Reaction of cinnamaldehyde and derivatives with Raney Ni-Al alloy and Al powder in water. Reduction or oxido-reduction?

Article abstract of DOI:10.1016/j.crci.2012.11.022

A series of experiments dealing with the reduction of cinnamaldehyde and parent compounds was carried out in completely aqueous media in order to assess the character of this process. We wish to show that the treatment of these substrates in water with Raney catalysts is an oxido-reductive process.

Full text of DOI:10.1016/j.crci.2012.11.022

C. R. Chimie 16 (2013) 476–481
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Full Paper/M e´ moire
Reaction of cinnamaldehyde and derivatives with Raney Ni–Al alloy and
Al powder in water. Reduction or oxido-reduction?
a
b
a,
Alina-Marieta Simion , Takashi Arimura , Cristian Simion *
a
‘
‘Politehnica’’ University of Bucharest, Faculty of Applied Chemistry and Material Science, Organic, Chemistry Department, Spl. Independentei nr. 313, Bucharest,
0
b
60042, Romania
National Institute of Advanced Science and Technology, AIST Central 5, Tsukuba, Ibaraki, 305-8565, Japan
A R T I C L E I N F O
A B S T R A C T
Article history:
A series of experiments dealing with the reduction of cinnamaldehyde and parent
compounds was carried out in completely aqueous media in order to assess the character
of this process. We wish to show that the treatment of these substrates in water with
Raney catalysts is an oxido-reductive process.
Received 24 September 2012
Accepted after revision 29 November 2012
Available online 19 January 2013
ß 2012 Acad e´ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Dedicated to the memory of Professors
Masashi Tashiro and Iwao Hashimoto.
Keywords:
Cinnamaldehyde
Aqueous reduction
Hydrogenation
Raney metal alloy
1
. Introduction
One of the most interesting and studied reductive
type of catalyst, the reaction conditions, the solvents and
the electronic effects of the support [7–15].
We have previously reported, for several types of
organic compounds, some mild reduction methods that
use noble metal catalysts in only pure water as solvent,
under atmospheric pressure or in sealed tube [16–18]. For
example, the carbonyl moiety of acetophenones or
benzophenones is effectively reduced to the corresponding
methylene group by either Raney Ni–Al alloy [17] or a
mixture of a noble metal catalyst and Al powder [18].
Two relatively and another one extremely recent
communications guided us toward a connection with
our studies: first, a report about the selective hydrogena-
tion of cinnamaldehyde in the presence of a bicatalytic
system formed of palladium black and Raney Ni, [19]
yielding a mixture of phenylpropanal 3 and phenylpropa-
nol 4, the ratio between them depending on the use of
ultrasonication (with ultrasonication activation, the major
compound was phenylpropanal 3), and another report of
processes is the one of cinnamaldehyde. From a mecha-
nistic point of view, reduction of cinnamaldehyde can be a
regioselective process, since this compound presents three
distinct reducible sites: the >C O double bond, the
>C
C< double bond and the aromatic nuclei [1,2]. On the
other hand, the reduction products, along with the starting
material, are important raw materials in the pharmaceuti-
cal, fragrance and aroma industries [3] (Scheme 1).
Most of the catalysts used in hydrogenation produce a
mixture of hydrogenated compounds requiring an expen-
sive separation, the number of selective catalysts being
rather scarce [4–6]. The selective hydrogenation of
cinnamaldehyde is affected by many factors, such as the
*
Corresponding author.
E-mail address: c_simion@chim.upb.ro (C. Simion).
4
an efficient method for the NaBH reduction of carbonyl
1
631-0748/$ – see front matter ß 2012 Acad e´ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.crci.2012.11.022

