Insights into the Optimization of Alkyl Phenol/Alkyl Halide Ratio in Gemini Surfactant Synthesis

Article abstract of DOI:10.1007/s11743-015-1723-5

¹H NMR and thin layer chromatography (TLC) were applied to analyze the component of two series of synthesized sulfonated Gemini surfactants with different spacer lengths (2, 4, and 6 carbons) and hydrophobic chain lengths (9, 12 carbons). Gemin

Full text of DOI:10.1007/s11743-015-1723-5

J Surfact Deterg
DOI 10.1007/s11743-015-1723-5
ORIGINAL ARTICLE
Insights into the Optimization of Alkyl Phenol/Alkyl Halide Ratio
in Gemini Surfactant Synthesis
LiJuan Guo2 YongJun Guo1 RuSen Feng1 JianXin Liu3
•
•
•
Received: 28 May 2014 / Accepted: 29 July 2015
Ó AOCS 2015
Abstract 1H NMR and thin layer chromatography (TLC)
were applied to analyze the component of two series of
synthesized sulfonated Gemini surfactants with different
spacer lengths (2, 4, and 6 carbons) and hydrophobic chain
lengths (9, 12 carbons). Gemini surfactants were prepared
by reacting alkylphenol with alkyl halide followed by
sulfonation with chlorosulfonic acid. The influence of the
molar ratio of alkyphenol to alkyl halide on the mono- to
diether ratio was investigated and the results indicated that
the molar ratio is a key factor to minimize impurities in the
target material, due to the high reactivity of alkyl halide. In
addition, the results showed that alkyl halide with a shorter
spacer group length required a higher molar ratio of alkyl
halide to alkylphenol. To synthesize the intermediate
Gemini product with 80 % diether content, the molar ratios
were optimized using n(alkylphenol):n(1,6-dibromohex-
Introduction
Gemini surfactants, made up of two hydrophobic chains
and two polar head groups covalently connected at the head
groups or very close to the head groups by a spacer group,
have attracted considerable interest in both scientific and
industrial applications [1–6]. Most researchers have
focused on cationic Gemini surfactants, whereas there are
only a few reports about the synthesis of anionic Gemini
surfactants, due to difficulties in purification. In the syn-
thesis of anionic Gemini surfactants, it is difficult to get a
pure product, since it is easy to generate single-stranded
products that have similar physical and chemical characters
to the Gemini structure.
According to previous reports [7–9], Gemini surfactants
can be purified by solvent extraction and recrystallization
and the yield determined by two-phase titration. However,
conventional separation and purification methods cannot
separate single and double chain products completely.
Therefore, the reaction mixture inevitably contains both
single-stranded and Gemini surfactants. In this situation, it
is difficult to obtain reproducible structure/property rela-
tionships for Gemini surfactants. There have been a few
literature reports on the separation and purification of sin-
gle- and double-stranded components [3, 6]. Therefore, it is
necessary to establish a method that has potential advan-
tages for simplifying and accelerating the analytical routes
for structure identification of constituents in complex
reaction mixtures.
ane) = 1:0.55,
n(alkylphenol):n(1,4-dibromobutane) =
1:0.7, and n(alkylphenol):n(1,2-dibromoethane) = 1:2.5,
respectively.
Keywords Gemini surfactant Á Nuclear magnetic
resonance Á Thin layer chromatography Á Reaction ratio
& YongJun Guo
gyfzgyj@126.com
1
State Key Laboratory of Oil and Gas Reservoirs Geology and
Exploration, Southwest Petroleum University,
Chengdu 610500, Sichuan, China
Dialkyl diphenyl diether disulfonate is a typical kind of
anionic Gemini surfactant. Many researchers have focused
on the design and synthesis of this kind of anionic Gemini
surfactant, exploring potential surface and interfacial
properties and aggregation behavior [3, 10, 11]. In order to
get pure Gemini surfactants, it is necessary to separate the
2
Aramco Far East (Beijing) Business Services Company
Limited, Beijing 100102, China
3
Petroleum Engineering College, Yangtze University,
Wuhan 430100, China
123

J Surfact Deterg
monether from the intermediate products. Separation of
intermediate products on siliconized chromatoplates can be
achieved using organic solvents. Generally, the separation
of these substances is influenced by the solvent polarity and
molecular weight of the compounds [12]. In this paper,
since monether and diether have similar functional groups,
the difference in polarity is too small to control for the
separation by siliconized chromatoplates. So the molecular
weight of each component in the mixture becomes the main
factor to control separation during the synthesis process of
the Gemini surfactant [12–14].
