Investigation of structural change and basicity of NaY zeolite upon loading KF and their application in Henry nitroaldol reaction under microwave irradiation condition

Article abstract of DOI:10.1007/s10562-014-1327-0

Potassium salt modified NaY zeolite along with methanol-water mixture as solvent under microwave irradiation offers an environmentally benign way to synthesize b-nitroalcohols rapidly with excellent yield and selectivities. Here, NaY zeolite was modified

Full text of DOI:10.1007/s10562-014-1327-0

Catal Lett (2014) 144:1751–1758
DOI 10.1007/s10562-014-1327-0
Investigation of Structural Change and Basicity of NaY Zeolite
upon Loading KF and Their Application in Henry Nitroaldol
Reaction Under Microwave Irradiation Condition
•
Rasna Devi Ruli Borah Ramesh C. Deka
•
Received: 24 April 2014 / Accepted: 24 July 2014 / Published online: 13 August 2014
Ó Springer Science+Business Media New York 2014
Abstract Potassium salt modified NaY zeolite along with
methanol–water mixture as solvent under microwave irra-
diation offers an environmentally benign way to synthesize
b-nitroalcohols rapidly with excellent yield and selectivi-
ties. Here, NaY zeolite was modified with 0.5–20 % KF (w/
w) by a wet impregnation method and characterized by
X-ray diffraction, FT-IR and Hammett base strength mea-
surement methods. It was observed that framework struc-
ture preserved even after 20 % loading of KF while
crystallinity decreased from lower to higher loading. The
obtained materials showed quite different base strengths
with varying percentage of the salt over the support and
with change of their activation temperatures. The effects of
different reaction parameters such as amount of solvents,
nature of solvents, microwave power and microwave irra-
diation time were studied to minimize the reaction time
without compromising the yields. Among the loaded cata-
lysts, 10 wt% KF loaded catalyst was found to be the best
catalyst and gave 97 % yield within 2 min under optimized
reaction conditions. Recovery of the catalysts was tested for
three times and it showed similar conversions in each cycle.
1 Introduction
Henry nitroaldol reaction has got interests from very early
days due to diverse applications of the product b-nitro alcohol
and its easy conversion possibility into other synthetically
important compounds [1–4]. In the recent years, strategies
have been made to improve the reaction conditions as well as
to minimize side products with various catalyst systems and
suitable reaction media [5–8]. Particularly, solid base catalysts
like alkali and alkaline earth metal exchanged zeolite X and
zeolite Y, supported zeolites and metal oxides, hydrotalcites
etc. are used for this reaction to take advantage of their tunable
basicity, easy product isolation and catalyst recycling [9–12].
In the flow of current research, a group of basic materials have
been prepared by exchanging extra framework cations of
zeolites with alkali and alkaline earth metal cations [13] and
loading alkali metal salts over a variety of solid supports
where potassium salt is the most common among other alkali
salts [14–17]. Various supports such as porous oxides Al2O3,
ZnO, ZrO2 and SiO2, zeolite NaX, NaY, ZSM-5, KL zeolite
etc. [18–20] are used to prepare solid bases byusingpotassium
salts as guest material. Although Al2O3 and ZrO2 have been
found as excellent basic materials in presence of potassium
salts, their use is limited due to low surface area and disor-
dered pore arrangements. Zeolites having aluminosilicate
compositions are preferred as host material due to their high
surface area, well organized pore channels, stability towards
heating and its environmentally benign nature. Potassium
fluoride has been supported onto a variety of solid host
materials due to its different advantages such as it is easy to
handle, inexpensive, thermally stable and can be easily dried.
Zhu and his co-workers reported only mild basicity of NaY
zeolite (H- = 9.3) after loading 16 wt% KF and activated at
400 °C while 16 wt% KF loading over Al2O3 coated NaY
zeolite and activated at 400 °C generates strong basic sites
Keywords NaY zeolite Á Microwave Á Nitroaldol
reaction Á b-Nitroalcohols Á Hammett indicator
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-014-1327-0) contains supplementary
material, which is available to authorized users.
