Alkyl-imidazolium glycosides: Non-ionic - Cationic hybrid surfactants from renewable resources

Article abstract of DOI:10.1016/j.carres.2015.04.022

A series of surfactants combining carbohydrate and imidazolium head groups were prepared and investigated on their assembly behavior. The presence of the imidazolium group dominated the interactions of the surfactants, leading to high CMCs and large molecular surface areas, reflected in curved rather than lamellar surfactant assemblies. The carbohydrate, on the other hand, stabilized molecular assemblies slightly and reduced the surface tension of surfactant solutions considerably. A comparative emulsion study discourages the use of pure alkyl imidazolium glycosides owing to reduced assembly stabilities compared with APGs. However, the surfactants are believed to have potential as component in carbohydrate based surfactant mixtures.

Full text of DOI:10.1016/j.carres.2015.04.022

Carbohydrate Research 412 (2015) 28e33
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Carbohydrate Research
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Rapid communication
Alkyl-imidazolium glycosides: non-ionicdcationic hybrid surfactants
from renewable resources
Abbas Abdulameer Salman*, Mojtaba Tabandeh, Thorsten Heidelberg*,
Rusnah Syahila Duali Hussen, Hapipah Mohd Ali
Chemistry Department, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of surfactants combining carbohydrate and imidazolium head groups were prepared and
investigated on their assembly behavior. The presence of the imidazolium group dominated the in-
teractions of the surfactants, leading to high CMCs and large molecular surface areas, reflected in curved
rather than lamellar surfactant assemblies. The carbohydrate, on the other hand, stabilized molecular
assemblies slightly and reduced the surface tension of surfactant solutions considerably. A comparative
emulsion study discourages the use of pure alkyl imidazolium glycosides owing to reduced assembly
stabilities compared with APGs. However, the surfactants are believed to have potential as component in
carbohydrate based surfactant mixtures.
Received 3 April 2015
Accepted 26 April 2015
Available online 5 May 2015
Keywords:
Emulsion
Cationic surfactant
Hexagonal phase
Self-assembly
Surface tension
© 2015 Elsevier Ltd. All rights reserved.
1. Introduction
Instead acylated products24,25 and derivatives of the corresponding
reduced glycamines, or amino-polyols,26e28 have gained more
Over the last decades sugar based surfactants1e7 have gained
both scientific and economic interest owing to increasing concerns
in biocompatibility8 and sustainable resources.9,10 Application
fields include emulsifiers11,12, detergents2 as well as medical de-
livery systems.13,14 Most investigations focus on non-ionic surfac-
tants, which utilize the polyhydroxy-character of carbohydrates as
hydrophilic surfactant antipode. While non-ionic surfactants pro-
vide advantages with respect to an enhanced assembly stability, e.g.
towards pH-changes or electrolytes,15 this insensitivity restricts the
application of certain formulation methods, which utilize medium
induced phase changes, like the pH-mediated transition of fatty
acid micelles into liposomes.16 Unfortunately, carbohydrate sur-
factants involving ionic charges have not been investigated exten-
sively. Typical examples are anionic alkyl glycuronates, i.e. salts of
oxidized glycosides with a carboxylic acid,17e19 on the one hand,
and cationic N-alkylated amino-derivatives of sugars on the other.
Chemical instability20,21 limits the application of glycosylamines22
and their subsequent ammonium ions,23 which resemble the
potentially most easily accessible sugar based cationic surfactants.
interest.
Both cationic and anionic surfactants are principally susceptible
for medium triggered assembly changes. However, the presence of
a carbohydrate in the surfactant head group should reduce the
impact of the latter. Therefore ionic carbohydrate surfactants are
expected to exhibit reasonable assembly stability despite their
susceptibility for medium-induced changes. This makes them
potentially interesting candidates for medical delivery systems. In
view of excess negative charges on biological cell membranes29,30
cationic surfactants are likely mediating better interactions of a
carrier with a cellular target; hence they are favored over anionic
surfactants. The introduction of a positive charge, referring to an
amino- or ammonium group, on a carbohydrate can be achieved in
various ways. Constraints, however, arise from economic consid-
erations. While glycamines provide the most direct access, the
resulting open chain structure does not match nature-typical car-
bohydrate patterns. This has implications on molecular interactions
based on the hydrogen bonding network in sugar-based surfactant
assemblies and potentially affects the bio-recognition of a drug
carrier, thus disfavoring the approach. The preparation of a glyco-
lipid19 and subsequent introduction of an amino-group,31,32 on the
other hand, requires a multi-step synthesis, which renders it non-
economic. In order to reduce the number of required chemical
transformations and optimize the production efficiency, an
* Corresponding authors.
