Synthesis and Evaluation of Novel Amido-Amine Cationic Gemini Surfactants Containing Flexible and Rigid Spacers

Article abstract of DOI:10.1007/s11743-017-1969-1

New amido-amine-based cationic gemini surfactants with flexible and rigid spacers and different hydrophobic tails were synthesized and characterized. These gemini surfactants were prepared by a modified procedure through amidation of long chain carboxylic acids using 3-(dimethylamino)-1-propylamine followed by treatment with halohydrocarbons. The effect of the trans and cis conformation of the spacer double bond was investigated by means of critical micelle concentration, surface tension reduction, and thermal stability. The short-term thermal stability of the gemini surfactants was assessed using thermogravimetric analysis (TGA) and the long-term thermal stability was examined by a unique approach based on structure characterization techniques including NMR (¹H and ¹³C) and FTIR analysis. TGA results demonstrated excellent short-term thermal stability since no structure degradation was observed up to 200?°C. Structural characterization revealed impressive long-term thermal stability of the gemini surfactants with no structure decomposition after exposing them to 90?°C for 10?days. The critical micelle concentration of gemini surfactants was found to be in the range of 0.77?×?10^?4–3.61?×?10^?4?mol?L^?1 and corresponding surface tension (γ_CMC) ranged from 30.34 to 38.12?mN?m^?1. The surfactant with the trans conformation of spacer double bond showed better surface properties compared to the surfactant with the cis conformation of spacer double bond. Similarly, increasing surfactant tail length and spacer length resulted in decreasing CMC values. Moreover, bromide counterion showed improved surface properties compared to chloride counterion.

Full text of DOI:10.1007/s11743-017-1969-1

J Surfact Deterg
DOI 10.1007/s11743-017-1969-1
ORIGINAL ARTICLE
Synthesis and Evaluation of Novel Amido-Amine Cationic Gemini
Surfactants Containing Flexible and Rigid Spacers
S. M. Shakil Hussain1 Muhammad Shahzad Kamal1 Bassam El Ali2
Abdullah S. Sultan3
•
•
•
Received: 28 January 2017 / Accepted: 20 April 2017
Ó AOCS 2017
Abstract New amido-amine-based cationic gemini sur-
factants with flexible and rigid spacers and different
hydrophobic tails were synthesized and characterized.
These gemini surfactants were prepared by a modified
procedure through amidation of long chain carboxylic
acids using 3-(dimethylamino)-1-propylamine followed by
treatment with halohydrocarbons. The effect of the trans
and cis conformation of the spacer double bond was
investigated by means of critical micelle concentration,
surface tension reduction, and thermal stability. The short-
term thermal stability of the gemini surfactants was
assessed using thermogravimetric analysis (TGA) and the
long-term thermal stability was examined by a unique
approach based on structure characterization techniques
including NMR (1H and 13C) and FTIR analysis. TGA
results demonstrated excellent short-term thermal stability
since no structure degradation was observed up to 200 °C.
Structural characterization revealed impressive long-term
thermal stability of the gemini surfactants with no structure
decomposition after exposing them to 90 °C for 10 days.
The critical micelle concentration of gemini surfactants
surfactant with the trans conformation of spacer double
bond showed better surface properties compared to the
surfactant with the cis conformation of spacer double bond.
Similarly, increasing surfactant tail length and spacer
length resulted in decreasing CMC values. Moreover,
bromide counterion showed improved surface properties
compared to chloride counterion.
Keywords Gemini surfactants Á Synthesis Á Surface
properties Á Thermal stability Á Rigidity
Introduction
Surfactants have been widely applied in various oilfield
applications including drilling mud, stimulation, comple-
tion, and enhanced oil recovery [1]. The primary role of
surfactants in oilfield applications is interfacial tension
(IFT) reduction and wettability alteration [2–5]; however,
they also act as wetting agents [6] and emulsifiers [7].
Gemini surfactants are composed of more than one
hydrophobic tail and head groups joined through a spacer
[8, 9]. Due to such unique structure, gemini surfactants are
superior to conventional single head single tail surfactants
[10] in terms of higher efficiency in IFT reduction, lower
critical micelle concentrations (CMC), solubility, vis-
coelastic behavior, gel formation, wetting properties, and
shear thickening [11, 12].
was found to be in the range of 0.77 9 10-4
3.61 9 10-4 mol L-1 and corresponding surface tension
(cCMC The
ranged from 30.34 to 38.12 mN m-1
–
)
.
& Muhammad Shahzad Kamal
shahzadmalik@kfupm.edu.sa
In the past decades, many reports have appeared in the
literature and focused on the study of cationic gemini
surfactants containing quaternary ammonium head group
with different tail and spacer length [13]. Cationic gemini
surfactants are extensively applied in medicine [14],
household [15], biotechnology [16], pharmacy [17], oilfield
[18], and other industries [19]. Ammonium-based cationic
1
Center for Integrative Petroleum Research, King Fahd
University of Petroleum and Minerals, Dhahran 31261,
Saudi Arabia
2
Chemistry Department, King Fahd University of Petroleum
and Minerals, Dhahran 1261, Saudi Arabia
3
Petroleum Engineering Department, King Fahd University of
Petroleum and Minerals, Dhahran 31261, Saudi Arabia
123

J Surfact Deterg
gemini surfactants can be economically feasible, environ-
mentally friendly, show excellent water solubility, and
have various oil field applications [20]. Cationic gemini
surfactants are strong candidates in carbonate reservoirs
(which represent almost 60% of the world’s oil reservoirs)
where anionic surfactants are not suitable because of high
adsorption on to the carbonate rocks [21]. Cationic sur-
factants change the wettability of carbonate rocks from oil-
wet to water-wet resulting in enhanced oil production [22].
