New soluble multi-site phase transfer catalysts and their catalysis for dichlorocarbene addition to citronellal assisted by ultrasound - A kinetic study

Article abstract of DOI:10.1016/j.molcata.2012.05.020

Two new soluble multi-site phase transfer catalysts (MPTCs), viz., 1,4-bis-(triethylmethylene ammonium chloride)-2,5-dimethyl benzene (BTMACD) containing di-site and 1,4-bis((3,5-bis(triethylmethyleneammonium chloride)phenoxy)methyl)benzene (TEMACPB) containing tetra-site were prepared and proved by FT-IR, ¹H NMR, ¹³C NMR, mass and elemental analysis. The enhancement of CN peak intensity at 1179 cm^-1 noticed in FT-IR, the agreement of m/z values, viz., 405 and 888 for di-site and tetra-site respectively with their theoretical values and the percentage of C, H, N elements noticed in elemental analysis has strongly supported the presence of di-site and tetra-site in the BTMACD and TEMACPB catalysts. Further, the presence of number of active-sites in each catalyst was again confirmed by determining their pseudo-first order rate constant for dichlorocarbene addition to citronellal in the presence of ultrasonic irradiation/mechanical stirring. The comparative study reveals that the k_obs determined with the combination of ultrasound and mechanical stirring has shown more activity (3 fold) than with their individual effect. Further, the detailed kinetic study performed with superior tetra-site MPTC (TEMACPB) reveals that the k _obs are dependent with the stirring speed, [substrate], [catalyst], [NaOH] and temperature. Based on the kinetic results, thermodynamic parameters are evaluated and an interfacial mechanism is proposed.

Full text of DOI:10.1016/j.molcata.2012.05.020

Journal of Molecular Catalysis A: Chemical 363–364 (2012) 81–89
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
New soluble multi-site phase transfer catalysts and their catalysis for
dichlorocarbene addition to citronellal assisted by ultrasound—A kinetic study
Eagambaram Murugan∗, Gurusamy Tamizharasu
Department of Physical Chemistry, School of Chemical Sciences, University of Madras, Maraimalai Campus, Guindy, Chennai 600025, Tamilnadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new soluble multi-site phase transfer catalysts (MPTCs), viz., 1,4-bis-(triethylmethylene
ammonium chloride)-2,5-dimethyl benzene (BTMACD) containing di-site and 1,4-bis((3,5-
bis(triethylmethyleneammonium chloride)phenoxy)methyl)benzene (TEMACPB) containing tetra-site
were prepared and proved by FT-IR, 1H NMR, 13C NMR, mass and elemental analysis. The enhancement
of C N peak intensity at 1179 cm−1 noticed in FT-IR, the agreement of m/z values, viz., 405 and 888 for
di-site and tetra-site respectively with their theoretical values and the percentage of C, H, N elements
noticed in elemental analysis has strongly supported the presence of di-site and tetra-site in the
BTMACD and TEMACPB catalysts. Further, the presence of number of active-sites in each catalyst was
again confirmed by determining their pseudo-first order rate constant for dichlorocarbene addition
to citronellal in the presence of ultrasonic irradiation/mechanical stirring. The comparative study
reveals that the kobs determined with the combination of ultrasound and mechanical stirring has shown
more activity (3 fold) than with their individual effect. Further, the detailed kinetic study performed
with superior tetra-site MPTC (TEMACPB) reveals that the kobs are dependent with the stirring speed,
[substrate], [catalyst], [NaOH] and temperature. Based on the kinetic results, thermodynamic parameters
are evaluated and an interfacial mechanism is proposed.
Received 20 February 2012
Received in revised form 9 May 2012
Accepted 27 May 2012
Available online 2 June 2012
Keywords:
Multi-site phase transfer catalyst
Dichlorocarbene addition
Ultrasonic irradiation
Kinetics
Interfacial mechanism
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
condensation, epoxidation, and polymerization reaction [2]. Even
though, various soluble single-site PTCs have extensively used for
Generally, the catalysis researchers have been frequently
encountering the inconvenience of conducting a reaction in biphase
system. The neutral organic molecule in organic phase and co-
reactants in aqueous phase, shows very little tendency to react even
at high agitation speed, presence of protic/aprotic solvents and sur-
factants, due to the shortage of molecular collision. Subsequently,
the complication of two immiscible reactants was first rectified
by Jarrouse [1] in 1951, by the addition of catalytic quantity of
quaternary ammonium salt. Afterwards, several researchers [2–5]
had also demonstrated different methods and thus accelerate the
rate of reaction in biphasic medium. In 1971, Starks [6] coined the
term called “Phase Transfer Catalysis” which meets all the require-
ments in solving the problems of mutual insolubility of non-polar
and ionic compounds. Nowadays, phase transfer catalysis (PTC) is
an inevitable potential tool for enhancing the efficiency, improv-
ing safety and reducing environmental impact. The advances of
the same in the recent years have made a remarkable impact in
organic synthesis and are being enormously employed to a multi-
tude of organic transformations such as substitution, displacement,
number of organic reactions, but again because of its inseparability,
its usage is often limited. In order to recover the catalyst for reuse,
the soluble single active site PTC has been immobilized onto the
polymer matrices and thus their insoluble heterogeneous single-
site phase transfer catalyst are derived. However, because of its
lower activity and diffusion limitation the applicability of insolu-
ble heterogeneous single-site phase transfer catalyst has always
received poor attention among the stakeholders. Subsequently,
with a view to improve further catalytic efficiency, soluble form of
multi-site phase transfer catalyst has emerged and is used for vari-
ous organic reactions especially in biphasic medium. Idoux et al. [7]
were the first to report the soluble and insoluble polymer supported
phosphonium multi-site PTCs having three active sites. The effec-
tiveness of the catalytic activities of these ‘multi-site’ PTCs towards
simple SN2 reactions and some weak nucleophile–electrophile
SnAr reactions were also reported.
