Didecyldimethylammonium bromide (DDAB): a universal, robust, and highly potent phase-transfer catalyst for diverse organic transformations

Article abstract of DOI:10.1016/j.tet.2007.05.017

Didecyldimethylammonium bromide (DDAB) has been scrutinized in comparison with traditional phase-transfer catalysts in variety of liquid-liquid reactions. It was found to be an exceptionally comprehensive, durable, and highly efficient phase-transfer catalyst (PTC) in a number of representative organic transformations such as C- and N-alkylations, isomerization, esterification, elimination, cyanation, bromination, and oxidation under very mild conditions of temperature and mixing. It was confirmed that DDAB is an exceedingly accessible and concurrently a highly liphophilic phase-transfer catalyst. This unprecedented characteristic renders DDAB to be a multipurpose catalyst that functions effectively both in mass transfer controlled and chemically controlled phase-transfer reactions.

Full text of DOI:10.1016/j.tet.2007.05.017

Tetrahedron 63 (2007) 7696–7701
Didecyldimethylammonium bromide (DDAB): a universal, robust,
and highly potent phase-transfer catalyst for diverse organic
transformations
*
Mandan Chidambaram, Sachin U. Sonavane, Jaima de la Zerda and Yoel Sasson
Casali Institute of Applied Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
Received 26 February 2007; revised 18 April 2007; accepted 3 May 2007
Available online 8 May 2007
Abstract—Didecyldimethylammonium bromide (DDAB) has been scrutinized in comparison with traditional phase-transfer catalysts in
variety of liquid–liquid reactions. It was found to be an exceptionally comprehensive, durable, and highly efficient phase-transfer catalyst
(
PTC) in a number of representative organic transformations such as C- and N-alkylations, isomerization, esterification, elimination, cyan-
ation, bromination, and oxidation under very mild conditions of temperature and mixing. It was confirmed that DDAB is an exceedingly ac-
cessible and concurrently a highly liphophilic phase-transfer catalyst. This unprecedented characteristic renders DDAB to be a multipurpose
catalyst that functions effectively both in mass transfer controlled and chemically controlled phase-transfer reactions.
Ó 2007 Elsevier Ltd. All rights reserved.
1
. Introduction
classified under the interfacial mechanism. The distinction
between these two mechanisms is not always very sharp
and in some cases both are operating in tandem. Thus it
was argued that the classical cyanide displacement reaction
in a liquid–liquid system, known to proceed via the extrac-
tion mechanism, operates under mass transfer control
when the stirring is not effective, namely below 200 rpm.
A slow anion transfer rate can also stem from high interfacial
tension between phases, highly hydrated anions or the use of
phase-transfer catalysts that are inhibited from approaching
the interphase. In general it is well established that the effect
of mixing on the observed reaction rate is the best experi-
mental method to determine if a system is transfer or chem-
Phase-transfer reactions are ordinarily classified according
to the nature and the solubility of the catalyst, and the num-
ber and type of the phases involved in the reacting systems.
Most familiar are liquid–liquid (LLPTC) and liquid–solid
SLPTC) reactions. Liquid–solid–liquid (LSLPTC) using
e.g., polymer supported phase-transfer catalysts or liquid–
liquid–liquid (TLPTC) where the catalyst forms a third liq-
uid phase is less typical. A more universal approach to the
categorization of phase-transfer systems is based on kinetic
criteria. Since all phase-transfer catalyzed reactions have at
least one transfer step and one chemical step they can be
broadly sorted into two major groups: mass transfer con-
trolled reactions (T-reactions) and chemically controlled
reactions (I-reactions). Accordingly, two main mechanisms
have been recognized in phase-transfer reactions: (a) the ex-
traction mechanism where anions are rapidly transferred as
ion-pairs from aqueous or solid phase into the organic phase
where they slowly react with a substrate and (b) the inter-
(
1
–3
4
6
ically controlled. Thus the latter phase-transfer catalyzed
reactions are not affected by stirring above approximately
200 rpm while the transfer controlled reactions will increase
in rate as a function of stirring up to 2000 rpm.
