Copper(II)-Catalyzed Oxidation of Alcohols to Carbonyl Compounds with Hydrogen Peroxide

Article abstract of DOI:10.1002/ejoc.200300324

Copper(II) complex 1 efficiently catalyses the oxidation of alcohols to the corresponding carboxylic acid analogues and ketones in the presence of H₂₂ in high yields. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

Full text of DOI:10.1002/ejoc.200300324

SHORT COMMUNICATION
Copper(II)-Catalyzed Oxidation of Alcohols to Carbonyl Compounds with
Hydrogen Peroxide
Subbarayan Velusamy[a] and Tharmalingam Punniyamurthy*[a]
Keywords: Oxidation / Alcohols / Catalysts / Copper() complexes / Hydrogen peroxide
Copper(II) complex 1 efficiently catalyses the oxidation of al-
cohols to the corresponding carboxylic acid analogues and
ketones in the presence of H2O2 in high yields.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
The selective oxidation of alcohols to the corresponding
carbonyl compounds is a frequently used functional trans-
formation in organic synthesis and numerous methods have
been developed.[1] However, most of these traditional oxi-
dations usually require stoichiometric amounts of the re-
agents and the purification of the reaction products is often
demanding. To circumvent these problems, a number of
catalytic oxidation processes based upon the combination
of metal salts and atom-efficient oxidants, such as molecu-
lar oxygen[2Ϫ4] or H2O2,[5] have been recently devised. Cop-
per() salts have been shown to catalyze the oxidation of
alcohols to aldehydes and ketones with molecular oxygen.[3]
Attention has also been focused on the development of
functional models of galactose oxidase (GO) and their ap-
plication for the aerobic oxidation of alcohols to alde-
hydes.[4] We now report the first example of copper-cata-
lyzed oxidation of alcohols to the corresponding carboxylic
acid analogues and ketones with H2O2 as the source of oxy-
gen (Scheme 1). This protocol is simple, clean and functions
in the absence of additives.
Scheme 1
to a 2:1 mixture of 4-chlorobenzaldehyde and 4-chloroben-
zoic acid (3b) in 30% yield in the presence of 1 mol % of 1
and 10 equiv. of H2O2. Alternatively, the reaction could be
driven to completion with 92% yield of 3b by heating at 80
°C for 4.5 h (Table 1, Entry 2). Control experiments without
complex 1 under the same reaction conditions showed no
oxidation. Similarly, no significant oxidation was observed
with molecular oxygen as a terminal oxidant. Cu(OAc)2
and CuII(salen) were also examined as catalysts for the oxi-
dation of 2b under the same reaction conditions. The reac-
tion of the latter afforded 65% of 3b, while the process of
the former was less effective and provided a 1:5 mixture of
3b and 4-chlorobenzaldehyde in 30% yield.
Results and Discussion
To evaluate the scope of this protocol, the oxidation of
Reaction of ethylenediamine with 2 equiv. of salicylal- other aromatic and aliphatic alcohols 2a and 2cϪn was
dehyde followed by NaBH4 reduction provided salen-H4 further examined with complex 1 (Table 1). As above, pri-
that was further treated with Cu(OAc)2 to afford the com- mary alcohols 2a and 2cϪh were consistently oxidized to
plex 1 as a green powder. In the presence of a catalytic give the corresponding carboxylic acids 3a and 3cϪj in the
amount of 1, the oxidation of 4-chlorobenzyl alcohol (2b) presence of 10Ϫ15 equiv. of H2O2. Secondary alcohols
was first examined with H2O2 under ambient conditions in 2kϪn were oxidized faster and could be converted into the
acetonitrile. We were pleased to find that 2b was oxidized corresponding ketones with 5 equiv. of H2O2. Substrates
2bϪh having both electron-donating as well as electron-
[a]
withdrawing substituents were compatible with this system.
The oxidations of cinnamyl alcohol and benzoin were also
examined, however, those reactions mainly afforded benzoic
acid due to cleavage of the carbonϪcarbon bonds.
Department of Chemistry, Indian Institute of Technology
Guwahati,
Guwahati 781039, India
Fax: (internat.) ϩ 91-361/2690762
E-mail: tpunni@iitg.ernet.in
Eur. J. Org. Chem. 2003, 3913Ϫ3915
DOI: 10.1002/ejoc.200300324
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3913

