Ionic liquid crystals derived from amino acids

Article abstract of DOI:10.1002/chem.201302319

Novel chiral amino acid derived ionic liquid crystals with amine and amide moieties as spacers between the imidazolium head group and the alkyl chain were synthesised. The key step in the synthesis utilised the relatively uncommon SO₃ leaving group in a microwave-assisted reaction. The mesomorphic properties of the mesogens were determined by differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction. All liquid crystalline salts exhibit a smecticA mesophase geometry with strongly interdigitated bilayer structures. An increase of the steric bulk of the stereogenic centre hindered the formation of mesophases. In case of phenylalanine-derived derivatives a mesomorphic behaviour was observed for shorter alkyl chains as compared to other amino acid derivatives indicating an additional stabilising effect by the phenyl moiety. Ionic liquid crystals from amino acids: Novel chiral amino acid derived imidazolium salts with amine or amide units were prepared through the sulfamidate. Depending on the steric bulk of the R group, the chain lengths and the type of anion X, stable SmA phases were detected (see scheme; Bn=benzyl). Copyright

Full text of DOI:10.1002/chem.201302319

DOI: 10.1002/chem.201302319
Ionic Liquid Crystals Derived from Amino Acids
Markus Mansueto, Wolfgang Frey, and Sabine Laschat*[a]
Abstract: Novel chiral amino acid de-
scanning calorimetry (DSC), polarising
optical microscopy (POM) and X-ray
diffraction. All liquid crystalline salts
exhibit a smectic A mesophase geome-
try with strongly interdigitated bilayer
structures. An increase of the steric
rived ionic liquid crystals with amine
and amide moieties as spacers between
the imidazolium head group and the
alkyl chain were synthesised. The key
step in the synthesis utilised the rela-
tively uncommon SO3 leaving group in
bulk of the stereogenic centre hindered
the formation of mesophases. In case
of phenylalanine-derived derivatives
a
mesomorphic behaviour was ob-
served for shorter alkyl chains as com-
pared to other amino acid derivatives
indicating an additional stabilising
effect by the phenyl moiety.
Keywords: amino acids · amino al-
cohols · chiral pool · ionic liquids ·
liquid crystals
a
microwave-assisted reaction. The
mesomorphic properties of the meso-
gens were determined by differential
Introduction
The combination of ionic liquids (ILs) and liquid crystals
(LCs) results in ionic liquid crystals (ILCs), which possess
chemical and physical properties found in both families of
compounds, that is, fluidity, low vapour pressure and ionic
conductivity from the ILs and anisotropic physical proper-
ties such as birefringence and orientational order from the
LCs. Consequently, they can be used in a manifold of appli-
cations.[1] The insertion of a stereogenic centre leads to
chiral ILCs, which are interesting compounds due to their
promising applications for asymmetric synthesis, stereoselec-
tive polymerisation, chiral chromatography, transport mem-
branes for CO2 and NMR chiral discrimination.[2] Recently,
we synthesised chiral imidazolium and pyridinium ILCs
starting from (R)-citronellol as a natural precursor.[3] Due to
the price of the starting material and difficulties with the up-
scaling, we wanted to use cheaper chiral building blocks,
which could be efficiently converted into chiral ILCs.
Amino acids from the chiral pool seemed to be ideal precur-
sors for this purpose due to their good availability and their
low price. Most examples, which use amino acids as precur-
sors or reagents, are from task-specific ILs,[2e,g,h,4] where the
amino acid can be either the cation[2g,j] or the anion.[2d,f,5] In
the case of ILs with amino acid anions 1-ethyl-3-methylimi-
dazolium hydroxide was neutralised with the neat amino
acid[2d,5] to yield compounds 1 (Scheme 1). Alternatively, the
amino acids were reduced to the corresponding amino alco-
Scheme 1. Ionic liquids derived from amino acid. Boc=butyloxycarbonyl,
tBu=tert-butyl.
hols and mixed with an amidine[2f,6] to get the desired prod-
ucts 2. To introduce an amino acid into the cation there are
often more synthetic steps required. Reduction to the amino
alcohols and further reactions to the oxazolinium deriva-
tives[2j] 3 or conversion with methylimidazole to the imidazo-
lium-based ILs 4, comprising an amine,[2g] are necessary.
Other approaches have been published recently, such as the
use of the pre-existing imidazole ring in histidine 5,[2h,7] the
assembly of the imidazole ring through a condensation of
the amino acid with glyoxal, formaldehyde and aqueous am-
monia[8] or ammonium acetate[9] to yield compounds 6 or
the reaction of the protected amino acids 7 with 2-tert-butyl-
aniline and further conversion with trimethylorthoformate
to give compounds 8.[10]
[a] Dipl.-Chem. M. Mansueto, Dr. W. Frey, Prof. Dr. S. Laschat
Institut fꢀr Organische Chemie, Universitꢁt Stuttgart
Pfaffenwaldring 55, 70569 Stuttgart (Germany)
Fax : (+49)711-685-64285
E-mail: sabine.laschat@oc.uni-stuttgart.de
LCs are broadly classified into two categories, according
to the dependency as to how their liquid crystalline phases
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201302319.
