Catalytic oxidation of alcohols by a novel manganese Schiff base ligand derived from salicylaldehyd and l-Phenylalanine in ionic liquids

Article abstract of DOI:10.1016/j.catcom.2011.11.035

A selective oxidation of alcohols to corresponding carbonyl compounds in ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate([bmim]BF₄) was achieved by using a novel salicylaldehyd amino acid Schiff base manganese ligand. The catalytic s

Full text of DOI:10.1016/j.catcom.2011.11.035

Catalysis Communications 20 (2012) 51–53
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Catalysis Communications
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Short Communication
Catalytic oxidation of alcohols by a novel manganese Schiff base ligand derived from
salicylaldehyd and l-Phenylalanine in ionic liquids
a
b
c
b,
Meizhu Rong , Juan Wang , Yanping Shen , Jinyu Han ⁎
a
Faculty of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming, China
Key Laboratory for Green Chemical Technology of State Education Ministry, School of Chemical Engineering & Technology, Tianjin University, Tianjin, China
School of Foreign Languages & Literature,Yunnan Normal University, Kunming, China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 August 2011
Received in revised form 22 November 2011
Accepted 30 November 2011
Available online 10 December 2011
A selective oxidation of alcohols to corresponding carbonyl compounds in ionic liquid 1-butyl-3-methylimi-
dazolium tetrafluoroborate([bmim]BF ) was achieved by using a novel salicylaldehyd amino acid Schiff base
4
manganese ligand. The catalytic system can be recycled and reused for four runs without any significant loss
of catalytic activity.
©
2011 Elsevier B.V. All rights reserved.
Keywords:
Oxidation
Alcohols
Ionic liquid
Schiff base
1
. Introduction
from amino acids because they are considered to constitute new
kinds of potential antibacterial and anticancer reagents [20–25].
However, to the best of our knowledge, the cheap and “green” Mn
catalytic systems for oxidation of alcohols in ILs have received less at-
tention, especially manganese metal ligands. Jing team [26] reported
the oxidation of secondary alcohols with iodobenzene diacetate cata-
The oxidation of alcohols to the corresponding aldehydes, ketones
and carboxylic acids is one of the important reactions in organic
chemistry both at the laboratory and in industrial synthetic chemistry
[
1]. Traditionally, this transformation is performed with stoichiomet-
ric, toxic and expensive inorganic oxidizing agents (i.e. KMnO , Cr(VI)
compounds, HNO , etc.) and in organic solvents which are volatile,
4
2 2
lyzed by Mn(Salen) in ionic liquid, but toxic CH Cl was also used as
3
the co-solvent in ionic liquid.
toxic, and flammable [2]. Due to the industrial importance of this pro-
cess and the ever-growing environmental concerns, the development
of effective, greener catalytic systems that use inexpensive oxidants is
an important challenge.
As one of the alternative approaches for tackling these problems,
ambient temperature ionic liquids (ILs) have been employed as the
promising alternative green solvents for the above reactions because
of their negligible vapor pressure, solvating ability, easy recyclability
and reusability. In the last several years, many transition metals
such as palladium [3–8], copper [9], ruthenium [10–12], manganese
Recently, we reported a copper Schiff base ligand derived from
acetylacetonate and L-Leucine that can be recycled and reused in
[bmim]BF . In continuation of our interest in exploring green oxida-
4
tion of alcohols in ILs by metal ligands, we herein report a mild and
effective procedure for the selective oxidation of alcohols using a
novel salicylic amino acid Schiff base manganese ligand (Sal–amino
2 2 4
acid–Mn)/H O system with an IL [bmim]BF as the solvent
(Scheme 1).
[13], tungsten [14,15], rhenium [16], iron [17] and vanadium [18]
2. Experimental
have been used as catalysts for alcohol oxidation with ILs as green sol-
vents [19].
2.1. General
The Schiff base transition metal complexes are attractive oxidation
catalysts because of their cheap, easy synthesis and their chemical
and thermal stability. Considerable attention has been paid to the
preparation of transition metal complexes of Schiff bases derived
Chromatographic analyses were performed on an HP-4890 gas chro-
matograph, a flame ionization detector, equipped with an HP-Innowax
capillary column. The 1H NMR measurements were carried out on an
Inova 500 MHz high-resolution liquid nuclear magnetic resonance
spectrometer. IR spectra were obtained with Nicolet Magna-IR 560
−
1
SXB and expressed in cm . Elemental analyses were performed with
a Vanio-EL analyzer and VISTA-MPS.
⁎
Corresponding author. Tel.: +86 22 27404066; fax: +86 22 27892855.
E-mail address: hanjinyu@tju.edu.cn (J. Han).
1566-7367/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2011.11.035

