Synthesis and surface properties of N,N-dimethyl-N-dodecyl polyoxyethylene amine-based surfactants: Amine oxide, betaine and sulfobetaine

Article abstract of DOI:10.1007/s11743-013-1540-7

Nonionic-zwitterionic hybrid surfactants, namely N,N-dimethyl-N-dodecyl polyoxyethylene (3) amine oxide, and the corresponding betaine and/or sulfobetaine, have been synthesized. Their molecule structures were characterized by means of electrospray ionization mass spectrometry and ¹H nuclear magnetic resonance. Compared to the structurally related conventional amine oxide, betaine and sulfobetaine, the critical micelle concentrations of the three hybrid surfactants are one order of magnitude smaller than those of traditional ones. The polyoxyethylene segment between the hydrophilic head group and the hydrophobic tail makes the surface activities of the hybrid surfactants superior to their structure-related counterparts.

Full text of DOI:10.1007/s11743-013-1540-7

J Surfact Deterg
DOI 10.1007/s11743-013-1540-7
ORIGINAL ARTICLE
Synthesis and Surface Properties of N,N-Dimethyl-N-dodecyl
Polyoxyethylene Amine-Based Surfactants: Amine Oxide,
Betaine and Sulfobetaine
•
Liya Hou Huinian Zhang Hui Chen Qibo Xia
•
•
•
•
Dongyang Huang Li Meng Xuefeng Liu
•
Received: 9 June 2013 / Accepted: 14 October 2013
Ó AOCS 2013
Abstract Nonionic–zwitterionic hybrid surfactants,
namely N,N-dimethyl-N-dodecyl polyoxyethylene (3)
amine oxide, and the corresponding betaine and/or sulf-
obetaine, have been synthesized. Their molecule structures
were characterized by means of electrospray ionization
mass spectrometry and 1H nuclear magnetic resonance.
Compared to the structurally related conventional amine
oxide, betaine and sulfobetaine, the critical micelle con-
centrations of the three hybrid surfactants are one order of
magnitude smaller than those of traditional ones. The
polyoxyethylene segment between the hydrophilic head
group and the hydrophobic tail makes the surface activities
of the hybrid surfactants superior to their structure-related
counterparts.
Introduction
Ethoxylated surfactants, especially those having a chain
segment of polyoxyethylene between hydrophilic head
group and hydrophobic tail, are called hybrid surfactants
[1, 2]. The traditional representatives are alcohol ether
sulfates (AES) [3, 4], alcohol ether carboxylates (AEC) [5]
and sodium alkyl-benzyl polyoxyethylenated propane sul-
fonates (ABEPS) [2]. These nonionic–ionic hybrid sur-
factants always present combined properties of nonionic
and ionic surfactants [2] and have better electrolyte and
water hardness tolerance. However, the literature reports
on hybrid surfactants are mainly on nonionic–anionic sur-
factants, the synthesis and the surface activity of nonionic–
zwitterionic hybrid surfactants have seldom been reported
up till now.
Keywords Hybrid surfactant Á N,N-Dimethyl-N-
dodecyl polyoxyethylene (3) amine Á Amine oxide Á
Betaine Á Sulfobetaine
One US patent [6] reveals the synthesis of N,N-dime-
thyl-N-alkyl polyoxyethylene amine and the corresponding
amine oxides from commercial available AES. One Japa-
nese patent [7] reveals the synthesis of N,N-dimethyl-N-
alkyl polyoxyethylene amine-based betaines from com-
mercial available fatty alcohols. However, the typical
physicochemical properties of these hybrid surfactants,
such as the critical micelle concentration (CMC), the sur-
face tension at CMC (cCMC), the adsorption efficiency
(pC20), the surface pressure at the CMC (PCMC), the
maximum surface excess (Cm), the minimum cross-sec-
tional area (Amin) have not been reported. Due to the length
distribution of the alkyl tail and the polyoxyethylene seg-
ment in commercially available AES and polyethoxylated
fatty alcohols, the corresponding amine oxides and betaines
are mixtures of different molecules. In order to get the
typical surface activity parameters of nonionic–zwitter-
ionic hybrid surfactants and to compare them with struc-
ture-related traditional ones, three hybrid surfactants,
Electronic supplementary material The online version of this
article (doi:10.1007/s11743-013-1540-7) contains supplementary
material, which is available to authorized users.