In view of such properties, the research is focused more
on the synthesis and development of new cationic gemini
surfactants with different lengths and nature of the spacers
as well as hydrophobic tail groups to investigate the rela-
tionship between aggregation behavior and molecular
structures [23]. Gemini surfactants aggregate in aqueous
media to form micelles and the size and shape of such
micelles mainly depend on the spacer group [24]. The
nature and the length of the spacer have been found to be
the most significant parameter determining the surface
properties of gemini surfactants [25, 26]. The spacer can be
flexible (hydrophobic methylene group [27] or hydrophilic
polyethylene oxide group [28]) and it can be rigid with a
double bond [29], triple bond [30], or benzene ring [31].
Previous literature reveals that polyether or phenyl
moieties are normally introduced to maximize or minimize
the spacer rigidity [32]. However, such polyether and
phenyl moieties could also alter the spacer chain length and
hydrophobicity. Therefore, the surfactants’ aggregation
morphologies could be affected by the spacer rigidity,
length, hydrophobicity, and p–p stacking interactions
between benzene rings [33]. Hence, the selections of
gemini surfactants that isolate the other parameters on the
aggregation morphologies play an important role.
conformation (trans and cis) of spacer double bond using
two sets of gemini surfactants (1–2 and 3–4) (Fig. 1) to
investigate the effect of the different conformation of the
double bond in spacer on aggregation. The gemini sur-
factant 6 (Fig. 1) with flexible larger spacer group was
synthesized for comparison purposes.
Experimental
Materials
Dodecanoic acid (98%, sigma), oleic acid (92%, bio-
chemical), 3-(dimethylamino)-1-propylamine (99%, GC,
Aldrich), 1,4-dibromobutane (99%, Aldrich), trans-1,4-di-
bromo-2-butene (99%, Aldrich), cis-1,4-dichloro-2-butene
(95%, Aldrich), 1,6-dibromohexane (96%, Aldrich), alu-
minum oxide (Fluka) were utilized as received. Distilled
solvents and water were used for the synthesis and purifi-
cation of gemini surfactants. Deionized water was used to
prepare aqueous solutions of surfactants.
Synthesis
Synthesis and Spectral Characterization of Amido-Amine
Intermediates (10 and 11)
The synthesis of amido-amine intermediate compound (10)
was achieved using an improved method presented by Chu
and co-workers [37] as outlined in Scheme 1. Dodecanoic
acid (7) (20.00 g, 99.84 mmol), 3-(dimethylamino)-1-
propylamine (9) (20.40 g, 200 mmol), and sodium fluoride
(NaF) (0.42 g, 9.98 mmol) were added in a 100-mL flask
connected with a reflux condenser. The condenser was
further connected with a bent distilling adapter filled with
Al2O3 in order to absorb the byproduct H2O. The experi-
ment was allowed to continue under reflux at 160 °C for
6-h in an argon atmosphere. After 6 h, further
3-(dimethylamino)-1-propylamine (15.30 g, 150 mmol)
was introduced into the flask and the reaction progressed
under the same experimental conditions for another 5 h.
After completion, the unreacted 3-(dimethylamino)-1-
propylamine was separated and the residue was washed
three times with a mixture of cold water:acetone (7:93)
then dried in a vacuum to achieve intermediate 10 [38].
In this report, six amido-amine-based cationic gemini
surfactants (1–6) (Fig. 1) containing different spacers and
hydrophobic tails were synthesized from the corresponding
carboxylic acids (Scheme 1). The effect of spacer length,
spacer rigidity, trans and cis conformation of the spacer
double bond, and hydrophobic tail length were studied in
terms of thermal stability and surface tension analysis.
Three amido-amine based cationic gemini surfactants (3–5)
(Fig. 1) have a similar hydrophobic tail group but differ by
the rigidity and flexibility of the spacer. Two spacer lengths
(C4 and C6) were selected because the noticeable changes
in surfactant properties were reported in relatively short
spacers [34]. The two sets of gemini surfactants (1, 3 and 2,
4) (Fig. 1) have similar spacer group but differ by the
hydrophobic tail groups. The dodecyl group was selected
as a hydrophobic tail because it was appropriate to deliver
good properties to surfactants [35] and the oleic tail was
chosen because it was reported that the CMC decreases
with the increase of the chain length [36]. Similarly, we
changed the rigidity of spacer in terms of different
Intermediate 11 was Prepared by Adopting the Same
Method of Intermediate 10 N-Dodecanamidopropyl-N,N-
1
Dimethylamine (10): White solid (25.90 g, 91% yield) H
NMR (500 MHz, CDCl3) d (ppm): 0.83 (t, J = 6.7 Hz,
3H), 1.15–1.25 (m, 16 H), 1.51–1.58 (m, 2H), 1.64–1.73
(m, 2H), 2.11 (t, J = 7.6 Hz, 2H), 2.30 (s, 6H), 2.47 (t,
J = 6.4 Hz, 2H), 3.29 (pent, J = 5.8 Hz, 2H), 6.99 (s, 1H
123

J Surfact Deterg
O
CH3
10
-
H3C
H
NH
H
H
-
+
2 Br
H3C
CH3
3
2 Cl
H
N
+
+
H3C
N
3
N
H
N
+
CH3
N
3
CH3 H3C
3NH
H
N
CH3
10
1
2
H3C
O
O
10CH3
10
H3C
O
trans conformation
cis conformation
H
C
H
C
O
CH3
-
-
H
H
7
7
2 Cl
H3C
H
NH
H3C
CH3
2 Br
+
+
+
3
H
N
N
N
H3C
+
CH3
HN
O
CH3 H3C
3NH
O
3
N
H
N
O
CH3
7
H3C
C
C
7 CH
C
C
3
7 H
H
H
7 H
4
3
3
7
H3C
C
H
C
7
H
trans conformation
cis conformation
CH3
N
CH3
O
CH3
H
N
H
C
7
H
C
+
-
+
CH3
7
2 Br
H3C
C
C
H
N
CH3
N
7
7 H
3 H
3
O
5
CH3
N
CH3
O
H
N
CH3
H
H
C
+
-
+
C
CH3
7
2 Br
H3C
C
C
H
N
CH3
N
3 H
7O
7 H
3
7
6
Fig. 1 Structures of all surfactants (1–6) with trans and cis conformation of the spacer double bond
(NH). 13C NMR (125 MHz, CDCl3) d (ppm): 14.0, 22.6,
25.7, 29.2, 29.3, 29.4, 29.5, 31.8, 36.8, 38.5, 44.8, 58.0,
173.3.