A.-M. Simion et al. / C. R. Chimie 16 (2013) 476–481
477
OH
X
2
OH
O
X
4
X
O
1
X
3
X = -H
Scheme 1. Partial/total reduction of cinnamaldehyde.
compounds (including cinnamaldehyde 1) in solvent-free
conditions, but using wet SiO as support [20]. Moreover, a
3.1. Reduction of cinnamaldehyde with Raney catalysts
3.1.1. Reduction of cinnamaldehyde with Raney alloy
2
Japanese team reported recently a highly efficient and
selective hydrogenation of unsaturated carbonyl com-
pounds using Ni–Sn alloy catalysts, working at high
temperatures (453 K) [21]. If Raney Ni or Raney alloys
need no introduction as hydrogenation/reduction cata-
lysts, the use of water (even as ‘‘wet support’’) in the
The chosen Raney alloy for this series of experiments
was Ni–Al. Since in our previous experiments for reductive
process in aqueous media we noticed the effect of Al
powder [18], we decided to use it as an additive in order to
boost the reactivity of the Raney Ni–Al alloy. We
investigated the process both under reflux conditions
(open vessel) or in a sealed tube. When working in open
flask, the stoichiometry used was: 0.01 moles of cinna-
maldehyde was mixed with 10 g of Raney Ni–Al alloy in
18 mL water. When sealed tubes were used, the stoichi-
ometry was changed to 0.01 moles of cinnamaldehyde, 2 g
Raney Ni–Al alloy in 5 mL water. The added quantities of Al
powder as well as other experimental conditions are
summarized in Table 2.
reduction of an
a,b-unsaturated carbonyl compound is
surprising. Moreover, it proved to be definitely beneficial,
improving dramatically the result of the process: indeed, a
dry support offered after 3 hours a 5% yield of alcohol,
while the wet support permitted a complete transforma-
tion of the aldehyde in the corresponding alcohol in less
than 1 minute.
Therefore, we decided to combine these aspects along
with our previous investigations and study the reductive
process of cinnamaldehyde in completely aqueous media,
in the presence of a Ni–Al Raney alloy.
Although no precise stereoselectivity is recorded,
reduction of cinnamaldehyde in aqueous media seems
to proceed according to a step-by-step reduction: first the
more sensitive >C C< double bond and next the >C
O
2
. Experimental
double bond. However, the final distribution of products is
clearly dependent on the reaction time and on the amount
of Al powder. Thus, when considering the experiments
carried out in open flask, under reflux conditions, it can be
seen that when only Raney Ni–Al alloy is used, phenyl-
propanal 3 is the major compound, while when Al powder
is added the reductive power of the system is enhanced
and phenylpropanol 4 is formed. When the reaction time is
prolonged, the reduction is completing the formation of
the final phenylpropanol 4 in almost quantitative yields. In
most of cases, two hydrocarbons are present in the final
reaction mixture: n-propylbenzene 5 and ethylbenzene 6.
If n-propylbenzene 5 is probably formed through a
Clemmensen-type reduction of the carbonyl moiety,
ethylbenzene 6 in its turn is formed either through
decarboxylation of cinnamic acid, eventually formed in
situ as an intermediate, either (more probably) by direct
decarbonalytion of cinnamaldehyde. Indeed, it has been
known for a while that aldehydes, in the presence of some
metallic catalysts, can undergo a decarbonylation process,
yielding the corresponding alkene [22,23]. Even recently,
the role of palladium catalyst in such decarbonylation of
aldehydes has been revisited [24]. However, in most of
these processes, the main reaction product was styrene.
Nevertheless, Keresszegi and coworkers have recorded the
presence of both compounds (ethylbenzene and styrene)
during the catalytic treatment of cinnamyl alcohol over an
All reagents were used as purchased, with no prior
purification step. Distilled water was used in all experi-
ments. Reactions were carried out in usual reflux
installation (50 mL round-bottom flask, reflux condenser)
or in sealed and pressure-resistant tube of 35 mL i.v. In
the reaction flask (open flask or sealed tube, as specified
for each case in the ‘‘Results and discussion’’ part),
cinnamaldehyde (0.01 moles) was introduced along with
the reduction catalyst (the amount is specified for each
case in the ‘‘Results and discussion’’ part) and 5-18 mL of
water. Powerful magnetic stirring (400 rpm) is applied
for the specified reaction time (Tables 1–5), at room
temperature. After completion of the process, the
reaction mixture is extracted with three portions of
4
ethyl ether. The organic layers are dried over MgSO ,
filtrated, evaporated and submitted to GC–MS analysis.
All experiments were performed in triplicate, giving
similar results.
3
. Results and discussion
Cinnamaldehyde was submitted to the catalytic action
of several Raney metals or alloys, in a completely aqueous
media, with different results. A brief picture of all
experiments is presented in Table 1.