L. Hou Á H. Zhang Á H. Chen Á Q. Xia Á D. Huang Á L. Meng
School of Chemical and Material Engineering,
Jiangnan University, Wuxi 214122, China
X. Liu (&)
The Key Laboratory of Food Colloids and Biotechnology,
Ministry of Education, School of Chemical and Material
Engineering, Jiangnan University, Wuxi 214122, China
e-mail: xfliu@jiangnan.edu.cn
123

J Surfact Deterg
obtained after the solvent was removed by rotary evapo-
rator under reduced pressure. Finally, the crude C12EO3
was purified by silica gel column chromatography. A
mixture of mineral ether–ethyl acetate (volume ratio 2:1)
was used as the eluent. A colorless liquid of C12EO3 was
obtained with a yield of 61 %.
Synthesis of C12EO3A
HSO3Cl (12.82 g) was added dropwise to C12EO3 (31.8 g)
at 25–30 °C, after that, the system was aged for 0.5 h.
After being neutralized by 15 % NaOH aqueous solution,
the product of C12EO3SD (Scheme 1, Step 2) was obtained.
According to the method in [6, 8], a light yellow oil liquid
of C12EO3A (Scheme 1, Step 3) was synthesized with a
yield of 94 %.
Scheme 1 The synthesis routes of C12EO3AO, C12EO3Be and
C12EO3SBe
Synthesis of C12EO3AO
namely N,N-dimethyl-N-dodecyl polyoxyethylene (3)
As shown in Scheme 1 (Step 4), C12EO3A (34.51 g) was
oxidized by 30 % H2O2 (45.37 g, dropwise) at 55–65 °C
with a trace amount of citric acid. The crude C12EO3AO
was extracted by CHCl3 and was purified by alumina
column chromatography. A mixture of CHCl3–CH3OH
(volume ratio 60:1) was used as the eluent. C12EO3AO was
obtained with a yield of 91 %.
amine-based amine oxide (C12EO3AO), and the corre-
sponding
betaine
(C12EO3Be)
and
sulfobetaine
(C12EO3SBe) were synthesized (see Scheme 1). The
molecular structures of the main intermediates and objec-
tive surfactants were confirmed by means of electrospray
1
ionization mass spectrometry (ESI–MS), and H nuclear
magnetic resonance (1H NMR), respectively. The typical
physicochemical properties of CMC, cCMC, pC20, Cm, and
Amin were determined and calculated from the results of c-
logc (concentration of surfactant) curves.
Synthesis of C12EO3Be
In a 250-mL round-bottom flask, C12EO3A (17.31 g) and
sodium chloroacetate (5.83 g) were dissolved in 100 mL
methanol–H2O (volume ratio 1:1), the pH of the above
system was adjusted to 7–8 by NaHCO3. The reaction was
carried out at 70 °C for 2 h, then 80 °C for a further 2 h. The
solvent was removed by rotary evaporation under reduced
pressure. The residue was dried in a vacuum oven at 70 °C.
The dried residue was dissolved in isopropanol, and inor-
ganic salts were filtered off. The crude C12EO3Be was
purified by silica gel column chromatography. A mixture of
ethyl acetate–CH3OH (volume ratio 3:1) was used as the
eluent. C12EO3Be was obtained with a yield of 89 %.
Experimental Section
Materials
1-Bromododecane (Br-C12), triethylene glycol (EO3),
sodium hydride (NaH), dimethylamine (DMA), sodium
chloroacetate, 1,3-propanesultone and H2O2 (30 wt%)
were used as received without further purification. Deion-
ized water was obtained from a Millipore Milli-Q water
purification system (Millipore, USA).
Synthesis of C12EO3SBe
Synthesis of C12EO3
In a 250-mL round-bottom flask, C12EO3A (17.31 g) was
dissolved in 80 mL acetone in an ice-water bath, then
6.72 g 1,3-propanesultone in 80 mL acetone was added
dropwise to the flask with stirring. After the addition of
1,3-propanesultone, the temperature of the system was
elevated to room temperature naturally. The reaction was
carried out for 5 days at room temperature with stirring.