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FULL PAPER
are formed. The two most common of these groups are lyo-
tropic (solvent dependent) and thermotropic (temperature
dependent). There are some examples in the literature
where LCs derived from amino acids form the lyotropic
mesophases. One type consists of hexa(phenylethinyl)ben-
zene with terminal amino acid esters.[11] Another example
describes third generation amino acid-based dendrons, in
which the lyotropic and thermotropic mesophases are partly
stabilised by ammonium and carboxylate units.[12] Further-
more, charged LCs have been reported, where the neat
amino acid is used as cation.[13] There are fewer examples
for amino acid-derived dendritic thermotropic LCs.[12] There
are also other approaches in the synthesis of thermotropic
LCs derived from amino acids like the formation of bisami-
no acid esters[14] or the introduction of aromatic,[15] amide[16]
or ester[17] groups, but these examples are all uncharged
LCs. To the best of our knowledge, we here describe the
first example of an amino acid derived thermotropic imida-
zolium ILC bearing amine 9
10(AA,Cm)X (Scheme 2). The results regarding the synthesis
and the mesomorphic properties are discussed below.
ACHTUNGRTEN(NUNG AA,Cn)X or amide moieties
ACHTUNGTRENNUNG
Scheme 3. Synthesis of amine imidazolium derivatives 9ACHTNUTRGNEUNG(AA,Cn)X. Re-
agents and conditions: i) Acyl chloride, NaOHaq, 08C, 18 h. ii) 1) NaBH4,
I2, THF, reflux, 18 h; 2) NaOHaq, reflux, 18 h. iii) Bromoalkane, NEt3,
EtOH, reflux, 18 h. iv) 1) SOCl2, imidazole (Im), CH2Cl2, ꢀ788C!RT,
18 h; 2) RuCl3, NaIO4, CH2Cl2, H2O, 0 8C, 2 h. v) 1) MeIm, microwave,
1408C, 2 h; 2) Et2O·HCl, MeOH, reflux, 18 h; 3) NaHCO3, CH2Cl2. vi)
NaOTf (Tf=trifluoromethanesulfonyl), MeCN, reflux, 1 h.
84%).[21] The sulfamidate 15
methylimidazole in a microwave-assisted reaction leading to
the zwitterionic species 16(AA,Cn), which was further con-
verted to the corresponding imidazolium salt 9(AA,Cn)Cl
ACHTUNGRTEN(NUGN AA,Cn) was reacted with
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
Scheme 2. Amino acid imidazolium derivatives with amine 9ACHTUNGTRENNUNG
with an etheric HCl solution (29–99%). A detailed tabular
survey of the yields is given in the Supporting Information.
and amide moieties 10ACHTUNGTRENNUNG
benzyl.
The synthesis of the amide compounds 10ACTHNURTGNENG(U AA,Cm)X com-
menced with the reduction of the amino acids 11 to the
amino alcohols 17(AA) (67–85%) (Scheme 4),[22] which
were protected with the Boc group to give compounds
18(AA)[23] in good yields (89–99%) and subsequently con-
verted to the corresponding sulfamidate species 19(AA)
with thionylchloride and NaIO4 (71–88%).[24] After depro-
tection with trifluoroacetic acid (TFA) to 20(AA)[25] (74–
98%) and amidation under Steglich conditions[26] (16–56%)
Results and Discussion
Synthesis: The synthesis of the amino-substituted ILCs 9-
ACHTUNGTRENNUNG(AA,Cn)X is shown in Scheme 3. The synthesis was accom-
plished either through the amidation of the amino acid 11
(S-alanine, S-leucine, S-phenylalanine, S-valine) with an acyl
chloride[18] and subsequent reduction[2g] or in the case of
aminoethanol 13 conversion with a bromoalkane[19] to the
the sulfamidates 21
assisted reaction with methylimidazole to the amide species
10(AA,Cm)Cl in moderate to good yields (46–99%).
The use of the Boc protecting group and the additional
ACHTUNGERTN(NUNG AA,Cm) were reacted in a microwave-
corresponding amino alcohols 14ACTHNUTRGNENUG(AA,Cn) in moderate to
good yields. A racemisation of the enantiopure starting ma-
terial during the reduction process could be excluded due to
single-crystal investigations (see the Supporting Informa-
tion) and optical rotation experiments. The use of halide
leaving groups for the quaternisation was not possible due
to the poor reactivity and consequently a relatively uncom-
mon SO3 leaving group was used instead.[20] This leaving
group was inserted through the reaction of the secondary
ACHTUNGTRENNUNG
reaction steps were necessary due to the formation of the di-
hydrooxazols 22 (see the Supporting Information). The poor
yield of the amidation might be explained as follows. With
a decreasing chain length of the carboxylic acid and there-
fore an increasing reactivity, the yield of the desired sulfami-
dates 21ACTHNUTRGNENG(U AA,Cm) decreased and an increase of the amida-
amino alcohol 14
N
tion/esterification side product 23a–23c was observed (see
quent oxidation to the sulfamidate species 15
N
the Supporting Information). Furthermore, with an increas-
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S. Laschat et al.
Figure 1. Typical texture of the imidazolium salt 9ACTHUNTRGNEUNG(Phe,C11)Cl at 608C
upon cooling from the isotropic phase. Focal conical textures and maltese
crosses indicative for a SmA mesophase. (maginification: 200ꢃ, cooling
rate: 10 Kminꢀ1). Due to homeotropic alignment silanised slides were
used.
AHCTUNGRTENGUN(N Phe,C11)Cl can be found in Figure S4 in the Supporting In-
formation. The melting and clearing points for the second/
third heating and first/second cooling cycles are identical.
