A catalyst for the selective dehydrogenation of 4,5,6,7-tetrahydroindole into indole

Full text of DOI:10.1134/S0012500811040057

ISSN 0012ꢀ5008, Doklady Chemistry, 2011, Vol. 437, Part 2, pp. 95–97. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © B.A. Trofimov, A.I. Mikhaleva, E.Yu. Schmidt, N.I. Protsuk, A.V. Ivanov, O.A. Ryapolov, 2011, published in Doklady Akademii Nauk, 2011, Vol. 437,
No. 4, pp. 504–506.
CHEMISTRY
A Catalyst for the Selective Dehydrogenation
of 4,5,6,7ꢀTetrahydroindole into Indole
Academician B. A. Trofimova, A. I. Mikhalevaa, E. Yu. Schmidta, N. I. Protsuka,
A. V. Ivanova, and O. A. Ryapolovb
Received October 4, 2010
DOI: 10.1134/S0012500811040057
Indole is widely used for preparation of perfume rahydroindole, 1ꢀ and 2ꢀethylindoles, indole, and a
formulations, pharmaceuticals [1, 2], catalysts for oleꢀ number of unidentified compounds in different ratios.
fin polymerization [3], epoxy resins [4], and materials The yield of indole did not exceed 66%.
for optoelectronics [5, 6].
The dehydrogenation of THI with the use of pallaꢀ
Aromatization of 4,5,6,7ꢀtetrahydroindole (THI)
is an expedient method for indole preparation.
diumꢀcontaining catalysts on ꢀAl2O3 and Sibunithave
γ
been briefly mentioned [11]. The yield of indole was
quantitative, but it was determined by GLC, which
provides no possibility to establish the content of highꢀ
boiling admixtures in the major product.
4
5
3
catalysis
6
2
–2H2
The dehydrogenation of THI on catalysts containꢀ
ing sulfidated palladium or a mixture of oxides (Cr2O3,
7
N
H
N1
H
THI
La2O3, K2O) deposited on
γꢀAl2O3 and Sibunit at
Initial THI is obtained by the Trofimov reaction [7]
from commercially available cyclohexanone oxime
(an intermediate of caprolactam synthesis) and acetyꢀ
lene in a yield up to 97% [8].
A catalytic system for dehydrogenation of 1ꢀbenꢀ
zylꢀ3ꢀphenylꢀ4,5,6,7ꢀtetrahydroindole into 1ꢀbenzylꢀ
3ꢀphenylindole comprising 10% of palladium on actiꢀ
vated carbon is known [9]. However, this catalytic sysꢀ
tem provides the dehydrogenation of substituted THI
and therefore could not be directly applied to THI.
360–480 C has been described [12]. Indole was
°
obtained in quantitative yield, although it was the yield
of liquid catalyzate that was given in the experimental
section. However, the stability of THI and indole at
such high temperatures is not typical.
With the aim to develop a technologically feasible
method for indole preparation, we have carried out a
systematic study whose results are briefly expounded
in [13, 14]. The use of nickel sulfide deposited on
γꢀAl2O3 provides the dehydrogenation of THI into
Moreover, the reaction is carried out at 140
C (boiling
°
indole in 96% yield and a selectivity close to 100%.
xylene) for 2 days (indole yield is 76%). The low proꢀ
cess rate and high palladium content in the catalytic
system are unacceptable for technology application.
NiS/Al2O3(N2)
–2H2, 300–370°C
Indole has been obtained by dehydrogenation of a
mixture of 1ꢀvinylꢀ4,5,6,7ꢀtetrahydroindole (VTHI)
and THI on catalytic systems containing palladium or
a mixture of chromium–rare earth oxides at 200–
N
H
N
H
THI
The catalyst was obtained by impregnation of
ꢀAl2O3 with an aqueous solution of a nickel salt (chloꢀ
ride or acetate) followed by treatment with a hydrogen
sulfide excess or an aqueous solution of alkali metal
(or ammonium) sulfide (or hydrosulfide).