The white crude C12EO3SBe was purified by silica gel
column chromatography. A mixture of CHCl3–CH3OH
As shown in Scheme 1 (Step 1), NaH (4.80 g) and EO3
(72.08 g) were added to a 250-mL three-neck round-bot-
tom flask. Br-C12 (26.54 g) was added drop wise to the
flask with stirring at 100 °C. The reaction was protected by
N2 and completed in 48 h. Then, 80 mL ethyl acetate was
added to the flask. The excess EO3 and the by-product
polyethylene glycol were washed off using saturated NaCl
aqueous solution. The faint yellow crude product was
123

J Surfact Deterg
100
65.4
65.2
65.0
64.8
64.6
64.4
64.2
64.0
56
55
54
53
52
362.3
363.3
C12EO3AO M=361 g mol-1
80
60
40
20
C12EO3Be
C12EO3AO
723.6
γ
724.7
384.3
400
725.7
0
300
500
600
700
800
0
2
4
6
8
10
0
1
2
3
4
5
m/z
t (min)
Fig. 1 The ESI–MS spectrum of C12EO3AO with positive ion mode
Fig. 3 The plot of surface tension (c in mN m-1) versus drop surface
aging time (t in min) for C12EO3AO and C12EO3Be aqueous solution
at 25 °C, the concentration of the surfactant was 3.0 9 10-5 mol L-1
time t (min) (Fig. 3). Finally, the drop volume was cor-
rected by the Harkins–Brown method [9]. The surface
activity parameters, such as the CMC, the c at CMC
(cCMC), the adsorption efficiency (pC20), the surface pres-
sure at the CMC (PCMC), the maximum surface excess
(Cm), and the minimum cross-sectional area (Amin) were
obtained or calculated [10] from the c-logc curves (Fig. 4).
e) C12EO3SBe
d) C12EO3Be
c) C12EO3AO
b) C12EO3A
a) C12EO3
5
4
3
2
1
0
Results and Discussion
(ppm)
Fig. 2 The 1H NMR spectrum of
c C12EO3AO, d C12EO3Be and e C12EO3SBe
a
C12EO3,
b
C12EO3A,
Structural Characterization of C12EO3, C12EO3A,
C12EO3AO, C12EO3Be and C12EO3SBe
The ESI–MS technique was employed to measure the
molecule weight of the products in this work. The ESI–MS
spectrum of C12EO3AO is shown in Fig. 1. With the
positive ion mode, various ions of [M?H]?, [M?Na]? and
[2M?H]? were detected. The ESI–MS spectra of the rest
samples (surfactants of C12EO3Be and C12EO3SBe, inter-
mediates of C12EO3 and C12EO3A) can be seen in Fig-
ure 1S as ESM. The results obtained of the mass-to-charge
ratio (m/z) for the three hybrid surfactants match well with
the calculated results. The interpretation of the ESI–MS
spectra can be seen in detail in the ESM.
(volume ratio 4:1) was used as the eluent. C12EO3SBe was
obtained with a yield of 76 %.
Analytical Methods
The ESI–MS measurements were carried out using a Maldi
Synapt Q-TOF MS (Waters) in the positive ion mode
(Fig. 1, ESM Figure 1S). The 1H NMR spectra were
obtained with an Avance III 400 MHz digital NMR spec-
trometer (Bruker) using CDCl3 as solvent (Fig. 2). And the
NMR peak of CDCl3 (d = 7.26 ppm) was used as the
reference in determining the chemical shifts (d, ppm) of the
protons.
In order to obtain the detailed molecule structural
1
information, the H NMR spectra of the objective com-
pound were obtained (Fig. 2). C12EO3 1H NMR [400 MHz,
(CDCl3)] d = 0.86–0.90 (t, 3H, –CH3), d = 1.26–1.29 (m,
18H, –(CH2)9–), d = 1.54–1.61 (m, 2H, C10–CH2–CH2–
O), d = 2.66 (s, 1H, –OH), d = 3.43–3.47 (t, 2H, C10–
CH2–CH2–O), d = 3.58–3.74 (m, 12H, C12–(OC2H4)3–).
C12EO3A 1H NMR [400 MHz, (CDCl3)] d = 0.86–0.90 (t,
3H, –CH3), d = 1.26–1.29 (m, 18H, –(CH2)9–),
The surface tension (c, mN m-1) measurements were
conducted with a drop volume tensiometer at 25 0.1 °C.
The outer radius of the glass capillary was 0.66 mm.
During the procedure of c measurements, a sufficient aging
time was necessary for the pendant drop surface to reach an
equilibrium state. The aging time of the drop surface was
determined by the plot of c versus the drop detachment
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J Surfact Deterg
60
55
50
45
40
35
30
25
C10H21–CH2–CH2–O), d = 3.34 (s, 6H, N–(CH3)2),
d = 3.41–3.44 (t, 2H, –CH2–N), d = 3.55–3.56 (t, 2H,
C11–CH2–O), d = 3.60–3.61 (t, 2H, O–CH2–CH2N),
d = 3.62–3.65 (m, 4H, C12–O–C2H4–O), d = 3.88 (s, 2H,
N–CH2COO), d = 3.93–3.96 (m, 4H, O–C2H4–OC2H4N).
