Triazole Linked N-Acetylglucosamine Based Gelators for Crude Oil Separation and Dye Removal

Article abstract of DOI:10.1021/acs.langmuir.9b02704

Marine oil-spills have a long-lasting impact on the environment; therefore, it is a major concern in the scientific community to find a solution for remediation. Recently, phase selective organo-gelators emerged as potential materials for removal of oil from water through selective gelation. Herein, we report synthesis of a series of C-6 triazole linked N-acetylglucosamine derivatives, among which three have shown excellent selective gelation of organic solvents, diesel, petrol, and crude oils in water and seawater. We have studied phase selective gelation against different API grade crude oils (from light to heavy), and the gelation was achieved using nontoxic carrier solvent at room temperature in less than 15 min, and gelators were found useful for recovering crude oils. Critical gel concentration (CGC) of crude oil gelators was found to be 2.3-12% (w/v). The variable temperature NMR and FTIR experiments reveal that intermolecular hydrogen bonding was responsible for gel formation. Furthermore, a gelator was utilized for selective dye removal from water.

Full text of DOI:10.1021/acs.langmuir.9b02704

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Interface Components: Nanoparticles, Colloids, Emulsions, Surfactants, Proteins, Polymers
Triazole Linked N-acetylglucosamine Based
Gelators for Crude Oil Separation and Dye Removal
chintam narayana, Priti Kumari, Ghanshyam Tiwari, and Ram Sagar
Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.9b02704 • Publication Date (Web): 27 Nov 2019
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Triazole Linked N-acetylglucosamine Based
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Gelators for Crude Oil Separation and Dye Removal
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Chintam Narayana,a Priti Kumari,a Ghanshyam Tiwari band Ram Sagara,b
aDepartment of Chemistry, School of Natural Sciences, Shiv Nadar University (SNU), NH91,
Tehsil-Dadri, Gautam Buddha Nagar, Uttar Pradesh, 201314, India.
bDepartment of Chemistry, Institute of Science, Banaras Hindu University, Varanasi, Uttar
Pradesh, 221005, India.
*E-mail (Corresponding author): ram.sagar@bhu.ac.in
ABSTRACT:
Marine oil-spills have along-lasting impact on environment, therefore is a major concern in
scientific community to find solution for its remediation. Recently, phase selective organo-
gelators emerged as potential materials for removal of oil from water through selective gelation.
Herein, we report synthesis of a series of C-6 triazole linked N-acetylglucosamine derivatives,
among which three of the derivatives have shown excellent selective gelation of organic
solvents, diesel, petrol and crude-oils in water and sea water. We have studied phase selective
gelation against different API grade crude oils (from light to heavy) and the gelation was
achieved using non-toxic carrier solvent at room temperature in less than 15 minutes, and
gelators were found useful for recovering crude oils. Critical gel concentration (C.G.C.) of crude
oil gelators was found to be 2.3-12% (w/v). The variable temperature NMR and FTIR
experiments reveal that, intermolecular hydrogen bonding was responsible for the gel formation.
Furthermore, a gelator was utilized for selective dye removal from water.
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INTRODUCTION
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Marine oil spillages have been one of the major environmental concerns because it damages the
environment by releasing toxic substances.1,2 Generally, oil spillages occur due to leakage of oil
from drilling the oil in the sea and transporting the oil from one place to another place. In 2010,
Gulf Mexico oil spillage was one of the biggest spillage in petroleum industry and it released
four million barrels of crude oil into sea water. The spillage caused extensive damage to the
marine, wild life habitats, fishing and tourism industries.3 These oil spills damages to
environment and forced researchers to design efficient remediation strategies for removal and
recovery of crude oil from sea water. Apart from these there are other pollutants which damage
the water bodies like dyes, heavy metals and industrial organic wastes.4-7 The mitigation of the
consequences of these pollutants is the need of hour.
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Conventional methods for oil spill recovery can be classified into three categories, physical,
chemical and biological methods. Skimmers are mechanical devices used to remove oil from
water surface.8 Sorbents are insoluble chemical materials which can soak oil from water.9-12
Another physical method known for spill oil recovery is using adsorption materials.13-15
However, Dispersants are a group of chemical products sprayed onto an oil phase to remove
crude oil.16,17 In situ burning of oil is another popular process to remove oil from water but it
requires ignition and controlled combustion of oil slicks.18 Bioremediation involves use of
microorganisms to detoxify the pollutants in order to accelerate the natural biodegradation.19
However, all these methods have certain drawbacks like human hazard, high cost, long
procedures storage and transport etc. Recently, phase selective organo-gelators (PSOG) have
received great attention because of its numerous applications in oil scavenging, dye removal,
nanoparticle synthesis etc.20-22 They forms gels by self-assembly of organic molecules in defined
three dimensional network fibers through non-covalent interactions such as hydrogen bonding, π-
π stacking, van der Walls forces and dipole-dipole interactions.23
Several research groups have reported different structural motifs of PSOG, such as amino acids,
carbohydrates, steroids, and peptides etc. Among all motifs, recently carbohydrate based low
molecular weight gelators (LMWGs) have attracted attention of scientific community because of
its benign nature and diverse properties.18 Carbohydrates are readily available renewable
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resources and having multiple chiral centers and hydroxyl groups. Most of the carbohydrates
based LMWGs involves hydrogen bond mediated self-assembly process.19
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After pioneer work by Bhattacharya and co-workers for oil water separation using amino acid
based gelators,24 several groups have been explored carbohydrate based gelators for crude oil
gelation.25-32 Somnath and co-workers reported phase selective gelation of crude oil using
arabinose based LMWGs.23 They further used C-1 triazole linked arabinose derivatives as
gelators for the crude oil separation.25 Sureshan and co-workers have reported benzilidine
masked glycopyranoside derivatives, which showed phase selective gelation of crude oil in
water.26 Mukherjee and co-workers and ourselves disclosed N-acetylglucosamine derived
gelators which shown instant gelation of oil in presence of water.27,28 Other than carbohydrates,
recently Zeng and co-workers revealed Fmoc protected amino acid derivatives29,30 and Chaudhuri
et al. discovered naphthalene based diimide derivatives, as potential gelators, have ability to
form gel in light to heavy crude oils.31
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We envisioned that C-6 triazole linked N-acetylglucosamine derivatives may serve as stable
carbohydrate based PSGs for crude oil gelation in water. Previously reported carbohydrate based
gelators, for crude oil gelation were having acid or base sensitive functional groups, therefore
were not suited, if acidic or basic impurities are present in crude oil.29 Further triazole motif is
robustically accessible through “click-chemistry” and known for structural backbone of gelators.
Its planar structure exhibits the ability of H-bonding due to the presence of both donor and
acceptor groups with similar relative positions having π-π stacking.
