Molecular mechanism of micellar catalysis of cross aldol reaction: Effect of surfactant chain length and surfactant concentration

Article abstract of DOI:10.1016/j.molcata.2014.09.023

The importance of alkyl chain length and concentration of quaternary ammonium surfactants (QAS) in the micellar catalysis of cross aldol reaction was investigated. The NaOH-micellar system catalyzed aldol reaction of benzaldehyde and cyclohexanone to α,α′-dibenzylidene cyclohexanone (di condensation/desired product) over mono condensation product was used as model reaction for this study. The C₁₆QAS micellar system (QAS with n-hexadecyl group) gave highest cyclohexanone conversion (90%) to desired product (82%) showing that C₁₆QAS micellar system possesses optimum properties and/or microenvironment for this reaction. Furthermore, the micellar system with high surfactant concentration (C₁₆QAS; >150mM) made the reaction faster giving >99% conversion to selectively desired product (>99%) within 30min The large interface created by C₁₆QAS micelles in the aqueous medium at high surfactant concentration makes the reaction faster by facilitating the interaction of hydrophobic reactants and water soluble catalyst (OH- ions). The activation of benzaldehyde molecules, their localization preferably near the interface and stabilization of enolate ions (reactive intermediates) by micellar system at high surfactant concentration were observed to be promoting the cross reaction selectively to the desired product.

Full text of DOI:10.1016/j.molcata.2014.09.023

Journal of Molecular Catalysis A: Chemical 396 (2015) 143–154
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Molecular mechanism of micellar catalysis of cross aldol reaction:
Effect of surfactant chain length and surfactant concentration
Manu Vashishthaa, Manish Mishraa,∗, Sachin Undreb, Man Singhb, Dinesh O. Shaha,c
a Department of Chemical Engineering & Shah-Schulman Center for Surface Science and Nanotechnology, Faculty of Technology,
Dharmsinh Desai University, College Road, Nadiad 387 001, Gujarat, India
b School of Chemical Sciences, Central University of Gujarat, Sector-30, Gandhinagar 382030, India
c Department of Chemical Engineering and Department of Anesthesiology, University of Florida, Gainesville, FL 32608, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The importance of alkyl chain length and concentration of quaternary ammonium surfactants (QAS)
in the micellar catalysis of cross aldol reaction was investigated. The NaOH-micellar system catalyzed
aldol reaction of benzaldehyde and cyclohexanone to ␣,␣ꢀ-dibenzylidene cyclohexanone (di condensa-
tion/desired product) over mono condensation product was used as model reaction for this study. The
Received 19 January 2014
Received in revised form 17 July 2014
Accepted 7 September 2014
C
16QAS micellar system (QAS with n-hexadecyl group) gave highest cyclohexanone conversion (90%)
Keywords:
Cross aldol condensation
Base catalysis
to desired product (82%) showing that C16QAS micellar system possesses optimum properties and/or
microenvironment for this reaction. Furthermore, the micellar system with high surfactant concentra-
tion (C16QAS; >150 mM) made the reaction faster giving >99% conversion to selectively desired product
(>99%) within 30 min The large interface created by C16QAS micelles in the aqueous medium at high
surfactant concentration makes the reaction faster by facilitating the interaction of hydrophobic reac-
tants and water soluble catalyst (OH− ions). The activation of benzaldehyde molecules, their localization
preferably near the interface and stabilization of enolate ions (reactive intermediates) by micellar sys-
tem at high surfactant concentration were observed to be promoting the cross reaction selectively to the
desired product.
␣,␣ꢀ-Dibenzylidene cyclohexanone
Cetyltrimethy ammonium bromide
Micellar catalysis
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
sensitive toward water as they can undergo side reactions (like oxi-
dation of aldehydes to acids) reducing the yield of desired product.
The solvent-free and water mediated organic synthesis are
in high demand to establish industrially viable ecofriendly pro-
cesses for synthesis of chemicals. The water, being inexpensive
and safe, is always preferred as green solvent in organic synthesis.
Its great potential in promotion of many organic reactions under
ambient reaction condition has been proven [1], which inspires
the researchers to explore the use of water as solvent in organic
synthesis. However, the limited solubility of organic reactants
(hydrophobic) in water is the major constrain in water mediated
synthesis especially when the other components (reactants and/or
catalysts) of the reaction are water soluble resulting into very slow
reaction. The less interfacial area between two phases (organic and
aqueous) in such biphasic reactions reduces the residence time of
water soluble and water insoluble components for their interac-
tion. There are many organic compounds (e.g., aldehydes) which are
The water can also be detrimental for some water sensitive catalysts
causing the catalyst decomposition or deactivation and therefore
cannot be reused. Therefore, the aqueous or biphasic reaction sys-
tems are required to be devised to overcome the above problems
and to have the benefits of water in organic synthesis.
The surfactant micelles are aggregates of amphiphilic surfactant
molecules in water having hydrophobic core and ionic surface. The
micelles have been used for making hydrophobic compounds com-
patible with aqueous system by solubilization in the core to carry
out the organic reactions in water [2]. The micelles facilitate the
reactions in water by concentrating the hydrophobic compounds
in the micelles and water soluble ionic species near micellar surface
[3]. This promotional effect of micelles in the catalytic reactions is
also known as micellar catalysis. The use of micellar system in catal-
ysis can play a foremost role in the development of economical,
energy efficient and environmentally benign processes avoiding
the use of organic solvents, high temperature, decay of catalyst, side
reactions, etc. In recent years, the use of surfactant micellar systems
has been widely explored for promotion of various reactions in
∗
Corresponding author. Tel.: +91 268 2520502; fax: +91 268 2520501.
E-mail address: manishorgch@gmail.com (M. Mishra).
http://dx.doi.org/10.1016/j.molcata.2014.09.023
1381-1169/© 2014 Elsevier B.V. All rights reserved.