The deviation of the first heating from the second and third
heating cycle could be due to inhomogeneity of the sub-
Scheme 4. Synthesis of imidazolium derivatives bearing an amide group
10(AA,Cm)X. Reagents and conditions: i) 1) NaBH4, I2, THF, reflux,
18 h; 2) NaOHaq, reflux, 18 h or 1) LiAlH4, THF, reflux, 18 h; 2) K2CO3aq
ACHTUNGTRENNUNG
,
08C, 2 h. ii) Boc2O, NEt3, CH2Cl2, RT, 18 h. iii) 1) SOCl2, pyridine,
MeCN, ꢀ20!08C, 2 h; 2) RuCl3, NaIO4, MeCN, H2O, 0 8C, 1 h. iv) TFA,
CH2Cl2, RT. v) dicyclohexlycarbodiimide (DCC), 4-dimethylaminopyri-
dine (DMAP), carboxylic acid, CH2Cl2, 08C!RT, 20 h. vi) 1) MeIm,
MeCN, microwave, 808C, 4 h; 2) Et2O·HCl, MeOH, reflux, 18 h;
3) NaHCO3, CH2Cl2. vii) NaOTf, MeCN, reflux, 1 h.
ing steric hindrance of the R group a decreased reactivity
and hence, lower yields (for R=H, CH3) or indeed no con-
version in the case of R=Bn was observed. Other esterifica-
tion methods, for example, the Yamaguchi reaction[27] or the
use of N’-(3-dimethylaminopropyl)-N-ethylcarbodiimide
(EDCI) failed to show any conversion of the compound pos-
sessing the Bn moiety.
Due to thermal decomposition of the chloride salts at
high temperatures (see the Supporting Information) an
anion exchange from Cl to OTf was performed (66–99%)
Figure 2. DSC traces of compound 9ACHTNUGTRENUNG(Gly,C15)OTf (heating/cooling rate:
10 Kminꢀ1). A) Third heating, B) second heating, C) first heating, D) first
cooling, E) second cooling cycle.
for both the amine 9
ACHTUNGRTEN(NUNG AA,Cm)Cl and amide species 10-
ACHTUNGTRENNUNG(AA,Cm)Cl. For an overview with a detailed summary of the
yields see the Supporting Information.
stance (i.e., isolating air bubbles, different crystal modifica-
tions). Compounds 9
(Ala,Cn)OTf showed small differences (ꢁ2–4 K) of the
melting and crystallisation temperatures due to supercool-
ing, whereas the values for 9(Phe,Cn)OTf were higher
(ꢁ20 K). This could be due to p–p interactions of the Ph
units and hence hindered crystallisation leading to broader
mesophase widths of the cooling cycles. The results are sum-
marised in Table 1 and visualised for liquid crystalline com-
pounds in Figure 3.
ACHTUNGTNERNUG(Gly,Cn)OTf, 10CAHTUNGTRNE(NGUN Gly,Cm)OTf and 9-
Mesomorphic properties: The imidazolium salts 9
and 10ACHTUNGTRENNUNG(AA,Cm)OTf were investigated by polarised optical
(AA,Cn)X
ACHTUNGTRENNUNG
microscopy (POM) and differential scanning calorimetry
(DSC). Only the glycine, alanine and phenylalanine deriva-
tives showed mesomorphic properties, whereas the com-
pounds derived from valine and leucine showed only crystal-
line behaviour. All liquid crystalline compounds displayed
focal conical domains and maltese cross textures under
POM investigation, which indicated a SmA mesophase ge-
ometry. A typical example is shown in Figure 1.
ACHTUNGTRENNUNG
In most cases, the mesophase ranges increased with an in-
creasing alkyl chain length (except for 9ACTHNURGTENUNG(Gly,C17)OTf). The
Phase transitions and mesophase ranges were obtained
from calorimetric investigations. DSC traces of 9-
compounds exhibited melting points between 31 and 568C
and clearing points up to 1168C. For the glycine-derived
A
amino triflates 9
ACHTUNGTNER(NUNG Gly,Cn)OTf a minimum chain length of
A
ACHTUNGTRENNUNG
fourteen (i.e., n+1) is required to obtain SmA phases,
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Ionic Liquid Crystals from Amino Acids
FULL PAPER
Table 1. DSC data and melting points of the imidazolium compounds 9-
that the layered packing of the ILCs is very sensitive to
steric hindrance, which can not be overcome by additional
stabilisation due to hydrogen bonding.[29] In contrast, the
ACHTUNGTRENNUNG(AA,Cn)X and 10ACHTUNGTRENNUNG(AA,Cm)OTf (second heating, heating/cooling rate:
10 Kminꢀ1).
Compound
Phase Transition T [8C] Phase Transition T [8C]
(enthalpy (enthalpy
[kJmolꢀ1]) [kJmolꢀ1])
phenylalanine-derived amino chlorides 9ACTHNURTGNENG(U Phe,Cn)Cl showed
already SmA phases with a total chain length of nine carbon
atoms. This could be due to p–p interactions of the Ph units.
After an anion exchange from Cl to OTf the liquid crystal-
line properties of the phenylalanine compounds 9-
N
ACHTUNGTRENNUNG
9
9
9
9
10
10
10
10
10
9
9
10
10
10
9
9
9
9
9
9
N
Cr
Cr
Cr
Cr
Cr
Cr
Cr
62[a]
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
31 (18.8)
44 (12.5)
51 (27.7)
37[a]
SmA 76 (0.5)
SmA 115 (0.6)
SmA 116 (0.9)
AHCTUNGERTG(NNUN Phe,Cn)OTf were completely lost.
