Synthesis of ester based cationic pyridinium gemini surfactants and appraisal of their surface active properties

Article abstract of DOI:10.1007/s11743-012-1380-x

New pyridinium gemini surfactants have been synthesized by esterification of halogenated carboxylic acids with long chain fatty alcohols furnishing respective esters (dodecyl-2-chloroacetate, tetradecyl-2-chloroacetate, hexadecyl-2-chloroacetate, dodecyl-2-bromoacetate, tetradecyl-2-bromoacetate and hexadecyl-2-bromoacetate) followed by their subsequent treatment with 4,4′-trimethylene dipyridine resulting in the formation of title Gemini surfactants: 4,4′-(propane-1,3-diyl)bis1-{2-(dodecyloxy)-2-oxoethyl}; 4,4′-(propane-1,3-diyl)bis{1-(2-(tetradecyloxy)-2-oxoethyl}; 4,4′-(propane-1,3-diyl)bis{1-(2-(hexadecyloxy)-2-oxoethyl} dipyridinium chlorides; 4,4′-(propane-1,3-diyl)bis{1-(2-(dodecyloxy)-2-oxoethyl}; 4,4′-(propane-1,3-diyl)bis{1-(2-(tetradecyloxy)-2-oxoethyl} and 4,4′-(propane-1,3-diyl)bis{1-(2-(hexadecyloxy)-2-oxoethyl} dipyridinium bromides. Their identifications are based on IR, ¹H-NMR, ¹³C-NMR, DEPT, COSY and Mass spectral studies. Their surface active properties were also evaluated on the basis of surface tension and conductivity measurements.

Full text of DOI:10.1007/s11743-012-1380-x

J Surfact Deterg
DOI 10.1007/s11743-012-1380-x
ORIGINAL ARTICLE
Synthesis of Ester Based Cationic Pyridinium Gemini Surfactants
and Appraisal of Their Surface Active Properties
•
Pankaj Patial Arifa Shaheen Ishtiaque Ahmad
•
Received: 22 January 2012 / Accepted: 25 June 2012
Ó AOCS 2012
Abstract New pyridinium gemini surfactants have been
synthesized by esterification of halogenated carboxylic
acids with long chain fatty alcohols furnishing respective
esters (dodecyl-2-chloroacetate, tetradecyl-2-chloroacetate,
hexadecyl-2-chloroacetate, dodecyl-2-bromoacetate, tetra-
decyl-2-bromoacetate and hexadecyl-2-bromoacetate) fol-
lowed by their subsequent treatment with 4,40-trimethylene
dipyridine resulting in the formation of title Gemini surfactants:
4,40-(propane-1,3-diyl)bis1-{2-(dodecyloxy)-2-oxoethyl}; 4,
40-(propane-1,3-diyl)bis{1-(2-(tetradecyloxy)-2-oxoethyl};
4,40-(propane-1,3-diyl)bis{1-(2-(hexadecyloxy)-2-oxoeth-
yl} dipyridinium chlorides; 4,40-(propane-1,3-diyl)bis
{1-(2-(dodecyloxy)-2-oxoethyl}; 4,40-(propane-1,3-diyl)-
bis{1-(2-(tetradecyloxy)-2-oxoethyl} and 4,40-(propane-1,
3-diyl)bis{1-(2-(hexadecyloxy)-2-oxoethyl} dipyridinium
Introduction
The development of surfactants based on natural renewable
resources is a concept that is gaining recognition in the
cosmetic and detergent industries. A new class of gemini
cationic surfactants is a response to the increasing con-
sumer demand for the products that are both greener and
more efficient. In order to achieve these objectives, it is
necessary to use renewable low-cost materials that are
available in large quantities and to design molecular
structures that show improved performance, favorable
properties and reduced environmental impact [1]. Several
series of new surfactants have been designed using envi-
ronmentally friendly processes and their production per-
mits us to attain various products and by-products of the
oleochemical industries or ones derived from marine
resources [2, 3].
1
bromides. Their identifications are based on IR, H-NMR,
13C-NMR, DEPT, COSY and Mass spectral studies. Their
surface active properties were also evaluated on the basis of
surface tension and conductivity measurements.
A wide range of original surfactants derived from
renewable resources have been developed with potential
applications notably, in detergent and cosmetic industries.
The production of these entirely natural molecules may
substitute the surfactants conventionally used.
