Synthesis and properties of dodecyldiethoxylamine oxide

Article abstract of DOI:10.1007/s11743-013-1460-6

Dodecyldiethoxylamine oxide (DDEAO) was synthesized by the reaction of dodecyldiethoxylamine with hydrogen peroxide in water as the solvent. Surface activity, wetting ability and emulsifying capacity were investigated and compared with that of dodecyldimethylamine oxide (DDMAO). Results indicate that the critical micelle concentration (CMC) of DDEAO is lower than that of DDMAO, while its surface tension at CMC (γ_CMC) is slightly higher. The wetting ability of DDEAO is similar to that of DDMAO. For its capacity of emulsifying liquid paraffin, DDEAO is found to be better than DDMAO, but it is the opposite for emulsifying soybean oil. The foaming properties and thickening function of DDEAO in mixtures with alcohol ether sulfate and alkylbenzene sulfonate were also studied. As expected, complex surfactant systems exhibit good foaming ability and DDEAO exhibits a good thickening function.

Full text of DOI:10.1007/s11743-013-1460-6

J Surfact Deterg
DOI 10.1007/s11743-013-1460-6
ORIGINAL ARTICLE
Synthesis and Properties of Dodecyldiethoxylamine Oxide
•
Ruitao Wang Yunling Li Qiuxiao Li
•
Received: 26 November 2012 / Accepted: 11 February 2013
Ó AOCS 2013
Abstract Dodecyldiethoxylamine oxide (DDEAO) was
synthesized by the reaction of dodecyldiethoxylamine with
hydrogen peroxide in water as the solvent. Surface activity,
wetting ability and emulsifying capacity were investigated
and compared with that of dodecyldimethylamine oxide
(DDMAO). Results indicate that the critical micelle con-
centration (CMC) of DDEAO is lower than that of
DDMAO, while its surface tension at CMC (cCMC) is
slightly higher. The wetting ability of DDEAO is similar to
that of DDMAO. For its capacity of emulsifying liquid
paraffin, DDEAO is found to be better than DDMAO, but it
is the opposite for emulsifying soybean oil. The foaming
properties and thickening function of DDEAO in mixtures
with alcohol ether sulfate and alkylbenzene sulfonate were
also studied. As expected, complex surfactant systems
exhibit good foaming ability and DDEAO exhibits a good
thickening function.
Introduction
Amine oxide surfactants show nonionic characteristic in
neutral or alkaline solution, and demonstrate cationic
behavior in acid solution. They show less irritation to the
skin, high foaming properties and an excellent thickening
function [1–3]. These surfactants are widely used in
detergents, shampoos, cosmetics and textile auxiliaries
based on their characteristics and advantages [2, 3]. Sur-
factant mixtures often behave synergistically and provide
more desirable properties than single surfactants [4–7]. So
amine oxides are usually used together with other
surfactants.
Among amine oxides, dodecyldimethylamine oxide
(DDMAO) is the most widely used surfactant and has been
extensively researched [8–10]. Mixtures of DDMAO and
sodium dodecylsulfate (SDS) or dodecyltrimethyl ammo-
nium bromide (DTAB) have been widely studied. Results
reported have shown good synergistic effects of mixed
solutions [11, 12]. Hydroxyl groups connected to surfactant
molecules often show advantageous properties such as a
better water-solubility, low CMC, highly favorable com-
patibility with other surfactants and so on [13]. Conse-
quently, amine oxide surfactants containing hydroxyl
groups not only retain the superior performance of amine
oxide, but also can achieve more than the expected
performance.
Keywords Amine oxide ꢀ Synthesis ꢀ Surface activity ꢀ
Properties
In this paper, dodecyldiethoxylamine oxide (DDEAO)
containing hydroxyl groups was synthesized. The synthesis
route and chemical structure are shown in Scheme 1. The
pH of DDEAO (the weight concentration is 1 %) is 6.0 in
aqueous media. The surface activity, wetting ability and
emulsifying capacity of DDEAO were investigated and
compared to those of dodecyldimethylamine oxide. The
foaming properties and the thickening function of DDEAO
Electronic supplementary material The online version of this
article (doi:10.1007/s11743-013-1460-6) contains supplementary
material, which is available to authorized users.
R. Wang ꢀ Y. Li (&) ꢀ Q. Li
China Research Institute of Daily Chemical Industry,
34# Wenyuan Str., Taiyuan 030001, Shanxi Province,
People’s Republic of China
e-mail: lyunl0068@sina.com
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J Surfact Deterg
4.06 (m, 4H, 29–CH2–CH2–OH), 4.26–5.31 (s, 2H,
29–CH2–CH2–OH).
