Synthesis and properties of novel cationic gemini surfactants with adamantane spacer

Article abstract of DOI:10.1016/j.cclet.2013.11.010

Novel quaternary ammonium cationic gemini surfactants, with two hydrocarbon chains and an adamantane core, were designed and synthesized by three-step reactions from adamantane. The structure of obtained surfactants were confirmed by ¹H NMR, FTIR and elements analysis and the surface properties of these surfactants were also studied by surface tension measurements. These target surfactants exhibit much lower critical micelle concentrations (CMC) and higher efficiency in lowering the surface tension of water than typical surfactants.

Full text of DOI:10.1016/j.cclet.2013.11.010

Chinese Chemical Letters 25 (2014) 367–369
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Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
Synthesis and properties of novel cationic gemini surfactants with
adamantane spacer
*
Xiao-Jian Xu, Jian-Wei Guo , Xing Zhong
School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou 510006, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Novel quaternary ammonium cationic gemini surfactants, with two hydrocarbon chains and an
adamantane core, were designed and synthesized by three-step reactions from adamantane. The
structure of obtained surfactants were confirmed by 1H NMR, FTIR and elements analysis and the surface
properties of these surfactants were also studied by surface tension measurements. These target
surfactants exhibit much lower critical micelle concentrations (CMC) and higher efficiency in lowering
the surface tension of water than typical surfactants.
Received 24 July 2013
Received in revised form 27 October 2013
Accepted 31 October 2013
Available online 5 December 2013
Keywords:
ß 2013 Jian-Wei Guo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights
reserved.
Gemini surfactants
Adamantane
Synthesis
1. Introduction
surfactants with adamantane are expected to be non hazardous,
unlike benzene surfactants.
Recently, gemini (or dimeric) surfactants, with two hydrophilic
groups and two hydrocarbon chains connected by a spacer chain,
have been investigated actively [1–3]. Gemini surfactants are a
novel class of amphiphilic compounds consisting of two hydro-
philic head groups and two hydrophobic chains linked by a spacer
within the molecule. Many reports have shown that the gemini
surfactants have much more superior surface activity than
conventional single-chained surfactants, such as lower critical
micelle concentrations (CMC), higher efficiency in lowering the
surface tension of water, and better wetting properties [4–7]. In
addition, the quaternary ammonium type gemini surfactants also
show good antimicrobial activity [8].
Adamantane (tricyclo[3.3.1.13,7]decane) is a highly symmetri-
cal cage hydrocarbon that consists of fused chair-form cyclohexane
rings [9]. The special structure of adamantane shows superior
chemical and thermal stability, such as extreme hydrophilicity,
good thermal and oxidative stabilities and low surface energy [10].
Functional groups can be introduced into the tert-carbons of
adamantanes by several methods, including radical reaction,
oxidation reaction, cross-coupling reaction, and Friedel–Crafts
reaction, to give a wide variety of adamantane derivatives [11]. So
it is interesting to design and synthesize novel gemini surfactants
with adamantane spacer, for the adamantane lipophilicity may
endow the resultant surfactants with unique surface activity. In
addition, due to the non-toxicity of adamantane, the novel gemini
In this paper, we successfully synthesized a series of quaternary
ammonium gemini surfactants containing adamantane as the
spacer group and investigated the surface properties of the
resultant surfactants.
2. Experimental
Melting points of obtained compounds were determined by
WRS-1B (Wuhan gelaimo detection equipment Co. Ltd., China).
Proton NMR spectra were obtained using a Varian Mercury-Plus
300 spectrometer, and chemical shift values (d) were reported as
parts per million (ppm) with DMSO as the solvent. FT-IR spectra
were recorded in KBr on a Nicolet 6700 FT-IR Spectrometer.
Elemental analyses for C, H, N and O were performed on a Vario EL
III elemental analyzer. The surface tensions of aqueous solutions
were measured by a Data Physics DCAT21 tensiometer.
The synthesis procedure of the target surfactants consists of
three steps, as shown in Scheme 1.
The synthesis of compounds 1: Firstly, to a solution of
adamantane (2.59 g, 19 mmol) in
a mixture of acetic acid
(100 mL) and concentrated sulphuric acid (0.52 mL 9.5 mmol)
was slowly added chromium trioxide (7.6 g, 76 mmol). The
resultant reaction system was stirred at 80 8C for 2 h. Then the
mixture was concentrated, washed with 30% NaOH solution, and
extracted with ethyl acetate. The organic extract was cooled down
at room temperature overnight to give a white precipitate which
was recrystallized from a mixed solvent of ethanol and hexane to
afford white solid 1. 1H NMR (300 MHz, DMSO-d6):
d 1.360–1.476
*
Corresponding author.
E-mail address: doctorgjw@163.com (J.-W. Guo).
(m, 12H), 2.104 (s, 2H), 4.390 (s, 2H).
1001-8417/$ – see front matter ß 2013 Jian-Wei Guo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2013.11.010