Keywords Dipyridinium gemini surfactants ꢀ Synthesis ꢀ
Surface tension and conductivity
Cationic surfactants, with almost 7 % of the total sur-
factant market, have many applications such as fabric
softeners, asphalt additives, corrosion inhibitors, biocides,
and textile auxiliaries. They adsorb strongly onto a wide
variety of materials by an ion exchange mechanism [4–6].
However, cationic surfactants have higher aquatic toxicity
than other surfactants and are also more irritating to the
skin and to the eyes. The toxicity of these surfactants is
believed to result from their tendency to adsorb on to
negatively charged surfaces [6, 7]. Different approaches
are taken to overcome this problem. One approach is to
introduce an easily cleavable bond into the surfactant
structure. The search for novel surfactants with higher
P. Patial ꢀ I. Ahmad (&)
Department of Chemistry, Guru Nanak Dev University,
Amritsar 143005, India
e-mail: chemi_ahmad@yahoo.co.in
A. Shaheen (&)
Department of Chemistry, Dr. B.R. Ambedkar National Institute
of Technology, Jalandhar, India
e-mail: chemarifa@gmail.com
123

J Surfact Deterg
efficiency and effectiveness gave birth to the concept of
gemini surfactants. Gemini surfactants are made up of two
monomeric surfactant molecules with their head groups
chemically bonded together by a spacer [8, 9]. It was found
that the surfactant properties of gemini-type surfactants,
such as a low critical micelle concentration (CMC) value
and surface tension lowering, were superior to those of the
corresponding single-type surfactants [10–17]. Since the
term was coined by Menger in 1991, many different types
of gemini surfactants have been synthesized, and their
physicochemical properties have been investigated
[18, 19].
acetic acids (0.01 mol; 0.945 g for chloroacetic acid and
0.1389 g for bromo acetic acid) was added in a fatty
alcohol (0.01 mol; dodecyl 1.863 g; tetradecyl 2.143 g;
hexadecyl 2.422 g) followed by the addition of catalytic
amount of sulfuric acid. The contents of the flask were then
stirred for 2–3 h at 60 °C. The progress of the reaction was
monitored by thin layer chromatography [silica gel G
coated (0.25 mm thick) glass plates using hexane/ethyl
acetate (98:2) as the mobile phase, the spots were visual-
ized in iodine]. The reaction was completed in 3 h. In each
case the crude reaction mixture was extracted with 50 ml
of chloroform and washed repeatedly (3 9 25 ml) with
water and then dried over sodium sulfate. Chloroform was
removed from crude reaction mixture under reduced pres-
sure in a rotary flash evaporator at 40 °C. The individual
crude product was then purified using aqueous methanol
i.e. (the crude compound was taken in a separating funnel
and 10 ml of methanol was added with 2–3 drops of water
which led to the settling of product at the bottom in its
purest form). The yields of resulting esters are reported in
parenthesis {hexadecyl-2-chloroacetate (1, 92 %), tetra-
decyl-2-chloroacetate (2, 92 %), dodecyl-2-chloroacetate
(3, 91 %), hexadecyl-2-bromoacetate (4, 90.1 %), tetra-
decyl-2-bromoacetate (5, 94.4 %) and) dodecyl-2-bromo-
acetate (6, 92 %)}.
Keeping in view the past work and perception on cat-
ionic gemini surfactants, we have attempted to synthesize
them from renewable raw materials like fatty alcohols and
halo-carboxylic acids. Here we have chosen the greener
approach to make the process environmentally friendly and
cost effective too. The purpose of this work was to prepare
and characterize the cationic gemini surfactants with ester
bonds inserted between the hydrocarbon tails and the
positively charged head groups and to evaluate their sur-
face active properties.
Experimental Section
Materials, Methods and Instrumentation
Synthesis of Gemini Surfactants (7–12)
Chloroacetic acid, bromoacetic acid and 4,40-trimethylene
dipyridine were purchased from Sigma-Aldrich Chemical
Co. USA. Lauryl alcohol (dodecyl alcohol), Myristyl
alcohol (tetradecyl alcohol), cetyl alcohol (hexadecyl
alcohol) and silica gel for T.L.C. were purchased from S.
