Synthesis and properties of dissymmetric gemini surfactants

Article abstract of DOI:10.1007/s11743-010-1207-6

A series of novel dissymmetric gemini cationics surfactants was synthesized by three-step reactions. The dissymmetric gemini surfactants contain a dodecanoic acid dimethylethylamine ester as the constant cationic part on one side of the hydroxypropyl center and a similar other cationic part, but with a different acid length (from octanoic to palmitic), on the other side. The critical micelle concentration (CMC) and the effectiveness of surface tension reduction (γ _CMC) were determined. The surface tension measurements of dissymmetric gemini surfactants showed good water solubility, and low CMC had great efficiency in lowering the surface tension and a strong adsorption at the air/water interface. The CMC was observed to increase initially with the increase of the ester bond alkyl group. They also showed good foaming properties and wetting capabilites.

Full text of DOI:10.1007/s11743-010-1207-6

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J Surfact Deterg (2011) 14:85–90
DOI 10.1007/s11743-010-1207-6
ORIGINAL ARTICLE
Synthesis and Properties of Dissymmetric Gemini Surfactants
•
Qun Xu Liyan Wang Fenglan Xing
•
Received: 30 December 2008 / Accepted: 23 April 2010 / Published online: 26 May 2010
Ó The Author(s) 2010. This article is published with open access at Springerlink.com
Introduction
Abstract A series of novel dissymmetric gemini cationics
surfactants was synthesized by three-step reactions. The
dissymmetric gemini surfactants contain a dodecanoic acid
dimethylethylamine ester as the constant cationic part on one
side of the hydroxypropyl center and a similar other cationic
part, but with a different acid length (from octanoic to pal-
mitic), on the other side. The critical micelle concentration
(CMC) and the effectiveness of surface tension reduction
(cCMC) were determined. The surface tension measurements
of dissymmetric gemini surfactants showed good water
solubility, and low CMC had great efficiency in lowering the
surface tension and a strong adsorption at the air/water
interface. The CMC was observed to increase initially with
the increase of the ester bond alkyl group. They also showed
good foaming properties and wetting capabilites.
Gemini surfactants consisting of two hydrophobic chains
and two polar headgroups covalently linked by a spacer
have been attracting much attention [1, 2]. A considerable
number of investigations have been carried out on gemini
surfactants, focusing on their unique surface and bulk
properties, such as high surface activity, low critical
micelle concentration (CMC), better wetting properties,
unusual viscosity behavior, and specific aggregation
structures. Some of the works have been well reviewed by
Menger and Zana [3–5]. Because of these unique proper-
ties, they have great potential to be used as effective
emulsifiers, bactericidal agents, dispersants, anti-foaming
agents, and detergents, etc. They are also applicable in the
solubilization of dyes and pigments in the textile industry
[6] and gene therapy [7]. In a report the surfactants with
ester could enhance more effects on biodegradation than
long-chain paraffin surfactants, and this will help to
improve the environment [8].
Keywords Dissymmetric gemini surfactants Á
Critical micelle concentration Á Properties Á Synthesis
Abbreviations
CTAC
In recent years, a new class of gemini surfactants, dis-
symmetric gemini surfactants that posses two identical
head groups but two hydrocarbon chains with different
lengths [9–19], appeared and gained much attention. They
are in general abbreviated as n-s-m, where s represents the
number of carbon atoms in the spacer, and n and m refer to
the numbers of carbon atoms in two acids, respectively.
Hydrophobic chains with ester bonds of quaternary
ammonium gemini surfactants with both the ordinary
double-alkyl chains of quaternary ammonium surfactants
of high surface activity and with esters bond of quaternary
ammonium salt of the biodegradable result in environ-
mentally friendly surfactants [8, 20].
