An efficient recyclable polymer-supported bis-quaternary onium phase-transfer catalyst for the synthesis of dihalocyclopropyl derivatives at low alkaline concentration-comparative kinetic aspects

Article abstract of DOI:10.1016/j.catcom.2012.02.010

In this work, a new polystyrene-bound bis-onium phase-transfer catalyst was synthesized, and their catalytic activities were investigated in the synthesis of dichlorocyclopropyl derivatives of olefins. The new polymer-anchored multi-site phase-transfer catalyst showed significant high catalytic activity as compared to single-site phase-transfer catalyst. The comparative kinetic investigation reveals that the dichlorocyclopropanation of 1-methyl-4-vinyl benzene is faster than styrene in the presence of the new catalyst. This catalyst can be used several times with consistent catalytic activity. Experimental observations support an interfacial-type mechanism. Furthermore, its catalytic utility was examined in alkylation reactions.

Full text of DOI:10.1016/j.catcom.2012.02.010

Catalysis Communications 22 (2012) 6–12
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
An efficient recyclable polymer-supported bis-quaternary onium phase-transfer
catalyst for the synthesis of dihalocyclopropyl derivatives at low alkaline
concentration-comparative kinetic aspects
P.A. Vivekanand, Maw-Ling Wang ⁎
Department of Environmental Engineering, Safety and Health, Hungkuang University, Taichung, Taiwan 43302
a r t i c l e i n f o
a b s t r a c t
Article history:
In this work, a new polystyrene-bound bis-onium phase-transfer catalyst was synthesized, and their catalytic
activities were investigated in the synthesis of dichlorocyclopropyl derivatives of olefins. The new polymer-
anchored multi-site phase-transfer catalyst showed significant high catalytic activity as compared to single-
site phase-transfer catalyst. The comparative kinetic investigation reveals that the dichlorocyclopropanation
of 1-methyl-4-vinyl benzene is faster than styrene in the presence of the new catalyst. This catalyst can be
used several times with consistent catalytic activity. Experimental observations support an interfacial-type
mechanism. Furthermore, its catalytic utility was examined in alkylation reactions.
Received 19 November 2011
Received in revised form 6 February 2012
Accepted 7 February 2012
Available online 15 February 2012
Keywords:
Dichlorocyclopropyl derivatives
bis-Onium salts
Triphase catalysis
Kinetics
© 2012 Elsevier B.V. All rights reserved.
Active sites
Catalytic efficiency
1
. Introduction
explored much in contrast to the soluble ‘multi-site’ PTCs. However,
the demand and requirement of these triphase catalysts are on the
Currently, phase-transfer catalysis (PTC) is a key green approach
1] for driving reactions involving immiscible reactants [2–6]. Howev-
er, application of this methodology to organic reactions has encoun-
tered two major problems viz.: (i) the recovery and reuse of the
catalyst and (ii) the separation and purification of the final product
rise due to their popularity.
[
With all these antecedents, we decided to synthesize a new multi-
active site onium salt with two active sites viz., polymer-supported-2-
benzyl-2-phenyl-1,3-bis(tributylmethylene ammonium chloride)
(PSBPBTBAC) by a facile method (Scheme 1). We investigated the cata-
lytic efficiency of the new catalyst by following the comparative kinetics
of dichlorocarbene addition to styrene and 1-(methyl)-4-vinylbenzene
(MVB) under pseudo-first-order conditions (Scheme 2). Also, to the best
of our knowledge, there is no systematic kinetic study of dichlorocarbene
addition to these olefins involving polymer-supported multi-site phase-
transfer catalysts. Kinetic investigation has been carried out by varying
experimental parameters and from the obtained kinetic results, a plausi-
ble reaction mechanism has been proposed. Comparative catalytic effi-
ciency of new onium salt and other onium salts (single-active site) were
evaluated.
[
7,8]. To circumvent the predicament of separation of catalyst from
the reaction mixture, for the first time Regen [9] reported anchoring
the phase-transfer catalysts to a polymer backbone and suggested
the name “Triphase Catalysis.” Organic reactions catalyzed by tri-
phase catalysts [10–13] have created remarkable attention for its ap-
plication in synthesis of organic compounds.