ACHTUNGTRENNUNG
A
39[a]
X-ray investigation: The proposed SmA phase geometry
was confirmed by small- and wide-angle X-ray diffraction
measurements (SAXS and WAXS, respectively). In Figure 4
N
67[a]
N
37 (17.0)
43 (17.0)
52[a]
SmA 84 (0.3)
SmA 106 (0.2)
ACHTUNGTRENNUNG
Cr
Cr
Cr
Cr
a representative WAXS pattern of 9ACTHNUGTRENNUG(Gly,C17)OTf is shown
35 (22.4)
SmA 58 (0.6)
with a strong fundamental diffraction peak (001) in the
small-angle region and a diffuse halo in the wide-angle
region from the molten alkyl chains.
ACHTUNGTRENNUNG
40[a]
N
54[a]
(Ala,C15)OTf Cr
55 (15.3)
Cr
Cr
Cr
Cr
Cr
Cr
38[a]
27[a]
34 (17.9)[b]
56 (19.2)
53 (11.1)
57[a]
SmA 55 (0.6)
SmA 87 (1.0)
SmA 113 (0.9)
[a] DSC data could not be obtained due to exothermal decomposition.
Therefore, melting points were determined. [b] Due to a monotropic be-
haviour the first cooling cycle is indicated.
Figure 4. Diffraction pattern of 9ACHTNUGRTNEUNG(Gly,C17)OTf at 898C with the corre-
sponding WAXS image (small picture).
Figure 3. Mesophase stabilities of the imidazolium derivatives. *=A
monotropic phase behaviour was observed. Black=Cr, grey=SmA.
Layer spacings d001 were obtained at different tempera-
tures by using a Gaussian distribution on the corresponding
diffraction signal (001). All compounds showed a linear tem-
perature dependency of the layer spacing (Figure 5). With
increasing temperature the layer spacing decreased. These
values indicate a bilayer structure of the molecules with
whereas the corresponding amido triflates 10
required a chain length of fifteen. In comparison with their
amido counterparts 10(Gly,C15)Cl and 10(Gly,C17)Cl the two
amino triflates 9(Gly,C15)OTf and 9(Gly,C17)OTf showed in-
ACHTUNGTERNN(UNG Gly,Cm)OTf
A
ACHTUNGTRENNUNG
A
U
strongly interdigitated alkyl chains and values of Lcalcd
<
creased melting and clearing transitions and thus broader
mesophase ranges than their linear 1-alkyl-3-methylimidazo-
lium triflate analogous of similar chain length,[28] despite the
higher polarity and the higher tendency of the amide tether
to form intermolecular hydrogen bonds as compared to the
amine tether. For the alanine-derived amino triflates 9-
d
001 <2Lcalcd, where Lcalcd is the length of the fully extended
molecule with an all-trans configuration of the alkyl moiety.
For better comparison, layer spacings dred at a reduced tem-
perature (d001 at 0.95 Tiso)[30] were determined (Tables 2 and
3). For example, the calculated molecular length of 9-
AHCTUNGTRENNUNG
(Gly,C17)OTf is 2900 pm,[31] whereas dred is 3582 pm. This
A
means that the mesogens are organised in a bilayer struc-
ture. The calculated layer spacing dcalcd is 3510 pm[31] (fully
interdigitated alkyl chains of the cations 2530 pm plus two
times the methylimidazolium core with 490 pm each), which
is close to the dred value of 3582 pm (Tables 2 and 3). Over-
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
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S. Laschat et al.
Figure 5. Temperature dependency of the d001 layer spacings obtained
~
*
from SAXS investigations. + =9
(Gly,C17)OTf, ꢃ =10(Gly,C15)OTf,
(Ala,C15)OTf.
G
ACHTUNGTRENNUNG
!
&
G
G
=10
G
=9-
ACHTUNGTRENNUNG
Table 2. Comparison of the layer spacings dred of the imidazolium com-
pounds 9(AA,Cn)OTf and 10(Gly,Cm)OTf.
A
ACHTUNGTRENNUNG
Compound
Tred
dred
Compound
Tred
dred
[8C]
[pm]
[8C]
[pm]
9
9
9
N
72
109
110
3205
3468
3582
9
10
10
G
55
83
107
3339
3616
3783
ACHTUNGTRENNUNG
A
Figure 6. Proposed packing model of the smectic phase (left) and exam-
ple of the calculated layer spacing dcalcd of 9ACHTUNTRGNEUNG(Phe,C9)Cl (right).
Table 3. Comparison of the calculated[31] and experimental layer spacings
dred of the imidazolium compounds 9(AA,Cn) and 10(Gly,Cm)OTf.