R. Devi Á R. Borah Á R. C. Deka (&)
Department of Chemical Sciences, Tezpur University, Napaam,
Tezpur 784 028, India
e-mail: ramesh@tezu.ernet.in
123

1752
R. Devi et al.
(H- = 17.2) without significant change in zeolite pore archi-
tecture [21]. Again, Sun et al. have reported quite low basicity
of NaY/KF (H- = 7.2) after activation at 600 °C and the
structure collapsed upon activation[22]. Thus, loadingof NaY
zeolite with different amount of KF and activation at different
temperatures would be interesting to observe their effect upon
the structure, base strengths and catalytic activities.
Germany; Phenolphthalein and Neutral red from Merck,
Germany; Nitromethane from G. S. Chemicals Testing Lab
& Allied Industries, New Delhi; potassium fluoride (KF),
sodium sulphate (Na2SO4), silica gel, iodine and the sol-
vents were purchased from RANKEM.
2.2 Preparation of the Catalysts
Synthetic protocol using microwave irradiation are gaining
value now a days due to its core heating mechanism and
shorter reaction time than classical conditions [23–25]. The
green approach lies in getting higher yields within short
reaction time, energy efficiency, higher selectivities and
possibility to carry out reactions under solventless conditions
[26, 27]. However, solventless synthesis has got limitations in
that they generally require liquid bases to ease mixing
between the reactants and catalysts when all reactants are
solid. Besides, larger amount of liquid reactants are used as
reaction medium when both catalysts and other reactants are
solid. Therefore, a large number of organic reactions have
been carried out during these days under microwave irradia-
tion using solid catalysts [28–30] with different reaction
media. Although Henry nitroaldol reaction has been carried
out with a variety of reaction media including water [31],
ionic liquids [32], fluorous biphasic system [33] etc., inves-
tigation of suitable reaction media with heterogeneous cata-
lytic system is an ongoing research. Moreover, the dehydrated
nitroalkene predominates over the desired nitroaldol product
in many cases [34, 35]. In this regard the use of microwave to
speed up the reaction and aqueous alcoholic water as solvent
is helpful due to its higher dielectric constant than most of the
commonly used organic solvents and thus can couple with
microwave easily. Although Henry nitroaldol reaction under
microwave irradiation condition is not a new approach [36],
the combined use of solid base along with microwave irra-
diation condition is not very common [37, 38].
In the typical synthesis of potassium loaded NaY zeolites,
sodium form of zeolite Y was used to impregnate KF in
different proportions. In this procedure, KF amounts of 0.5,
1, 2, 3, 5, 10, 15 and 20 % KF (w/w) were impregnated
over NaY zeolite by a wet impregnation method. To
impregnate 10 % KF over NaY, 50 mg of KF was first
dissolved in 10 mL distilled water and then added to
500 mg NaY zeolite. NaY zeolite was dried in an oven at
80 °C overnight before impregnation. The solution was
stirred at room temperature for 24 h, slurries were dried at
100 °C for overnight and stored in a desiccator. Following
the same procedure other catalyst samples were prepared
by taking appropriate amount of KF and NaY zeolite. The
catalysts were then calcined in a muffle furnace at tem-
perature range of 450–800 °C for the required time.
2.3 Characterization
X-ray diffraction patterns of the prepared samples were
recorded using a Rigaku (miniflex UK) X-ray diffractom-
˚
eter with Cu Ka radiation (k = 1.548 A) operated at 30 kV
and 15 mA at a scan speed of 2°min-1 and 2h range of
2–50°. The % crystallinity of the samples were calculated
from XRD peaks by using the formula, % Crystallin-
ity = (AS 9 100)/AR, where, AR = Integrated area of the
reference material under the peaks between a set of 2h
limits and AS = Integrated area of the sample under the
peaks between the same set of 2h limits as that of the
reference. The crystallite sizes were calculated by X-ray
line broadening method considering reflection planes at 2h
values 7.25, 24.05 and 30 using the Debye–Scherrer
equation [t = Kk/bcosh, where t is the crystallite size, K is
shape factor (taken as 1), k is the X-ray wavelength
At this time we have impregnated 0.5–20 wt% KF in
NaY zeolite by a wet impregnation method from aqueous
solution of KF and calcined at a temperature range of
450–800 °C, measured basicities and checked catalytic
activities towards Henry nitroaldol reaction under micro-
wave irradiation conditions. The effect of KF loading upon
zeolite framework structure, change in basic properties,
their catalytic behaviour and selectivities towards Henry
nitroaldol reaction with a variety of solvents under micro-
wave irradiation conditions was studied systematically.