D. Fine Chemicals Ltd; Mumbai, India. Sulfuric acid was
purchased from Merck, Germany. IR spectra were recorded
as a thin film on KBr Pellet on a Shimadzu 8,400 s FT-IR
(Kyoto, Japan) instrument. Mass spectra were recorded on
a Waters Q-T of Micro mass using ESI as an ion source at
sophisticated analytical instrumentation facility (SAIF),
Each resulting ester (1–6) was immediately reacted with
4,40-trimethylene dipyridine in 2:1 molar ratio (0.01 mol)
at 60 °C for 1 h (for chloro esters) and 30 min (for bromo
esters) i.e. for 1, 6.378 g; for 2, 5.817 g; for 3, 5.256 g; for
4, 7.267 g; for 5, 6.706 g; for 6, 6.145 g and 4,40-tri-
methylene dipyridine (1.982 g) were taken. In each case
the resulting crude product was crystallized with ether and
subsequently recrystallized in cold acetone to get the pure
compounds (7-12) which were characterized on the basis of
1
IR, H-NMR, 13C-NMR, COSY and DEPT experiments
and mass spectral analysis as 4,40-(propane-1,3-diyl) bis(1-
(2-(hexadecyloxy)-2-oxoethyl) dipyridinium chloride (7);
(4,40-(propane-1,3-diyl)bis(1-(2-(tetradecyloxy)-2-oxoeth-
yl)dipyridinium chloride (8); 4,40-(propane-1,3-diyl)bis
(1-(2-(dodecyloxy)-2-oxoethyl)dipyridinium chloride (9);
4,40-(propane-1,3-diyl) bis(1-(2-(hexadecyloxy)-2-oxoeth-
yl) dipyridinium bromide (10); 4,40-(propane-1,3-diyl)-
bis(1-(2-(tetradecyloxy)-2-oxoethyl)dipyridinium bromide
(11) and 4,40-(propane-1,3-diyl)bis(1-(2-dodecyloxy)-2-
oxoethyl)dipyridinium bromide (12) (Scheme 1).
1
Panjab University, Chandigarh. H-NMR, DEPT (Distor-
tionless enhanced polarization Transfer), COSY (correla-
tion spectroscopy) and 13C-NMR spectra were recorded on
a JEOL AL-300 (JEOL, Japan) and (Bruker Advance II
400 NMR spectrometer) system as a solution in CDCl3,
using tetramethylsilane (TMS) as an internal standard.
Synthesis of Dodecyl/Tetradecyl/Hexadecyl
2-Chloro/Bromo Acetate
The preparation of these esters from halogenated fatty
acids has earlier been reported [20]. However, we herein
report the modified procedure for their preparation with
excellent yield, that too in a short time. Chloro/bromo
Conductivity Measurements [21, 22]
The critical micelle concentrations (CMC) of these sur-
factants (7–12) were determined by the conductivity
123

J Surfact Deterg
O
Scheme 1 Scheme of reactions
O
X
°
6 0 C , Stirring
X
+
ROH
OH
OR
3 Hours
1-6
O
X
+
N
N
OR
1-6
°
60 C
N
N
X
X
RO
O
O
OR
7-12
method. The conductance as a function of surfactant con-
centration was measured at 25 °C. Measurements were
performed with an Equiptronic Conductometer (Auto
temperature conductivity meter model E.Q.661) with stir-
ring to control the temperature. The solutions were
thermostated in the cell at 25 °C. For each series of mea-
surements, an exact volume of 25 ml Millipore water
(resistivity 18 MX) was introduced into the vessel and the
specific conductivity of the water was measured. For the
determination of CMC, adequate quantities of concentrated
stock surfactant solutions in water (i.e. 0.25, 2, 3, 0.25, 2
and 3 mM for surfactants 7, 8, 9, 10, 11 and 12, respec-
tively) were added in order to change the surfactant con-
centration from concentrations well below the critical
micelle concentration (CMC) and repeated to verify our
results. The intersection point of specific conductivity
versus surfactant concentration was taken as the CMC. The
degree of counterion binding (b) was calculated as (1-a),
where a = Smicellar/Spremicellar, i.e. ratio of the slope
before and after CMC.
(circumference 5.992 cm) at 25 °C. The tensiometer was
calibrated using triple distilled water. For the determination
of CMC and surface tension, adequate quantities of a
concentrated stock solution (i.e. 0.25, 2, 3, 0.25, 2 and
3 mM, stock solution for surfactants 7, 8, 9, 10, 11 and 12,
respectively) were used. The data of this determination is
presented in Table 1.
Where X = Cl, Br and R = CH3 (CH2)11-; CH3(CH2)13-
and CH3(CH2)15-.
Results and Discussion
The structures of ester based gemini pyridinium surfactants
(7–12) were established by IR, 1H-NMR, 13C-NMR,
COSY, DEPT and mass spectral data.