The most significant merit for MPTCs is that it has an ability
to transfer more number of anionic species (M+Y−) from aque-
ous phase to organic phase. In contrast, the single-site quaternary
onium phase transfer catalyst can transfer only one molecule of
anionic species, i.e., M+Y− from aqueous phase per cycle. Espe-
cially, nowadays much emphasis has been given to economy of
scale and efficiency of onium salts particularly for the industrial
∗
Corresponding author. Tel.: +91 44 22202818/9; fax: +91 44 22352494.
E-mail address: dr.e.murugan@gmail.com (E. Murugan).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.05.020

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E. Murugan, G. Tamizharasu / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 81–89
scale preparation of organic compounds. Balakrishnan et al. [8–10]
have developed soluble multi-site phase transfer catalyst contain-
ing two and three active sites to catalyze the various organic
reactions. Wang et al. [11,12] also reported a kinetic study of
dichlorocyclopropanation of 4-vinylcyclohexne and etherification
of 4,4ꢀ-bis(chloromethyl)-1,1ꢀ-biphenyl and 1-butanol catalyzed by
using new soluble MPTC containing two active sites and showed
that MPTC exhibits more reactivity than single-site PTC. In our lab-
oratory too, several multi-site phase transfer catalysts are reported
for alkylation [13–16], dichlorocarbene addition [17,18], asymmet-
ric synthesis [19–22], decarboxylation [23], functionalization of
multi-walled carbon nano tubes [24,25] and polymerization [26]
reactions.
Dichlorocarbene addition is an important class of reaction from
both industrial and academic perspectives. Dichlorocarbenes are
valuable compounds that can be reduced to cyclopropane deriva-
tives, by treating with magnesium or sodium to give allenes and
it can be converted to a number of valuable other compounds.
The literature surveys stress the necessity for generation and reac-
tion of various dichlorocarbene additions. It is also emphasized
that the reaction should carry out only at very strict anhydrous
conditions due to its ready and rapid hydrolysis. This problem
can be overcome simply by performing the reaction in biphasic
system using sodium hydroxide and ‘single-site’ PTCs [27]. Partic-
ularly, if the reaction is performed with “multi-site PTCs” then the
rate of the reaction is more, because, the MPTCs generate more
dichlorocarbene and thus lead to effective addition to the olefins.
In 1969, Makosza and Wawrzyniewicz [28] have first reported the
dichlorocarbene addition reaction under biphasic conditions, high
yield of dichlorocyclopropane product was obtained by using 50%
NaOH and chloroform in excess. Subsequently, various reports have
appeared for the dichlorocarbene addition in different olefins using
PTCs [27,29,30].
parameters such as stirring speed, [substrate], [catalyst], [NaOH]
and temperature on the rate of the reaction.
2. Experimental
2.1. Chemicals
The following chemicals were used as received: p-xylene (CDH),
paraformaldehyde (Lancaster), Con. HCl (SRL), zinc chloride (SRL),
sodium chloride (SDS), 3,5-dimethylphenol (Aldrich), citronellal
(Aldrich), N-bromosuccinimide (SRL), N-chlorosuccinimide (SRL),
methanol (SRL), benzoylperoxide (SRL), carbon tetrachloride (SRL),
acetonitrile (SRL), triethylammine (SRL), chloroform (SRL), hexane
(SRL), diethylether (SRL), benzene (SRL), ethyl acetate (SRL), sodium
hydroxide (CDH), tetrabutylammonium chloride (TBAC), and ben-
zyltriethylammonium chloride (BTEAC).
2.2. Instrumentation
The FT-IR spectra were recorded on a Bruker-Tensor 27 FT-
IR spectrophotometer. The 1H NMR and 13C NMR spectra were
recorded using Bruker 500 MHz and 125 MHz spectrometers. The
mass spectra were recorded on a JEOL GC mate mass spectrometer.
Elemental analysis was performed on a Perkin-Elmer 240B elemen-
tal analyzer. The ultrasonic cleaner apparatus (model RZ-08895-22)
was used for enhancing the rate of reaction. The kinetics of the
dichlorocarbene addition to citronellal was studied by quantitative
analysis of sample with a gas chromatography (Varian-3700 inter-
faced with a chromatograph I/F module) system that included a
flame ionization detector. The column used for the product analy-
sis was a 5% SE-30, chrom WHP 80/100, 3 m × 1/8 in., stainless steel
tube.
In recent years, the application of ultrasound irradiation in
organic synthesis has been broadly extended. It can increase the
rate of reaction, yield and selectivity of desired product under very
milder condition [31–34]. Hence, this technique has been con-
sidered as a convenient and environmentally benign technique
[31,35–40]. Several studies have been already reported, in which it
is observed that the combination of PTC with ultrasound is proved
to be an effective technique for organic transformation [41–46]. The
Cannizarro reaction catalyzed by a PTC under ultrasonic condition
showed that an ultrasonic wave of 20 kHz dramatically accelerated
the rate of reaction [47]. Wang et al. investigated the liquid–liquid
phase transfer catalyzed epoxidation and dichlorocyclopropana-
tion of 1,7-octadiene and ethoxylation of p-chloronitrobenzene
assisted by ultrasound wave energy, the reaction rates were greatly
enhanced in all the reactions [48–50].