˚
(1.542 A for Cu target), b is the full width at half maxi-
mum (FWHM) in radians and h is the Bragg’s angle of
diffraction] [39].The specific surface areas were deter-
mined from N2 adsorption–desorption isotherms by Brun-
aur-Emmett-Teller method using a Quantachrome NOVA
1000e Surface area and Pore Size Analyzer at 77 K. FT–IR
spectra were recorded on a Nicolet Impact Model-410
spectrometer at 32 scans and 1 cm-1 resolution in the mid
IR (400–4,000 cm-1) region using the KBr pellet tech-
2 Experimental
2.1 Materials
1
nique. H and 13C NMR spectra were recorded on a JEOL
NaY zeolite was purchased from HiMedia Laboratories
Pvt. Ltd.; aldehydes from Sigma Aldrich and Merck,
JNM-ECS 400 by taking Me4Si as internal standard in
CDCl3 and CD3OD solvents. Thin-layer chromatography
123

Investigation of Structural Change and Basicity of NaY zeolite
1753
was carried out on glass plates with silica gel and pre-
parative column chromatography was carried out with sil-
ica gel having 60–120 mesh size.
with flexible proble up to 600 °C (Fig. 1). In a typical pro-
cedure of synthesis of b-nitroalcohols, 15 mg of calcined
catalyst was added to a mixture of 1 equivalent aldehyde, 4
equivalent Nitromethane and 3 mL solvent in a long necked
microwave flask fitted with a reflux condenser in at
280 Watt (40 % of 700 Watt) microwave power and 50 °C.
The reaction was monitored by thin layer chromatography,
stopped after completion of the reaction and cooled to room
temperature. Organic portion was then extracted, dried over
sodium sulphate (Na2SO4) and concentrated under vacuum
to obtain the crude product. The product was then purified
by thin layer chromatographic technique and analyzed by 1H
and 13C NMR techniques. The conversions and selectivities
The strength of basic sites was measured by using
Hammett indicators [40]. The following Hammett indica-
tors were used: Neutral red (H_ = 6.8–8.0), Phenolphtha-
lein (H_ = 8.0–9.6) and Tropaeolin-O (H_ = 11.1–12.7).
In this method 25 mg of solid calcined at 450, 600 and
800 °C was shaken with 1 mL solution of indicator (0.1 %
in methanol) and left to equilibriate for 2 h. The colour of
the catalyst was then noted. The aqueous soluble amount of
basic sites was determined by acid–base titration technique
reported previously [22]. In this procedure 100 mg of
calcined sample was shaken in 10 mL water at room
temperature for 24 h and the catalyst was separated by
centrifugation. The filtrate was neutralized with 10 mL of
aqueous HCL (0.05 M) and then the remained acid was
titrated with 0.01 M standard aqueous NaOH. Oxalic acid
dihydrate was used for standardization of NaOH and a
methanol solution of phenolphthalein (1 mL, 0.1 mg/mL)
was taken as indicator.
1
were calculated on the basis of integration of H NMR
signals of the reactants and products from crude reaction
mixture. Catalysts were recovered by centrifuge, dried at
100 °C for overnight calcined and reused. Catalytic activi-
ties of the recovered catalysts were then checked under
similar reaction conditions.
3 Results and Discussion
2.4 Catalytic Test
The X-ray diffraction patterns of parent NaY zeolite and
KF modified zeolites calcined at 450 °C (Fig. 2) suggests
that zeolite framework structure remains preserved even
after 20 % loading of KF. However, peak intensities
(Fig. 2) and crystallinity (Fig. 3) decrease gradually from
All catalytic reactions were performed in ‘‘Catalyst system
Scientific Microwave systems’’ scientific microwave reactor
having power output 700 Watt (2,450 MHz), power levels
from 140 to 700 Watt and automatic temperature sensors
Fig. 1 Catalyst system scientific microwave
123

1754
R. Devi et al.
Table 1 Surface properties and particle size of zeolites
Sample
BET area
Crystallite size (nm)
(m2g-1
)
7.25 (2h)
24.05 (2h)
30 (2h)
NaY
450
447
63
73
52
48
45
46
10 %KF/NaY
FTIR spectra of parent as well as modified samples were
recorded after calcinations at 450, 600 and 800 °C.