Herein, we report design and synthesis of C-6 triazole linked N-acetylglucosamine based
compounds 5a-5g. Selective compounds were identified as potential phase selective gelators for
gelation of organic solvents, mineral oils, and crude oils in water and sea water. Additionally, the
PSOGs were found to be efficient for removal of waterborne pollutant (dye).
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R
N
O
O
OH
OH
O
OMe
OH
O
N
O
N
Ph
O
O
AcO
OAc
OH
OAc
B
C
A
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Hydrogen
bonding
H

stacking
O
OMe
N
N
N
NHAc
BnO
Our Designed &
Synthesised
Crude Oil Gelator
OBn

stacking
Hydrogen
bonding
5a
Figure 1. Carbohydrate based crude oil gelators (A-C) and our designed crude oil gelator 5a.
RESULTS AND DISCUSSION
Synthesis
The synthesis commenced with the glycosidation reaction on commercially available N-acetyl
glucosamine 1 with methanol in the presence of Amberlite IR-120 H⁺ resin which afforded
methyl glycoside as a mixture α: β (9:1) in quantitative yield. Subsequently, selective tosylation
of C-6 OH using tosyl chloride in dry pyridine afforded the mixture of α- and β-tosyl derivatives.
The major α-isomer compound 2 was separated through column chromatography and obtained in
good isolated yield (70%).32 Azidation reaction on compound 2 was carried out by sodium azide
in DMF at elevated temperature which furnished azide derivative 3 in 79% isolated yield.
Further, benzylation on azide derivative 3 led to di-O-benzylated compound 4 in 78% isolated
yield (Scheme 1). Copper catalyzed click-chemistry was carried out on azido derivative 4 using
different commercially available alkyne under microwave irradiation, which furnished C-6
triazole linked N-acetyl glucosamine derivatives in good to very good isolated yields. In order to
understand the effect of substitution on triazole ring towards gelation, we have install different
groups (aliphatic and aromatic) on traizole ring and synthesized amides, esters, phenyl
substituted derivatives 5a-5g in good yield (Scheme 1).
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OTs
N3
OH
i) Amberlite IR-120 H+
MeOH, 80 °C, 24 h, 90%
ii) Tosyl chloride
O
O
NaN3, DMF,
80 °C
6 h, 79%
O
O
O
OH
BnBr/
NaH/THF
rt, 1.5 h
78%
HO
R
NHAc
HO
NHAc
HO
NHAc
Pyridine, rt, 24 h, 70%
OH
OH
3
OH
1
2
9
H
N
R =
N
O
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N
N3
N
O
R
O
5c
O
O
NHAc
O
O
5a
5b
sodium ascorbate
CuSO4, DMF,
µW, 70 °C, 15 min
56-70%
BnO
BnO
NHAc
OBn
HO
OBn
MeO
4
OMe
5f
5a-5g
5d
5e
5g
Scheme 1. Synthesis of triazole linked N-acetylglucosamine compounds 5a-5g.
Gelation test: The gelation ability of C-6 triazole linked N-acetylglucosamine compounds 5a-5g
was tested in several different solvents and results are summarized in Table 1. Compounds 5a,
5b and 5f displayed excellent ability to gelate different non polar organic solvents such as
toluene, benzene, o-xylene, mesitylene etc. These gels were found to be transparent and stable at
room temperature for more than 3 days. Furthermore, m-methoxy phenyltriazole derivative 5f
was found to forms stable gel selectively in aromatic solvents, whereas, p-methoxy phenyl
triazole derivative 5g forms unstable gel in all these solvents. These results are demonstrated that
the changing the position of same functional group on phenyl ring influences the gel formation
property. However, alkyl 5d, hydroxyl alkyl 5e, substituted C-6 triazole derivatives neither form
gels in non-polar and nor in polar organic solvents. On the other hand, amide linked triazole
derivative 5c was insoluble in all the solvents (Table 1). Among all the identified gelators (5a, 5b
and 5f), gelator 5a was found best which exhibits minimum C.G.C. ranging between 0.14-0.8%
(w/v) in all the tested solvents (Figure 2) and form stable gel (SI, Figure S1-S2). The lowest
C.G.C. for 5a was observed 0.14% (w/v) in mesitylene gel (Table 1). We observed that electron
withdrawing group on triazole ring is essential for the gel formation, because it allows triazole
ring proton to participate in intermolecular hydrogen bonding. In addition to that, π-π stacking
interaction of phenyl ring and hydrogen bonding of the amide proton are also helpful for the gel
formation. These gels display good thermal reversibility with a gel-sol transition temperature.
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(a)
(b)
(c)
(d)
(e)
(f)
Figure 2: Transparent gels formed by 5a in different organic solvents: (a) Benzene (b) Toluene
(c) o-Xylene (d)m-Xylene (e) p-Xylene (f) mesitylene
Gel formation time is very important and it contributes wide range functions and applications to
gelator.33 Thus we studied gelation property of compound 5a in various solvents and noticed its
gel formation time. We found that thermal induced gelation of 5a took more than five minutes;
whereas, ultrasonication induced gelation took less than one minute. It’s worth to mention here
that the ultrasonic energy can induce powerful stimulus to cause gelation.34
Table 1. Study of gel formation in different solvents at different concentration and conditions.
Time
Solvents
5a
5b
5c 5d 5e 5f
5g
Gelation of Gelation of
5a in cold 5a under
condition
Sonication
Benzene
TG (0.80) TG (0.92)
TG (0.62) TG (0.41)
TG (0.45) TG (0.31)
TG (0.27) TG (0.22)
TG (0.31) TG (0.38)
TG (0.14) TG (0.33)
P
P
P
P
P
P
P
S
S
S
S
S
S
S
S
S
S
S
S
S
S
TG (0.80)
TG (0.80)
TG (0.80)
TG (0.38)
TG (0.45)
TG (0.25)
S
PG
PG
PG
PG
PG
PG
S
10 min
35 sec
Toluene
3 min 50 sec 28 sec
4 min 50 sec 25 sec
3 min 20 sec 27 sec
3 min 40 sec 35 sec
o-xylene
m-Xylene
p-xylene
Mesitylene
Chlorobenzene
50 sec
S
20 sec
S
S
S
S
S
S
S
Bromobenzene
Iodobenzene
P
P
S
S
S
S
S
S
S
S
S
S
S
S
Compounds were tested in 5 mg/mL concentration. S is soluble at room temperature, P is precipitated, () is C.G.C in
mg/mL.TG is transparent gel, PG means partial gel. All C.G.C. were determined using heating and cooling method
(thermal induced), which involves heating of gel mixture followed by quick cooling in ice cold water.