E-mail addresses: abbass@um.edu.my (A.A. Salman), heidelberg@um.edu.my
(T. Heidelberg).
http://dx.doi.org/10.1016/j.carres.2015.04.022
0008-6215/© 2015 Elsevier Ltd. All rights reserved.

A.A. Salman et al. / Carbohydrate Research 412 (2015) 28e33
29
Table 1
approach comprising of glycosylation and subsequent amination
Synthesis of glycosyl imidazolium surfactants
was targeted, where the latter not only introduces the cation to the
sugar but the hydrophobic domain as well. This approach reflects
the previously reported strategy for the synthesis of alkyl triazole
glycosides (ATG).33
Compd
Alkyl chain
C8H17
Yield (basis: 4)
6a
6b
6c
91%
91%
92%
C12H25
16H33
C
2. Results and discussion
2.1. Synthesis
methyl-imidazolium counterparts, 8. The structures of the surfac-
tants are displayed in Fig. 2, while their behavior is summarized in
Table 2.
The surfactants were synthesized in a 3-stage process, involving
glycosylation of bromoethanol,34 its subsequent use for the alkyl-
ation35 of mono-N-alkylated imidazoles36 and a final deprotection
step.37 The synthetic scheme is displayed in Fig. 1.
The investigation on Krafft and cloud points indicated no tem-
perature limitations for the use of the surfactants 6; none of the
compound exhibited clouding behavior at high temperature, while
all enabled the formation of micelles below room temperature. This
behavior is in agreement with the corresponding methyl-
imidazolium chlorides,38 which were referred to in lieu of pub-
lished data for the corresponding bromides 8. However, similar
behavior of quaternary ammonium surfactants with chloride and
bromide ions40 justifies this reference. In contrast, APG models 8
with alkyl chains above 10 carbon atoms exhibit Krafft points above
room temperature, which moreover, increase upon extension of the
Alkyl-imidazolium glycoside surfactants (AIGs) with C8 (6a), C12
(6b) and C16 (6c) hydrocarbon chains were obtained in practically
identical high yields, as shown in Table 1. This indicates high effi-
ciency and suggests a wide application range for the surfactant
synthesis. The overall yield, however, was limited by the carbohy-
drate precursor 4,34 which's preparation was not yield optimized.
The use of xylene as solvent instead of the more common toluene35
enabled a higher reaction temperature and considerably sped up
the conversion of 4 into the surfactant precursor 5. Despite the
short reaction time the conversion was not affected by the chain
length.
alkyl chain.39 The lower Krafft temperatures for
6 indicate
increasing water solubility upon introduction of the imidazolium
ion. The latter is also reflected in significantly increased CMC values
for the surfactants 6 with respect to the APG-analogs 7.40,41 How-
ever, the water solubility of AIGs remains far below that of the
imidazolium surfactants 8,42,43 thus proposing dominance of the
sugar over the cation with respect to interactions with water. This
dominance is mirrored in the surface tension of solutions above the
CMC, which resemble those of the APG-models42,44 rather than the
imidazolium surfactants.44,45 A similar behavior has previously
been reported for ester-linked cationic carbohydrate surfactants
involving a head group comprising of a sugar and an ammonium
salt.45
2.2. Physical properties
In order to rationalize the physical behavior of AIGs their sur-
factant properties were compared with those of the corresponding
alkyl glycosides, 7 (resembling APG surfactants), as well as their
OAc
Contact penetration experiments with water, an example is
shown in Fig. 3, only indicated the presence of a hexagonal phase
for compounds 6. It was assumed to be the normal HI phase. The
exclusive formation of this phase is in contrast to the previous re-
ports on the behavior of alkyl glycosides, for, which a diversity of
phases was found in case of the C8 surfactant 7a,46e48 while only
lamellar lyotropic phases were reported for the higher homolog
7b.49 In order to understand the different lyotropic phase behavior
of 6 and 7, the molecular surface area of compound 6b was deter-
mined based on the slope for the concentration depending region
of the surface tension plot displayed in Fig. 4.
