Hydrogenation on granular palladium-containing catalysts: II. Hydrogenation of nitroheterocyclic compounds

Article abstract of DOI:10.1023/A:1015586205191

Nitroheterocyclic compounds were reduced in a classical reactor with an agitator equipped with a cell for fixed bed of catalyst. As catalysts were applied granular palladium catalysts (0.5% of Pd on γ-Al₂O ₃ and 2% of Pd on granulated carbon). Anilines and 3-amino-2(1H)-pyridones were obtained in high yield at reduction of the appropriate nitro compounds, and the activity of the catalyst samples only slightly decreased. Yet aminopyrazoles and aminoimidazoles obtained by hydrogenation on palladium were very sensitive to the presence of air even as hydrochlorides. In the course of hydrogenation of nitropyrazoles and nitroimidazoles the activity of the catalyst markedly decreased.

Full text of DOI:10.1023/A:1015586205191

Russian Journal of Organic Chemistry, Vol. 38, No. 2, 2002, pp. 269 271. Translated from Zhurnal Organicheskoi Khimii, Vol. 38, No. 2, 2002,
pp. 290 293.
Original Russian Text Copyright
2002 Kislyi, Tolkacheva, Semenov.
Hydrogenation on Granular Palladium-containing Catalysts:
II.* Hydrogenation of Nitroheterocyclic Compounds
V. P. Kislyi, L. N. Tolkacheva, and V. V. Semenov
Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 119992 Russia
Received February 23, 2001
Abstract Nitroheterocyclic compounds were reduced in a classical reactor with an agitator equipped with a
cell for fixed bed of catalyst. As catalysts were applied granular palladium catalysts (0.5% of Pd on -Al2O3
and 2% of Pd on granulated carbon). Anilines and 3-amino-2(1H)-pyridones were obtained in high yield at
reduction of the appropriate nitro compounds, and the activity of the catalyst samples only slightly
decreased. Yet aminopyrazoles and aminoimidazoles obtained by hydrogenation on palladium were very
sensitive to the presence of air even as hydrochlorides. In the course of hydrogenation of nitropyrazoles and
nitroimidazoles the activity of the catalyst markedly decreased.
We have formerly described [1] a construction of
reactor providing a possibility to use in a classical
reactor with agitator granular palladium-containing
catalysts (GPC), e.g. commercial ShPAK-0.5 (0.5%
of Pd on -Al2O3), for hydrogenation of alkynes into
alkenes. Although hydrogenation of nitro group is
comprehensively described in the literature [2, 3], the
interest is conserved to performing this process under
milder conditions (at room temperature, with no
strong acids or alkali). Therefore we undertook
investigation of GPC application to hydrogenation of
nitro compounds from aromatic and heterocyclic
series.
ly twice, but further dilution did not accelerate the
process.
The repeated use of the catalyst (lifetime) is of
great interest. We found that decrease in the catalyst
activity significantly depended on the procedure of
nitrobenzene charging. When after hydrogenation run
the reactor was opened in air, we observed a con-
siderably reduced catalyst activity (procedure A). If
the fresh portion of nitrobenzene was charged
immediately after the hydrogenation product dis-
charge (procedure B) the catalyst activity was only
slightly reduced (Table 1).
The chemical yield changed insignificantly and in
both procedures approached 97 95% (according to
GLC of the reaction mixture) and after distillation it
was 91 89%.
We found that at hydrogenation of nitrobenzenes
Ia, b in the reactor of the previously described con-
struction [1] (with a fixed bed of GPC and a turbo-
type agitator) the rate of hydrogen consumption was
1.5 3 times higher than in a classical rotating auto-
clave. This difference in rates is apparently due to the
considerably more efficient stirring.
Table 1. Duration of several successive hydrogenation
runs on a single portion of catalysta
Time, h
The rate of hydrogen consumption depends also
on the presence of a solvent. For instance, on diluting
the trifluoromethoxynitrobenzene (Ia) with methanol
(1: 1) resulting in decreased viscosity of the reaction
medium the hydrogenation rate increased approximate-
Run no.
A
B
1
2
3
4
5
4
4
5
5
5
6
10
12
23
35
a
I, II, R = CF3O (a), CF2ClO (b).
Into the reactor was charged 50 of ShPAK-0.5 and in each
run 160 g of compound Ia, 200 ml of methanol. The hydro-
genation was performed at 44 46 C, 40 42 at.
*
For communication I see [1].
1070-4280/01/3802-269$27.00 2002 MAIK Nauka/Interperiodica