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Morphological Properties of gels:
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To gain insight into the aggregation mode, we recorded morphologies of xerogels formed by
compounds 5a and 5b in mesitylene and toluene solvent using field emission scanning electron
microscopy (FESEM). The images are shown in figure 3; a1, a2 are SEM images belongs to
xerogel of 5a and 5b prepared in mesitylene solvent respectively. These images shows dense and
entangled network of fibers with diameter less than 100 nm and length on a 5 micrometer scale
which showed effective entrapment and immobilization of the solvent. On the other hand,
xerogel images of 5a and 5b prepared in toluene displayed lamellar type texture (Figure 3; a3
and a4).The morphology of xerogels was clearly demonstrated the role of solvent influences in
self-assembly of these gelators.
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Figure 3. SEM images of mesitylene gel of compound 5a-(a1) and 5b-(a2) and toluene gel of
compound 5a-(a3) and 5b-(a4).
For understanding mechanism of self-assembly resulting in to gel formation, we have performed
variable temperature (VT) NMR experiment in DMSO-d6 for compounds 5a (Figure 4) and
compound 5b (SI, Figure S3). The triazole C-H proton in compound 5a shifted from δ 8.605
ppm to 8.495 ppm, while increasing the temperature from 25 to 60 ºC. This upfield shift (Δδ =
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0.117 ppm) clearly indicates that, triazole C-H proton was involved in intermolecular hydrogen
bonding and it got weaken with increasing the temperature. Similarly, N-H proton of acetamido
group was shifted to upfield (Δδ = 0.262 ppm) suggesting that N-H proton was involved in
hydrogen bonding interactions as well (Figure 4). The protons of OCH3 slightly shifted to
downfield by Δδ 0.047 ppm upon increasing the temperature. This reflects that intramolecular
hydrogen bond between NH and OCH3 groups. These results support that, hydrogen bonding and
π-π stacking interactions were responsible for gel formation in these compounds.
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Figure 4. 1H NMR spectra of compound 5a at different temperature in DMSO-d6
Phase selective organo-gelators are capable of congeal the oil in presence of water. The main
advantage with this is that, gelled oil float on water, which can easily be separated from water.
There are different methods reported for phase selective gelation of oil in presence of water,35-37
i) dissolution of the gelator in a suitable environment friendly solvent followed by drop wise
addition it to the oil phase or ii) applying xerogels directly to the oil phase. In our study, we have
investigated phase selective gelation ability of compounds 5a, 5b and 5f in petroleum products
such as diesel, petrol, pump oil and silicon oil. The gelation ability of gelators was found in
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decreasing order of 5a > 5f > 5b (Table 2). All oil gels are scoopable, thermo reversible and
stable for several months (SI, Figure S4). In case of diesel and petrol C.G.C. for compound 5a
was 2.8% (w/v) and 2.0% (w/v) respectively.
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Table 2. Phase selective gelation different oils in water.
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Solvents (1:2 v/v)
Diesel-water
5a
5b
5f
G (2.8)
G (2.0)
G (3.0)
G (3.6)
G (5.7)
G (3.9)
G (5.5)
G (6.4)
G (3.2)
G (2.3)
G (3.2)
G (4.0)
Petrol-water
Silicon Oil-water
Pump Oil-water
G = Gel, () C.G.C. = critical gelation concentration, 0.2 mL of EtOAc was used as co-solvent in each case.
X-ray Diffraction study:
To understand the molecular packing, we have performed powder XRD for 1% (w/v) toluene gel
of 5a. The XRD pattern of the xerogel showed three reflection peaks 2θ = 14.8°, 19.4°, 24.4°.
Their corresponding d spacing is 5.9 Å, 4.5 Å and 3.6 Å. Strong peak at 2θ value 24.4° can be
attributed to π-π stacking interactions and corresponding d-spacing 3.6 Å. And another peak at
2θ = 19.4° corresponding to H-bonding interactions with an average distance of d = 4.5 Å
(Figure 5).23
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Figure 5. Powder XRD pattern of xerogel of 5a
In order to understand the non-covalent interactions, we have acquired and studied the IR spectra
of solid compound 5a and its gel formed in diesel. We observed N-H stretch vibration 3295 cm-1
in powder form shifted to 3290 cm-1 in gel state, which further indicates intermolecular hydrogen
bonding taking place for gel formation. In solid state Ar C-H and triazole C-H stretch vibration
for compound 5a appears at 2911 and 2832 cm-1 respectively. Slightly red shift was observed for
these C-H stretches in gel state from 2911 to 2922 cm-1 and 2832 to 2853 cm-1. The shift is due to
strong hydrophobic interactions in the gel state of 5a. Moreover, these signals got enhanced in
the gel state. The amide C=O bond stretch band in powder form at 1645cm-1 shifted to gel state
1648 cm-1 and amide N-H bending frequency shifted from 1548 cm-1 to 1549 cm-1. These
findings indicate hydrogen bonding and hydrophobic interactions were responsible for gel
formation in this compound (Figure 6).
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Figure 6. FT-IR spectra of gelator 5a in powder form and in diesel gel form.
Oil spill recovery:
Crude oils have different ratio of composition of hydrocarbons and non-hydrocarbons. The
hydrocarbon contains alkenes, aromatic compounds and non-hydrocarbons are mostly Sulphur
and transition metals (Hg, V, Pb and Ni) containing compounds. We have studied three different
crude oils for phase selective gelation using our gelators 5a, 5b and 5f (SI, Figure S5-S7). We
have applied different methods for phase selective gelation with Erha crude oil in water and sea
water. The powder form gelator 5a did not exhibit gelation property with Erha crude oils.
Whereas, selective crude oil gelation was achieved by dissolving gelator in non-toxic carrier
solvent at room temperature. We found ethyl acetate as a suitable carrier solvent, which is less
toxic than crude oil and better carrier solvent for gelation.
When compound 5a was applied to crude oil in carrier solvent, the crude oil layer became gel
within 15 min it holds the water layer. The C.G.C..of gelator was 2.39% (w/v), (Figure 7) which
is higher compare to aromatic solvents. The high C.G.C. value in crude oil is due to long chain
hydrocarbons and contaminated with elemental sulfur (Table 3).
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Figure 7. C.G.C. of crude oil gelation of compound 5a for (a) 8 mg of 5a in ethyl acetate 0.5 mL
crude oil: 1.0 mL water (b) 9 mg of 5a in ethyl acetate 0.5 mL crude oil: 1.0 mL water (c) 10 mg
of 5a in ethyl acetate (d) scooped crude oil gel from water.