Solid–liquid phase-transfer reactions, where the function of
the catalyst is to transfer anions from a solid crystalline salt
into the organic phase, are usually considered to be transfer
5
facial mechanism, typical in reactions promoted by alkali,
7
,8
where interfacial deprotonation converts an anion (such as
a carbanion, oxanion or azanion), which is slowly extracted
into the organic phase to swiftly react with an electrophilic
substrate. Other processes where the transfer step (or steps)
is slow relative to the intrinsic chemical reaction are also
controlled under all conditions, although some exceptions
are known.
Several authors have realized that the nature of the quater-
nary ammonium phase-transfer catalyst required for transfer
controlled reactions is entirely different from the character-
istics of the preferred catalyst for reaction controlled
processes. The typical, widely spread, accessible catalyst in-
Keywords: Didecyldimethylammonium bromide; DDAB; Phase-transfer
catalysts; Organic transformations; Catalytic applications.
Corresponding author. Tel./fax: +972 2 6528250; e-mail: ysasson@huji.
ac.il
9
troduced by Makosza in 1966 is triethylbenzylammonium
chloride (TEBA), which is very effective and extensively
*
0
040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.05.017

M. Chidambaram et al. / Tetrahedron 63 (2007) 7696–7701
7697
used in T-reactions (mainly reactions of organic anions) but
perform poorly where the extraction mechanism is domi-
to high cost and limited availability. This has evidently
changed since the syntheses of the latter compounds have
been recently dramatically simplified via a procedure based
10
nant. Cetyltrimethylammonium bromide (CTMAB) is
also a weak catalyst in I-reactions but quite active in
solid–liquid mass transferred controlled PTC reactions.
1
8,19
on simple and mild alkylation of dimethylformamide.
1
1
DDAB is being used in various industrial fields including
2
0
It was concluded that for reactions proceeding via the extrac-
tion mechanism, the preferred catalysts were the more orga-
bio-chemical industries. DDAB has not been previously
proposed as a phase-transfer catalyst except for one example
in which we have demonstrated its unique activity in an
oxidation reaction using aqueous hydrogen peroxide, where
1
2
nophilic and symmetrical quaternary cations. The latter
demonstrate higher extraction coefficients and more reactive
nucleophilic anions (due to lower Coulombic interaction
energies with the larger cation). Conversely, in transfer con-
trolled reactions the supreme phase-transfer catalysts are the
more ‘accessible’ or ‘open faced’ quaternary ammonium
2
1
it showed superior activities among the PTCs screened.
2. Results and discussion
1
3
cations. The latter carry smaller alkyl groups, and thus
readily occupy positions close to the interphase thus creating
a higher catalyst concentration at the site of the rate-
Prior to our catalytic experiments, we assessed the physio-
chemical properties of DDAB in comparison with some
standard phase-transfer catalysts such as TEBA (Makosza’s
1
4
determining step. Mason et al. have demonstrated the cor-
relation between the surface properties of several quaternary
ammonium salts (quats) and their catalytic activity in C-
alkylation process, a typical I-reaction. It was concluded
that quats that more effectively reduce the surface pressure
at the water–organic interphase are also the more potent
PT catalysts. It was also proven that the catalytic activity
did not directly stem from the reduction in surface pressure.
