d): 88 (m, 9H), 1.25–147 (br m,
by a lament extrusion method where the material is heated to 54H), 1.76 (m, 6H), 3.88 (s, 3H), 4.00 (m, 6H), 7.25 (s, 2H).
its deformable state in order to extrude it as a thin lament. In
13C NMR (75 MHz, CD2Cl2, d): 14.10, 22.68, 23.50, 26.06,
this process, the deformed samples are processed mechanically 29.28, 29.38, 29.55, 29.62, 29.64, 29.68, 30.31, 31.91, 52.08,
through a piston along the cylinder by a constant-rate motion. 69.13, 73.47, 107.94, 124.62, 142.32, 152.80, 166.94.
A number of parameters such as the velocity of the piston,
FD-MASS: Cal. 519; found 519.
diameter of the cylinder and orice, and the shape of the die
3,4,5-tris(dodecyloxy)benzyl alcohol (3a). To a suspension of
govern this process. The macroscopic draw ratio (l ¼ (R/r)2) can LiAlH4 (9.22 mmol, 350 mg) in THF (10 mL) was added a solu-
be described by the ratio of the cylinder to orice diameters tion of 3,4,5-tris(dodecyloxy)benzoate (2a) (7.10 mmol, 4.90 g) in
whereas the drawing rate prole can be dened by the shape of THF (5 mL) at 0 ꢁC under argon. The reaction mixture was
the die used.
stirred at room temperature for 3 h. The progress of the reaction
The drawing rate remains constant in the conical die, was monitored by TLC. The reaction was quenched by the slow
whereas it becomes zero inside the cylinder and at the orice of addition of propanol (5 mL) followed by the addition of water
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(5 mL) and 30% solution of NaOH. The aqueous phase obtained
was extracted with 400 mL of EtOAc. A colorless solid was
Yield: 1.048 g, 98%.
1H NMR (250 MHz, CD2Cl2, d): 0.88 (m, 9H) 1.26 (br m, 48H),
afforded aer column chromatography (1 : 10 hexane : EtOAc). 1.43 (br m, 6H), 1.73 (br m, 6H), 2.88 (d, 2H), 3.89 (m, 6H), 6.41
Yield: 3.87, 87%.
(s, 2H), 9.40 (br s, 2H).
1H NMR (250 MHz, CD2Cl2, d): 0.88 (m, 9H), 1.26 (br m, 48H)
1.77 (m, 6H), 3.95 (m, 6H), 4.59 (s, 2H), 6.55 (s, 2H).
13C NMR (75 MHz, CD2Cl2): d 14.10, 22.69, 26.13, 26.21,
29.34, 29.48, 29.56, 29.66, 29.72, 29.78, 30.31, 31.94, 69.10,
13C NMR (75 MHz, CD2Cl2, d): 14.10, 22.68, 26.09, 26.13, 73.55, 108.34, 126.66, 136.70, 152.88.
29.36, 29.40, 29.65, 26.69, 26.75, 30.31, 31.92, 65.67, 69.09,
73.42, 105.32, 136.00, 137.57, 153.27.
FD-MASS: Cal. 725.0; found 725.3.
3,4,5(Octyloxy)benzyl phosphonic acid (6b)
3,4,5-Tris(octyloxy)benzoate (2b). To a solution of 3,4,5-trihy-
FD-MASS: Cal. 659; found 658.3.
3,4,5-Tris(dodecyloxy)benzyl chloride (4a). To a solution of droxybenzoate (3.80 g, 21.16 mmol) and DMF (20 mL) in
3,4,5-tris(dodecyloxy)benzyl alcohol (3a) (3.22 mmol), 2.13 g a round bottom ask, 250 mL, was added 1-iodooctane (17.78 g,
in DCM (50 mL) was added thionyl chloride (1 mL, 9.98 74.04 mmol) and K2CO3 (11.69 g, 84.58 mmol). The reaction
ꢁ
mmol) at 0 ꢁC. The reaction mixture was stirred at room mixture was reuxed at 70 C under argon for 15 h. The crude
temperature for 4 h. The progress of the reaction was moni- mixture was extracted with EtOAc. The organic layer was washed
tored by TLC. Aer 4 h, the reaction was quenched with with water, saturated aqueous NH4Cl and saturated aqueous
a saturated solution of NaHCO3. The aqueous phase was NaCl successively. Aer this, the organic phase was dried over
extracted with 400 mL of EtOAc. The organic phase was MgSO4 and ltered. All solvents were removed under vacuum. A
washed three times with a saturated solution of NaCl, dried brownish crude mixture was obtained which was further puri-
over MgSO4, and ltered. All solvents were removed under ed by crystallization.
vacuum. A viscous liquid was afforded which was the puried
by column chromatography.