The vital considerations in the selection of the catalyst are econo-
my of scale and efficiency of the PTC, particularly on the explicit in-
dustrial scale preparation of organic compounds. To cater these
requirements, multi-site phase-transfer catalysts (MPTC) have been
developed and revealed more efficient in activity than conventional
single-site phase-transfer catalysts [14–18], and these catalysts are
successfully employed for the generation of dihalocyclopropanes
2. Experimental
[19], which are generally prepared traditionally with lot of predica-
2.1.
Preparation
of
polymer-supported-2-benzyl-2-phenyl-1,3-
ments[20]. Synthesis of polymer-supported ‘multi-site’ phase-trans-
dicholromethylpropane (2)
fer catalysts (PS-MPTC) of the ammonium type have not been
To a stirred solution of 3 g of polymer-supported-2-benzyl-2-phe-
nylpropane-1,3-diol (1) [21] in toluene (20 ml), SOCl (20 ml) was
2
added slowly to the flask through an addition funnel in the presence
⁎
Corresponding author.
E-mail address: chmmlw@sunrise.hk.edu.tw (M.-L. Wang).
of catalytic amount of pyridine. The reaction mixture was stirred
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2012.02.010

P.A. Vivekanand, M.-L. Wang / Catalysis Communications 22 (2012) 6–12
7
Scheme 1. Preparation of polymer-supported bis-onium salt (PSBPBTBAC).
vigorously for 6 h. After 6 h, the crude polymer was washed with water
consisting of chloroform (30 ml) and 1 g of hexadecane (as internal
GC standard). The biphasic mixture was stirred at 300 rpm for
30 min at 50 °C to condition the catalyst. The stirring speed was in-
creased to 700 rpm and then 1 ml of preheated olefin (styrene/
MVB) was added at zero time. Samples were collected from the or-
ganic layer of the mixture at regular time intervals. The kinetics was
followed by estimating the amount of olefin that disappeared using
a gas chromatography (Varian model 3700) by injecting an aliquot
of reaction mixture (0.5 μl). The pseudo-first-order reaction rate con-
stant was evaluated from the plot of log(a-x) vs. time, where (a-x) is
the concentration of olefin at a given time t [17,19,22–26], i.e., using
Eq. (1).
(
2×100 ml) and dried for 10 h in a vacuum oven (80 °C).
FT-IR (KBr), cm : 746(C―Cl), 1435(C―C), 1598(Aromatic C C),
907(Alkyl stretching), 3019(Aromatic C―H).
−
1
2
2
.2. Preparation of new polymer-supported bis-onium phase-transfer cata-
lyst (polymer-supported-2-benzyl-2-phenyl-1,3-bis(tributylmethylene am-
monium chloride, PSBPBTBAC, 3)
In the next step, polymer-supported-2-benzyl-2-phenyl-1,3-
dicholromethylpropane (2) (4 g) was swelled in acetonitrile (150 ml)
for about 24 h and transferred into a 500 ml three-necked round-
bottomed flask with excess tri-butylamine. The reaction mixture was
stirred continuously using a mechanical stirrer equipped with a poly
logða−xÞ ¼ −Kobst=2:303 þ loga
The products were identified by FT-IR and NMR ( H NMR and 13C
NMR).
ð1Þ
(tetrafluoroethylene) (PTFE) half-moon blade agitating at 600 rpm
1
under a nitrogen atmosphere. The reaction was carried out at reflux con-
dition for 50 h. The solvent was then completely removed under vacuo
and the onium salt viz., polymer-supported-2-benzyl-2- phenyl-1,3-
bis(tributylmethyleneammonium chloride) (PSBPBTBAC, 3) was washed
with diethyl ether, methanol and acetone (Scheme 2). PSBPBTBAC was
3
. Results and discussion
3.1. Characterization of polymer-bound onium salts
2
stored in a CaCl desiccator. The extent of quaternization, the amount
of chloride ion present in the PSBPBTBAC was quantitatively estimated
Comparison of the SEM micrographs of the single and multi-site
−
1
by Volhard's method and found to be 2.2 mequiv
.