Further, we have studied gelation of compound 5a with three different crude oils which are Erha,
Kuwait export, and WCS crude oils (Figure 8). American petroleum institute (API) is divided
Erha, Kuwait export and WCS crude oils on the basis of API gravity. The API gravity of Erha,
Kuwait export and WCS crude oils 32.8°, 31.4° and 21° respectively, which are classified as
light, medium and heavy crude oils respectively (SI, Table S1). Heavy crude oil contains higher
resins and asphaltenes in larger quantities compare to lighter crude oil.38 The gelation property of
C-6 triazole linked N-acetylglucosamine derivatives 5a, 5b and 5f was studied with these three
crude oils and resulted gel formation are shown in figure 8.
Figure 8. C.G.C. of different crude oils gelation of compound 5a (a) Erha crude oil (b) kuwait export (c)
WCS crude oil.
The C.G.C. for compound 5a in these different crude oils were calculated and results are
summarized in Table 3. Compounds 5a, 5b and 5f showed gelation in three different crude oils.
The critical gelation concentration of compound 5a was having higher C.G.C. value in heavy
crude oil and lower C.G.C. value in light crude oil. The C.G.C. of compound 5a in light API
grade oil was 4.6% (w/v) and 8.4% (w/v) in medium crude oil (Table 3 entry 2 and 3). Whereas,
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Compound 5f C.G.C. was 4.9% (w/v) in medium crude oil. These results indicate C.G.C. of
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gelation by different gelators was dependent on composition of crude oil (Table 3).
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Table 3. Phase selective gelation of different crude oils in presence of water.
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Entry
Crude oils-water (1:2 v/v)
Erha-water
5a
5b
5f
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G (2.3)
G (8.4)
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G (2.7)
G (4.9)
G (4.6)
Kuwait export-water
WCS crude oil-water
G = Gel, () C.G.C. = critical gelation concentration
We have performed a glass bath experiment, where Erha crude oil (2.5 mL) was poured over a
100 mL of tap water and gelator 5a (60 mg) was dissolved in ethyl acetate (1.2 mL) and added
drop wise on top of crude oil layer, the entire crude oil layer was completely congealed within
less than 15 minutes, which was scooped off leaving behind clear water.
Crude oil gelation with gelator 5a was also carried out with natural seawater, collected from Bay
of Bengal, to realise its real application for crude oil spillage recovery. As shown in figure 9 the
gelator 5a at C.G.C. selective gelated crude oil from the surface of sea water (Crude oil:Sea
water 1:10 v/v) within 15 minutes. which was scooped off leaving behind clear sea water. Same
experiment was performed using gelator 5a at C.G.C. by adding 1 mL of Erha crude oil in
different ratio of sea water (1:20, 1:50, 1:200, 1:500 and 1:1000 v/v) and indeed the gelation of
crude oil was obsrved in all tested cases.
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Figure 9. Erha crude oil gelation in natural sea water (a) 2.5 mL of Erha crude oil gel was
placed in 25 mL of natural sea water (b) Addition of 57 mg of gelator 5a dissolved in 1.2 mL of
EtOAc (c) Crude oil gelation within 15 min.
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The crude oil gel strength was studied by rheological experiments with 2.3% (w/v) erha crude oil
gel from gelator 5a. Frequency sweep and stress sweep experiments presented in figure 10.
Storage modulus (G') and loss modulus (G") were important parameters for these experiments,
where G' measures elasticity of the material and G" measures viscosity of the material. It’s
documented that, stable gelator showed storage modulus is always higher than the lose
modulus.39
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In frequency sweep experiment G' and G" was measured as a function of frequency at constant
strain 0.01%. The crude oil gelator from 5a showed G' is higher than the G" over the frequency
range 0.1-600 Hz and they did not cross each other. These results indicate that the crude oil gel
was elastic in nature.
The stress sweep experiments were also conducted for crude oil gels obtained from 5b and 5f
(SI, Figure S8). In stress sweep experiment of where G' and G" measured as a function of stress
amplitude at constant frequency 0.1 Hz. Storage modulus (G') and loss modulus (G") with
respect to constant frequency at particular pressure cross each other and the cross section point
called yield stress. Gelator 5a yield stress was found 97.4 Pa. The high value of yield stress
indicates crude oil stiffness and good tolerance to external pressure (Figure 10).
Figure 10. Rheology of Erha crude oil gels: (a) frequency sweep of 5a gel (b) stress sweep of
5a gel
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Selective dye Removal:
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Highly toxic dyes are non-biodegradable, when it releases into environment and it causes
deleterious effects on environment as well as human health. LMWGs are playing an important
role for dye removal because of their larger nano surface area which effectively adsorbs the dye
molecules.40 We have studied removal of three types of toxic dyes from artificially polluted
water. We have taken 10 mL of Rhodamine B dye or crystalline violet or methylene blue
(0.05M) solution in a vial, 5 w/v % mesitylene gel of compound 5a was added to this and
removal of dye was observed. The dye removal was monitored by UV-Visible spectroscopy and
the adsorption was recorded at different time intervals (Figure 11). UV-Visible spectra reveals
complete absorption of Rhodamine B dye molecules on gel surface in 15 h (Figure 11 (a)),
whereas, crystalline violet adsorption takes 10 h 30 min (Figure 11 (b)). But in case of
methylene blue, it could not able to entrap on gel surface (SI, Figure S9).These results suggest
that the gelator 5a can be utilized for the dye removal of waterborne organic pollutants such as
dyes from the pollutant water.
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(a
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(b
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Figure 11. UV spectra for removal of dyes: (a) rhodamine B; (b) crystalline violet.
CONCLUSION
In a conclusion, C-6 triazole linked N-acetylglucosamine derivatives were designed and
efficiently synthesized. Compound 5a was identified as an excellent phase selective gelator for
different hydrocarbon solvents, oils and crude oils in water as well as in natural sea water. The
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gelator 5a formed stable and strong gel in a lesser time, which qualifies it as a suitable gelator for
the crude oil spill recovery application. FT-IR and 1H NMR studies reveal that hydrogen bonding
and π-π stacking interactions were responsible for gel formation. The gelator 5a was successfully
utilized for entrapment of the waterborne synthetic dyes which makes this gelator was suitable
for water treatment. The gelator 5a was successfully utilized for crude oil recovery application at
experimental level using sea water which makes it a potential candidate for future development
in larger applications.
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EXPERIMENTAL SECTION
General experimental material and methods.
All reagents and solvents were purchased from commercial sources. TLC was visualized either
by UV light or by treating with 10% H2SO4 in EtOH followed by heating.1H NMR and 13C NMR
spectra were recorded on Bruker 400 MHz spectrometer at ambient temperature. 1H recorded by
400 MHz and 13C recorded by 100 MHz. Proton chemical shifts are given in ppm relative to the
internal standard (tetramethylsilane) or referenced relative to the solvent residual peaks (CDCl3:δ
7.26; DMSO-d6:δ 2.50; CD3OD: δ 3.31). Multiplicity was stated as follows: s (singlet); d
(doublet); t (triplet); q (quartet), m (multiplet): dd (doublet of doublet); dt (doublet of triplet); td
(triplet of doublet); ddd (doublet of doublet of doublet), etc. Coupling constants (J) were reported
in Hz. Column chromatography was performed by using silicagel 60-120 and 100-200 mesh.
