Synthesis and characterization of glycoside-based trisiloxane surfactant

Article abstract of DOI:10.1007/s11743-011-1265-4

The synthesis of glycoside-based trisiloxane surfactants of the general formula Me₃SiOSiMeR¹OSiMe₃ (R¹ = (CH₂)₃(OCH₂CH₂)₂OR ², R² = gl

Full text of DOI:10.1007/s11743-011-1265-4

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J Surfact Deterg (2011) 14:515–520
DOI 10.1007/s11743-011-1265-4
ORIGINAL ARTICLE
Synthesis and Characterization of Glycoside-Based Trisiloxane
Surfactant
•
•
•
Fu Han Yan-hong Chen Ya-wen Zhou
Bao-cai Xu
Received: 24 February 2011 / Accepted: 4 March 2011 / Published online: 27 March 2011
Ó AOCS 2011
Abstract The synthesis of glycoside-based trisiloxane
surfactants of the general formula Me3SiOSiMeR1OSiMe3
(R1 = (CH2)3(OCH2CH2)2OR2, R2 = glycosyl) is descri-
bed, and the surface activity properties of the surfactant are
studied. Diethylene glycol monoallyl ether glycoside is
synthesized by reacting the diethylene glycol monoallyl
ether with glucose. The glycoside-based trisiloxane sur-
factant is prepared by hydrosilylation of the precursor
glycoside with hydrogen-containing trisiloxane. The
Trisiloxanes customarily considered to consist of two
types, namely, ‘‘MD’M’’ and ‘‘M’DM’’, where M is a
trimethylsiloxy group (CH3)3–SiO1/2–, D is –O1/2Si(CH3)2
O1/2–, D’ is –O1/2Si(CH3)RO1/2–, M’ is –O1/2Si(CH3)2R, R
is the hydrophilic head-group which is attached to the
hydrophobic tail through a –(CH2)3– spacer. The excep-
tional surface properties of the ‘‘MD’M’’ trisiloxanes, some
having ‘‘super-wetting’’ ability, are attributed to their
unique molecular architecture. They aroused the great
interests of many scientific researchers [1–51]. The type of
‘‘MD’M’’ scattering at the air/water surface caused by the
‘‘umbrella’’ structure in a configuration where the methyl
groups are closely packed and exposed to the air with
surface tension values of approximately 21 mN m-1 being
commonly achieved. By comparison, hydrocarbon surfac-
tants generally have many –CH2– groups in their hydro-
phobic portions, which have an intrinsically higher surface
energy than methyl groups.
1
product is structurally characterized by IR, H NMR and
MS. The surface tension of an aqueous solution is reduced
to approximately 20 mN m-1 at concentration level of
10-4 mol L-1
.
Keywords Synthesis ꢀ Characterization ꢀ Glycoside ꢀ
Trisiloxane ꢀ Hydrosilylation
Introduction
In contrast, alkyl polyglucoside (APG) surfactants have
been known for many years. In recent years, they have
begun to be produced on an industrial scale and their use
has been gradually increasing because of their valuable
properties, such as good dermatological compatibility,
excellent biodegradability, and the absence of toxic effects.
However, the trisiloxane with the glycoside as the
hydrophilic head-group has been only rarely reported in the
literature [52, 53].
In recent years silicone surfactants have attracted consid-
erable interest because of their many technical applica-
tions. Owing to their unique molecular structure compared
with that of normal hydrocarbon surfactants, they have
excellent surface-active properties for special purposes.
They can also reduce the surface tension of water to lower
values than can be attained using traditional hydrocarbon
surfactants. Silicone surfactants are also known for their
low physiological risk in cosmetic applications.
In this paper, we report the preparation of a glycoside-
based trisiloxane surfactant and study the surface activity
of this compound by measuring the equilibrium surface
tension of the dilute aqueous solutions. The parameters
studied include CAC (the critical aggregation concentra-
tion), pC20 (negative log of the surfactant molar concen-
tration required to reduce the surface tension of the solvent
by 20 mN m-1, which is a measurement of the efficiency
F. Han (&) ꢀ Y. Chen ꢀ Y. Zhou ꢀ B. Xu
School of Chemical and Environmental Engineering,
Beijing Technology and Business University,
No. 11 Fucheng Road, 100048 Haidian District,
Beijing, People’s Republic of China
e-mail: hanricher@gmail.com
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J Surfact Deterg (2011) 14:515–520
100 °C. The mixture was stirred for 3 h and subse-
quently distilled under a reduced pressure and at
80 °C to give a viscous and clear product. The
structure of the compound was confirmed by IR and
1H NMR.
of adsorption), cCAC (the surface tension at the CAC), Cm
(the maximum surface excess concentration at the air/water
interface), asm (the minimum area per surfactant molecule at
the air/water interface), and the CAC/C20 ratio (a mea-
surement of the factors inhibiting aggregation relative to
adsorption at the air/water interface), DGoagg (the standard
free energy of aggregation), DGoads (the standard free
energy of adsorption).
