Catalytic synthesis of indole from tetrahydroindole on Pd-and Cr-containing catalysts

Article abstract of DOI:10.1007/s10593-006-0197-9

In the presence of Pd-and Cr-containing catalysts applied to γ-Al₂O₃ or sibunite 4,5,6,7-tetrahydroindole is converted into indole. Indole was obtained in quantitative yield on sulfided 0.15-0.5% Pd/γ-Al₂O₃ catalyst at 360°C and on catalysts containing 5% Cr₂O₃, 5% La₂O ₃ (or 5% polirit), 1% K₂O/89% γ-Al₂O ₃ at 475-480°C.

Full text of DOI:10.1007/s10593-006-0197-9

Chemistry of Heterocyclic Compounds, Vol. 42, No. 8, 2006
CATALYTIC SYNTHESIS OF INDOLE
FROM TETRAHYDROINDOLE ON Pd-
AND Cr-CONTAINING CATALYSTS
M. A. Ryashentseva
In the presence of Pd- and Cr-containing catalysts applied to γ-Al O or sibunite 4,5,6,7-tetra-
2
3
hydroindole is converted into indole. Indole was obtained in quantitative yield on sulfided 0.15-0.5%
Pd/γ-Al O catalyst at 360°C and on catalysts containing 5% Cr O , 5% La O (or 5% polirit), 1%
2
3
2
3
2
3
K O/89% γ-Al O at 475-480°C.
2
2
3
Keywords: indole, applied palladium-containing and chromium and lanthanum oxide-, polyrit-, and
potassium-containing catalysts, 4,5,6,7-tetrahydroindole, toluene, dehydrogenation, carriers: γ-Al O ,
2
3
sibunite.
The conversion was studied previously of 1-vinyl-4,5,6,7-tetrahydroindole and mixtures of it with
4
,5,6,7-tetrahydroindole (1) in benzene or toluene on applied Pd- and Cr-containing catalysts. On 1 and 1.5%
Pd/γ-Al O catalysts treated with hydrogen sulfide 1-ethyltetrahydroindole, 2-ethylindole, and indole 2 were
2
3
-
1
formed, the yield of indole being 7% (300°C, volume rate of supply V = 0.9 h , duration of experiment
wt
-
1
τ = 20 min). On Cr oxide catalyst (500-525°C, V = 0.3-1.5 h , τ = 30 min) mainly indole 2 is formed in 80%
yield. With the aim of developing a method for obtaining pure indole we studied the dehydrogenation of
tetrahydroindole 1. Compound 1 is available and is obtained by the Trofimov reaction [2, 3] from cyclohexanone
oxime and acetylene.
In the present work the conversion of tetrahydroindole 1 on Pd- and Cr-containing catalysts applied to a
carrier has been studied and optimal conditions were found for the catalytic synthesis of indole 2 by the
dehydrogenation of compound 1 in toluene on processed sulfided catalysts containing 0.15, 0.25, and 0.5% Pd
on γ-Al O , and an industrial sample of 0.15% Pd on sibunite (carbon carrier). The catalyst consisted of 0.15%
2
3
Pd, 99.85% γ-Al O treated with H S, processed for 8 h periodically (experiment, heating in a stream of
2
3
2
hydrogen on various days), while not reducing its high activity. The analogous catalyst on sibunite possesses the
same activity, but is not as stable.
cat.
toluene
N
H
N
H
1
2
_
_________________________________________________________________________________________
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 119991; e-mail:
secretary@ioc.ac.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1176-1178, August,
2
006. Original article submitted September 23, 2005.
1
018 0009-3122/06/4208-1018©2006 Springer Science+Business Media, Inc.

