International Journal of Organic Chemistry, 2011, 1, 119-124
doi:10.4236/ijoc.2011.13018 Published Online September 2011 (http://www.SciRP.org/journal/ijoc)
Phase Transfer Catalysis of Henry and Darzens Reactions
Layla Mhamdi1, Hafedh Bohli1, Younes Moussaoui1,2, Ridha ben Salem1*
1Physical Organic Chemistry Laboratory, Science Faculty of Sfax, Sfax University, Sfax, Tunisia
2Science Faculty of Gafsa, Gafsa University, Zarroug City, Gafsa, Tunisia
Received April 28, 2011; revised June 23, 2011; accepted August 16, 2011
Abstract
We describe in this work the influence of the addition of phase transfer catalyst in heterogeneous medium
liquid/liquid on the output of the reactions of Darzens and Henry. It proves that the reaction of Darzens is
favoured in the presence of low base such as K2CO3 and Et3N. Phase transfer catalysis is an efficient activa-
tion method in Darzens and Henry reactions. Thus, the Ethylene Diammonium Diacetate (EDD) has a com-
parable catalytic activity has that of quaternary ammonium salts in the reaction of Darzens.
Keywords: Darzens, Henry, Phase Transfer Catalysis, Mechanism
1. Introduction
The formation of a carbon-carbon bond is the fundamen-
tal reaction in organic synthesis [1-5]. To this respect,
Henry [6-9] and Darzens [10-12] reactions can be con-
sidered as excellent tools to give access to multifunc-
tional compounds [13,14]. The Darzens reaction gives
α,β-epoxy carbonyl compounds, whereas the Henry reac-
tion leads to nitroaldols.
The Henry reaction [15] consists of the addition of a
nitronate nucleophile on the double bond of a carbonyl
compound. It proceeds usually at room temperature in
the presence of a base to afford a β-nitroalcool. The pre-
ferred bases are alcali hydroxides [16], carbonates [17],
bicarbonates [18] and alkali oxides. The reaction, how-
ever, is often carried out in protic media such as metha-
nol or, even, water [19]. Henry adducts are very useful in
organic synthesis as precursors for pharmaceutical and
biological purposes [20,21]. In order to improve the effi-
ciency of the reaction, new catalytic or non-catalytic
methods have been divised such as alumina [22], potas-
sium fluoride on alumina as support [23], lanthanides
[24], high pressures [25] and microwaves [26]. In the
same way, the Darzens reaction permits the synthesis of
adducts simultaneously involving the formation of a
carbon-carbon bond and a carbon-oxygen bond [12].
Several authors have tried to improve the enantioselec-
tivity and the yields. Arai et al. [27] showed that the en-
antioselectivity of the Darzens reaction can be excellent
when using a chiral auxiliary such as cinchonine, an al-
caloid structurally close to quinine. Later on, the same
group [28] introduced a phase transfer catalyst derived
from cinchonine to synthetize Darzens products. In the
same way, Ku et al. [29] reported the asymmetric syn-
thesis of trans-α,β-epoxysulfones by the catalytic phase-
transfer Darzens reaction of chloromethyl phenyl sulfone
with various aromatic aldehydes in the presence of the
cinchona alkaloid-derived chiral phase-transfer catalysts.
In the goal to continue our works on the activation by
the phase transfer catalysis of organic reactions such as:
Wittig reaction [30], Baylis-Hillman reaction [31,32],
Michael reaction [32,33], Knoevenagel reaction [34],
Heck reaction [35,36]. In this work, we study the activa-
tion of Henry and Darzens reactions by means of phase
transfer catalysis (PTC).
2. Experimental
2.1. Henry Reaction
Procedure A: A solution of nitroalkane (7.5 mmol),
solvent (15 mL), and base (5 mmol) was introduced in a
25 mL flask equipped with a magnetic stirrer. 5 mmol of
carbonyl compound was added. The mixture was stirred
during 24 h at ambient temperature. The organic phase
was extracted with diethyl ether. When the carbonyl
compound was an aldehyde, the organic phase was wash-
ed with a saturated solution of anhydrous sodium hydro-
genosulfite to remove the unreacted aldehyde. The or-
ganic phase was dried over anhydrous sodium sulphate.
After evaporation of the solvent the product was purified
on silicagel column chromatography with hexane-ether

L. MHAMDI ET AL.
120
mixtures as eluent.
Procedure B: As procedure A with addition of 2
mmol of the phase transfer catalyst.
