Catalytic transfer hydrogenation of nitro arenes, aldehydes, and ketones with propan-2-ol and KOH/NaOH over mixed metal oxides

Article abstract of DOI:10.1081/SCC-120016330

Mixed metal oxides such as ZrO₂-NiO, ZrO₂-CoO, and ZrO₂-Fe₂O₃ effectively reduce nitro arenes, aldehydes and ketones with propan-2-ol and KOH/NaOH in liquid phase reaction. The catalysts also have considerable level of reusability.

Full text of DOI:10.1081/SCC-120016330

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Catalytic Transfer Hydrogenation of Nitro Arenes,
Aldehydes, and Ketones with Propan-2-ol and KOH/
NaOH over Mixed Metal Oxides
Sachin U. Sonavane a & Radha V. Jayaram a
a Department of Chemical Technology , Applied Chemistry Division , University of Mumbai ,
Matunga, Mumbai, India
Published online: 17 Aug 2006.
To cite this article: Sachin U. Sonavane & Radha V. Jayaram (2003) Catalytic Transfer Hydrogenation of Nitro Arenes,
Aldehydes, and Ketones with Propan-2-ol and KOH/NaOH over Mixed Metal Oxides, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 33:5, 843-849, DOI: 10.1081/SCC-120016330
To link to this article: http://dx.doi.org/10.1081/SCC-120016330
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 5, pp. 843–849, 2003
Catalytic Transfer Hydrogenation of
Nitro Arenes, Aldehydes, and Ketones with
Propan-2-ol and KOH/NaOH over
Mixed Metal Oxides
*
Sachin U. Sonavane and Radha V. Jayaram
Department of Chemical Technology, Applied Chemistry
Division, University of Mumbai, Matunga,
Mumbai, India
ABSTRACT
Mixed metal oxides such as ZrO2–NiO, ZrO2–CoO, and ZrO2–Fe2O3
effectively reduce nitro arenes, aldehydes and ketones with propan-2-ol
and KOH/NaOH in liquid phase reaction. The catalysts also have
considerable level of reusability.
The selective and rapid reduction of nitro compounds is an interest-
ing area of research particularly when other potentially reducible moieties
*Correspondence: Radha V. Jayaram, Department of Chemical Technology,
Applied Chemistry Division, University of Mumbai, Matunga, Mumbai
400 019, India; Fax: 91-22-4145619; E-mail: rvj@aplchem.udct.ernet.in.
843
DOI: 10.1081/SCC-120016330
Copyright & 2003 by Marcel Dekker, Inc.
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844
Sonavane and Jayaram
are presentin the molecule. [1] Complete reduction of nitro compounds to
amines is very important, as they are potential intermediates for a variety
of fine chemicals.[2,3]
A wide range of homogeneous and heterogeneous catalytic systems
in combinations with different hydrogen donors have been employed for
reduction of major functional groups attached to aliphatic and aromatic
structures.[4]
Reduction of functional groups can be achieved by classical Meerwein
Pondrof-Verley reduction. However the use of aluminium isopropoxide
in stoichiometric amounts under severe reaction conditions often leads to
undesired side reactions.[5]
Recently, transfer hydrogenation using homogeneous complexes
of Cu, Fe, Rh, Pd, and Ni with propan-2-ol as hydrogen donor has
gained much interest.[6] But reduction rates are considerably low with
these catalysts.[7] On the other hand, use of heterogeneous catalysts has
several advantages over these homogeneous systems, which includes ease
of recovery and enhanced stability. In recent years different catalyst
systems such as mixed metal oxides, hydrous oxides, metallic Sm, Indium
metal and clay minerals have been exploited for reduction of nitro
compounds.[8–12]
In this paper, we present the results of transfer hydrogenation of
some aromatic nitro compounds, ketones and aldehydes with propan-
2-ol over mixed metal oxides of the type ZrO2–NiO, ZrO2–CoO and
ZrO2–Fe2O3.
EXPERIMENTAL SECTION
All chemicals and solvents used were of A.R. grade. The catalysts
were characterized by XRD and FTIR spectroscopy. XRD patterns
were recorded on a Siemens D-500 X-ray diffractometer using CuKa
radiation and a Ni filter.
FTIR spectra were recorded with a JASCO FTIR spectro-
photometer by KBr pellet method. The progress of the reaction was
monitored by TLC (SiO2–I2 vapor) for qualitative purpose. The
products were further analyzed using a gas chromatograph (Model
Esheeta, Eshika, India) fitted with an OV 101 column and FID
detector.