onium salts indicates major morphology changes. From the SEM
image of polymer-supported benzyl tributyl ammounium chloride
PSBTBAC [10] (Fig. 1a), it can be observed that the sphericity of
PSBTBAC beads is fine, and their size is more uniform, i.e., it is clear
that its surface is homogeneous in nature. On the other hand,
Fig. 1b shows that the surfaces of PSBPBTBAC beads exhibit heteroge-
neous character, with tiny nodules. Hence, it can be inferred from the
SEM images that the availability of more tiny nodules on the surface
−
1
FT-IR (KBr), cm : 1152(C―N), 1443(C―C), 1605(Aromatic C C),
2
931(Alkyl stretching).
2
.3. Kinetics of dichlorocyclopropanation under triphase conditions
Initially a known quantity of aqueous NaOH (30 ml, 15% w/w) and
.1 g of catalyst were added to a 100 ml reactor with an organic layer
0
Scheme 2. Dichlorocyclopropanation of olefins catalyzed by PSBPBTBAC.

8
P.A. Vivekanand, M.-L. Wang / Catalysis Communications 22 (2012) 6–12
a) Dichlorocyclopropanation of styrene in presence
of different amounts of NaOH
a)
2
1
1
1
1
1
.00
.95
.90
.85
.80
.75
3
4
5
6
8
.57 M NaOH
.41 M NaOH
.30 M NaOH
.25 M NaOH
.33 M NaOH
b)
0
20
40
60
80
100
Time(min.)
b) Dichlorocyclopropanation of MVB in presence
of different amounts of NaOH
2
2
1
1
1
1
.1
.0
.9
.8
.7
.6
Fig. 1. Comparison of SEM micrographs: (a) PSBTBAC (single-site) and (b) PSBPBTBAC
multi-site).
3
4
5
6
.57 M NaOH
.41 M NaOH
.30 M NaOH
.25 M NaOH
(
8.33 M NaOH
of PSBPBTBAC indicates the formation of more number of active sites
+
−
(
−N But
3
Cl ) on the surface, which results in higher catalytic activ-
0
20
40
60
80
100
ity than the single-site PSBTBAC. Analogous surface morphology stud-
ies for single-site polymer-supported onium salts are well
documented [27,28].
Polymer-supported-2-benzyl-2-phenylpropane-1,3-diol was chlori-
nated by treating the polymer-supported-2-benzyl-2-phenylpropane-
Time(min.)
Fig. 3. Variation curve of the rate of dichlorocyclopropanation with different amount of
NaOH.
1
,3-diol with SOCl
pearance of a absorption band at 746 cm
presence of dichloro functionality. Quaternization of polymer-supported
2
and the FT-IR spectrum of the sample shows the ap-
the addition of excess tri-butylamine in the presence of acetonitrile,
resulting in the formation of the desired polymer-supported-2-ben-
zyl-2-phenyl-1,3-bis(tributylmethylene ammonium chloride) (3). The
−
1
(C–Cl) [29] indicating the
−
1
2-benzyl-2-phenyl-1,3-dicholromethylpropane (2) was carried out by
FT-IR shows disappearance of absorption band centered at 746 cm
−
1
and appearance of new band at 1152 cm , indicating the presence of
C–N peak [21,29]. The above-mentioned band changes reveal quaterni-
zation of the polymer. The amount of chloride ion present in the
6
1-methyl-4-vinylbenzene
styrene
PSBPBTBAC was quantitatively estimated by Volhard's method [27,30]
5
4
3
2
1
0
−1
and found to be 2.2 mequiv g 156
.
3.2. Effect of stirring rate
The influence of stirring speed on the rate of dichlorocarbene ad-
dition reaction of olefins was investigated in the range of
3
00–1100 rpm. The rate of the reaction increases as the stirring
speed increases and levels off to a constant value above the optimum
Table 1
Influence of catalyst amount on the rate of dichlorocyclopropanation of olefins.