52
M. Rong et al. / Catalysis Communications 20 (2012) 51–53
Table 1
a
Optimization of the reaction conditions.
b
Yield (%)c
Entry
Solvent
[bmim]BF
Con (%) /Sel (%)
1
4
6
100/>98
34/95
94
12
–
2
3
4
5
6
7
8
9
1
1
1
[bmim]PF
[bmim]CF
CH CN
3
COO
23/98
3
47/100
16/100–
14/40
48 />98
43 />98
65 />98
22 />98
75 />98
58 />98
20
–
3 6
C H O
CH
3
OH
–
d
[bmim]BF
[bmim]BF
[bmim]BF
[bmim]BF
[bmim]BF
[bmim]BF
4
4
4
4
4
4
43
38
56
18
73
56
e
f
g
0
1
2
h
i
a
2
mmol benzyl alcohol, 5 mol% catalyst 1, 10 mmol 30% H
2
O
2
4
, 1 mL [bmim]BF ,
room temperature for 30 min.
b
Based on GC.
Isolated yield by flash chromatography.
c
d
10 mmol 10% aqueous NaClO as the oxidant.
e
f
10 mmol 70% t-BuOOH in 2 ml CH Cl as the oxidant.
2
2
as the oxidant.
10 mmol PhI(OAc)
2
Scheme 1. Salicylic L-Phenylalanine Schiff base manganese complex catalyzed oxida-
tion of alcohols.
g
h
i
O
was used.
was used.
2
mmol 30% H
2 2
O
6
mmol 30% H
2 2
The reaction time was 15 min.
2
.2. Chemicals
Ionic liquids and other chemicals used without further purification
As shown in Table 1, the oxidation proceeded rapidly in BF
4
-type IL,
in the present study were of analytical grade and procured from Che-
mer Chemical Co. Ltd, China and Acros Organics, respectively.
but far more slowly in acetonitrile, PF -type and CF COO-type ILs,
and, in acetone and methanol, no reaction occurred at all (Table 1,
6
3
2
.3. Synthesis of manganese amino acid Schiff base (catalyst 1)
Table 2
Oxidation of alcohols.
a
Sodium hydroxide (8 mmol) and L-Phenylalanine (8 mmol) were
stirred in ethanol (100 mL). Once the L-Phenylalanine and sodium hy-
droxide were dissolved, a further 20 mL of ethanol, containing a dis-
solved 8 mmol of salicylaldehyd, was added. After refluence for 3 h,
b
Entry
Substrate
Products
Time
(min)
Con /yield
(%)c
3 2
an aqueous (8 mmol) Mn(CH COO)2·H O (30 mL) solution was
added slowly. The color of the solution changed to brown, and the so-
lution was continuously refluxed for 10 h. Left out for one night, the
complex was settled out. The precipitate of manganese complex
was collected by filtration, washed with water, ethanol and ether, re-
spectively, and dried in a vacuum to afford complex purification
1
2
3
4
5
6
7
8
9
30
30
30
30
30
30
30
30
60
60
30
>98/94
93/86
99/93
93/88
93/89
95/87
95/88
67/62
53/48
63/56
99/62
−
1
−1
(
1
4
yield 79%). IR(KBr): 3408 cm (\OH), 1641 cm (C_N),
601 cm 1(COO\),
−
1385 cm (COO\),
37 cm (Mn\O). Anal. Calcd for C16 18NO
−1
521 cm (Mn\N),
−1
−
1
H
6
Mn: C, 51.20; H, 4.80;
N, 3.73; Mn, 14.67. Found: C, 51.20; H, 4.83; N, 3.70; Mn, 14.68.
2
.4. Representative procedure for the oxidation of alcohols
The reactions were performed at room temperature in a batch re-
actor (glass vial).
0.1 mmol) and [bmim]BF
stirred for 1 min, after which 30% aqueous H
A
mixture of alcohol (2 mmol), catalyst
(1 mL) was added in the micro-reactor
(10 mmol) was
1
(
4
2 2
O
added to the mixture. After completion of the oxidation, the mixture
was extracted with hexane (3×5 mL). The combined hexane phase
was concentrated in vacuo and monitored by GC and 1H NMR. The
residue was then purified with flash chromatography to afford corre-
sponding carboxylic acids and ketones in 48–94% yield.
3
. Results and discussion
1
1
0
1
The initial investigation was carried out using α-Phenylethanol as
the substrate to optimize the reaction conditions, and the results are
summarized in Table 1.
First, six different solvents including three kinds of ILs ([bmim]PF
bmim]BF and [bmim]CF COO) and acetonitrile, acetone, methanol
were tested with the compound 1 as the catalyst for the oxidation.
6
,
a
b
c
2
2 2
mmol alcohol, 5 mol% catalyst 1, 10 mmol 30% H O , 1 mL [bmim]BF4.
[
4
3
Conversion by GC of the crude product complex.
Isolated yield by flash chromatography.

M. Rong et al. / Catalysis Communications 20 (2012) 51–53
53
Table 3
handle, and can be recycled and reused for four runs without any sig-
nificant loss of the catalytic activity.
a
Recycling of the catalytic system for the oxidation of benzyl alcohol.
Run
Conversion (%)b
Yield (%)c
Acknowledgments
1
2
3
4
100
94
89
94
88
84
82
This research was financially supported by the Doctor Initial Fund-
ing of Yunnan Normal University (No. 01100206999903001).
88
a
2
2 2 4
mmol benzyl alcohol, 5 mol% catalyst 1, 10 mmol 30% H O , 1 mL [bmim]BF ,
room temperature for 30 min.
References
b
Conversion by GC of the crude product complex.
c
Isolated yield by flash chromatography.
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[
2 2
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(
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2 2
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(
[
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In summary, a novel, very mild and efficient protocol for the oxi-
dation of alcohols to corresponding carbonyl compounds with excel-
lent conversions using an salicylic amino acid Schiff base manganese
(
[
[
[
ligand as the catalyst has been developed in the IL [bmim]BF
4
. Most
importantly, this catalytic system is straightforward and easy to