reflux (80 °C) for 48 h (Scheme 1). After completion, the
product was separated and recrystallized using solvent
mixture acetone/ethyl acetate to obtain the required gemini
surfactant 1 as a white solid [39].
N-Oleamidopropyl-N,N-dimethylamine (11): Pale yellow
1
viscous liquid (22.7 g, 87% yield). H NMR (500 MHz,
Gemini Surfactant 2 was Synthesized by Adopting the Same
Procedure as 1 (E)-Dodecanoic acid [3-({4-[(3-Dode-
canoylamino-propyl)-dimethyl-amino]but-2-enyl}-dimethyl-
amino)-propyl]-amide dibromide (1): White solid (9.70 g,
88% yield based on trans-1,4-dibromo-2-butene). 1H NMR
(500 MHz, CDCl3) d (ppm): 0.82 (t, J = 6.7 Hz, 6H),
1.16–1.26 (m, 32 H), 1.52–1.58 (m, 4H), 2.06–2.12 (m,
4H), 2.26–2.33 (m, 4H), 3.31 (s, 12H), 3.32–3.36 (m, 4H),
3.64–3.72 (m, 4H), 4.41–4.49 (m, 4H), 6.77–6.85 (m, 2H),
8.16 (s, 2H (NH). 13C NMR (125 MHz, CDCl3) d (ppm):
14.0, 22.6, 22.8, 25.9, 29.3, 29.4, 29.5, 29.6, 29.7, 31.8,
36.1, 36.6, 51.0, 62.6, 65.0, 130.2, 175.3. FTIR (KBr pel-
let) t (cm-1) 3441 (tN–H, secondary amine), 2922 and
CDCl3) d (ppm): 0.83 (t, J = 6.7 Hz, 3H), 1.18–1.28 (m,
20 H), 1.52–1.59 (m, 2H), 1.62–1.69 (m, 2H), 1.91–1.98
(m, 4H), 2.10 (t, J = 7.6 Hz, 2H), 2.26 (s, 6H), 2.42 (t,
J = 6.4 Hz, 2H), 3.28 (pent, J = 5.8 Hz, 2H), 5.25–5.31
(m, 2H), 7.0 (s, 1H (NH). 13C NMR (125 MHz, CDCl3) d
(ppm): 14.0, 22.6, 25.7, 25.8, 27.1, 29.1, 29.2, 29.4, 29.6,
29.7, 31.8, 36.8, 38.7, 44.9, 58.0, 129.7, 129.9, 173.2.
Synthesis and Spectral Characterization of Amido-Amine
Cationic Gemini Surfactants (1 and 2)
The amido-amine intermediate compound (10) (10.0 g,
35.15 mmol) was treated with trans-1,4-dibromo-2-butene
(12) (3.0 g, 14.06 mmol) in dry ethanol (5 mL) under
2850 (tC–H
,
aliphatic asymmetric and symmetric
123

J Surfact Deterg
O
O
CH3
CH3
CH3
CH3
NaF
+
H2N
N
R
N
H
N
R
OH
Al2O3, heat
(9)
(10)
R =
7
( )
R = H3C
R = H3C
H3C
10
10
R =
(11)
8
( )
H3C
7
7
7
7
Br
O
CH3
N
CH3
CH3
+
H
N
Br
Cl
+
-
(12)
EtOH, heat
R
R
2 Br
R
N
H
N
O
CH3
(1)
R = H3C
(3)
;
R = H3C
10
7
7
O
O
O
CH3
CH3
CH3
Cl
+
+
13
(
)
-
2 Cl
R
N
H
N
R
N
H
N
N
N
H
EtOH, heat
CH3
CH3
CH3
H3C
(10 and 11)
(2)
R = H3C
(4)
;
R =
10
7
7
Br
Br
s
O
O
14
CH3
+
CH3
s = 2 (
)
+
= 4 (15)
-
2 Br
R
N
H
N
N
N
H
R
s
EtOH, heat
CH3
CH3
R =
R = H3C
H3C
7
7
(6)
(5)
7
7
;
s = 4
s = 2
Scheme 1 Synthesis of amido-amine-based cationic gemini surfactants (1–6)
Synthesis and Spectral Characterization of Amido-Amine
respectively), 1641 (amide I band), 1555 (amide II band).
Anal. Calcd for C38H78O2N4Br2 (782.86): C, 58.30; H,
10.04; N, 7.16. Found: C, 58.17; H, 10.19; N, 7.08.