Spectral Results
The IR spectra of the pyridinium gemini surfactants (7–12)
showed the absorption bands in the region at
2,915–2,849 cm-1 indicating the presence of methylene
groups. The absorptions at 1,741–1,730 cm-1 indicate the
presence of ester carbonyl group whereas other absorptions
at 1,641–1,620 cm-1 indicate the presence of C–N. The
band at 1,570–1,540 cm-1 very well established the
Surface Tension Measurements
Surface tension values were used to calculate CMC using a
CSC Du Nouy interfacial tensiometer (Central Scientific
Co., Inc.) equipped with platinum-iridium ring
123

J Surfact Deterg
Table 1 Data reporting the
CMC values by conductivity
and surface tension
measurements, degree of
counter ion binding and surface
tension at CMC at 25 °C
S.
CMC (mM) by
The degree of counter CMC by surface tension
ion binding (b) (%)
Surface tension at
CMC (mN/m)
no. conductivity
measurements
measurements in (mM)
7
8
9
0.059
0.144
0.359
36
42
56
50
53
59
0.057
0.105
0.381
0.035
0.085
0.167
62.4
58.8
40.8
68.4
60.1
58.7
10 0.036
11 0.121
12 0.172
presence of aromatic C=C in (7–12). The two terminal
methyl protons of these gemini surfactants (7–12) are
oxoethyl) dipyridinium chloride (9); 4,40-(propane-1,
3-diyl)bis(1-(2-(hexadecyloxy)-2-oxoethyl)dipyridinium
bromide (10); 4,40-(propane-1,3-diyl)bis(1-(2-(tetradecyl-
oxy)-2-oxoethyl)dipyridinium bromide (11) and 4,40-(pro-
pane-1,3-diyl)bis(1-(2-(dodecyloxy)-2-oxoethyl)dipyridinium
bromide (12). The structures of these gemini surfactants
(7–12) are further consolidated by ESI–MS (positive ion)
mass spectral data. Important peaks in these spectra are
found at m/z 763.3, 764.4, 765.5, 707.4, 708.4, 651, 652.4,
763.3, 764.4, 765.5, 707.4, 708.4, 651, 652.4. These ion
peaks account for the loss of proton and two chloride/
bromide ions from the molecule leading to the formation of
positively charged parent ion {M-2Cl)-1)}?/{M-2Br)-1)}?
and direct loss of two chloride/bromide ions from the mole-
cule leading to the formation of (M-2Cl)?/(M-2Br)? posi-
tively charged ions.
1
observed as a distorted triplet at d 0.61–0.87 in their H
NMR spectra. Broad doublets in (7–12) are observed at d
1.07–1.26 accountable for methylene protons of chain.
Multiplet signals are observed at d 1.29–1.65 due to pres-
ence of methylene protons next to terminal methyl groups.
Multiplets are observed at d 1.48–2.17 due to sandwiched
methylene protons of spacer (PyCH2CH2CH2Py). Triplets
of a second type are observed at 2.67–2.99 due to a
methylene proton of the spacer (PyCH2CH2CH2Py). Trip-
lets of a third type are observed at d 4.01–4.21 due to a
methylene proton. A doublet is observed at d 5.84–6.04 due
to methylene protons attached to nitrogen of pyridine. The
two sets of ring protons of pyridine methine are observed
as a doublet at d 7.88–8.04 and d 8.97–9.12. 13C/DEPT
NMR spectra displayed sp3 carbon of terminal methyl
group at d 14.00–14.08. The carbons next to terminal
methyl groups are observed in the range of d 22.58–22.66.
The carbons (COOCH2CH2) are observed at 25.63–25.69.