dichloromethane (99 %) were all purchased from Chengdu
Chemical Reagent and used without further purification.
1,6-dibromohexane (99.2 %) was purchased from Beneer
Chemistry, USA, and used without further purification.
Distilled water was used throughout this study.
Synthesis of Gemini Surfactants
Six Gemini surfactants (GS n-m-n) were synthesized using
a two-step reaction as shown in Scheme 1. The synthesis
and purification procedures I and II have been reported in
the literature [3].
1
In recent years, H NMR has been used for quantitative
analysis of mixed compounds, such as polyester and cotton
plant grass active extract, and the determination of the
absolute content of each component in new medicines [12,
The intermediate product (Mid n-m-n) of diether (DE)
and monoether (ME) was obtained as follows. Phase
transfer catalyst triethylbenzylammonium chloride (TEBA)
and NaOH solution were added to alkylphenol at 70 °C.
The solution was heated to 95 °C under stirring, and then
alkyl halide was added dropwise into the mixture and
allowed to react for 4 h. The target product (GS n-m-n) was
acquired by sulfonating DE with chlorosulfonic acid fol-
lowed by neutralization with sodium hydroxide.
1
15, 16]. There have been no reports on using H NMR for
quantitative analysis of single-stranded and double-stran-
ded components in the synthesis of Gemini surfactants. In
1
quantitative analysis of mixed compounds using H NMR
spectra [17], the integrated area of the absorption peak is
proportional to the number of protons. Therefore, the peak
area ratio reflects the relative number of different proton
types. A new spectrum analysis method has been used to
simplify the process of separation and analysis of complex
mixtures, and to identify complex ingredients without
complete separation [15–17]. This method shows unique
analytical capabilities, especially for trace composition or
components with similar polarity which are difficult to
separate under conventional separation conditions.
Purification-I
Theintermediateproductwascooledtoambientconditionand
dried. The residual solution was washed with 3 wt% glacial
acetic acid and distilled water until pH was around at 7, and
then the solvent was removed by distilling under reduced
pressure at 120 °C to obtain a mixture of DE and ME. The
yield of Mid n-m-n was calculated at the end of purification-I.
In this paper, a series of Gemini surfactants were syn-
thesized and the single-stranded components and double-
stranded products were separated by TLC from the reaction
mixture. The relative contents of mono- and diether were
Purification-II
1
determined based on H NMR spectra. Furthermore, the
DE and ME were separated by silica gel thin layer chro-
matography (TLC) after the preliminary purification I. TLC
plates were spotted at 10.0 ng level with the help of
graduated capillaries (10.0 lL). Because the polarity dif-
ference of the raw materials and Mid-products is relatively
small, and polarity difference between diether and mono-
ether is also small, low polarity solvents were used for the
separation. Attempts have been made to optimize TLC
conditions using different solvents, such as methanol,
ethanol, acetone, dichloromethane, cyclohexane and ethyl
acetate [17, 18]. The solvent system was optimized by
varying the concentration of cyclohexane and dichlor-
omethane. The intermediate product (Mid n-m-n) was
purified using a solution of cyclohexane and dichlor-
omethane (5:6, v/v). Pure DE and ME were obtained by
stripping each component from the TLC plates. Products
obtained by this stripping-method had very high purity and
were used as magnetic resonance spectroscopy standards.
influence of different ratios of raw materials on interme-
diate products (mixture of diether and monoether) was
studied, and an effective method to monitor the synthesis,
optimize strandedreaction conditions and examine strand-
edperformance is provided.