O
N
NH
AcO
AcO
OAc
OAc
BrC2H4OH
[BF3]
CnH2n+1Br
OAc
CnH2n+1
N
N
O
AcO
AcO
O
Br
OAc
OH
O
HO
HO
O
CnH2n+1
N
N
OH
OR
OH
O
RO
RO
O
CnH2n+1
N
N
O
H3C
HO
HO
CnH2n+1
OR
N
N
OCnH2n+1
OH
R = Ac
R = H
Fig. 1. Synthetic scheme for glycosyl imidazolium surfactants.
Fig. 2. Structure comparison of surfactants.

30
A.A. Salman et al. / Carbohydrate Research 412 (2015) 28e33
Table 2
Surfactant properties in comparison
Compd
Alkyl chain
C8H17
TK [ꢂC]
TC [ꢂC]
CMC [mmol Lꢀ1
]
gCMC [mN mꢀ1
]
Ref.
6a
6b
6c
7a
7b
8a
8b
8c
<10
<10
<10
N/A
37.5
d
>90
>90
>90
>80
>80
d
16
1.5
24.8
25.5
39.8
30.0
~30.5
41.3
37.2
41
C
C
12H25
16H33
0.31
6.5
0.19
170/121
9.0/4.3
0.8
C8H17
C12H25
C8H17
[39,40]
[39,41,42]
[42]
[42,43]
[43]
C
C
12H25
16H33
d
d
d
d
1020
Form the Gibbs adsorption isotherm the surface excess con-
centration can be calculated according to Eq. 1,50
Amin
¼
;
(2)
NG
max
where N is Avogadro's number (6.022ꢁ1023 mol-1). The application
of Eqs. 1 and 2 on the graph displayed in Fig. 4 led to a molecular
surface area of 53 Å2 for compound 6b. This substantially exceeds a
value of below 40 Å2, reported for APG analog 7b and its homo-
logs.51,52 In fact, the value gets near the 63 Å2, found for octyl
ꢀ
ꢁ
10ꢀ3
2:303nRT vlog C
vg
G
max
¼ ꢀ
;
(1)
maxT
where [vg/v log c] is the surface tension slope, T is the absolute
temperature, R is the universal gas constant (8.314 J molꢀ1 Kꢀ1), and
n is the number of surfactant species at the interface (here n¼1).
The minimum area per surfactant molecule Amin is obtained by
applying Eq. 2,
b
-glucoside in a hexagonal lyotropic phase,53 and is in line with the
exclusive formation of curved assembly structures for sugar-based
Y-shape surfactants, for, which similar molecular surface areas
were reported.54 It is assumed that the expansion of the hydrophilic
domain by the hydrated imidazolium ion and repulsive charge in-
teractions are responsible for the increased surface area and the
related disappearance of the lamellar phase for the AIGs 6.
Surface tensions of micellar solutions below 30 mN mꢀ1 char-
acterize AIGs with chain lengths of up to 12 carbon atoms as good
surface active surfactants, thus suggesting their application as
emulsifier. In order to evaluate the emulsifying abilities of 6, oil-in-
water emulsions were prepared and the stability of the latter was
compared to formulations based on structurally related surfactants
7 and 8. Due to accessibility constraints, surfactants with different
alkyl chain length were applied as reference, i.e. 7b and 8c. How-
ever, the investigation of a wide range of chain lengths for 6 enables
a differentiation of head group and chain effects. The results are
summarized in Table 3.
AIGs are less effective emulsifiers for W/O systems than APGs, as
indicated by the relative emulsion stabilities of 6b and 7b. The
emulsion stability depends strongly on a balance of the surfactant
antipodes, i.e. the hydrophilic chain and the hydrophobic combined
sugar-imidazolium head group. Among the investigated AIGs the
C12-surfactant 6b was most effective. This is in line with previous
Fig. 3. OPM image for water penetration of 6c showing the hexagonal HI phase.
reports on the behavior of non-ionic surfactants, indicating
enhanced emulsion stability upon increasing the alkyl chain length
55
from C7 to C10
,
but reduced interfacial activity upon further in-
crease from C12 to C18
.
