Catalytic transfer hydrogenation of nitro and carbonyl compounds over novel Fe(III) substituted hexagonal mesoporous aluminophosphates

Article abstract of DOI:10.1246/cl.2003.142

Catalytic transfer hydrogenation (CTH) of aromatic nitro and carbonyl compounds over novel Fe(III) substituted hexagonal mesoporous aluminophosphate (FeHMA) molecular sieve catalyst showed excellent regioselectivity/chemoselectivity as well as superior recycling capability. Furthermore, the reduction occurs without affecting other functional groups such as -CN, -CHO, -Cl,-CH₃,-OCH₃ and -NH₂.

Full text of DOI:10.1246/cl.2003.142

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Chemistry Letters Vol.32, No.2 (2003)
Catalytic Transfer Hydrogenation of Nitro and Carbonyl Compounds over Novel Fe(III)
Substituted Hexagonal Mesoporous Aluminophosphates
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Sachin U. Sonavane, Susanta K. Mohapatra, Radha V. Jayaram, and Parasuraman Selvam
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Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai 400 076, India
Applied Chemistry Division, University of Mumbai Institute of Chemical Technology, Matunga, Mumbai 400 019, India
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New Industry Creation Hatchery Center, Tohoku University, Aoba-yama 04, Sendai 980-8579
(Received October 18, 2002; CL-020888)
Catalytic transfer hydrogenation (CTH) of aromatic nitro and
column. For recycling purpose, the catalyst was recovered by
simple filtration, after the first reaction, and washed several times
carbonyl compounds over novel Fe(III) substituted hexagonal
mesoporous aluminophosphate (FeHMA) molecular sieve cata-
lyst showed excellent regioselectivity/chemoselectivity as well as
superior recycling capability. Furthermore, the reduction occurs
without affecting other functional groups such as –CN, –CHO,
Table 1. CTH of nitro and carbonyl compounds over FeHMAa
–Cl, –CH3, –OCH3 and –NH2.
Reduction of nitro and carbonyl compounds is an important
step in the synthesis of dyes, biologically active compounds,
pharmaceuticals, rubber chemicals, photographic and agricultur-
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al chemicals. Although a wide variety of homogeneous catalysts
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has been reported for such reductions, the control of the reaction
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rates is highly difficult. On the other hand, catalytic transfer
hydrogenation (CTH)4 employing hydrogen donors and hetero-
;5
geneous catalysts is easy, safer, highly selective, and eco-friendly
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compared to commonly practiced reduction processes. In
general, CTH of organic compounds is centered on the expensive
Pd/C, Pt/C, Ru/C, Raney-Ni catalysts as well as systems like
Raney-Ni/hydrazine, Pd-C/triethyl ammonium formate or formic
4;5;7;8
acid.
However, these systems require much longer reactions
times. Moreover, nucleophilic attack (hydrazine) and low yields
associated with the formation of by-products make these
processes unattractive. Hence, attempts have been made to
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develop suitable heterogeneous catalysts for CTH reactions.
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In the case of iron oxide hydroxide/hydrazine hydrate system,
hydroxylamine is also formed with selectivity of the product
reaching 40% when electron-attractive substituent is present on
the aromatic ring. In addition, a significant decrease in activity
was noticed as a consequence of the formation of a-Fe2O3 as well
as the increase of particles size of the active catalysts. On the other
hand, the heterogeneous nature of the catalysts has not been
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demonstrated for the nickel based oxides. Furthermore, our own
studies on the metal oxide supported systems showed a
continuous decrease in activity upon recycling.11
In this letter, we present a very efficient and highly selective
heterogeneous catalyst, viz., trivalent iron substituted hexagonal
mesoporous aluminophosphate (FeHMA), for CTH of nitro and
carbonyl compounds using propan-2-ol as hydrogen donor. The
synthesis and characterization of FeHMA ([Al+P]/Fe = 50) was
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carried out as per the methods described elsewhere. The CTH
reactions were performed as per the following standard proce-
dure. In a typical reaction, KOH pellets (20 mmol) were dissolved
in propan-2-ol (20 ml) to which substrate (20 mmol) was added
along with the catalyst (100 mg), and refluxed at 356 K for few
hours depending upon nature of the substrate. The products were
analyzed using a gas chromatograph (Eshika) fitted with OV-101
Copyright ꢀ 2003 The Chemical Society of Japan