368
X.-J. Xu et al. / Chinese Chemical Letters 25 (2014) 367–369
Scheme 1. The synthesis route of compounds 3a–c. Condition and regent: (a) acetic
acid, concentrated sulphuric acid, chromium trioxide, 80 8C, 2 h, 71%; (b) dry
pyridine, dry acetonitrile, 4-(dimethylamino)pyridine, BrCH2COBr, 60 8C, 6 h, 46%;
and (c) acetone, tertiary amine, room temperature, 12 h, 49–56%.
Fig. 1. Surface tension of aqueous 3a–c at 25 8C.
3. Results and discussion
Synthesis of compounds 2: 1,3-Dihydroxyadamantane (3.2 g,
19 mmol) was added to the mixed solvent of dry pyridine (6.2 mL,
76 mmol), dry acetonitrile (40 mL) and 4-(dimethylamino) pyri-
dine (64 mg) under nitrogen atmosphere. The stirred solution was
placed in an ice bath, and then BrCH2COBr (6.63 mL, 76 mmol) was
dropwise added in 1 h. Then, the ice bath was removed, and the
mixture was stirred at 60 8C for 6 h to afford the transparent
and homogeneous solution. After addition of HCl (6 mol/L, 20 mL)
and dichloromethane (30 mL) to the reaction mixture, the solution
was layered. The collected organic extract was concentrated to give
a light-brown solid. The solid was dissolved in dichloromethane
(35 mL) and washed with brine and Na2CO3 solution (0.5 mol/L,
35 mL). After that the organic layer turned brown-black, which was
concentrated and purified by filtering through a silica gel column
(eluted with dichloromethane) to give a yellow oily substance. The
obtained crude product was passed through a silica gel column
with dichloromethane again to afford a white oily substance 2. 1H
The structures of the target compounds 3a–c synthesized
herein were fully characterized by melting points, 1H NMR, IR, and
Elemental analyses. The characterization results of compounds
3a–c are listed in Table 1.
The surface tension of aqueous solutions was measured by Data
Physics DCAT21 tensiometer at 25 8C. Fig. 1 shows the results of
critical micelle concentration (CMC) of the target gemini surfactant
and their corresponding surface tensions. We can see from Fig. 1
that plots of surface tension versus log concentration for gemini
surfactants 3a, 3b and 3c give sharp breaks corresponding to CMC
values of 2.00 Â 10À5, l.00 Â l0À4, 5.00 Â 10À4 mol/L, respectively.
For comparison purposes, the CMC values of normal quaternary
ammonium gemini surfactants Cm–s–CmÁ2Br (m = 12; s = 2, 4) [12]
and quaternary ammonium monomeric surfactants ADM–CmÁBr
(m = 8, 10, 12, 16; ADM: adamantyl) [13] which also contains
adamantane, are listed in Table 2.
NMR (300 MHz, DMSO-d6):
2.429 (br s, 2H), 2.548 (s, 2H), 3.79 (s, 4H).
d
1.536 (br s, 2H), 2.067–2.093 (m, 8H),
From Table 2, we can see that the CMC value of gemini
surfactant 3c was much lower than that of normal gemini
surfactants Cm–s–CmÁ2Br with the same hydrophobic chains. It
may resulted from the spacer, adamantane, which has tremendous
lipophilic properties. The adamantane can also be regarded as the
hydrophobic chain resulting in a lower the CMC value. It is
noteworthy that the CMC values of 3a–c are lower than those of
monomeric surfactants ADM–CmÁBr with the same adamantane
spacer group. These results can be explained with the fact that the
Synthesis of compounds 3a–c: Compound 2 (3.90 g, 9.5 mmol)
was added to the mixed solvent of acetone (120 mL) and tertiary
amine (28.5 mmol) at room temperature. Then the mixture was
vigorously stirred for 12 h to afford a white precipitate. After it
was filtered and washed several times with acetone, white solid
3a was obtained. Solids 3b and 3c were synthesized via similar
procedures.
Table 1
The characterizing results of compounds 3a–c.
Compound
Yield (%)
56
Mp (8C)
1H NMR (300 MHz, DMSO-d6):
d
Elements analysis (%, calcd.)
FTIR (KBr, cmÀ1):
v
3a
177.1–177.6
0.827–0.869 (t, 6H), 1.151–1.233 (m, 52H),
1.554 (br s, 2H), 1.636–1.656 (m, 4H),
2.050–2.078 (m, 8H), 2.369 (br s, 2H),
2.534 (s, 2H), 3.162 (s, 12H),
C, 63.33 (63.53); H, 10.47 (10.35);
O, 6.73 (6.64); N, 3.15 (2.91);
Br, 16.32 (16.58)
2920, 2852, 1736, 1471, 1271,
1212, 1066, 721
3.379–3.479 (t, 4H), 4.346 (s, 4H)
0.827–0.871 (t, 6H), 1.237–1.261 (m, 44H),
1.552 (br s, 2H), 1.640–1.662 (m, 4H),
1.994–2.102 (m, 8H), 2.339 (br s, 2H),
2.533 (s, 2H), 3.165 (s, 12H),
3b
3c
52
49
174.9–175.4
170.9–171.2
C, 62.29 (62.17); H, 9.77 (10.10);
O, 7.21 (7.05); N, 2.86 (3.09);
Br, 17.87 (17.60)
2920, 2851, 1738, 1471, 1274,
1209, 1066, 721
3.403–3.459 (t, 4H), 4.353 (s, 4H)
0.827–0.870 (t, 6H), 1.241–1.263 (m, 36H),
1.553 (br s, 2H), 1.621–1.666 (m, 4H),
1.999–2.096 (m, 8H), 2.369 (br s, 2H),
2.532 (s, 2H), 3.165 (s, 12H),
C, 60.81 (60.62); H, 8.98 (9.82);
O, 7.75 (7.51); N, 3.43 (3.29);
Br, 19.03(18.76)
2920, 2852, 1739, 1471, 1275,
1212, 1066, 721
3.402–3.459 (t, 4H), 4.351 (s, 4H)

