Ni(0)-CMC-Na nickel colloids in sodium carboxymethyl-cellulose: Catalytic evaluation in hydrogenation reactions

Article abstract of DOI:10.3390/molecules16010367

A recyclable catalyst, Ni(0)-CMC-Na, composed of nickel colloids dispersed in a water soluble bioorganic polymer, sodium carboxymethylcellulose (CMC-Na), was synthesized by a simple procedure from readily available reagents. The catalyst thus obtained is stable and highly active in alkene hydrogenations.

Full text of DOI:10.3390/molecules16010367

Molecules 2011, 16, 367-372; doi: 10.3390/molecules16010367
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molecules
ISSN 1420-3049
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Communication
Ni(0)-CMC-Na Nickel Colloids in Sodium
Carboxymethyl-Cellulose: Catalytic Evaluation in
Hydrogenation Reactions
Mohamed Anouar Harrad 1, Pedro Valerga 2,*, M. Carmen Puerta 2, Issam Houssini 1,
Mustapha Ait Ali 1, Larbi El Firdoussi 1 and Abdallah Karim 1
1
Coordination Chemistry and Catalysis Team, Department of Chemistry, Faculty of Science,
Semlalia, Cadi Ayyad University, BP 2390, 40001 Marrakech, Morocco
2
Department of Materials Science, Metallurgical Engineering and Inorganic Chemistry, Faculty of
Science, Campus Rıo San Pedro, Puerto Real 11510, Spain
* Author to whom correspondence should be addressed; E-Mail: pedro.valerga@uca.es;
Tel.: +34 956 016340; Fax: +34 956 016288.
Received: 29 November 2010; in revised form: 22 December 2010 / Accepted: 5 January 2011 /
Published: 7 January 2011
Abstract: A recyclable catalyst, Ni(0)-CMC-Na, composed of nickel colloids dispersed in
a water soluble bioorganic polymer, sodium carboxymethylcellulose (CMC-Na), was
synthesized by a simple procedure from readily available reagents. The catalyst thus
obtained is stable and highly active in alkene hydrogenations.
Keywords: colloids; hydrogenation; bioorganic polymer
1. Introduction
In recent years, metal colloids have fascinated scientists because of their outstanding electronic and
optical properties [1-3]. They have become important catalysis research candidates [4], used in a wide
variety of hydrosilylation [5], oxidation [6], C-C coupling [7-8] and selective hydrogenation
reactions [9-11]. Their potential utilities are evaluated in terms of activity, selectivity, physical and
chemical stability [3]. Colloids have major applications in heterogeneous catalysis [12] due to their
high specific surface area. The organometallic approach followed in the laboratory for the synthesis of
colloids provides access to various metal colloids (Pd, Rh, Ru…) in a controlled and reproducible way,
but it would be of interest to develop other types of colloidal catalyst using less expensive transition

