B. Hong et al. / Journal of Molecular Catalysis A: Chemical 397 (2015) 142–149
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be interesting to have a tuning controllable and reversible param-
eter such as the temperature. This can be achieved with strongly
thermo-sensitive surfactants such as the nonionic polyethoxylated
alcohols, CiEj. Since a relevant catalytic em reaction medium must
and nonionic surfactants can lead to beneficial synergistic effects
[8,9]. Several applications take advantage of mixing surfactants to
are concerned, a dramatic enhancement of the efficiency of the non-
ionic surfactant, reflected by the minimal amount required to reach
the monophasic em, can be obtained by addition of very small
amounts (<1%) of an ionic surfactant [15–18]
In this paper, the well-defined nonionic tetraethylene glycol
monooctyl ether surfactant, abbreviated as C8E4, was used to elab-
orate a thermo-responsive catalytic em. The synergistic effect
between [DiC8]2[MoO4] and C8E4 is discussed in terms of cloud
point, surface tension and self-aggregation. The mixed micelle size
in the binary system is studied by dynamic light scattering (DLS).
The H2O/C8E4-[DiC8]2[MoO4]/cyclohexane system is successfully
applied to the dark singlet oxygenation (i.e. [4+2] cycloaddition, ene
reaction and sulfide oxidation) of organic substrates. The reaction
is thus conducted in the effective one-phase Winsor IV em while
cooling down the final reaction medium triggers a phase transi-
tion from the monophasic Winsor IV em to a biphasic Winsor I
em, allowing the recovery of product and catalyst in two different
phases.
the detection of small size micelle (<5 nm). Each sample was cen-
trifuged directly in the glass cell to avoid dust signal (30 min,
4500 rpm) during the DLS analysis. 13 angles from 30 to 150◦ were
record to determine the diffusion coefficient (Rh 0.1 nm). Cumu-
lant method was applied as data treatment of the correlogram for
each angle and polydispersity index was in all cases lower than 0.2
indicating that only monodisperse micelles were observed.
2.4. Binary diagrams
The water/surfactant mixture pseudo-binary diagram as a func-
tion of temperature was determined by visual inspection. At each
constant ˛, the solutions of different concentrations were prepared
and kept in the thermostatic bath. The temperature was increased
slowly (1.0 ◦C/min) from 15 to 80 ◦C and then decreased to 15 ◦C,
the temperature resulted in the turbid and phase separation for
each sample was recorded and this process was repeated for three
times to affirm the deviation under 0.1 ◦C.
2.5. Fish diagrams.
The Winsor types in the H2O/surfactant/cyclohexane fish dia-
gram were also determined by visual inspection with the same
volume of water and cyclohexane. For each constant ˛, sev-
eral microemulsions with increased ꢀ were prepared. From 10
to 45 ◦C with 1.0 ◦C increment for each time, all microemul-
sion tubes were kept in the thermostatic bath for 6 h for each
temperature and the Winsor types were recorded. The Fish dia-
grams were constructed by investigating the phase behavior of
the C8E4-[DiC8]2MoO4/cyclohexane/water systems at a constant
water-to-oil weight ratio as a function of temperature (ordinate)
and surfactant mass percentage (abscissa). The “Fish-tail” point
located at the intersection of the four Winsor (Winsor I, II, III and
IV) regions, corresponds to the minimal surfactant concentration
required to obtain a one-phase microemulsion (Winsor IV). Water,
oil and surfactant were introduced in a thin glass tube (Ø = 2 mm),
the headspace of which was filled with Argon and then frozen at
−78 ◦C with a dry ice/acetone mixture. The tubes were sealed by
flame to avoid any loss of oil or water during the experiment. Sam-
ples were gently shaken and placed in a water bath, maintained at a
constant temperature T 0.1 ◦C, until the equilibrium was reached.
The fish diagrams were constructed by visual inspection of the Win-
sor phases. The “fish-tail” temperature T* values were obtained
with an accuracy better than 1 ◦C.
2. Experimental
2.1. Specific notation
To specify the amount of [DiC8]2[MoO4] (surfactant 1), C8E4
(surfactant 2), H2O (W) and oil (O) in the phase diagrams, the total
mass fraction of surfactant 1 and surfactant 2, ꢀ, was defined as:
m1 + m2
ꢀ =
mO + mW + m1 + m2
The mole fraction of the ionic surfactant [DiC8]2[MoO4] in the
surfactant mixture, ˛, was defined as:
˛
1
˛ =
˛
1 + ˛2
2.6. Typical catalytic experiments
2.2. Surface tension measurements
[DiC8]2[MoO4] (11.1 mg, 15.8 mol), C8E4 (211.1 mg,
0.689 mmol), H2O (1.0 g), cyclohexane (1.0 g) were added con-
secutively to prepare the microemulsion in a reaction tube. Then
␣-terpinene (50 mg, 0.367 mmol) was added into the mixture and
kept at 30 ◦C (Winsor IV), the H2O2 (50 wt.%, 17 M) was added
stepwise (10 L, each 20 min). The conversion was complete after
the addition of 6× 10 L (1.02 mmol). Then the reaction tube
was kept still at 5 ◦C for 3 h, the oil phase was separated and the
microemulsion phase was washed with cyclohexane (1 mL) at
5 ◦C, the organic phases were combined and cyclohexane was
removed by evaporation, the crude product was purified by a
small chromatography on silica gel (cyclohexane/AcOEt = 5:1) and
pure colorless oil was obtained (56.6 mg, 92%). 1H NMR (300 MHz,
CDCl3, 20 ◦C, TMS): ı (ppm) = 1.01 (d, J = 2.25, 3H; CH3), 1.03 (d,
J = 2.25, 3H; CH3), 1.39 (s, 3H; CH3), 1.19–1.57 (m, 2H, –CH2–CH2–),
1.87–2.03 (m, 1H; isopropyl), 2.03–2.14 (m, 2H; –CH2–CH2–), 6.47
(dd, J = 25.77, 8.55 Hz; CH CH). 13C NMR (75 MHz, CDCl3, 20 ◦C): ı
(ppm) = 17.2, 17.3, 21.4, 25.6, 29.5, 32.1, 133.0, 136.4.
The CMCs of the surfactants were obtained by the surface ten-
sion measurements with the tensiometer K11 (Krüss) using the
Wilhelmy plate method with the precision of the force transducer
to 0.1 mN m−1. For each surfactant mixture of specified ˛, the
surface tensions of different concentrations were recorded after
equilibration. The average quantity of at least three measurements
was adopted for all equilibrium surface tension values. Before
each experiment, the platinum plate was cleaned in red/orange
color flame. The temperature was stabilized at 25 0.05 ◦C with
a thermo-regulated bath Lauda RC6.
2.3. Dynamic light scattering (DLS)
DLS measurements were performed on a ALV/CGS-3 Super Com-
pact Goniometer System at 25 ◦C (thermo regulated bath 0.1 ◦C).
Pseudo cross correlation mode is used with two APD to improve