3
k
obs ×10− (min−1
)
200
400
600
800
1000
1200
Amount of PSBPBTBAC
0.05 g
0.10 g
0.15 g
0.20 g
0.3 g
Stirring Speed(rpm)
Styrene
MVB
1.2
1.5
2.3
3.5
3.0
3.9
5.9
7.7
7.1
9.9
Fig. 2. Influence of stirring speed on rate of dichlorocyclopropanation of olefins.

P.A. Vivekanand, M.-L. Wang / Catalysis Communications 22 (2012) 6–12
9
6
5
4
3
2
1
has reached a constant value. Fig. 1 is indicative of a Makosa's interfa-
cial mechanism [17] rather than extraction mechanism [31].
Styrene
MVB
3.3. Temperature effect
The present work investigates the dichlorocarbene addition to
olefins (styrene and MVB) catalyzed by a new catalyst PSBPBTBAC
in the presence of chloroform and aqueous sodium hydroxide solu-
tion in the temperature range of 35–55 °C. As expected, the rate of
the reaction increases with the increase in temperature. From the Arrhe-
nius plot, we calculated the energy of activation: E
a
=11.44 kcal mol−
(
1
−1
MVB) and 14.69 kcal mol (Styrene). In the present study, the higher
energy of activation value is indicative of the interfacial mechanism
17,26].
[
4
5
6
7
8
9
10
Amount of Substrate(mmol)
Fig. 4. Effect of amount of substrate on rate of dichlorocyclopropanation of olefins.
3.4. Effect of NaOH concentration
The effect of base amount on the kinetics was analyzed by varying
the sodium hydroxide concentration from 3.57 to 8.33 M under oth-
erwise similar reaction conditions. From the kinetic study, we found
that the rate of the reaction increases tremendously with increase in
the concentration of NaOH (Fig. 3). A bilogarithmic plot of the
stirring speed, 700 rpm (Fig. 2). Hence, subsequent studies were car-
ried out at 700 rpm. Agitation increases interfacial area between or-
ganic and aqueous phases, speeding transfer of reactive species and
therefore increasing the reaction rate. Furthermore, the mass transfer
Table 2
a,b
Comparison of alkylation reactions catalyzed by various polymer-anchored onium salts.
obs ×10− (min−1
3
)
Entry no.
1
Substrate
Reagent
Catalyst
Product
k
PSBTEACc
1.3
1.8
4.7
0.5
2
3
4
PSBTBACd
PSBPBTBACe
PSBTEAC
5
6
PSBTBAC
0.7
PSBPBTBAC
1.93
a
C-alkylation reaction condition: A mixture of 10 ml of 15% w/w aqueous NaOH, 2.0 ml alkylating agent, 0.1 g of the catalyst and substrate (10 ml) was stirred at 45°C for 1h.
N-alkylation reaction condition: A mixture of 10 ml of 15% w/w aqueous NaOH, 2.0 ml alkylating agent, 0.1 g of the catalyst and substrate (10ml) was stirred at 40 °C for 1h.
b
c
Polymer-supported benzyl triethyl ammounium chloride (single-site salt). [22].
d
Polymer-supported benzyl tributyl ammounium chloride (single-site salt) [10].
Polymer-supported-2-benzyl-2-phenyl-1,3-bis(tributylmethylene ammonium chloride) (multi-site salt).
e

10
P.A. Vivekanand, M.-L. Wang / Catalysis Communications 22 (2012) 6–12
reaction rate constants against sodium hydroxide concentration gives
a straight line with a slope of 1.65(styrene) and 1.95 (MVB).
3.7. Comparative catalytic efficiency of different onium salts
Dichlorocarbene (:CCl
2
), which can be generated from chloroform in
We compared the catalytic activity of newly synthesized multi-
site onium salt with other polymer-supported onium salts under
identical conditions in the dichlorocarbene addition of olefins
(Fig. 5a). The other onium salts used for the study are: Polymer-
supported benzyl tributyl ammounium chloride (PSBTBAC, single-
site salt) [10] and Polymer-supported benzyl triethyl ammounium
chloride (PSBTEAC, single-site salt) [22,24]. The kinetic examination
prove that PSBPTBAC is more active than PSBTBAC and PSBTEAC, i.e.,
PSBPBTBAC is more efficient than the single-site PTCs. This observa-
tion proves that, in PSBPBTBAC, all the catalytic sites appear to be
co-operatively involved in the dichlorocarbene addition reaction.