A quantitative empirical parameter q introduced by Hal-
2
2
catalyst),
336, Starks’ catalyst), and TBAB (Brandstrom’s cata-
tricaprylmethylammonium chloride (aliquat
2
3
2
4
lyst). According to the standard evaluation of quaternary
ammonium salts as phase-transfer catalysts, Makosza’s
catalyst is unsymmetrical but has a shorter alkyl chain, and
hence is an accessible catalyst. Starks’ catalyst possesses
one short alkyl chain, and is liphophilic in nature but inferior
from the symmetry perspective, and Brandstrom’s catalyst is
in perfect symmetry but is only partially accessible due to
the masking of C4 alkyl chains. Considering the extraction
mechanism, the relative performance of these three catalysts
is: Starks’ catalyst>Brandstrom’s catalyst>Makosza’s cata-
lyst, whereas for the interfacial mechanism, the order is:
Makosza’s catalyst>Brandstrom’s catalyst>Starks’ cata-
lyst. In comparison with the above, DDAB has a potential
advantage in being both highly accessible and highly orga-
nophilic at the same time. Initially, the surface pressure
was measured for water/air and toluene/air interfaces in
the presence of DDAB. It was found to be 2.78 dynes/cm
and 2.41 dynes/cm, respectively. These figures are an order
of magnitude smaller than the surface pressure reported
15
pern can be used to assess the T versus I activity of various
quaternary ammonium catalysts. The q value is calculated
by adding the reciprocals of the number of carbons on
each of the alkyl chains of the ammonium cations. Thus
for TEBA q¼1.64 and for tetrahexylammonium bromide
(
THAB) q¼0.67. It is generally accepted that for T-reactions
the q-value should be higher than 1. Best results are obtained
with catalysts with q value between 1.5 and 2.0. It should be
noted, however, that a certain critical level of organophilicity
is still required for interfacial reactions. Thus tetramethyl-
and tetraethylammonium catalysts are not considered as ac-
tive T-type catalysts. For I-reactions q should preferably be
<
(
1. Despite the high q value of surfactants such as CTAB
q>3), these are not useful catalysts due to the formation
1
4
for other PTCs such as TBAB, TEBA, and aliquat 336 sig-
nifying that DDAB is a potentially more active catalyst.
of emulsions in water–organic mixtures when the latter are
present. Another important criterion in phase-transfer cata-
lyst selection is the thermal and chemical stability of the cat-
Further, we have examined the thermal stability of DDAB in
comparison with both TBAB and tributylmethylammonium
bromide (TBMAB). This was performed using differential
scanning calorimetry (DSC). The substances were dissolved
in a neutral organic medium (isopropanol) and heated at
a rate of 10 C/min and the thermal events recorded. We
established that DDAB decomposed at 255 C, TBAB at
213 C, and TBMAB at 206 C. At a second stage we
assessed the thermal stability of these catalysts under basic
conditions. This was accomplished using the catalytic iso-
1
6
alyst, and also the ease of its separation from the reaction
mixture after the process is completed.
1
7
In view of these and other guidelines, most practitioners
have chosen tetrabutylammonium bromide (TBAB) (q¼1)
as the default catalyst for exploratory PTC applications.
Indeed this catalyst performs satisfactorily in essentially
all I- and T- PTC reactions and it is also reasonably stable
to alkaline and thermal conditions and swiftly washed
away from product mixtures once the reaction is completed.
However it is rarely the optimal catalyst for a given process.
ꢀ
ꢀ
ꢀ
ꢀ
2
5
merization reaction of anethole in the presence of 50%
aqueous NaOH (Eq. 1) as a reporter reaction indicative to
the presence of an active catalyst.
We have now recognized that another family of quaternary
ammonium salts, represented by the commercially available
surfactant didecyldimethylammonium bromide (DDAB), is
far more pertinent to the label of ‘universal’ or ‘default’
phase-transfer catalyst. As is demonstrated in this work,
DDAB is an excellent PT catalyst in both I- and T-reactions.
The group of dialkyldimethylammonium halides has been
overlooked in the past by PTC researchers, probably due
Table 1 presents the maximum conversions obtained in Eq. 1
at different temperatures in the presence of 8 mol % of
TBMAB, TBAB, and DDAB. The table also displays the
time required to achieve the maximum conversion. The latter
is actually the life span of the particular catalyst under the
given conditions, as the reaction stops once the catalyst is
totally decomposed. We can safely conclude that DDAB is

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M. Chidambaram et al. / Tetrahedron 63 (2007) 7696–7701
Table 1. Study of stability of different phase-transfer catalysts by means of
isomerization of 4-propenyl anisole to b-anethole (Eq. 1)
Table 2. Comparison of DDAB with TBAB and TBMAB in catalytic activ-
ity as PTC
a
b
Catalysts
Entry Temperature Time to
ꢀ
Maximum
achieve maximum conversion
Reaction
DDAB
TBAB
TBMAB
c
(
C)
Conv. Selec. Conv. Selec. Conv. Selec.