Chemistry Letters Vol.32, No.2 (2003)
143
with acetone followed by a thorough washing with water to
remove any alkali, if any present, and dried at 373 K. This catalyst
was reused for the subsequent runs.
practically unaffected for up to six cycles (Table 1).
In conclusion, the present study clearly demonstrates that the
mesoporous-based FeHMA is an efficient, ecofriendly hetero-
geneous catalyst for the chemoselective/regioselective hydrogen
transfer reduction of nitroarenes and carbonyl compounds
including bulkier molecules.
Table 1 summarizes the results of regioselective (entries 1–
) and chemoselective (entries 4–7) reduction of several aromatic
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nitro and carbonyl compounds over FeHMA. The reduction of
nitro and carbonyl groups produces the corresponding amines and
alcohols, respectively as the only products. Since the nitro group
attached to ring can pull electrons more strongly from the benzene
ring compared to the carbonyl or nitrile group, the former can
easily be adsorbed on the catalyst surface leading to chemose-
lective products. In this context, it is also interesting to note that
the reduction of substituted dinitrobenzenes, a is a time dependent
process (entries 1–3). That is, up to a maximum reaction time of
References and Notes
1
G. W. Kabalka and R. S. Verma, in ‘‘Comprehensive Organic
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S. Iyer and J. P. Varghese, J. Chem. Soc., Chem. Commun.,
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D. J. Pasto, J. Am. Chem. Soc., 101, 6852 (1979).
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2.5–5.0 h, only substituted nitro anilines, b were formed with high
yields along with negligible amounts (<2%) of substituted
diaminobenzenes, c. However, with a further increase of the
reaction time, the yields of substituted c increases at the expense
of b. It is possible that the successive reduction of the nitro groups
occurs in consecutive reaction steps as given in Scheme 1, where
k1 ꢁ k2. Accordingly, the reaction has a long induction period for
the accumulation of b, as it is also known that the time required to
reach at maximum concentration is higher since k1 is much larger.
If the reaction is stopped well within this period then we obtain b
as the major product.
5
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7
A. Furst, R. E. Berlo, and S. Hooton, Chem. Rev., 65, 51
(1965).
For a monograph, see: M. Hudlicky, ‘‘Reductionin Organic
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T. L. Gilchrist, in ‘‘Comprehensive Organic Synthesis,’’ ed.
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8T. L. Ho and G. A. Olah, Synthesis, 1977, 169; N. A. Cortese
and R. F. Heck, J. Org. Chem., 42, 3491 (1977); M. J.
Andrews and C. N. Pillai, Indian J. Chem., Sect. B, 16, 465
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1978); N. R. Ayyanger, A. G. Lugade, P. V. Nikrad, and V. K.
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Foubister, Synthesis, 1982, 1036.
9
T. Hirashima and O. Manabe, Chem. Lett., 1975, 259; T.
Miyata, Y. Ishino, and T. Hirashima, Synthesis, 1987, 834; M.
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(2000).
Scheme 1. CTH of substituted dinitrobenzenes (x = Cl, CH3 or
NH2).
It can also be seen from Table 1 that the reduction process is
also successful for bulkier molecules (entries 8–10). It is,
however, worth mentioning here that the microporous iron
substituted aluminophosphate (FeAPO-5) catalyst showed much
lower yields than FeHMA. The lower activity of the former may
ꢀ
be attributed to the small pore opening of the former (7.3 A) than
10 T. T. Upadhya, V. Ramaswamy, D. P. Sabade, D. P. Katdure,
and A. Sudalai, J. Chem. Soc., Chem. Commun., 1997, 1119;
T. M. Jyothi, T. Raja, M. B. Talwar, K. Sreekumar, R.
Rajagopal, and B. S. Rao, Bull. Chem. Soc. Jpn., 73, 1425
(2000).
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the latter (26 A), which in principle restricts the diffusion of the
larger substrates. Furthermore, it is also important to note that the
activity is significantly influenced by the nature/position of the
substituents on the aromatic ring. On the other hand, electron
withdrawing/donating groups such as –CN, –CHO, –Cl, –CH3,
11 The reduction of nitrobenzene was carried out over NiO/ZrO2
(7.85% Ni) under identical reaction condition, which gives
>95% yield in the 1st run, and 83% yield for 6th run.
Likewise, Fe2O3/ZrO2 and CoO/ZrO2 systems also show a
continuous decrease in activity upon cycling.
–OCH3, and –NH2 do not have a significant influence on the
reaction. The catalyst was also used for the reduction of
heterocyclic compounds with high yields (entries 11 and 12).
Finally, the catalyst was tested for its reusability. Interestingly,
12 S. K. Mohapatra, B. Sahoo, W. Keune, and P. Selvam, Chem.
Commun., 2002, 1466.
13 The observed yields were 13, 25 and 21% respectively for
entries 8–10.
11
unlike the supported systems, the performance of FeHMA was