The following order illustrates the relative catalytic activity of differ-
ent catalysts: PSBTEACbPSBTBACbPSBPBTBAC.
the presence of alkaline solution, reacts with organic phase reactant to
produce the desired products. Therefore, the rate of dichlorocyclopropa-
nation is highly influenced by the concentration of alkali in aqueous solu-
tion [26,32,33]. In the absence of phase-transfer catalyst, the generated
dichlorocarbene can be easily hydrolyzed [34]. It is thus obvious that hy-
−
droxide ions (OH ) in the aqueous phase also affect the degree of hydro-
lyzing dichlorocarbene [34]. The increase in rate of the reaction can be
ascribed to the fact that hydroxide ions are less solvated by water mole-
cules and thereby the activity of hydroxide ions increases [19,35]. For
such, the hydrolysis of dichlorocarbene is also minimized. Chiellini et al.
[
36] ascribed a drastic increase in the reaction rate to the increase in
the basicity of the hydroxide ion. Landini et al. [35] observed that, on in-
creasing the aqueous hydroxide concentration, the quantity of hydroxide
extracted decreases. The overall activity of the hydroxide actually in-
creases due to the dependence of hydroxide basicity on hydration.
Further, we compared the catalytic activity of PSBPBTBAC with various
polymer-anchored single site onium salts by following C-alkylation of
Phenylacetonitrile (PAN) and N-alkylation of pyrrole (Schemes 3 and 4)
under identical conditions. The experimental results (Table 2) further in-
dicate that PABPBTAC is superior to other single-site onium salts.
3
.5. Catalyst amount
The amount of triphase catalyst (PSBPBTBAC) was varied from 0.05
3.8. Recycle study
to 0.3 g under otherwise similar conditions. The rate constants are line-
arly dependent on the amount of catalyst used in each reaction
The reusability of PSBPBTBAC was tested four times in the dichlor-
ocyclopropanation of olefins. After each run, the catalyst was suffi-
ciently soaked and washed with methanol and distilled water in
(Table 1), which may be attributed to the increase in number of catalyt-
ic reactive sites [19]. Furthermore, the increase can be ascribed to the in-
+
−
crease in opportunity of collision between Na CCl3(interface) and
+
−
3
catalytic intermediate (Q CCl ) by increasing catalyst concentration,
a)
thereby resulting in corresponding increase in the concentration of
dichlorocarbene (organic phase). Control experiments were carried
out; there was absolutely no reaction even after 3 h of stirring. A biloga-
rithmic plot of the reaction rate constant versus the concentration of the
catalyst gives a straight line over a wide range of concentration. In the
current study, the reaction rate of MVT is faster than styrene, and this
can be attributed to electron rich nature of MVT. Literature reports re-
veals that dicholorocarbene addition to olefins with electron-rich sub-
stituents are faster than unsubstitiuted olefins [37].
Dichloropropanation to Styrene
Dichlorocyclopropanation to MVB
3
3
2
.5
.0
.5
2.0
1
1
0
.5
.0
.5
3
.6. Influence of amount of substrate
By changing the amount of olefins (styrene and MVB) under standard
reaction conditions, the rate of dichlorocyclopropanation was examined.
Both the rate constants decrease with an increase in the amount of olefins
0.0
PSBTEAC
PSBTBAC
PSBPBTBAC
(Fig. 4). Current kinetic investigation reveals the adverse impact of sub-
Different Catalysts(Single-site and Multi-site)
strate concentration on the rate of dichlorocyclopropanation. This could
be ascribed to two facts, which are explained as follows:
b)
(
i) It is possible that the increased concentration of the substrate
affects adversely the catalytic process. For example, the un-
adsorbed substrate molecules lingering free (free molecules)
4
3
3
2
.0
.6
.2
.8
Dichlorocyclopropanation to Styrene
Dichlorocyclopropanation to MVB
[38] may collide with the molecules that are adsorbed at the
active sites and displace them before they could react (i.e., be-
fore the contact time elapses) [24]. We believe that this ad-
verse effect will apparently increase with every increase in
the substrate concentration since the number of such collisions
will correspondingly increase.