Cationic Gemini Surfactants (3–6)
The
amido-amine
intermediate
compound
(11)
(Z)-Dodecanoic acid [3-({4-[(3-dodecanoylamino-propyl)-
dimethyl-amino]but-2-enyl}-dimethyl-amino)-propyl]-amide
dichloride (2): White solid (11.85 g, 71% yield based on
cis-1,4-dichloro-2-butene). 1H NMR (500 MHz, CDCl3) d
(ppm): 0.83 (t, J = 6.7 Hz, 6H), 1.18–1.28 (m, 32 H),
1.55–1.61 (m, 4H), 2.06–2.12 (m, 4H), 2.28–2.34 (m, 4H),
3.29 (s, 12H), 3.30–3.36 (m, 4H), 3.63–3.71 (m, 4H),
4.67–4.73 (m, 4H), 6.38–6.44 (m, 2H), 8.52 (s, 2H (NH).
13C NMR (125 MHz, CDCl3) d (ppm): 14.1, 22.7, 22.9,
26.0, 29.3, 29.4, 29.5, 29.6, 29.7, 31.9, 35.9, 36.6, 50.5,
60.8, 62.3, 128.1, 175.5. FTIR (KBr pellet) t (cm-1) 3475
(tN–H, secondary amine), 2924 and 2852 (tC–H, aliphatic
asymmetric and symmetric respectively), 1642 (amide I
band), 1545 (amide II band). Anal. Calcd for C38H78O2-
N4Cl2 (693.96): C, 65.77; H, 11.33; N, 8.07. Found: C,
65.65; H, 11.41; N, 8.02.
(10.0 g 9 27.28 mmol) was treated with trans-1,4-di-
bromo-2-butene (12) (2.33 g, 10.91 mmol) in dry ethanol
(5 mL) for 48 h under reflux (80 °C). After completion, the
reaction product was purified using silica gel column
chromatography with methanol:acetone (3:7) as eluent to
afford the required gemini surfactant 3 [39].
Gemini Surfactants 4–6 of this Series were Synthesized by
Adopting the Same Procedure of 3 (E)-Oleic acid [3-({4-
[(3-oleamidopropyl)-dimethyl-amino]but-2-enyl}-dimethyl
-amino)-propyl]-amide dibromide (3): Pale yellow viscous
oil (8.49 g, 82% yield based on trans-1,4-dibromo-2-
1
butene). H NMR (500 MHz, CDCl3) d (ppm): 0.82 (t,
J = 6.7 Hz, 6H), 1.18–1.28 (m, 40H), 1.49–1.55 (m, 4H),
1.91–1.97 (m, 8H), 2.0–2.06 (m, 4H), 2.21 (t, J = 7.6 Hz,
123

J Surfact Deterg
4H), 3.23 (s, 12H), 3.24–3.30 (m, 4H), 3.52–3.58 (m, 4H),
4.27–4.33 (m, 4H), 5.23–5.33 (m, 4H), 6.62–6.68 (m, 2H),
7.79 (s, 2H (NH). 13C NMR (125 MHz, CDCl3) d (ppm):
14.0, 22.6, 23.0, 25.7, 27.2, 29.3, 29.4, 29.5, 29.7, 29.8,
31.8, 36.4, 51.1, 62.6, 64.9, 129.5, 129.9, 130.2, 174.8.
FTIR (KBr pellet) t (cm-1) 3445 (tN–H, secondary
amine), 2926 and 28547 (tC–H, aliphatic asymmetric and
symmetric respectively), 1643 (amide I band), 1551
(amide II band). Anal. Calcd for C50H98O2N4Br2 (947.15):
C, 63.40; H, 10.43; N, 5.92. Found: C, 63.32; H, 10.57; N,
5.82.
4H), 8.40 (s, 2H (NH). 13C NMR (125 MHz, CDCl3) d
(ppm): 14.1, 21.6, 22.6, 22.7, 24.6, 25.9, 27.1, 29.1, 29.2,
29.3, 29.4, 29.6, 29.7, 31.8, 35.8, 51.1, 62.3, 65.0, 129.6,
129.9, 175.3. FTIR (KBr pellet) t (cm-1) 3440 (tN–H
,
secondary amine), 2924 and 2852 (tC–H, aliphatic asym-
metric and symmetric respectively), 1633 (amide I band),
1549 (amide II band). Anal. Calcd for C52H104O2N4Br2
(977.22): C, 63.91; H, 10.73; N, 5.73. Found: C, 63.78; H,
10.80; N, 5.64.
Analytical Equipment
(Z)-Oleic acid [3-({4-[(3-oleamidopropyl)-dimethyl-ami-
no]but-2-enyl}-dimethyl-amino)-propyl]-amide dichloride
(4): Pale yellow viscous oil (12.80 g, 80% yield based on
The structures of the amido-amine-based cationic gemini
surfactants (1–6) were established by using NMR, FTIR,
and elemental analysis. The NMR data was acquired on a
500-MHz NMR instrument (Jeol 1500 model). Deuterated
chloroform was used as the solvent, tetramethylsilane
(TMS) as an internal standard, and chemical shifts in NMR
spectra were recorded in ppm. The FTIR (Fourier Trans-
form Infrared) spectroscopy was carried out using a FTIR
spectrophotometer (Perkin-Elmer 16F model). Elemental
analysis was obtained using a Perkin Elmer Series 11
(CHNS/O) Analyzer 2400.