S. Velusamy, T. Punniyamurthy
SHORT COMMUNICATION
Table 1. Oxidation of alcohols with complex 1 in the presence of H2O2
[a]
[b]
Catalyst 1 (1 mol %), alcohol (2 mmol), 30% H2O2 (10Ϫ30 mmol) and acetonitrile (2 mL) were stirred at ca. 80 °C. Isolated yield.
[c]
GC yield.
3914
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2003, 3913Ϫ3915

Copper(II)-Catalyzed Oxidation of Alcohols
SHORT COMMUNICATION
Acknowledgments
Conclusion
This work was supported by the Department of Science and Tech-
nology (Sanction No. SR/S1/OC-092002), New Delhi and the
Council of Scientific and Industrial Research [Sanction No.
01(1804)/02/EMR-II], New Delhi.
An efficient catalytic oxidation procedure that allows the
transformation of simple alcohols into carboxylic acids and
ketones has been described.
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Preparation of Complex 1: The reaction of salicylaldehyde (122 mg,
1 mmol) with ethylenediamine (30 mg, 0.5 mmol) in methanol (5
mL) afforded salen-H2 as a lemon-yellow powder in 81% (217 mg),
which was further treated with NaBH4 (1 mmol, 37.83 mg) in meth-
anol (5 mL) at ambient temperature for 2 h. Removal of the solvent
in a rotary evaporator followed by treatment with water afforded
salen-H4 as a colorless powder in 72% (162 mg) yield. 1H NMR
(CDCl3, 90 MHz): δ ϭ 6.7Ϫ7.2 (m, 8 H), 3.9 (s, 4 H), 2.85 (s, 4 H)
ppm. IR (KBr): ν˜ ϭ 3288, 2909, 2868, 2827, 1608, 1565, 1398,
1260, 999 cmϪ1. C16H20N2O2 (272.3): calcd. C 70.56, H 7.40, N
10.29; found C 70.59, H 7.38, N 10.25. The salen-H4 (150 mg,
0.55 mmol) was then treated with Cu(OAc)2 (200 mg, 1 mmol) in
methanol (10 mL) at 50 °C for 2.5 h under nitrogen. Evaporation
of the solvent in a rotary evaporator gave a powder which was
purified on silica gel (60Ϫ120 mesh) column chromatography using
EtOAc and MeOH (15:5) as a eluent to afford complex 1 as a green
powder in 70% yield. UV/Vis (CH3CN): λmax ϭ 328, 584 nm. FAB-
MS: m/z ϭ 334 [Mϩ]. C16H18CuN2O2 (333.9): calcd. C 57.55, H
5.43, Cu 19.03, N 8.39; found C 57.51, H 5.42, Cu 19.00, N 8.40.
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Typical Procedure for the Oxidaiton: Alcohol (2 mmol), complex 1
(1 mol %) and 30% H2O2 (10 mmol, 2.26 mL) were dissolved in
acetonitrile (2 mL) and the homogeneous solution was heated at
ca. 80 °C under atmospheric oxygen for the appropriate time. After
completion of the reaction, the reaction mixture was treated with
dimethyl sulfide (ca. 50 µL) at room temperature and the aqueous
acetonitrile was removed in a rotary evaporator under reduced
pressure. The residue was treated with ethyl acetate and the insol-
uble copper salt was separated. The organic solution was concen-
trated and passed through a short pad of silica gel (60Ϫ120 mesh)
using ethyl acetate and hexane to afford the analytically pure com-
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and melting point (solid) and by comparison with authentic
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Received May 27, 2003
[5]
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