Measurement of Properties
Surface Activity
The surface tensions of the DDEAO and DDMAO were
measured at 25 0.2 °C from a series of aqueous solu-
tions with a platinum ring tensiometer. The surface tension
of double-distilled water, 72.0 0.3 mN/m, was used for
the calibration purposes. Surfactant solutions were pre-
pared with the double-distilled water. The samples were
stabilized for 10 min in the instrument before measure-
ments were taken.
Scheme 1 Synthesis route of dodecyldiethoxylamine oxide
mixed with alcohol ether sulfate and alkyl benzene sulfo-
nate in complex systems were also measured.
Wetting Ability
Experimental
The wetting ability was measured according to the canvas
descending method [14]. A canvas disk was immersed in
surfactant solution at room temperature, after some time,
the disk was permeated by surfactant solution and started to
sink. The wetting ability is determined by this period from
immersion to sinking. The shorter the wetting time, the
better is the wetting ability. The wetting ability was
determined as the average value from five measurements.
Materials and Instruments
Dodecyldiethoxylamine was synthesized from dodecan-
amine and ethylene oxide. Dodecyldimethylamine oxide,
sodium alcohol ether sulfate (AES) and dodecylbenzene-
sulfonate (LAS) were from China Research Institute of
Daily Chemical Industry. Hydrogen peroxide (30 wt%) and
Liquid paraffin were purchased from Tianjin University
Chemical Reagents Co.
Emulsifying Capacity
Surface activity was studied using a Kru¨ss K12 Pro-
cessor Tensiometer. Foaming properties were measured
using a Ross-Miles apparatus. Viscosities were measured
using a NDJ-79 rotating viscometer.
Emulsifying capacity was measured in a 100-ml glass
cylinder with a stopper at room temperature [15]. First,
40 ml of liquid paraffin or soybean oil and then 40 ml of a
series of surfactant solutions at different concentrations
was poured into a 100-ml cylinder. The stopper was placed
in the cylinder, and it was shaken up and down five times
then left to stand for 1 min. The experiment was repeated
five times, and the time for the separation of 10 ml water
was the emulsifying capacity. The longer the time for the
separation of 10 ml water, the better is the emulsifying
capacity.
Synthesis of DDEAO
In a four-necked flask, 0.1 mol dodecyldiethoxylamine was
put into 27.5 ml water. Then, 0.12 mol hydrogen peroxide
(diluted to 10 wt%) was added dropwise into the four-
necked flask at 75–80 °C for 40–60 min with continuous
stirred. The reaction was maintained for 4 h at 80–85 °C.
The active content was about 30 wt%. The molecular
structures of DDEAO were characterized by IR (FTLA200-
104, Boman, Canada) and 1H NMR (Avance III 400 MHz,
Bruker, USA). IR spectra of DDEAO showed absorption
bands at 3,274, 3,385 cm-1 (–OH stretching), 2,919,
2,851 cm-1 (C–H stretching), 1,467 cm-1 (C–H bending),
1,075 cm-1 (C–N stretching), 1,047 cm-1 (C–O stretch-
ing), and 726 cm-1 (C–H rocking). 1H NMR (CDCl3,
ppm): d 0.87 (t, 3H, CH3–(CH2)9–CH2–CH2–N), 1.25
(d, 18H, CH3–(CH2)9–CH2–CH2–N), 1.63 (s, 2H, CH3–
(CH2)9–CH2–CH2–N), 3.32 (m, 2H, CH3–(CH2)9–CH2–
CH2–N), 3.47 (m, 4H, HO–CH2–CH2–N–CH2–CH2–OH),
Foaming Properties
The foaming properties were measured by the Ross-Miles
method at 50 °C [16]. A 50-ml sample of 2.5 g/l surfactant
solution was placed in the bottom of a flask and 500 ml of
the same solution in a funnel was allowed to fall into the
flask from the top. After solution had run out of the funnel,
the time and foam volume were recorded at 30 s, 5 and
10 min. Foaming ability was determined by the foam
volume after 30 s. Foam stability was determined by
comparing the foam volumes after 10 min and 30 s in the
Ross-Miles apparatus.