High resolution mass spectra obtained from quadrapole/Q-TOF mass spectrometer with an ESI
source. FTIR measurements were recorded using ATR FTIR spectroscopy (Thermo Scientific
NicoletTMIsTM5 FTIR) with diamond ATR accessory. Gel samples were taken out from the
closed vial and after subtle drying to remove physically absorbed solvents gels were mounted on
the ATR crystal to record spectra. Rheological measurements were performed on Anton Paar
MCR 302 rheometer equipped with steel coated parallel-plate geometry (25 mm diameter). The
gap distance was fixed at 1 mm and a solvent-trapping device was placed above the plate to
prevent solvent evaporation. All measurements were done at 25°C. UV-vis spectrum of dye
removal was recorded by (Thermo Scientific Evolution-201). The Morphology of the gels was
examined using scanning electron microscopic (SEM) FEI Nova Nano SEM-450. A small
amount of gel was placed on a carbon tape pasted to a copper grid and the gel was subjected to
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ambient drying, as prepared sample was coated with gold. The sea water used in this study was
collected from Bay of Bengal.
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Gelation test:
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8 mg compound 5a was taken in 2.0 mL glass vial and added 1.0 mL of benzene was added into
it. The compound was partially soluble at room temperature upon heating it was completely
soluble. After that glass vial allowed to cool at room temperature, if inverted vial having no flow
of the solution then it’s confirmed as a gel.
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Critical gel concentration (C.G.C.):
Initially 10 mg of gelator 5a was dissolved in 1.0 mL of mesitylene solvent to make mesitylene
gel. After that every cycle small amount of solvent was added and this process was repeated
several times until gel became unstable. The maximum amount of solvent required for the stable
gel formation used for the C.G.C. calculation.
Scanning electron microscopy (SEM) studies:
Gels using compounds 5a and 5b were prepared in toluene and mesitylene solvents at their
respective C.G.C. These gels were coated on carbon plates, after 15 minutes gel gets dried.
Morphology of gels examined by scanning electron microscopy FE Nova Nano SEM-450.
Rheology experiment:
Rheological experiment was conducted on MCR-102 Anton par (25 mm, stainless steel). The
distance between the plates was 25 mm. The experiment carried out by Erha crude oil gels
obtained from compounds 5a, 5b and 5f at C.G.C. 2.3% (w/v), 3.6% (w/v) and 2.7% (w/v)
respectively. The gels samples were kept in between parallel plates and it’s covered complete
plates. Frequency sweep and strain sweep experiments were performed to find the viscoelastic
nature of the gels. Frequency sweep experiment was conducted 0.1 Hz to 600 Hz at constant
strain 0.01%. Stress sweep experiment was conducted at constant frequency 1.0 Hz.
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Phase selective gelation of different oils and crude oils:
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Phase selective gelation experiments (Table 2) were performed using different oils (0.5 mL) and
water (1.0 mL) in ratio of 1:2, using ethyl acetate as co-solvent (0.2 mL). The gelator 5a (~ 14
mg) was dissolved in 0.2 mL of ethyl acetate and applied to oil water mixture at room
temperature. The oil layer was completely congealed within 15 min. The experiments of gelators
5b and 5f with different oils were performed adopting similar protocol.
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For crude oils gelation (Table 3), we have performed a glass bath experiment, where Erha crude
oil (2.5 mL) was poured over a 100 mL of tap water and gelator 5a (60 mg) was dissolved in
ethyl acetate (1.2 mL) and added drop wise on top of crude oil layer, the entire crude oil layer
was completely congealed in less than 15 minutes, which was scooped off leaving behind the
clear water. The experiments of gelators 5b and 5f with different crude oils were performed
using similar protocol.
Dye removal experiment:
10 mL 0.05 M Rhodamine B dye solution was taken in a vial and then added 0.5% (w/v)
mesitylene gel of compound 5a. After some time the dye absorbed on the gel surface which was
measured by UV absorption experiment. Similar experiment was performed with methyl orange
and methylene blue dyes (Figure 11 and S9).
Powder XRD experiment:
Powder XRD experiment carried out using Bruker D8 discover diffractometer using Cu-Kα
radiation (λ=1.54Å) with a secondry graphite crystal monochromator. 1.0% (w/v) toluene gel of
compound 5a used in this experiment.
Synthesis and spectral data of compounds:
((2R,3S,4R,5R,6S)-5-acetamido-3,4-dihydroxy-6-methoxytetrahydro-2H-pyran-2-yl) methyl 4-
methylbenzenesulfonate 2. Amberlite IR 120-H+ resin (20 g) was added to a pre-stirred solution
of N-acetylglucosamine1 (20 g, 90.41 mmol) in methanol (200 mL). The resulting mixture was
stirred at 80 °C for 24 h. After completion of the reaction, reaction mixture was cooled down to
room temperature, and filtered to remove the resin. The filtrate was evaporated under reduced
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pressure to obtain methyl glycoside as white solid (19 g) in 89% isolated yield anomeric
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mixture (α:β, 9:1). Methyl glycoside was used for tosylation without further purification.
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To a stirred solution of Methyl glycoside (10 g, 42.55 mmol) in pyridine was added tosyl
chloride (9.7 g, 51.06 mmol) portion wise. The reaction mixture was stirred at room temperature
for 24 h. After completion of the reaction, reaction mixture was evaporated to dryness. crude
compound purified by column chromatography (ethyl acetate/ methanol 95:5) to afford pure α-
isomer of compound 2 (11.7 g, 70%) as a sticky solid. 1HNMR (400 MHz, CD3OD): δ 7.81 (d,
J = 8.4 Hz, 2H, ArH), 7.45 (d, J = 8.4 Hz, 2H, ArH), 4.55 (d, J = 3.6 Hz, 1H, H-1), 4.35 (dd, J =
10.8 Hz, 1.6 Hz, 1H, H-6a), 4.21 (dd, J = 10.8 Hz and 6.0 Hz,1H, H-6), 3.63 (dd, J = 8.8 Hz
,10.0 Hz, 1H, H-3), 3.57 (ddd, J = 2 Hz, 5.6 Hz, 10Hz, 1H, H-6b), 3.84 (dd,J = 10.4 Hz, 3.6 Hz,
1H, H-2), 3.69-3.66 (m, 1H, H-5), 3.59 (dd, J = 10.8 Hz and J = 9.0 Hz, 1H, H-3), 3.30 (s, 3H,
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OCH3), 3.27 (t, J = 9.2 Hz, 1H, H-4), 2.47 (s, 3H, CH3C6H4), 1.98 (s, 3H, COCH3) C NMR
(100 MHz, CD3OD): δ 173.7, 146.5, 134.4, 131.0, 129.1, 99.7, 72.8, 71.8, 71.1, 71.0, 55.6,
55.0, 22.5, 21.6, HRESI-MS (m/z): C16H23NO8S, [M+H]+ : 390.1217, found 390.1216.