Yield: 8.6 g, 95%.
1H NMR (250 MHz, CD2Cl2, d): 0.81 (m, 9H), 1.21–1.40 (br m,
30H), 1.60–1.75 (m, 6H), 3.76 (s, 3H), 3.80–3.93 (m, 6H), 7.15 (s,
Yield: 1.77 g, 87%.
1H NMR (250 MHz, CD2Cl2, d): 0.88 (m, 9H), 1.26 (br m, 48H) 2H).
1.77 (m, 6H), 3.95 (m, 6H), 4.47 (s, 2H), 6.55 (s, 2H).
13C NMR (75 MHz, CD2Cl2, d): 14.26, 23.08, 26.48, 26.21,
13C NMR (75 MHz, CD2Cl2, d): 14.10, 22.68, 26.09, 26.69, 29.69, 29.75, 29.90, 30.72, 32.24, 32.31, 69.47, 73.77, 107.98,
26.75, 29.36, 29.40, 29.65, 30.31, 31.92, 42.12, 65.67, 73.42, 125.17, 142.51, 153.24, 167.03.
105.32, 136.00, 137.57, 153.27.
FD-MASS: Cal. 680; found 679.8.
FD-MASS: Cal. 520.0; found 519.0.
3,4,5-Tris(octyloxy)benzyl alcohol (3b). To a suspension of
3,4,5-Tris(dodecyloxy)benzyl phosphonate (5a). In a round LiAlH4 (17.26 mmol, 655 mg) in THF (10 mL) was added
bottom ask of 250 mL, 3,4,5-tris(dodecyloxy)benzyl chloride a solution of 3,4,5-tris(octyloxy)benzoate (2b) (13.29 mmol,
(4a) ꢁ(1.78 g, 4.33 mmol) and triethylphosphite were reuxed at 6.92 g) in THF (5 mL) under argon. The reaction mixture was
135 C for 48 h. Aer this period, the excess triethylphosphite stirred at room temperature for 3 h. The progress of the reaction
was removed by vacuum. The obtained crude mixture was was monitored by TLC. The reaction was quenched by the slow
puried by column chromatography. A colorless solid was addition of propanol (5 mL) followed by the addition of water
afforded aer the evaporation of all solvents under vacuum.
(5 mL) and 30% solution of NaOH. The aqueous phase obtained
was extracted with 400 mL of EtOAc. A colorless solid was
Yield: 1.42 g, 86%.
1H NMR (250 MHz, CD2Cl2, d): 0.88 (m, 9H), 1.26 (br m, 48H), afforded aer column chromatography (1 : 10 hexane : EtOAc).
1.43 (br m, 6H), 1.73 (br m, 6H), 2.88 (d, 2H), 3.89 (m, 6H), 6.41
(s, 2H).
Yield: 5.40, 88%.
1H NMR (250 MHz, CD2Cl2, d): 0.77–0.83 (m, 9H), 1.21–1.41
13C NMR (75 MHz, CD2Cl2, d): 14.25, 16.58, 16.68, 23.07, (br m, 30H), 1.56–1.76 (m, 6H), 3.78–3.90 (m, 6H), 4.46 (s, 2H),
26.44, 30.03, 30.09, 32.32, 32.45, 34.28, 62.24, 62.32, 69.63, 6.46 (s, 2H).
69.72, 114.32, 114.36, 115.94, 116.04, 122.37, 122.47, 124.67,
124.79, 143.53, 143.58, 149.45, 149.49.
13C NMR (75 MHz, CD2Cl2, d): 14.20, 22.7, 25.9, 29.3, 31.9,
65.5, 69, 105.6, 134, 137.5, 153.3.
FD-MASS: Cal. 781.8; found 781.0.
FD-MASS: Cal. 492.79.0; found 491.53.0.