The middle carbon of spacer i.e. (PyCH2CH2CH2Py) is
observed at 28.31–28.35. The chain carbons are observed
at 29.10–29.90. The methylene carbons i.e. (CH2CH2CH3)
are observed at 31.83–31.89. The a methylene carbons of
spacer i.e. (PyCH2CH2CH2Py) are observed at
34.89–35.00. The methylene carbons attached to pyridine
nitrogen are observed at d 60.36–60.58. Other signals are
observed at d 67.26–67.35 due to methylene carbons a to
carbonyl groups. Other structure revealing signals are
observed at d 127.78–127.90 due to ring carbons located b
to nitrogen of pyridine. Other structure revealing signals
are observed at d 145.96–146.15 due to quaternary carbon
joined to the methylene group of the spacer. More signif-
icant signals are observed at d 162.74–162.85 due to ring
carbons attached a to nitrogen of pyridine. The carbonyl
carbons are observed at d 166.61–166.78. All these data are
in almost comparable with the previous report [23]. On all
these accounts the structures of (7–12) are deduced as 4,40-
(propane-1,3-diyl)bis(1-(2-(hexadecyloxy)-2-oxoeth-
(4,40-(Propane-1,3-diyl)bis(1-(2-(hexadecyloxy)-2-oxo-
ethyl)dipyridinium chloride(7). Brown solid, Yield is
92 %. Melting point 128 °C. IR (KBr pellet, cm-1) 2,910,
1
1,744, 1,643, and 1,570. H NMR (d ppm CDCl3): 0.67 (t,
6H, 2XCH3), 1.07 (d, chain 56H, 2X(–CH2–)14), 1.46(m,
4H, 2XCH2 next to terminal methyl groups), 1.48 (m, 2H,
PyCH2CH2CH2Py), 2.82 (t, 4H, PyCH2CH2CH2Py), 4.01
(t, 4H 2XCO2CH2), 5.84(d, 4H, 2XNCH2CO2), 7.88 (d,
4H, 4XCH ring protons b to nitrogen of pyridine), 8.97 (d,
4H, 4XCH ring protons a to nitrogen of pyridine). 75 MHz
13C/DEPT NMR (d ppm CDCl3): 14.05(terminal methyl
carbons), 22.63(CH3CH2), 25.67(CH2CH2CO2), 28.33
(PyCH2CH2CH2Py), 29.31(chain methylene carbons),
31.86(CH2CH2CH3), 34.99(PyCH2CH2CH2Py), 60.36(CH2
CO2), 67.26(CO2CH2), 127.79 (methine carbon b to
nitrogen of pyridine), 145.96 (quaternary carbon of pyri-
dine nucleus bearing spacer), 162.74 (methine carbon a to
nitrogen of pyridine), 166.61(carbonyl carbon). ESI–MS
positive ions m/z 763.3(100 %) {(M-2Cl)-1)}?, 764.4
(90 %) (M-2Cl)?.
(4,40-(Propane-1,3-diyl)bis(1-(2-(tetradecyloxy)-2-oxo-
ethyl)dipyridinium chloride (8). Brown solid, Yield,
95.5 %. Melting point 122 °C. IR (KBr pellet, cm-1) 2871,
1
yl)dipyridinium chloride (7); (4,40-(propane-1,3-diyl)
1743, 1643, and 1570. H NMR (d ppm CDCl3): 0.87 (t,
bis(1-(2-(tetradecyloxy)-2-oxoethyl) dipyridinium chloride
4,40-(propane-1,3-diyl)bis(1-(2-(dodecyloxy)-2-
6H, 2XCH3), 1.26 (d, chain 48H, 2X(–CH2–)12), 1.65 (m,
(8);
4H, 2XCH2 next to terminal methyl groups), 1.99 (m, 2H,
123

J Surfact Deterg
20
15
10
5
PyCH2CH2CH2Py), 2.97 (t, 4H, PyCH2CH2CH2Py), 4.19
(t, 4H 2XCO2CH2), 6.04 (d, 4H, 2XCH2CO2), 7.96 (d, 4H,
4XCH ring protons b to nitrogen of pyridine), 9.12 (d, 4H,
4XCH ring protons a to nitrogen of pyridine). 75 MHz 13C/
DEPT NMR (d ppm CDCl3): 14.05 (terminal methyl car-
bons), 22.63 (CH3CH2), 25.67 (CH2CH2CO2), 28.35
(PyCH2CH2CH2Py), 29.31 (chain methylene carbons),
31.87 (CH2CH2CH3), 34.89 (PyCH2CH2CH2Py), 60.39
(CH2CO2), 67.24(CO2CH2), 127.89 (methine carbon b to
nitrogen of pyridine), 145.85 (quaternary carbon of pyri-
dine nucleus bearing spacer), 162.87 (methine carbon a to
nitrogen of pyridine), 166.66 (carbonyl carbon). ESI–MS
positive ions m/z 707.4 (100 %) {(M-2Cl)-1)}?, 708.4
(51 %) (M-2Cl)?.