In the past efforts, the application of ultrasound in liquid–liquid
phase transfer catalysis was rarely studied. However, to the best
of our knowledge, there is no report available on the kinetics of
dichlorocarbene addition to citronellal using newly synthesized
soluble MPTC along with ultrasonic irradiation. Hence, in this
study, we have aimed to design and develop two types of new
multi-site phase transfer catalysts, viz., 1,4-bis-(triethylmethylene
ammonium chloride)-2,5-dimethyl benzene (BTMACD, 3) having
two active site and 1,4-bis((3,5-bis(triethylmethyleneammonium
chloride)phenoxy)methyl)benzene (TEMACPB, 7) containing four
active sites through simplified procedures with inexpensive
starting materials. Further, the catalytic activity of newly pre-
pared MPTCs and commercial single-site PTCs were studied with
dichlorocarbene addition to citronellal under pseudo-first order
rate condition in biphasic medium combined with ultrasonic wave
energy (42 kHz and 100 W). Further, the catalytically superior tetra-
site MPTC was employed for thorough kinetics of dichlorocarbene
addition to citronellal and by varying the different experimental
2.3. Synthesis of soluble multi-site phase transfer catalysts
(MPTCs) (Scheme 1)
2.3.1. Preparation of di-site PTC, viz.,
1,4-bis-(triethylmethyleneammonium chloride)-2,5-dimethyl
benzene (BTMACD, 3)
In the first step, the compound 2, viz., 1,4-bis(chloromethyl)-
2,5-dimethyl benzene was prepared by following the simple
procedure. That is, p-xylene (3.7 ml; 30 mmol) and conc. HCl (21 ml)
were taken in to a 150 ml three necked round bottom flask and
it was equipped with a reflux condenser, thermometer and a
stirrer. The whole setup was kept on oil bath. Then paraformalde-
hyde (3.6 g, 120 mmol), zinc chloride (4 g, 30 mmol) and sodium
chloride (1 g, 17.11 mmol) were added in to the flask. The whole
reaction mixture was refluxed at 110 ◦C and continuously stirred
for 36 h. The resulting white precipitate was filtered and recrys-
tallized using hexane solvent and thus obtained precipitate, viz.,
1,4-bis(chloromethyl)-2,5-dimethyl benzene 2 was stored in a des-
iccator (yield 63% and melting point 102–104 ◦C, Scheme 1). To
confirm the chloromethylation, this product (2) was analyzed with
FT-IR and 1H NMR analyses.
FT-IR (KBr, cm−1): 683 (C Cl stretching), 2977 (aliphatic stretch-
ing), 1391 (aliphatic C H bending); 1H NMR (300 MHz, CDCl3): ı
2.408 (s, 6H, CH3), 4.586 (s, 4H, CH2), 7.176 (s, 2H, Ar H).
In the second step, 1,4-bis(chloromethyl)-2,5-dimethyl ben-
zene 2 (3 g, 7.39 mmol) was dissolved in dry acetonitrile (25 ml)
and then transferred into a 100 ml double necked round bot-
tom flask and the solution was deaerated by passing nitrogen
gas. Then, triethylammine (excess) dissolved in acetonitrile
(25 ml) was added to that. The reaction mixture was refluxed
at 80 ◦C and stirred for 12 h under the nitrogen atmosphere and
thus a white precipitate of quaternized product of di-site PTC,
viz., 1,4-bis-(triethylmethyleneammonium chloride)-2,5-dimethyl

E. Murugan, G. Tamizharasu / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 81–89
83
Scheme 1. Synthesis of di-site BTMACD and tetra-site TEMACPB catalysts.
benzene (BTMACD, 3) was obtained. Then the precipitate was fil-
tered and washed with ether solvent (3 × 10 ml) and stored in CaCl2
desiccators. The yield was 85% (Scheme 1).
pale yellow solid, viz., 1,4-bis(bromomethyl)benzene 4. The yield
was 90% and the melting point was 142–144 ◦C.
FT-IR (KBr, cm−1): 568 (C Br), 1625 (C C); 1H NMR (300 MHz,
CDCl3): 4.28 (s, 4H, methylene), 7.182 (s, 4H, aromatic).
FT-IR (KBr, cm−1): 1179 (C N stretching), 2984 (aliphatic C
H
str.), 1393 (aliphatic C H bending); 1H NMR (500 MHz, D2O): ı
2.396 (s, 6H, CH3), 1.278–1.306 (t, 18H, CH3), 3.264–3.306 (q,
12H, CH2 ), 4.423 (s, 4H, CH2 ), 7.340 (s, 2H, aromatic); 13C
NMR (125 MHz, D2O): ı 7.510, 18.902, 53.419, 58.207; 128.657,
136.284. 138.174; MS [m/z] = 405.15. Elemental Analysis: Calc.: C,
65.16; H, 10.44; N, 6.91. Found: C, 64.95; H, 10.23; N, 6.71.
2.3.2.2. Synthesis of 1,4-bis-((3,5-dimethylphenoxy)methyl)benzene
5. 1,4-Bis(bromomethyl)benzene
4
(3 g, 11.37 mmol), 3,5-
dimethylphenol (2.78 g, 22.74 mmol), methanol (60 ml) and
NaOH (0.5 g, 12.5 mmol) were taken in a 250 ml round bottom
flask. The reaction mixture was refluxed in an oil bath at 70 ◦C for
24 h. Then the solvent was removed from the reaction mixture by
vacuum evaporator. The condensed product, viz., 1,4-bis-((3,5-
dimethylphenoxy)methyl)benzene 5 was obtained. This product
was purified by silica gel column chromatography using benzene:
ethyl acetate (80:20, v/v). The yield was 69%, melting point was
123–125 ◦C.
2.3.2. Synthesis of tetra-site PTC, viz.,
1,4-bis-((3,5-bis(triethylmethyleneammonium
chloride)phenoxy)methyl)benzene (TEMACPB, 7)
2.3.2.1. Synthesis of 1,4-bis(bromomethyl)benzene 4. In a 250 ml
round bottom flask p-xylene 1 (5 ml, 40.78 mmol), and 70 ml of
carbon tetrachloride were taken and then the flask was kept on an
oil bath. N-bromosuccinimide (29.86 g, 167.80 mmol) and benzoyl
peroxide (5.83 g, 24.08 mmol) were added into the flask and the
whole solution was refluxed for 12 h at 70 ◦C. After the completion
of reaction, the solution was cooled to room temperature and thus
formed solid imide which in turn was removed by filtration. From
the filtrate, the solvent was eliminated by distillation to give the
FT-IR (KBr, cm−1): 1075 (C O), 1614(C C); 1H NMR (300 MHz,
CDCl3): ı 2.391 (s, 12H, methyl), 5.257 (s, 4H, phenoxymethylene),
7.145–7.819 (m, 10H, aromatic).