144
M. Vashishtha et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 143–154
water showing significant enhancement in reaction rate and prod-
uct selectivity [4]. Recently we demonstrated the effectiveness and
reusability of NaOH-cationic (quaternary ammonium surfactant:
QAS) micellar system for equimolar aldol reaction of benzaldehyde
and n-heptanal to cross aldol product (jasminaldehyde) giving its
highest selectivity as compared to other heterogeneous catalysts
reported till date [5]. We reported that the alkyl chain length and
concentration of QAS play important role in micellar catalysis of
cross aldol reaction of benzaldehyde and n-heptanal showing high-
est activity of C16QAS (cetyltrimethylammonium bromide) micellar
system at high concentration (200 mM).
In continuation of our work on micellar catalysis of cross aldol
reactions, we did a detail study on NaOH-QAS micellar system
catalyzed cross aldol condensation of benzaldehyde and cyclohex-
anone to ␣,␣ꢀ-bisbenzylidene cyclohexanone (Scheme 1) as model
reaction to investigate the importance of QAS’s alkyl chain length
and concentration on the cross aldol reactions. The ␣,␣ꢀ-bis (sub-
stituted benzylidene) cycloketones are important precursors for
the synthesis of bioactive pyrimidine derivatives, intermediates
of perfumes, pharmaceuticals, and agrochemicals [6,7]. The mono
condensation product (␣-benzylidene cyclohexanone) is the co-
product of the reaction, which is considered to be intermediate (it
reacts with second molecule of benzaldehyde) of the di conden-
sation product (␣,␣ꢀ-bisbenzylidene cyclohexanone). Incomplete
conversion of mono condensation product to di condensation
product reduces the selectivity or yield of ␣,␣ꢀ-bisbenzylidene
cyclohexanone. The synthesis of ␣,␣ꢀ-bis (substituted benzylidene)
cycloketones by cross aldol reaction of aromatic aldehydes with
cyclic ketones using NaOH-cationic micellar (15 mM) system has
already been reported by Janhavi et al. [8].
Supporting our previous observation this study also shows that
the QAS’s alkyl chain length and concentration are major factors in
micellar system mediated cross aldol reaction of benzaldehyde and
cyclohexanone influencing the reaction rate and product selectiv-
ity. The reaction in C16QAS micellar system at high concentration
(150 mM) gave complete conversion to >99% ␣,␣ꢀ-bisbenzylidene
cyclohexanone. Therefore, we were interested to investigate the
role of surfactant’s alkyl chain length and concentration in the
promotion of cross aldol reactions. In the present study, by char-
acterizing the reactants-micellar systems, we could explicate that
C16QAS micellar system (which possesses optimum properties
and/or microenvironment for the reaction) at high concentration
not only create large interface but also populates the reactants and
reaction intermediates at interface for fast and selective conver-
sion. It was also found that C16QAS micellar aggregates activate the
benzaldehyde molecules and stabilize the enolate ions of cyclo-
hexanone and intermediate product (mono condensation product)
for selective di-condensation reaction. The study revealed that
NaOH-C16QAS micellar system at high surfactant concentration is
an efficient catalytic system for promotion of cross aldol reactions.
The cross aldol reaction of benzaldehyde (1) and cyclohexanone
(2) (Scheme 1) was performed to evaluate the catalytic property
of different NaOH-QAS micellar systems with varied alkyl chain
length of surfactant and concentration studying their influence on
the reaction (conversion and selectivity). For comparison biphasic
reaction was also carried out in water (without QAS).
In a 50 mL reaction tube of reaction station (12 Place Heated
Carousel Reaction Station, RR99030, Radleys Discovery Tech-
nologies, UK), 10 mL of QAS aqueous solution (of required
concentration) or water (without surfactant) was taken and a mix-
ture of benzaldehyde (10 mmol) and cyclohexanone (5 mmol) was
added in the solution under stirring. The NaOH was dissolved in
the solution and the reaction mixture was stirred at 60 ◦C for the
required period of time. After the completion of reaction, the reac-
tion mixture was neutralized with concentrated HCl and excess of
saturated NaCl solution was added to reduce the surfactant con-
centration below the cmc. The organic phase was extracted with
ethyl acetate (10 mL) and was analyzed by gas chromatography
(Agilent 5975) having a HP-5 (60 m, 250 ␮m diameter) capillary
column with a programmed oven temperature from 50 to 280 ◦C, at
1 mL min−1 flow rate of N2 as carrier gas and FID detector. The con-
version of cyclohexanone was calculated on the basis of its weight
percent as follows:
conversion (wt.%) of cyclohexanone
[initial wt.% of cyclohexanone − final wt.% of cyclohexanone]
= 100 ×
.
initial wt.% of cyclohexanone
The selectivity of the products 3 and 4 was calculated as below:
selectivity (%) of3 or4
GC peak area% of product3 or4
ꢀ
= 100 ×
.
total peak area for all the products
The di and mono condensation products were characterized by
GC–MS analysis and the data were matched with those reported in
the literature. GC–MS analysis was carried out using gas chromato-
graph mass spectrometer (Agilent 5975 GC/MSD with 7890A GC
system) having HP-5 capillary column of 60 m length and 250 ␮m
diameter with a programmed oven temperature from 50 to 280 ◦C,
at 1 mL min−1 flow rate of He as carrier gas and ion source at 230 ◦C.
The aqueous solutions of reactants (1 and 2 separately as well
as their mixture) with and without QASs were analyzed using a
Magnus light microscope (model-OLYMPUS CH 20iBIMF). A drop
of solution was placed on a graduated glass slide (with least count
0.1 mm) without a cover slip. The images were captured with
microscope fitted with a digital Sony color video camera (model-
E413P) using TV home media software at 10× objective lance
magnification. The UV–vis spectra of benzaldehyde and cyclohex-
anone in water and QAS aqueous solutions were performed on an
Agilent, Carry 5000 spectrometer at room temperature. The path
length of the quartz cell used in this experiment was 1 cm The
UV absorptions of benzaldehyde and cyclohexanone in water and
surfactant aqueous solutions were studied by using their sepa-
rate solutions (benzaldehyde: 0.05 mM; cyclohexanone: 5 mM) in
water and in surfactant solutions. This amount of benzaldehyde
was completely soluble in the water and in QAS solutions giving
a transparent solution, however, these concentrations of benzal-
dehyde and cyclohexanone were different from those used in the
catalysis experiments. The 1H NMR analysis of QASs solutions with
and without reactants (benzaldehyde-cyclohexanone) mixture in
D2O was carried out using a Bruker Avance III 500 MHz spectrom-
eter. The reactants mixture (benzaldehyde and cyclohexanone in
2:1 molar ratio; 10 ␮L) was solubilized in 1 mL D2O or QAS solution
in D2O. The number of acquisitions was 32 for each sample. The
2. Materials and experimental methods
Benzaldehyde (>99%), cyclohexanone (99%), sodium hydroxide
(NaOH; 97%), ethyl acetate (99%), concentrated hydrochloric acid
(HCl; 35%) and sodium chloride (NaCl; 99%) were purchased from
Merck, India. The quaternary ammonium surfactants (QASs) like
decyl trimethyl ammonium bromide (C10QAS; 98%) was from Spec-
trochem, India, dodecyl trimethyl ammonium bromide (C12QAS;
98%), tetradecyl trimethyl ammonium bromide (C14QAS; 98%) and
hexadecyl trimethyl ammonium bromide (C16QAS; 98%) were from
s.d. Fine Chemicals, India and octadecyl trimethyl ammonium bro-
mide (C18QAS; 99%) was procured from Sigma–Aldrich. All the
chemicals were used without any further purification. The milli-
pore deionized water was used in preparation of all the solutions.