G
ACHTUNGTRENNUNG
Conclusion
Compound
Alkyl chain
length [pm]
2ꢃcore
[pm]
dcalcd
[pm]
dred
[pm]
We have presented the first example of thermotropic chiral
ILCs utilising amino acids as starting materials. The key step
in the synthesis was the use of the relatively uncommon SO3
leaving group. Imidazolium derivatives bearing amine and
amide groups with different chain lengths and anions were
synthesised. It turned out that the presence of mesophases
was very sensitive to the steric hindrance in the amino acid
derived tether. Only the glycine-derived amines 9-
9
9
9
10
10
9
9
9
N
2020
2270
2530
1780
2040
2030
1270
1520
980
980
980
1820
1820
1380
1380
1380
3000
3250
3510
3600
3860
3410
2650
2900
3205
3468
3582
3616
3783
3339
2617
2847
G
ACHTUNGTRENNUNG
A
ACHTUNGTERN(NUNG Gly,Cm)OTf (m=
all, the layer spacings d001 increase with an increasing alkyl
ACHTUNGTRENNUNG
chain length. The temperature-dependent layer spacings of
the phenylalanine compounds 9ACHTUNRGTNEUNG(Phe,Cn)Cl can be found in
rivatives were not mesomorphic. In contrast, despite the in-
creased steric bulkiness of phenylalanine as compared to
Figure S1 in the Supporting Information.
glycine, the phenylalanine-derived amine 9ACTHNGUETRNNU(G Phe,Cn)Cl (n=8,
The glycine amide derivatives showed increased dred
values compared to the amine compounds with the same
9, 11) showed stable mesophases for much shorter chain
lengths suggesting beneficial p–p-stacking of the phenyl
groups. It should be noted that no evidence for cholesteric
mesomorphism was found.
XRD experiments showed a nearly linear dependency of
the layer spacing values d001 with a decreasing temperature
and a bilayer alignment of the mesogens. The existence of
an amide group or a stereogenic centre hinders the interdi-
gitation of the alkyl chains leading to increased layer spac-
ing values. Despite the absence of cholesteric phases the
phenylalanine-derived ILCs provide the opportunity to use
them as chiral dopands for known nematic ILCs,[32] which
gives access to novel chiral ordered reaction media. The re-
chain lengths. Compounds
(Gly,C15)OTf displayed comparable dred values, additionally
the value of 9(Ala,C15)OTf is between 9(Gly,C15)OTf and 9-
(Gly,C13)OTf. This means that the stereogenic centre as well
9ACHTUNGTRENNU(G Gly,C17)OTf and 10-
ACHTUNGTRENNUNG
A
U
ACHTUNGTRENNUNG
as the amide group hinders the interdigitation of the alkyl
moieties, which is in good agreement with previous observa-
tions with citronellyl-derived side chains.[3] For all com-
pounds the dred values are close to the calculated dcalcd
values, where a maximal degree of interdigitation up to the
atom adjacent to the stereocentre or the amide group is as-
sumed (Table 3, Figure 6).
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Ionic Liquid Crystals from Amino Acids
FULL PAPER
(CH3), 22.7, 27.1, 29.36, 29.44, 29.58, 29.60, 29.64, 29.66, 29.93, 31.9
(CH2), 37.8 (PhCH2), 46.9 (NCH2), 60.2 (NCH), 62.1 (CH2O), 126.5 (p-
Ar), 128.6 (o-Ar), 129.2 (m-Ar), 138.2 ppm (i-Ar); FTIR (ATR): n˜ =3268
(w), 3029 (w), 2917 (vs), 2849 (s), 2733 (w), 2015 (w), 1967 (w), 1605 (w),
1492 (w), 1469 (m), 1453 (m), 1377 (w), 1343 (w), 1246 (w), 1110 (m),
1046 (w), 1029 (m), 977 (w), 955 (w), 934 (m), 897 (w), 849 (m), 815 (m),
767 (w), 744 (m), 727 (m), 718 (s), 697 (vs), 658 (w), 649 (w), 641 (w),
619 (w), 599 cmꢀ1 (m); MS (ESI): m/z: 320 [M+H+], 302 [M+H+
ꢀH2O], 228, 186, 117, 105, 91; HRMS (ESI): m/z calcd for C21H38NO+:
320.2948 [M+H+]; found: 320.2933; elemental analysis calcd (%) for
C21H37NO: C 78.94, H 11.67, N 4.38; found: C 78.94, H 11.60, N 4.26.
sults also revealed that the counterion has a considerable in-
fluence on the mesomorphic properties and further SAR
studies are needed to fully explore the effect of the anion.