2.4
(
ii) On increasing the concentration of substrate, the amount of
active-site catalysts remains constant since only a fixed
amount of catalysts is employed, i.e., as the amount of organic
phase reactant is increased, the ratio of the active-site catalyst
molecules over the reactant molecules is decreased [26].
2
1
1
.0
.6
.2
Hence the rate decreases with an increase in the amount of the
0
1
2
3
4
substrate [34]. Analogous decrease in rate constant values for C-alkyl-
ation of phenylacetone in the literature [24] reveals that the rate-
limiting step of the reaction might take place at the ionic sites within
or on the surface of the polymer.
Recycle Number
Fig. 5. (a) Comparison of catalytical efficiency of multi-site and single-site on rate of dichlor-
ocyclopropanation and (b) effect of recycled catalyst on the rate of dichlorocyclopropanation.

P.A. Vivekanand, M.-L. Wang / Catalysis Communications 22 (2012) 6–12
11
hydroxide ions, temperature and higher E
a
value are consistent with
the interfacial mechanism [32] rather than extraction mechanism [31].
−
As depicted in Scheme 5, trichloromethyl anion (CCl
converted to dichlorocarbene (:CCl
3
), which can be
2
), is generated from chloroform in
the presence of alkaline solution. However, the organic olefin does not
react with dichlorocarbene to form dichlorocyclopropane product be-
cause of easy hydrolysis of dichlorocarbene. Therefore, the addition of
Scheme 3. C-alkylation of phenylacetonitrile.
+
−
phase-transfer catalyst (e.g., quaternary ammonium salt, Q X ) to
the aqueous solution, to generate dichlorocarbene in the organic solu-
tion, is essential. Hence, on the addition of onium salt, an intermediate
+
−
(
Q CCl
3
) is formed from the reaction of trichloromethyl anion and
quaternary ammonium salt at the interface of two phases. This interme-
diate then transfers to the organic phase preparing for reaction with
olefins to produce the product. A similar mechanism is expected during
the dichlorocyclopropanation of MVB (Scheme 5).
Scheme 4. N-alkylation of pyrrole.
5
. Conclusions
turn and then dried under vacuum. The results, shown in Fig. 5b, in-
dicate that the activity of the triphase catalyst almost remained
same for four recycles. Thus, the catalyst was not deactivated and
was reusable. In PTC-assisted reactions, there is a possibility that qua-
ternary ammonium salts get decomposed and side reactions may
occur when the reaction is carried out at high alkaline concentration.
In the current investigation, the reaction was conducted using low
concentration of NaOH (15% w/w), and hence, the catalytic activity
remains almost unchanged even after four cycles.
Based on the results of this study, the following conclusions may
be drawn:
1
. A new polymer-supported bis-quaternary ammonium salt
PSBPBTBAC), for the efficient synthesis of diclorocyclopropyl de-
(
rivatives, has been reported.
2. PSBPBTBAC catalyzed dichlorocyclopropanation reactions are rapid
when compared to that of single-site polymer-supported onium salts.
3. The catalytic investigation reveals higher reactivity of the catalyst
for MVB than styrene.
4
4
. Proposed mechanism
. Kinetic study indicates that rate of the reaction is directly propor-
tional to amount of base, amount of catalyst, stirring speed and
temperature.
In the current study, the dependencies of the kinetic data on the en-
tire stirring speed range, concentration of the catalyst, aqueous
Scheme 5. Proposed mechanism for the dichlorocyclopropanation of olefins.

12
P.A. Vivekanand, M.-L. Wang / Catalysis Communications 22 (2012) 6–12
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6
. The rate decreases with increase in the amount of substrate.
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. Based on the experimental results, an interfacial reaction mecha-
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