Characterization of the Glycoside-Based Trisiloxane
Surfactant and Surface Activity Measurements
The proton nuclear magnetic resonance (1H NMR) spectra
were acquired on a 300 MHz Bruker DRX-300 NMR
spectrometer. Samples were prepared in 5-mm OD tubes
with deuterated solvents CDCl3 or D2O. Chemical shifts
were referenced to tetramethylsilane. The infrared (IR)
spectra were recorded on an Avater FT-IR Spectrometer
Tensor 370 (KBr). The mass spectra were scanned on an
Agilent 5975C instrument at 70 eV.
Experimental Procedures
Preparation of Glycoside-Based Trisiloxane Surfactant
(1) Preparation of diethylene glycol monoallyl ether 1.
4.0 g (0.1 mol) of NaOH and the solvent (dioxane)
were introduced into a 500-mL reaction vessel. Then
7.6 g (0.1 mol) of allyl chloride and 21.2 g (0.2 mol)
of diethylene glycol were added dropwise with rapid
stirring at 50–55 °C. After the completion of the
addition, stirring was continued for 6 h at 50–55 °C.
The crude product was dried with magnesium sulfate.
The solid material was filtered off. The solvent was
distilled off and the residue was purified by column
chromatography to give the compound in a yield of
82.5% and a purity of 99.2% (Agilent 7890A gas
chromatography). The structure of the compound was
Aqueous solution equilibrium surface tension values
were obtained by the Wilhelmy plate method using a
Dataphysics tensiometer, model DCAT11. The CAC value
was taken at the intersection of the linear portions of the
plots of the surface tension against the logarithm of the
surfactant concentration. Surfactant solutions were pre-
pared with distilled, de-ionized water. Sample temperatures
were stable to 25 0.2 °C. Prior to measurements on
surfactant solutions, the surface tension of the distilled,
de-ionized water was measured. These water values were
in the range of 72.3 0.3 mN m-1. Samples were aged
15 min prior to the surface tension measurement.
1
confirmed by IR, H NMR and MS.
(2) Preparation of diethylene glycol monoallyl ether
glycoside 2. 87.6 g (0.6 mol) of the diethylene glycol
monoallyl ether and 18.0 g (0.1 mol) of the glucose
anhydrous were introduced into a 500-mL round-
bottomed flask and heated with stirring to a temper-
ature of 110 °C. Then 0.6 g of the p-toluenesulfonic
acid was then added and the stirring continued under
reduced pressure and at 110 °C for 5 h. The clear
mixture was neutralized with aqueous NaOH solution
to neutrality and decolorized by activated carbon
adsorption. The excess diethylene glycol monoallyl
ether was distilled off in vacuum to give a vitreous
product. An average degree of glycosidation of 1.1
was determined by 1H NMR [54]. The structure of the
Results and Discussion
Preparation and Spectroscopic Characterization
of the Glycoside-Based Trisiloxane Surfactant
The general formula and process of the glycoside-based
trisiloxane surfactant is shown in Scheme 1. Herein, the
diethylene glycol monoallyl ether 1 was prepared by
the Williamson reaction in the aprotic solvent (dioxane).
The more monoallyl ether was produced by using excess
allyl chloride. The small amount of diallyl ether byproduct
was separated and removed by column chromatography.
The diethylene glycol monoallyl ether glycoside 2 was
prepared by glycosidation using p-toluenesulfonic acid
catalyzed. The water formed in the glycosidation was
distilled off in vacuum in time to promote the reaction
continue. An average degree of glycosidation of 1.1 was
obtained by using the excess diethylene glycol monoallyl
ether.
1
compound was confirmed by IR and H NMR.
