Reduction of carbonyl groups to the corresponding methylenes with Ni-Al alloy in water

Article abstract of DOI:10.1039/b211571a

The reduction of carbonyl compounds 1a-h using Ni-Al alloy in water under reflux proceeded to give the corresponding methylene compounds 2a-h within 2 h in 89.0-99.8% relative yields.

Full text of DOI:10.1039/b211571a

Reduction of carbonyl groups to the corresponding methylenes with
Ni–Al alloy in water
Keiko Ishimoto,a Yoshiharu Mitoma,b Satoko Nagashima,a Hideki Tashiro,c G. K. Surya Prakash,c
George A. Olahc and Masashi Tashiro*c
a Department of Industrial Chemistry, Faculty of Engineering, Tohwa University, 1-1-1 Chikushigaoka,
Minami-ku, Fukuoka 815-8510, Japan. E-mail: keiko@tohwa-u.ac.jp
b Department of Bioscience Development, School of Biosciences, Hiroshima Prefectural University, 562
Nanatsuka-cho, Shobara, City, Hiroshima 727-0023, Japan. E-mail: mitomay@bio.hiroshima-pu.ac.jp
c
Loker Hydrocarbon Research Institute, University of Southern California, 837 Bloom Walk, LHI, Los
Angeles, California 90089-1661, USA. E-mail: mtashiro@usc.edu
Received (in Corvallis, OR, USA) 21st November 2002, Accepted 31st December 2002
First published as an Advance Article on the web 23rd January 2003
The reduction of carbonyl compounds 1a–h using Ni–Al
alloy in water under reflux proceeded to give the correspond-
ing methylene compounds 2a–h within 2 h in 89.0–99.8%
relative yields.
was carried out in refluxing water with Ni–Al, Co–Al, Cu–Al,
and Fe–Al alloys7 for 2 h, the results are summarized in Table
1.
Table 1 Reduction of 1a with alloy in water under reflux for 2 hab
The Clemmensen reduction1 under acidic conditions and Wolf–
Kishner reduction2 under basic conditions are widely used for
the reduction of carbonyl groups to the corresponding methy-
lene units. A good review about the reduction of organic
compounds with Ni–Al alloy in alkaline media3 is available. In
1942, Papa et al.4 reported that acetophenone and benzaldehyde
were reduced to ethylbenzene and toluene by using Ni–Al alloy
in 10% aq. NaOH solution, respectively. This method is carried
out under basic conditions and thus the Wolf–Kishner reduction
can not be applied for base sensitive substrates. The Clem-
mensen reduction is carried out under strongly acidic conditions
and sometimes poisonous mercury must be used. Thus, the
method is not suitable for acid sensitive precursors. It has been
found that the reduction of halophenols5 and 4-chlorobiphenyl6
using Ni–Al alloy in highly dilute aq. NaOH alkaline solution or
weakly basic Ba(OH)2 solution afforded the reduced aromatic
rings, respectively (Scheme 1). As shown in Scheme 1, it was
found that the reduction of halophenols using Ni–Al alloy in
10% aq. NaOH solution afforded the phenol itself, however, the
reaction of halophenols in saturated Ba(OH)2 solution gave not
phenol but cyclohexanol. Also 4-chlorobiphenyl was reduced to
biphenyl itself by treating with Ni–Al alloy in 10% aq.
Products
(Relative yield, %)
Recovered 1a
Run
Alloy
2a
3a
0.4
18.0
20.1
26.2
(%)
1
2
3
4
Ni–Al
Co–Al
Cu–Al
Fe–Al
97.1
0.9
(+)
2.5
72.1
79.9
73.8
(+)
a 1a: 5 g, Alloy: 25 g, Water: 50 ml. b Measured by GC-Mass.
Ni–Al alloy (50+50 composition) appears to be the best
reducing system. The reduction of carbonyl compounds 1a–1h
with Ni–Al alloy was carried out in water under similar
conditions as described below (Scheme 2), the results are
summarized in Table 2.
The typical procedure was the following. To a mixture of 1a
(5.00 g, 41.6 mmol) in 50 mL of water at room temperature was
NaOH solution at 90 °C. However, when it was reduced in
0.5–1% aq. NaOH solution, cyclohexylbenzene was obtained.
The above results prompted us to investigate the reduction of
carbonyl compounds with Raney alloys in only water without
any organic solvent, or a base. Reduction of acetophenone 1a
Scheme 2
Table 2 Reduction of 1 with alloy in water under reflux for 2 hab
Products
Run
Ketone
(Relative yield %)
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
2a (99.0)
2b (98.6)
2c (89.0)
2d (96.2)
2e (99.8)
2f (93.1)
2g (99.8)
2h (99.8)
3a (1.0)
4a (+)
4b (+)
4c (9.0)
3b (1.4)
3c (2.0)
3d (3.8)
3e (0.2)
3f (6.9)
3g (0.2)
3h (0.2)
1g
1h
a 1a: 5 g, Alloy: 25 g, Water: 50 ml. b Measured by GC-Mass.
Scheme 1
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CHEM. COMMUN., 2003, 514–515
This journal is © The Royal Society of Chemistry 2003