56 Both longer and shorter alkyl chain lengths
led to a significant drop of the emulsion stability. The C8-surfactant
6a was particularly instable, as indicated by complete phase sepa-
ration within a single day. The emulsion behavior of 6c and 8c were
almost identical. However, a comparison of the turbidity of the
water phase after 4 days revealed a slightly higher separation for
the pure imidazolium surfactant 8c. The observations suggest
dominance of ionic interactions for the surfactant at the water-oil
Table 3
Emulsion stability (W/O)
Compd
Visible phase separation
Full phase separation
6a
6b
6c
7b
8c
3 h
<1 d
2e3 d
1e2 d
>14 d
1e2 d
>14 d
> 4 d
>30 d
> 4 d
Fig. 4. Surface tension behavior of AIG 6b.

A.A. Salman et al. / Carbohydrate Research 412 (2015) 28e33
31
interface with only minor impact of the carbohydrate. It is believed
that repulsive charge interactions of surfactant head groups
destabilize assemblies at the water-oil interface, thus giving rise to
a phase separation. Unfortunately, this discourages the use of pure
AIGs as W/O-emulsifier.
4.1.2. Synthesis of alkylated imidazoles36
A solution of imidazole 3 (30 mmol) in THF (60 mL) was treated
with NaOH (25 mL, 40% aq) and the alkyl bromide (30 mmol), and
the reaction was refluxed overnight. The solvent was evaporated
and the crude reaction mixture was extracted with CH2Cl2 against
water. The organic layer was washed with water, dried over MgSO4
and concentrated. The final product was distilled under vacuum
(~5 mbar) to provide 4 as yellow oily liquid in 80e85% yield.
3. Conclusion
Alkyl imidazolium glycosides are easily accessible cationic-
nonionic hybrid surfactants. Although the applied synthetic
scheme suffers of high production costs owing to the number of
reaction steps, the latter may be substantially reduced by applica-
tion of a Fischer glycosylation approach similar to previously re-
ported ATG surfactants.33 The cationic imidazolium ion dominates
the surfactants, assembly behavior, both in presence and absence of
an oil phase. However, the presence of the carbohydrate enables a
significant reduction of the surface tension. While charge domi-
nated surfactant interactions discourage the application of pure
AIGs for both delivery systems and emulsions, a stabilizing effect of
the sugar on the assembly behavior suggests potential for combi-
nations with non-ionic or anionic sugar based surfactants.
4.1.3. Synthesis of alkyl-imidazolium glycoside
A solution of 2-bromoethyl glucoside 2 (1.1 mmol) and the
alkylated imidazole 4 (3.3 mmol) in xylene (2 mL) was heated to
125 ꢂC for 1 h. The solvent was evaporated and the crude product
was taken up in MeCN (10 mL) and extracted 4 times with hexane
(60 mL) to remove remaining imidazole 4. The acetonitrile phase
was concentrated under reducing pressure to provide the desired
product 5 as a pale yellow syrup in ~95% yield.
4.1.4. Deacetylation of surfactant precursors
The surfactant precursor 5 (0.5 mmol) was dissolved in meth-
anol (30 mL) and treated with a catalytic amount of sodium
methoxide to obtain a basic medium (pH~9). The mixture was
stirred for overnight at room temperature and subsequently
neutralized with Amberlite IR 120 (Hþ). Evaporation of the solvent
furnished the final surfactant 6 in ~95% yield.
4. Experimental
4.1. General methods
4.2. 1-(2-
bromide (6a)
b-D-Glucopyranosyloxyethyl)-3-octyl-imidazolium
Starting materials and reagents of synthesis grade and solvents
of AR grade were obtained from various commercial sources and
used without prior treatment. Purification of the surfactants and
their precursors applied extraction, crystallization and distillation
but avoided chromatography. All surfactants were NMR spectro-
scopically analyzed (1H and 13C, recorded on 400 MHz spectrome-
ters) in both acetylated and deprotected form, and their identities
were confirmed by high-resolution mass spectrometry based on
electrospray ionization. The 1H NMR spectra indicated high chem-
ical and diastereomeric purity of the surfactants. Physical investi-
4.2.1. 1-Octyle3-[2-(2,3,4,6-tetra-O-acetyl-b-D-
glucopyranosyloxy)-ethyl]-imidazolium bromide (5a)
Compound 2 (0.50 g, 1.1 mmol) and 4a (0.60 g, 3.3 mmol) were
reacted in xylene (2 mL) according to general procedure 4.1.3 to
25
provide 5a (0.66 g, 95%) as pale yellow syrup. [
a
]
D
ꢀ25 (c 0.1,
CHCl3). 1H NMR (400 MHz, CDCl3):
d
10.17 (s, N]CHeN), 7.57 (s,
CH]NeCH), 7.20 (s, CHeCHeN), 5.18 (dd~t, H-3), 5.00 (dd~t, H-4),
4.92 (dd, H-2), 4.80e4.65 (m, 2H, CH2N), 4.60 (d, H-1), 4.27e4.20
(m, 4H, H-6a, CH2O-a, a-CH2), 4.12 (dd~bd, H-6b), 4.07 (ddd~dt,
gation applied distilled water with a conductivity of 1.1 0.1 m .