M. Vashishtha et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 143–154
145
O
H
C
O
O
O
NaOH (5 mmol)
+
+
Water or QAS aq. sol.
(10 mL)
60oC
Benzaldehyde (1) Cyclohexanone (2)
Di condensation product (3)
Mono condensation product (4)
(α-benzylidene cyclohexanone)
(10 mmol)
(5 mmol)
(α,α'-bisbenzylidene cyclohexanone)
Scheme 1. Cross aldol reaction of benzaldehyde (1) and cyclohexanone (2) in NaOH-QAS solution/in water.
100
Br
N
a
Conv. of 2
Select. of 3
Select. of 4
CH3
CH3
80
60
40
20
0
C10QAS (cmc = 64.6 mM)
C12QAS (cmc = 14.2 mM)
CH3
Br
N
CH3
CH3
CH3
Br
N
CH3
CH3
CH3
C14QAS (cmc = 3.6 mM)
C16QAS (cmc = 0.92 mM)
Br
N
In water C10QAS C12QAS C14QAS C16QAS C18QAS
CH3
CH3
Reaction in different medium
b100
CH3
80
60
40
20
0
Br
N
CH3
CH3
C18QAS (cmc = 0.4 mM)
CH3
0
0
0
10
10
10
20
20
20
30
30
30
40
40
40
50
50
50
60
60
70
70
70
80
80
90
90
90
100
100
80
60
40
20
0
Scheme 2. Different QASs (and their CMC values in water at 25 ◦C [9]) used in cross
aldol reaction of benzaldehyde and cyclohexanone in NaOH-QASs micellar solutions.
1H chemical shifts are reported in ı units (ppm) relative to that of
tetramethylsilane (TMS) as external standard.
100
100
90
80
70
60
50
40
3. Results and discussion
3.1. Cross aldol reaction of benzaldehyde and cyclohexanone in
NaOH-QAS micellar systems of different surfactants with varied
alkyl chain length
C
C
QAS
QAS
C
C
QAS
QAS
10
14
12
16
C
QAS
100
18
60
80
3.1.1. Conversion and product selectivity with different QAS
micellar systems
QAS conc. (mM)
The cross aldol reaction of benzaldehyde and cyclohexanone
was first carried out in NaOH-QAS micellar systems (QAS concen-
tration: 15 mM) of different surfactants with varied alkyl chain
length (Scheme 2) to study the effect of alkyl chain length of QAS
on the micellar catalysis of aldol reaction.
The reactions in NaOH-QAS micellar solutions (Fig. 1a) gave
remarkably higher conversion of cyclohexanone (61–90%) than
biphasic reaction (44% conversion) showing faster reaction rate in
micellar media. There was no formation of di-condensation product
(3) in biphasic reaction (i.e. without QAS), while di-condensation
product was formed in good amount (17–82%) in NaOH-QAS micel-
lar solutions. This is an interesting result that the presence of
surfactant in reaction medium not only enhances the conversion
rate but also promotes the di-condensation reaction. From Fig. 1a
it is clearly evident that the alkyl chain length of QAS has significant
influence over reaction rate as well as di-condensation reaction
(i.e., selectivity to 3). The C16QAS micellar system showed highest
Fig. 1. (a) Conversion and selectivity of di (3) and mono (4) condensation products in
NaOH base catalyzed cross aldol condensation of benzaldehyde and cyclohexanone
in water and in different QAS micellar solutions [reaction condition: 10 mmol benz-
aldehyde, 5 mmol cyclohexanone, 5 mmol NaOH, 10 mL aqueous surfactant solution
(15 mM), 60 ◦C, 30 min]. (b) Conversion and selectivity of di (3) and mono (4) conden-
sation products in NaOH base catalyzed cross aldol condensation of benzaldehyde
and cyclohexanone in QAS miceller solutions at different concentrations [reaction
condition: 10 mmol benzaldehyde, 5 mmol cyclohexanone, 5 mmol NaOH, 10 mL
aqueous surfactant solution (0.25 mM, 5 mM, 15 mM, 70 mM and 100 mM), 60 ◦C,
30 min].
activity giving highest cyclohexanone conversion (90%) and selec-
tivity of 3 (82%) as compared to other QAS micellar systems. On
increasing the alkyl chain length of QAS from C10 to C16, the conver-
sion and selectivity of 3 were gradually increased from 61% to 90%
and 18% to 82%, respectively. With C18QAS system, the conversion
and the selectivity for 3 were reduced to 66% and 17%, respectively.

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M. Vashishtha et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 143–154
The faster reaction rate in micellar media than pure water is
of QAS from C12 to C16 at same concentration, will also enhance
the interfacial area in the micellar system. The increasing chain
length of a surfactant increases the stability of micelles due to
strong van der Waals forces as well as hydrophobic association
between the alkyl chains [26], which can provide stable micellar
interface (common platform) for better interaction of hydrophobic
and water soluble reagents of the reaction. In addition to this, the
strong interaction between surfactant molecules (close molecular
packing) in the micelles also influences the surface charge [21,23].
As the quaternary ammonium group of QAS will come closer on
increasing chain length due to close molecular packing in micelles,
the surface pH (OH− ion concentration) at micellar interface will be
enhanced, which will accelerate the reaction rate. Thus the highest
catalytic performance of C16QAS micellar system in comparison of
attributedto largemicellarinterfacegeneratedin aqueousmedium,
which provides micellar surface as a platform for the interac-
tion of hydrophobic and water soluble components. The positively
charged micellar surface can have high OH− ions concentration by
attracting more OH− ions due to Coulombic force increasing the
local pHs (i.e. pH near the surface of the micelle) of the micel-
lar surface than the pH of bulk solution [10,11]. The micelles will
also concentrate the reactants by solubilizing within the micelles
in required orientation [12]. The high OH− ions concentration (high
pH) at the micellar surface and concentrated reactants within the
micelles can have better interaction giving faster conversion and
preferred product in the reaction. The positively charged micellar
surface may also assist in populating and stabilizing the reactants
and intermediates (enolate ions) at the interface for their reaction
[13,14].
It is well recognized that micelles are dynamic structures. They
form and break at the time scale of milliseconds [15]. Thus at any
time, there are submicellar fragments in equilibrium with micelles
and monomers. By the same token, when micelles form, it is not
abrupt phenomenon but as concentration increases toward Criti-
cal Micelle Concentration (CMC), the concentration of submicellar
aggregate increases and at CMC, full micelles form and upon further
addition of surfactant, the number of micelles increases, whereas
the monomer concentration remains constant. Using filtration
through nanoporous membranes, Smith et al. [16] have shown that
sodium dodecyl sulfate micellar solutions are not only made up
of micelles and monomers, but also contain a high concentration
of sub-micellar aggregates and the concentration of sub-micellar
aggregates decreases as the micellar stability increases. Thus, in the
15 mM C10QAS solution, very likely there are monomers and submi-
cellar aggregates as the concentration is less than CMC (64.6 mM).
However, the increased cyclohexanone conversion (61%) and for-
mation of 3 (18%) in 15 mM C10QAS micellar solution (Fig. 1a)
indicates the involvement of surfactant molecules, presumably in
the form of submicellar aggregates, in catalysis of the reaction. This
has been reported by several researchers that in the micellar medi-
ated reactions below CMC, also known as premicellar concentration
(pre-CMC), a small number of surfactant monomers may aggre-
gate with a substrate molecule to form a catalytic micelle, which
contributes in enhancement of the reaction rate [17–20]. Brinchi
et al. [19], reported that didodecyldialkylammonium chloride and
bromide accelerate the spontaneous decarboxylation reactions
showing first-order rate constants, kobs, maxima in very dilute
surfactant solution. The phenomena were interpreted in terms of
substrate-induced micellization, depletion of water at the reac-
tion center and association of substrate and quaternary ammonium
centers. In 15 mM C10QAS solution, the reactant molecules may
get associated with sub-micellar aggregates, which may catalyze
the di-condensation reaction giving di-condensation product and
enhancement in the reaction rate. Thus the reaction in 15 mM
C12QAS and C14QAS systems can be attributed to more number of
micelles, higher hydrophobicity of micelles, large interfacial area,
stable micellar interface and high surface pH effect facilitating the
solubilization of water insoluble components (reactants), enhance-
ment of OH–ion concentration at interface and the interaction of
water soluble and water insoluble components. The C18QAS sys-
tem (15 mM solution) showed least activity giving low conversion
and selectivity of 3, which is due to very strong solubilization of the
reactant molecules owing to compact molecular packing and high
hydrophobicity, which restrict the diffusion of reactant molecules
for interaction with OH− ion at interface.
The reactions were also studied in C10 to C18QAS solutions by
using different concentrations covering their premicellar concen-
trations, CMC and higher concentrations (0.25–100 mM solutions;
Fig. 1b). The results clearly reveal that C16QAS micellar system
possesses optimum properties and/or microenvironment for this
reaction giving highest conversion and selectivity of 3 (at all con-
centrations) as compared to other QAS. At less concentrations
(e.g., 10 and 15 mM), C16QAS gave reasonably high conversion
and selectivity of 3. The lower QAS (C10–C14) also increased the
conversion and selectivity of desired product, but at high concen-
trations (70 and 100 mM). The lower surfactants (C10QAS, C12QAS
and C14QAS) require high surfactant concentration to achieve the
enhanced catalytic activity as C16QAS micellar system possesses
at less concentration (15 mM). The enhanced activity of C10 to
C14QAS micellar systems at higher concentrations can be attributed
to enhanced number of micelles and increased interface, which
facilitate the interaction of water soluble and water insoluble
reagents by enhancing the solubilization of water insoluble reac-
tants and populating more OH− ions at interface. The C18QAS
systems (0.25–100 mM solutions) always give lower conversion
and selectivity of 3 at all concentrations showing decreased activity
of the C18QAS systems in comparison of C16QAS systems. In spite of
higher number of micelles (less CMC) and huge interface in C18QAS
systems than other QAS systems, the lower conversion and selectiv-
ity of 3 clearly shows that very strong solubilization of the reactant
molecules by micelles due to close packing of surfactant molecules
might be reducing their availability at interface decreasing the reac-
tion rate and selectivity to di-condensation reaction.
C
10QAS solution is due to presence of submicellar aggregates in
the pre-CMC region.
The increasing cyclohexanone conversion with increasing alkyl
chain length of QAS from C12 to C16 (15 mM solutions; Fig. 1a)
might be a collective effect of important features of micellar sys-
tem such as number of micelles and their size, stability of micelles,
hydrophobicity, inter molecular distance of surfactant molecules
in the micelles (molecular packing), surface charge density (sur-
face pH), etc. These properties significantly change on varying the
alkyl chain length of a surfactant [16,21–27]. With increasing chain
length of QAS from C12 to C16 at same concentration (15 mM), the
solubilization of reactant molecules by the micelles will increase
due to increasing number of micelles (owing to decreasing CMC),
micelle volume and hydrophobic nature of micelles [25]. In addi-
tion, the increasing number of micelles, on varying the chain length
The formation of 3 in micellar systems (Fig. 1a and b) indicates
that micelles might be concentrating benzaldehyde in sufficient
amount and in proper orientation for di-condensation with cyclo-
hexanone (i.e., its enolate ion). In addition, the formed mono
condensation product (4) may also be retained by micelles,
probably at micellar interface, for further condensation with sec-
ond benzaldehyde molecule (i.e., di-condensation reaction). The
hydrophobic nature of 4 and stabilization of its enolate ions by
micellar interface (ionic interaction with ammonium group) may
be the attributes for the localization of 4 at micellar interface
for di-condensation reaction. The increasing selectivity of 3 with
increasing alkyl chain length of QAS from C10 to C16 (Fig. 1a and b)
can be attributed to increasing interface (due to increasing number

