Selective oxidation of aryl ketones to α-diketones with 4-aminoperoxybenzoic acid supported on silica gel in presence of air

Article abstract of DOI:10.1007/s00706-004-0199-1

4-Aminoperoxybenzoic acid supported on silica gel in presence of air was found to be a selective and convenient oxidant for the oxidation of methylene groups in aryl ketones to convert them to α-diketones. Springer-Verlag 2004.

Full text of DOI:10.1007/s00706-004-0199-1

Monatshefte f€ur Chemie 135, 1409–1413 (2004)
DOI 10.1007/s00706-004-0199-1
Selective Oxidation of Aryl Ketones
to a-Diketones with 4-Aminoperoxybenzoic
Acid Supported on Silica Gel
in Presence of Air
ꢀ
Dadkhoda Ghazanfari , Fariba Najafizadeh, and Fereshteh Khosravi
Department of Chemistry, Kerman Branch, Islamic Azad University,
P.O. Box 194, Kerman, Iran
Received January 14, 2004; accepted (revised) March 18, 2004
Published online August 13, 2004 # Springer-Verlag 2004
Summary. 4-Aminoperoxybenzoic acid supported on silica gel in presence of air was found to be a
selective and convenient oxidant for the oxidation of methylene groups in aryl ketones to convert them
to ꢀ-diketones.
Keywords. Aryl ketones; 4-Aminoperoxybenzoic acid; Oxidation; Silica gel; ꢀ-Diketones.
Introduction
Oxidation of a methylene group ꢀ to a carbonyl can be carried out with SeO2, N2O3,
and other oxidizing agents [1–3]. There have been few reports concerning the con-
version of unactivated ꢀ-methylene ketones to corresponding ꢀ-diketones. The
representative examples include the selenium dioxide oxidation of ketones [4, 5],
the reaction of ꢀ-bromo ketones with dimethyl sulfoxide (DMSO) in presence of
sodium carbonate [6], reaction of pyridine N-oxide with ꢀ-nosyloxy ketone inter-
mediates [7], and oxidation of enamino ketone intermediates with singlet oxygen
[3]. Although some of these reactions are carried out under mild and neutral condi-
tions [3, 7], some of them have the drawback of using either strong acidic or basic
reaction conditions [4–6] and they suffer from inherent vigorous reaction conditions
and tedious purification steps [4, 5]. Therefore, development of a more convenient
method for oxidation of ꢀ-methylene ketones to ꢀ-diketones to permit better yields
under mild, neutral reaction conditions and easier work up is required.
The use of mineral support attracted much attention because of improved selec-
tivity and reactivity associated ease of manipulation [8–13]. Peroxyacids are used
ꢀ
Corresponding author. E-mail: dadkhodaghbk@yahoo.com

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D. Ghazanfari et al.
for oxidation of organic compounds [14–19]. We have previously presented a
convenient and selective method for the oxidation of benzylic methylene compounds
to corresponding ketones by 4-aminoperoxybenzoic acid supported on silica gel in
presence of oxygen or air [20]. Herein, we wish to report that ꢀ-methylene aryl
ketones can also be oxidized to ꢀ-diketones with this supported reagent in presence
of air in high yields.
Results and Discussions
Our approach to a clean and efficient preparation of ꢀ-diketones is to make use of
4-aminoperoxybenzoic acid supported on silica gel in presence of air. 4-Amino-
peroxybenzoic acid easily prepared by the reaction of 4-aminobenzoic acid with
activated silica gel which then was oxidized to 4-aminoperoxybenzoic acid using
hydrogen peroxide as an oxidant. When the supported reagent was mixed with a
solution of p-CH3OC6H4COCH2CH3 in CH2Cl2 and the mixture was stirred at room
temperature in presence of air, the reaction was completed in 11 h in 96% yield. The
work up procedure involves mere filtration, evaporation of the solvent, and passing
the residue through a small pad of silica gel using a suitable solvent. It is noteworthy
to mention that the reaction remained incomplete in absence of air (in presence of
nitrogen), even with a higher ratio of reagent (1:3) or longer reaction time (16 h).
To assess the generality of the method, a variety of ꢀ-methylene ketones were
treated likewise to afford the corresponding ꢀ-diketones in high yield (Scheme 1,
Table 1). As shown in Table 1, various types of ꢀ-methylene aryl ketones were
oxidized efficiently to their corresponding ꢀ-diketones in 88–97% yields without
any side products (entries 1–6). It is noteworthy to mention that benzylacetone
was converted to benzoylacetone (entry 7), clearly showing that oxidation of a
benzylic methylene is easier than that of a methylene ꢀ to a carbonyl group. Other
ꢀ-methylene ketones remained intact under these reaction conditions (entries
11–12), furthermore partial oxidation of cyclic ketones (entries 8–10) to corre-
sponding lactones was observed.
In order to show chemoselectivity of this method for the oxidation of different
ꢀ-methylene ketones, we have performed a number of competitive reactions and
their results are summarized in Table 2. These results clearly show that the pre-
sented procedure is potentially applicable for the chemoselective oxidation of aryl
ketones versus other ketones.
The supported reagent is recovered in each experiment and can be reused.
Table 3 demonstrates the reusability of this supported reagent after three times
of oxidation of p-CH3OC6H4COCH2CH3 to the corresponding ꢀ-diketone. In each
experiment the supported 4-aminobenzoic acid was recovered quantitatively.
Scheme 1

