A novel and selective catalytic oxidation of hydrocarbons to ketones using chloramine-T/O2/Fe(TPP)Cl system

Article abstract of DOI:10.1016/j.tetlet.2005.09.055

A novel and highly selective oxidation of hydrocarbons to the corresponding ketones using the Fe(TPP)Cl/chloramine-T/O₂ system was described.

Full text of DOI:10.1016/j.tetlet.2005.09.055

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 8013–8015
A novel and selective catalytic oxidation of hydrocarbons to
ketones using chloramine-T/O2/Fe(TPP)Cl system
Shi-Jun Li and Yan-Guang Wang*
Department of Chemistry, Zhejiang University, Hangzhou 310027, PR China
Received 28 July 2005; revised 9 September 2005; accepted 12 September 2005
Available online 26 September 2005
Abstract—A novel and highly selective oxidation of hydrocarbons to the corresponding ketones using the Fe(TPP)Cl/chloramine-T/O2
system was described.
Ó 2005 Elsevier Ltd. All rights reserved.
Catalytic oxidation of hydrocarbons to alcohols or car-
bonyls is an important transformation in both organic
synthetic chemistry and industry.1 A number of oxygen-
ation systems composed of a variety of oxygen donors
such as Bu4NHSO5,2 PhI(OAc)2,3 PhIO,4 NaOCl,5
H2O2,6 pyridine N-oxide7 and periodates,8 in combina-
tion with different metalloporphyrin catalysts have been
employed for the oxidation of hydrocarbons. Metallo-
porphyrins promoted oxidations of alkanes with oxygen
and acetaldehyde have also been reported.9 However,
these metalloporphyrins-catalyzed methods usually give
the mixture of alcohols and carbonyls. In addition, most
of the other traditional metallic and metal-free organic
catalysts used for oxidation of hydrocarbons could not
yield single product, neat alcohols or carbonyls.10
Recently, we found that chloramine-T combined with
air or oxygen as an oxidant could selectively convert
hydrocarbons to ketones using metalloporphyrins as a
catalyst at room temperature, and no alcohol was
detected in this oxidation system. To the best of our best
knowledge, it is the first example for oxidation of
alkanes using chloramine-T. Herein, we disclose the
results of this research.
NHTs
1 (not found)
Chloramine-T
O
Fe(TPP)Cl
CH3CN
2
R
R
R
R
R
R
R
NH
N
N
HN
R
TPP:
R=H
TDCPP: R=Cl
Scheme 1. Oxidation of tetralin.
well known that chloramine-T is not only an aziridin-
ation and amidation reagent, but also an efficient oxi-
dant in many reactions.12
Originally, we intended to amidate tetralin with chlor-
amine-T as a nitrene source via metalloporphyrin cata-
lyzed aziridination of alkenes and amidation of satu-
rated C–H bonds.11 However, when the Fe complex of
meso-tetrakisphenyl porphyrin (TPP) was used as the
catalyst, an oxidation product tetralone (2) instead of
the amidized product 1 was obtained (Scheme 1). It is
Encouraged by this result, we examined the catalytic
activity of several metalloporphyrins derived from
TPP and meso-tetrakis(2,6-dichloro-phenyl)porphyrin
(TDCPP) for the aerobic oxidation of tetralin using
chloramine-T.13 As shown in Table 1, the catalytic activ-
ity of porphyrin complexes was strongly dependent
upon both central metal and ligands. The Fe and Mn
complexes with porphyrin ligands showed better
catalytic activity (Table 1, entries 2, 3 and 7–11) than
*
Corresponding author. Tel.: +86 571 8795 1512; fax: +86 571 8795
1512; e-mail: orgwyg@zju.edu.cn
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.09.055