M. Vashishtha et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 143–154
147
of micelles) and hydrophobicity, which help in stabilization of the
intermediate product (4) at micellar interface for di-condensation
reaction. The bis-alkylation of ␥-phenylcyclohexanone with benzyl
halides in two steps to bis-alkylation products in higher amount
has been reported in cationic micellar system suggesting that the
hydrophobic nature of intermediate and its stabilization by micellar
aggregates facilitate di-alkylation reactions [13]. The less selectiv-
ity of 3 with C18QAS systems may be due to less availability of
benzaldehyde molecules at interface for di-condensation reaction
with 4, which may be due to very compact packing of surfactant
molecules and their strong hydrophobicity, which restrict the diffu-
sion of solubilized benzaldehyde molecules from bulk to interface.
In addition, the strong solubilization of 4 within the micelles may
also reduce its availability at interface for interaction with OH–ions
and reaction with benzaldehyde to form 3.
In biphasic reaction, the reaction takes place at water–oil inter-
face, where no surfactant molecules are available to hold the
mono-condensation product to form its carbanions (with the help
of OH− ions) followed by reaction with second molecule of benz-
aldehyde. The mono-condensation product may go away from
interface in bulk (probably in oil phase due to its hydrophobic
nature) and may not be assessable to OH− ions for carbanion for-
mation and to react with benzaldehyde molecule. This may be the
probable reason for no di-condensation reaction, when reaction is
carried out in the pure water. The presence of surfactant molecules
at interface not only speeds up the reaction, but it also helps in
holding the intermediate product (mono-condensation product) at
interface for di-condensation reaction.
It can be seen that the extremely high hydrophobicity of C18QAS
micellar system is unfavorable for the aldol reaction and di-
condensation reaction. The very high hydrophobicity of C18QAS
micelles and tight packing of surfactant molecules in micelles
may strongly solubilize the reactant(s) and/or intermediate prod-
uct (4) within the micelles reducing their availability at interface,
which will slow down the reaction rate as well as formation of
di-condensation product (3). This indicates that C16QAS micel-
lar system possesses optimum properties for this reaction. We
have reported the similar effect of QAS’s alkyl chain length on the
reaction rate of cross aldol reaction between benzaldehyde and n-
heptanal, and selectivity to cross aldol product (jasminaldehyde)
showing highest cross product selectivity with C16QAS micellar
system [5]. To investigate the role of alkyl chain length of QAS on
the performance of micellar systems in cross aldol reaction, the
micellar-reactants systems were characterized.
within the micelles may also reduce the size of emulsion droplets.
Gao et al. [25], demonstrated the higher solubilization capacity
of C16QAS micelles for polystyrene than C12QAS due to higher
hydrophobicity resulting into enhanced degree of chloromethyla-
tion of polystyrene in C16QAS solution. The benzaldehyde emulsion
droplets are of very small size in C18QAS solution indicating very
high solubilization of benzaldehyde in their micelles. The C10QAS
solution will have only monomers and submicellar aggregates as
the concentration is below CMC (Scheme 2), therefore, benzalde-
hyde droplets in C10QAS solution are not much changed as compare
to the droplet size in water. The C10QAS monomers and submicel-
lar aggregates may emulsify the benzaldehyde droplets by getting
adsorbed over droplets producing bigger size droplets. The droplet
size of benzaldehyde-cyclohexanone mixture in water and QAS
solutions were almost similar to that in water and QAS solutions.
The NaOH catalyzed aldol reaction of benzaldehyde and cyclo-
hexanone in water is under biphasic condition (NaOH and
cyclohexanone will be in aqueous phase), which has very limited
interfacial area for interaction of hydrophobic and hydrophilic com-
ponents giving less conversion to mono-condensation product.
We observed that benzaldehyde-water mixture gets phase sepa-
rated very quickly (within 30–40 s), however benzaldehyde-QASs
solutions give comparatively stable emulsions. The benzaldehyde
droplets are stabilized by QAS micelles and submicelles and the
reaction in QAS solutions occurs at the interface of micelles or
emulsion droplets. The optical microscopy results clearly support
that the increasing substrate conversion with increasing alkyl chain
length of QAS from C10 to C16 is attributed to huge interface created
in the aqueous medium. From the optical microscopy results, it was
expected that the C18QAS giving smallest benzaldehyde droplets
should be best micellar system providing high interfacial area for
reaction. In spite of having smallest droplet size (high interfacial
area) in the C18QAS micellar system, its reduced performance in
micellar catalysis can be attributed to close packing of surfactant
molecules and very high hydrophobicity of the micelles resulting
into strong solubilization of reactants and/or reaction intermediate
reducing their availability at interface for reaction.
3.1.3. UV spectroscopic study of reactant-QAS micellar systems
In addition to creating huge interface by C16QAS micelles in the
aqueous medium, their optimum properties and/or microenviron-
ment seems to be playing important role in promotion of the cross
aldol reaction. To prove this, UV absorption characteristics of both
the reactants (benzaldehyde and cyclohexanone) were separately
studied in water and in different QAS micellar solutions (15 mM).
The UV absorption spectrum of benzaldehyde in water (Fig. 3a)
shows an intense band at 249.5 nm ascribed to ␲→␲* transition.
This band does not show any shift in QAS solutions, however, the
intensity of the band changes as the alkyl chain length of QAS is
varied. In C10QAS solution, the band intensity is decreased as com-
pared to water. Whereas the band intensity gradually increases
on varying the alkyl chain length of QAS from C12 to C16 and a
very high increase in band intensity can be seen in C18QAS solu-
tion. It indicates the increasing solubilization of benzaldehyde in
micelles due to increasing hydrophobicity of QAS micelles. The
decreased intensity of the band in C10QAS solution may be due to
encapsulation of benzaldehyde droplets with the help of C10QAS
molecules/submicelles (as the concentration is less than CMC). The
greatly elevated intensity of the benzaldehyde band in C18QAS sys-
tem is indicative of very high solubilization of benzaldehyde due
to very strong hydrophobicity of micelles i.e., strong interaction of
benzaldehyde with hydrophobic core of C18QAS micelles.
3.1.2. Optical microscopy analysis of reactants-QAS micellar
systems
The benzaldehyde (10 mmol) and cyclohexanone (5 mmol)
were separately mixed with water (10 mL) and QAS solutions
(15 mM, 10 mL) to analyze their miscibility in both media by
optical microscopy. The optical microscopy (Fig. 2a) analysis of
benzaldehyde-water mixture indicates the existence of micron
size droplets of benzaldehyde indicating that the benzaldehyde
(the amount used in the reaction) is not completely miscible with
water. Whereas cyclohexanone was found to be completely dis-
solved in water as no droplets were observed in optical microscopy
analysis. The micellar-reactants systems can have micelles with
solubilized molecules of reactants and emulsion droplets of dif-
ferent size. In QAS solutions (15 mM), the emulsion droplet size
of benzaldehyde can be seen to be decreasing (Fig. 2b–f) with
increasing QAS’s alkyl chain length from C10 to C18. The increase
in alkyl chain length of QAS increases the hydrophobicity (solu-
bilization capacity) of micelles [25,27]; this will cause depletion
of benzaldehyde droplets solubilizing within the micelles and
will form smaller emulsion droplets. On varying the chain length
of QAS from C10 to C18, the increasing chain-chain interaction
The major absorption band for cyclohexanone in water was
occurred at 276 nm (n→␲*). The band intensity was not much
changed in the C12 to C18QAS solutions as compared to water indi-
cating no significant effect of increasing hydrophobicity of QAS