Selective Oxidation of Aryl Ketones to ꢀ-Diketones
1411
Table 1. Oxidation of ꢀ-methylene ketones with 4-aminoperoxybenzoic acid supported on silica gel
in presence of air
Entry
Substrate
Time=h
Product
Yield=%a
1
2
3
4
5
6
7
C6H5COCH2C6H5
10
11
11
11
11
12
12
C6H5COCOC6H5
97
91
94
96
88
92
90
C6H5CO(CH2)2CH3
C6H5CO(CH2)3CH3
p-MeOC6H4COCH2CH3
p-MeC6H4COCH2CH3
p-ClC6H4COCH2CH3
C6H5(CH2)2COCH3
C6H5COCOCH2CH3
C6H5COCO(CH2)2CH3
p-MeOC6H4COCOCH3
p-MeC6H4COCOCH3
p-ClC6H4COCOCH3
C6H5COCH2COCH3
8
15
22
9
15
31
10
14
50
11
12
CH3(CH2)2CO(CH2)2CH3
CH3CH2COCH2CH3
15
15
CH3(CH2)2(CO)2CH2CH3
CH3(CO)2CH2CH3
–
–
a
Isolated yields
Table 2. Selective oxidation of ꢀ-methylene ketones with 4-aminoperoxybenzoic acid supported on
silica gel in presence of air
Entry
1
Substrate
Product
Yield=%a
C6H5COCH2C6H5
C6H5COCOC6H5
100
[0]
100
[0]
85
[CH3(CH2)2CO(CH2)2CH3]
p-MeOC6H4COCH2CH3
[CH3(CH2)2CO(CH2)2CH3]
C6H5COCH2C6H5
[CH3(CH2)2(CO)2CH2CH3]
p-MeOC6H4COCOCH3
[CH3(CH2)2(CO)2CH2CH3]
C6H5COCOC6H5
2
3
[15]
4
p-MeOC6H4COCH2CH3
p-MeOC6H4COCOCH3
70
[20]
a
GC yield
In summary, the present method for oxidation of ꢀ-methylene ketones has all
these advantages of using supported 4-aminoperoxybenzoic acid as a nontoxic
material, mild reaction conditions, high selectivity of the method, an easy work
up procedure, high yields, and reusability of the supported reagent.