Cetyl trimethyl ammonium chloride
Dissymetric gemini surfactant with 12
and 8 alkyl acid groups
I-1 or 12-S-8
I-2 or 12-S-10 Dissymetric gemini surfactant with 12
and 10 alkyl acid groups
I-3 or 12-S-14 Dissymetric gemini surfactant with 12
and 14 alkyl acid groups
I-4 or 12-S-16 Dissymetric gemini surfactant with 12
and 16 alkyl acid groups
Q. Xu Á L. Wang (&) Á F. Xing
College of Chemistry and Chemical Engineering,
Qiqihar University, Qiqihar 161006,
People’s Republic of China
In this work, we synthesized with ester bond dissym-
metric gemini surfactants of bis-quaternary ammonium
e-mail: wlydlm@126.com
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J Surfact Deterg (2011) 14:85–90
salts by three-step reactions and investigated their physi-
cochemical properties by measuring equilibrium surface
tension. In addition, we also compared them with those of
symmetric gemini surfactants and discussed the effect of
the chain length and the chain numbers on the properties.
Scheme 1 shows the synthesis routes of dissymmetric
gemini surfactants in this study.
order to remove p-toluenesulfonic and unreacted materials,
then evaporated. The yellow viscous liquid a was obtained
and was used for the synthesis without further purifican-
tion. The synthesis route is the first reaction in Scheme 1.
Synthesis of b Product
A 1.1-fold molar excess of a type with dodecane alkyl
group (n = 12) was added to epichlorohydrin (1.0 mol)
and hydrochloric acid (0.2 mol) containing methanol
(15 ml) and continuously stirred at room temperature for
28–30 h. The solvent and unreacted epichlorohydrin were
then evaporated under reduced pressure (12–15 mmHg) at
room temperature until a constant mass was achieved. The
reaction product was recrystallized from a mixture of
hexane and ethyl acetate, and then a mixture of acetone and
methanol, or purified by column chromatography (silica
gel, 100–200 mesh: eluent: acetone and methol); the cor-
responding pure compound was dried in a vacuum oven for
6–8 h. The synthesis route of b is shown in Scheme 1, the
second reaction.
Experimental Procedures
Materials and Equipment Setup
2-Dimethylamino-ethanol, epichlorohydrin (EPIC) and
isopropyl alcohol were obtained from Tianjin Chemical
Company (China). Ethyl acetate, n-hexane, acetone, meth-
anol, and ethanol were obtained from Beijing Chemical Co.
(China). p-Toluene sulphonic acid and hydrochloride acid
were obtained from Harbin Chemical Co. (China). Lauric
acid, octanoic acid, n-decanoic acid, tetradecanoic acid, and
palmitic acid were obtained from Zhejiang Cleaned
Chemical Industry Limited Company (China). An FT-IR
20DXB infrared spectrophotometer was used for infrared
analyses (Nicolet, American); a DRX 400 nuclear magnetic
resonance (NMR) spectrometer was used for 1H NMR
analyses (Bruker, 400 MHz, Russ, Germany). Perkin-Elmer
2400II CHNS/O was used for elemental analysis.
Synthesis of Gemini Surfactants I
The gemini surfactants were synthesized by reacting b
(1.1 mol) with (1.2 mol) of one of the a products (n = 8,
10, 14, 16) in isopropyl alcohol (10 ml) and continuously
stirred at 85 °C for 10–12 h, respectively. The synthesis of
I is shown as the third reaction in Scheme 1. The crude
yellow oil was obtained and frozen in the refrigerator until
the crystal precipitated. The crystal was filtered and washed
with a cool mixture of hexane and ethyl acetate, and then
recrystallized from a mixture of acetone and methanol for
at least four to six times till the purity of the compound was
confirmed by thin liquid chromatography (TLC). The yield
of this reaction step was approximately 39.2%.
Synthesis of a Products
A 1.2-fold molar excess of n-alkyl acid (i.e., octanoic,
decanoic, dodecanoic, tetradecanoic, and palmitic acids
indicated according to the number of C atoms in the acid,
n = 8, 10, 12, 14, 16) was dissolved in ethanol (10 ml) or
chloroform (10 ml) and added to 2-dimethylaminoethanol
(1.0 mol) containing 3% p-toluenesulfonic. The reaction
was heated and continuously stirred at 150 °C for 8–10 h.