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368
metals, such as nickel. Our work was focused on the synthesis of a new colloidal species based on
nickel, stabilized by a water soluble bioorganic polymer, sodium carboxymethylcellulose (CMC-Na).
The colloids obtained were used as catalysts in the hydrogenation of functionalized olefins. With the
aim of optimizing the operating conditions, we have studied different parameters influencing the
course of the reaction such as the molar ratio substrate/catalyst (S/C), nature of solvent, polymer
concentration and the nature of the substrate.
2. Results and Discussion
The nickel(0) colloids were generated from nickel(II) chloride, sodium borohydride and a catalytic
amount of sodium carboxymethylcellulose (CMC-Na) in a mixture of water/methanol at room
temperature. The prepared material was characterized by X-ray diffraction according to literature
procedures [13-17].
Figure 1. XRD patterns of the prepared nickel colloid.
Figure 1 shows the typical X-ray diffraction pattern of the Ni-CMCNa nanoparticles. Due to the
small size effect and incomplete inner structure of the particle, the XRD peaks are low and broad. On
the other hand, the XRD pattern shows that the sample is two-phase. The peaks with 2θ values around
44.5° and 53° correspond to the (111) and (200) planes of the metallic Ni phase respectively, which is
in accordance with that of the standard spectrum (JCPDS, No. 88-2326) [13-17].
In order to optimize the hydrogenation conditions, a preliminary study was carried out using
cinnamyl alcohol (1) as a model substrate. The reaction was conducted at room temperature, using
different solvents, various concentrations of CMC-Na polymer and under different hydrogen pressures
(Table 1). The hydrogenation of 1, in aqueous solution under one atmosphere of hydrogen, yielded
dihydrocinnamyl alcohol (2) in moderate yield after 7 h (entry 1, Table 1). A combination of water and
alcohol as solvent is necessary to increase the activity of catalyst, and the best results were obtained
when mixtures of water and methanol or water and isopropanol were used as solvent (entries 2 and 7).
Increasing the hydrogen pressure has a favorable effect on the catalyst activity and minimizes the
reaction time considerably (entries 8, 9 and 10). However, increasing the polymer concentration is
unfavourable for the catalytic activity. When more than 0.5 g/L of CMC-Na is used, the conversion

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369
decreases considerably (entries 11-14). In all cases, dihydrocinnamyl alcohol 2 was the sole product
obtained with 100% selectivity.
Table 1. Hydrogenation of cinnamyl alcohol (1) catalyzed by Ni(0)-CMC-Na colloids:
Influence of nature of solvent, concentration of polymer and hydrogen pressure.
Ni-CMC-Na
OH
OH
2
1
Polymer
H2 pressure
Conversion
Entry
Solvent
H2O
Time (h)
concentration g/L
(bars)
%
45
87
5
1
2
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1.0
1.5
2.0
3.0
1
1
7
7
H2O/iPrOH
H2O/CHCl3
H2O/THF
3
1
24
12
16
24
7
4
1
2
5
H2O/Acetonitril
H2O/toluene
H2O/MeOH
H2O/MeOH
H2O/MeOH
H2O/MeOH
H2O/MeOH
H2O/MeOH
H2O/MeOH
H2O/MeOH
1
5
6
1
0
7
1
90
91
92
98
62
57,5
40
12
8
10
20
40
1
5
9
3.5
2.0
7
10
11
12
13
14
1
7
1
7
1
7
Reaction conditions: S/C = 100, 10 mL of solvent (8/2), room temperature. a The conversions were
determined by gas chromatography.
We note here that the recyclability of the catalyst was verified by submitting the same recovered Ni
colloid catalyst to three subsequent reaction cycles. No appreciable loss in activity was observed
before two cycles, as shown in Table 2.
Table 2. Hydrogenation of cinnamyl alcohol catalyzed by Ni(0)-CMC-Na colloids:
catalyst recyclability.
Entry
7
Reuses
Conversion %
0
1
2
3
90
81
63
40
15
16
17
Reaction conditions: S/C = 100, 10 mL of solvent: H2O/MeOH (8/2), room
temperature, 7 h. a The conversion were determined by gas chromatography.
Reduction of other functionalized olefins: 1,3-diphenylpropenone (3), 4-phenylbut-3-en-2-one (4),
5-allylbenzo[1,3]dioxole (5) and 5-propenylbenzo[1,3]dioxole (6) under identical conditions using
Ni(0)-CMC-Na colloid catalyst led to the corresponding products in good to excellent yields (60–90%)
(Table 3). In all cases these good yields were achieved using low hydrogen pressure, at room