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Nitro Compound Reduction with Mixed Metal Oxides
Transfer Hydrogenation Reaction
845
Here we report catalytic transfer hydrogenation of nitro compounds
(Sch. 1) (Table 1) and carbonyl functions (Sch. 2) in the liquid phase with
propan-2-ol as hydrogen donor.
Since ZrO2–NiO gave maximum conversion to aniline this catalyst
was chosen to study the reduction of other substrates (Table 2).
It is worth noting here that the reduction was not possible either in
the absence of catalyst or promotor. Also equimolar quantities of either
KOH or NaOH gave comparable yields. An increase in the promotor
Scheme 1.
Table 1. Liquid phase catalytic transfer hydrogenation of
nitrobenzene to aniline with propan-2-ol.
% Yield
Number
Catalyst (promotor KOH/NaOH)
Aniline
1
2
3
4
5
6
Catalyst without promotor
Promotor without catalyst
ZrO2
0.0
0.0
15.0
100.0
94.8
93.5
ZrO2–NiO
ZrO2–CoO
ZrO2–Fe2O3
Reaction condition: Nitrobenzene (20 mmol), KOH/NaOH pellets
(20 mmol), catalyst 2.5% w/w in propan-2-ol (20 mL) refluxed for 3–5 h.
Scheme 2.

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846
Sonavane and Jayaram
Table 2. Transfer hydrogenation of nitroarenes and carbonyl compounds with
propan-2-ol on ZrO2–NiO.
No.
Substrate
Nitrobenzene
Product
% Yield
1
2
Aniline
4-Chloroaniline
3-Nitroaniline
100.0
96.5
75.1
80.9
81.0
00.0
00.0
00.0
85.0
75.0
97.0
99.2
95.1
93.0
4-Chloronitrobenzene
3-Dinitrobenzene
2,4-Dinitrochlorobenzene
2-Nitrotoluene
3
4
4-Chloro-3-nitroaniline
2-Toludine
4-Toludiene
5
6
4-Nitrotoluene
7
4-Nitrobenzoic acid
4-Nitrophenol
4-Nitroanisole
4-Aminobenzoic acid
4-Aminophenol
4-Anisidine
8
9
10
11
12
13
14
3-Nitroaniline
Benzaldehyde
1,3-Diaminobenzene
Benzylalcohol
Acetophenone
Cyclohexanone
Benzophenone
1-Phenethyl alcohol
Cyclohexanol
Benzhydrol
Reaction conditions: Substrate (20 mmol), KOH/NaOH pellets (20 mmol),
catalyst 2.5% w/w in propan-2-ol (20 mL), refluxed for 3–5 h (83ꢀC).
Table 3. Effect of promotor concentration on the product
selectivity and nitrobenzene conversion.
% Yield
Amountof promotor
(mmol)
Catalyst
Aniline
ZrO2–NiO
28.0
25.0
20.0
15.0
10.0
100.0
100.0
100.0
94.8
69.0
Reaction condition: Nitrobenzene (20 mmol), catalyst, 2.5%
w/w in propan-2-ol (20 mL) refluxed for 3–5 h.
concentration increases the product selectivity/activity. The effect of
promotor concentration on the reaction is shown in Table 3.
The activity of the catalyst was maintained for at least 6 cycles
without any regeneration treatment after which there was a gradual
decrease. In a typical experiment the % yield to aniline decreased from
99% to 83% after six cycles and then to 54% after 8 cycles. Also the

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Nitro Compound Reduction with Mixed Metal Oxides
847
selectivity was 100%. There was no other side reaction as checked by
material balance.
RESULTS AND DISCUSSION
It is possible that propan-2-ol gets adsorbed on basic site of the
catalyst and the substrates on an adjacent acidic site [Schs. 3 and 4].[8–11]
These basic sites could be active Mo sites (M ¼ Ni, Fe, Co) promoted by
KOH/NaOH. During adsorption of propan-2-ol the hydrogen from –OH
gets adsorbed as proton and hydrogen of C–H migrates via hydride
transfer to the substrate. Hence rate of reaction can show dependence
on the strength of adsorption of both propan-2-ol and substrate.
It has been observed in the present case that the presence of electron
releasing groups reduces the reduction of –NO2. If adsorbtion of the
substrate is rate determining, presence of electron-releasing group at
para positions should enhance the reduction. This is not found to be
the case. However, an electron releasing substituent at para position
will hinder the hydride transfer from the adsorbed propan-2-ol to the
Scheme 3.
Scheme 4.

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848
Sonavane and Jayaram
adsorbed species of nitro compound. Hence it is possible that the rate of
reduction is more decided by the subsequent hydride transfer rather than
the initial adsorbtion of the substrates. However more systems of nitro
and carbonyl compounds have to be studied in detail to arrive at the
complete mechanism of the reduction process.
Preparation of Catalysts
Appropriate amounts of respective soluble metals salts were
dissolved in minimum amountof deionized waetr. To htis, aqueous
ammonia solution was added under vigorous stirring until pH 10.0 was
achieved. Then the co-precipitated hydroxides were washed repeatedly
to get neutral filtrate free of the anions of precursor materials. The
precipitate was then dried in an air oven for 24 h at 383K, ground
below 100 mesh. The hydroxide was then calcined in a muffle furnace
at773K for 8 h.
General Procedure for Liquid Phase Reactions
The liquid phase reaction was carried out in a 100 cm3 two necked
round bottom flask equipped with a reflux condenser and a thermometer.
The reaction mixture was stirred and heated to the desired temperature
with a magnetic stirrer-heater and a Teflon coated magnetic bob.
The products were analyzed by gas chromatographic method.
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849
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Received in the UK January 2, 2002

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