Experimental
Materials
Nonyl phenol (NP, 97 %) and dodecyl phenol (DP, 98 %)
were purchased from Chengdu Chemical Reagent, China,
and purified by distillation under reduced pressure at
200 °C prior to use. 1,2-dibromoethane (99 %), 1,4-di-
bromobutane (98.5 %), chlorosulfonic acid (99 %),
methanol (99 %), ethanol (99 %), acetone (99 %),
123

J Surfact Deterg
Scheme 1 Mid-n-m-n
H
Cn
n+
2
1
H
Cn
(intermediate product mixture),
DE (diether), ME (monoether)
and GS n-m-n (target product);
n = 9, 12; m = 2, 4, 6
n+
2
1
O
O
TEBA
r
m
B
+
r
B
m
a
N
H
H2 Cn
n+
1
O
DE
(
)
H
O
-n-m-n
M
id
l
C
+
3
O
N
S
H
H
O
a
H
Cn
a
O
n+
2
1
r
B
m
O
H2
1Cn
n+
O
m
a
ME
(
)
N
SO3
H2
N
1Cn
n+
SO3
-n-m-n
GS
=
1
H
H19
Cn
C9
n+
2
m=
2 4 6
,
,
H25
C12
NMR Spectra Area Method
Results and Discussion
According to the literature and chemical shift laws, the
biggest difference in hydrogen spectral peaks between
dialkyl diphenyl ether sulfonate (diether) [3, 19] and sin-
gle-alkylphenyl ether sulfonate (monoether) [20] are as
follows: the proton chemical shift of hydrogen in aromatic
ether linkage of DE is in the range of d4.0–4.1. The length
of the surrounding carbon chain influenced the chemical
shift [12]. Monoether carried both an ether bond and a
hydrogen bond with bromine methylene (chemical shift:
d3.4–3.6) [21].
After preliminary purification of the mixture, the areas
of the chemical shifts of both monoether and diether in the
NMR spectra can be compared when both monoether and
diether exist in the mixture. The proportion of theoretical
total hydrogen number Hs0 of monoether and diether in the
mixture must be equal to Hs, the actual hydrogen number
obtained by the spectrum integral value, which ensures that
there are no other interfering substances in the mixture. By
this method, the content of monoether and diether is
determined quantitatively.
Effect of the Molar Ratio (Wm) Between Alkylphenol
and Alkyl Halide
After purification-I, the intermediate product will be a
mixture of unreacted alkyphenol, diether and side product
monoether. To reduce the unreacted alkyphenol and pro-
duce more diether, it is necessary to adjust the molar ratio
(Wm) between alkylphenol and alkylhalide (Wm is defined
as the molar ratio of alkylphenol/alkyhalide). Conse-
quently, the molar ratio plays a key role in the synthesis of
the Gemini surfactant with less single-stranded surfactant
produced [22–24].
Results by TLC
Figure 1 shows the TLC identification of the raw material
and Mid n-m-n (Mid 9-2-9 and Mid 12-6-12) with
Wm = 1:0.5–1:2.5. According to our previous study, the
molecular weight is the main factor that affects the speed
of separation and the retention factor (Rf) of each sub-
stance. That is because there was a slight polarity differ-
ence between monoether and diether while great difference
existed in the molecular weight. The point ‘‘a’’ in Fig. 1 is
the starting raw material with stronger polarity, point ‘‘b’’
is diether and ‘‘c’’ is the monoether.