(
conversion (min)
(%)
%)
(%)
(%)
(%)
(%)
(%)
TBMAB
TBAB
1
2
3
90
110
130
45
20
10
50
38
27
a
Isomerization
Alkylation
Esterification
80
97
100
—
100
100
28
61
75
—
100
100
50
73
83
—
100
100
b
c
1
2
3
90
110
130
120
60
20
28
22
18
a
Reaction condition: 4-propenyl anisole (10 mmol), catalyst (8 mol %),
ꢀ
toluene (10 mL), NaOH (50% w/w, 10 mL), temperature (90 C), and
time (24 h).
Phenylacetonitrile (10 mmol), bromobutane (10 mmol), DDAB
DDAB
1
2
3
90
110
130
1080
1140
120
76
67
52
b
c
(
(
2 mol %), toluene (10 mL), NaOH (50% w/w, 10 mL), temperature
ꢀ
40 C), and time (2 h).
a
Benzyl chloride (10 mmol), sodium formate (10 mmol), DDAB
(
Reaction condition: 4-propenyl anisole (10 mmol), catalyst (8 mol %),
toluene (10 mL), and NaOH (50% w/w, 10 mL).
TBMAB (tributylmethylammonium bromide), TBAB (tetrabutylammo-
nium bromide), and DDAB (didecyldimethylammonium bromide).
Conversion based on gas chromatography analysis with area minimiza-
tion.
5 mol %), toluene (10 mL), NaOH (50% w/w, 10 mL), temperature
ꢀ
b
c
(120 ), and time (2 h). Conversion and selectivity are based on gas chro-
matography analysis.
ꢀ
under temperatures of 40–120 C. The reactions were mon-
itored using gas chromatographic analyses, which were also
the basis of calculation for the final conversions. All the
tested reactions showed >99% selectivity and very high con-
versions.
by far more stable than the other two catalysts examined,
surviving 120 min at 130 C versus TBAB that endured
ꢀ
for 20 min and TBMAB that degraded after merely
10 min. These experiments were repeated twice with excel-
lent reproducibility.
Alkylation of phenylacetonitrile (Entry 1 in Table 3) and
iminostilbene (Entry 2 in Table 3) proved that DDAB can
effectively catalyze these processes at mild reaction temper-
ature to achieve high conversion and selectivity of products.
Phenylacetonitrile and iminostilbene were alkylated to attain
CH CH=CH
CH=CHCH3
2
2
9
7% and 95% selectivity of products with 2 and 10 mol %
PTC
0% aq NaOH
ð1Þ
DDAB catalysts at 2 and 4 h reaction time, respectively.
Further, alkylation of phenylacetonitrile has been screened
using DDAB, TBAB, and TBMAB for comparison study,
which reveals that DDAB is more active (Table 2) than the
other two mentioned PTCs.
5
OMe
OMe
We then examined the catalytic activity of DDAB in several
illustrative I-type and T-type phase-transfer reactions. All
the processes were reported previously using other different
quaternary ammonium catalysts. The reactions studied
were:
The performance of DDAB in an isomerization reaction was
tested in 4-propenyl anisole to b-anethole (p-methoxy-
b-methylstyrene) reaction (Eq. 1, Entry 3 in Table 3). The
ꢀ
system was refluxed at 90 C for 24 h and found to achieve
2
6
(
1) Alkylation of phenylacetonitrile with n-butylbromide
80% conversion using 8 mol % of DDAB. Further, isomeri-
zation was also studied with other quaternary salts (Table 2)
where it was found that DDAB is notably more active.
2
7
and of iminostilbene with allyl bromide. Both are
typical T-reactions.
2) Isomerization of 4-propenyl anisole to b-anethole, an
I-type reaction.