cmc
0.055
0
0
0.11
0.165
0.22
Concentration in mM
(7)
250
200
150
100
50
4,40-(Propane-1,3-diyl)bis(1-(2-(dodecyloxy)-2-oxoeth-
yl)dipyridinium chloride (9): Brown sticky solid, Yield,
92.5 %. Melting point 117 °C. The IR (KBr Pellet, cm-1):
1
cmc
2915, 1746, 1639, and 1570. H NMR (d ppm, CDCl3):
0
0
0.1
0.2
0.3
0.4
0.5
0.61 (t, 6H, 2XCH3), 1.10 (d, chain 40H, 2X(–CH2–)10),
1.29 (m, 4H, 2XCH2 next to terminal methyl groups), 1.69
(m, 2H, PyCH2CH2CH2Py), 2.67 (t, 4H, PyCH2CH2
CH2Py), 4.19 (t, 4H, 2XCO2CH2), 5.92 (d, 4H, 2X
CH2CO2), 7.75 (d, 4H, 4XCH ring protons b to nitrogen of
pyridine), 8.98 (d, 4H, 4XCH ring protons a to nitrogen of
pyridine). 75 MHz 13C/DEPT NMR (d ppm, CDCl3): 14.08
(terminal methyl carbons), 22.66 (CH3CH2), 25.69
(CH2CH2CO2), 28.34 (PyCH2CH2CH2Py), 29.33 (chain
methylene carbons), 31.89 (CH2CH2CH3), 34.95 (PyCH2
CH2CH2Py), 60.40 (CH2CO2), 67.30 (CO2CH2), 127.78
(methine carbon b to nitrogen of pyridine), 146.01 (qua-
ternary carbon of pyridine nucleus bearing spacer), 162.68
(methine carbon a to nitrogen of pyridine), 166.62 (car-
bonyl carbon). ESI–MS positive ions at m/z (relative
intensity %) 651.4 (100 %) {(M-2Cl)-1)}?, 652.4 (60 %)
(M-2Cl)?.
(4,40-(Propane-1,3-diyl)bis(1-(2-(hexadecyloxy)-2-oxo-
ethyl)dipyridinium bromide (10). Brown solid, Yield,
95.5 %. Melting point 145 °C, IR (KBr pellet, cm-1) 2870,
1741, 1641, 1570 and 1514. 1H NMR (d ppm CDCl3): 0.79
(t, 6H, 2XCH3), 1.20 (d, chain 56H, 2X(–CH2–)14), 1.57
(m, 4H, 2XCH2 next to terminal carbons), 1.82 (m, 2H,
PyCH2CH2CH2Py), 2.83 (t, 4H, PyCH2CH2CH2Py), 4.11
(t, 4H, 2XCO2CH2), 5.98 (d, 4H, 2XCH2CO2), 7.93 (d, 4H,
4XCH ring protons b to nitrogen of pyridine), 9.06 (d, 4H,
4XCH ring protons a to nitrogen of pyridine). 75MHz13C/
DEPTNMR (d ppm CDCl3): 14.01 (terminal methyl car-
bons), 22.58 (CH3CH2), 25.63 (CH2CH2CO2), 28.31
(PyCH2CH2CH2Py), 29.46 (chain methylene carbons),
31.83 (CH2CH2CH3), 34.91 (PyCH2CH2CH2Py), 60.50
(CH2CO2), 67.36 (CO2CH2), 127.88 (methine carbon b to
nitrogen of pyridine), 145.70 (quaternary carbon of pyri-
dine nucleus bearing spacer), 163.05 (methine carbon a to
nitrogen of pyridine), 166.23 (carbonyl carbon). ESI–MS
Concentration in mM
(8)
200
150
100
50
cmc
0
0
0.2
0.4
0.6
0.8
1
Concentration in mM
(9)
Fig. 1 Specific conductivity versus concentration plot of gemini
surfactants 7, 8 and 9
Positive ions m/z 763.3 (20 %) {(M-2Br)-1)}?, 764.4
(10 %) (M-2Br)?.