3,4,5-Tris(dodecyloxy)benzyl phosphonic acid (6a). To a solu-
3,4,5-Tris(octyloxy)benzyl chloride (4b). To a solution of 3,4,5-
tion of 3,4,5-tris(dodecyloxy)benzyl phosphonate (5a) (2.233 tris(octyloxy)benzyl alcohol (3b) (9.308 mmol, 4.58 g) in DCM
mmol, 1.74 g) in DCM in a round bottom ask of 250 mL was (50 mL) was added thionyl chloride (2 mL, 28.85 mmol) at 0 ꢁC.
added trimethyl silane bromide (13.67 mmol, 1.17 mL) at room The reaction mixture was stirred at room temperature for 4 h.
temperature. The solution was stirred at room temperature for The progress of the reaction was monitored by TLC. Aer 4 h,
14 h. Aer this, the solvent of the reaction mixture was removed the reaction was quenched with a saturated solution of
under vacuum. The obtained crude mixture was treated with an NaHCO3. The aqueous phase was extracted with 400 mL of
excess of MeOH, in order to carry out methanolysis. The reac- EtOAc. The organic phase was washed three times with a satu-
tion mixture was stirred at room temperature for another 14 h. rated solution of NaCl, dried over MgSO4, and ltered. All
Aer this period, the solvent was removed from the reaction solvents were removed under vacuum. A viscous liquid was
mixture under vacuum. A colorless solid compound was afforded and was puried by column chromatography.
obtained.
Yield: 2.74 g, 76%.
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1H NMR (250 MHz, CD2Cl2, d): 0.77–0.83 (m, 9H), 1.21–1.43
13C NMR (75 MHz, CD2Cl2, d): 11.53, 14.41, 14.45, 23.64,
(br m, 30H), 1.59–1.73 (m, 6H), 3.80–3.90 (m, 6H), 4.44 (s, 2H), 23.69, 24.30, 24.34, 29.63, 29.86, 31.04, 40.21, 41.14, 65.67,
6.49 (s, 2H).
13C NMR (75 MHz, CD2Cl2, d): 14.1, 22.7, 25.9, 29.3, 29.6,
71.68, 76.39, 105.0, 136.9, 137.6, 153.8.
FD-MASS: Cal. 492.79; found 492.7.
31.9, 46.8, 105, 130.6, 138.6, 153.3.
FD-MASS: Cal. 511.24; found 510.3.
3,4,5-Tris(ethylhexyloxy)benzyl chloride (4c). SOCl2 was used to
carry out the chlorination of the benzyl alcohol precursor as
3,4,5-Tris(octyloxy)benzyl phosphonate (5b). In a round bottom described for 3,4,5-tris(octyloxy)benzyl chloride.
ask of 250 mL, 3,4,5-tris(octyloxy)benzyl chloride (4b) (2.209 g,
4.33 mmol) and triethylphosphite (43.39 mmol, excess) were
reuxed at 135 ꢁC for 48 h. Aer this period, the excess trie- (m, 27H), 3.7–3.77 (m, 6H), 4.45 (s, 2H), 6.50 (s, 2H).
Yield: 75%.
1H NMR (250 MHz, CD2Cl2, d): 0.82–0.87 (m, 18H), 1.23–145
thylphosphite was removed by vacuum. The obtained crude
13C NMR (75 MHz, CD2Cl2, d): 11.38, 11.50, 14.37, 14.41,
mixture was puried by column chromatography. A colorless 23.59, 23.65, 24.25, 24.32, 29.59, 29.81, 31.0, 40.1, 47.6, 71.7,
solid was afforded aer the evaporation of all solvents under 76.3, 106.9, 132.8, 138.6, 153.8.
vacuum. The crude mixture was puried by column chroma-
tography (30% EtOAc : hexane).
FD-MASS: Cal. 511.24; found 510.5.
3,4,5-Tris(ethylhexyloxy)benzyl phosphonate (5c). The phos-
phonation was carried out using the Arbuzov reaction as
Yield: 1.42 g, 68%.
1H NMR (250 MHz, CD2Cl2, d): 0.79–0.85 (m, 12H), 1.25–1.46 described for 3,4,5-tris(octyloxy)benzyl phosphonate.
(br m, 30H), 1.59–1.75 (m, 6H), 3.90–4.0 (m, 6H), 6.49 (s, 2H).