Synthesis of N-((2S,3R,4R,5S,6R)-6-(azidomethyl)-4,5-dihydroxy-2-methoxytetrahydro-2H-
pyran-3-yl) acetamide3. To a stirred solution of compound 2 (7.2 g, 18.5mmol) in DMF was
added NaN3 (0.7 g, 6.46 mmol) at room temperature. The reaction mixture was stirred at 100°C
for 12h.TLC showed that the starting material was consumed completely. The reaction mixture
was concentrated under vacuum to obtain a residue. The residue was purified by column
chromatography (ethyl acetate/methanol: 95:5) to furnish compound 3as a white solid (3.8 g) in
79% isolated yield. 1HNMR (400 MHz, CDCl3): δ 8.01 (s, 1H), 5.99 (d, J = 8.5 Hz, 1H), 4.70 (d,
J = 3.8 Hz, 1H), 4.09 (ddd, J = 10.3, 8.6, 3.8 Hz, 1H), 3.83 (s, 1H), 3.76 – 3.70 (m, 1H), 3.62 (d,
J = 10.1 Hz, 1H), 3.60 – 3.44 (m, 4H), 3.43 (s, 2H), 3.16 (s, 1H), 2.06 (s, 3H).13CNMR (100
MHz, CDCl3): δ 172.4, 98.4, 72.5, 70.8, 55.4, 51.6, 23.3 (COCH3). HRESI-MS (m/z): Calcd for
C9H16N4O5 [M+H]+: 261.1193, found 261.1194.
Synthesis of N-((2S,3R,4R,5R,6R)-6-(azidomethyl)-4,5-bis(benzyloxy)-2-methoxytetrahydro-2H-
pyran-3-yl) acetamide 4. To a stirred solution of compound 3 (2.1 g, 8.07mmol) in dry THF,
sodium hydride (0.8 g, 1.44mmol) was added at 0 °C. After 20 min benzyl bromide (2.3 mL,
20.17mmol) was added drop wise and the resulting mixture was allowed to heat at 80 °C with
stirring for 1.5 h. After completion of reaction, the reaction mixture was allowed to cool down
at room temperature then it was quenched by adding methanol (50 mL) and concentrated under
reduced pressure. The residue was dissolved in ethyl acetate (500 mL) washed with water (2 x
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250 mL) and saturated brine solution (1 × 500 mL). The organic layer was dried over anhydrous
sodium sulfate, filtered and evaporated under reduced pressure to get the yellow colour residue.
The residue was purified by column chromatography (ethyl acetate: hexane 20:80) to furnish
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10H), 5.30 (d, J = 9.3 Hz, 1H), 4.90 (d, J = 10.8 Hz, 1H), 4.86 (d, J = 11.6 Hz, 1H), 4.67-4.61
(m, 3H), 4.30-4.24 (m, 1H), 3.80-3.76 (m, 1H), 3.71-3.67 (m, 1H), 3.61-3.56 (m, 1H), 3.49 (dd,
J = 13.1, 2.3 Hz, 1H), 3.37 (s, 3H), 3.36 – 3.32 (m, 1H), 1.87 (s, 3H).13CNMR
(100MHz,CDCl3): δ 128.7, 128.3, 128.1, 128.0, 98.7 (C-1), 80.3, 79.2, 75.3, 75.0, 70.8, 55.3,
52.6, 23.5. HRESI-MS(m/z): Calcd. for C23H28N4O5 [M+H]+ : 441.2137; found 441.2132.
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Synthesis of N-((2S,3R,4R,5R,6R)-4,5-bis(benzyloxy)-2-methoxy-6-((4-phenyl-1H-1,2,3-triazol-1-
yl)methyl)tetrahydro-2H-pyran-3-yl)acetamide 5a.
Toa solution of compound 5 (0.4 g, 0.98 mmol) in DMF was added phenyl acetylene (0.11 g,
1.078 mmol), CuSO4 (0.019 g, 0.098 mmol) and sodium ascorbate (0.007 g, 0.0294 mmol). The
reaction mixture was stirred at70 °C for 3h. After completion of the reaction, reaction mixture
was quenched with ice cold water (50 mL) diluted with ethyl acetate (1 × 400 mL), combined
organic layer was washed with brine solution (1 × 100 mL), dried over anhydrous sodium sulfate
filtered and evaporated under reduced pressure to give a residue. The residue was purified by
flash column chromatography (ethyl acetate) to yield compound 5a as a white solid, (0.35 g,
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71%). H NMR (400 MHz, DMSO-d6) δ 8.60 (s, 1H), 8.14 (d, J = 9.2 Hz, 1H), 7.90 – 7.83 (m,
2H), 7.45-7.25 (m, 12H), 4.82 (d, J = 11.0 Hz, 1H), 4.76 – 4.70 (m, 4H), 4.67 – 4.59 (m, 1H),
4.52 (d, J = 3.5 Hz, 1H), 4.03 – 3.95 (m, 2H), 3.74 (dd, J= 10.6, 8.9 Hz, 3H), 3.45-3.40 (m, 1H),
3.04 (s, 3H).13CNMR (100MHz, DMSO-d6): δ 169.8, 146.5, 138.6, 138.3, 132.9, 130.8, 129.1,
128.6, 128.4, 128.1, 128.0, 127.8, 125.3, 122.7, 98.3, 80.1, 79.2, 74.4, 69.4, 54.5, 52.7, 50.7,
22.7.HRESI-MS (m/z) Calcd. for C31H34N4O5 [M+H]+:543.2628; found 543.2637.
Synthesis of Methyl 1-(((2R,3R,4R,5R,6S)-5-acetamido-3,4-bis(benzyloxy)-6-methoxy–
tetrahydro-2H-pyran-2-yl) methyl)-1H-1,2,3-triazole-4-carboxylate 5b.