S cmꢀ1
Cloud points (TC) were determined by heating clear surfactant
solutions (20 mmol Lꢀ1 for C8, 7.5 mmol Lꢀ1 for C12 and 1 mmol Lꢀ1
for C16) slowly up to 100 ꢂC while monitoring for visible changes.
Krafft points (TK) were estimated based on the behavior of these
solutions to cooling (4 ꢂC) for several days. The lyotropic phase
behavior of the surfactant was investigated by optical polarizing
microscopy using the contact penetration technique.57,58 System-
atic surface tension measurements based on the Du Nouy ring
method were applied to study the surfactants, aggregation and
surface behavior. CMCs were determined from a logarithmic
display of the surface tension against the surfactant concentration
as intersection of linear regressions for the concentration
depending region and the plateau at high surfactant concentration.
Emulsions, containing 3.8 g water and 0.2 g methyl laurate, were
prepared based on a surfactant content of 0.5% m/m. Samples were
homogenized with an IKA T10 basic mixer for 2 min at maximum
speed (~14,000 rpm) in 5 mL vials and subsequently stored at room
temperature and monitored on phase separation over a period of a
few weeks.
CH2O-b), 3.77 (ddd, H-5), 2.07, 2.00, 1.97 (3 s, 3þ6þ3H, Ac), 1.90
(mc, 2H,
b
),1.37e1.20 (m,10H, bulk-CH2), 0.85 (t, 3H, CH3); 3J1,2¼8.0,
3J2,3¼9.5, 3J3,4¼9.5, 3J4,5¼10.0, 3J5,6a¼5.0, 3J5,6b¼1.5, 2J6¼12.0 Hz. 13
C
NMR (100 MHz, CDCl3): 170.51, 169.85, 169.65, 169.46 (CO), 137.17
(N]CHeN), 123.83 (CH]NeCH), 120.64 (CHeCHeN), 100.49 (C-1),
72.28 (C-3), 72.01 (C-5), 71.16 (C-4), 68.14 (C-2), 68.11 (CH2O), 61.66
(C-6), 50.17 (
(bulk-CH2), 26.21 (
13.96 ( ).
a
-CH2), 49.87 (CH2N), 31.56 (
u-2), 30.05, 28.91, 28.80
g
), 22.47 ( -1), 20.79, 20.76, 20.49, 20.47 (Ac)
u
u
4.2.2. 1-(2-b-D-Glucopyranosyloxyethyl)-3-octyl-imidazolium
bromide (6a)
Compound 5a (0.35 g, 0.55 mmol) was dissolved in methanol
(30 mL) and treated with a catalytic amount of sodium methoxide
according to general prodecure 4.1.4 to furnish 6a (0.29 g, 96%) as
25
pale yellow syrup. [
CD3OD):
a]
þ18 (c 0.1, MeOH). 1H NMR (400 MHz,
D
d
7.72 (d~bs, CH]NeCH), 7.66 (d~bs, CHeCHeN),
4.56e4.43 (m, 2H, CH2N), 4.37 (d, H-1), 4.25 (t, 2H, a-CH2), 4.20
(ddd~dt, CH2O-a), 4.04 (ddd, CH2O-b), 3.91 (dd, H-6a), 3.67 (dd, H-
6b), 3.40 (dd~t, H-3), 3.36e3.30 (m, H-5), 3.28 (dd~t, H-4), 3.20
4.1.1. Synthesis of base-glycoside34
(dd~t, H-2), 1.91 (p, 2H, b-CH2), 1.44e1.26 (m, 10H, bulk-CH2), 0.92
3
3
3
3
3
b-Glucose pentaacetate 1 (6.00 g, 15 mmol) and bromoethanol
(t, 3H, CH3); J1,2¼8.0, J2,3¼9.0, J3,4¼9.0, J4,5¼9.5, J5,6a¼1.5,
2
(2.1 g, 17 mmol) were dissolved in CH2Cl2 (50 mL) and treated with
BF3ꢁOEt2 (3.3 g, 23 mmol). The reaction was stirred at rt for 3 h and
then washed with a satd NaHCO3 (aq) and water. The organic layer
was dried over MgSO4 and concentrated. The product was crys-
tallized from ethanol to give 2 as colorless crystals (3.85 g, 55%).