13C NMR (75 MHz, CD2Cl2): d 14.1, 16.3, 22.7, 25.9, 29.3, 29.6,
31.9, 40.3, 62.2, 105.4, 125.5, 130.6, 135.6, 153.3.
FD-MASS: Cal. 612.88; found 611.1.
Yield: 72%.
1H NMR (250 MHz, CD2Cl2, d): 0.81–0.87 (m, 18H), 1.16 (t,
6H), 1.22–1.45 (m, 27H), 2.93 (d, 2H), 3.69–3.75 (m, 6H), 3.85–4
(m, 4H), 6.38 (d, 2H).
3,4,5-Tris(octyloxy)benzyl phosphonic acid (6b). To a solution
13C NMR (75 MHz, CD2Cl2, d): 14.28, 14.32, 16.62, 23.52,
of 3,4,5-tris(octyloxy)benzyl phosphonate (5b) (2.48 mmol, 1.52 23.57, 24.21, 29.50, 29.74, 30.9, 30.95, 33.24, 35.07, 40.08, 41.01,
g) in DCM in a round bottom ask of 250 mL was added tri- 62.33, 62.42, 71.62, 76.25, 108.03, 108.11, 127.0, 127.12, 137.28,
methyl silane bromide (13.67 mmol, 1.17 mL) at room 137.33, 153.61, 153.66.
temperature. The solution was stirred at room temperature for
FD-MASS: Cal. 613.0; found 612.9.
15 h. Aer this, the solvent of the reaction mixture was removed
3,4,5-Tris(ethylhexyloxy)benzyl phosphonic acid (6c). The
under vacuum. The obtained crude mixture was treated with an hydrolysis was carried out using a similar procedure as
excess of MeOH, in order to carry out methanolysis. The reac- described for 3,4,5-tris(octyloxy)benzyl phosphonic acid.
tion mixture was stirred at room temperature for another 15 h.
Aer this period, the solvent was removed from the reaction
Yield: 98%.
1H NMR (250 MHz, CD2Cl2, d): 0.81–0.87 (m, 18H), 1.22–1.45
mixture under vacuum. A colorless solid compound was (m, 27H), 2.93 (d, 2H), 3.69–3.75 (m, 6H), 6.8 (d, 2H).
obtained.
Yield: 1.42 g, 97%.
13C NMR (75 MHz, CD2Cl2, d): 22.53, 23.25, 30.46, 30.74, 30.9,
30.95, 33.24, 35.07, 40.08, 41.01, 62.33, 62.42, 71.62, 76.25,
1H NMR (250 MHz, CD2Cl2, d): 0.79–0.85 (m, 9H), 1.17–1.29 108.03, 108.11, 127.0, 128.12, 135.28, 136.33, 151.61, 152.66.
(br m, 30H), 1.69–1.72 (m, 6H), 3.90–4.0 (m, 6H), 6.49 (s, 2H),
3,4-Bis(dodecyloxy)phosphonic acid (6d)
8.90 (s, H).
3,4-Bis(dodecyloxy)benzaldehyde (2d) (Scheme 2). To a solution
13C NMR (300 MHz, CD2Cl2): d 14.3, 22.9, 26, 29.7, 29.9, 32.0, of 3,4-dihydroxybenzaldehyde (1.55 g, 11.22 mmol) in DMF
40.7, 105.8, 125.9, 130.8, 135.8, 153.7.
(25 mL) in a round bottom ask of 250 mL was added 1-bro-
3,4,5-Tris(ethylhexyloxy)phosphonic acid (6c)
mododecane (6.99 g, 28.04 mmol) and K2CO3 (4.65 g,
3,4,5-Tris(ethylhexyloxy)benzoate (2c). Alkylation of 3,4,5-tri- 33.64 mmol). The above reaction mixture was reuxed at 70 ꢁC
hydroxybenzoate was carried out as reported above for 3,4,5- for 6 h. Aerwards, to this DCM, 400 mL, was added in order to
tris(octyloxy)benzoate. 2-Ethylhexylbromide was used as an extract organic products. The organic phase was washed with
alkylating reagent.
Yield: 98%.
water and a saturated solution of NaCl. The resulting organic
phase was dried over MgSO4 and ltered. All solvents were
1H NMR (250 MHz, CD2Cl2, d): 0.77–0.88 (m, 18H), 1.24–130 removed under vacuum. An off-white product was obtained
(m, 27H), 3.77 (s, 3H), 3.79–3.82 (m, 6H), 7.16 (s, 2H).