Experimental Section
General methods: Commercially obtained chemicals were used as re-
ceived. For a better clarity and simplicity a non-IUPAC nomenclature
was used. Column chromatography was carried out on silica 60Dm (40–
70 mm). For thin layer chromatography silica gel sheets TLC silica gel 60
F 254 from Merck were used. 1H and 13C NMR spectra were recorded
with Bruker Avance 300 and Avance 500 spectrometers at 296 K. FTIR
spectra were recorded with a Bruker Vektor22 spectrometer with an
MKII Golden Gate Single Reflection Diamant ATR system. Mass spec-
trometry was performed on a Varian MAT 711 mass spectrometer with
EI ionisation (70 eV) and a Bruker micrOTOF Q with electrospray ioni-
sation. Elemental analyses were performed on a Carlo Erba Strumenta-
zione Elemental Analyzer Model 1106. Differential scanning calorimetry
was performed by using a Mettler Toledo DSC822 with a heating/cooling
rate of 10 Kminꢀ1 (ꢂ1 K), melting points (uncorrected) and mesophase
textures were obtained by optical polarising microscopy by using an
Olympus BX 50 polarising microscope combined with a Linkam LTS 350
hot stage. X-ray powder experiments were performed by using a Bruker
Nanostar with a monochromatic CuKa1 beam (l=1.5405 ꢄ), which was
obtained by using a ceramic tube generator (1500 W) with cross-coupled
Gçbel mirrors as the monochromator. Optical rotation values were mea-
sured with a Polarimeter 241 (Perkin–Elmer). Calibration of the patterns
was carried out with the powder pattern of Ag-Behenate. Samples were
prepared by using glass tubes (0.7 mm outside diameter) from Fa. Hilgen-
berg GmbH and tempered on a temperature-controlled hot stage (ꢂ
1 K).
General procedure for the alkylation of ethanolamine: A solution of
ethanolamine 13 (0.72 g, 11.7 mmol), the corresponding bromoalkane
(5.85 mmol) and NEt3 (0.65 g, 6.44 mmol) in EtOH (60 mL) was stirred
under reflux for 18 h. After cooling to room temperature the solvent was
removed under reduced pressure. The residue was dissolved in water and
extracted with CH3Cl (3ꢃ20 mL) and the combined organic phases were
dried over anhydrous MgSO4. The solvent was removed under reduced
pressure and the crude product was recrystallised from EtOAc to obtain
the pure secondary amino alcohol 14
ACHTUNGTNER(NUNG Gly,Cn).
2-(Octadecylamino)ethanol (14(Gly,C17)): White solid (1.15 g, 3.67 mmol,
AHCTUNGTRENNUNG
63%); m.p. 458C; 1H NMR (300 MHz, CDCl3, TMS): d=0.88 (t, J=
6.7 Hz, 3H; CH3), 1.20–1.36 (m, 32H; CH2), 1.44–1.53 (m, 2H;
OCH2CH2), 1.74 (brs, 2H; NH, OH), 2.57–2.65 (m, 2H; NCH2), 2.75–
2.80 (m, 2H; NHCH2CH2OH), 3.60–3.66 ppm (m, 2H; CH2OH);
13C NMR (75 MHz, CDCl3, TMS): d=14.1 (CH3), 22.7, 27.3, 29.37, 29.57,
29.63, 29.67, 29.70, 31.9 (CH2), 49.5 (CH2NH), 50.9 (NHCH2CH2OH),
60.9 ppm (CH2OH); FTIR (ATR): n˜ =2922 (vs), 2852 (s), 2361 (w), 1466
(m), 1059 (w), 908 (s), 733 (vs), 645 cmꢀ1 (w); MS (ESI): m/z: 314
[M+H+], 296 [M+H+ꢀH2O]; HRMS (ESI): m/z calcd for C20H44NO+:
314.3417 [M+H+]; found: 314.3428.
General procedure for the synthesis of sulfamidates 15ACTHUNRGTNEUNG(AA,Cn): Imida-
zole (4.52 g, 66.4 mmol) was dissolved in CH2Cl2 (60 mL), the mixture
was cooled to 08C and a solution of SOCl2 (1.45 mL, 2.37 g, 19.9 mmol)
in CH2Cl2 (30 mL) was added dropwise. The solution was slowly warmed
to room temperature and stirred for an additional hour. After cooling to
General procedure for the amidation of the amino acids: The respective
amino acid 11(AA) (25.4 mmol) and NaOH (1.02 g, 25.4 mmol) were dis-
solved in H2O (16 mL). At 08C the corresponding neat acyl chloride
(28.0 mmol) and NaOH (1.02 g, 25.4 mmol) dissolved in H2O (16 mL)
were added simultaneously. The reaction mixture was allowed to reach
room temperature and stirred for 18 h. The aqueous phase was acidified
to pH 3 with HCl (37%), extracted with CH2Cl2 (3ꢃ20 mL) and the com-
bined organic phases were dried over anhydrous MgSO4. After evapora-
ꢀ788C
a solution of the respective amino alcohol 14ACHTUNGTRENNUNG(AA,Cn)
(9.49 mmol) in CH2Cl2 (60 mL) was added dropwise and the reaction
mixture was allowed to warm to room temperature overnight. The reac-
tion mixture was filtered over celite and washed with CH2Cl2 (50 mL).
The organic phase was washed with water (2ꢃ50 mL), dried over anhy-
drous MgSO4 and the solvent was removed under reduced pressure. The
residue was dissolved in CH2Cl2 (60 mL) and NaIO4 (4.73 g, 22.1 mmol)
dissolved in H2O (50 mL) was added. After cooling to 08C, RuCl3
(0.30 g, 1.42 mmol) was added and the reaction mixture was stirred vigo-
rously at 08C for 2 h and afterwards for 18 h at room temperature. The
phases were separated, activated charcoal (2 g) was added to the organic
phase and the solution was stirred overnight. Anhydrous MgSO4 was
added and after filtration over celite the solvent was removed under re-
tion of the solvent the crude product 12ACTHNUTRGNEUNG(AA,Cn) was used in the next
step without further purification. For long-chained acyl chlorides (ꢃ C12)
a H2O/EtOH mixture was used instead and additional EtOH was added
to solve the precipitate if necessary.