TABLE 1. Conversion in Toluene of Tetrahydroindole on Pd- and
Cr-Containing Catalysts
Yield
Experimental conditions* of liquid
catalyzate,
Composition
of catalyzate,
wt.%
Toluene
content,
wt.%
Catalyst composition,
wt.%
-
1
Т, °С
V
wt, h τ, min
wt.%
1
2
0
.15% Pd/γ-Al
2
O
S
3
,
84.4
84.4
300
355
360
360
360
360
0.5
0.5
0.5
0.47
0.6
0.5
30
20
38
39
30
30
100
100
98
100
97.9
99.1
14.2
1.7
85.8
98.3
100
100
100
100
treated with H
2
8
8
8
8
6.7
6.8
2.8
5.0
0
.25% Pd/γ-Al
2
O
S
3
,
85.5
85.5
350
370
300
0.5
0.5
0.6
0.6
0.7
0.5
30
20
30
25
30
25
97.5
100
100
100
100
100
100
100
100
100
100
100
treated with H
2
8
2.3
3
50
375
00
7
9.2
4
0
.5% Pd/γ-Al
2
O
3
,
79.5
84.4
370
400
1.0
1.4
30
30
97.5
87.2
100
100
treated with H
0
2
S
.15% Pd/sibunite
300
355
360
360
360
360
0.5
0.5
0.5
0.47
0.6
0.5
30
20
38
39
30
30
100
100
98.0
100
97.9
99.1
14.2
85.8
98.3
100
100
100
100
8
8
8
8
8
4.4
6.7
6.8
2.8
5.0
1
.66
5
1
% Cr
% K
2
O
3
, 5% La
2
O
3
,
83.0
83.0
474
473
477
480
480
0.3
0.3
0.3
0.3
0.25
45
35
47
49
37
90.0
89.4
91.7
94.0
91.0
100
100
100
O, 89% γ-Al
2
O
3
trace
trace
2
8
8
8
3.0
3.2
4.0
1.1
98.9
5
5
1
% Cr
% polirit,
% K O, 89% γ-Al
2
O
3
,
79.6
83.5
83.6
475
476
483
0.36
0.3
0.3
26
26
30
95.9
89.7
99.2
100
97.1
97.0
2.9
3.0
2
2
O
3
_
*
______
Hydrogen supply rate 2.6 l/h.
It was shown that the activity of the catalysts was reduced at >380°C, on heating to 600°C the catalyst
activity was reduced by half. At a catalyst composition of 0.25% Pd, 99.75% γ-Al O , H S (350°C,
2
3
2
-
1
V = 0.5-0.6 h ) and Cr-oxide catalyst of composition 5% Cr O , 5% La O (or 5% Polirit: 27% CeO , 1.3%
La O , 0.75% Nd O , 0.25% Pr O ), 1% K O, 89% γ-Al O , obtained as in [6], (475-480°C, V = 0.3-0.4 h )
2
3
2
3
2
-
1
2
3
2
3
2
3
2
2
3
tetrahydroindole 1 (14% solution in toluene) is converted into indole 2 in ~100% yield.
Efficient Pd- and Cr-containing catalysts on carriers and conditions have been found for the synthesis of
indole 2 by the dehydrogenation of tetrahydroindole 1.
EXPERIMENTAL
Tetrahydroindole, given by B. A. Trofimov and his coworkers, synthesized by the method of [4], was
used in the work. The author is most grateful for this. The sample of 0.15% Pd/sibunite catalyst (in the form of
-
3
pellets of diameter 2-3 mm, poured weight 0.6 g·cm , specific surface measured by nitrogen absorption
2
-1
2
-1
6
80 m ·g , and by phenol absorption 230 m ·g ) was obtained from V. A. Semikolenov [5], for which the author
is grateful.
1
019

The conversion of tetrahydroindole 1 in toluene was carried out in a flow-through installation at
-
1
atmospheric pressure, 300-480°C, Vwt = 0.3-1.4 h , and duration 0.5-0.8 h. Palladium on aluminum catalysts
2
-1
containing 0.15, 0.25, and 0.5% Pd on an industrial sample of γ-Al O (specific surface 200-220 m .g , particle
2
3
size 2 × 3 mm) as carrier. Catalysts were prepared by soaking. Reduction was effected with hydrogen at 350°C,
sulfidation with hydrogen sulfide at 120°C. The preparation of Cr oxide catalyst of composition 5% Cr O ,
2
3
5
% La O , (or 5% Polirit: 27% CeO , 1.3% La O , 0.75% Nd O , 0.25% Pr O ), 1% K O, 89% γ-Al O was
2
3
2
2
3
2
3
2
3
2
2
3
described in [6]. The reaction products were analyzed on a LKhM 8MD gas-liquid chromatograph
catharometer, temperature programing in the range 110-250°C, rate 12 deg/min), column 2000 × 3 mm,
% OV 225 on chromaton N-Super (0.125-0.161 mm) and 1500 × 3 mm, 2% OV 225 on chromosorb G
(
3
(
0.147-0.175 mm) at 190°C, carrier gas was helium.
Indole 2 was isolated from the catalyzate by vacuum distillation. Bp 130°C (35 mm Hg) and mp 52.5°C
correspond to the data of [7]. The results obtained are given in Table 1.
A sample of indole 2 was sent for testing in the All-Union Research Institute for Synthetic and Natural
Perfume Substances and obtained a high assessment.
REFERENCES
1
.
M. A. Ryashentseva, Yu. B. Vol'kenshtein, V. M. Polosin, A. I. Mikhaleva, and R. N. Nesterenko, Izv.
Akad. Nauk SSSR, Ser. Khim., 1417 (1991).
2
3
4
.
.
.
B. A. Trofimov and A. I, Mikhaleva, N-Vinylpyrroles [in Russian], Nauka, Novosibirsk (1984), 260 pp.
B. A. Trofimov, Usp. Khim., 58, 1703 (1989).
B. A. Trofimov and A. I. Mikhaleva, Khim. Geterotsikl. Soedin., 1299 (1980). [Chem. Heterocycl.
Comp., 16, 979 (1980)].
5
6
.
.
V. A. Semikolenov, Usp. Khim., 61, 320 (1992).
M. A. Ryashentseva, E. P. Belanova, and Kh. M. Minachev, Izv. Akad. Nauk SSSR, Ser. Khim., 2756
(
1978).
7
.
Beilstein, 20, 304.
1
020