2.2 Darzens Reaction
Procedure C: A solution of α-chloroester or α-chl-
oroaacid or α-chloronitrile (3.6 mmol), solvent (15 mL),
base (3.6 mmol) was introduced in a 25 mL flask eq-
uipped with a magnetic stirrer. 3 mmol of carbonyl com-
pound was added. The mixture was stirred during 24h at
ambient temperature. The organic phase was extracted
with diethyl ether and dried over anhydrous sodium sul-
phate. After evaporation of the solvent the product was
purified on silicagel column chromatography with hex-
ane-ether mixtures as eluent.
Procedure D: As procedure C with tetrahydrofurane
as solvent and potassium hydroxide as the base with ad-
dition of 2mmol of the phase transfer catalyst.
2.3. Synthesis of Ethylene Diammonium
Diacetate (EDD)
Ethylene diamine (3 g) in anhydrous diethylether was
introduced in a 50mL flask. The flask was immersed into
a liquid bath maintained at 35˚C. Then, glacial acetic
acid (6 g) was added. The mixture was stirred until boil-
ing of ether. After 24 h cristallization occurred. The solid
product was filtered and washed with ether. Finally, it
was recrystallized in methanol.
2.4. Recording of Spectra
1H (300 MHz) and 13C (75 MHz) NMR spectra are re-
corded on a Bruker spectrometer in DMSO-d6, with
tetramethysilane as internal reference.
The products were analysed by GC-MS (Hewlett-
Packard computerised system consisting of a 5890 gas
chromatograph coupled to a 5971A mass spectrometer)
ionisation mode used was electronic impact at 70 eV.
Microanalyses were performed using a C, H, N Ana-
lyzer Model 185 from Hewlett-Packard. I.R. spectra are
recorded in KBr on a Bruker Tensor 27 spectrometer in
the range 4000 - 400 cm–1.
All the products were confirmed by comparing their
IR, MS, 1H NMR and 13C NMR data with literature data
[9,10,12,37,38].
3. Results and Discussion
3.1. Henry Reaction
Effect of the base:
We have examined the nature of the base in the Henry
reaction involving benzaldehyde and various nitroal-
kanes in aqueous solution (Table 1).
Inspection of the results of Table 1 shows that the re-
activity is modest in the presence of bases such as
triethylamine and weak in the presence of carbonate
anions such as K2CO3. There is no reaction with sodium
alcoolates.
This may be explained by the formation of secondary
products issued from Cannizzaro reactions or hydrolysis
in the presence of alcoolates on the contrary of reactions
involving triethylamine or alkali carbonates. The results
are in agreement with those of Zhou et al. [39] who
found that Henry reaction of aromatic and aliphatic al-
dehydes with nitromethane is promoted by triethylamine
in water.(Figure 1.)
Effect of the carbonyl compound:
The effect of the carbonyl compound was studied in a
next step using nitromethane and various carbonyl com-
pounds (Figure 2, Table 2).
As shown in Table 2, the reaction does not occur with
ketones. Apparently this is due to the very weak reactiv-
ity of ketones toward the carbanion formed by deproto-
nation of nitromethane. Steric effects and the positive in-
ductive effect lead in the case of ketones to a reduction
Table 1. Effect of the base in the Henry reaction.
R1R2 ProductBase Yield (%)
CH3ONa 0
EtONa 0
Et3N 46
H 1a
K2CO3 21
CH3ONa 0
EtONa 0
Et3N 42
CH3 1b
K2CO3 18
CH3ONa 0
EtONa 0
Et3N 47
H
C2H51c
K2CO3 24
CH3ONa 0
EtONa 0
Et3N 32
CH3CH3 1d
K2CO3 17
Procedure A
+
C
6
H
5
CHO
R
1
R
2
CH NO
2
Base (1eq)
H
2
O ; 25°C ; 24hCH
R
2
CNO
2
R
1
OH
C
6
H
5
Figure 1. Henry reaction of benzaldehyde with nitroalkane.
R
1
R
2
C
O
H
3
CNO
2 +Et
3
N (1eq)
H
2
O ; 25°C ; 24hR
2
O
H
CCH
2
R
1
NO
2
Figure 2. Henry reaction of nitromethane with carbonyl
compound.

121 L. MHAMDI ET AL.
Table 2. Effect of the carbonyl compound in the Henry re-
action.
R1 R
2 Product Yield (%)
H C6H5 1a 46
H C3H7 1e 48
H Cl-C6H4 1f 54
CH3 C
2H5 1g 0
CH3 C
6H5 1h 0
-(CH2)5- 1i 0
-(CH2)4- 1j 0
Procedure A.
of the electrophilicity of the carbon in the carbonyl group.
This makes the attack of the resulting carbanion more
difficult.
Effect of phase transfer catalysis:
In the following step we examined the nature of the
phase transfer catalyst in Henry reactions involving
various aldehydes and ketones.(Figure 3.)