3) Oxidation of thiophene 2-carboxaldehyde to thiophene
(
(
2
8
DDAB also showed a good stability and activity in reactions,
which took place in the presence of oxidants such as sodium
hypochlorite and hydrogen peroxide (Entry 4 in Table 3),
where within 1 h, thiophene aldehyde exclusively converted
2
9
2
-carboxylic acid using hypochlorite as oxidant.
3
0
(
(
(
(
4) Dehydrobromination of 2-phenylethyl bromide.
5) Cyanation of benzyl chloride—a classical I-reaction.
6) Hydrobromination of 1-decanol with aqueous HBr.
7) Esterification of benzyl chloride with sodium formate,
this is also a typical I-reaction.
3
1
ꢀ
to acid (100% conversion and selectivity) at 45 C using
3
2
1.5 mol % of DDAB catalyst. Entry 5 in Table 3 demon-
strates that DDAB catalyst can also be used in elimination
reactions to selectively eliminate HBr from 2-phenylethyl
bromide by means of sodium hydroxide as base to yield
88% of styrene, with just 1 mol % of catalyst within 4 h of
3
3
Reactions 1, 2, and 7 were performed under identical condi-
tions with TBAB, TBMAB, and DDAB as catalysts. Results
are presented in Table 2 where the superiority of DDAB in
all the three processes is clearly demonstrated. Table 3 dis-
plays the experimental conditions and results of the above
eight model reactions in the presence of DDAB catalyst. De-
tailed procedures are given in Section 4. In general, experi-
ments were carried out under mild conditions using a 50 mL
reactor (10 mmol scale) equipped with a magnetic stirrer
ꢀ
reaction time at 90 C.
The cyanation reaction of benzyl chloride to obtain aceto-
nitrile (Entry 6 in Table 3) was also performed. In a typical
reaction, benzyl chloride was mixed with DDAB catalyst
and then kept in a glove box, sodium cyanide added, and
the reaction carried out for 1 h and achieved 100% con-
version of benzyl chloride and 100% selectivity to

M. Chidambaram et al. / Tetrahedron 63 (2007) 7696–7701
7699
a
Table 3. Catalytic reactions of didecyldimethylammonium bromide
j
k
Conversion (%)
k
Selectivity (%)
Entry
Reaction
Reactants
CH CN
Products
C H
4
9
2
CHCN
b
1
Alkylation
97
95
100
100
+
C H Br/NaOH
4 9
c
2
Alkylation
N
H
N
CH -CH=CH
2
2
+
CH =CH-CH Br / NaOH
2
2
CH -CH=CH
CH=CH-CH3
2
2
d
3
Isomerization
80 cis+trans
—
+
NaOH
OMe
OMe
e
+ NaOCl/NaOH
CHO
4
Oxidation
100
88
100
100
COOH
S
S
CH -CH Br
CH=CH
2
2
2
f
5
+
NaOH
Elimination
CH Cl
CH CN
2
2
g
6
Cyanation
100
100
+
NaCN (s)
h
7
Bromination
Esterification
C
C
10
H
21OH+HBr/H
2
O
CH Cl+HCOONa
C
10
H
21Br
HCOOCH C H
100
100
100
100
i
8
6
H
5
2
2 6 5
a
Reactions were conducted in a batch reactor under liquid phase condition.
Phenylacetonitrile (10 mmol), bromobutane (10 mmol), DDAB (2 mol %), NaOH (50% w/w, 10 mL), toluene (10 mL), temperature (40 C), and time (2 h).
b
c
d
e
ꢀ
ꢀ
Iminostilbene (10 mmol), 3-bromopropene (10 mmol), DDAB (10 mol %), NaOH (50% w/w, 10 mL), toluene (10 mL), temperature (55 C), and time (4 h).
ꢀ
4-Allylanisole (10 mmol), DDAB (8 mol %), NaOH (50% w/w, 10 mL), toluene (10 mL), temperature (90 C), and time (24 h).
Thiophene aldehyde (10 mmol), sodium hypochlorite (10 mmol), DDAB (1.5 mol %), NaOH (50% w/w, 10 mL), toluene (10 mL), temperature (45 C), and
ꢀ
time (1 h).