13C NMR (75 MHz, CD2Cl2, d): 11.62, 23.69, 23.74, 14.51, 29.7,
29.92, 31.10, 31.15, 40.27, 41.29, 76.34, 107.95, 125.23, 142.91,
153.62, 167.14.
FD-MASS: Cal. 521.2; found 520.0.
3,4,5-Tris(ethylhexyloxy)benzyl alcohol (3c). LiAlH4 was used to
aer crystallization with EtOAc.
Yield: 2.46 g, 65%.
1H NMR (250 MHz, CD2Cl2, d): 0.80 (t, 6H), 1.19–1.33 (m,
36H), 1.70–177 (br m, 4H), 3.90 (q, 4H), 6.90 (d, 1H), 7.28 (d,
1H), 7.32 (d, 1H), 9.72 (s, 1H).
13C NMR (75 MHz, CD2Cl2, d): 15.28, 15.32, 16.66, 23.48,
carry out the reduction of the benzoate precursor as described 23.54, 24.22, 29.47, 29.74, 30.9, 30.95, 33.24, 35.07, 40.08, 41.01,
for 3,4,5-tris(octyloxy)benzyl alcohol.
Yield: 88%.
62.33, 62.42, 71.62, 76.25, 108.03, 108.11, 127.0, 126.12, 134.23,
136.35, 150.56, 152.26.
1H NMR (250 MHz, CD2Cl2, d): 0.77–0.88 (m, 18H), 1.24–130
(m, 27H), 3.6–3.7 (m, 6H), 4.47 (d, 2H), 6.47 (s, 2H).
FD-MASS: Cal. 474.77; found 475.12.
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3,4-Bis(dodecyloxy)benzyl alcohol (3d) (Scheme 2). To
Journal of Materials Chemistry A
13C NMR (75 MHz, CD2Cl2, d): 16.76, 18.67, 22.50, 24.67,
27.46, 28.75, 32.9, 32.95, 33.56, 35.70, 40.08, 41.01, 62.33, 62.42,
71.62, 76.25, 108.03, 110.11, 125.24, 127.15, 128.36, 128.96,
138.40, 150.46.
a suspension of NaBH4 (0.118 g, 3.12 mmol) in THF, 5 mL in
a round bottom ask of 250 mL was added a solution of
ꢁ
compound 2d (0.74 g, 1.56 mmol) in THF 10 mL at 0 C. The
FD-MASS: Cal. 540.77; found 541.0.
3,4-Bis(octyloxy)benzyl phosphonic acid (6e) (Scheme 2)
3,4-Bis(octyloxy)benzaldehyde (2e) (Scheme 2).
synthetic procedure was followed for obtaining 2e (as described
for 2a) from its precursor.
above reaction mixture was stirred at room temperature for 3 h
and aerwards heated up to 70 ꢁC for 8 h. The reaction was
quenched with water, 10 mL, and then extracted with DCM, 400
mL. The organic phase was washed with a saturated solution of
NaCl and then dried over MgSO4 and ltered. All solvents were
removed under vacuum. A colorless product was obtained.
Yield: 0.740 g, 88%.
A similar
Yield: 92%.
1H NMR (250 MHz, CD2Cl2, d): 0.79 (t, 6H), 1.21–1.33 (m,
20H), 1.67–177 (m, 4H), 3.22 (s, 2H), 3.90–4.0 (m, 4H), 6.88 (d,
1H), 7.28–7.35 (td, 2H), 9.72 (s, 1H).
1H NMR (250 MHz, CD2Cl2, d): 0.80 (t, 6H), 1.19 (m, 32H),
1.42 (br m, 4H), 1.76 (m, 4H), 3.99 (m, 4H), 4.47 (d, 2H), 6.75 (d,
2H), 6.82 (s, 1H).
13C NMR (75 MHz, CD2Cl2, d): 12.62, 22.69, 22.74, 23.51, 29.7,
29.92, 31.10, 31.15, 40.27, 41.29, 76.34, 107.95, 125.23, 142.91,
153.62, 167.14.