To a solution of compound 5 (0.5 g, 1.13 mmol) in DMF was added acetylene compound (0.113
g, 1.35 mmol), CuSO4 (0.018 g, 0.113 mmol) and sodium ascorbate (0.006 g, 0.033 mmol). The
reaction mixture was stirred at 70°C for 3h. After completion of the reaction, reaction mixture
was quenched with ice cold water (50 mL) diluted with ethyl acetate (1 × 500 mL), combined
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organic layer was washed with brine solution (1 × 200 mL), dried over anhydrous sodium
sulfate, filtered and evaporated under reduced pressure to give a residue. The residue was
purified by flash column chromatography (ethyl acetate: methanol, 9:1) to yield compound 5b
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as a white solid (0.4g, 67 %). H NMR (400 MHz, DMSO-d6): δ 8.75 (s, 1H), 8.11 (d, J = 9.2
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Hz, 1H), 7.37 – 7.24 (m, 10H), 4.82-4.62 (m, 6H), 4.50 (d, J = 4.5 Hz, 1H), 4.01 – 3.94 (m, 2H),
3.82 (s, 3H), 3.73 (dd, J = 10.6, 8.8 Hz, 2H), 3.41 (d, J = 9.5 Hz, 3H), 3.01 (s, 6H), 1.83 (s,
3H).13CNMR (100MHz, DMSO-d6): δ 169.2, 160.6, 138.42, 130.41, 130.0, 128.2, 128.1, 127.8,
127.6, 127.5, 98.1, 79.8, 78.9, 74.0, 68.8, 54.2, 52.3, 51.6, 50.6, 22.4. HRESI-MS (m/z) Calcd.
for C27H32N4O7 [M+H]+: 525.2344; found 525.2345.
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Synthesis of N-((1-(((2R,3R,4R,5R,6S)-5-acetamido-3,4-bis(benzyloxy)-6-methoxytetrahydro-2H-
pyran-2-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl)benzamide 5c.
To a solution of compound 5 (0.2 g, 0.45 mmol) in DMF was added acetylene compound (0.078
g, 1.078 mmol), CuSO4 (0.008 g, 0.045 mmol) and sodium ascorbate (0.003 g, 0.0135 mmol).
The reaction mixture was stirred at 70°C for 3h. After completion of the reaction, reaction
mixture was quenched with ice cold water (50 mL) diluted with ethyl acetate (1 × 400 mL),
combined organic layer was washed with brine solution (1 × 100 mL), dried over anhydrous
sodium sulfate, filtered and evaporated under reduced pressure to give a residue. The residue
was purified by flash column chromatography (ethyl acetate: methanol 9:1) to yield compound
5b as a white solid, (0.15 g, 56%). 1HNMR (400 MHz, CDCl3): δ 7.78 (d, J = 7.4 Hz, 1H), 7.49
– 7.26 (m, 8H), 6.85 (bs, 1H), 5.23 (d, J = 9.6 Hz, 1H), 4.90 – 4.78 (m, 3H), 4.64 – 4.54 (m,
4H), 4.15 – 4.10 (m, 1H), 3.93 (m, 1H), 3.71-3.66 (m, 2H), 3.29 (dd, J = 19.6, 9.9 Hz, 1H), 3.12
(s, 3H), 1.82 (s, 3H).13CNMR (100MHz, CDCl3): δ 169.8, 167.4, 138.1, 137.8, 134.0, 131.8,
128.7, 128.4, 128.2, 128.1, 127.1, 98.7, 80.3, 78.5, 75.2, 75.1, 69.7, 55.3, 52.4, 50.6, 35.5, 23.5.
HRESI-MS (m/z) Calcd. for C33H37N5O6 [M+H]+: 600.2817; found 600.2816.
Synthesis of N-((2S,3R,4R,5R,6R)-4,5-bis(benzyloxy)-6-((4-butyl-1H-1,2,3-triazol-1-yl)methyl)-
2-methoxytetrahydro-2H-pyran-3-yl)acetamide 5d. To a solution of compound 5 (0.3 g, 0.68
mmol) in DMF was added acetylene compound (0.066 g, 0.816 mmol), CuSO4 (0.010 g, 0.068
mmol) and sodium ascorbate (0.004 g, 0.020 mmol). The reaction mixture was stirred at 70°C
for 4h. After Completion of the reaction, reaction mixture was quenched with ice cold water (50
mL) diluted with ethyl acetate (1 × 400 mL), combined organic layer was washed with brine
solution (1 × 100 mL), dried over anhydrous sodium sulfate, filtered and evaporated under
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reduced pressure to give a residue. The residue was purified by flash column chromatography
(ethyl acetate: methanol 9:1) to yield compound 5d as a brown colour solid, (0.2g, 57%).
1HNMR (400 MHz, CDCl3) δ 7.41 – 7.28 (m, 10H), 5.22 (d, J = 9.3 Hz, 1H), 4.87 – 4.76 (m,
3H), 4.63-4.60 (m, 2H), 4.52-4.50 (m, 2H), 4.14 – 4.08 (m, 2H), 3.94 – 3.90 (m, 2H), 3.72 –
3.67 (m, 2H), 3.26 – 3.22 (m, 2H), 3.14 (s, 3H), 2.73 – 2.69 (m, 2H), 1.81 (s, 3H), 1.64 (dd, J =
15.0, 6.9 Hz, 2H), 1.37 (dt, J = 14.9, 7.5 Hz, 2H), 0.93 (t, J = 7.3 Hz, 3H); 13CNMR (100MHz,
CDCl3): δ 137.9, 128.74, 128.71, 128.4, 128.1, 98.7, 80.3, 78.8, 75.1, 70.0, 55.1, 52.6, 50.4,
31.6, 25.4, 23.5, 22.4, 13.9. HRESI-MS (m/z) Calcd. for C29H38N4O5 [M+H]+: 523.2915; found
523.2936.
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Synthesis of N-((2S,3R,4R,5R,6R)-4,5-bis(benzyloxy)-6-((4-(hydroxymethyl)-1H-1,2,3-triazol-1-
yl)methyl)-2-methoxytetrahydro-2H-pyran-3-yl)acetamide 5e.