(3) Preparation of glycoside-based trisiloxane 3. First
32.4 g (0.1 mol) of the diethylene glycol monoallyl
ether glycoside was introduced into a 500-mL round-
bottomed flask and heated with stirring to a temper-
ature of 80 °C and 0.4 g of a solution of 1 g of
H2PtCl6ꢀ6H2O in 76 g of isopropanol (platinum
content of the solution: 50 ppm) was added. Subse-
quently, 44.4 g (0.2 mol) of the 1,1,1,3,5,5,5-heptam-
ethyltrisiloxane was added dropwise over the course
of 30 min, during which the temperature rose to
The glycoside-based trisiloxane 3 was prepared by hy-
drosilylation using chloroplatinic acid as catalyst. The
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J Surfact Deterg (2011) 14:515–520
517
Scheme 1 The general process
of the glycoside-based
trisiloxane surfactant
CHCH2Cl
OH
H2C
CHCH2(OCH2CH2)2OH
H2C
HO(CH2CH2O)2H
HO
HO
O
OH
OH
HO
H
HO
CH2
CH3
Si
CH3
CH3
Si O
H
CH
H3C Si O
CH3
CH3
CH3
CH3
CH3
CH3
H3C Si O
CH3
CH2
O
O
H
(OCH2CH2)2O
Si
Si O
CH3
Pt
OH
HO
(CH2)3 CH3
HO
n
O
O
OH
H
n
(OCH2CH2)2O
n=1-2
HO
excess hydrogen-containing heptamethyl trisiloxane was
added, which allowed the reaction to proceed to comple-
tion and distilled off after reaction.
(t, 2H, Si–C–C–CH2), 3.12–3.84 (m, 8H, –O(CH2CH2O)2–,
and about 7H, in sugar, overlap), 4.35,4.82 (d, 1H, a, b-H
in glycosidic bond).
These compounds were structurally characterized by
1
their IR, H-NMR and MS spectra. The details of these
Equilibrium Surface Tension Measurements
spectral characterizations were as follows. In all cases, the
spectra acquired were consistent with the assigned struc-
tures of the compounds.
The equilibrium surface tension of dilute aqueous solu-
tions of the glycoside-based trisiloxane surfactant was
measured. For comparison, the 3-(polyoxyethylene-pro-
pyl)-1,1,1,3,5,5,5-heptamethyltrisiloxane (ethoxylated tri-
siloxane Silwet L-77 from GE, abbreviated as EOTS in
what follows) was also listed. The minimum surface
tension (cCAC) values were acquired by analyzing the
plateau region of the plots. The critical aggregation con-
centrations (CAC) of the surfactants were acquired by
analyzing the intersection point of the plateau region and
the steeply downward sloping portion of the plots. The
surface excess concentration (Cmax) and the surface area
per molecule (asm) were acquired by analyzing the appli-
cation of the Gibbs equation to the steeply downward
sloping section of the plots. A summary of the data was
compiled in Table 1 and in Fig. 1. These surfactants all
reduced the surface tension of water to a minimum value
of approximately 20 mN m-1 at concentrations of
Diethylene glycol monoallyl ether 1
IR (KBr, t, cm-1): 3,380–3,400 (–OH), 2,850–2,950 (C–H),
1,652 (C=C), 1,030–1,100 (C–O–C); 1H NMR (CDCl3,
300 MHz, d ppm): 2.50 (s, 1H, –OH), 3.57–3.71 (m, 8H,
–O(CH2CH2O)2–), 4.00–4.02 (d, 2H, C=C–CH2–),
5.15–5.30 (m, 2H, CH2=C–C–), 5.85–5.94 (m, 1H, C=CH–
C–); MS: m/z = 41 (CH2=CHCH2–), m/z = 45 (–CH2
CH2OH), m/z = 115 (M– –CH2OH).
Diethylene glycol monoallyl ether glycoside 2
IR (KBr, t, cm-1): 3,350–3,450 (–OH in sugar), 2,910–2,930
(C–H), 1,645 (C=C), 1,020–1,100 (C–O–C), 840 (a-glyco-
sidic bond), 886 (b-glycosidic bond); 1H NMR (D2O,
300 MHz, d ppm): 3.15–3.85 (m, 8H, –O(CH2CH2O)2–, and
about 7H, glucose ring, overlap), 4.39,4.84 (d, 1H, a, b-H in
glycosidic bond), 3.96–3.98 (d, 2H, C=C–CH2–), 5.14–5.27
(m, 2H, CH2=C–C–), 5.80–5.89 (m, 1H, C=CH–C–).
10-4 mol L-1
.
Inspection of the data in the Table 1 shows that the
glycoside-based trisiloxane surfactant and EOTS signifi-
cantly reduce the surface tension of the solution at low
concentration, indicating that these molecules adsorb
strongly at the air/water surface and they are highly
effective aqueous surfactants, reducing the surface tension
Glycoside-based trisiloxane 3
IR (KBr, t, cm-1): 3,350–3,450 (–OH in sugar), 2,850–
2,950 (C–H), 1,050–1,120 (C–O–C, Si–O–Si), 840
(a-glycosidic bond), 886 (b-glycosidic bond), 1,260, 840,
760 (Si(CH3)3), 2,150 (Si–H, disappeared), 1,645 (C=C,
of water to approximate 20 mN m-1
.