General procedure for the synthesis of the amino alcohols 14
ACHTUNGRTEN(NUNG AA,Cn):
The corresponding amido alcohol 12(AA,Cn) (25.3 mmol) was dissolved
AHCTUNGTRENNUNG
in dry THF (100 mL) and NaBH4 (4.79 g, 126.5 mmol) was added in
small portions. A solution of I2 (23.5 g, 88.5 mmol) in THF (50 mL) was
added dropwise to the reaction mixture at room temperature and after
complete addition the solution was stirred under reflux for 18 h. After
cooling to room temperature MeOH (21 mL, 500 mmol) was added care-
fully and the solvents were removed under reduced pressure. The residue
was dissolved in 2n NaOH (6.07 g, 152 mmol) in H2O (38 mL) and
stirred under reflux for 18 h. After cooling to room temperature the
aqueous phase was extracted with CH2Cl2/EtOAc (1:1; 3ꢃ20 mL) and
the combined organic phases were dried over anhydrous MgSO4. After
evaporation of the solvent under reduced pressure the crude product was
purified by flash chromatography (1) EtOAc, 2) MeOH/EtOAc 1:1) to
duced pressure to yield the sulfamidates 15
ACHTUNGRTEN(NUNG AA,Cn).
(S)-4-Benzyl-3-dodecyl-1,2,3-oxathiazolidine 2,2-dioxide (15ACHTUNGTRENNUNG(Phe,C11)):
Yellow oil (2.72 g, 7.14 mmol, 82%); [a]2D0 =ꢀ7.9 (c=1.0, CH2Cl2);
1H NMR (300 MHz, CDCl3, TMS): d=0.88 (t, J=6.8 Hz, 3H; CH3),
1.17–1.39 (m, 18H; CH2), 1.54–1.69 (m, 2H; CH2), 2.75–2.87 (m, 1H;
PhCH2), 2.91–3.02 (m, 1H; NCH2), 3.10–3.25 (m, 2H; NCH2, PhCH2),
3.73–3–87 (m, 1H; NCH), 4.19 (dd, J=5.8, J=8.7 Hz, 1H; CH2OS), 4.33
(dd, J=6.5, J=8.7 Hz, 1H; CH2OS), 7.13–7.38 ppn (m, 5H; ArH);
13C NMR (75 MHz, CDCl3, TMS): d=14.1 (CH3), 22.7, 26.8, 27.8, 29.13,
29.35, 29.47, 29.56, 29.63, 31.9 (CH2), 38.5 (PhCH2), 47.5 (NCH2), 61.1
(NCH), 70.4 (CH2OS), 127.4 (p-Ar), 129.00, 129.13 (o-/m-Ar), 135.2 ppm
(i-Ar); FTIR (ATR): n˜ =2922 (s), 2853 (m), 1710 (w), 1604 (w), 1467 (w),
1456 (w), 1343 (s), 1180 (vs), 1030 (w), 978 (m), 831 (w), 796 (s), 748 (m),
700 (s), 628 (w), 587 cmꢀ1 (w); MS (ESI): m/z: 404 [M+Na+], 382
[M+H+], 320, 302, 186; HRMS (ESI): m/z calcd for C21H35NNaO3S+:
404.2230 [M+Na+]; found: 404.2231; elemental analysis calcd (%) for
C21H35NO3S: C 66.10, H 9.25, N 3.67; found: C 65.89, H 9.12, N 3.47.
yield 14
ACHTUNGTRENNUNG(AA,Cn).
(S)-2-(Dodecylamino)-3-phenylpropan-1-ol (14ACHTUNGTRNE(NUG Phe,C11)): White solid
(3.63 g, 11.3 mmol, 48%); m.p. 548C; [a]2D0 =ꢀ4.7 (c=1.0, CH2Cl2);
1H NMR (300 MHz, CDCl3, trimethylsilane (TMS)): d=0.88 (t, J=
6.8 Hz, 3H; CH3), 1.20–1.35 (m, 18H; CH2), 1.37–1.50 (m, 2H;
NCH2CH2), 2.42 (brs, 2H; NH, OH), 2.53–2.69 (m, 2H; NHCH2), 2.70–
2.86 (m, 1H; PhCH2), 2.87–2.97 (m, 1H; NCH), 3.34 (dd, J=5.5, J=
10.7 Hz, 1H; CH2OH), 3.63 (dd, J=3.8, J=10.7 Hz, 1H; CH2OH), 7.14–
7.35 ppm (m, 5H; ArH); 13C NMR (75 MHz, CDCl3, TMS): d=14.1
General procedure for the preparations of the imidazolium chlorides 9-
ACHUTNRGEN(NUG AA,Cn)Cl: The corresponding sulfamidate 15CAHTUGNTRNEN(UGN AA,Cn) (1.52 mmol) and
Chem. Eur. J. 2013, 19, 16058 – 16065
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
16063

S. Laschat et al.
methylimidazole (0.12 mL, 0.13 g, 1.52 mmol) were given in an micro-
wave vial and irradiated in a microwave at 1408C for 1 h. The residue
was dissolved in MeOH, a solution of Et2O·HCl (2 mL) was added and
the reaction mixture was heated to reflux overnight. The solvent was re-
moved and the crude product was either recrystallised from EtOAc or
washed several times with Et2O and EtOAc to obtain the imidazolium
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chloride 9
(S)-3-(2-(Dodecylamino)-3-phenylpropyl)-1-methyl-1H-imidazol-3-ium
chloride (9(Phe,C11)Cl): White solid (0.35 g, 0.84 mmol, 61%); recrystal-
ACHTUNGTRENNUNG(AA,Cn)Cl.