The specific formulae used are as follows:
4X þ 2Y ¼ Hd3:9À4:1
ð1Þ
ð2Þ
ð3Þ
2Y ¼ Hd3:4À3:6
Hs ¼ ðN1X þ N2YÞ=ðX þ YÞ ¼ Hs0
Figure 1 (left) shows that Mid 9-2-9 consists mainly of
unreacted nonylphenol, diether and monoether when Wm
values were 1:0.7 and 1:1. The conversion of the raw
material nonylphenol was increased with the increment of
the Wm value. As the Wm value is 1:2.5, the raw material
spot disappeared and two obvious spots of diether and
monoether were found on the TLC plates. Therefore, the
Theoretical hydrogen of X mole diether at the range of
d3.9–4.1 = 4X; theoretical hydrogen of Y mole monoether
at the range of d3.9–4.1 = 2Y; theoretical hydrogen of
X mole diether = N1X; theoretical hydrogen of Y mole
monoether = N2Y; Hs0 is the theoretical total hydrogen
number; Hs is the actual total hydrogen of one mole mix-
ture in the spectra.
123

J Surfact Deterg
unreacted 1, 6-dibromohexane and target product diether in
the mixture of Mid 12-6-12. When the molar ratios were
changed to 1:0.55, 1:0.7 and 1:1, the area ratio of
S(d4.02):S(d3.47) was 4:0.44, 4:1.14 and 4:1.9, respec-
tively. According to the formula in the experimental sec-
tion, the exact content of diether and monoether was
calculated, and listed in Table 1. When the molar ratio was
changed to 1:0.55, 1:0.7 and 1:1, the ratio between diether
and monoether in the Mid 12-6-12 was 80.9:19.1 %,
55.8:44.2 %, and 34.5:65.5 %, respectively. The results
show that the molar ratios between dodecylphenol to 1,
6-dibromohexane are responsible for the distribution of
diether, monoether and unreacted dodecylphenol in the
crude product Mid 12-6-12.
c
c
c
c
c
c
b
b
b
b
a
a
Based on the investigation of optimizing reaction con-
ditions, we found that different alkyl halides should require
different optimal reaction ratios of n(alkyl phenol):n(alkyl
halide). Under different reaction ratios, a series of inter-
mediate products with different spacer lengths (2, 4, and 6)
and hydrophobic chain lengths (9, 12) were synthesized. 1H
NMR spectra of Mid 9-4-9, Mid 12-4-12 and Mid 12-2-12
obtained at different molar ratios of n(alkylphenol):n(alkyl
halide) are shown in Fig. 3. The calculated species distri-
Fig. 1 TLC identification of Mid n-m-n at different reaction ratios
after 4 h. Left 1 Nonylphenol, 2 Mid 9-2-9 (Wm = 1:0.7), 3 Mid 9-2-9
(Wm = 1:1), 4 Mid 9-2-9 (Wm = 1:2), 5 Mid 9-2-9 (Wm = 1:2.5).
Right 1 Dodecyl phenol, 2 Mid 12-6-12 (Wm = 1:0.5), 3 Mid 12-6-12
(Wm = 1:0.55), 4 Mid 12-6-12 (Wm = 1:0.7), 5 Mid 12-6-12
(Wm = 1:1), 6 Mid12-6-12 (Wm = 1:1.5)
1
optimal molar ratio for the synthesis of Mid 9-2-9 was
taken to be 1:2.5.
bution from the H NMR analytical results are given in
Table 2.
Figure 1 (right) shows the synthesis results of the
reaction between dodecylphenol and 1, 6-dibromohexane
with different molar ratios from 1:0.5 to 1:1.5. When the
value of Wm was 1:0.5, there was unreacted dodecylphenol
in Mid 12-6-12. However, increasing the Wm value to
1:0.55, dedocylphenol can be reacted completely with 1,
6-dibromohexane, which indicated that 1, 6-dibromohex-
ane has higher reactivity than 1, 2-dibromoethane. As the
Wm value was increased in the range of 1:0.55 to 1:1, the
distribution of diether and monoether was changed regu-
larly. However, quantitative conclusions were hard to draw
using the TLC method [24–26].