C12EO3SBe 1H NMR [400 MHz, (CDCl3)] d = 0.86–0.90
(t, 3H, –CH3), d = 1.29 (m, 18H, –(CH2)9–),
d = 1.52–1.57 (m, 2H, C10H21–CH2–CH2–O), d = 2.27
(m, 2H, –CH2–CH2–CH2–S), d = 2.90 (t, 2H, –CH2–CH2–
CH2–S), d = 3.28 (s, 6H, N–(CH3)2), d = 3.43–3.45 (t,
2H, –CH2–N), d = 3.50–3.55 (t, 2H, C11–CH2–O),
d = 3.57–3.67 (m, 8H, C12H25–(OC2H4)2–O), d = 3.79 (t,
2H, O–CH2–CH2N), d = 3.95 (t, 2H, –CH2–S).
A
C12EO3AO
C12EO3SBe
C12EO3Be
-5.0
-4.5
-4.0
-3.5
-3.0
-2.5
log c
65
60
55
50
45
40
35
30
The Surface Activity Parameters of C12EO3AO,
C12EO3Be and C12EO3SBe
B
C12AO
C12SBe
C12Be
As shown in Fig. 3, the
c
of the solution
(3.0 9 10-5 mol L-1) decreases with the drop detachment
time increasing with breakpoints at t & 3 min (for
C12EO3Be) and t & 6 min (for C12EO3AO), respectively.
The result of C12EO3SBe is similar to that of C12EO3Be.
The change of c is \ 0.1 mN m-1 in the region of
t [ 10 min. Under this condition, the c could be considered
as an equilibrium surface tension. The lower concentration
sample solution needs longer aging time for the drop sur-
face to reach the equilibrium state. Thus, in order to make
the drop surfaces reach the equilibrium state, all the drops
of the surfactant solutions were aged for at least 10 min.
The plots of the c versus logc for the hybrid surfactants
in this work and the corresponding traditional surfactants
are shown in Fig. 4. One can see that the c gradually
decreases to a plateau region with the surfactant concen-
tration increasing. A decrease in surface tension indicates
that the surfactant molecules adsorbed at the air-solution
interfaces. The break point appearing in the c-logc curves
suggests the formation of micelles in aqueous solutions.
Here, it is worth mentioning that no evidence of surface
tension minima appears in the c-logc curves [11]. The
surface activity parameters, such as CMC, cCMC, pC20,
-3.5
-3.0
-2.5
-2.0
log c
Fig. 4 The plots of the surface tension (c in mN m-1) versus
logc (concentration of surfactant in mol L-1) at 25 °C
d = 1.56–1.59 (m, 2H, C10–CH2–CH2–O), d = 2.26 (s,
6H, N–(CH3)2), d = 2.49–2.52 (t, 2H, –CH2–N),
d = 3.43–3.46 (t, 2H, C11–CH2 –O), d = 3.57–3.66 (m,
10H, C12–(OC2H4)2–OCH2–). C12EO3AO 1H NMR
[400 MHz, (CDCl3)] d = 0.86–0.90 (t, 3H, –CH3),
d = 1.26–1.29 (m, 18H, –(CH2)9–), d = 1.55–1.59 (m, 2H,
C10–CH2–CH2–O), d = 3.25 (s, 6H, N–(CH3)2),
d = 3.40–3.44 (t, 2H, C11–CH2–O), d = 3.48–3.52 (t, 2H,
–CH2–N), d = 3.55–3.65 (m, 8H, C12–(OC2H4)2–O),
d = 4.00 (t, 2H, –O–CH2CH2N). C12EO3Be 1H NMR
[400 MHz, (CDCl3)] d = 0.86–0.89 (t, 3H, –CH3),
d = 1.26 (m, 18H, –(CH2)9–), d = 1.52–1.57 (m, 2H,
P
CMC, Cm and Amin were obtained and/or calculated [10]
from the c-logc curves and are listed in Table 1.