4
78
A.-M. Simion et al. / C. R. Chimie 16 (2013) 476–481
Table 1
Cinnamaldehyde reduction experiments in aqueous media.
in some cases the yield in phenylpropanol 4 is over 90%
runs 2 and 13). Higher amounts of cinnamyl alcohol 2 are
(
Entry
Reduction catalyst
Additive
obtained when Raney Co is used, which confirms the
selectivity of this metal in the reduction of the carbonyl
moiety of cinnamaldehyde 1 [26]. Paradoxically, cobalt
chloride yielded the highest amount of phenylpropanol 4.
Iron permitted the formation of somehow higher quanti-
ties of phenylpropanal 3, but in a mixture with the other
reduced compounds. The addition of Zn powder to the
reaction mixture seemed to drive the reductive process to a
new level, since n-propylbenzene 5 is formed in almost
equimolecular quantities with phenylpropanol 4. In some
cases, traces of ethylbenzene were also recorded.
1
2
3
Raney alloy: Ni–Al
Al
Raney metals: Ni, Cu, Fe, Co
Al, Zn
Al
2 2 2
Salts: NiCl , CuCl , CoCl
alumina-supported palladium catalyst [25], along with
cinnamaldehyde and dihydrocinnamaldehyde as inter-
mediates. These previous results support our assumption
that the treatment of cinnamaldehyde with metal catalyst
is in fact an oxido-reduction process. It is interesting to
mention that in our processes, although we have recorded
the presence of both n-propylbenzene 5 and 1-propenyl-
benzene 7, but only ethylbenzene 6, we did not obtain any
styrene.
3.2. Reduction of cinnamaldehyde derivatives with Raney
catalysts
3.2.1. Reduction of
a-substituted cinnamaldehydes
Similar results are obtained when switching from open
to closed systems.
In order to investigate how the existence of an electron-
donating or electron-withdrawing substituent on the
>
C
C< double bond influences the reductive process,
3
.1.2. Reduction of cinnamaldehyde with Raney metals and
salts
The results registered in the reaction of cinnamalde-
we submitted 2-methyl respectively 2-chlorocinnamalde-
hyde to the following experimental conditions. Thus,
0.01 moles of substrate was treated with 10 g of Raney Ni–
Al alloy in 18 mL water, under reflux conditions. The
results are listed in Table 4 (Scheme 2).
The introduction of the 2-methyl group accelerated the
complete reduction process toward the corresponding
phenylpropanol. On the other hand, reduction of 2-
chlorocinnamaldehyde proceeded poorly, high amount
of starting material being recovered. Moreover, the
composition of the final reaction mixture is complicated
by the presence of both chlorinated and dechlorinated
compounds.
hyde in water with various Raney metals (with or without
any additives) are displayed in Table 3. Simultaneously
with these processes, we carried out similar reactions, but
in the presence of different salts of the same metals. All
reactions were performed in classic reflux apparatus. The
stoichiometry of these reactions is as follows: for
0
1
.01 moles of cinnamaldehyde, 10 g of metal or salt and
8 mL of water were used. In several cases, Al powder was
used as additive.
2
With the exception of Raney Cu and partly NiCl at
lower reaction time, all other reagents afforded complex
mixture of reduced compounds. The addition of metallic Al
powder seemed to enhance the reductive capacity of the
aqueous system. No special selectivity is observed, though
3.2.2. Reduction of other cinnamyl derivatives
Two derivatives were considered for the next step:
cinnamyl chloride 9 and cinnamyl alcohol 2. Because of its
Table 2
Reduction of cinnamaldehyde with Raney alloy.
a
Run
Flask type
Reaction time (h)
Added Al (g)
Final reaction mixture (%)
1
2
3
4
Others
–C
C
6
H
5
3
H
7
6 5 2 5
C H –C H
1
2
3
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Sealed
Sealed
Sealed
Sealed
Sealed
Sealed
0.5
1
–
–
2
4
4
–
1
2
1
1
–
–
–
0.4
1
1
39.6
3.8
1.5
86.0
–
0.5
0.8
–
40.0
55.0
20.9
12.0
9.5
18.0
37.1
74.3
1.0
1.3
1.7
1.0
0.4
0.5
3.8
2.5
3.0
0.8
1.0
1.4
3.3
2.0
1.8
0.4
3.7
0.6
1.6
2.4
0.1
2.0
3.1
1.5
4.0
5.5
4.0
–
1
b
4
1
0.1
–
5
6
7
8
9
1
88.0
40.4
45.0
90.0
83.5
95.0
0.1
3
3.4
4.0
–
–
49.4
47.0
3.0
3
–
3
–
5
–
–
8.5
1
1
1
1
1
1
1
0
1
2
3
4
5
6
12
1
–
–
–
70.0
5.8
–
–
28.4
56.4
13.2
39.4
44.2
9.0
2
–
31.3
76.3
–
3.2
8.3
–
3
–
1
58.5
20.3
–
0.2
–
1
32.1
81.7
3.0
5.5
2
–
a
Determined through GC–MS.
Raney Ni–Al alloy: 5 g.
b