13C NMR (75 MHz, CD2Cl2, d): 14.23, 14.40, 15.64, 22.42,
23.46, 25.26, 28.47, 28.74, 30.9, 30.95, 33.24, 35.07, 40.08, 41.01,
62.33, 62.42, 71.62, 76.25, 108.03, 108.11, 127.0, 127.18, 132.24,
134.46, 146.48, 150.46.
FD-MASS: Cal. 362.56; found 361.5.
3,4-Bis(octyloxy)benzyl alcohol (3e) (Scheme 2). The reduction
of 3,4-bis(octyloxy)benzaldehyde into its corresponding alcohol
was carried out as described for 3,4-bis(dodecyloxy)benzyl
alcohol.
FD-MASS: Cal. 476.79; found 476.0.
3,4-Bis(dodecyloxy)benzyl chloride (4d) (Scheme 2). To a solu-
tion of compound 3d (0.605 g, 1.27 mmol) in DCM, 15 mL
thionyl chloride (3.94 mmol) was added at 0 ꢁC. Aerwards, the
reaction mixture was stirred at room temperature for 8 h. The
reaction was quenched with a saturated solution of NaHCO3
and extracted with DCM, 400 mL. The obtained organic phase
was washed with a saturated solution of NaHCO3 and dried over
MgSO4 and subsequently ltered. All solvents were removed
under vacuum.
Yield: 86%.
1H NMR (250 MHz, CD2Cl2, d): 0.77–0.83 (m, 6H), 1.21–1.4
(m, 20H), 1.61–1.73 (m, 4H), 3.8–3.9 (m, 4H), 4.46 (s, 2H), 6.75
(d, 1H), 6.81 (td, 2H).
13C NMR (75 MHz, CD2Cl2, d): 13.64, 20.67, 22.84, 23.64, 29.7,
29.92, 31.10, 31.15, 40.27, 41.29, 76.34, 108.95, 126.23, 138.91,
148.62, 159.14.
FD-MASS: Cal. 364.57; found 363.9.
Yield: 0.357 g, 78%.
1H NMR (250 MHz, CD2Cl2, d): 0.80 (t, 6H), 1.19 (m, 32H),
1.42 (br m, 4H), 1.76 (m, 4H), 3.89 (m, 4H), 4.47 (s, 2H), 6.75 (td,
2H), 6.82 (s, 1H).
3,4-Bis(octyloxy)benzyl chloride (4e) (Scheme 2). The chlorina-
tion was carried out similarly as described for other benzyl
alcohol derivatives.
13C NMR (75 MHz, CD2Cl2, d): 15.24, 15.40, 15.70, 22.42,
23.46, 25.26, 28.47, 28.74, 30.9, 30.95, 33.24, 35.07, 40.08, 41.01,
62.33, 62.42, 71.62, 76.25, 108.03, 110.12, 122.28, 127.15,
132.80, 133.80, 148.50, 153.44.
Yield: 87%.
1H NMR (250 MHz, CD2Cl2, d): 0.77–0.83 (m, 6H), 1.21–140
(m, 20H), 1.64–1.76 (m, 4H), 3.86–3.91 (m, 4H), 4.47 (s, 2H), 6.71
(d, 1H), 6.76–6.83 (td, 2H).
13C NMR (75 MHz, CD2Cl2, d): 14.54, 16.56, 19.84, 22.64, 26.7,
27.92, 30.10, 31.15, 40.27, 41.29, 76.34, 108.95, 126.23, 138.91,
148.62, 159.14.
FD-MASS: Cal. 494.0; found 493.7.
3,4-Bis(dodecyloxy)benzyl phosphonate (5d) (Scheme 2). A
similar synthetic procedure was followed for 3,4-bis(dodecyloxy)
benzyl phosphonate 5d as that described for 3,4,5-tris(octyloxy)
benzyl phosphonate 5b.
FD-MASS: Cal. 383.02; found 381.8.
3,4-Bis(octyloxy)benzyl phosphonate (5e) (Scheme 2). The
phosphonation was carried out as mentioned before for 3,4-
bis(dodecyloxy)benzyl phosphonate (5d).
Yield: 69%.
1H NMR (250 MHz, CD2Cl2, d): 0.79 (t, 6H), 1.13 (t, 6H), 1.18–
120 (m, 32H), 1.73 (m, 4H), 2.94 (s, 2H), 3.83–3.95 (m, 8H), 6.75
(td, 2H), 6.82 (s, 1H).