The residue was washed with ethyl ether several times in
IR spectra of all the intermediate a showed absorption
bands at 2,925, 2,856 cm-1 (C-H stretching), 1,728 cm-1
Scheme 1 Synthetic routines
for the preparation of
dissymmetric gemini surfactants
CH3
CH3
NCH2CH2OH
CH3
Cn-1H2n-1COOCH2CH2N
Cn-1H2n-1COOH
a
CH3
n = 8,10,12,14,16
CH3
CH3
H
C
11H23COOCH2CH2N
C11H23COOCH2CH2N
CH2CHCH2Cl
HCl
H2C
CH3
C
CH2Cl
Cl
CH3
O
CH3
OH
b
CH3
N
C11H23COOCH2CH2N
CH2CHCH2
OH
CH2CH2OOCCn-1H2n-1
n = 8,10,14,16
b
a
Cl
CH3
Cl
CH3
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J Surfact Deterg (2011) 14:85–90
87
(C = O stretching), 1,463 cm-1 (C-H bending),
1,146 cm-1 (C-O stretching), 1,118 cm-1 (C-N stretch-
ing), and 720 cm-1 (C-H rocking).
C39H80N2O5Cl2; C, 71.29; H, 12.27; N, 4.26%. Found: C,
71.18; H, 12.35; N, 4.32%.
IR spectra of all the intermediate b showed absorption
bands at 3,396 cm-1 (-OH stretching), 2,923, 2,855
cm-1 (C-H stretching), 1,725 cm-1 (C = O stretching),
1,461 cm-1 (C-H bending), 1,157 cm-1 (C-O stretching),
1,115 cm-1 (C-N stretching), and 723 cm-1 (C-H rocking).
IR spectra of all the gemini surfactants showed absorp-
tion bands at 3,243–3,450 cm-1 (-OH stretching), 2,923,
2,852 cm-1 (C-H stretching), 1,736 cm-1 (C = O stretch-
ing), 1,465 cm-1 (C-H bending), 1,166 cm-1 (C-O
stretching), 1,110 cm-1 (C-N stretching), and 721 cm-1
(C-H rocking).
Analytical Methods
Structures of the prepared compounds were confirmed by
their spectral data. 1H NMR (400 MHz) spectra were
recorded of solutions in CDCl3 using a Bruker DRX 400
spectrometer with tetramethylsilane as a standard. IR
spectra were recorded of pellets in KBr using a Nicolet FT-
IR 20DXB spectrometer.
Surface tensions of surfactant aqueous solutions at dif-
ferent concentrations were measured at 25 0.1 °C by
using a drop-volume tensiometer [21]. The surface tensions
were averaged values from three measurements. Accuracy
of the surface tension measurements was 0.1 mN/m [22].
Wettability was measured at 25 °C with the canvas
descending method [21]. Aqueous surfactant solution
containing 2 g/l of the gemini surfactant (from I-1 to I-4)
was prepared. Standard thin canvas (diameter 35 mm,
weight 38–39 mg) was used, and the detailed operation has
been reported [23]. The foaming power was estimated by
measuring the foam height of 0.1% aqueous surfactant
solution at 5 min after vigorous shaking 100 times at 25 °C
with the modified Ross-Miles method [24]. Foam stabilities
were determined by comparing the foam height after 5 min
to the initial value in the Ross-Miles apparatus [21].
Emulsification properties were investigated by mixing in
a graduated cylinder with a standard ground-glass joint and
plastic stopper at room temperature (20 °C) [21]. A 20-ml
volume of aqueous surfactant solution containing 0.1% of
the gemini surfactant was poured into a 100-ml cylinder
with 20 ml of solvent (benzene) in the bottom. The stopper
was placed in the cylinder, and it was inverted up and down
five times successively, then rested for 1 min. The exper-
iment was repeated five times with high repeatability, and
the time for the separation of 10 ml water was noted in
seconds as indicated in Table 2 [25].
1H NMR of the intermediate a (n = 12). 1H NMR
(CDCl3) d 0.88 (t, 3H, -CH3), 1.19–1.25 (m, 18H), 1.69
(m, 2H, CH2CC = O), 2.29 (s, 6H, 2 9 N CH3), 2.56
(t, 2H, NCH2), 4.20 (t, 2H, NCCH2-O).