The results of Table 3 show that
1) There is no reaction in the absence of PTC with C5
and C6 cyclic ketones. With the addition of PTC cata-
lysts, the reaction occurs in fair yields.
2) In the other reactions, the reaction occurs whatever
the addition or not of phase transfer catalysts. The cata-
lyst, however, leads to an improvement of yields. This
can be explained by the stability of the reaction interme-
diate formed by the addition of the PT catalyst to the
carbanion. Such intermediate inhibits any possible retro
Henry reaction.
3) Among the quaternary ammonium salts listed in
Table 3, the most appropriate seems to be Aliquat-336.
The catalytic activity of the ammonium salt depends on
R
1
R
2
C
O
CH NO
2
+Et
3
N
H
2
O ; PTCR
2
OH
CC
R
1
NO
2
R
3
R
4
R
3
R
4
Figure 3. Henry reaction of nitroalkanes with carbonyl
compounds.
Table 3. Effect of the PT catalysts in the Henry reaction.
Yield %
R1 R
2 R 3 R 4 Prod-
uct no
PTC TBAB TEBACAliquat -336
C6H5 H H H 1a 46 52 53 70
C6H5 H H CH3 1b 36 - 55 68
C3H7 H H H 1c 48 51 60 72
C6H5 H CH3 CH3 1d 16 - 56 39
(CH2)5 H H 1i 0 17 22 44
(CH2)4 H H 1j 0 12 24 47
C3H7 H H CH3 1k 38 - 63 41
C3H7 H CH3 CH3 1l 18 - - 42
Procedure B. TBAB: bromure de tétrabutylammonium; TEBAC: chlorure
de benzyltriéthylammonium; Aliquat-336: chlorure de méthyltrioctylammo-
nium.
the structure of the alkyl or aryl groups on the nitrogen
atom and, also, on the nature of the counter-ion. It may
also be noticed that the presence of a lipophilic group
(this is the case of Aliquat-336) is beneficial for the for-
mation of the Henry adduct as it facilitates the nucleo-
philic attack on the aldehyde [31].
4) At last, the yield depends on the nature of the anion
associated with the ammonium cation. It is higher with
tetrabutylammonium chloride than with the correspond-
ing bromide. The same result was also found by D’Incan
in his study examining the effect of the phase transfer
agent on the Horner-Emmons reaction between benzal-
dehyde and 1-cyanoethyl diethyphosphonate [40].
We propose the following mechanism of the Henry
reaction involving benzaldehyde and nitromethane under
PTC conditions (Figure 4).
3.2. Darzens Reaction
Effect of solvent:
The effect on the nature of the solvent in the Darzens
reactions was studied in condensations between benzal-
dehyde and a α-chloroester, α-chloroacid or α-chloro-
acetonitrile in the presence of potassium hydroxide as the
base. (Figure 5.)
According to the results of Table 4, there is no reac-
tion in aqueous solution in reactions involving α-chloro-
esters or α-chloroacetonitrile. In organic phase, the reac-
tivity remains low. With an acidic α-chloroacetate, how-
ever, there is no reactivity at all whatever the medium,
aqueous or organic. This may be ascribed to a decompo-
sition of the acidic function supported by the release of
carbon dioxide.
Tetrahydrofurane seems to be the most adequate sol-
vent for the Darzens reactions between benzaldehyde and
+
H
2
CNO
2
H
Et
3
N
H
2
CNO
2
Et
3
NH
(Oct)
3
NMe , Cl
+H
2
CNO
2
Et
3
NH , Cl
(Oct)
3
NMe
+
H
2
CNO
2
(Oct)
3
NMe
C
O
HC
6
H
5
+CH
O
CH
2
C
6
H
5
NO
2
(Oct)
3
NMe
CH
O
CH
2
C
6
H
5
NO
2
(Oct)
3
NMe
Et
3
NH , Cl
+
CH
OH
CH
2
C
6
H
5
NO
2
Et
3
N
(Oct)
3
NMe , Cl
Organic phase
Aqueous phase
Figure 4. Mechanism of the Henry reaction between nitro-
methane and benzaldehyde under PTC conditions (liq-
uid-liquid heterogeneous catalysis).
C
6
H
5
CHO +KOH
RCHEWG
C
l
O
R
EWG
C
6
H
5
Figure 5. Darzens reaction of benzaldehyde with a α-chlo-
roester, α-chloroacid or α–chloroacetonitrile.

L. MHAMDI ET AL.
122
Table 4. Effect of the base in the Henry reaction.