added Ni–Al alloy (25.0 g, Ni: 50%) in one portion. The
reaction mixture was stirred vigorously under reflux for 2 h.
During the reaction, the pH of solution remained close to
neutral. The mixture was extracted with ether (10 mL 3 3
times). The combined organic layers were washed with brine,
dried over magnesium sulfate, and concentrated. The 2a was
obtained in a 99.8% yield (4.41 g). The hydrocarbon products
can also be isolated by simple steam distillation.
As shown in Table 2, the reduction of ketones 1a–g with Ni–
Al alloy in water afforded corresponding methylene compounds
2a–g in good yields (89–99.8%), respectively, with small
amount of alcohols 3a–g. The reduction of acetophenone 1a,
propiophenone 1b, butyrophenone 1c, and isobutyrophenone
1d under similar conditions shown in Table 2 afforded the
corresponding alkylbenzenes 2a–d in excellent yields. The
formation of a small amount of alcohols 3 in these reactions
suggests that they are the de facto intermediates en route to the
formation of 2. When 3a was treated with Ni–Al alloy in water
under similar conditions to those described above, expected 2a
was obtained in good yield.
Surprisingly, it was found that 1a was reduced to 2a in
excellent yield, even at room temperature over a 24 h period.
Also, reduction of acetyltoluenes 1e–g and benzophenone 1h
afforded the corresponding ethyltoluenes 2e–g and diphenyl-
methane 2h with a small amount of intermediate alcohol
products 3e–h.
Scheme 3
used (Scheme 3). A longer reaction time is necessary for the
formation of 6 in good yield.
Financial support of the work at USC by the Loker
Hydrocarbon Research Institute is gratefully acknowledged.
Notes and references
1 E. L. Martin, Org. React., 1942, 1, 155; E. Vedejs, Org. React., 1975, 22,
401.
2 D. Todd, Org. React., 1948, 4, 378.
3 L. K. Keefer and G. Lunn, Chem. Rev., 1989, 89, 459–502.
4 D. Papa, E. Schwenk and B. Whitman, J. Org. Chem., 1942, 7,
587–590.
5 M. Mukumoto, T. Mashimo, H. Tsuzuki, T. Tsukinoki, N. Uezu, S.
Mataka, M. Tashiro and T. Kakinami, J. Chem. Res. (S), 1995,
412–413.
6 G.-B. Liu, T. Tsukinokki, T. Kanda, Y. Mitoma and M. Tashiro,
Tetrahedron Lett., 1998, 39, 5991–5994.
7 It should be noted that sometimes commercial Ni–Al alloy has varying
reactivities. The reactivities of the batch should be tested before the
reductions.
The formation of 4a–c under the moderate reaction condi-
tions used is a very interesting phenomenon since usually
reduction of an aromatic ring with Raney Ni catalyst needs high
pressure and high temperature to proceed.
Similar reduction of benzaldehyde 5 afforded benzyl alcohol
7 and/or the desired toluene 6 according to the reaction time
CHEM. COMMUN., 2003, 514–515
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