3J5,6b¼5.5, J6,6ˉ¼12.0 Hz. 13C NMR (100 MHz, CD3OD):
d 138.2
(NeC]N), 122.84 (CH]NeCH), 121.94 (CHeCHeN), 103.11 (C-1),
76.70, 76.59 (C-3, C-5), 73.54 (C-2), 70.15 (C-4), 67.33 (CH2O), 61.23
(C-6), 49.61, 49.51 (
(bulk-CH2), 25.91 (
a
,CH2N), 31.67 (
u
-2), 29.72 (
b), 28.82, 28.67
g), 22.26 ( -1), 13.02 (u
u
). HRMS: Calcd for

32
A.A. Salman et al. / Carbohydrate Research 412 (2015) 28e33
C19H35N2O6 387.2495, 388.2529 (21%); found 387.2485, 388.2514
(21%).
(bulk-CH2), 26.31 (
g), 22.66 (u-1), 20.85, 20.83, 20.56, 20.53 (Ac)
14.0 ( ).
u
4.3. 1-(2-b-D-Glucopyranosyloxyethyl)-3-dodecyl-imidazolium
4.4.2. 1-(2-b-D-Glucopyranosyloxyethyl)-3-hexadecyl-imidazolium
bromide (6b)
bromide (6c)
Compound 5c (0.20 g, 0.27 mmol) was dissolved in methanol
(20 mL) and treated with a catalytic amount of sodium methoxide
4.3.1. 1-Dodecyle3-[2-(2,3,4,6-tetra-O-acetyl-b-D-
glucopyranosyloxy)-ethyl]-imidazolium bromide (5b)
Compound 2 (0.5 g, 1.1 mmol) and 4b (0.8 g, 3.3 mmol) were
reacted in xylene (2 mL) according to general procedure 4.1.3 to
according to general procedure 4.1.4 to furnish 6c (0.15 g, 96%) as
þ12 (c 0.1, MeOH). 1H NMR (400 MHz,
25
pale yellow syrup. [
CD3OD):
2H, CH2N), 4.36 (d, H-1), 4.24 (t, 2H,
a
]
D
d
7.74 (d, CH]NeCH), 7.68 (d, CHeCHeN), 4.55e4.42 (m,
25
provide 5b (0.73 g, 96%)as pale yellow syrup. [
a
]
ꢀ13 (c 0.1,
a-CH2), 4.20 (ddd~dt, CH2O-a),
D
CHCl3). 1H NMR (400 MHz, CDCl3):
d
10.17 (s, N]CHeN), 7.59 (s,
4.04 (ddd, CH2O-b), 3.92 (dd, H-6a), 3.67 (dd, H-6b), 3.37 (dd~t, H-
CH]NeCH), 7.21 (s, CHeCHeN), 5.20 (dd~t, H-3), 5.02 (dd~t, H-4),
4.94 (dd, H-2), 4.84e4.68 (m, 2H, CH2N), 4.63 (d, H-1), 4.30e4.20
(m, 4H, H-6a, CH2O-a, a-CH2), 4.16 (dd~bd, H-6b), 4.10 (ddd~bdt,
3), 3.36e3.30(m, H-5), 3.27 (dd~t, H-4), 3.19 (dd, H-2), 1.92 (p, 2H,
3
b
-CH2), 1.45e1.21 (m, 24H, bulk-CH2), 0.91 (t, 3H, CH3); J1,2¼8.0,
3
3
3
3
3J2,3¼9.0, J3,4¼9.0, J4,5¼9.5, J5,6a¼1.5, J5,6b¼5.5, 2J6¼12.0,
3Jimidazole~2 Hz. 13C NMR (100 MHz, CD3OD):
d 138.1 (NeC]N),
CH2O-b), 3.80 (ddd, H-5), 2.08, 2.02, 1.99 (3 s, 3þ6þ3H, Ac), 1.92 (p,
2H,
b
-CH2), 1.40e1.20 (m, 18H, bulk-CH2), 0.87 (t, 3H, CH3);3J1,2¼8.0,
122.82 (CH]NeCH), 121.92 (CHeCHeN), 103.11 (C-1), 76.72, 76.60
(C-3, C-5), 73.52 (C-2), 70.14 (C-4), 67.30 (CH2O), 61.23 (C-6), 49.60,
3
3
3
3
3J2,3¼9.0, J3,4¼9.5, J4,5¼9.5, J5,6a¼5.0, J5,6b¼1.5, 2J6¼12.0 Hz. 13
C
NMR (100 MHz, CDCl3): 170.57, 169.91, 169.71, 169.53 (CO), 137.23