R EWG Product Solvent Yield (%)
T.H.F 36
CH2Cl2 22
CN 2a
Water 0
T.H.F 28
CH2Cl2 18 COOEt 2b
Water 0
T.H.F 0
CH2Cl2 0
H
COOH 2c
Water 0
T.H.F 21
CH2Cl2 12 CH3 COOEt 2d
Water 0
Procedure C.
α-chloroester or α-chloroacetonitrile, in agreement with
the results given by Wang et al. [12].
Effect of the base:
Using THF as the solvent we have studied the effect of
the base in the Darzens reaction at ambient temperature
(Figure 6).
Table 5 shows that the Darzens reaction of benzalde-
hyde and α-chloroesters or α-chloroacetonitrile is fa-
voured in the presence of KOH. Sodium hydroxide, how-
ever, is not indicated. This is probably due to the opening
of the epoxy cycle with NaOH, a result also given by
Wang et al. [12].
Effect of the carbonyl compound
From Table 6, we note that the Darzens reaction pro-
ceeds better with aldehydes than with ketones. The latter
do not react with α-chloroacetonitrile. This seems to be
due to the weak reactivity of ketones toward the carbanion
formed by deprotonation of α-chloroacetonitrile. Steric
C
6
H
5
CHO +Base
RCH
EWG
C
lO
R
EWG
C
6
H
5
THF
Figure 6. Darzens reaction: effect of the base.
Table 5. Effect of the base in the Darzens reaction.
R EWG ProductBase Yield (%)
K2CO3 16
NaOH 0
KOH 36
CN 2a
Et3N 10
K2CO3 12
NaOH 0
KOH 28
COOEt 2b
Et3N 12
K2CO3 0
NaOH 0
KOH 0
H
COOH 2c
Et3N 13
K2CO3 14
KOH 0 CH3 COOEt 2d
Et3N 14
Table 6. Effect of the carbonyl compound in the Darzens
reaction.
R1 R
2 Product Yield (%)
36
H C6H5
C3H7
2a
2e 32
CH3 C
2H5 2f 0
effects and the inductive effect (+I) lead in the case of
ketones to a reduction of the electrophilic character of
the carbon in the carbonyl group making the attack of the
generated carbanion more difficult (Figure 7).
Effect of phase transfer catalysts
All the above results reveal that the yield in the inves-
tigated Darzens reactions is generally low. In order to
improve such yields, we have turned to the use of phase
transfer catalysts (Figure 8).
There is no reaction in the condensation between ben-
zaldehyde and α-chloroacetate even under PTC condi-
tions (Table 7).
The addition of a phase transfer catalyst on the me-
dium noticeably enhances the reactivity (Table 7). This
may be ascribed to the exaltation of the nucleophilicity
of the carbanion formed by the addition of the PTC cata-
lyst on the carbanion (Figure 9).
R
1
R
2
C
O
+KOH
O
CN
THF
Cl CH
2
CN
R
1
R
2
Figure 7. Darzens reaction of α-chloroacetonitrile with var-
ious carbonyl compounds.
+Base
O
EWG
C6H5
THF
Cl CH2EWG
C6H5CHO
Figure 8. Effect of phase transfert catalyst in the Darzens
reaction of benzaldehyde with α–chloroacetonitrile, α–chl-
oroacetic acid and ethyl α–chloro-acetic acid.
Table 7. Effect of PT catalyst in the Darzens reaction
Yield %
EWG Productno PTC Aliquat-336 EDD*
CN 2a 36 60 64
COOEt2b 28 41 48
COOH2c 0 0 0
Procedure D. *EDD: Ethylene Diammonium Diacetate
(Oct)
3
NMe , Cl
+
Organic phase
Aqueous phase
KOH (Oct)
3
NMe , HO
+
KCl
(Oct)
3
NMe , HO
ClCH CN
HClCH CN
(Oct)
3
NMe
CHC
6
H
5
O
CH
O
CHC
6
H
5
CN
(Oct)
3
NMe
Cl
CH CHC
6
H
5
CN
O
(Oct)
3
NMe , Cl
Figure 9. Mechanism of the Darzens reaction involving be-
nzaldehyde and α–chloroacetonitrile under PTC conditions.

123 L. MHAMDI ET AL.
4. Conclusions
The anionic activation in Henry and Darzens reactions
has been achieved by the addition of quaternary ammo-
nium salts leading to an exaltation of the reactivity of the
generated anions. The addition of a phase transfer cata-
lyst in the reaction medium leads to an increase in the
yield for the Henry reaction involving nitromethane and
various ketones as well as a remarkable reactivity in the
Darzens reaction. On the contrary, there is no reaction
with a α-chloroacetate acid whatever the medium, even
under PTC conditions.
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