Table 1 The calculated parameters of surfactants from c-logc curves at 25 °C
C12EO3AO
C12AO
C12EO3Be
C12Be
C12EO3SBe
C12SBe
CMC (mol L-1
)
1.32 9 10-4
29.66
1.53 9 10-3
34.15
2.30 9 10-4
36.24
3.42 9 10-3
36.79
2.25 9 10-4
38.39
3.38 9 10-3
40.40
cCMC (mN m-1
)
PCMC (mN m-1
)
42.36
37.87
35.78
35.23
33.63
31.62
pC20
Cm (mol cm-2
Amin (m2)
4.52
5.02 9 10-6
3.31 9 10-19
3.55
4.71 9 10-6
3.53 9 10-19
4.28
4.74 9 10-6
3.50 9 10-19
3.09
4.52 9 10-6
3.68 9 10-19
4.29
3.82 9 10-6
4.35 9 10-19
2.99
4.49 9 10-6
3.70 9 10-19
)
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(C12AO) is 1.18 9 10-3 mol L-1 (ring method) [12], for N,N-
dimethyl-N-dodecyl betaine (C12Be) 2.00 9 10-3 mol L-1
(ring method) [13], and for N,N-dimethyl-N-dodecyl sulfobe-
taine (C12SBe) is 2.20 9 10-3 mol L-1 (maximum bubble
pressure method) [14], respectively. As can be seen in Table 1,
the CMC values of C12AO, C12Be and C12SBe in this work
match well with those in the literature [12–14] despite the dif-
ference in the c determination methods. All the CMC values of
the hybrid surfactants in this work fall within the 10-4 mol L-1
range, which is one order of magnitude smaller than those of
structure related traditional surfactants. The similar relations
hold true for sodium dodecyl sulfate and dodecyl polyoxyeth-
ylene sulfates [2, 15]. It could be attributed to the hydrophilicity
of the hybrid surfactants in this work ‘continuously’ increasing
from hydrophobic (C12) to less hydrophobic/less hydrophilic
(EO3) then to hydrophilic (AO, Be, and SBe). As regards the
change in the hydrophilicity at the water–air interface, one can
argue that it changes from hydrophobic (air) over a less
hydrophobic/less hydrophilic interfacial zone (EO3) between
the two bulk phases to hydrophilic (water) [1]. However, the
hydrophilicity of the structure-related counterparts changes
‘discontinuously’ from hydrophobic tails to hydrophilic head
groups without a less hydrophobic/less hydrophilic transition
zone (EO3), which, in turn, explains the higher surface activity
of the hybrid surfactants in this work.
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If one looks at the structure difference among the hybrid
surfactants in this work, one sees the main structure dif-
ference lies in the head groups of AO, Be and SBe. Due to
AO being a totally non-ionic head group, it has the smallest
hydrophilicity among these three head groups. Be and SBe
are zwitterionic head groups, possessing higher hydrophi-
licity than that of AO. However, the head group of Be is
more hydrophilic than the SBe ones [14]. The hydrophilic
difference of the head groups leads to the difference in the
CMC values. The order of the CMC values for the hybrid
surfactants in this work is CMCAO \ CMCSBe \ CMCBe,
a similar relation can be observed in structure related un-
ethoxylated ones. It could be attributed to the hydrophilic
difference of the head groups [14].
Author Biographies
Liya Hou is a graduate student, majoring in applied chemistry at the
School of Chemical and Material Engineering, Jiangnan University,
Wuxi, People’s Republic of China.
Acknowledgments This work was jointly supported by the National
Natural Science Foundation of China under Grant No. 21071065, the
Scientific Research Foundation for the Returned Overseas Chinese
Scholars (2011), State Education Ministry, and Qinlan Project (2010)
of Jiangsu Province.
Huinian Zhang is a graduate student, majoring in applied chemistry
at the School of Chemical and Material Engineering, Jiangnan
University, Wuxi, People’s Republic of China.
Hui Chen is a graduate student, majoring in applied chemistry at the
School of Chemical and Material Engineering, Jiangnan University,
Wuxi, People’s Republic of China.
References
Qibo Xia is a graduate student, majoring in applied chemistry at the
School of Chemical and Material Engineering, Jiangnan University,
Wuxi, People’s Republic of China.
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Dongyang Huang is a undergraduate student, majoring in applied
chemistry in the School of Chemical and Material Engineering,
Jiangnan University, Wuxi, People’s Republic of China.
Xuefeng Liu received his M.Sc. degree from Wuxi University of
Light Industry, and his Ph.D. from Jiangnan University in China. He
is
a professor at the Key Laboratory of Food Colloids and
Biotechnology, Ministry of Education, and the Chairman of the
Department of Applied Chemistry, School of Chemical and Material
Engineering, Jiangnan University, Wuxi, People’s Republic of China.
His research field is colloid and interface chemistry.
Li Meng is a undergraduate student, majoring in applied chemistry in
the School of Chemical and Material Engineering, Jiangnan Univer-
sity, Wuxi, People’s Republic of China.
123