(4,40-(Propane-1,3-diyl)bis(1-(2-(tetradecyloxy)-2-oxo-
ethyl)dipyridinium bromide (11). Brown solid, Yield
)
93.4 %, Melting point 139 °C. IR (KBr pellet, cm-1
1
2,860, 1,742, 1,642 and 1,560. H NMR (d ppm CDCl3,)
0.87 (t, 6H, 2XCH3), 1.26 (d, chain 48H, 2X(–CH2–)12),
1.64 (m, 4H, 2XCH2 next to terminal methyl groups), 2.17
(m, 2H, PyCH2CH2CH2Py), 2.99 (t, 4H, PyCH2CH2
CH2Py), 4.21 (t, 4H, 2XCO2CH2), 6.01(d, 4H, 2XCH2
CO2), 8.04 (d, 4H, 4XCH ring protons b to nitrogen of
pyridine), 9.12 (d, 4H, 4XCH ring protons a to nitrogen of
pyridine). 75 MHz 13C/DEPT NMR (d ppm CDCl3): 14.06
(terminal methyl carbons), 22.64 (CH3CH2), 25.68
(CH2CH2CO2), 28.35 (PyCH2CH2CH2Py), 29.21 (chain
methylene carbons), 31.87 (CH2CH2CH3), 35.01 (PyCH2
CH2CH2Py), 60.55 (CH2CO2), 67.43 (CO2CH2), 127.90
(methine carbon b to nitrogen of pyridine), 145.79
123

J Surfact Deterg
(quaternary carbon of pyridine nucleus bearing spacer),
163.01 (methine carbon a to nitrogen of pyridine), 166.25
(carbonyl carbon). ESI–MS positive ions m/z 707.4
(100 %) {(M-2Br)-1)}? 708.4 (40 %) (M-2Br)?.
(CH2CO2), 67.41 (CO2CH2), 127.89 (methine carbon b to
nitrogen of pyridine), 145.76 (quaternary carbon of pyri-
dine nucleus bearing spacer), 163.01 (methine carbon a to
nitrogen of pyridine), 166.24 (carbonyl carbon). ESI–MS
positive ions m/z 651.4 (50 %) {(M-2Br)-1)}?, 652.4
(40 %) (M-2Br)?.
(4,40-(Propane-1,3-diyl)bis(1-(2-(dodecyloxy)-2-oxoeth-
yl)dipyridinium bromide (12). Brown sticky solid, Yield
93.4 %, Melting point 131 °C. IR (KBr pellet, cm-1) 2910,
1
1746, 1640 and 1574. H NMR (d ppm CDCl3): 0.68 (t,
Critical Micelle Concentration
6H, 2XCH3), 1.09 (d, chain 40H, 2X(–CH2–)10), 1.49 (m,
4H, 2XCH2 next to terminal methyl groups), 1.83 (m, 2H,
PyCH2CH2CH2Py), 2.72 (t, 4H, PyCH2CH2CH2Py), 4.02
(t, 4H, 2XCO2CH2), 5.94 (d, 4H, 2XCH2CO2), 7.87 (d, 4H,
4XCH ring protons b to nitrogen of pyridine), 9.01 (d, 4H,
4XCH ring protons a to nitrogen of pyridine) 0.75 MHz
13C/DEPT NMR (d ppm CDCl3): 14.05 (terminal methyl
carbons), 22.63 (CH3CH2), 25.67 (CH2CH2CO2), 28.34
(PyCH2CH2CH2Py), 29.30 (chain methylene carbons),
31.86 (CH2CH2CH3), 34.98 (PyCH2CH2CH2Py), 60.52
Gemini surfactants have astonishingly low CMC values,
much lower than the corresponding single tail surfactants
[24]. Only a few reports are available regarding synthesis
and CMC values of gemini pyridinium surfactants [25, 26].
Critical micelle concentration and the degree of counter ion
binding of these new pyridinium amphiphiles have been
determined by the conductivity method. These new gemini
pyridinium amphiphiles have low CMC values. It has been
found that the CMC of these gemini amphiphiles decreases
25
20
15
10
5
74
72
70
68
66
64
62
cmc
0.04
0
cmc
0
0.02
0.06
0.08
0.1
60
0
0.05
0.1
0.15
Concentration in mM
Concentration in mM
(10)
(7)
200
75
70
65
60
150
100
50
cmc
cmc
0
55
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Concentration in mM
Concentration in mM
(8)
(11)
75
70
65
60
55
50
45
40
35
70
60
50
40
30
20
10
0
cmc
cmc
0
0.1
0.2
0.3
0.4
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
Concentration in mM
Concentration in mM
(12)
(9)
Fig. 2 Specific conductivity versus concentration plot of gemini
surfactants 10, 11 and 12
Fig. 3 Plot of surface tension versus surfactant concentration of
gemini surfactants 7, 8 and 9
123

J Surfact Deterg
with increasing chain length. The values of CMC and
degrees of counter ion binding are given in Table 1. The
graphs of the specific conductivity versus concentration
have been plotted (Figs. 1, 2). It is found that the pyridi-
nium gemini surfactants with bromine as a counter ion
have low values of CMC as compared to the pyridinium
gemini surfactants with chlorine as a counter ion [27].
the electrostatic force that opposes micelle formation.