2.3.2.3. Synthesis of 1,4-bis((3,5-bis(chloromethyl)phenoxy)methyl)
benzene 6. In
dimethylphenoxy)methyl)benzene
a
250 ml round bottom flask 1,4-bis-((3,5-
(3 g, 8.66 mmol),
5

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column was maintained at 200 ◦C. An aliquot of reaction mixture
(0.5 ␮l) was injected into the column and the product was analyzed.
The retention time for each compound was noted such as citronel-
lal (1.14 min), chloroform (0.71 min), and dichlorocyclopropane
product (4.50 min). The pseudo-first order rate constants were
calculated from the plots of log (a–x) versus time. The kinetic exper-
iments were carried out in duplicate to confirm reproducibility of
the results.
Scheme 2. Dichlorocarbene addition to citronellal using TEMACPB.
3. Results and discussion
N-chlorosuccinimide (6.02 g, 44.93 mmol), benzoylperoxide (7 g,
28.89 mmol) and carbon tetrachloride were taken and kept in an
oil bath. The reaction mixture was refluxed for 12 h at 70 ◦C. After
the completion of reaction time, the solution was cooled and the
formation of imide was filtered. The filtrate containing CCl4 solvent
was removed by vacuum evaporator. The crude yellow color prod-
uct, viz., 1,4-bis((3,5-bis(chloromethyl)phenoxy)methyl)benzene
6 was obtained. The yield was 78% and melting point was
134–136 ◦C.
Nowadays, phase transfer catalysis is a vital and very fas-
cinating technique to conduct the reaction between immiscible
reactants available in the heterogeneous system. In order to
perform this immiscible substrate reaction more effectively,
many researchers have devoted their attention to develop
multi-site phase transfer catalyst to replace the low active single-
site PTC. Particularly, dichlorocarbene addition to olefin using
MPTCs aided by ultrasonic wave energy is an active area for
current study. To strengthen further, two different new solu-
ble MPTCs such as di-site PTC, viz., 1,4-bis-(triethylmethylene
ammonium chloride)-2,5-dimethyl benzene (BTMACD, 3) and
tetra-site PTC, viz., 1,4-bis((3,5-bis(triethylmethyleneammonium
chloride)phenoxy)methyl)benzene (TEMACPB, 7) were prepared
by adopting the simplified procedures. The availability of number
of quaternary ammonium groups (catalytic-site) in each catalyst
was established with FT-IR, 1H NMR, 13C NMR, mass, and ele-
mental analyses. The structure of di-site (3) and tetra-site (7)
MPTCs were confirmed by the disappearance of C Cl stretch-
ing at 700 cm−1 and appearance of C N stretching at 1179 cm−1
in FT-IR spectrum. However, the number of quaternary onium
group present in each catalyst was estimated semiquantitatively
through comparative FT-IR study. The comparative FT-IR stud-
ies obtained from single-site (BTEAC) to tetra-site (TEMACPB)
reveals that the C N peak intensity at 1179 cm−1 has been grad-
ually increased from BTEAC (single-site) to TEMACPB (tetra-site)
and it proves the presence of more number of quaternary onium
groups in BTMACD (di-site) and in TEMACPB (tetra-site) catalysts.
In the 1H NMR analysis, the quaternized ethyl group consisting
of methyl and methylene proton appeared as triplet and quartet
at 1.278–1.306 ppm and 3.264–3.306 ppm respectively for di-site
and 1.342–1.360 and 3.063–3.089 ppm respectively for tetra-site
and thus supporting the formation of quaternizing groups. Simi-
larly, in 13C NMR, the methyl and methylene carbon showed high
intense peaks at 7.510 and 53.419 ppm respectively for di-site and
8.46 and 53.03 ppm respectively for tetra-site, thus strongly sup-
ported the formation of quaternizing sites. Further, in mass analysis
the experimentally found m/z values, i.e., 405 for di-site and 888
for tetra-site were agreed well with their theoretical values. In
the case of elemental analysis, the percentage of C, H, N elements
determined experimentally were found to agree with their theo-
retical values irrespective of catalyst and thus strongly supported
the presence of di-site in BTMACD (3) and tetra-site in TEMACPB
(7) catalysts. On the other hand, although the number of qua-
ternary onium groups (active sites) in each catalyst was proved
beyond doubt through various techniques, but again its presence
in the respective catalyst should also be confirmed through cat-
alytic activity. To determine the catalytic activity of these newly
synthesized soluble MPTCs, they were employed individually for
the catalysis of dichlorocarbene addition to citronellal under iden-
tical pseudo-first order reaction conditions in association with
ultrasonic irradiation (42 kHz, 100 W) and mechanical stirring. The
pseudo-first order rate constant was determined by measuring
the disappearance of citronellal under regular intervals using gas
chromatography.
FT-IR (KBr, cm−1): 700 (C Cl), 1073 (C O); 1H NMR (300 MHz,
CDCl3): ı 4.728 (s, 8H, methylene), 5.264 (s, 4H, phenoxymethy-
lene), 7.846–8.367 (m, 10H, aromatic).
2.3.2.4. Synthesis of 1,4-bis((3,5-bis(triethylmethyleneammonium-
chloride)phenoxy)methyl)benzene
100 ml double necked round bottom flask, 1, 4-bis((3,5-
bis(chloromethyl)phenoxy)methyl)benzene (2 g, 2.25 mmol)
(TEMACPB
7). In
a
6
dissolved in dry acetonitrile (50 ml) was taken. The solution was
deaerated by passing nitrogen gas. Then the excess of triethy-
lammine (25 ml) dissolved in acetonitrile was added into the
flask. The solution was refluxed at 80 ◦C for 24 h under inert
atmosphere. Then the excess solvent and unreacted triethy-
lammine were removed from the reaction mixture by vacuum
evaporator. The obtained white color precipitate of quaternized
compound, viz., 1,4-bis((3,5-bis(triethylmethyleneammonium
chloride)phenoxy)methyl)benzene (TEMACPB, 7) was filtered,
then washed with diethylether (3× 10 ml), dried and stored in a
CaCl2 desiccator’s. The obtained yield was 72% (Scheme 1).