8014
S.-J. Li, Y.-G. Wang / Tetrahedron Letters 46 (2005) 8013–8015
Table 1. Oxidation of tetralin catalyzed by different metalloporphyrins
Using the optimized reaction conditions, the catalytic
oxidation of various hydrocarbons was investigated.
As shown in Table 3, tetralin and other aryl-substituted
alkanes were oxidized into the corresponding aromatic
ketones in good conversions (Table 3, entries 1–7, 11
and 12). The oxidation of toluene gave benzaldehyde
(26% conversion) along with a small amount of benzoic
acid (Table 3, entry 8). The oxidation of cyclohexene
offered cycohexenone in moderate conversion (52%)
(Table 3, entry 9). Although inactive cyclohexane only
gave 13% conversion, the result had a significant
improvement compared with the industrial process
(about 3–7% conversion).14 It was noteworthy that no
alcohol was detected in all cases.
with chloramine-T under aira
Entry
Catalyst
Solvent
Yield (%)b
1
2
3
4
5
6
7
8
None
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH2Cl2
THF
5
77
81
43
40
57
50
58
9
Mn(TPP)Cl
Fe(TPP)Cl
Co(TPP)
Ni(TPP)
Ru(TPP)CO
Mn(TDCPP)Cl
Fe(TDCPP)Cl
Fe(TPP)Cl
Fe(TPP)Cl
Fe(TPP)Cl
9
10
11
16
38
DMSO
a Tetralin (2 mmol) was oxidized by chloramine-T (1 mmol) and air
(1 atm) in the presence of metalloporphyrins (5 mol %) in solvent
(5 mL) at room temperature for 24 h.
b Yields were determined by GC analyses based on tetralin used.
Table 3. Oxidation of different hydrocarbons using the chloramine-
T/O2/Fe(TPP)Cl systema
Entry
Substrate
Product
Yield (%)
the corresponding Co, Ni and Ru complexes (Table 1,
entries 4–6). The complex Fe(TPP)Cl in acetonitrile
was found to be the most effective catalyst (Table 1,
entry 3). The Fe and Mn complexes of chlorinated por-
phyrin ligand had lower catalytic activity due to their
slight solubility in acetonitrile. The solvent effects were
also investigated. Acetonitrile was superior to other sol-
vents due to its good solubility to chloramine-T.
O
83b,d
87c
1
O
2
67c
O
3
4
63b
78b
Cl
The reaction conditions are further optimized, and the
results were summarized in Table 2. Both chloramine-
T (Table 2, entry 1) and air or molecular oxygen (Table
2, entry 2) were found to be necessary to this oxidation
system. Increasing the amount of chloramine-T from 0.2
to 0.5 equiv could increase the yields (Table 2, entries 3–
6), but further increase led to a significant reduction in
the yields (Table 2, entries 7–9). The amount of catalyst
was also examined. Fe(TPP)Cl (5–10 mol %) was found
to be the most effective (Table 2, entries 5, 10 and 11).
The temperature had no obvious effect on the reaction
(Table 2, entries 5 and 12).
Cl
O
O
5
6
72b
COOMe
COOMe
O
84b
86b
O
7
8
Table 2. Oxidation of tetralin with different amounts of Fe(TPP)Cl
and chloramine-Ta
PhCH3
PhCHO
PhCO2H
23c
3c
Entry
Chloramine-T amount
(mol equiv)
Fe(TPP)Cl amount
(mol equiv)
Yieldb
(%)
9
52c
13c
62b
O
1
2
3
4
5
6
7
8
0
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.01
0.10
0.05
3
11
42
69
81
84
72
68
54
55
87
82
0.5c
0.2
0.4
0.5
0.5d
0.6
0.75
1.0
0.5
0.5
0.5e
10
11
O
O
NMe2
NMe2
9
71b
10
11
12
12
O
Me2N
Me2N
a Typically tetralin (2 mmol) was oxidized with different amounts of
chloramine-T and Fe(TPP)Cl under air atmosphere (1 atm) in aceto-
nitrile (5 mL) at room temperature for 24 h.
b Yields were determined by GC analyses based on tetralin used.
c Reaction under N2 atmosphere.
d Reaction under O2 atmosphere.
e Reaction at 80 °C.
a Typically reactions were carried out with substrate (2 mmol), chlo-
ramine-T (1 mmol) and Fe(TPP)Cl (5 mol %) in acetonitrile (5 mL)
under O2 atmosphere (1 atm) at room temperature for 24 h.
b Isolated yields.
c Yields was determined by GC analyses based on substrates used.
d Reaction for 48 h.

S.-J. Li, Y.-G. Wang / Tetrahedron Letters 46 (2005) 8013–8015
8015
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Chloramine-T(0.5 equiv)
Fe(TPP)Cl (0.05 equiv)
OH
O
O
2 (1 atm), CH3CN, rt
98%
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Acknowledgements
Authors would like to thank the National Natural Sci-
ence Foundation of China (No. 20272051) as well as
the Teaching and Research Award Program for Out-
standing Young Teachers in Higher Education Institu-
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