2-Phenylethyl bromide (10 mmol), DDAB (1 mol %), NaOH (50% w/w, 10 mL), toluene (10 mL), temperature (90 C), and time (4 h).
f
ꢀ
g
h
ꢀ
Benzyl chloride (10 mmol), sodium cyanide (10 mmol), DDAB (1.5 mol %), toluene (10 mL), temperature (105 C), and time (1 h).
1-Decanol (10 mmol), hydrogen bromide (10 mmol), DDAB (10 mol %), hydrogen peroxide (30%, 3 mL), NaOH (50% w/w, 10 mL), toluene (10 mL), tem-
perature (120 C), and time (16 h).
ꢀ
i
ꢀ
Benzyl chloride (10 mmol), sodium formate (10 mmol), DDAB (5 mol %), NaOH (50% w/w, 10 mL), toluene (10 mL), temperature (120 ), and time (2 h).
Products are identified by GC–MS or by comparison with authentic samples.
Conversion and selectivity of products are based on gas chromatography analysis.
j
k
phenylacetonitrile. The stability of DDAB under strongly
acidic conditions was checked in a hydrohalogenation reac-
tion by means of hydrogen bromide (48% aqueous solution)
and achieved 100% conversion of 1-decanol to 1-bromo-
mechanisms under very mild condition and retains its activ-
ity for long periods of time even in highly basic conditions.
Since DDAB is sparingly soluble in water (100 mg DDAB in
30 mL water) it can be extracted and removed from organic
reaction mixtures by repeated washing with water.
ꢀ
decane after 16 h of heating at 120 C reflux temperature
(
Entry 7 in Table 1). Esterification of benzyl chloride using
sodium formate as esterification agent achieved 100% con-
version of benzyl chloride, in 2 h of reaction time using
5
mol % of DDAB catalyst. Further, this reaction was also
3. Conclusions
studied and evaluated in comparison with TBAB and
TBMAB, which again confirms the superiority of DDAB
DDAB is ascertained as a general purpose and universal
phase-transfer catalyst that performs very effectively in a va-
riety of highly diversified liquid–liquid reactions. This novel
quaternary ammonium salt was shown to operate effectively
both via the extraction mechanism and the interfacial mech-
anism, and in addition was realized to be exceptionally
stable in relatively high temperatures and high pH.
(
Table 2).
The excellent high conversions obtained, across the board,
for this diversified group of PTC reactions are indeed re-
markable and as far as we know unprecedented. It is evident
that DDAB functions extraordinarily at different PTC

7700
M. Chidambaram et al. / Tetrahedron 63 (2007) 7696–7701
4
. Experimental
4.2.5. Cyanation of benzyl chloride. Cyanation of benzyl
chloride was performed using 1.5 mol % of DDAB. In a typ-
ical procedure, benzyl chloride (10 mmol) was mixed with
4
.1. Materials and instruments
1
0 mmol of sodium cyanide followed by the addition of
10 mL toluene and NaOH (50% w/w) and the whole system
Didecyldimethylammonium bromide (DDAB) was pur-
chased from Aldrich and characterized for its chemical
and physical properties prior to catalytic experiments. Other
chemicals (reagents and solvents) were purchased from
commercial firms (>99% pure) and used without further pu-
rification. The reaction mixtures were analyzed with a gas
chromatograph (HP 5890) equipped with a flame ionization
detector and a capillary column (5% cross-linked phenyl
methyl silicone gum, 0.2ꢁ50 m). The products were also
compared with authentic samples wherever possible.
ꢀ
was subjected to heating at 105 C for 1 h under stirring.
Precautionary measures were made to avoid the leakage of
cyanide vapor during reaction. The reaction has to be done
in a glove box using a water condenser connected to batch
reactor to prevent the loss of volatile cyanide vapor from
the mixture.