The value of cCAC is significantly lower than those
reported for organic glycosides [55] which are in the range
of 30–40 mN m-1 and is comparable to those reported for
other trisiloxane surfactants [1–10].
1
disappeared); H NMR (D2O, 300 MHz, d ppm): 0.006 (s,
3H, Si–CH3), 0.09 (s, 18H, Si(CH3)3ꢀ2), 0.35–0.45 (t, 2H,
The low surface tension of silicone surfactants has been
attributed to both the preponderance of highly surface
Si–CH2–), 1.45–1.55 (m, 2H, Si–C–CH2–), 2.55–2.57
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Micelle formation by siloxane surfactants in aqueous
solution has not been extensively investigated. Most of the
studies to date report critical micelle concentrations (CMC)
values from surface tension versus log surfactant concen-
tration plots. Although the structure of the micelles formed
was investigated in past few years, no conclusion was
drawn on the tendency of these surfactants to form well-
defined micelles [1–10].
Table 1 Aqueous surface activity of the glycoside-based trisiloxane
surfactant
Compound
Glycoside-based trisiloxane EOTS
CAC (molꢀL-1
)
1.30 9 10-4
20.18
1.68 9 10-4
cCAC (mNꢀm-1
)
19.09
2.40
Cmax (lmolꢀm-2
)
2.31
asm 102 (nmꢀmolecule-1
)
71.89
69.19
-31.50
-53.61
6.19
DGoagg (KJꢀmol-1
)
-32.14
-54.64
6.32
Assuming that the changes in slopes of the surface
tension versus log concentration curves in Fig. 1 represent
the onset of surfactant aggregation, possibly into micelles,
the CAC values for the surfactants are reported in Table 1.
Our interpretation of the plots is that aggregation is
occurring in solution, not necessarily micellization, and
that the CAC values can be determined by extrapolation.
This type of extrapolation is universally applied to this type
of plot to estimate critical aggregation concentration, and
we use it uncritically here. Some caution is that the pres-
ence of a break point in the surface tension versus log
concentration plot is only circumstantial evidence of
aggregate formation.
DGoads (KJꢀmol-1
pC20
)
CAC/C20
258.88
268.23
The CAC values are determined from extrapolation to
the break points in the surface tension versus log surfactant
concentration curves (Fig. 1). The CAC values vary with
the structure of the hydrophilic group.
The saturation adsorption values, Cmax, at the air/water
interface and the minimum area per surfactant molecule,
asm, at the air/water interface were obtained from the slope
of the surface tension versus log concentration plots
(Fig. 1) by using the approximate form of the Gibbs
adsorption isotherm equations (Eqs. 1 and 2).
Fig. 1 Plots of equilibrium surface tensions of aqueous solutions of
trisiloxane surfactants versus log moles concentration. (closed
squares), glycoside-based trisiloxane; (closed circles), ethoxylated
trisiloxane EOTS
ꢀ
ꢁ
1
oc
Cmax ¼ ꢁ
ð1Þ
2:303nRT o log C
T
active methyl substituents and a flexible polymer backbone
which allows the methyl groups to orient in low energy
configurations. By comparison, hydrocarbon surfactants
generally have many methylene groups in their hydro-
phobic portions, which have an intrinsically higher surface
energy than methyl groups. The surface tension values of
these surfactants suggest that the siloxane portion lies flat
on the water surface, exposing the methyl groups to the air.
When such a parallel orientation of the silicone back-
bone with respect to the water is adopted, it results in
relatively large areas of molecular surface coverage and
low CAC values.
1016
as ¼
ð2Þ
ð3Þ
ð4Þ
m
NACmax
ꢀ
ꢁ
CAC
DGo ¼ RT ln
agg
55:5
ꢀ
ꢁ
Cp
DGo ¼ RT ln
ꢁ 6:022pasm
ads
55:5
where R = 8.3144 J mol-1 K-1, NA = Avogadro’s num-
ber, Cmax is in mol cm-2, and ams is in 102 nm2 mole-
cule-1. In our solution, we can set n = 1. p (=c0 – c) is the
surface pressure in the region of surface saturation and Cp
is the molar concentration of surfactant in the aqueous
phase at a surface pressure p (in mN m-1).
In general, for both the known ionic and nonionic sur-
factants present, the value of the surface area per molecule,
asm, appears to be determined by the area occupied by the
hydrated hydrophilic groups, rather than by the hydro-
phobic group, because the chains in typical ionic or
Examination of Fig. 1 shows that the two plots have
significant changes in slope as a minimum surface tension
is reached. For most surfactants, this behavior implies that
aggregation is occurring in bulk solution. For the organic
glycosides mentioned in the previous section, the break
points were considered to be the critical micelle
concentrations.
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