270
KISLYI et al.
Table 2. Yields, melting points, and elemental analyses of compounds IIa, b, IVa c, VIa, b, VII, IX
Found, %
Calculated, %
Compd. Yield,
mp, oC
bp (p, mm Hg)
Formula
no.
%
C
H
N
C
H
N
IIa
IIb
89
91
82
90
75
55
37
41
63
65 69 (7)a
93 95(7)
125 128 (BuOAc)
208 209 (DMF)
145 146 (benzene hexane, 1: 1) 57.2
111 113 (benzene)
145 147 (benzene)
232 233 (Ac2O)
47.3
43.0
54.1
60.3
3.2
3.6
5.7
7.7
6.3
4.7
4.8
4.6
6.1
7.6
7.1
C7H6F3NO
C7H6ClF2NO 43.41 3.10 7.24
C5H6N2O
C7H10N2O
C10H14N2O3
C5H7N3O2
C10H10N4O
C8H9N3O4
C8H11N3O2
47.46 3.39 7.91
IVa
IVb
IVc
VIa
VIb
VII
IX
25.2
21.1
13.7
29.1
27.0
19.7
23.4
54.54 5.45 25.45
60.87 7.25 20.29
57.14 6.67 13.33
42.55 4.96 29.79
59.41 4.95 27.72
45.49 4.26 19.91
53.04 6.08 23.20
42.8
59.7
45.2
53.3
247 249 (MeOH)
a
73 75 C (10 mm Hg) [4].
the hydrogenation products of 4-nitropyrazole-3-carb-
oxylic acid (Vc) and 4(5)-nitro-2-methylimidazole
(VIII) we failed to obtain of sufficient purity even
when the substances were separated as hydrochlorides
Similarly a hydrogenation was carried out with
several 2-hydroxy-3-nitropyridines IIIa c. The
pattern of the process was like that of nitrobenzenes
Ia, b hydrogenation: the hydrogenated products were
fairly stable and were obtained in a high yield (75
90%) on evaporating methanol.
1
(the peaks in the H NMR spectra were strongly
broadened due to the presence of a paramagnetic
compound, presumably, of palladium complexes). At
the same time the hydrogenation of pyrazole Vb with
aluminum amalgam in methanol afforded product VIb
that was considerably more stable than the same
compound prepared by hydrogenation on a palladium
catalyst (the product did not turn dark on storage for
2 months).
I, II, R,R = H (a), Me, H (b), Me, CH2COOMe (c).
The hydrogenation of compounds Vc, VIII in acetic
acid in the presence of acetic anhydride afforded the
corresponding acetylated compounds VII, IX that
turned out to be quite stable.
In going to hydrogenation of nitropyrazoles Va c
and nitroimidazole (VIII) the products obtained were
considerably less stable than amines IIa, b, IVa c.
Although 4-aminopyrazoles with electron-withdraw-
ing substituents VIa, b were isolated in a pure state,
The structure of compounds synthesized was con-
firmed by 1H NMR and mass spectra and by
elemental analyses (Tables 2, 3).
It is commonly assumed that palladium on carbon
support shows the maximal activity. Therefore we
tested a new granular catalyst, 2% Pd on granulated
carbon. This catalyst unexpectedly did nit notably
accelerate the hydrogenation: at the same weight of
Pd per 1 gram of the compound to be hydrogenated
the hydrogenation rate increased only 1.05 1.2 times
V, VI, R = OMe (a), NHPh (b), COOH (c).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 2 2002