ACHTUNGTRENNUNG
lised from EtOAc; [a]D20 =ꢀ17.7 (c=1.0, CH2Cl2); 1H NMR (500 MHz,
CDCl3, TMS): d=0.88 (t, 6.8 Hz, 3H; CH3), 1.06–1.42 (m, 22H; CH2),
2.44–2.52 (m, 1H; NCH2), 2.55–2.65 (m, 1H; NCH2), 2.65–2.74 (m, 1H;
PhCH2), 2.85–2.94 (m, 1H; PhCH2), 3.12–3.23 (m, 1H; NCH), 4.06 (s,
3H; ImCH3), 4.29 (dd, J=6.9, J=13.7 Hz, 1H; CH2Im), 4.33 (dd, J=2.9,
J=13.7 Hz, 1H; CH2Im), 7.13–7.44 (m, 7H; ArH), 10.39 ppm (s, 1H;
NCHN); 13C NMR (125 MHz, CDCl3, TMS): d=14.1 (CH3), 22.7, 27.1,
29.35, 29.42, 29.62, 29.64, 29.67, 29.81, 31.9 (CH2), 36.6 (ImCH3), 37.8
(PhCH2), 47.1 (NCH2), 52.4 (CH2Im), 58.6 (NCH), 122.1, 123.0 (Im),
127.0 (i-Ar), 128.9, 129.2 (o-/m-Ar), 137.0 (i-Ar), 139.0 ppm (NCHN);
FTIR (ATR): n˜ =3399 (w), 2923 (m), 2853 (w), 1573 (w), 1455 (w), 1169
(w), 903 (vs), 723 (vs), 650 cmꢀ1 (s); MS (ESI): m/z: 384 [M+], 302 [M+
ꢀC4H6N2], 198; HRMS (ESI): m/z calcd for C25H42N3+: 384.3373 [M+];
found: 384.3375; DSC: Cr 538C (11.1 kJmolꢀ1); SmA 1138C
(0.9 kJmolꢀ1) I.
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New York, 2007, pp. 246–258; b) V. Zgonnik, S. Gonella, M.-R. Ma-
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General procedure for the anion exchange: The respective imidazolium
chloride 9ACHTUNGTRENNUNG(AA,Cn)Cl (0.13 mmol) was dissolved in MeCN (10 mL), the
corresponding sodium or potassium salt (0.14 mmol) was added and
stirred under reflux for 1 h. After cooling to room temperature the sol-
vent was removed under reduced pressure, the residue was dissolved in
CH2Cl2 (10 mL) and filtered. The solvent was removed under reduced
pressure to obtain the imidazolium derivative 9
(S)-3-(2-(Tetradecylamino)-3-phenylpropyl)-1-methyl-1H-imidazol-3-ium
triflate (9 =
(Phe,C13)OTf): Yellow oil (62 mg, 0.11 mmol, 99%); [a]D20
ACHTUNGRTENN(UNG AA,Cn)OTf.
R
ꢀ13.5 (c=1.0, CH2Cl2); 1H NMR (500 MHz, CDCl3, TMS): d=0.88 (t,
6.9 Hz, 3H; CH3), 1.06–1.36 (m, 26H; CH2), 2.41–2.48 (m, 1H; NCH2),
2.50–2.58 (m, 1H; NCH2), 2.58–2.66 (m, 1H; PhCH2), 2.74–2.83 (m, 1H;
PhCH2), 3.06–3.14 (m, 1H; NCH), 3.93 (s, 3H; ImCH3), 4.03 (dd, J=7.0,
J=14.0 Hz, 1H; CH2Im), 4.25 (dd, J=3.4, J=14.0 Hz, 1H; CH2Im),
7.11–7.40 (m, 7H; ArH), 9.02 ppm (s, 1H; NCHN); 13C NMR (125 MHz,
CDCl3, TMS): d=14.1 (CH3), 22.7, 27.1, 29.37, 29.42, 29.61, 29.63, 29.67,
29.68, 29.70, 29.85, 31.9 (CH2), 36.4 (ImCH3), 38.0 (PhCH2), 47.1 (NCH2),
52.5 (CH2Im), 58.5 (NCH), 120.7 (q, J=320.4 Hz, CF3), 122.5, 123.3
(Im), 127.0 (i-Ar), 128.9, 129.1 (o-/m-Ar), 137.0 (i-Ar), 137.6 ppm
(NCHN); FTIR (ATR): n˜ =3115 (w), 2923 (s), 2853 (m), 1573 (w), 1456
(w), 1377 (w), 1255 (vs), 1224(s), 1158 (vs), 1030 (vs), 908 (w), 732 (m),
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702 (m), 666 (w), 637 (vs), 573 cmꢀ1 (m); MS (ESI): m/z: 412 [M+], 330
+
[M+ꢀC4H6N2], 226, 149 [Mꢀ]; HRMS (ESI): m/z calcd for C27H46N3
:
412.3686 [M+]; found.: 412.3683; calcd for CF3O3Sꢀ: 148.9515 [Mꢀ];
found: 148.9526; elemental analysis calcd (%) for C28H46F3N3O3S: C
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Acknowledgements
Financial support by the Bundesministerium fꢀr Bildung und Forschung
(BMBF), the Deutsche Forschungsgemeinschaft, the Ministerium fꢀr
Wissenschaft, Forschung und Kunst des Landes Baden-Wꢀrttemberg, and
the Fonds der Chemischen Industrie is gratefully acknowledged. We
would like to thank Christof Schneck for measuring the thermogravimet-
ric analysis.
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16064
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Chem. Eur. J. 2013, 19, 16058 – 16065

Ionic Liquid Crystals from Amino Acids
FULL PAPER
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Received: June 18, 2013
Published online: October 7, 2013
Chem. Eur. J. 2013, 19, 16058 – 16065
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
16065