The alkyl halide with the shorter spacer group required a
higher optimal molar ratio. When the molar ratio was 1:0.5
for Mid 9-6-9 and Mid 12-6-12, there was unreacted alkyl
phenol. When the reaction molar ratios were changed to
1:0.55, 1:0.7 and 1:1, the ratios between diether and
monoether in the Mid 9-6-9 were 79.3:21.7 %, 53.4:46.6 %
and 32.8:66.2 %, respectively. This was consistent with the
regularity of Mid 12-6-12, which proved that the alkyl
phenol had little influence on the optimal reaction ratio.
When the reaction molar ratios were 1:0.5 and 1:0.55, there
was unreacted alkyl phenol in the product of Mid 9-4-9 and
Mid 12-4-12. When the reaction ratio was increased to
1:0.7, the alkyl phenol reacted completely with the alkyl
halide. When the molar ratios were changed to be 1:0.7, 1:1
and 1:2.5, the ratio between diether and monoether in the
Mid 12-4-12 were 80.7:19.3 %, 64.6:35.4 % and
37.8:63.2 %, respectively, where in Mid 9-4-9 the corre-
sponding ratios were 79:21 %, 62.9:38.1 and 31.5:69.5 %.
When the molar ratio varied from 1:0.5 to 1:1, there were
still some unreacted alkyl phenol left in the product of Mid
9-2-9 and Mid 12-2-12. Therefore, in order to obtain the
product of around 85 % diether and 15 % monoether, the
optimal molar was taken as 1:2.5.
The Content of Diether and Monoether
in the Intermediate Products
The TLC method is a simple method for qualitative
1
research, while the H NMR spectra area method is good
for quantitative research. The content of diether and
monoether in the intermediate product after purification-I
was analyzed using the 1H NMR spectra area method.
1
Figure 2 shows the H NMR spectra of DE 12-6-12 and
Mid 12-6-12 obtained at different reaction ratios
Wm = 1:0.5–1:1. Based on the results in Fig. 2, the char-
acteristic groups of dodecylphenol, diether and monoether
were at chemical shifts, d & 5.1; d & 4; d & 3.47,
respectively. When the Wm value was 1:0.5, peaks at
d & 5.1 and d & 4 were observed, which indicates
Based on this study, the reactivity and steric effect of the
alkyl halide had a strong influence on the required amount
of the corresponding alkyl phenol. According to the
chemical reaction equation, the molar ratio between alkyl
phenol and alkyl halide should ideally be 1:0.5 to generate
123

J Surfact Deterg
Fig. 2 1H NMR spectra of
Mid12-6-12 under different
ratios of n(alkylphenol):n(alkyl
halide). (1:0.5), (1:0.55), (1:0.7)
and (1:1) represent the different
ratios of
E Mid12-6-12(1:1)
n(dodecylphenol):n(alkyl
halide)
D Mid12-6-12(1:0.7)
C Mid12-6-12(1:0.55)
B Mid12-6-12(1:0.5)
A DE 12-6-12(pure)
Table 1 Effect of
n(dodecylphenol):n(alkyl halide)
1:0.5
1:0.55
1:0.7
1:1
n(dodecylphenol):n(alkyl
halide) on the synthesis of Mid
12-6-12
S(d4.02):S(d3.47)
4:0
4:0.44
80.2:19.8
64.8
4:1.14
55.8:44.2
57.8
4:1.9
34.5:65.5
51
n(DE):n(ME) = X %:Y %
Hs0 = (70X ? 41Y)/(X ? Y)
Hs
100:0
70
69.3
65.7
64.1
57.2
49.8
Total yield (DE ? ME) %
81.6
86.5
83.2
Fig. 3 1H NMR spectra of Mid
n-m-n under different ratios of
n(alkylphenol):n(alkyl halide).
1:0.7 and 1:2.5 represent the
different ratios of
n(alkylphenol):n(alkyl halide)
1 mol of diether. However, differences existed in the real
reaction because the alkyl halides with different spacer
lengths have different reactivity and varied steric effects.