1
cis-1,4-dichloro-2-butene). H NMR (500 MHz, CDCl3) d
(ppm): 0.83 (t, J = 6.7 Hz, 6H), 1.17–1.27 (m, 40H),
1.47–1.55 (m, 4H), 1.91–1.97 (m, 8H), 1.99–2.05 (m, 4H),
2.20 (t, J = 7.6 Hz, 4H), 3.23 (s, 12H), 3.24–3.30 (m, 4H),
3.53–3.59 (m, 4H), 4.52–4.58 (m, 4H), 5.22–5.32 (m, 4H),
6.32–6.38 (m, 2H), 8.0 (s, 2H (NH). 13C NMR (125 MHz,
CDCl3) d (ppm): 14.0, 22.6, 23.0, 25.9, 27.2, 29.3, 29.4,
29.5, 29.7, 29.8, 31.8, 36.3, 50.6, 60.6, 62.3, 127.7, 129.5,
129.9, 174.8. FTIR (KBr pellet) t (cm-1) 3431 (tN–H
,
secondary amine), 2924 and 2853 (tC–H, aliphatic asym-
metric and symmetric respectively), 1642 (amide I band),
1552 (amide II band). Anal. Calcd for C50H98O2N4Cl2
(858.24): C, 69.97; H, 11.51; N, 6.53. Found: C, 69.84; H,
11.57; N, 6.63.
Thermogravimetric Analysis
Thermogravimetric analysis (TGA) was conducted using
an SDT Q600 apparatus from TA instruments with a
constant heating rate of 20 °C/min and in the temperature
range 30–500 °C. The experiment was run using an alu-
minum sample pan and a nitrogen flow rate of 100 mL/
min.
Oleic acid [3-({4-[(3-Oleamidopropyl)-dimethyl-amino]-
butyl}-dimethyl-amino)-propyl]-amide dibromide (5): Pale
yellow gel (9.3 g, 91% yield based on 1,4-dibromobutane).
1H NMR (500 MHz, CDCl3) d (ppm): 0.83 (t, J = 6.7 Hz,
6H), 1.18–1.28 (m, 40H), 1.50–1.56 (m, 4H), 1.91–1.97
(m, 12H), 1.99–2.05 (m, 4H), 2.21 (t, J = 7.6 Hz, 4H),
3.19 (s, 12H), 3.25-3.31 (m, 4H), 3.44–3.50 (m, 4H),
3.54–3.60 (m, 4H), 5.23–5.33 (m, 4H), 7.81 (s, 2H (NH).
13C NMR (125 MHz, CDCl3) d (ppm): 14.1, 19.6, 22.6,
22.9, 25.9, 27.2, 29.3, 29.4, 29.5, 29.7, 29.8, 31.8, 36.4,
51.4, 62.3, 63.2, 129.6, 129.9, 174.9. FTIR (KBr pellet) t
(cm-1) 3439 (tN–H, secondary amine), 2923 and 2851
(tC–H, aliphatic asymmetric and symmetric respectively),
1632 (amide I band), 1548 (amide II band). Anal. Calcd for
C50H100O2N4Br2 (949.16): C, 63.27; H, 10.62; N, 5.90.
Found: C, 63.21; H, 10.57; N, 5.87.
Long-Term Thermal Stability
Long-term thermal stability was assessed using a novel
approach based on an aging technique. Aqueous solutions
of gemini surfactants (1–6) were aged in a sealed tube for
10 days at 90 °C. NMR (1H, 13C) and FTIR instruments
were used to identify the changes in the structure of the
surfactants after aging.
Surface Properties
Oleic acid [3-({6-[(3-oleamidopropyl)-dimethyl-amino]-
hexyl}-dimethyl-amino)-propyl]-amide dibromide (6):
White solid (8.7 g, 93% yield based on 1,6-dibromohex-
ane). 1H NMR (500 MHz, CDCl3) d (ppm): 0.82 (t,
J = 6.7 Hz, 6H), 1.17–1.27 (m, 40H), 1.46–1.52 (m, 4H),
1.54–1.60 (m, 4H), 1.91–1.97 (m, 12H), 2.02–2.08 (m,
4H), 2.33 (t, J = 7.6 Hz, 4H), 3.26 (s, 12H), 3.33–3.39 (m,
4H), 3.53-3.59 (m, 4H), 3.69-3.75 (m, 4H), 5.23–5.33 (m,
Surface tensions were identified with the help of the pen-
dant drop method at 20 °C using Biolin Scientific Atten-
sion instrument. Water was used as the solvent for all
surface tension experiments. The reported data points of all
surface tension measurements are average equilibrium
values. The critical micelle concentration was estimated
from the break point in the plot of surface tension versus
concentration.
123

J Surfact Deterg
surfactant 1 has been also detected. The olefinic protons in
the spacer group [–N–CH2–CH = CH–CH2–N–] appeared
at d = 6.77–6.85 ppm which further confirmed the for-
mation of the gemini surfactant 1. According to 13C-NMR
spectra of the gemini surfactant (1), the terminal methyl
carbon [–(CH2)n–CH3)] resonated at d = 14.0 ppm and the
methylene carbons [–(CH2)n–CH3)] in the hydrophobic tail
resonated at d = 22.6–36.6 ppm. The two methyl carbons
of the tertiary nitrogen [–CH2–N–(CH3)2] that were res-
onated at d = 44.8 ppm in the intermediate (10) have
shifted downfield to d = 51.0 ppm as evidence of the
formation of the gemini surfactant 1. The two new peaks
that appeared at d = 62.6 ppm and 65.0 ppm correspond to
2 methylene groups connected with nitrogen [–CH2–N–
(CH3)2–CH2–]. The olefinic carbon in spacer group [–N–
CH2–CH = CH–CH2–N–] resonated at d = 130.2 ppm.