525
C [10]. The reaction led to a complex mixture of
°
γ
products containing VTHI, THI, 1ꢀethylꢀ4,5,6,7ꢀtetꢀ
a Favorskii Irkutsk Institute of Chemistry, Siberian Branch,
Russian Academy of Sciences, ul. Favorskogo 1, Irkutsk,
664033 Russia
b UAB Prekybos namai Waldis, D. Vandens 7ꢀ6, Klaipeda
LT91246, Lithuania
In continuation of these studies, we developed an
improved catalyst for the dehydrogenation of THI into
indole. The catalyst was obtained in an aqueous susꢀ
pension containing nickel chloride, sodium sulfide,
95

96
TROFIMOV et al.
granulated aluminum oxide, hydrochloric acid, and a
surfactant at ambient temperature.
EXPERIMENTAL
Catalyst preparation. The catalyst was obtained
using commercial aluminum oxide
cific surface of 200 m2/g and granule size 3
A mixture of 50 g of ꢀAl2O3 and 0.1 g of surfactant
in 100 mL of distilled water was stirred vigorously for
30 min, then 2.47 g (1%) of NiCl2 6H2O was added
and stirred for 30 min. A 2ꢀmL portion of an HCl soluꢀ
tion (36%) was added and stirred for another 30 min.
With continuous stirring, a solution of 2.5 g of
γ
ꢀAl2O3 with a speꢀ
A substantial difference of the new catalyst from
those described in [13, 14] consists in the use of a surꢀ
factant for its preparation. This provides the purificaꢀ
tion and efficient wetting of the aluminum oxide surꢀ
face, which facilitates the penetration of active comꢀ
ponents of the catalytic system into granules of the
catalyst and their uniform distribution over the supꢀ
port surface. Commercial longꢀchain sulfonates, for
example, sodium dodecylsulfonate, can be used as
surfactants.
×
5 mm.
γ
⋅
Na2S ⋅ 9H2O in 50 mL of distilled water was added
over 30 min. After stirring for 5 h, the resultant suspenꢀ
sion was allowed to stand overnight, filtered, and
In the course of preparation, the catalyst is doped
with Na+ and Cl– ions; the resulting suspension is filꢀ
dried (100 C, 20 h) to give 52.1 g of the catalyst conꢀ
°
taining 97.98% Al2O3, 0.99% Ni, 0.65% S, 0.10% Na,
tered without washing and then heated in air at 100 C
°
0.28% Cl.
for 20 h. The optimal content of Na+ and Cl– ions is
within 0.1–0.2 and 0.2–1.0%, respectively. The dopꢀ
ing extent can be varied by varying the strength of
pressing of catalytic mixture in the course of filtration.
Dehydrogenation of THI into indole on the freshly
prepared catalyst. A reactor as a vertical quartz tube
10 mm in diameter and 38 cm long with external tunꢀ
able heating was charged with 4.6 g (9 cm3) of the catꢀ
alyst and heated at 370 C in a nitrogen flow (8.0 L/h)
°
It is reasonable to consider that NaCl and NaOCl2
microcrystals increase the polarization of amphoteric
aluminum oxide molecules, thus enhancing the affinꢀ
ity of nickel sulfide microcrystals toward support
mesopores. As a result, the mechanical strength and
activity of catalyst increase.
for 5 h. At the same temperature, 0.5 g of THI disꢀ
solved in 10 mL of toluene was passed through the
reactor during 4 h. Toluene was distilled off from the
condensate to give 0.46 g of indole containing 2% of
THI (according to GLC data). No other admixtures
were found. The yield of indole was 94%, selectivity
was 100%. Indole, mp 53.0
52.5 C [15].
°
C (from hot water); lit. mp
The catalyst contains 0.30–2.00% Ni, 0.20–1.50%
S, 0.1–0.20% Na, and 0.20–1.00% Cl.
°
Dehydrogenation of THI into indole on regenerated
catalyst. A solution of 0.25 g of THI in 10 mL of toluꢀ
ene was passed for 5.5 h through the same portion of
the catalyst, 4.6 g (9 cm3), worked during 89 h under
the same conditions. Toluene was distilled off from the
condensate to give 0.23 g of indole. No THI and other
admixtures were detected (according to GLC). The
yield of indole was 96%, and the selectivity was 100%.