The results show that 1,6-dibromohexane has a better
activity than the others. Therefore, the reactions for dif-
ferent alkyl halides required different optimal reaction
ratios of alkyl phenol and alkyl halide. In addition, com-
pared with the alkyl halide, the results indicated that
alkylphenol had only slight effects on the reaction
condition.
The diether reaction is a classic nucleophilic bimolec-
ular substitution (SN2). The functional group in the alkyl
halides is a carbon-halogen bond, the common halogens
being fluorine, chlorine, bromine and iodine. With the
exception of iodine, these halogens have electronegativities
significantly greater than carbon. During the reaction, more
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1 %:1 % 1 %:2.5 %
Table 2 Effect of n(alkyl
phenol):n(alkyl halide) on the
systhesis of Mid m-n-m
n(alkyl phenol):n(alkyl halide)
1:0.5
1 %:0.55 %
1 %:0.7 %
Mid12-6-12
Mid9-6-9
n(DE):n(ME)
n(DE):n(ME)
n(DE):n(ME)
n(DE):n(ME)
n(DE):n(ME)
n(DE):n(ME)
–
–
–
–
–
–
80.9:19.1
55.8:44.2
53.4:46.6
80.7:19.3
79:21
–
34.5:65.5
32.8:66.2
64.6:35.4
62.9:38.1
–
–
79.3:21.7
–
Mid12-4-12
Mid9-4-9
–
–
–
–
37.8:63.2
31.5:69.5
85.2:14.8
84.6:15.4
Mid12-2-12
Mid9-2-9
–
–
reactive species dibromoalkane (Br-C-C-Br) was used, and
RArO- was used as a nucleophile. Consequently, the
functional group in the alkyl halide is polarized so that the
carbon is electrophilic and the halogen is nucleophilic.
Alkyl halides undergo two basic types of reactions in
organic chemistry: substitutions and eliminations. Some of
the most important information concerning nucleophilic
substitution and elimination reactions of alkyl halides has
come from studies in which the structure of the alkyl group
has been varied. There are a few factors that affect sub-
stitution and elimination reactions: nucleophilicity, leaving
group, steric effect, solvent effect, alkyl moiety, and
molecularity. With primary alkyl halides, the SN2 mecha-
nism almost always predominates. However, the strong
steric effect in dibromoalkane may cause elimination (E2)
to occur accompanied by SN2 substitution. The transition
state is too crowded to go through the inversion process.
The rate of the SN2 reaction is directly linked to the
concentration of the two species, the nucleophile (Nuc) and
the alkyl halide (RX) undergoing substitution. Changing
the concentration means changing the number of possible
collisions. When it came to 1,2-dibromoethane, because of
a stronger steric effect during the substituent process, it was
easy for the elimination reaction or SN2 on one side of the
dibromoetheane which resulted in an excess of 1,2-dibro-
moethane being required to generate the target product
diether. As n(alkylphenol):n(1, 2-dibromoethane) was
below 1:2.5, most of the 1,2-dibromoethane was sacrificed
in the elimination reaction and only a small part reacted
with alkylphenol to produce diether or monoether. Con-
sequently, the conversion of alkyl phenol was very low. As
for 1,4-dibromoethane and 1,6-dibromohexane, the dis-
tance between the two halogen atoms was greater so the
steric effect was not as strong as that in 1,2-dibromoethane.
It was more active for them to generate SN2 substitution
with alkylphenol. At the condition of n(alkylphe-
nol):n(alkyl halide) = 1:0.55–1:0.7, more than 80 % of the
products was diether. When the amount of the alkyl halide
increased, the surplus C-Br made more monoether.
a shorter spacer group required a higher optimal molar
ratio, and by increasing the molar ratio of alkyl phenol to
alkyl halide, more monoether was generated in the inter-
mediate product. Few literature reports mention the effect
of chain length on the reactivity of alkyl halides and how
they influence the synthesis procedure of Gemini
surfactants.