Figure 4 shows vibrations in the region 400–1200 cm-1
which is a clear evidence of the presence of zeolite
framework structure in the parent as well as modified
samples. Band at around 1,650–1,700 cm-1 can be ascribed
to bending vibration of water molecules [41, 42] attached to
zeolite structure which remain intact in all samples acti-
vated at 450 °C while it disappeared after calcinations at
600 °C (b1) and 800 °C (b2, b3). This clearly shows that
high activation temperature is not recommended for zeolite
structure in presence of guest species. Distinct bands for
internal tetrahedral vibrations i.e. in the ranges
1,050–1,000 cm-1 and 700–650 cm-1 are due to asym-
metric and symmetric T-O (Si or Al) stretching mode
respectively in tetrahedral co-ordination while band in the
range 650-500 cm-1 is for tetrahedral T-O-T bending mode
and 500–410 cm-1 is for external linkages between tetra-
hedra which is assigned for double ring [43]. Figure 4
shows that no alteration of all these bands takes place up to
15 % loading of KF while 20 % loaded samples have very
weak vibrations for these bands (a9). This is in good
agreement with XRD observation that KF loading beyond
10 % is restricted for NaY zeolite structure. We have also
observed from the XRD pattern of the calcined samples that
both internal and external zeolite structure exists for 5 %
loaded sample activated at 600 °C (b1) while the band for
double ring is absent in samples activated at 800 °C (b2,
b3). It shows that both high activation temperature and
higher loading of KF have harmful effect over the support.
Therefore, 10 % KF loaded catalyst calcined at 450 °C can
be considered as optimum in this study.
Fig. 2 XRD patterns of NaY and KF/NaY zeolites calcined at 450 °C
Fig. 3 Differences of (%) crystallinity of NaY and different KF/NaY
zeolites calcined at 450 °C
lower to higher loading. Again, occurrence of no additional
peaks up to 10 % KF loading suggests high dispersion of
KF over zeolites while emergence of an additional peak at
2h position 39.95° for both 15 and 20 % loaded zeoiltes
can be attributed to the formation of KAlF4 phase (JCPDS
card number 84-1009). This observation indicates some
interaction of zeolite structure with KF and thus loading of
KF beyond 10 % is strictly prohibited. Crystallinity dif-
ferences between modified samples and the original NaY
zeolite are compared by taking three high intensity peaks at
2h positions of 24°, 27° and 30°. Figure 3 shows a gradual
decrease of % crystallinity upon increased loading of KF.
However, calculation of crystallite sizes from XRD peaks
of both NaY zeolite and 10 %KF/NaY zeolites shows that
crystallite sizes of 10 %KF/NaY are almost similar to the
original zeolites (Table 1). This further confirms that KF
loading up to 10 % is not harmful for zeolite structure..
The basic property investigation of different samples
shows quite different basicities of parent and modified
zeolites (Table 2). The base strengths of parent NaY and
0.5–3 % KF loaded NaY zeolites are the same and lies in
the range of 8.0 \ H_ \ 10 while it lies in the range
10 \ H_ \ 11.1 for 5–20 % loaded samples. This shows
that basicity increases on increasing KF loading. It is
interesting to note that the framework structure remains
preserved even after activation of 20 % loaded zeolite at
450 °C and simultaneously basicities increases. This indi-
cates that KF does not have negative effect on zeolite
structure at 450 °C. However, appearance of an additional
phase (XRD) upon 15 % loading prohibits the possibility to
123

Investigation of Structural Change and Basicity of NaY zeolite
1755
Table 2 Base strength of KF modified zeolites calcined at 450 °C
Sample
Base strength (H_)
Amount of
soluble basic
sites (mmol g-1
)
NaY
8.0 \ H_ \ 10
8.0 \ H_ \ 10
8.0 \ H_ \ 10
8.0 \ H_ \ 10
8.0 \ H_ \ 10
10 \ H_ \ 11.1
10 \ H_ \ 11.1
10 \ H_ \ 11.1
10 \ H_ \ 11.1
8.0 \ H_ \ 10
10 \ H_ \ 11.1
10 \ H_ \ 11.1
8.0 \ H_ \ 10
10 \ H_ \ 11.1
0.292
0.419
0.5 %KF/NaY
1 % KF/NaY
2 %KF/NaY
3 %KF/NaY
5 %KF/NaY
10 %KF/NaY
15 %KF/NaY
20 %KF/NaY
0.5–5 % KF/NaYa
10 %KF/NaYa
15 %KF/NaYa
3–10 %KF/NaYb
15 %KF/NaYb
a
0.475
0.507
0.797
The activation temperature was 600 °C
The activation temperature was 800 °C
b
their role on basic properties. Hence, 5 and 10 % loaded
catalysts were further activated at 600 and 800 °C and
basicities were checked (Table 2). The base strengths
decrease upon increasing activation temperature. It may be
attributed to the interaction of KF with zeolite structure
thus reducing some basic sites at high temperature. The
result of titrimetric analysis shows that the original NaY
itself have some soluble basicities and it goes on increasing
upon increasing KF loading.