HYDROGENATION ON GRANULAR PALLADIUM-CONTAINING CATALYSTS: II.
271
1
Table 3. H NMR and mass spectra of compounds IIa, b,
in DMSO-d6. Mass spectra were measured on
Finnigan Mat instrument (electron impact, 70 eV).
Nitrobenzenes Ia, b were obtained by procedure [5].
The catalyst ShPAK-0.5 was prepared as in [1].
IVa c, VIa, b, VII, IX
Compd.
no.
, ppm (DMSO-d6)a
m/z
(Irel, %)
Hydrogenation of nitro compounds on
ShPAK-0.5 catalyst. General procedure for com-
pounds Ia, b, IIIa c, Va, b. Nitro compounds (0.25
0.9 mol) were dissolved in 200 300 ml of methanol
(compound IIIb was dissolved in DMF), and the
solution was charged into the reactor with 50 ml of
the catalyst. The hydrogenation was performed at
30 40 C and 20 40 at till the hydrogen consumption
stopped (4 8 h). Then the solution was discharged,
the solvent was evaporated, and the residue was dis-
tilled (with compounds IIa, b) or recrystallized. The
yields, melting points and solvents for recrystalliza-
tion are listed in Table 2.
IIa
IIb
5.0 br.s (2H, NH2)
6.6 d (2H, Ar)
6. 9d (2H, Ar)
3.7 br.s (2H, NH2)
6.65 d (2H, Ar)
7.0 d (2H, Ar)
193 (63)
107 (100)
92 (69)
85 (53)
80 (52)
110 (100)
82 (28)
81 (22)
55 (43)
54 (45)
138 (100)
109 (23)
95 (43)
IVa
IVb
IVc
4.95 br.s (2H, NH2)
6.0 t (1H, CH5)
6.4 d (1H, CH4)
6.6 d (1H, CH6)
11.2 br.s (1H, NH)
1.93 s (3H, CH3)
2.04 s (3H, CH3)
4.4 br.s (2H, NH2)
5.7 s (1H, CH5)
11.26 br.s (1H, NH)
2.00 s (3H, CH3)
2.18 s (3H, CH3)
3.7 s (3H, OCH3)
4.4 br.s (2H, NH2)
4.75 s (2H, CH2CO)
5.85 s (1H, CH5
Hydrogenation of nitro compounds Vc, VIII in
the presence of acetic anhydride. General procedure.
In a mixture of 300 ml of Ac2O and 150 ml of AcOH
was dissolved 0.05 mol of nitro compound, and the
solution was charged into the reactor with 50 ml of
ShPAK-0.5 catalyst. The hydrogenation was carried
out at 25 28 C, 10 at for 10 12 h. Then the solution
was discharged, evaporated to the volume of 30 ml,
and cooled. The separated precipitate was filtered off
and recrystallized. The yields, melting points and
solvents for recrystallization are listed in Table 2.
210 (100)
187 (45)
179 (18)
150 (47)
121 (22)
Procedure for preparation of catalyst with com-
position 2% Pd on granulated carbon. In 200 ml of
distilled water at heating to 70 C was dissolved
1.79 g of PdCl2, the solution was acidified with
hydrochloric acid to pH 2. To 50 g (56 ml) of
granulated carbon in a wide beaker was added the
above solution of palladium chloride, and the beaker
was maintained at 70 C till water totally evaporated.
Then the catalyst was placed into a muffle and heated
VIa
VIb
VII
IX
3.8 s (3I, OCH3)
4.8 br.s (2H, NH2)
7.1 s (1H, CH)
141 (100)
114 (14)
110 (19)
109 (32)
202 (80)
110 (95)
93 (100)
40 (43)
12.8 br.s (1H, NH)
4.7 br.s (2H, NH2)
7.0 7.8 m (6H, Ph+CH)
9.5 br.s (1H, NHCO)
12.65 br.s (1H, NH)
2.17 s (3H, CH3CO)
2.7 s (3H, CH3CO)
8.7 s (1H, CH)
211 (9)
1
at a rate 100 deg h till 400 C and kept at this
169 (29)
127 (62)
109 (32)
181 (8)
temperature for 2 h. The calcined catalyst was placed
into a quartz reactor with electric heating, and hydro-
gen was passed through for 1 h at 180 200 C.
9.2 br.s (1H, NHCO)
2.2 s (3H, CH3)
2.55 s (3H, CH3CO)
2.65 s (3H, CH3CO)
7.6 s (1H, CH)
139 (13)
129 (58)
97 (27)
REFERENCES
1. Tolkacheva, L.N., Kislyi, V.P. , Taits, S.Z., and Se-
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pp. 150 152.
8.4 br.s (1H, NHCO)
87 (67)
1H NMR spectrum of compound IIb was recorded in DCl3.
2. Seebach, D., Calvin, E.W., Lear, F., and Weller, T.,
a
Chimia, 1979, vol. 33,
no.
1,
p.
1.
as compared with that on catalyst of composition
0.5% of Pd on -Al2O3.
3. Ioffe, S.L., Tartakovskii, V.A., and Novikov, S.S.,
Usp. Khim., 1966, vol. 35, no. 1, p. 43.
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p. 2907.
EXPERIMENTAL
1H NMR spectra were registered on spectrometer
Bruker WM-250 at operating frequency 250.13 MHz
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 2 2002