1H NMR of the intermediate b. 1H NMR (CDCl3) d 0.89
(t, 3H, -CH3), 1.19–1.25 (m, 18H), 1.65 (m, 2H,
CH2CC = O), 2.29 (t, 2H, CCH2C = O), 3.32 (s, 6H,
2N?CH3), 3.36–3.55 (t, 6H, N?CH2, and CH2Cl), 4.20 (m,
1H, CH-O), 4.20 (m, 1H, CH-O), 4.55 (t, 2H, N?CCH2).
1
I-1, represented as (12-S-8). H NMR (CDCl3) d 0.86–
0.89 (t, 6H, 2 9 CH3), 1.21–1.27 (m, 24H), 1.61–1.73
(m, 4H, 2 9 CH2CC = O), 2.29–2.35 (m, 4H, 2 9
CH2C = O), 3.28 (s, 12H, 4 9 N?CH3), 3.35–3.62 (m, 8H,
4N?CH2), 4.56 (t, 4H, 2NCCH2-O), 4.40–4.51 (m, 1H, CH-
O); elemental analysis calculated for C31H64N2O5Cl2; C,
60.47; H, 10.48; N, 4.55%. Found: C, 60.36; H, 10.57; N,
4.56%.
I-2, represented as (12-S-10). 1H NMR (d, ppm, CDCl3)
0.86–0.89 (t, 6H, 2 9 CH3), 1.22–1.25 (m, 28H), 1.61–
1.65 (m, 4H, 2 9 CH2CC = O), 2.29–2.34 (m, 4H,
2 9 CH2C = O), 3.30 (s, 12H, 4 9 N?CH3), 3.33–3.60
(m, 8H, 4N?CH2), 4.52 (t, 4H, 2NCCH2-O), 4.43–4.49
(m, 1H, CH-O); elemental analysis calculated for
C33H68N2O5Cl2; C, 61.56; H, 10.65; N, 4.35%. Found: C,
61.43; H, 10.72; N, 4.37%.
I-3, represented as (12-S-14). 1H NMR (d, ppm, CDCl3)
0.86–0.89 (t, 6H, 2 9 CH3), 1.22–1.27 (m, 36H), 1.58–
1.63 (m, 4H, 2 9 CH2CC = O), 2.27–2.33 (m, 4H,
2 9 CH2C = O), 3.28 (s, 12H, 4 9 N?CH3), 3.31–3.56
(m, 8H, 4N?CH2), 4.55 (t, 4H, 2NCCH2-O), 4.43–4.49
(m, 1H, CH-O); elemental analysis calculated for
C37H76N2O5Cl2; C, 70.65; H, 12.18; N, 4.45%. Found: C,
70.38; H, 12.21; N, 4.47%.
I-4, represented as (12-S-16). 1H NMR (d, ppm, CDCl3)
0.86–0.89 (t, 6H, 2 9 CH3), 1.20–1.25 (m, 40H), 1.56–
1.65 (m, 4H, 2 9 CH2CC = O), 2.26–2.35 (m, 4H,
2 9 CH2C = O), 3.26 (s, 12H, 4 9 N?CH3), 3.30–3.53
(m, 8H, 4N?CH2), 4.58 (t, 4H, 2NCCH2–O), 4.44–4.50
(m, 1H, CH-O); elemental analysis calculated for
Results and Discussion
Surface Properties
The surface tension (c) for the water solution-prepared bis-
quaternary ammonium salts (I-1, I-2, I-3, I-4) at 25 °C
versus log molar concentration (log c) is shown in Fig. 1.
The surface tension decreased gradually with increasing
surfactant concentration and exhibited a break point, which
was taken as the critical micelle concentration (CMC) as
indicated in Table 1.
Gemini surfactant structure variation indicates that there
is some change with the increasing length of the alkyl
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group. As n increases (from I-1 to I-4), the CMC increases
and the tension also increases at a concentration lower than
CMC, and also the minimum tension above the CMC.
When compared with the single C16 tail CTAC cationic
surfactant results, it is seen that the properties are quite
similar, in spite of a very different size of the structure.