X.-J. Xu et al. / Chinese Chemical Letters 25 (2014) 367–369
369
Table 2
gemini surfactants exhibit lower CMC values and exhibit high
efficiency in lowering the surface tension of water.
Value of the CMC,
gCMC and PC20 for surfactants Cm–s–CmÁ2Br, ADM–CmÁBr and 3a–c.
Surfactant
CMC (mol/L)
gCMC (mN/m)
PC20
a
8.20 Â 10À4
9.60 Â 10À4
1.20 Â l0À2
8.00 Â 10À3
4.00 Â l0À3
2.00 Â l0À3
2.00 Â 10À5
1.00 Â 10À4
5.00 Â 10À4
30.600
38.000
43.053
40.953
38.906
37.902
32.543
35.588
37.543
3.75
3.66
3.25
3.62
4.30
4.65
5.15
4.80
4.02
Acknowledgments
C12–2–C12Á2Br
C12–4–C12Á2Br
a
b
ADM–C8ÁBr
The authors greatly appreciate the financial support by the Key
Program for Scientific and Technological Innovations of Higher
Education Institutes in Guangdong Province (No. CXZD1022).
b
ADM–C10ÁBr
b
ADM–C12ÁBr
b
ADM–C16ÁBr
3a
3b
3c
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gemini surfactants 3a–c contain two alkyl chains, rather than one,
which facilitates the formation of micelles in the aqueous solution.
The efficiency can be characterized by the value of the
logarithm of the surfactant concentration C20 at which the surface
tension of water is reduced by 20 mN/m (pC20). Larger pC20 values
indicate higher efficiency. The value of pC20 is also listed in Table 2.
It can be seen that target gemini surfactants with a longer
hydrophobic chain have higher adsorption efficiency. For compar-
ison, the pC20 values of the gemini surfactants Cm–s–CmÁ2Br and
the ADM–CmÁBr are also listed in Table 2. It can be found that the
pC20 values of 3a–c are larger than those of Cm–s–CmÁ2Br,
indicating that target gemini surfactants makes it easy to adsorb
at the air–water interface [14]. This is because 3a–c contain
lipophilic adamantane and exhibit high efficiency in lowering the
surface tension of water.
4. Conclusion
In summary, a series of novel adamantane-based cationic
gemini surfactants were synthesized by three-step reactions from
adamantane and characterized by 1H NMR, FTIR and elements
analysis. The surface properties of these surfactants were also
studied by surface tension measurements. It was found that the
target gemini surfactants show unusual properties. The target
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(2012) 9322–9331.