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M. Vashishtha et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 143–154
Fig. 2. Optical micrographs of benzaldehyde in (a) water, (b) C10QAS, (c) C12QAS, (d) C14QAS, (e) C16QAS and (f) C18QAS solutions (conc.: 15 mM; the scale bar equals 200 ␮m).
on solubilization of cyclohexanone in the QAS micelles (Fig. 3b).
However, the band intensity was observed to be increased in
interface to facilitate the cross reaction. The free cyclohexanone
molecules (which are not solubilized in micelles and are in aque-
ous medium) will form its enolate ions with the help of NaOH and
can approach the positively charged micellar surface to react with
benzaldehyde molecules solubilized in the micelles. The cationic
micelles may also stabilize the enolate ions of cyclohexanone and
mono-condensation product by interacting through quaternary
ammonium group of surfactant. This has been reported that the
cationic surfactants significantly enhance the acidity of aromatic
ketones in micellar solution on account of a strong interaction of
the enolate ions with the micellar aggregates [28].
C10QAS solution indicating the solubilization of cyclohexanone in
their micelles, which may be due to association of cyclohexanone
molecules with submicelles making their micellar aggregates.
The lower band intensity with higher QAS (C12 to C18QAS) indi-
cates lesser solubilization of cyclohexanone in their micelles.
The enhanced chain-chain interaction between QAS molecules on
increasing alkyl chain length, structural incompatibility of cyclo-
hexanone molecules in hydrophobic core and good solubility of
cyclohexanone in water might be reducing the partitioning of
cyclohexanone molecules into the micelles.
In spite of high solubilization of benzaldehyde in C18QAS
micelles, the reduced conversion and selectivity to di condensa-
tion product (3) is clearly indicating that the strong solubilization
of benzaldehyde in the core of C18QAS micelles slow down the
reaction rate reducing the availability of reacting molecules at
interface. The catalysis results and UV study revealed that C16QAS
micellar system possesses optimum properties and/or microen-
vironment sufficiently populating the benzaldehyde molecules at
3.2. Cross aldol reaction of benzaldehyde and cyclohexanone in
NaOH-C16QAS micellar systems with varied surfactant
concentrations
3.2.1. Effect of surfactant concentration on conversion and
product selectivity
The cross aldol reaction of benzaldehyde and cyclohex-
anone was carried out in C16QAS micellar solutions of varied
2
(b)
Water
Water
(a)
C10QAS
C12QAS
C14QAS
C16QAS
C QAS
0.20
0.15
0.10
0.05
10
C QAS
12
C QAS
14
C QAS
16
λ
= 249.5 nm
C18QAS
max
C QAS
λ
= 276 nm
18
max
1
0
230 240 250 260 270 280 290 300 310 320 330 340
220
240
260
280
300
320
340
Wavelength (nm)
Wavelength (nm)
Fig. 3. UV absorption spectra of (a) benzaldehyde and (b) cyclohexanone in water and in aqueous solutions of different QASs (conc.: 15 mM).