The carbonyl carbon (–CH2–C = O–NH–) peak was
detected at d = 175.3 ppm. In general, the NMR (1H and
13C) spectral data appeared to be compatible with the
proposed structures of the gemini surfactant 1. In FTIR
spectra of the gemini surfactant 1, a disappearance of the
hydroxyl group of fatty acid (7) (–CH2–C = O–OH) ran-
ged from 2400 to 3400 cm-1 and an existence of amide
(–CH2–C = O–NH) at 3441 cm-1 as well as a shifting of
the band of carbonyl stretching (–C = O–) from the region
of acid (–CH2–C = O–OH) at 1710 cm-1 to the region of
amide (–CH2–C = O–NH–) at 1641 cm-1 were observed.
Amide I band resonated at 1641 cm-1 and amide II band
resonated at 1555 cm-1 [38]. The two stretching vibrations
at 2922 cm-1 (CH aliphatic symmetric) and 2850 cm-1
(CH aliphatic asymmetric) were also detected which con-
firmed the formation of the gemini surfactant 1 [40–42].
Results and Discussion
The synthesis of amido-amine-based cationic gemini sur-
factants (1–6) was achieved using an improved method
outlined in scheme 1 [37]. The condensation of commer-
cially available carboxylic acid (7 and 8) with
3-(dimethylamino)-1-propylamine (9) generated the amide
intermediates (10 and 11). The reaction was followed by
quaternization reaction with halohydrocarbons (12–15)
yielding the desired amido-amine cationic gemini surfac-
tants (1–6) at high yield [38, 39].
The structures of the gemini surfactants and corre-
sponding intermediates were confirmed by characterization
techniques such as NMR, FTIR, and elemental analysis.
The six amido-amine-based cationic gemini surfactants
exhibited nearly the same peak pattern, therefore, we
highlight here the spectral characterization of gemini sur-
factant (1) and its intermediate (10) as examples. Accord-
ing to 1H-NMR spectra of the intermediate compound (10),
the terminal methyl protons [–(CH2)n–CH3)] resonated at
d = 0.83 ppm and the methylene protons [–(CH2)n–CH3)]
in the hydrophobic tail resonated at d = 1.15–1.25 ppm.
The disappearance of a hydroxyl proton in the carboxylic
acid (–CH2–C = O–OH) (8) at d = 10.25 ppm and the
appearance of the amide proton (–CH2–C = O–NH) (10)
at d = 6.99 ppm were observed. The appearance of the
methyl proton directly attached to the tertiary nitrogen
[–CH2–N–(CH3)2] at d = 2.30 confirmed the formation of
intermediate compound (10). According to 13C NMR
spectra of intermediate compound (10), the terminal
methyl carbon [–(CH2)n–CH3)] resonated at d = 14.0 ppm
and the methylene carbons [–(CH2)n–CH3)] in the
hydrophobic tail resonated at d = 22.6–36.8 ppm. The two
methyl carbon directly attached to the tertiary nitrogen
[–CH2–N–(CH3)2] resonated at d = 44.8 ppm. The
methylene carbon next to tertiary nitrogen [–CH2–CH2–N–
(CH3)2] in compound (10) resonated at d = 58.0 ppm. The
appearance of the carbonyl carbon of fatty acid (7) (–CH2–
C = O–OH) resonated at d = 180.4 ppm and then clear up
field shift of the same carbonyl carbon in amide (10)
(–CH2–C = O–NH–) at d = 173.3 ppm confirmed the
formation of intermediate (10). According to 1H-NMR
spectra of gemini surfactant (1), the terminal methyl pro-
tons [–(CH2)n–CH3)] resonated at d = 0.82 ppm and the
methylene protons [–(CH2)n–CH3)] in the hydrophobic tail
resonated at d = 1.16–1.26 ppm. The methyl protons
directly attached to the nitrogen [–CH2–N–(CH3)2] that
previously appeared at d = 2.30 ppm in intermediate (10)
has shifted downfield to d = 3.31 ppm in the gemini sur-
factant (1) [–CH2–N–(CH3)2–CH2–]. The downfield shift
of the amide proton (–CH2–C = O–NH) from
d = 6.99 ppm in compound 10 to d = 8.16 ppm in gemini
Thermal Stability of Gemini Surfactants (1–6)
Thermal stability is an essential property of surfactants for
various oilfield applications. A surfactant designed to be
used in surfactant flooding should be thermally stable at
high reservoir temperatures (C90 °C) because it may stay
inside the oil reservoir for many days. The high tempera-
ture in a reservoir can cause surfactant precipitation due to
thermal degradation and the surfactant ability to reduce
interfacial tension between water and oil can decrease
significantly.
Therefore, we investigated the short-term and long-term
thermal stability of the synthesized gemini surfactants
(1–6). TGA indicates excellent thermal stability of the
gemini surfactants (1–6) with no thermal degradation up to
200 °C (Fig. 2). The long-term thermal stability of the
gemini surfactants (1–6) was examined using a novel
approach based on an aging technique where the aqueous
solutions of surfactants were aged in a sealed tube at 90 °C
123

J Surfact Deterg
spacer group of 10 days aged sample of gemini surfactants
1 (Fig. 3) were also detected. Likewise, the methylene
protons in the spacer group of gemini surfactants 6 (Fig. 5)
equally appeared. The protons of methyl group directly
attached to quaternary nitrogen [–CH2–N?–(CH3)2–CH2–]
are clearly observed. In addition, the appearance of the
amide proton (–CH2–C = O–NH–) confirmed the survival
of gemini surfactants 1 and 6 under harsh conditions. An
additional peak at d = 4–5 ppm corresponds to residual
water [43]. According to 13C-NMR spectra of the 10 days
aged samples of gemini surfactants 1 and 6 (Fig. 4 and 6),
the methyl [–(CH2)n–CH3)] and methylene carbon in the
hydrophobic tail of gemini surfactants 1 and 6 were clearly
identified. The two methyl carbon [–CH2N?–(CH3)2–CH2–
] and two methylene carbon [–CH2–N?–(CH3)2–CH2–]
directly attached to the quaternary nitrogen were similarly
observed in both surfactants (1 and 6) (Figs. 4, 6). The
olefinic carbon in hydrophobic tail of gemini surfactant 6
(Fig. 6) as well as the olefinic carbon in spacer group of
gemini surfactant 1 (Fig. 4) were also detected. The car-
bonyl carbon of amide group [–CH2–C = O–NH] was
clearly shown in both surfactants. In general, the NMR (1H
and 13C) spectra of the aged samples of gemini surfactants
(1 and 6) confirmed that no structural changes occurred.