To a solution of compound 5 (0.15 g, 0.34mmol) in DMF was added acetylene compound
(0.030 g, 0.408 mmol), CuSO4 (0.027 g, 0.489 mmol) and sodium ascorbate (0.002 g, 0.0122
mmol). The reaction mixture was stirred at 70 °C for 3h. After completion of the reaction,
reaction mixture was quenched with ice cold water (50 mL) diluted with ethyl acetate (1 × 400
mL), combined organic layer was washed with brine solution (1 × 100 mL), dried over
anhydrous sodium sulfate, filtered and evaporated under reduced pressure to give a residue. The
residue was purified by flash column chromatography (ethyl acetate: methanol, 9:1) to yield
1
compound 5e as an off white solid (0.11g, 65%). H NMR (400 MHz, CDCl3) δ 7.64 (s, 1H),
7.40 – 7.28 (m, 10H), 5.27 (d, J = 9.3 Hz, 1H), 4.87 (d, J = 10.8 Hz, 1H), 4.84 – 4.76 (m, 4H),
4.62 (d, J = 11.5 Hz, 1H), 4.59 (d, J = 3.5 Hz, 1H), 4.55 (d, J = 4.4 Hz, 2H), 4.13 – 4.07 (m,
1H), 3.96 – 3.91 (m, 1H), 3.70 (dd, J = 10.8, 8.8 Hz, 1H), 3.23 (dd, J = 12.3, 6.4 Hz, 1H), 3.15
(s, 3H), 3.11 (dd, J = 14.8, 7.5 Hz, 2H), 2.32 (s, 1H), 1.82 (s, 3H).13CNMR (100MHz, CDCl3):
δ 170.0 (C=O), 138.0, 137.8, 128.7, 128.4, 128.2, 128.1, 123.5, 98.7 (C-1), 80.2, 78.6, 75.2,
75.1, 69.8, 56.8, 55.3, 52.5 (C-2), 50.5, 46.0, 23.5. HRESI-MS (m/z) Calcd. for C26H32N4O6
[M+Na]+: 519.2214; found 519.1377.
Synthesis of N-((2S,3R,4R,5R,6R)-4,5-bis(benzyloxy)-2-methoxy-6-((4-(3-methoxyphenyl)-1H-
1,2,3-triazol-1-yl) methyl)tetrahydro-2H-pyran-3-yl)acetamide 5f.
To a solution of compound 5 (0.25 g, 0.56 mmol) in DMF was added acetylenecompound (0.078
g, 1.078 mmol), CuSO4 (0.009 g, 0.056 mmol) and sodium ascorbate (0.003 g, 0.0168 mmol).
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The reaction mixture was stirred at 70 °C for 3h. After Completion of the reaction, reaction
mixture was quenched with ice cold water (50 mL) diluted with ethyl acetate (1 × 400 mL),
combined organic layer was washed with brine solution (1 × 100 mL), dried over anhydrous
sodium sulfate, filtered and evaporated under reduced pressure to give a residue. The residue was
purified by flash column chromatography (ethyl acetate: hexane 8:2) to yield compound 5f as a
white solid (0.2 g, 62%).1H NMR (400 MHz, CDCl3) δ 7.86 (s, 1H), 7.49 – 7.27 (m, 14H), 6.89
(ddd, J = 7.7, 2.5, 1.5 Hz, 1H), 5.25 (d, J = 9.3 Hz, 1H), 4.89 (t, J = 11.9 Hz, 1H), 4.81 (d, J =
10.4 Hz, 2H), 4.68 – 4.53 (m, 4H), 4.18 – 4.10 (m, 1H), 3.99 (ddd, J = 9.3, 6.0, 2.9 Hz, 1H), 3.88
(s, 3H), 3.72 (dd, J = 10.5, 8.8 Hz, 1H), 3.35 – 3.25 (m, 1H), 3.15 (s, 3H), 1.81 (s, 3H).13CNMR
(100MHz, CDCl3): δ 169.9 , 138.1, 137.8, 130.0, 128.7, 128.49, 128.44, 128.2, 128.1, 121.6,
118.3, 114.5, 110.8, 98.7, 80.3, 78.7, 76.8, 75.2, 75.1, 69.9, 55.5, 55.3, 52.5, 50.7, 23.5. HRESI-
MS (m/z) Calcd. For C32H36N4O6 [M+H]+: 572.2707; found 573.2725.
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Synthesis of N-((2S,3R,4R,5R,6R)-4,5-bis(benzyloxy)-2-methoxy-6-((4-(4-methoxyphenyl)-1H-
1,2,3-triazol-1-yl) methyl)tetrahydro-2H-pyran-3-yl)acetamide 5g. To a solution of compound 5
(0.2 g, 0.45 mmol) in DMF was added acetylene compound (0.133 g, 0.9mmol), CuSO4 (0.007 g,
0.045 mmol) and sodium ascorbate (0.002 g, 0.0135 mmol). The reaction mixture was stirred at
70°C for 3h. After completion of the reaction, reaction mixture was quenched with ice cold water
(50 mL) diluted with ethyl acetate (1 × 400 mL), combined organic layer was washed with brine
solution (1 × 100 mL), dried over anhydrous sodium sulfate, filtered and evaporated under
reduced pressure to give a residue. The residue was purified by flash column chromatography
(ethyl acetate: methanol 8:2) to yield compound 5g as a white solid, (0.2 g, 76 %). 1H NMR (400
MHz, CDCl3) δ 7.78 (s, 1H), 7.76 (dd,J = 2.4, 6.8 Hz, 2H), 7.43-7.27 (m, 10 H), 6.96 (dd,J =
2H), 5.24 (d, J = 9.3 Hz, 1H), 4.88 (t, J = 10.5 Hz, 2H), 4.81 (d, J = 11.3 Hz, 2H), 4.64 (d, J =
6.0 Hz, 1H), 4.62 – 4.53 (m, 3H), 4.16 – 4.10 (m, 1H), 4.00 – 3.96 (m, 1H), 3.84 (s, 3H), 3.72
(dd, J = 10.5, 8.8 Hz, 1H), 3.30 (dd, J = 15.0, 6.0 Hz, 1H), 3.16 (s, 3H), 1.81 (s, 3H).13CNMR
(100MHz, CDCl3) δ 169.9, 159.7, 147.8, 138.1, 137.9, 128.7, 128.49, 128.44, 127.2, 120.6,
114.3, 98.7, 80.3, 78.7, 75.2, 75.1, 69.9, 55.4, 55.3, 52.5, 50.7, 23.5. HRESI-MS (m/z) Calcd. for
C32H36N4O6[M+H]+: 573.2707; found 573.2723.
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ASSOCIATED CONTENT
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The supporting information is available free of charge on the
https//
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Copies of 1H NMR and 13C NMR spectra of all compounds, Crude oil
gelation and recovery of diesel from gelator, Rheology data of toluene
and mesitylene gel, Rheology of Erha crude oil gels with compound 5b and 5f, Crude oil
gel formation with gelator 5a and sea water, VT NMR studies of
compound 5b
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AUTHOR INFORMATION
Corresponding Author
Email: ram.sagar@bhu.ac.in
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
PK and CN are thankful to Council of Scientific and Industrial
Research (CSIR), India for senior research fellowships. RS is
thankful to the Science and Engineering Research Board (SERB-
DST) India for financial support (SERB-EMR/2014/000320). Authors
acknowledged the lab facilities of Shiv Nadar University and
Banaras Hindu University, India. Authors are thankful to Indian
oil corporation limited, Faridabad, India for kindly providing
all the crude oils used in this study. Authors are also thankful
to JNCASR Bangalore, India for permitting to use their rheology
facility for this work.
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