FT-IR (KBr, cm−1): 1074 (C O), 1178 (C N); 1H NMR (500 MHz,
CDCl3): ı 1.342–1.360 (t.36H, N+CH2-methyl), 3.063–3.089 (q,
24H, N+-methylene), 4.658 (s, 8H, methylene), 5.278 (s, 4H,
phenoxymethylene), 8.045–8.786 (m, 10H, aromatic), 13C NMR
(125 MHz, CDCl3): ı 8.46, 53.03, 61.56, 66.83, 119.20, 127.28,
129.43, 130,73, 132.52, 146.71. MS (m/z) = 888.12. Elemental
Analysis: C, 64.85; H, 9.30; N, 6.30. Found: C, 64.68; H, 9.06;
N, 6.12.
2.4. Kinetics of dichlorocarbene addition to citronellal
The kinetics of the reaction was performed in an ordinary 150 ml
three-necked round bottom flask fitted with flat-bladed stirring
paddle and a reflux condenser. The dichlorocarbene addition of
citronellal reaction was carried out by reverse addition method,
i.e., by delayed addition of citronellal (Scheme 2). Into the reaction
flask, 25 ml of (20%, w/w) aqueous NaOH, 0.23 mmol of respective
catalyst and 20 ml chloroform (solvent) were added and stirred
at 200 rpm for 5 min at 40 ◦C to stabilize the catalyst. Citronellal
(1.0 ml, 5.58 mmol) preheated to 40 ◦C was added to the reac-
tion mixture at zero time. The reaction mixture was stirred at
600 rpm and simultaneously the ultrasonic wave energy (42 kHz
and 100 W) was passed through the reactor. Samples were col-
lected from the organic layer of the mixture at regular intervals
of time and each run consists of the seven samples. The kinetics
of the reaction was followed by estimating the amount of citronel-
lal disappeared using gas chromatograph. The temperature of the

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85
3.1. Comparative catalytic study of newly developed MPTCs, viz.,
BTMACD and TEMACPB with known single-site PTCs
presence of ultrasonic wave energy used to disrupt the interface
by cavitational collapse near the liquid–liquid interface and impels
jets of one liquid into other, forming fine emulsions and it leads
to a dramatic enhancement in the interfacial contact area through
which transfer of species can take place [56]. Therefore, the combi-
nation of quaternary onium ions (PTC) and ultrasound energy has
proved to be a best and environmentally benign catalytic method to
conduct the organic addition reaction [57,58]. In view of the impact
of ultrasonic wave energy, it is decided to conduct detailed kinetic
study for dichlorocarbene addition to citronellal using the superior
tetra-site MPTC, viz., TEMACPB in association with ultrasonic wave
energy and by varying the experimental parameters such as stirring
speed, [substrate], [MPTC], [NaOH], and temperature.
In order to investigate the number of quaternary
onium groups (active-site) available in newly synthe-
sized di-site viz., 1,4-bis-(triethylmethylene ammonium
chloride)-2,5-dimethyl benzene (BTMACD, 3) and tetra-site,
viz.,
1,4-bis((3,5-bis(triethylmethyleneammonium
chlo-
ride)phenoxy)methyl)benzene (TEMACPB, 7), the pseudo-first
order rate constants (kobs) for the dichlorocarbene addition to
citronellal was determined and the same was compared with the
rate constant determined with two different known (commercial)
single-site PTCs, viz., benzyltriethylammonium chloride (BTEAC)
and tetrabutylammonium chloride (TBAC). Of course, as it was
mentioned in the experimental section, the reaction was per-
formed under identical experimental conditions irrespective of the
catalyst and in the presence of ultrasound wave energy of 42 kHz
(100 W). From the obtained result (Table 1), it infers that the kobs
was increased on par with number of quaternary onium groups
available in each catalyst (molecule). That is, the activity lies in
the order of BTEAC (single-site) < TBAC (single-site) < BTMACD
(di-site) < TEMACPB (tetra-site) irrespective of reaction performed
in mechanical stirring, ultrasonic wave energy and combination of
both.
To describe elaborately, the kobs determined individually with
the help of ultrasonic wave energy and mechanical stirring (Table 1)
reveals that in both the cases, the di-site and tetra-site has shown
approximately 2 and 4 times higher active than that of single-site
PTCs. Similarly, in the case of combination of ultrasonic irradiation
and mechanical stirring, the kobs for di-site MPTC and tetra-site
MPTC shows approximately 2.5 and 5 times higher active than
that of BTEAC single-site PTC. This observation has strongly sup-
ported that the number of quaternary onium groups present in each
catalyst has contributed directly to the reaction and thus in turn
reflected in activity. Further, on comparing the kobs determined
with mechanical stirring and ultrasonic irradiation, the mechan-
ical stirring has influenced the reaction more effectively than the
ultrasonic irradiation. Furthermore, the comparative study reveals
that the kobs determined with the combination of ultrasound and
mechanical stirring has shown 3 fold more activity than with their
individual effect. The previously reported studies reveal that the
presence of ultrasonic wave energy increases the collision rate
between the reactants which are present in the organic and aque-
ous phase and decrease the surface area between the two layers
[51]. We have already reported similar observation [13–18,26].
Generally, the effect of ultrasonic irradiation for the promo-
tion of dichlorocarbene addition to citronellal was caused by the
production of intense local conditions due to cavitations bubble
dynamics, i.e., the nucleation, formation, disappearance and coa-
lescence of vapors or gas bubbles in the ultrasonic field [52–55].