M. Vashishtha et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 143–154
149
100
90
80
70
60
50
40
30
20
10
0
Conversion
3
4
0.00
0.25
0.50
0.75
1.00
5
10
15
20
25
50
75
100
125
150
175
200
C QAS concentration
16
Fig. 4. Conversion and products selectivity in base catalyzed cross aldol condensation of benzaldehyde and cyclohexanone in NaOH-C16QAS miceller solutions of different
concentrations [reaction condition: 10 mmol benzaldehyde, 5 mmol cyclohexanone, 5 mmol NaOH, 10 mL aqueous surfactant solution, 60 ◦C, 30 min].
concentrations (from 1 mM to 200 mM) to study the effect of sur-
factant concentration on the reaction. The result (Fig. 4) shows
that surfactant concentration has significant effect on the micel-
lar catalyzed aldol reaction showing variation in cyclohexanone
conversion and selectivity of products (3 and 4) with surfactant
concentration.
soluble components to undergo reaction giving enhanced conver-
sion at high surfactant concentration.
The UV absorptions of benzaldehyde and cyclohexanone in
water and in C16QAS solutions of different concentrations (0, 5,
50, 100, 150 and 200 mM) were also measured by using their
solutions. The gradually increasing intensity of characteristic UV
bands of benzaldehyde and cyclohexanone (Fig. 6a and b) with
increasing the surfactant concentration can be ascribed to their
increasing solubilization or high localized concentration in the
micelles. The solubility of aromatic aldehydes (benzaldehyde and
p-methylbenzaldehyde) in aqueous solutions of non-ionic sur-
factants (polyoxyethylene glycol ethers) has been reported to
be increasing with surfactant concentration [30]. The ꢀmax for
benzaldehyde was observed to be slightly shifted to lower wave-
length (i.e., blue shift) with increasing surfactant concentration.
This shift is indicative of benzaldehyde molecule’s interaction with
The cyclohexanone conversion was slightly higher in the reac-
tions using surfactant solutions with less than 1 mM concentration
as compared to the biphasic reaction (surfactant free solution); and
like biphasic reaction only mono-condensation product (4) was
formed in these solutions showing that micelles are not involved
in the catalysis of reaction. At 1 mM concentration of surfactant
(which is CMC of pure C16QAS in water), the conversion was not
much changed but the di-condensation product (3) was started to
be formed (12% selectivity) indicating the involvement of micelles
in the catalysis of reaction facilitating di-condensation reaction.
The increasing conversion and selectivity of 3 with increasing sur-
factant concentration from 1 mM to 10 mM is indicative of the
important role of micelles in promotion of di-condensation reac-
tion. Further increase in surfactant concentration from 10 mM to
75 mM shows very small rise in conversion and selectivity to 3
in the reactions. However, when the surfactant concentration was
increased from 75 mM to 150 mM, significant increase in conver-
sion and selectivity of 3 was observed (99% conversion with >99%
selectivity to 3). This study clearly shows the significance of increas-
ing surfactant concentration for enhancement of reaction rate and
selectivity of desired product in micellar catalyzed aldol reactions.
For cross aldol reaction of benzaldehyde with n-heptanal, the high-
est cross product selectivity was also obtained in the reaction using
200 mM C16QAS micellar system [5].
C16QAS molecules in the micelles; probably this interaction can
be between functional groups of benzaldehyde (aldehydic group)
and surfactant head group (ammonium group). The UV absorption
study showed that on increasing the concentration of surfac-
tant in solution, the increased solubility of reactants promotes
the reaction giving high conversion at high surfactant concentra-
tion.
The 1H NMR techniques have been widely used to investigate
the location and orientation of the organic compounds as probe
molecules in the micelles by studying the differences in chemi-
cal shifts of the probe molecules [31–33]. The 1H NMR analysis
of reactants (benzaldehyde and cyclohexanone) in C16QAS solu-
tions of different concentration revealed the location, orientation
and interaction of reactant molecules within the micelles/emulsion
droplets. The 1H NMR spectra (Fig. 7) of benzaldehyde in 1 mM and
15 mM surfactant solutions show the shielding of aldehydic and
aromatic protons indicating the location of solubilized benzalde-
hyde molecules in the core of micelles or emulsion. In the solutions
with higher surfactant concentrations (50–250 mM), the benzalde-
hyde molecules seems to be located in hydrophilic zone/Stern layer
of micelles showing the deshielding of aldehydic proton of benz-
aldehyde. At higher surfactant concentrations, the ortho protons of
benzaldehyde are also slightly deshielded but meta and para pro-
tons are always observed to be shielded. The highest deshielding
of aldehydic proton ( CHO) as compared to aromatic protons (o-,
p- and m-1Hs) with increasing surfactant concentration revealed
that the CHO group of benzaldehyde must be orientated toward
interface and aromatic ring is embedded in the micelle. It is usu-
ally observed that a substituted aromatic molecule (with polar
group) is solubilized in a micelle with an orientation such that
the polar group directs toward the bulk water phase [12,32]. With
3.2.2. Characterization of reactant-C16QAS micellar systems
In C16QAS solutions of different concentrations (15 mM, 50 mM,
100 mM and 200 mM), the droplet size of benzaldehyde was seen
to be decreasing (Fig. 5) with increasing surfactant concentra-
tion. The decrease in size of benzaldehyde droplets is attributed to
increasing number of micelles in the solution on increasing sur-
factant concentration, which deplete the benzaldehyde droplets
into smaller emulsion droplets. The repulsive force between the
positively charged micelles at high surfactant concentration may
reduce the size of micelles showing the decreased droplet size at
high surfactant concentration [29]. From the optical microscopy
results it was found that with increasing concentration of surfac-
tant in solution, the increased number of micelles helps in splitting
up bigger droplets of benzaldehyde in smaller size as well as cre-
ate huge interfacial area for interaction of hydrophobic and water

150
M. Vashishtha et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 143–154
Fig. 5. Optical micrographs of benzaldehyde droplets in (a) 15 mM C16QAS, (b) 50 mM C16QAS, (c) 100 mM C16QAS and (d) 200 mM C16QAS micellar solutions (the scale bar
equals 200 ␮m).
increasing the surfactant concentration from 50 mM to 250 mM,
the gradually increasing deshielding of aldehydic proton of benz-
aldehyde indicates that benzaldehyde molecules are successively
moving toward Stern layer. It shows that at very high surfactant
concentrations, the benzaldehyde molecules are located in the
Stern layer of micelles or at interface. The interaction of quater-
nary ammonium group of surfactant molecules with CHO group
of benzaldehyde may also cause the deshielding of aldehydic pro-
ton (Scheme 3i). The shift in UV band of benzaldehyde also shows
the benzaldehyde molecule’s interaction with C16QAS molecules
in the micelles. The similar interaction has been reported for sol-
ubilization of ketocyanine dyes in cationic surfactant micelles by
interaction of carbonyl group of dye molecules and surfactant’s
head group [14].
Above 100 mM concentration, the ortho protons of benzalde-
hyde are also deshielded showing that ortho positions are also in
hydrophilic zone at higher C16QAS concentration. The meta and
para protons of benzaldehyde molecules also show slight shielding
and deshielding effect with variation in surfactant concentration
showing interaction of meta and para protons with surfactants
molecules. However, the meta and para protons always remain
shielded which indicates that the meta and para positions are
located in hydrophobic zone of micelles. The protons of cyclohex-
anone molecules were not much influenced by micellar system
0.25
0.20
0.15
0.10
0.05
0.00
(a)
1.75
0 mM
(a)
(b)
0 mM
5 mM
5 mM
50 mM
100 mM
150 mM
200 mM
1.50
1.25
1.00
0.75
0.50
0.25
0.00
50 mM
100 mM
150 mM
200 mM
220 230 240 250 260 270 280 290 300 310 320 330 340
230 240 250 260 270 280 290 300 310 320 330 340 350
Wavelength (nm)
Wavelength (nm)
Fig. 6. UV absorption spectra of (a) benzaldehyde and (b) cyclohexanone in aqueous solutions of C16QAS at different concentrations (0, 5, 50, 100, 150 and 200 mM).