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65
60
55
50
45
40
35
30
25
20
Table 1 Surface properties of DDEAO and DDMAO at 25 °C
DDMAO
DDEAO
Surfactant
CMC
(mM)
cCMC
(mN/m)
Umax
Amin
(A )
pC20
´
2
˚
(lmol/cm2)
DDMAO
DDEAO
0.75
0.38
23.9
25.4
4.97
5.20
33.4
31.9
4.17
4.39
obviously lower than that of DDMAO, which can be
ascribed to the hydroxyethyl group of DDEAO giving a
higher steric hindrance than the methyl of DDMAO and the
better solubility of DDEAO. This result indicates that the
surface activity of DDEAO is somewhat superior to that of
DDMAO. For DDEAO, a higher value of Umax and a lower
value of Amin than that of DDMAO, suggest a higher
compactness of the aggregation. It is well established that
the hydroxyethyl group of DDEAO is a dominant factor in
the determination of Umax and Amin values.
0.1
1
c/(mM)
Fig. 1 Surface tension versus concentration for DDEAO and
DDMAO at 25 °C
The adsorption of surfactants can be expressed by the pC20
value. The larger the pC20 value, the higher is the adsorption
efficiency of the surfactant. The values of pC20 obtained for
DDEAOandDDMAOarealsopresentedinTable 1. Fromthe
values of pC20 in Table 1, the pC20 value of DDEAO is higher
compared with that of DDMAO. This indicates that DDEAO
ismore easilyadsorbed than DDMAO. This is probablydue to
the hydroxy group of DDEAO being able to form a hydrogen
bond with water more easily.
Thickening Function
The viscosities of DDEAO/AES and DDEAO/LAS com-
plex solutions (the total active contents of the solutions
were 20 wt%) were measured using a NDJ-79 rotating
viscometer at room temperature.
Results and Discussion
Wetting Ability
Surface Activity
Wetting ability is an important property for surfactants. The
wetting abilities of DDEAO and DDMAO with different
concentrations measured at room temperature are shown in
Fig. 2. As shown in Fig. 2, the wetting ability of the sur-
factants improved with the increase in the concentration of
the surfactants. That is because when surfactants wet the
The critical micelle concentration (CMC) values and the
surface tensions at CMC (cCMC) of DDEAO and DDMAO
were determined from the plots of surface tension (c)
versus surfactant concentration as shown in Fig. 1. From
the surface tension curves, the surface excess concentra-
tions of DDEAO and DDMAO (Umax) were calculated
from the Gibbs adsorption equation (1). The minimum
surface area per surfactant molecule (Amin) was obtained
from the Gibbs equation (2).
180
DDMAO
DDEAO
160
140
120
100
80
ꢀ
ꢁ
1
oc
Cmax ¼ ꢁ
ð1Þ
ð2Þ
2:303 nRT o log C
T
1
Amin
¼
NACmax
60
where R is the gas constant, T is the absolute temperature,
NA is Avogadro’s number and C is the concentration of
surfactant in solution. For nonionic and zwitterionic sur-
factant, n = 1 [17–20]. The values of the surface excess
concentration and the minimum surface area per surfactant
molecule are presented in Table 1. As shown in Table 1, a
slightly lower cCMC value for DDMAO than that of
DDEAO was obtained, and the CMC value of DDEAO was
40
20
0
0.5
1.0
1.5
2.0
2.5
Concentration/(g/L)
Fig. 2 The relation of different concentrations of DDEAO and
DDMAO with wetting times
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J Surfact Deterg
canvas disk, it will form a three-phase interface of ‘‘solid–
liquid–gas.’’ Surfactants will adsorb to the interface of
‘‘solid–liquid’’ and that of ‘‘liquid–gas;’’ the more the
surfactants adsorb onto the solid surface, the stronger is the
wetting power on the canvas [15]. DDEAO and DDMAO
show similar wetting ability. This is probably due to the fact
Table 2 Foaming ability and foam stability of samples
Surfactant (weight
proportion)
The volume of foam (ml)
V10 min/V30 s
After 30 s
After 10 min
DDEAO: AES
0:1
340
390
405
440
445
550
285
365
375
415
410
495
0.84
0.94
0.92
0.94
0.92
0.90
that DDEAO and DDMAO have a similar cCMC
.
1:5
1:10
1:15
1:20
1:0
Emulsifying Capacity
Emulsification is very important in many application pro-
cesses, and it is therefore worth determining. The emulsi-
fying capacity of the different concentrations of DDEAO and
DDMAO for soybean oil and liquid paraffin were measured
in a graduated cylinder with a glass stopper at room tem-
perature. The time for the separation of 10 ml of water was
taken as an estimate of the emulsifying capacity. Figure 3
shows the results of the emulsifying capacity of DDEAO and
DDMAO to emulsify soybean oil and liquid paraffin,
respectively. The emulsifying capacity tends to increasewith
the increase in the concentration of DDEAO and DDMAO.