4.2.6. Hydrobromination of 1-decanol. Hydrobromination
of 1-decanol was performed in a 50 mL Schlenk flask using
1
0 mol % of DDAB. In a representative procedure, 1-
Surface pressure measurements were performed by Du Noy
ring method using a Lauda Tensiometer. Using the ‘pre-
vented ruptured’ technique, in which the interface is not bro-
ken during the measurements, readings were taken every
decanol (10 mmol) was mixed with 10 mmol of hydrogen
bromide in water and 3 mL of 30% hydrogen peroxide
added. The whole system was stirred at 120 C for 16 h.
ꢀ
5
ment, 100 mg of DDAB was dissolved in 20 mL toluene/
min until a stable value was obtained. For this measure-
4.2.7. Esterification of benzyl chloride with sodium for-
mate. Benzyl chloride (10 mmol) was mixed with sodium
formate (10 mmol), 5 mol % of DDAB, 10 mL of NaOH
2
4
4
0 mL water separately and measured.
.2. Catalytic reactions
(50% w/w), and 10 mL toluene were added and the reaction
mixture was magnetically stirred and heated to the required
ꢀ
temperature (120 C) in a preheated oil bath for 2 h.
.2.1. Alkylation of phenylacetonitrile and iminostilbene.
Alkylation of phenylacetonitrile and iminostilbene was
done with 1-bromobutane and 3-bromopropene, respec-
tively, using a 1:1 molar ratio of reactants. In a typical run,
phenylacetonitrile (10 mmol) was taken in a 50 mL Schlenk
flask and 2 mol % of DDAB was added followed by the
addition of 10 mL of toluene. Then 1-bromobutane
4.2.8. General work up procedure. The progress of reac-
tions was monitored by GC. After completion of the reac-
tion, the reaction mixture was stirred and washed with
5ꢁ35 mL of water to remove DDAB and NaOH. The or-
ganic layer was dried over MgSO and was concentrated
4
under reduced pressure to give a dried compound as product.
The products were analyzed with an analytical tool, gas
chromatograph, identified by GC–MS, injecting authentic
(10 mmol) was added followed by the addition of 10 mL
of NaOH (50% w/w in water). The reaction mixture was
1
magnetically stirred and heated to the required temperature
(
samples, and by H NMR.
ꢀ
40 C) in a preheated oil bath for 2 h. The same procedure
was followed for the alkylation of iminostilbene using the
required amounts of substrates and catalyst (see Entry 2
of Table 3).
Acknowledgements
M.C. is grateful to the Pikovski-Valazzy Fund for their
support.
4
.2.2. Isomerization of 4-propenyl anisole. Isomerization
of 4-propenyl anisole was executed using toluene as solvent.
In a typical procedure, 4-propenyl anisole (10 mmol) was
taken in a 50 mL Schlenk flask and 8 mol % of DDAB fol-
lowed by the addition of 10 mL of toluene and 10 mL of
NaOH (50% w/w in water). The reaction mixture was stirred
References and notes
1. Sasson, Y.; Rothenberg, G. Handbook of Green Chemistry
and Technology; Clark, J., Macquarrie, D., Eds.; Blackwell:
Oxford, UK, 2002; p 206.
ꢀ
at 90 C over a preheated oil bath for 24 h.
2
. Jwo, J.-J. Catal. Rev. 2003, 45, 397.
4
.2.3. Oxidation of thiophene 2-aldehyde. Oxidation of
3. Wu, H.-S.; Yang, H.-M. Catal. Rev. 2003, 45, 463.
4. Halpern, M. In Phase-Transfer Catalysis Mechanism and
Synthesis; Halpern M., Ed.; ACS Symposium Series 659;
American Chemical Society: Washington, DC, 1996; p 97.
5. Makosza, M.; Krylowa, I. Tetrahedron 1999, 55, 6395.
6. Starks, C. M. Tetrahedron 1999, 55, 6261.
thiophene 2-aldehyde was performed in a 50 mL Schlenk
flask using 1.5 mol % of DDAB in 10 mL toluene. In a repre-
sentative course of action, thiophene aldehyde (10 mmol)
was mixed with 10 mmol of sodium hypochlorite and
1
was stirred at 45 C for 1 h.
0 mL of NaOH (50% w/w in water), and the whole system
ꢀ
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1
1
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