However, in phase transfer catalyst reactions, rate enhancements
are typically due to mechanical effects, mainly through an enhance-
ment in mass transfer. In liquid–liquid bi-phase system, the
3.2. Effect of varying the stirring speed
With a view to study the effect of stirring speed on the rate of
dichlorocarbene addition to citronellal using new tetra-site MPTC,
viz., TEMACPB, the reaction was studied by varying the stirring
speed in the range of 100–800 rpm along with ultrasonic irradi-
ation. The other parameters such as [substrate], [catalyst], [NaOH]
and temperature were kept constant. The pseudo first order rate
constants were evaluated from the plots of log(a–x) versus time
(Fig. 1). From the observed kobs, it is understood that the rate of the
reaction increases on increasing the stirring speed, i.e., the rate con-
stant was gradually increased from 100 to 400 rpm and then sharply
increased to 500 rpm and then reaches a maximum at 600 rpm.
Further, the rate constant of the reaction was not improved on
increasing the stirring speed above 600 rpm. Similar trend of obser-
vation is already reported in effect of varying the stirring speed
[2,3,59,60] and it was suggested that the reaction has followed
interfacial mechanism. Similarly, Starks et al. [1] reported ana-
logue behavior displayed by reactions with a real ‘phase transfer’
(Stark’s extraction mechanism); there is much smaller limit of stir-
ring speed between physical and chemical control (100–300 rpm).
Therefore, based on the kobs trend noticed in stirring speed, it is
suggested that the reaction kinetics is controlled by the chemical
reaction in the organic phase for stirring speed at above 600 rpm.
Further, at stirring rate of 600 rpm, there is a rapid anion exchange
equilibrium which is relative to the organic displacement reaction.
From the 100 to 400 rpm, the requirement for the adequate mass
transfer of the reaction anion was not found and diffusion con-
trolled kinetics was observed, but at 500 rpm there was a sharp
increase in the kobs and this is due to the “effective mass trans-
fer” of reactant from aqueous phase to organic phase. This kind
of observation was reported earlier by Landini et al. [61] in the
study of n-octylmethane sulfonate catalyzed by quaternary salts
Table 1
Comparative catalytic study of newly developed MPTCs, viz., BTMACD and TEMACPB
with known single-site PTCs: 5.58 mmol of citronellal, 25 ml of NaOH (20%, w/w),
20 ml of chloroform, 0.23 mmol of PTC, 40 ◦C, 600 rpm, under ultrasound conditions
(42 kHz, 100 W).
Catalysts
kobs × 103 (min−1
)
Ultrasound only
Stirring only
Stirring with ultrasound
BTEAC
TBAC
BTMACD
TEMACPB
1.48
1.67
2.93
6.12
1.96
2.16
3.98
8.25
5.14
5.82
11.79
24.37
Fig. 1. Effect of stirring speed: 5.58 mmol of citronellal, 25 ml of NaOH (20%, w/w),
20 ml of chloroform, 0.23 mmol of TEMACPB, 40 ◦C, under ultrasound conditions
(42 kHz, 100 W).

86
E. Murugan, G. Tamizharasu / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 81–89
Q+X− under the PTC condition in a chlorobenzene–water bipha-
sic medium. Balakrishnan et al. [8,62] reported the same trend in
dichlorocarbene addition to styrene and in the study of C-alkylation
of phenylacetone using ethyl iodide. Wang et al. [11,63] observed
a similar behavior in the kinetic study of dichlorocyclopropanation
of 4-vinyl-1-cyclohexene and in the dichlorocarbene addition to
allyl phenyl ether and proposed an interfacial mechanism. Recently,
Murugan et al. [16] also reported the similar trend of observation
in the C-alkylation of dihydrocarvone reaction in which the rate
of the reaction increased up to 600 rpm and at above 600 rpm the
rate constant reaches constant. In the present study also, kobs is
independent of the stirring speed at above 600 rpm, and this trend
indicates that the reaction has proceeded through interfacial mech-
anism. Hence, the stirring speed was set as an optimum at 600 rpm
for further kinetic experiments.
Fig. 3. Effect of [catalyst] on kobs: 5.58 mmol of citronellal, 25 ml of NaOH (20%, w/w),
20 ml of chloroform, 40 ◦C, 600 rpm, under ultrasound conditions (42 kHz, 100 W).
3.3. Effect of [substrate]
The effect of varying the concentration of citronellal on the
rate of dichlorocarbene addition was studied in the range of
2.79–13.94 mmol and keeping the other reagents as constant under
the ultrasonic irradiation condition. From the plot of log(a–x)
versus time, the pseudo-first order rate constants were evaluated
(Table 2, Fig. 2). The observed rate constants were increased on
increasing the amount of substrate. This observation may be due
to the presence of more number of active sites in the MPTC and
higher concentration of substrate had co-operatively influenced
the reaction and thus enhanced the more number of contacts
between catalyst and substrate and hence reflected in enhanced
kobs. Balakrishnan et al. reported similar results in the study of C-
alkylation of phenylacetone [62] and phenylacetonitrile [8] with
n-bromobutane using PTC. Recently, Murugan et al. [14,18] have
also reported the same dependency of rate constants for the
dichlorocarbene addition to citral and ␣-pinene using MPTC.