According to the FTIR spectra of samples of gemini sur-
factants aged during 10 days (1 and 6) (Figs. 7, 8), the two
clear stretching bands in the region of 2921 and 2850 cm-1
were detected and they correspond to aliphatic symmetric
CH and aliphatic-asymmetric CH, respectively. The car-
bonyl stretching and C–N stretching was also observed
which confirmed the structure of gemini surfactants (1 and
6) and demonstrated the thermal stability of amido-amine
Fig. 2 TGA curves of the gemini surfactants (1–6) under nitrogen
atmosphere
for 10 days. NMR (1H, 13C) and FTIR instruments were
used to study the change in the structure of the surfactants
after aging after different periods. Only FTIR and NMR
spectra of surfactants aged during 10 days are presented
here. The six amido-amine cationic gemini surfactants
(1–6) exhibited excellent long-term thermal stability with
no thermal degradation after 10 days aging. We highlight
here the spectral characterization of aged samples of
gemini surfactant 1 and 6 as examples. The 1H-NMR
spectra of the 10 days aged samples of the gemini surfac-
tants 1 and 6 (Figs. 3, 5) demonstrated the appearance of
the protons of the terminal methyl group [–(CH2)n–CH3)]
as well as protons of the methylene group [–(CH2)n–CH3)]
of the surfactant hydrophobic tail. The olefinic protons in
the hydrophobic tail of the gemini surfactants 6 (Fig. 5)
were also revealed. Similarly, the olefinic protons in the
Fig. 3 1H-NMR spectra of the
gemini surfactant (1) before and
after aging
123

J Surfact Deterg
Fig. 4 13C-NMR spectra of the
gemini surfactant (1) before and
after aging
Fig. 5 1H-NMR spectra of the gemini surfactant (6) before and after aging
cationic gemini surfactants. There was no cloudiness and
surfactant above CMC induced no change in the surface
tension. The surfactant 2 showed the highest surface ten-
sion while the surfactant 6 showed the lowest surface
tension at all investigated concentrations. The surface
properties can be related to the different chain lengths,
spacer lengths, spacer rigidities, and to the presence of
different counterions in the gemini surfactants.
phase separation before and after aging at 90 °C.
Surface Tension Measurements
The synthesized gemini surfactants (1–6) showed good
water solubility. Figures 9 and 10 show the surface tension
of all surfactants at different concentrations; derived sur-
face properties are given in Table 1. The surface tension
remarkably decreased with increasing surfactant concen-
tration up to the breakpoint at CMC. Further addition of
Figure 9 shows the effect of the spacer length and
rigidity on the surface tension of the gemini surfactants. By
comparing the surfactant 5 and 6, it was observed that the
surfactant with a larger spacer (6) showed a lower CMC
123

J Surfact Deterg
Fig. 6 13C-NMR spectra of the
gemini surfactant (6) before and
after aging
which could be associated with the hydrophobic nature of
the longer spacer [44]. The rigidity of spacer is another
important parameter in determining the aggregation mor-
phologies of the gemini surfactants. Surfactant 3 and sur-
factant 5 possess almost similar structures but the spacer of
surfactant 3 is more rigid compared to the surfactant 5. The
gemini surfactant 3 with more rigid spacer showed a higher
CMC and higher surface tension at CMC (cCMC). The
CMC and cCMC of gemini surfactant 3 were 1.58 9 10-4
mol L-1 and 35.67 mN m-1, respectively, which is much
higher as compared to the surfactant 5 that has a relatively
flexible spacer. The gemini surfactants containing rigid
spacer usually form vesicles. On the other hand, less rigid
gemini surfactants form mixtures of vesicles and micelles
[31]. The shape of aggregates depends on the packing
parameter of the surfactant.
Fig. 7 FTIR spectra of the gemini surfactant (1) before and after
aging
The surfactant chain length is another critical parameter
that affects the surface properties of surfactant. Figure 10
compares the surface tension of the gemini surfactants with
different chain lengths and spacer conformations. By
comparing the surfactants 1 and 3, the CMC and the cor-
responding cCMC decrease when the hydrophobic tail is
increased from 12 carbons (1) to 18 carbons (3). A similar
trend was observed with the surfactants 2 and 4, which also
have the same spacer and counterions but differ from each
other by the length of the hydrophobic tail.
The double bond in the spacer of the surfactant 1 and 3
was in trans conformation with bromide counterions while
the double bond in the spacer of surfactant 2 and 4 was in
cis conformation with chloride counterions. The CMC and
the cCMC of the surfactants 2 and 4 were higher as
Fig. 8 FTIR spectra of the gemini surfactant (6) before and after
aging
123

J Surfact Deterg
the surfactant 2 while the surfactant 6 showed the lowest
CMC and cCMC
.