M. Vashishtha et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 143–154
151
250 mM
250 mM
200 mM
200 mM
150 mM
150 mM
125 mM
100 mM
75 mM
125 mM
100 mM
75 mM
50 mM
50 mM
15 mM
1 mM
15 mM
1 mM
o-1Hs
p-1H
m-1Hs
In D O
2
In D O
2
Fig. 7. 1H NMR signals for aldehydic proton and aromatic protons of benzaldehyde in C16QAS solutions of different concentrations.
(ii)
(i)
(iii)
Na
O
Na
O
250 mM
Br
Br
Br
−δ
O
Me
Me
Me
Me
Me
Me
N
N
+δ
N
Me
Me
Me
200 mM
150 mM
125 mM
100 mM
75 mM
50 mM
15 mM
1 mM
Scheme 3. Interactions of (i) benzaldehyde, (ii) enolate ion of cyclohexanone and
(iii) enolate ion of mono-condensation product (␣-benzylidene cyclohexanone)
with quaternary ammonium surfactant (C16QAS) in the micellar system.
showing no significant change in chemical shifts of ␣, ␤ and ␥
methylene protons of cyclohexanone molecules in 1H NMR spectra
(Fig. 8).
The weak intensity of the signals for the protons of benzal-
dehyde and cyclohexanone in the 1–150 mM surfactant solutions
as compared to pure D2O solution is indicative of tight packing
of solubilized reactant molecules within the micelles. At higher
concentrations (200 mm and 250 mm), the intensity of the signals
again increased showing comparatively less tight packing of the
reactant molecules in the micelles. This may be attributed to elon-
gation of micelles at higher concentration [29], which will have
loosely packed surfactant molecules with their parallel orientation
within the micelles (See ESI; Scheme 4). The less compact molecu-
lar packing in these micelles can accommodate more number of
reactant molecules at interface. The interaction of CHO group
of benzaldehyde molecules with surfactant molecules and parallel
orientation of loosely packed surfactant molecules in the micelles at
1
1
1
γ Ηs
α Ηs
β Ηs
In D2O
2.4
2.2
2.0
1.8
1.6
1.4
Chemical shift (ppm)
Fig. 8. 1H NMR signals for different protons of cyclohexanone in C16QAS solutions
of different concentrations.
high surfactant concentrations might be forcing the benzaldehyde
molecules to be located at the stern layer.
From the optical microscopy results it is evident that the fast
conversion with C16QAS micellar system at high concentration
may be due to increased number of micelles, which will split up

152
M. Vashishtha et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 143–154
Scheme 4. Schematic presentation for decreasing size of different C16QAS micelles/emulsion droplets having solubilized reactants with increasing surfactant concentration
(from A to D surfactant concentration gradually increases).
benzaldehyde phase into smaller droplets and create large
interfacial area for interaction with water soluble components
(cyclohexanone’s enolate, OH− ions, etc.) for reaction making the
reaction faster. The UV and 1H NMR studies revealed that higher
surfactant concentration in the micellar solution not only cre-
ates large interface and solubilize the reactant molecules but
also it helps in orienting the reactant molecules (e.g., benzalde-
hyde) in large proportion at interface or in Stern layer. The high
solubilization of cyclohexanone in micelles at higher concentra-
tion of surfactant and stabilization of the cyclohexanone’s enolate
(Scheme 3ii) also enhance the rate of reaction. Furthermore, largely
populated activated benzaldehyde molecules at interface may also
promote the di-condensation of cyclohexanone giving highest
selectivity of 3 at higher concentration of surfactant. The loosely
packed surfactant molecules in elongated micellar system (at high
surfactant concentration) can accommodate the reaction interme-
diate (4) at interface in its stabilized enolate form (Scheme 3iii)
for further condensation with benzaldehyde. At lower surfactant
concentration, cyclohexanone is less available with micelles (most
of the cyclohexanone molecules are in aqueous medium) and the
solubilized benzaldehyde molecules are also mostly located in the
core of micelles, which reduces the benzaldehyde concentration
at Stern layer/interface showing slow conversion with formation
of significant amount of mono-condensation product. The very
high deshielding of aldehydic proton at higher surfactant concen-
tration, which may be due to interaction of carbonyl oxygen of
benzaldehyde with quaternary ammonium group, indicates that
the benzaldehyde molecules are in activated form (having more
electrophilic carbonyl carbon) for electrophilic reaction with eno-
late of cyclohexanone. The plausible mechanism of micellar system
catalyzed cross aldol reaction of benzaldehyde and cyclohexanone
is shown in Scheme 5. The micellar system (micelles/emulsion) ori-
ents the benzaldehyde molecules and cyclohexanone/its enolate
ions (either formed at interface from solubilized cyclohexanone
or came from aqueous medium) at interface to form mono-
condensation product, which remains at interface and further
undergoes reaction (through its enolate ion) with second molecule
of benzaldehyde to di-condensation product. The study shows that
the micellar system with high surfactant concentration (>150 mM)
is more appropriate medium for the aldol reaction. The similar

M. Vashishtha et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 143–154
153
Scheme 5. Plausible mechanism of micellar catalysis of cross aldol reaction (selective di-condensation) of benzaldehyde and cyclohexanone to ␣,␣ꢀ-bisbenzylidene cyclo-
hexanone using NaOH-QAS micellar system.
observation was reported for cross aldol reaction of benzaldehyde
and n-heptanal; the highest cross product (jasminaldehyde) selec-
tivity was obtained with 200 mM C16QAS micellar system [5]. It
is evident from the present study that the highest cross product
(jasminaldehyde) selectivity achieved at high C16QAS concentra-
tion (200 mM) might also be attributed to presence of significantly
more number of activated benzaldehyde molecules at Stern layer
of micelles or interface of emulsion.
at high surfactant concentration promote the reaction selectively
to the desired product with faster rate.
Acknowledgements
Authors are thankful to Dr. H.M. Desai, Vice-Chancellor, DDU for
providing necessary facilities to pursue the research work. We are
also thankful to the reviewers of this manuscript for their valuable
and constructive comments.
4. Conclusion
Appendix A. Supplementary data
The quaternary ammonium surfactant chain length and concen-
tration were found to be playing important role in the micellar
catalysis of cross aldol reaction showing influence over reaction
rate and products selectivity. The QAS surfactant micelles with
C16 alkyl chain possess optimum properties and/or microenviron-
ment for the reaction giving highest conversion rate and selectivity
toward desired cross aldol product in NaOH-micellar catalyzed
reaction of benzaldehyde and cyclohexanone. The C16QAS micellar
system with high surfactant concentration (>150 mM) made the
reaction faster giving selectively complete conversion to desired
product. The characterization of reactant molecules in micellar
solutions of different concentrations by optical microscopy, UV–vis
and 1H NMR analyses revealed that large interface, high localization
of reactant molecules in active form preferably near the interface
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.molcata.
2014.09.023.
References
[1] L. Liu, S. Zhang, X. Fu, C.-H. Yan, Chem. Commun. 47 (2011) 10148–10150;
R.N. Butler, A.G. Coyne, Chem. Rev. 110 (2010) 6302–6337;
T.J. Dickerson, T. Lovell, M.M. Meijler, L. Noodleman, K.D. Janda, J. Org. Chem.
69 (2004) 6603–6609;
S. Narayan, J. Muldoon, M.G. Finn, V.V. Fokin, H.C. Kolb, K.B. Sharpless, Angew.
Chem. Int. Ed. 44 (2005) 3275–3279.
[2] J.H. Fendler, E.J. Fendler, Catalysis in Micellar and Macromolecular Systems,
Academic Press, London, 1975.
[3] T. Dwars, E. Paetzold, G. Oehme, Angew. Chem. Int. Ed. 44 (2005) 7174–7199.