The catalyst is obtained as follows. First, an aqueꢀ
ous suspension containing 10–50% Al2O3, 0.3–5%
NiCl2, and 0.1% surfactant is obtained under vigorous
stirring for 15–60 min. A 36% aqueous HCl solution is
added to the stirred suspension to pH 1–3, and then
an equimolar amount (with respect to NiCl2) of
Na2S
of 1
pension is stirred for another 30 min, allowed to stand
overnight, then filtered, and heated for 20 h at 100 C.
⋅
9H2O in an aqueous solution (concentration
⎯
15%) is added over a period of 30 min. The susꢀ
ACKNOWLEDGMENTS
°
This work was supported by the Council for Grants
of the President of the Russian Federation for Support
of Leading Scientific Schools (grant no. NShꢀ
3230.2010.3).
The catalyst can be readily regenerated by heating
at 370 C for 10 h in air.
°
It is substantial that the new catalyst provides a posꢀ
sibility to carry out THI dehydrogenation to give
indole without the use of hydrogen or an inert gas carꢀ
rier but only in a solvent vapor flow (toluene, petroꢀ
leum ether, gasoline).
REFERENCES
1. Comprehensive Organic Chemistry, Barton, D.H., Ed.,
Amsterdam: Elsevier, 1982. Translated under the title
Obshchaya organicheskaya
khimiya
,
Moscow:
Khimiya, 1985.
2. Sundberg, R.J., The Chemistry of Indoles, San Diego:
Academic, 1997.
3. Ezerton, B.P. and Nad’, Sh., RF Patent No. 2 164 228,
Thus, we have developed the new catalyst of THI
dehydrogenation into indole that allows the preparaꢀ
tion of the latter in a yield up to 96% and selectivity of
100%.
Byul. Izobret., 2001, no. 6.
DOKLADY CHEMISTRY Vol. 437
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2011

A CATALYST FOR THE SELECTIVE DEHYDROGENATION
97
4. Masashi, K. and Hisashi, Y., US Patent Appl.
,
10. Ryashentseva, M.A., Vol’kenshtein, Yu.B., Poloꢀ
sin, B.M., et al., Izv. Akad. Nauk SSSR, Ser. Khim.
,
no. 2005/0131167 A1.
1991, no. 6, pp. 1417–1422.
5. Saxena, V., Shirodkar, V., and Prakash, R., J. Solid
State Electrochem., 2000, no. 4, pp. 231–233.
11. Ryashentseva, M.A., Izv. Akad. Nauk SSSR, Ser.
Khim., 1993, pp. 1832–1833.
12. Ryashentseva, M.A., Khim. Geterotsikl. Soed., 2006,
6. Trung, V.Q. and Huyen, D.N., J. Phys: Conf. Ser., 2009,
no. 8, pp. 1176–1178.
vol. 187, no. 012058, pp. 1–6.
13. Trofimov, B.A., Mikhaleva, A.I., Schmidt, E.Yu., et al.,
7. Wang, Z., Comprehensive Organic Name Reactions and
Reagents, London: Wiley, 2009.
RF Patent No. 2 345 066, Byull. Izobret., 2009, no. 3.
14. Trofimov, B.A., Mikhaleva, A.I., Vasil’tsov, A.M., et al.,
Dokl. Chem., 2010, vol. 434, part 2, pp. 257–259 [Dokl.
Akad. Nauk, 2010, vol. 434, no. 5, pp. 636–638].
15. Khimicheskaya entsiklopediya (Chemical Encyclopeꢀ
dia), Moscow: Sovetskaya entsiklopediya, 1990, vo. 2,
pp. 456–457.
8. Trofimov, B.A., Mikhaleva, A.I., Schmidt, E.Yu., et al.,
RF Patent No. 2 297 410, Byull. Izobret., 2007, no. 11.
9. Lim, S., Jabin, I., and Revial, G., Tetrahedron Lett.
,
1999, vol. 40, pp. 4177–4180.
DOKLADY CHEMISTRY Vol. 437
Part 2
2011