Quagliotto et al. [22] determined the b value for a series of
gemini bispyridinium bromides having different spacers
where they had shown that a different spacer is responsible
for a different b value. The b value signifies the ability of
counter ion to bind micelles. We, in our study, on new
series of gemini pyridinium surfactants (7–12), have found
that the b value decreases with increases in hydrophobicity
[22].
The Degree of Counterion Binding (b)
The ratio of the slopes of the specific conductivity versus
concentration curve above and below CMC gives degree of
counterion dissociation a (i.e. a = Smicellar/Spremicellar)
and (1-a) gives the degree of counterion binding, b. It is
an important parameter because it manifests the counteri-
ons that are contained in the Stern layer to counterbalance
Surface Tension Measurements
The CMC of new pyridinium gemini surfactants were
calculated by using surface tension measurements. The
graphs of the surface tension versus concentration are
shown for gemini surfactants (7–12). A clear break is
observed in all the pyridinium gemini surfactants (Figs. 3,
4). It is observed from the graphs that pyridinium gemini
surfactants having bromine as a counter ion have low CMC
values as compared to the pyridinium gemini surfactants
having chlorine as a counter ion. The CMC values are
reported in Table 1 for all the gemini surfactants. The
values of CMC found by both the conductivity method and
surface tension method correspond well with each other.
74
73
72
71
70
69
68
cmc
0.04
67
0
0.02
0.06
0.08
0.1
Conclusions
Concentration in mM
(10)
In the present study we have described a new protocol
for the synthesis of six new ester based cationic gemini
pyridinium surfactants starting from renewable long
chain fatty alcohols through an environmentally friendly,
energy saving and cost effective process. All the gemini
cationic surfactants (7–12) are produced in excellent
yields and these surfactants have been examined and are
found to have good surface active properties. The results
show that gemini pyridinium surfactants with longer
hydrophobic chains have lower CMC values than those
with shorter hydrophobic chains. Also it is found that
gemini surfactants having bromine as a counter ion have
lower CMC values as compared to gemini surfactants
having chlorine as a counter ion. In a previous report
[28] ester-containing gemini surfactants are more readily
degradable than their non-ester counterparts. In addition,
pyridinium cationic gemini surfactants may show good
antimicrobial properties, DNA binding capability if tes-
ted properly.
75
70
65
60
55
cmc
0
0.05
0.1
0.15
Concentration in mM
(11)
70
65
60
55
cmc
0
0.1
0.2
0.3
0.4
0.5
0.6
Acknowledgments Pankaj Patial is thankful to the UGC (Univer-
sity Grant Commission, India) for providing the research grant for this
work and Sophisticated Analytical Instrumentation Facility (SAIF),
Panjab University, Chandigarh for the mass spectral and NMR
analysis of the compounds. We are thankful to Dr Sukhprit Singh and
Mr. Avinash Bhadani for their help and fruitful discussions.
Concentration in mM
(12)
Fig. 4 Plot of surface tension versus surfactant concentration of
gemini surfactants 10, 11 and 12
123

J Surfact Deterg
20. Kanjilal S, Sunitha S, Reddy SP, Kumar PK, Upadyayula SNM,
Rachapudi BNP (2009) Synthesis and evaluation of micellar
properties and antimicrobial activities of imidazole based sur-
factants. Eur J Lipid Sci Technol 111:941–948
21. Rodrguez A, Graciani MM, Moya ML (2007) Effects of ethylene
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ionic dimeric surfactants. Langmuir 23:11496–15505
22. Viscardi G, Quagliotto P, Barolo C, Savarino P, Barni E, Fisicaro
E (2000) Gemini pyridinium surfactants synthesis and conduc-
tometric study of novel class of amphiphiles. J Org Chem
65:8197–8203
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Pankaj Patial obtained his M.Sc. degree in Industrial Chemistry in
2008 from Guru Nanak Dev University, Amritsar, India. He is
currently working on his Ph.D. in the field of Surfactant Chemistry
from Guru Nanak Dev University, Amritsar, India.
Arifa Shaheen obtained her Ph.D. in Analytical Chemistry in 2009
from Guru Nanak Dev University, Amritsar, India. She is currently
working as an Assistant Professor in Department of Chemistry at Dr.
B.R. Ambedkar National Institute of Technology, Jalandhar, India.
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Ishtiaque Ahmad obtained his Ph.D. degree in Organic Chemistry in
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2010 as Professor in Chemistry from Guru Nanak Dev University,
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123