1412
D. Ghazanfari et al.
Table 3. Reusability of 4-aminoperoxybenzoic acid supported on silica gel for oxidation of
p-CH3OC6H4COCH2CH3 to the corresponding ꢀ-diketone
Experiment
Yield=%
1st
2nd
3rd
96
88
87
Experimental
Chemical were purchased form Merck, Aldrich, and Riedel de Haen AG and were used without further
purification. IR and NMR spectra were recorded on FT-IR Unicam Mattson 1000 and Bruker AC-80
(80 MHz). All products are known compounds and they were identified by comparison of their
physical and spectral data with those of authentic samples. All yields refer to pure isolated products.
Activation of Silica Gel
Chromatographic grade silica gel (30 g, 70–230 mesh) was heated in an electric furnace at 700ꢁC for
3 h. Then it was cooled to room temperature to obtain 27.9 g of activated silica gel.
Supporting of 4-Aminobenzoic Acid on Activated Silica Gel
To a stirred solution of 6.9g of 4-aminobenzoic acid (50 mmol) in 200 cm3 of ethylacetate 27.9g of
activated silica gel were added and the mixture was refluxed under magnetic stirring for 16h. Then it
was cooled to room temperature, filtered, and the solid matter was continuously extracted with
ethylacetate in a Soxhlet apparatus for 18h. Then it was dried at 80ꢁC for 3 h to yield 33.7 g of silica
gel supported 4-aminobenzoic acid. 4-Aminobenzoic acid (5.8g, 42mmol) was supported on 27.9 g of
activated silica gel.
Oxidation of Silica Gel Supported 4-Aminobenzoic Acid
to the Corresponding Peroxyacid
Silica gel supported 4-aminobenzoic acid (33.7 g) containing 5.8g of 4-aminobenzoic acid was added
to a stirred solution of a commercial 30% solution of H2O2 at room temperature and the reaction
mixture was stirred for 8 h. Then it was filtered, washed with distilled water (5ꢂ20cm3), and dried over
anhydrous CaCl2 at room temperature in vacuum (40 torr) to obtain 34.3 g of silica gel supported
4-aminoperoxybenzoic acid.
General Procedure for the Oxidation of ꢀ-Methylene Ketones
to the Corresponding ꢀ-Diketones
ꢀ-Methylen ketones (20 mmol) were dissolved in 100cm3 of CH2Cl2, then 33g of silica gel supported
4-aminoperoxybenzoic acid (containing 40mmol of 4-aminoperoxybenzoic acid) were added and the
mixture was stirred at room temperature for the indicated time during which air was bubbled into
the solution at a rate of 50cm3 minꢃ1. Progress of the reaction was monitored by TLC (petroleum
ether:ethylacetate ¼ 3:1). Then the reaction mixture was filtered to recover the solid material. The solid
material was washed with 2ꢂ10cm3 of CH2Cl2. The solvent was evaporated and the product purified
by column chromatography using silica gel. The pure products were obtained in yields indicated in
Table 1.

Selective Oxidation of Aryl Ketones to ꢀ-Diketones
1413
Reusability of Silica Gel Supported 4-Aminoperoxybenzoic Acid
After using silica gel supported 4-aminoperoxybenzoic acid as oxidant for the oxidation of ꢀ-methy-
lene ketones, it can be reconverted to the corresponding peroxyacid by treatment with hydrogen
peroxide. Then it was reused for the oxidation of p-CH3OC6H4COCH2CH3 to the corresponding
ꢀ-diketone. The second use of this reagent for the oxidation of p-CH3OC6H4COCH2CH3 to the
corresponding ꢀ-diketone showed about 8% decrease in reactivity. However, the third use showed
no further decrease in the reaction yields (cf. Table 3).
Acknowledgement
Financial support from the Research Council of Kerman Branch of Islamic Azad University is grate-
fully acknowledged.
References
[1] Hudlicky (1990) Oxidation in Organic Chemistry. American Chemical Society, Washington
[2] Wasserman HH, Ives JL (1978) J Org Chem 5238
[3] Wasserman HH, Ives JL (1985) J Org Chem 50: 3573
[4] Rabjohn N (1976) Org React 24: 261
[5] Corey EJ, Schaefer P (1960) J Am Chem Soc 82: 918
[6] Baur DP, Macomber RS (1975) J Org Chem 40: 1990
[7] Jong CL, Hong PJ (2002) Tetrahedron Lett 43: 5661
[8] Baogh M, Laszlo P (1993) Organic Chemistry Using Clays. Springer, Berlin
[9] Clark JH (1994) Catalysis of Organic Reactions by Supported Inorganic Reagents. VCH,
New York
[10] Sanjay B, Subrata KC (2003) Tetrahedron 59: 3493
[11] Mengos DMP, Baghusst DR (1991) Chem Soc Rev 20: 1
[12] Varma RS, Dahiya R (1997) Tetrahedron Lett 38: 2043
[13] Hashemi MM, Ghazanfari D, Akhbari M (2004) Monatsh Chem (accepted)
[14] Dawei M, Chengfeng X, Hongqi T (1999) Tetrahedron Lett 40: 8915
[15] Krow GR (1993) Org React 43: 251
[16] Mori K, Ueda H (1981) Tetrahedron Lett 461
[17] Hirsch JA, Truc VC (1986) J Org Chem 51: 2218
[18] Querci C, Ricci M (1990) Tetrahedron Lett 31: 1779
[19] Ruchnovsky SD, Vaidyanathan R (1999) J Org Chem 64: 310
[20] Hashemi MM, Ghazanfari D, Karimi-Jaberi Z (2004) Monatsh Chem 135: 185