The ability of gemini surfactants to lower the surface
tension of water (pCMC), the surface access (umax) at the
interface of air–water, as well as the surface area per
molecule (Amin) are given in Table 1; these parameters
were estimated following the literature [45]. The surface
area per molecule decreases by increasing the hydrophobic
tail and the spacer length, but it increases with spacer
rigidity. The surface access at the air–water interface
increases with hydrophobic tail length and the spacer
length. The CMC values of the synthesized gemini sur-
factants ranged from 0.077 mmol/L to 0.36 mmol/L which
are comparable with the reported values of a similar class
of gemini surfactants (0.008–12.5 mmol/L) [38]. Similarly,
Fig. 9 Surface tension versus concentration for surfactants with
different spacer lengths and spacer rigidities
cCMC
of
the
synthesized
gemini
surfactants
(30.38–38.12 mN m-1
)
were in agreement with the
reported values (22.76–41.07 mN m-1) [38]. It is note-
worthy that the pCMC decreased with increasing rigidity
and increased with increasing spacer length (5 and 6). A
similar trend was also observed by Chauhan et al. using
pyridinium based cationic gemini surfactants [46]. The
umax of the synthesized gemini surfactants were increased
by increasing tail length, spacer flexibility, and spacer
length. Geng et al. also observed a similar change in umax
by increasing spacer and chain length using di-hydroxyl-
sulfate-betaine-type zwitterionic gemini surfactants [47].
The literature values of the surface area per molecule were
also found to be in agreement with the synthesized gemini
surfactants i.e. Amin decreased with increasing tail length,
spacer flexibility, and spacer length [48]. In summary, the
lowest CMC and cCMC was observed for surfactant 6
containing a longer tail and large spacer with low rigidity.
Fig. 10 Surface tension versus concentration for surfactants with
different chain lengths and spacer conformations
Conclusions
compared to the analogous surfactant 1 and 3 respectively.
The difference of surface properties between the surfac-
tants 1, 2 and 3, 4 may be associated with the different
conformation of the spacer double bond and counters ions.
It has been reported previously that the presence of dif-
ferent counterions in the spacer can alter the CMC value
[30]. In summary, high CMC and cCMC was observed for
Amido-amine-based cationic gemini surfactants (1–6) have
been synthesized with excellent yields and high purity from
the commercially available carboxylic acids. The short-
term and long-term thermal stabilities, as well as the sur-
face tensions, were examined. Thermogravimetric analysis
demonstrated excellent thermal stability of the synthesized
Table 1 Surface properties of
the gemini surfactants (1–6)
Surfactant CMC (mol L-1
)
cCMC (mN m-1
)
pCMC (mN m-1
)
umax 9 106 (mol m-2
)
Amin (nm2)
1
2
3
4
5
6
2.56 9 10-4
3.61 9 10-4
1.58 9 10-4
2.91 9 10-4
1.05 9 10-4
0.77 9 10-4
36.23
38.12
35.67
37.23
32.92
30.34
35.77
33.88
36.33
34.77
39.08
41.66
1.81
1.60
1.92
1.64
2.26
2.38
0.91
1.05
0.86
1.01
0.73
0.70
123

J Surfact Deterg
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S. M. Shakil Hussain accomplished his Ph.D (2009) in synthetic
organic chemistry in collaboration with Queen’s University, Canada,
and University of Karachi. He had been a Postdoctoral Fellow at
Queen’s University, Canada. Currently, he is working as a Research
Scientist in Center for Integrative Petroleum Research at the King
Fahd University of Petroleum and Minerals (KFUPM), Saudi Arabia.
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Muhammad Shahzad Kamal received his B.Sc. (2008) in chemical
engineering and M.Sc. (2010) in polymer engineering from UET
Lahore. He completed his Ph.D. in chemical engineering at the King
Fahd University of Petroleum and Minerals (KFUPM), Saudi Arabia.
Currently, he is working as a Research Engineer in Center for
Integrative Petroleum Research at KFUPM.
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Dr. Bassam El Ali is a Professor of Catalysis and Organic Chemistry
at the Chemistry Department at the King Fahd University of
Petroleum and Minerals (KFUPM). He is the Managing Editor
(Editor-in-Chief) of the Arabian Journal for Science and Engineering,
a journal published by Springer. He has published more than 80
research articles in refereed journals, six patents, 12 book chapters,
and one book published by McGraw-Hill. He received from KFUPM
the Distinguished Research Award from KFUPM, the Distinguished
Teaching Award, and the Distinguished Best Short Course Award.
42. El-Lateef HMA, Abo-Riya MA, Tantawy AH. Empirical and
quantum chemical studies on the corrosion inhibition perfor-
mance of some novel synthesized cationic gemini surfactants on
carbon steel pipelines in acid pickling processes. Corros Sci.
2016;108:94–110.
43. Fulmer GR, Miller AJ, Sherden NH, Gottlieb HE, Nudelman A,
Stoltz BM, Bercaw JE, Goldberg KI. NMR chemical shifts of
trace impurities: common laboratory solvents, organics, and gases
in deuterated solvents relevant to the organometallic chemist.
Organometallics. 2010;29(9):2176–9.
Abdullah S. Sultan received his B.Sc. (2002) and M.Sc (2005) in
chemical engineering from the King Fahd University of Petroleum
and Minerals (KFUPM), Saudi Arabia. He completed Ph.D. (2009) in
petroleum engineering from Texas A&M University, USA, Texas.
Currently, he is an Assistant Professor in the Department of
Petroleum Engineering at KFUPM.
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