3.4. Effect of [catalyst]
The effect of variation of [catalyst] on the rate of the dichloro-
carbene addition to citronellal was studied in the range of
0.11–0.34 mmol of the MPTC, viz., TEMACPB and keeping the
other experimental parameters as constant under the ultrasonic
irradiation condition. The pseudo-first order rate constants were
evaluated from the plot of log(a–x) versus time (Fig. 3). From
the observed results, the rate constants are linearly dependent
on the concentration of catalyst. The increased rate constants
are attributed to increase in number of catalytic active site
which in turn en−hance the more number of effective collisions
between Na+CCl3 and N+Et3Cl− (active site) in the interface. In
other words, at higher concentration of N+Et3Cl−, the genera-
tion of:CCl2 have been increased which in turn leads to increase
in the formation of complex between N+Et3Cl− and:CCl2 in the
organic phase. Further, not only higher rate of reactions were
obtained due to the presence of more amount of catalyst but
also intensification of the rate had occurred [64] and also there
was a total suppression of side reactions leading to 100% selec-
tivity of the product. The control experiments were also carried
out for dichlorocarbene addition to citronellal, negligible amount
of product was formed even after 3 h of reaction. The linear
dependence of the reaction rate constants on [catalyst] shows
that the reaction is believed to proceed through the interfacial
mechanism. The bi-logarithmic plot of the reaction rate con-
stant versus the concentration of the catalyst gave a straight
line with a slope of 1.18. Similar report was observed by Starks
[65] in the study of dichlorocarbene addition to cyclohexene
using tridecylmethylammonium chloride as catalyst. Halpern et al.
[66] have studied the dehydrobromination of phenethyl bro-
mide using tetraoctylammonium bromide as a catalyst, zero order
kinetics with respect to the catalyst amount was observed. The
effect of catalyst structure was studied by Dehmlow’s [27] in the
dichlorocarbene addition to cyclohexene and reported the higher
yield.
Table 2
Effect of [substrate] on kobs: 25 ml of NaOH (20%, w/w), 20 ml of chloroform,
0.23 mmol of TEMACPB, 40 ◦C, 600 rpm, under ultrasound conditions (42 kHz,
100 W).
[Citronellal] mmol
kobs × 103 (min−1
)
log [citronellal]
3 + log kobs
2.79
5.58
8.36
11.15
13.94
14.21
24.37
30.19
34.68
39.33
0.4456
0.7466
0.9222
1.0473
1.1443
1.1709
1.3869
1.4799
1.5401
1.5947
3.5. Effect of [NaOH]
The rate of the dichlorocarbene addition strongly depends on
the concentration of NaOH. In the presence of aqueous NaOH,
the dichlorocarbene is generated by the abstraction of proton
from chloroform and further it reacts with substrate present
in the organic phase to give the desired product. Hence, the
rate of dichlorocarbene addition has strongly accelerated by
the concentration of alkali in aqueous solution. The effect of
[NaOH] on the rate of dichlorocarbene addition to citronellal was
Fig. 2. Effect of [substrate] on kobs: 25 ml of NaOH (20%, w/w), 20 ml of chloro-
form, 0.23 mmol of TEMACPB, 40 ◦C, 600 rpm, under ultrasound conditions (42 kHz,
100 W).

E. Murugan, G. Tamizharasu / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 81–89
87
Table 3
Effect of [NaOH] on kobs: 5.58 mmol of citronellal, 20 ml of chloroform, 0.23 mmol of
TEMACPB, 40 ◦C, 600 rpm, under ultrasound conditions (42 kHz, 100 W).
% of NaOH (w/w)
[NaOH] (M)
kobs × 103 (min−1
)
log [NaOH]
3 + log kobs
10
15
20
25
30
2.78
4.41
6.25
8.33
10.71
7.22
13.89
24.37
32.66
44.65
0.4440
0.6444
0.7959
0.9206
1.0298
0.8588
1.1427
1.3869
1.5140
1.6498
studied by varying [NaOH] from 2.78 to 10.71 M and keeping other
parameters as constant under the ultrasonic irradiation condition.
From the observed experimental results, the rate constant has
been increased on increasing the concentration of NaOH (Table 3,
Fig. 4). The main reason is that at higher [NaOH], hydroxide ions
are less solvated by water molecules and thereby the activity
of hydroxide ion is increased. Further, under this condition the
hydrolysis of dichlorocarbene is also minimized which in turn facil-
itates the reaction. A bilogarithmic plot of the reaction rate against
[NaOH] gives a straight line with a slope of 0.96. Balakrishnan
and Jayachandran [8] observed the same trend with quaternary
onium salts.
Fig. 4. Effect of [NaOH] on kobs: 5.58 mmol of citronellal, 20 ml of chloroform,
0.23 mmol of TEMACPB, 40 ◦C, 600 rpm, under ultrasound conditions (42 kHz,
100 W).
3.6. Effect of temperature
The effect of varying the temperature on the rate of dichloro-
carbene addition to citronellal was carried out in the temperature
Scheme 3. Interfacial mechanism for dichlorocarbene addition to citronellal.

88
E. Murugan, G. Tamizharasu / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 81–89
subsequent reaction. In interfacial mechanism, the addition of:CCl2
to alkene is the slowest reaction, considering the other steps as
fast equilibrium processes. In view of these backgrounds, in our
study also it is concluded that the dependence of kinetic data on
the stirring speed, [catalyst], [NaOH], temperature and higher Ea
value and these observation has strongly proved that the reac-
tion may be proceeded through an interfacial mechanism. In the
interfacial mechanism, the hydroxide anion first reacted with the
chloroform in the organic phase without the help of quaternary
onium cations to produce CCl3−Na+. Then the anion of MPTC cat-
alyst was exchanged by CCl3−Na+ to form an active intermediate
−
of MPTC/CCl3 which can react with the double bond containing
citronellal to form dichlorocyclopropanated product, viz., 5-(2,2-
dichloro-3,3-dimethylcyclopropyl)-3-methylpentanal (Scheme 3).
Fig. 5. Arrhenius plot: effect of temperature on kobs: 5.58 mmol of citronellal, 25 ml
of NaOH (20%, w/w), 20 ml of chloroform, 0.23 mmol of TEMACPB, 600 rpm, under
ultrasound conditions (42 kHz, 100 W).