Yield: 85%.
1H NMR (250 MHz, CD2Cl2, d): 0.77–0.83 (m, 6H), 1.15 (t, 4H),
1.21–1.32 (m, 20H), 1.63–175 (m, 4H), 3.83–3.95 (m, 8H), 6.72 (d,
1H), 6.78–6.81 (td, 2H).
13C NMR (75 MHz, CD2Cl2, d): 12.26, 13.46, 14.65, 20.42,
23.46, 25.26, 28.47, 28.74, 30.9, 30.95, 33.24, 35.07, 40.08, 41.01,
62.33, 62.42, 71.62, 76.25, 108.03, 108.11, 127.0, 128.15, 130.28,
132.48, 145.40, 153.46.
13C NMR (75 MHz, CD2Cl2, d): 13.84, 16.18, 16.26, 22.65,
26.03, 29.27, 29.38, 31.83, 33.88, 61.84, 61.93, 69.22, 69.31,
113.91, 113.95, 115.53, 115.61, 121.97, 122.07, 124.25, 124.37,
148.13, 148.18, 149.04, 149.08.
FD-MASS: Cal. 596.88; found 595.
3,4-Bis(dodecyloxy)benzyl phosphonic acid (6d) (Scheme 2). A
similar procedure was followed for the hydrolysis as described
for 3,4,5-tris(octyloxy)benzyl phosphonic acid 6b.
Yield: 98%.
FD-MASS: Cal. 484.66; found 484.1.
3,4-Bis(octyloxy)benzyl phosphonic acid (6e) (Scheme 2). The
hydrolysis was carried out by treatment with TMSiBr and MeOH
as described for 3,4-bis(dodecyloxy)benzyl phosphonic acid 6d.
Yield: 97%.
1H NMR (250 MHz, CD2Cl2, d): 0.78 (t, 6H), 1.10–127 (m,
32H), 1.73 (m, 4H), 2.94 (s, 2H), 6.75 (td, 2H), 6.82 (s, 1H).
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1H NMR (250 MHz, CD2Cl2, d): 0.77–0.83 (m, 6H), 1.21–1.32
(m, 20H), 1.63–175 (m, 4H), 3.83–3.95 (m, 4H), 6.72 (d, 1H),
6.78–6.81 (td, 2H).
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13C NMR (75 MHz, CD2Cl2, d): 11.37, 11.94, 12.65, 12.86,
18.65, 19.56, 20.65, 25.56, 26.12, 28.56, 28.78, 29.46, 30.45,
30.95, 35.56, 40.24, 58.67, 110.56, 124.65, 133.67, 144.56,
157.45.
FD-MASS: Cal. 383.2; found 382.1.
Conclusions
This research study has shown a new strategy that combines the
concepts of molecular assembly and disassembly for investi-
gating the proton conductivity; rst, in an immobilized system
where the molecules were self-organized as evidenced by X-ray
analysis, and second, in an isotropic phase where the molecules
were free to move. Proton conductors with a low density of
insulating alkyl chains have shown a higher proton conductivity
of up to 8 ꢂ 10ꢀ2 S cmꢀ1 at 140 ꢁC. The activation energy (0.09–
2.11 eV) has indicated that the conduction was driven by the
hopping of the protons from one site to another. Further, due to
their ability to withstand a higher temperature up to 190 ꢁC
without any degradation, organophosphonates presented here
would further open the door for developing new proton con-
ducting membranes in which ionic molecules with reversible
self-assembly can operate both at low and high temperature,
and thereby can be promising polyelectrolytes for fuel cell
applications. Obviously, the weak mechanical properties of
small ionic molecules do not generally allow stable lm
formation. A system comprising these phosphonated molecules
and a suitable polymer matrix can be envisioned to reapply our
approach and to integrate the system into a fuel cell device.
Nevertheless, these organic phosphonated molecules decorated
with lyophilic hydrocarbon chains can also withstand any threat
of washing out during operation due to their insolubility in
water. A further aim and extension of this work will be the
identication and choice of an appropriate polymer lm to
interpenetrate these proton conductors into the polymer matrix
that can be directly integrated into a device.
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Acknowledgements
The generous nancial support from the German Research
Foundation (Deutsche Forschungsgemeinscha) is greatly
appreciated.
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