Optimization of reaction conditions for Henry Niroaldol
reaction was carried out first by performing the reaction
under solvent free conditions and then in presence of
variety of solvents. Thin layer chromatography monitoring
showed no conversion at all (entries 1 & 2, Table 3) in case
of solvent free conditions. This may be due to inability of
the catalyst to abstract a proton in the absence of a reaction
medium. In our previous report [44], we have found
methanol as the optimized solvent among a variety of polar
and non-polar solvents for this reaction at room tempera-
ture. Therefore, a variety of alcohols and H2O–alcohol
mixtures as solvents were screened at this time to under-
stand the role of reaction medium (Table 3) under micro-
wave irradiation. The reaction is faster for alcohols
containing small alkyl groups than with alcohols contain-
ing bulky alkyl groups. Octanol shows only 12 % con-
version in comparison to methanol which gives 95 %
conversion within 2 min and this can be attributed to
decrease of polarity of alcohols on increasing bulky nature
of alkyl groups. This result goes hand in hand with our
previous report and the conversions follow the order
Fig. 4 FTIR spectra of parent as well as KF modified samples
calcined at various temperatures. (a1) NaY, (a2) 0.5 % KF/NaY, (a3)
1 % KF/NaY, (a4) 2 % KF/NaY, (a5) 3 % KF/NaY, (a6) 5 % KF/
NaY, (a7) 10 % KF/NaY, (a8) 15 % KF/NaY and (a9) 20 % KF/NaY
(calcined at 450 °C); (b1) 5 % KF/NaY (calcined at 600 °C); (b2)
5 % KF/NaY (calcined at 800 °C); (b3) 10 % KF/NaY (calcined at
800 °C)
load KF beyond 10 %. Thus 10 % loading has been con-
ceded as the optimum amount in this study. This shows
concomitant result with previous reports confirming that
activation temperature and amount of loading both have
123

1756
R. Devi et al.
Table 3 Henry nitroaldol reaction of 4-nitrobenzaldehyde and
Nitromethane catalyzed by 10 %KF/NaY in different solvents
Entry
Solvents
% Conversion
(time in min)
% Selectivityc
A
B
C
1
Solvent freea
Solvent freeb
MeOH
No (5)
No (5)
95 (2)
97 (2)
86 (2)
12 (2)
51 (2)
6 (2)
–
–
–
–
8
–
–
2
3
92
4
EtOH
98
94
2
5
n-Butanol
3
2
5
3
6
Octanol
88
7
Isopropanol
Isobutanol
93
2
8
100
97
9
H2O
71 (1)
97 (1)
94 (1)
21 (1)
21 (1)
96 (1)
40 (1)
50 (30)
58 (30)
3
5
3
10
11
12
13
14
15
16
17
MeOH–H2O
EtOH–H2O
Butanol–H2O
Octanol–H2O
Isopropanol–H2O
Isobutanol–H2O
Ethylene glycol
Ethylene glycol–H2O
95
97
Fig. 5 Effect of microwave irradiation time on different polar
solvents
100
100
98
2
3
nitromethane. This further increases the acidity of acidic
protons of nitromethane and thus basic sites of zeolites can
easily abstracts a proton from it. We have also observed
that the catalytic activity of used zeolite decreases in the
next run which may be due to blockage of some active sites
of zeolite by these solvent molecules in the process of the
polar interaction as described above. The feasibility of the
reaction in aqueous alcoholic mixture has been further
confirmed by observing the absorbed microwave energy by
some polar solvents when irradiated with 40 % microwave
power for 10 min and keeping the amount of solvents fixed
(Fig. 5). The highest microwave energy (in terms of tem-
perature) was absorbed by H2O–MeOH (1:1 ratio) amongst
a variety of screened solvents. In addition, a gradual
increase of absorbed energy was observed on increasing
microwave irradiation time for the same solvent and fixed
amount of solvent. Thus, aqueous methanol has been
considered as the best solvent in our study.
