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Russian Chemical Bulletin, International Edition, Vol. 67, No. 8, pp. 1412—1418, August, 2018
Study of the products of platinum-catalyzed hydrogenation of chlorinated
nitro and amino aromatic compounds at high degree of dehalogenation
V. G. Dorokhov, G. F. Dorokhova, and V. I. Savchenko
Institute of Problems of Chemical Physics, Russian Academy of Sciences,
prosp. Akad. Semenova, 142432 Chernogolovka, Moscow Region, Russian Federation.
Fax: +7 (496) 522 3507. E-mail: vicd@icp.ac.ru
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The kinetics of formation and consumption of the dehalogenation products during hydro-
genation of 3,4-dichloronitrobenzene under static and gradient-free flow conditions and hydro-
genation of p-chloroaniline under static conditions were studied in the presence of platinum
supported on active carbon. In the former case, p-chloroaniline and aniline are the primary
dehalogenation products; in the presence of the catalyst, they can react with each other giving
biphenyl derivatives, whose synthesis and accumulation in the reaction mixture occur with
a considerable delay and have not been investigated before.
Key words: liquid-phase hydrogenation, catalysis, aromatic nitro compounds, dehalogenation.
Liquid-phase hydrogenation of chlorinated aromatic
these conditions, the composition of hydrodechlorination
products is quite predictable and virtually no other com-
pounds are formed.
nitro compounds in the presence of heterogeneous cata-
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lysts is used in industry to produce amino derivatives,
being the most efficient method for their synthesis.
However, this catalytic hydrogenation process is compli-
cated by the side elimination of chloride ions, which occurs
to a higher or lower extent on all known hydrogenation
catalysts. Together with chloride ion elimination from the
obtained amino compounds, more extensive transforma-
tions of amines also take place and give additional side
This study is devoted to catalytic hydrodechlorination
of chloroanilines formed from the corresponding nitro
derivatives on a platinum catalyst supported on active
carbon, including identification of transformation steps of
the starting reactants and intermediates formed at higher
(more than 20—50%) degrees of chlorine elimination.
The present publication outlines the results of static
experiments on catalytic hydrogenation of the amino
compounds, 3,4-dichloroaniline (3,4-DCA) and p-chloro-
aniline (PCA), which are formed in situ upon 2.5%Pt/C-
catalyzed hydrogenation of chlorinated nitro compounds
(3,4-dichloronitrobenzene (3,4-DCNB) and p-chloro-
nitrobenzene (PCNB)) at high (more than 20—50%)
degrees of chlorine elimination. We expected that binuclear
derivatives of chlorinated aromatic amines will be detected
at these high degrees of chlorine elimination. However,
static experiments consider two processes that are assumed
to be independent of each other, namely, the initial
hydrogenation of the nitro compound and the intermediate
chlorinated N-arylhydroxylamine and the subsequent
products.2 Previously,
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6—9
the kinetics of dehalogenation
of the chloroanilines formed was investigated by measur-
ing the initial rates of chloride ion accumulation, and the
process was shown to be retarded by the reaction products
and the solvent. No quantitative description of the stepwise
elimination of chloride ions from chloroanilines contain-
ing more than one Cl in the molecule is available from the
literature.
Most of the studies dealing with hydrogenation of
halogenated nitro compounds are aimed at increasing the
yield of halogenated amino compounds. Some recent
studies in heterogeneous catalysis are directed towards the
preparation of valuable products such as arylhydroxyl-
amines,1 which are formed as intermediates of reduction
of substituted aromatic nitro compounds. A number of
publications are devoted to hydrodechlorination of chloro
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transformation of the resulting amino compound. In
a real process, especially in hydrogenation in stirred reac-
tors, the above-indicated reactions occur simultane-
ously and affect each other. Therefore, hydrogenation of
3,4-DCNB and dehalogenation of 3,4-DCA were studied
also under gradient-free flow conditions, in which hydro-
genation of the nitro group and intermediates of its reduc-
tion proceed simultaneously with hydrodechlorination.
Thus, it was possible to evaluate the influence of the start-
ing nitro compound and intermediates on elimination of
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amino compounds formed during hydrogenation.
In
the published studies on hydrodechlorination, metals sup-
ported on new type materials, e.g., nanocarbon materials
or γ-Fe O nanoparticles, have been recently used. The
2
3
extents of halogen elimination, in particular, on contact
with platinum, are, most often, moderate (not more than
3
—5% and, only in rare cases, up to 10—12%). Under
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1412—1418, August, 2018.
066-5285/18/6708-1412 © 2018 Springer Science+Business Media, Inc.
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