LETTER
1623
Supported Nickel-Catalyzed Hydrogenation of Aromatic Nitriles under Low
Pressure Conditions
Supported
N
ic
a
kel-Catalyz
t
ed
H
yd
o
rogenation
o
s
f
A
romat
h
N
itriles i Takamizawa, Noriko Wakasa, Takamasa Fuchikami*
Sagami Chemical Research Center, 4-4-1 Nishi-Ohnuma, Sagamihara, Kanagawa 229-0012, Japan
Fax +81-42-749-7631; E-mail: scrc1@sagami.or.jp
Received 17 July 2001
(
SiO –Al O ) are best catalysts in the hydrogenation of ar-
2 2 3
Abstract: Hydrogenation of aromatic nitriles takes place under the
mild conditions using supported nickel catalysts to afford amino-
methyl-substituted aromatics in good yields.
omatic nitriles bearing a variety of substituents.
The Ni/SiO -catalyzed hydrogenation of p-methoxy-, p-
2
methyl- and unsubstituted benzonitriles smoothly takes
Key words: nickel, catalysis, hydrogenations, nitriles, amines
place on using 2 M NH in MeOH as a solvent (Table,
3
Runs 1, 5 and 6), and 2.5% aqueous NH can be also used
3
as a suitable solvent (Run 2). The yield diminished to
some extent in water, which may be attributed to lower
solubility of the substrate (Run 3). The amount of catalyst
used can be reduced to 1 mol% without decreasing the
yield of the product (Run 6). Under these conditions, o-,
m-, and p-trifluoromethyl substituted benzonitriles gave
the desired benzylamines in 97, 86, and 98% yields, re-
spectively (Runs 7, 8 and 9). It makes sharp contrast with
the results obtained by Ru/C catalyst mentioned above.
The yield of the desired product remarkably decreased
The catalytic hydrogenation of aliphatic and aromatic ni-
triles should be the most straightforward way to the prep-
aration
of
aminomethyl-substituted
compounds.
However, existing methods in the liquid phase, where
1
,2
Raney Ni has been mainly used as a catalyst, requires
high pressure conditions because of the formation of sec-
ondary and tertiary amines via exchange reaction between
the produced primary amines and the intermediately
3
formed imines. Recently, NaY-supported transition met-
al catalysts have been studied in detail where the selectiv-
without NH in the solvent (Run 10). o-, m-, and p-Fluoro
ity to the primary amines decreases in the order of Ru >
3
4
substituted benzonitriles also easily underwent the hydro-
genation to give fluorobenzylamines in 98, 86, and 99%
yields, respectively (Runs 12, 13 and 14). The slightly
lower yields in the reaction of m-trifluoromethyl- and m-
fluoro-substituted benzonitriles (Runs 8 and 13) may be
ascribed to the electronic effects. The catalyst Ni/(SiO2–
Al O ) has almost the same activities as Ni/SiO (Runs 4,
Rh > Ni > Pd > Pt. The Ni-containing bimetallic catalysts
(
Cu-Ni and Fe-Ni) supported on silica have been also in-
5
vestigated in the liquid phase hydrogenation of nitriles.
We wish to report here the supported nickel-catalyzed hy-
drogenation of aromatic nitriles under the mild conditions.
Initially, we surveyed the active catalysts toward the hy-
drogenation of benzonitrile as a substrate in methanol un-
der 10–20 atm of hydrogen pressure at 100–160 °C. Many
examined catalysts such as Raney Ni, Ni boride, Pd/C,
and Ru (CO) gave secondary amine (dibenzylamine) as
2
3
2
1
1 and 15). The hydrogenation of 3,5- and 2,4-bis(trifluo-
romethyl)benzonitriles can be also converted into the cor-
responding amines under similar conditions (Runs 16 and
3
12
1
7). In the case of 3,5-bis(trifluoromethyl)benzonitriles,
a main product. The desired benzylamine was obtained in
the better result was obtained on using 2-propanol as a sol-
vent. The presence of chloride or bromide substitutent on
benzene ring has no influence on catalytic activity, and the
corresponding amines were obtained in good yields with-
out the elimination of halides (Runs 18 and 19). Under the
present conditions, ester group was found to be inactive,
that is, no amide formation was observed by the reaction
with ammonia in solvent as well as formed primary amine
moiety (Run 20). 1,3-Dicyanobenzene was also hydroge-
nated into 1,3-di(aminomethyl)benzene in good yields at
more elevated temperature (170 °C) (Run 21), which is a
useful compound for new barrier nylons. The hydrogena-
tion of heteroaromatic rings did not take place by the
8
2
4% yield on using 5% Ru/C (0.5 mol%) as a catalyst in
M NH in MeOH under 10 atm of hydrogen at 120 °C.
3
Under these conditions, benzonitriles bearing electron-
donating substituent such as p-methoxy and p-methyl
groups gave satisfactory results in 84 and 98% yields of
the products, respectively. However, in the hydrogenation
of fluoro- or trifluoromethyl-substituted benzonitriles,6
the yields of the desired products varied markedly by the
position of the substituents (m-F : 60%, p-F : 89%, o-CF3:
9
8%, m-CF : 18%, and p-CF : 7%), and secondary amines
3 3
(
(ArCH ) NH) or imines (ArCH = N-CH -Ar), and un-
2
2
2
desired products derived from the reduction of C-F bonds
were obtained as side products. We resurveyed the desired
catalyst using p-trifluoromethylbenzonitrile as a sub-
7
present catalysts. Therefore, 3-cyanopyridine and cyan-
opyradine can be easily converted into 3-aminomethylpy-
ridine and aminomethylpyradine in good yields,
respectively (Runs 22 and 23). The present catalysts was
found to be also active in the hydrogenation of aralkyl and
alkyl cyanides (Runs 24 and 25).
strate, and found that 60wt% Ni/SiO and 65wt% Ni/
2
Synlett 2001, No. 10, 28 09 2001. Article Identifier:
1
©
437-210X,E;2001,0,10,1623,1625,ftx,en;Y14601st.pdf.
Georg Thieme Verlag Stuttgart · New York
ISSN 0936-5214