4. Conclusion
New soluble multi-site phase transfer catalysts, viz., 1,4-
bis-(triethylmethylene
ammonium
chloride)-2,5-dimethyl
benzene (BTMACD) with two active sites and 1,4-bis((3,5-bis
(triethylmethyleneammonium chloride)phenoxy)methyl)benzene
(TEMACPB) having four active sites were prepared from inexpen-
sive starting material by adopting the simplified procedures. The
presence of active sites in BTMACD and TEMACPB catalyst was
confirmed by FT-IR, 1H NMR, 13C NMR, mass and elemental analy-
sis techniques. Especially, in FT-IR studies, the C N peak intensity
noticed at 1179 cm−1 has been increased from BTEAC (single-site)
to TEMACPB (tetra-site) and thus suggests the enhancement of
number of quaternary onium group. Similarly, in 1H NMR analysis,
the quaternized N-ethyl group containing of methyl and methylene
proton peaks appeared as triplet and quartet at 1.34 and 3.06 ppm
respectively and in 13C NMR, the methyl and methylene carbon has
shown high intense peak at 8.46 and 53.03 ppm respectively, these
results has confirmed the formation of active site in the respective
MPTC. Further, in mass and elemental analyses, the observed
experimental values are almost equal with that of theoretical
value, and they have strongly supported the presence of number of
quaternary onium groups. Further, the catalytic efficiency of newly
prepared MPTCs and known single-site PTCs were ascertained from
the rate of dichlorocarbene addition to citronellal individually with
ultrasonic irradiation/mechanical stirring and also with combina-
tion of both. That is, in the comparative study, the kobs determined
by ultrasonic wave energy/mechanical stirring and combination of
both, were found in the order of BTEAC (single-site) < TBAC(single-
site) < BTMACD (di-site) < TEMACPB (tetra-site), and thus in turn
proves the number of quaternary onium groups in the respec-
tive MPTCs. Similarly, the kobs determined with ultrasonic wave
energy/mechanical stirring reveals that, in both cases, di-site and
tetra-site MPTC has shown 2 and 4 fold more active than single-site
PTC. Similarly, in the case of combination, the kobs for di-site and
tetra-site MPTC has shown 2.5 and 5 fold more active than that of
BTEAC single-site PTC and thus it confirms the presence of number
of quaternary onium groups in the respective MPTC. Further,
the superior tetra-site MPTC, viz., TEMACPB has been studied for
the thorough kinetics of dichlorocarbene addition to citronellal.
The rate of reaction increased on increasing the stirring speed,
[substrate], [catalyst], [NaOH], and temperature. Furthermore, the
activation energy Ea and other thermodynamic parameters such as
entropy of activation (ꢀS#), enthalpy of activation (ꢀH#), and free
energy of activation (ꢀG#) values were also evaluated. From the
observed kinetic results, it is apparent that the reaction follows an
interfacial reaction mechanism.
range of 303–323 K and keeping the other experimental param-
eters as constant under the ultrasonic irradiation condition. The
pseudo-first order rate constants were evaluated from the plot
of log(a–x) versus time (Fig. 5). The observed values indicate
that the reaction rate constants were increased on increasing the
temperature in association with ultrasonic wave energy [67]. The
energy of activation is calculated from Arrhenius plot (Fig. 5),
Ea = 15.76 kcal mol−1. The other thermodynamic parameters such
as entropy of activation (ꢀS#), enthalpy of activation (ꢀH#) and
free energy of activation (ꢀG#) for dichlorocarbene addition to cit-
ronellal were determined from Eyring’s equation and the obtained
values are −14.7 kcal−1 mol−1, 15.1 kcal mol−1 and 16.9 kcal mol−1
respectively.
The activation energy (Ea) reported by Chiellini et al. [68] for
ethylation of phenylacetonitrile was 20 kcal mol−1 and for this an
interfacial mechanism was proposed. Reeves and Hilbrich [60]
reported that the Ea value for ethylation of pyrrolidin-2-one under
PTC condition was 12.4 kcal mol−1 and suggested for an interfa-
cial mechanism. Tomi and Ford [69] observed a higher Ea value for
the polystyrene bound triethylammonium ion catalyzed reaction,
which was controlled by strict intrinsic reactivity under triphase
reactions. Wang et al. [11] reported that the Ea value for dichlorocy-
clopropanation of 1,7-octadiene was 13.42 kcal mol−1 and for this
also an interfacial mechanism has been proposed. Recently, Muru-
gan et al. [18] reported the higher Ea value for the dichlorocarbene
addition to ␣-pinene was 15.3 kcal mol−1 and proposed an interfa-
cial mechanism. Therefore, this study also gives higher Ea value (i.e.,
15. 76 kcal mol−1), and hence, it is suggested that dichlorocarbene
addition to citronellal should be proceed through an interfacial
mechanism.
3.7. Mechanism
Generally, in dichlorocarbene addition, reaction has been per-
formed in two steps. In the beginning, concentrated sodium
hydroxide was treated with chloroform which abstracts a pro-
ton and then an intermediate species CCl3−Na+ was generated.
Further, it was catalyzed by MPTC and followed by the addition
of electrophile. In the phase transfer catalyzed reaction, the two
important classes of mechanisms are believed to be operative,
viz., Stark’s extraction mechanism [70] in which the hydroxide ion
might be extracted from the aqueous reservoir into the organic
phase with the help of quaternary onium cations. In the case of
Makosza’s interfacial mechanism [71], the abstraction of proton
from the organic substrate by the hydroxide ion occurs at inter-
face and the resulting organic anion is ferried from the interface
into the bulk organic phase by the phase transfer catalyst for
Acknowledgments
One of the authors Mr. G. Tamizharasu acknowledges the UGC,
New Delhi, Government of India and Pachaiyappa’s College for men,

E. Murugan, G. Tamizharasu / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 81–89
89
Pachaiyappa’s Trust, Kancheepuram for providing Faculty Develop-
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[35] G.J. Price (Ed.), Current Trends in Sonochemistry, Royal Society of Chemistry,
Cambridge, 1993.
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