The much longer time for soybean oil emulsion compared
with that of liquid paraffin, suggests that DDEAO and
DDMAO have a greater capacity to emulsify soybean oil
than liquid paraffin. The capacity of DDMAO to emulsify
soybean oil seems better than that of DDEAO, while
DDEAO has a better emulsifying capacity for liquid paraffin.
DDEAO: LAS
0:1
315
520
495
485
455
165
455
400
395
300
0.52
0.90
0.81
0.81
0.66
1:5
1:10
1:15
1:20
Foaming Properties
Foaming is one of the important applications of surfactants.
Foamability and foam stability are the two main measures
of foam performances. The Ross-Miles method was used to
test foaming properties of different times of different weight
proportions of DDEAO/AES and DDEAO/LAS complex
Fig. 4 The comparison of foam stability between DDEAO/AES and
DDEAO/LAS mixture systems
DDMAO emulsify soybean oil
6000
systems with sample concentration of 2.5 g/l at 50 °C. The
foaming ability is defined as the foam volume at 30 s and
the foam stability is expressed by the ratio of the foam
volumes after 10 min and 30 s. From the results presented
in Table 2 and Fig. 4 two things may be said. First, DDEAO
and the mixed surfactants have greater foaming abilities
than that of single AES and LAS. Second, the foam stability
of mixed surfactants is higher than that of single AES and
LAS. For DDEAO/LAS complex systems, foam stabilities
increase with increasing the DDEAO content. The results
indicate that DDEAO is a superior foam stabilizer.
DDEAO emulsify soybean oil
DDMAO emulsify iquid paraffin
DDEAO emulsify iquid paraffin
5000
4000
3000
2000
1000
0
0.5
1.0
1.5
2.0
2.5
Thickening Function
Concentration(g/L)
Amine oxides generally exhibit a thickening effect and for
this reason are usually added to shampoos. This effect of
Fig. 3 The emulsifying capacity of DDEAO and DDMAO for
soybean oil and liquid paraffin
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DDEAO
(wt%)
The viscosity of DDEAO/ The viscosity of DDEAO/
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(mPa s)
LAS mixed surfactants
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1,500
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DDEAO was studied by a rotating viscometer. The vis-
cosities of DDEAO/AES and DDEAO/LAS mixed sur-
factants, with a 20 wt% total active matter concentration,
are shown in Table 3. Table 3 shows that for the DDEAO/
AES mixed system, the viscosity achieved was the maxi-
mum when the content of DDEAO was 15 wt%, while it
was at 5 wt% DDEAO for the DDEAO/LAS mixture.
Conclusions
Dodecyldiethoxylamine oxide (DDEAO) was synthesized,
and its properties were compared with that of dodecyldim-
ethylamine oxide (DDMAO). Surface activity measure-
ments show that DDEAO has a slightly higher cCMC value
and obviously a lower CMC than that of DDMAO. The two
amine oxides have a similar wetting ability. Compared with
DDMAO, the emulsifying capacity of DDEAO for liquid
paraffin is superior. However, the emulsifying capacity of
DDMAO for soybean oil is better than DDEAO. For AES
and LAS, the foamingability and foam stability are increased
by adding DDEAO. The viscosity of DDEAO/AES and
DDEAO/LAS mixed surfactants appears the maximum
value at 15 wt% and 5 wt% DDEAO concentration,
respectively. Consequently, DDEAO has potential applica-
tions as a foam stabilizer and thickening agent.
Acknowledgments The authors acknowledge the financial support
of the National Science and Technology Support Project of China
(No. 2012BAD32B10).
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Author Biographies
2. Lim JC, Han DS (2011) Synthesis of dialkylamidoamine oxide
surfactant and characterization of its dual function of detergency
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Ruitao Wang received
a B.Sc. in chemical engineering and
technology from Baoji University of Arts and Sciences, P. R. China
in 2011 and is currently an M.Sc. student in applied chemistry at the
China Research Institute of Daily Chemical Industry, P. R. China. He
is involved in synthesis and applications of surfactants.
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Yunling Li received a Ph.D. in applied chemistry from Shanxi
University, P. R. China and is currently a professor of engineering at
the China Research Institute of Daily Chemical Industry, P. R. China.
Her research interests include surfactants and industrial catalysis.
Qiuxiao Li is currently a dean of China (RIDCI). He received his
Ph.D. from the Chinese Academy of Sciences (2003). His research
interests are focused on the engineering development related to
manufactures of surfactants and their physical chemistry.
123