A.-M. Simion et al. / C. R. Chimie 16 (2013) 476–481
479
Table 3
a
Reduction of cinnamaldehyde with Raney metals and salts .
b
Run
Raney metal or salt
Added Al (g)
Final reaction mixture (%)
1
2
3
4
Others
–C
C
6
H
5
3
H
7
6 5 2 5
C H –C H
1
Ni
Ni
Cu
Cu
Fe
Fe
–
3.4
–
–
49.4
3.0
40.4
90.0
0.3
3.8
3.0
–
3.1
4.0
–
2
3
4
5
6
7
2
–
–
91.6
91.9
45.8
0.8
11.9
0.6
47.5
–
1.1
2.8
21.0
14.6
37.3
44.0
12.3
–
7.0
2
5.1
0.2
–
–
–
28.0
37.8
14.2
3.8
5.2
–
–
2
46.8
36.4
51.3
15.0
80.3
81.6
50.3
93.1
–
–
c
Co
–
0.2
0.3
0.6
7.5
5.3
–
c
8
Co
1
–
d
g
9
NiCl
NiCl
NiCl
2
2
2
(4.45)
(4.45)
1.25
1.25
2.50
1.13
1.25
24.6
12.2
7.0
–
g
1
0
–
d
g
1
1
d,e
(4.45)
5.4
–
0.6
–
0.1
–
g
1
2
CuCl
CoCl
2
(4.74)
–
49.7
0.3
f
g
1
3
2
(4.74)
5.7
–
0.9
–
a
b
c
d
e
f
Cinnamaldehyde 0.01 moles, metal/salt 10 g, water 18 mL, stirring, reflux 3 h.
Determined through GC–MS.
Raney cobalt 5 g.
Reaction time 1 h.
1
.13 g of Zn was also added.
Reaction time 0.5 h.
g
The quantity of metal is given in brackets.
high reactivity, reactions with cinnamyl chloride were
carried out in sealed tube. Thus, 200 mg of 9 were mixed
with 200 mg of Raney catalyst in 2 mL of water and stirred
for 2 hours at 120 8C (Scheme 3) (Table 5).
Although catalyst poisoning due to chlorine species
(especially HCl) is a possibility, [27] it has been known that
when a base or a basic modifier is added in the reaction
mixture, the activity and the selectivity of hydrogenation
reactions conducted using catalysts such as Pt/C, Pd/C or
Raney Ni, can change significantly [28,29]. In these
processes, the role of the basic additive is to prevent
catalyst poisoning by trapping the HCl produced by the
reaction. An advantage of our process is that there is no
need for a supplementary compound (base or modifier) in
Transformation of cinnamyl chloride
through numerous pathways:
9 occurred
ꢀ
ꢀ
reduction and hydrolysis, affording phenylpropanol 4;
reduction, hydrolysis and oxidation, affording phenyl-
propanal 3;
ꢀ
ꢀ
ꢀ
reduction and hydrodechlorination, affording n-propyl-
benzene 5;
simple hydrodechlorination, affording n-propenylben-
zene 7;
Wurtz-type coupling, affording three 1,v-diphenyl-C6-
3
the reaction mixture, since Al(OH) is generated in situ
through the necessary reaction of Al with water, reaction
which generates the reductive species of hydrogen.
Nevertheless, these mixed results are an indication that
the process that occurs in aqueous media is not a simple
reduction, but an oxido-reduction. This assumption was
derivatives, with two double bonds, one double bond and
no double bond.
Table 4
Reduction of
a-substituted cinnamaldehydes.
a
Run
X
Reaction time (h)
Final reaction mixture (%)
1
2
3
4
Others
5
6
7
8
1
2
3
4
5
6
7
8
-CH
3
1
2
3
1
3
1
2
0.5
–
–
–
–
–
84.5
–
–
6.0
5.6
6.6
–
9.0
0.4
0.4
–
–
94.0
–
–
–
–
93.0
–
–
–H
3.8
3.4
33.5
10.4
8.1
0.8
–
55.0
37.1
1.7
3.8
0.3
1.5
0.8
1.6
3.1
0.3
2.0
1.4
49.4
40.4
–
–
b
b
b
b
–Cl
–
7.2 + [26.5]
[32.1]
[62.6]
[66.5]
–
–
b
b
–
10.2 + [13.3]
12.0 + [10.9]
–
–
c
3
–
–
–
a
Determined through GC–MS.
b
c
[
] represents percentage of corresponding compound with the loss of the chlorine atom.
A phenyl–chloropropene derivative (0.3%) was also detected by GC–MS.