(N]CHeN), 123.89 (CH]NeCH), 120.69 (CHeCHeN), 100.55 (C-1),
72.35 (C-3), 72.07 (C-5), 71.22 (C-4), 68.20 (C-2, CH2O), 61.72 (C-6),
49.50 (
29.33, 29.27, 29.16, 29.06, 28.72 (bulk-CH2), 25.92 (
13.03 ( ). HRMS: Calcd for C27H51N2O6 499.3747, 500.3781 (30%);
a, CH2N), 31.66 (
u
-2), 29.72 (
b
-CH2), 29.37 (3ꢁ), 29.34 (2ꢁ),
g
), 22.32 ( -1),
u
u
50.23 (
29.29, 28.93 (bulk-CH2), 26.29 (
20.53 (Ac) 14.0 ( ).
a
), 49.94 (CH2N), 31.62 (
u
g
-2), 30.11, 29.55 (2ꢁ), 29.45, 29.34,
found 499.3744, 500.3773 (29%).
), 22.65 ( -1), 20.85, 20.82, 20.55,
u
u
Acknowledgments
4.3.2. 1-(2-
bromide (6b)
b-D-Glucopyranosyloxyethyl)-3-dodecyl-imidazolium
Financial support for the investigation by the University of
Malaya under research grant UM.C/625/1/HIR/MOHE/SC/09 and by
the Malaysian Ministry of Education under FRGS grant FP032-
2013B is gratefully acknowledged.
Compound 5b (0.37 g, 0.53 mmol) was dissolved in methanol
(30 mL) and treated with a catalytic amount of sodium methoxide
according to general procedure 4.1.4 to furnish 6b (0.26 g, 95%) as
25
pale yellow syrup. [
CD3OD):
2H, CH2N), 4.38 (d, H-1), 4.26 (t, 2H,
a
]
þ20 (c 0.1, MeOH). 1H NMR (400 MHz,
D
Supplementary data
d
7.74 (d, CH]NeCH), 7.68 (d, CHeCHeN), 4.58e4.45 (m,
a
-CH2), 4.25e4.19 (m, CH2O-a),
Supplementary data (Details of the synthetic procedures as well
as characteristic data for the intermediates are provided in the
Supplementary data that can be obtained from the journal web-
page. The material also contains images of NMR spectra, enabling
the evaluation of the surfactant purity.) related to this article can be
found at http://dx.doi.org/10.1016/j.carres.2015.04.022.
4.05 (ddd, CH2O-b), 3.90 (dd~bd, H-6a), 3.67 (dd, H-6b), 3.39 (dd~t,
H-3), 3.37e3.31 (m, H-5), 3.28 (dd~t, H-4), 3.20 (dd~t, H-2), 1.92 (p,
2H, b-CH2), 1.38 (mc, 2H, g-CH2), 1.30 (mc, 16H, bulk-CH2), 0.91 (t,
3
3
3
3
3
3H, CH3); J1,2¼8.0, J2,3¼9.0, J3,4¼9.0, J4,5¼9.0, J5,6a¼1.5,
3J5,6b¼5.5, 2J6¼12.0, 3Jimidazole¼1.5 Hz. 13C NMR (100 MHz, CD3OD):
d
138 (NeC]N), 124.25 (CH]NeCH), 123.34 (CHeCHeN), 104.46
(C-1), 78.05, 77.96 (C-3, C-5), 74.93 (C-2), 71.55 (C-4), 68.74 (CH2O),
62.62 (C-6), 51.01, 50.91 ( ,CH2N), 33.05 ( -2), 31.15 (
), 30.74 (2ꢁ),
30.67, 30.56, 30.45, 30.13 (bulk-CH2), 27.32 ( ), 23.72 ( -1), 14.48
). HRMS: Calcd for C23H43N2O6 443.3121, 444.3155 (26%); found
443.3123, 444.3149 (25%).
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