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temperature and after acceptable reaction times. We note here that only the double band was
hydrogenated with 100% selectivity and other functional groups remain intact.
Table 3. Hydrogenation of olefins catalyzed by Ni(0)-CMC-Na colloid.
Conversion
%
Isolated
yield %
Entry
18
Substrate
Product
Time (h)
O
O
48
72
86
80
63
3
7
O
O
19
20
48
36
4
8
O
O
O
O
100
88
5
9
9
O
O
O
21
48
93
79
O
6
Conditions: S/C=100, 0.5 g/L CMC-Na, solvent: MeOH/H2O (8/2), P H2: 40 bars, room
temperature. a The conversions were determined by gas chromatography.
3. Experimental
3.1. Instrumentation
NMR studies were performed on a Bruker Avance 300 spectrometer in CDCl3. Chemicals shifts are
given in ppm relative to external TMS and coupling constants (J) in Hz, Mass spectra were recorded
on a GC-MS Thermofinnigan Polaris-Q mass spectrometer. The synthesized nanoparticles were
characterized by wide angle X-ray diffraction (Philips XPERT-MPD diffractometer,
Goniometer = PW3050/10 with Cu(0) anode material).
3.2. Preparation of the Metal Colloid Precursors
Sodium borohydride (5 mg) was added to an aqueous solution of CMC-Na surfactant (5 mg, in 40 mL
H2O). The obtained solution was quickly added under vigorous magnetic stirring to an aqueous solution
of the precursor NiCl2x6H2O (50 mg, 0.42 mmol) in H2O (10 mL). The initial green solution darkened
immediately and after one night, the suspensions obtained remain stable for a week under nitrogen.
3.3. General Hydrogenation Procedure
A round-bottom flask (25 mL), charged with the aqueous suspension of Ni(0)-CMC-Na (10 mL)
and a magnetic stirrer, was connected to a gas burette (500 mL) with a flask to balance the pressure.
The flask was closed with a septum and the system filled with hydrogen. The appropriate substrate

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(S/C = 100) was injected through a septum and the mixture was stirred. The reaction was monitored by
volume of gas consumed and by gas chromatography (Varian 3800 equipped with a RTX5 capillary
column and a FID detector). At the end of the reaction, the two phases were separated and the aqueous
phase was extracted with ether (3 × 25 mL). The combined ether solution was dried over anhydrous
Na2SO4. The solvent was removed under reduced pressure and the residue was purified by column
chromatography over silica gel.
3.4. Typical Spectral Data
1
1,3-Diphenyl-propan-1-one (7): H-NMR (CDCl3, 300 MHz) δ: 1.98 (t, 2H), 2.2 (t, 2H), 7.2-7.94 (m,
10H); 13C-NMR (CDCl3, 75 MHz) δ: 33.14, 46.70, 122.03, 126.18, 128.11, 46, 128.71, 129.25,
130.50, 132.95, 135.05, 138.34, 144.16, 203.12.
4-Phenylbutan-2-one (8): 1H-NMR (CDCl3, 300 MHz) δ: 1.63 (s, 3H), 1.92 (t, 2H), 2.09 (t, 2H), 7-7.2
13
(m, 5H); C-NMR (CDCl3, 75 MHz) δ: 30.03, 32.14, 45.17, 125.43, 125.81, 126.46, 127.29, 128.71,
140.16, 205.8.
1
5-Propylbenzo[1,3]dioxole (9): H-NMR (CDCl3, 300 MHz) δ: 1.16 (t, 3H), 1.8 (m, 2H), 2.7 (t, 2H),
13
6.13 (s, 2H), 8.8-6.95. (m, 3H); C-NMR (CDCl3, 75 MHz) δ: 13.6, 24.5, 37.73, 100.44, 107.86,
108.79, 120.71, 136.16, 145.4, 147.37.
4. Conclusions
Nickel(0) colloids prepared at room temperature from nickel(II) chloride, sodium borohydride and
sodium carboxy-methylcellulose (CMC-Na) in a mixture of water/methanol, have shown to promote
the ready hydrogenation of a variety of functionalized olefins at room temperature and moderate
hydrogen pressures. Moreover, the nickel colloids could be re-utilized several times, maintaining a
moderate to high activity.
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