97
77
1
6
16
18
76
All reactions were carried out with aldehyde (0.5 mmol), Nitro-
methane (2 mmol), 10 %KF/NaY (10 mg), solvent (3 ml), MW
power (40 %), Temperature (50 °C)
Solvent free condition between p-Nitrobenzaldehyde and
Nitromethane
a
b
Solvent free condition between Benzaldehyde and Nitromethane
c
Conversions and selectivities of the products were obtained from
1H NMR data of crude reaction mixture [[A: 1-(4-nitrophenyl)-2-
nitroethanol, B: 1-(4-nitrophenyl)-2-nitroethene and C: 1,3- dinitro-
2-(4-nitrophenyl)-propane]]
MeOH * EtOH [ n-butanol [ isopropanol [ octanol [
isobutanol for pure alcohols. This shows that straight chain
alcohols with smaller alkyl groups are more favourable
than the bulkier alkyl group containing alcohols. With
50 % aqueous alcoholic solution, the reaction becomes
more rapid giving excellent conversions and selectivities
within 1 min irradiation time. Water miscible alcohols
offer a reaction medium suitable for both reactant and
catalysts thus making the conditions favourable for the
reaction. On the other hand bulky alcohols are less soluble
in water and place the reactants and catalysts in different
phases thus lowering the feasibility of the reaction. At this
time, the trend follows H2O–MeOH * H2O–EtOH *
H2O–iso-propanol [ H2O–isbutanol [ H2O–butanol [
H2O–Octanol. This shows that water miscible alcohols
speed up the reaction. The feasibility of the reaction in
water miscible alcohols can be suggested that the tendency
of H-bonding of alcohols with basic sites of zeolites makes
the alkoxide ions to interact with acidic protons of
The investigation of effect of microwave energy on
amount of solvent is important as well to minimize energy
used in the process and is summarized in Fig. 6. This was
studied at constant irradiation time where the microwave
power was changed first by keeping amount of solvent
fixed and then changed the amount of solvents by keeping
microwave power fixed. In both cases absorbed energy
increases on increasing amount of solvent and MW power.
However, no significant effect was observed upon chang-
ing MW power for small amount of solvents. On increasing
MW power from 140 to 560 Watt, temperature rise for
1 mL H2O is from 36 to 47 °C respectively i.e. a rise of
11 °C while it shows 20 °C rise (71–91 °C) for 4 ml H2O
under same conditions. This shows that MW power does
not have vast effect for small amount of solvents. Hence,
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Investigation of Structural Change and Basicity of NaY zeolite
1757
Table 4 Henry Nitroaldol reactions with various aldehydes
NO2
NaY/KF
OH
O
NO2
+
+
CH3NO2
+
NO2
NO2
R
R
R
R
H
MeOH-
H2O
R = Aryl or Alkyl groups
Entry
R
Time (min)
% yielda
1
2
3
C6H5 (No catalyst)
C6H5
5
5
0
75
92
92b
99c
81d
88
84
76
73
64
70
77
88
4-(NO2)C6H4
1
4 h
2.5 h
7 h
2
4
3-(NO2)C6H4
2-(NO2)C6H4
4-ClC6H4
5
2
6
10
15
15
10
15
3
7
4-CH3C6H4
2-OHC6H4
2-Furyl
Fig. 6 Effect of microwave irradiation power on amount of solvent
8
9
40 % power with 3 mL solvent has been chosen as opti-
mum amount in this study.
10
11
1-Naphthyl
4-(NO2)C6He4
Following this step, Henry reaction with variety of
aldehydes have been carried out by taking 3 mL H2O–
MeOH, 1 mmol aldehyde, 4 mmol Nitromethane and
280 Watt microwave power at 50 °C (Scheme 1) to
understand the effect of specific heating of microwave on
formation of the desired product. The results are summa-
rized in Table 4. In comparison to room temperature
methodology [43], the reaction time greatly reduces from
hours to minute (Table 4) under microwave irradiation
giving moderate to excellent yields (64–92 %) within
2–15 min. The improved conversions and selectivites is not
only the effect of rise of temperature of MeOH–H2O sol-
vent under microwave can be suggested by heating the
reaction mixture at 50 °C without any microwave source.