The wetting and foaming ability of prepared dissym-
metric gemini surfactants measured at 25 °C are summa-
rized in Table 2.
surfactant adsorption quantity on the canvas surface is
much larger than the corresponding single quaternary
ammonium surfactants. And the number of molecules of
gemini surfactants with shorter hydrophobic alkyl chains
arranged at the interface is more than that of the gemini
surfactants with longer hydrophobic alkyl chains. This
shows that gemini surfactants with short hydrophobic alkyl
chains have stronger wetting power than gemini surfactants
with longer hydrophobic alkyl chains. Table 2 shows that
the wetting abilities of I-1, I-2, I-3, and I-4 compounds
were superior to the corresponding CTAC (179 s) value. In
the series the I-1 and I-2 products demonstrated very good
wetting power.
As estimation of wetting power, it is stronger when the
time (ability in seconds) is shorter. When surfactants wet
the canvas fiber, it will form a three-phase interface of
‘‘solid-liquid-gas.’’ When added to solution, surfactants
will adsorb the interface of ‘‘solid-liquid’’ and that of
‘‘liquid-gas;’’ the more surfactants adsorb on the solid
surface, the stronger the wetting power is on the canvas. In
the molecular structure of bis-quaternary ammonium sur-
factants, two quaternary ammonium ion head groups are
linked by chemical bonds, depending on the linking group
containing the hydroxyl group. This structure significantly
improves the head group positive density of the bis-
quaternary ammonium surfactant unit molecules and the
density of the hydrophobic alkyl chain. This makes it easier
to be adsorbed on negatively charged surface of the canvas,
and the adsorption is more solid, the orientation more
closely aligned. The gemini bis-quaternary ammonium
The main factors that can affect foamability and sta-
bility of surfactants are the interfacial tension and the
properties of interfacial film. When generating foam of the
same total surface area, a lower surface tension system
needs less work. This means that low surface tension is
good for foam formation, but also it is good for the foam
burst (foam unstable). The stability of the foam mainly
depends on the drain speed and intensity of the liquid film,
and also on the solution viscosity. Viscosity can increase
the strength of liquid film; with higher surface viscosity,
liquid does not easily flow and discharge, and the speed of
the liquid film thickness to get smaller becomes slower,
delaying the damage of liquid film and increasing the
stability of foam. Double-layer adsorption is formed in the
liquid film surrounding the gas, and hydrophilic groups of
surfactants form hydration layer within liquid film. With
increasing of the hydrophobic chain length, hydrophobic
groups of surfactants attract and tighten, which increases
the intensity of the double-layer adsorption film and vis-
cosity of the liquid-in-liquid film leading to stable film
formation. The foam-producing ability of all these pre-
pared compounds (from I-1 to I-4) was slightly less than
the CTAC value. However, all the compounds exhibited a
decrease in the foam height after 5 min. Table 2 shows
that by increasing n from 8 to 16, the foam stability
become stronger. In addition, all these compounds exhibit
a low foam height and are thus good for oilfield water
treatment.
Fig. 1 Surface tension (mN.m) versus logarithm of aqueous molar
concentration (log C mol/l) of bis-quaternary ammonium salts at
25 °C. See Scheme 1 for compounds
Table 1 CMC and surface tensions for the prepared surfactants at
25 °C
Surfactants can prompt emulsion formation and improve
its stability. The emulsification is realized by the effect of
adsorption, and it forms a layer of adsorptive film in the
interface of dispersed droplets, which can prevent or delay
collision among droplets and may cause gathering and
condensation. The adsorption effect of the oil-water surface
in the emulsion O/W is determined by the degree to which
hydrophobic groups damage the structure of the water
phase, and with the increase in length of the hydrophobic
chain, the adsorption effect increases. The emulsifying
power of I-4 was found to be the best in the series, and it
was even better than that for CTAC shown in Table 2.
Compounda
CMC (mol/L)
cCMC (mN/m)
I-1
I-2
I-3
I-4
CTAC
a
1.0 9 10-3
1.1 9 10-3
1.6 9 10-3
2.5 9 10-3
1.5 9 10-3
30.4
36.2
40.0
45.2
37.0
The structures of I-1*I-4 are presented in Scheme 1; CMC, critical
micelle concentration
cCMC, surface tension at the CMC; CTAC cetyl trimethyl ammonium
chloride
123