Conclusions
In this paper, two series of sulfonated Gemini surfactants
GS m-n-m (m = 9, 12; n = 2, 4, 6) with different spacer
lengths and hydrophobic chain lengths were synthesized
and characterized. The relationship between spacer length,
hydrophobic chain length, and the molar ratio of alkyl
phenol to alkyl halide were determined by TLC and NMR.
At a constant n(alkyl phenol):n(NaOH) rato of 1:5.4, the
reaction ratio of n(alkyl phenol):n(alkyl halide) can be
adjusted to improve the yield of diether, and the difficulty
of the purification was reduced. A series of proportional
and controllable mixtures of diether and monoether were
obtained. The results drawn by NMR area and TLC
methods were consistent as follows: alkyl halides with
shorter spacer group lengths required higher optimal molar
ratios, and by increasing the molar ratio of alkyl phenol to
alkyl halide, more monoether was generated in the inter-
mediate product.
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LiJuan Guo graduated from the Southwest Petroleum University,
China with a Master’s degree in applied chemistry. She focuses on the
theory, development, and application technology of functional
surfactants, polymers, and working fluids for oilfields to create a
series of original-theory study results and special applications
technology. She is currently working as a petroleum engineer at
Aramco Asia.
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reversed phase thin-layer chromatography.
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J Chromatogr
YongJun Guo is a professor at Southwest Petroleum University. He
focuses on investigating salt-resistant and temperature-resistant
hydrophobically associating polymer for flooding, smart gel plugging
agents for well blowouts and leakage accidents. He has taken charge
of over ten research projects from the National ‘‘863’’ Plan Major
Program of China, Major National Science and Technology Oil &
Gas Projects, National ‘‘973’’ Program of China and the projects of
Province or Ministry, and has worked as a main investigator to study
the novel polymer for EOR. He has published over 40 professional
papers on the theory, development, and application technology of
functional polymers.
14. Yang J, Xie J, Chen G, Chen X (2009) Surface, interfacial and
aggregation properties of sulfonic acid-containing Gemini sur-
factants with different spacer lengths. Langmuir 25(11):
6100–6105
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studied by NMR. Chin J Magn Reson 24(3):374–376
16. Dongmei D, Jiuming H, Chao L, Ruixiang S, Ping ZR, Aisa HA,
Abliz Z (2011) Simultaneous structural identification of con-
stituents in active herbal extract of gossypium herbaceam using
nuclear magnetic resonance/liquid chromatography-mass spec-
trometry hetero-correlation spectroscopy. Chin J Anal Chem
6(39):781–787
17. Hu M, Hu C-Q, Liu W-Y (2004) Determination of drug reference
substance content by 1H nuclear magnetic resonance spec-
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face active properties of amphipathic compounds with two sulfate
groups and two lipophilic alkyl chains. J Am Oil Chem Soc
67(7):459–463
RuSen Feng is associate professor in Southwest Petroleum Univer-
sity. He is engaged in teaching and research job in oilfield chemistry,
mainly focusing on salt-resistant and temperature-resistant hydropho-
bically associating polymer for EOR. He has took charge of over 10
research projects from National ‘‘863’’ Plan Major Program of China,
Major National Science and Technology Oil & Gas Projects, National
‘‘973’’ Program of China and the projects of Province or Ministry. He
had published 35 professional papers and patents on the application
technology of functional polymer.
19. Zhu S, Cheng F, Zheng BJ, Yu JG (2004) Aggreagation prop-
erties of a new anionic Gemini surfactant in aqueous solution.
Acta Phys Chim Sin 20(10):1245–1248
20. Zhu YP, Masuyama A, Okahara M (1988) Method for surface
pretreatment before formation of photocatalytic hydrophilic film,
JianXin Liu PhD, Petroleum Engineering College, Yangtze Univer-
sity. He is engaged in teaching and research job in oilfield chemistry.
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