4
80
A.-M. Simion et al. / C. R. Chimie 16 (2013) 476–481
OH
X
2
OH
O
X
4
X
O
1
X
3
X = -Cl, -H, -CH
3
Other products:
X
5
6
7
8
Scheme 2. Reaction products.
X
1
+ 2 + 3 + 4 + 5 + 6 + 7 + 1,ω-diphenyl-C6 hydrocarbons
2
, X = -OH
, X = -Cl
9
Scheme 3. Reduction of other cinnamyl derivatives.
confirmed by the results obtained when cinnamyl alcohol
was used as starting material. Indeed, in many cases,
necessary (e.g. benzaldehyde afforded toluene, acetophe-
none–ethylbenzene). In the case of cinnamaldehyde,
although there is a conjugation between the carbonyl
moiety and the aromatic nuclei (through the >C C<
double bond), a certain number of oxygenated derivatives
are obtained, especially phenylpropanol. This confirms the
higher sensitivity toward reduction of the middle >C C<
double bond, breaking up the conjugation and leaving thus
the >CH O group as substrate for a simple and mild
2
considerable amounts of cinnamaldehyde were obtained, a
clear sign that an oxidative process is also occurring. This is
even more obvious when treating cinnamyl alcohol with a
noble metal catalyst, when only reductive processes
occurred. The reductive effect of metallic Al powder is
again exemplified by the result in run 2, when the yield in
n-propylbenzene is doubled compared to runs 1 and 3.
Compared to some of our previous researches [16–18],
the reduction in aqueous media of cinnamaldehyde is a
little different. In our previous research, we have
established that aromatic carbonyl compounds in similar
conditions afforded hydrocarbons, a conjugation between
the aromatic nuclei and the carbonyl group being
2
reduction to a–CH -OH group, and in the same time,
leaving the–CH -OH group to suffer mild oxidation back to
2
the >CH O group.
The evidences brought in this material show therefore
that the treatment of carbonyl compounds in an aqueous
media is an oxido-reductive process.
Table 5
a
Reduction of other cinnamyl derivatives .
b
Run
X
Raney catalyst
Added metal (mg)
Final reaction mixture (%)
2/9
1
3
4
5
6
7
Others
1,v-
1
2
3
–Cl
Ni–Al
Ni–Al
Co–Al
Ni–Al
Ni–Al
Ni–Al
Co–Al
–
–
–
–
–
18
3
47
25
54
40
35
95
38
9
16
30
16
1
–
–
2
2
1
1
2
1
3
2
1
6
13
42
5
c
200 (Al)
–
–
–
–
12
13
9
–
e
4
–OH
–
41
54
1
20
12
21
9
1
–
f
5
–
–
–
–
6
200 (Zn)
–
–
3
–
–
e
7
57
27
–
1
2
1
–
d
8
9
Rh/C
100 (Al)
100 (Al)
100 (Al)
100 (Al)
2
3
2
16
–
–
d
Pd/C
1
–
75
7
10
2
–
d
1
1
0
1
Ru/C
34
87
–
15
–
18
1
–
d
Pt/C
1
1
1
–
a
b
c
d
e
f
Substrate 200 mg, catalyst 200 mg, water 2 mL, sealed tube, 120 8C, 2 h.
Determined through GC–MS.
Three derivatives were obtained: with two double bonds (22%), one double bond (16%) and no double bond (4%).
Hundred milligrams of catalyst.
Reaction time = 3 h.
Reaction time = 1 h.

A.-M. Simion et al. / C. R. Chimie 16 (2013) 476–481
481
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