Table 4 shows that the reaction takes 2.5 h [43] to com-
plete with reduced selectivity while it takes only 1 min
under microwave. The usefulness of MeOH–H2O as reac-
tion media under microwave can again be noted by com-
paring the previous reports where performing nitroaldol
reaction at 50–60 °C ionic liquid medium [45], supercrit-
ical CO2 medium [46] shows inferior results in comparison
to the present system. The reaction goes well with aro-
matic, heterocyclic and polycyclic aromatic aldehydes to
afford the desired nitroaldol product in good yields where
aromatic aldehydes having electron withdrawing groups
(entries 3–5, Table 4) are comparatively faster than alde-
hydes containing electron donating groups (entries 6–8,
Table 4) and gives excellent yields within 1 min (entry 3,
Table 4). Again, reaction with substituted nitrobenzalde-
hyde at para position (entry 3) is faster than that at ortho
and meta positions (entries 4 and 5) while heterocyclic and
ploycyclic aromatic aldehydes (entries 9 and 10) react
All reactions were carried out with aldehyde (1 mmol), Nitromathane
(4 mmol), 10 %KF/NaY (15 mg, calcined at 450 °C), MeOH–H2O
(3 ml), MW power (40 %) at 50 °C
a
Isolated yields
b
Reactions with 1:2 of 4-nitrobenzaldehyde/Nitromethane, 2 mL
solvent (MeOH–H2O) and 0.02 g NaY/KF at room temperature
c
Reaction with 1:1 of 4-nitrobenzaldehyde/Nitromethane, 2 mL
solvent (MeOH–H2O) and 0.02 g NaY/KF at 50 °C
d
Reactions 0.5 mmol of aldehyde, 0.75 mmol of nitromethane,
19–30 mg Mg–Al HT in 1 mL of ionic liquid
e
Reactions with recovered catalysts
slowly and gives good to moderate yields within 15 min.
The conversion with recovered catalysts was lowered
somewhat and gives 88 % conversion of the product within
3 min.
To confirm effect of aqueous wash basicity upon con-
version, we have stirred the catalyst with water–methanol
mixture for 24 h and separated the catalyst by centrifuga-
tion and perfomed the reaction with the filtrate under same
reaction conditions. No conversion was observed from thin
layer chromatography observation and this proves that the
basicity was imparted by the catalyst itself and the reaction
was heterogeneously catalyzed.
4 Conclusions
In conclusion, we have described microwave assisted
Henry nitroaldol reaction with KF modified NaY zeolite as
a suitable method to obtain b-nitro alcohol in good yield
within short time. The reaction rate greatly enhances due to
123

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R. Devi et al.
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4.1 Spectral Data
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4.1.1 2-Nitro-1(4-nitrophenyl)ethan-1-ol:(entry 3,
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1H NMR (400 MHz, CDCl3): d 8.22 (d, 2H), d 7.62 (d,
2H), d 5.59–5.61 (m, 1H), d 4.48–4.60 (m, 2H), d 3.52 (s,
1H); 13C NMR (400 MHz, CDCl3): 147.7, 144.9, 126.7,
123.8, 80.3 and 69.7 ppm.
4.1.2 2-Nitro-1(4-chlorophenyl)ethan-1-ol:(entry 6,
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1H NMR (400 MHz, CDCl3): d 7.40 (d, 2H), d 7.35 (d,
2H), d 5.47–5.43 (m, 1H), d 4.46–4.46 (m, 2H), d 3.92 (s,
1H); 13C NMR (400 MHz, CDCl3): 140.1, 134.8, 129.8,
126.1, 80.7 and 70.3 ppm.
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1H NMR (400 MHz, CDCl3): d 8.0–7.98 (m, 1H), d
7.90–7.88 (m, 1H), d 7.86–7.85 (m, 1H), 7.74–7.70 (m,
1H), d 7.60–7.51 (m, 3H), d 6.28–6.27 (m,1H), d 4.68–4.66
(m, 2H), d 2.93 (bs, 1H); 13C: 133.6, 133.5, 130.7, 130.2,
129.6, 129.5, 126.2, 124.6, 123.8, 121.9, 80.8 and
68.3 ppm.
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Acknowledgments This work was supported by the Department of
Science and Technology, New Delhi. The authors acknowledge Dr.
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