154
M. Vashishtha et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 143–154
[14] P.K. Das, R. Pramanik, D. Banerjee, S. Bagchi, Spectrochim. Acta A 56 (2000)
[4] (a) M. Schwarze, J.S. Milano-Brusco, V. Strempel, T. Hamerla, S. Wille, C. Fischer,
W. Baumann, W. Arlt, R. Schomacker, RSC Adv. 1 (2011) 474–483;
(b) P.-C. Wang, M. Lu, J. Zhu, Y.-M. Song, X.-F. Xiong, Catal. Commun. 14 (2011)
42–47;
2763–2773.
[15] D.O. Shah, in: D.O. Shah (Ed.), Micelles, Microemulsions and Monolayers, Marcel
Dekker, New York, 1998 (Chapter 1).
(c) J.-H. Ryu, C.-J. Jang, Y.-S. Yoo, S.-G. Lim, M. Lee, J. Org. Chem. 70 (2005)
8956–8962;
[16] M.A. James-Smith, D. Shekhawat, D.O. Shah, Tenside Surfactants Deterg. 44
(2007) 142–144, 146–154.
(d) G.-P. Lu, C. Cai, Catal. Commun. 11 (2010) 745–748;
(e) Q. Liu, W. Wei, M. Lu, F. Sun, J. Li, Y. Zhang, Catal. Lett. 131 (2009) 485–493;
(f) B.S. Samant, Y.P. Saraf, S.S. Bhagwat, J. Colloid Interface Sci. 302 (2006)
207–213;
(g) S. Kobayashi, K. Manabe, Acc. Chem. Res. 35 (2002) 209–217;
(h) K. Bica, P. Gartner, P.J. Gritsch, A.K. Ressmann, C. Schroderb, R. Zirbsc, Chem.
Commun. 48 (2012) 5013–5015;
(i) T. Dwars, G. Oehme, Adv. Synth. Catal. 344 (2002) 239–260;
(j) P. Gaudin, R. Jacquot, P. Marion, Y. Pouilloux, F. Jerome, ChemSusChem 4
(2011) 719–722;
(k) J.E.W. Cull, A. Richard, J. Scott, Green Chem. 15 (2013) 362–364;
(l) K. Bahrami, M.M. Khodaei, A. Nejati, Green Chem. 12 (2010) 1237–1241.
[17] P.K. Sen, N. Gani, B. Pal, Ind. Eng. Chem. Res. 52 (2013) 2803–2813.
[18] E.R. Macedo, L. De Boni, L. Misoguti, C.R. Mendonc, H.P. de Oliveira, Colloids
Surf. A: Physicochem. Eng. Aspects 392 (2011) 76–82.
[19] L. Brinchi, P.D. Profio, R. Germani, L. Goracci, G. Savelli, N.D. Gillitt, C.A. Bunton,
Langmuir 23 (2007) 436–442.
[20] N.D. Gillitt, G. Savelli, C.A. Bunton, Langmuir 22 (2006) 5570–5571.
[21] J.R. Kanicky, D.O. Shah, Langmuir 19 (2003) 2034–2038.
[22] S.Y. Shiao, V. Chhabra, A. Patist, M.L. Free, P.D.T. Huibers, A. Gregory, S. Patel,
D.O. Shah, Adv. Colloid Interface Sci. 74 (1998) 1–29.
[23] J.R. Kanicky, D.O. Shah, J. Colloid Interface Sci. 256 (2002) 201–207.
[24] S.Y. Shiao, A. Patist, M.L. Free, V. Chhabra, P.D.T. Huibers, A. Gregory, S. Patel,
D.O. Shah, Colloids Surf. A 128 (1997) 197–208.
[5] M. Vashishtha, M. Mishra, D.O. Shah, Appl. Catal. A: Gen. 466 (2013) 38–44.
[6] J. Deli, T. Lonard, D. Szabo, A. Foldesi, Pharmazie (1984) 539–544.
[7] M. Ogawa, Y. Ishii, T. Nakano, S. Irifune, Jpn. Kokai Tokkyo JP 63192446 A2
Chem. Abstr. 63 (1988) 238034.
[25] B. Gao, Q. Liu, L. Jiang, Chem. Eng. Process. 47 (2008) 852–858.
[26] E. Aniansson, S. Wall, M. Almgren, H. Hoffmann, I. Kielman, W. Ullbricht, R.
Zana, J. Lang, C. Tondre, J. Phys. Chem. 80 (1976) 905–922.
[27] J. Mata, D. Varade, P. Bahadur, Thermochim. Acta 428 (2005) 147–155.
[28] P. De Maria, A. Fontana, G. Cerichelli, J. Chem. Soc. Perkin Trans. 2 (1997)
2329–2334.
[8] J.J. Shrikhande, M.B. Gawande, R.V. Jayaram, Catal. Commun.
1010–1016.
9 (2008)
[9] P. Mukerjee, K.J. Mysels, Critical Micelle Concentrations of Aqueous Surfactant
Systems, 1971, NSRDC-NBS-36, Washington, DC.
[10] J.T. Davies, E.K. Rideal, Interfacial Phenomena, Academic Press, New York, 1961,
pp. 94–95.
[29] H.U. Kim, K.H. Lim, Bull. Korean Chem. Soc. 25 (2004) 382–388.
[30] A.G. Mitchell, L.S.C. Wan, J. Pharm. Sci. 53 (1964) 1467–1470.
[31] S.K. Mehta, S. Chaudhary, K.K. Bhasin, J. Colloid Interface Sci. 321 (2008)
426–433.
[11] P. Mukerjee, K. Banerjee, J. Phys. Chem. 68 (1964) 3567–3574.
[12] K.N. Ganesh, P. Mitra, D. Balsubramanian, J. Phys. Chem. 86 (1982)
4291–4293.
[32] P. Sabatinoa, A. Szczygiel, D. Sinnaeve, M. Hakimhashemi, H. Saveyn, J.C. Mar-
tins, P. Van der Meeren, Colloids Surf. A: Physicochem. Eng. Aspects 370 (2010)
42–48.
[13] G. Cerichelli, S. Cerritelli, M. Chiarini, P. De Maria, A. Fontana, Chem. Eur. J. 8
(2002) 5204–5210.
[33] N. Dharaiya, S. Chavdaa, K. Singh, D.G. Marangoni, P. Bahadur, Spectrochim.
Acta A 93 (2012) 306–312.