An efficient oxidation of benzylic and alicylic

compounds with water-soluble copper catalysts

in t-butyl hydroperoxide at room temperature

Ateeq Rahman a,*, S. M. Al Zahrani a, Abdel Aziz Nait Ajjou b

a College of Engineering, Department of Chemical Engineering, King Saud University, Riaydh-11421, Saudi Arabiab Department of Chemistry and Biochemistry, University of Moncton, Moncton, New Brunswick, E1A3E9, Canada

Received 10 September 2010

Abstract

The water soluble catalytic system comprising of CuCl2 and 2,2-biquinoline-4,4-dicarboxylic acid dipotassium salt (BQC) is

highly efficient organic metallic catalysts for selective oxidation of benzylic and alicyclic compounds to the corresponding ketones,

ex: indan to indanone, ethyl benzene to acetophenone.

# 2010 Ateeq Rahman. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Keywords: Oxidation; Bibenzyl; Allyl benzene; Indan; 2-Biquinoline-4,4-dicarboxylic acid dipotassium salt (BQC); Tetrabutyl ammonium

bromide (TBAC)

The Oxidation of benzylic and alicylic compounds to the corresponding carbonyl functionality laid foundation of

many important industrial chemical processes starting from academic interest. Traditionally, stoichiometric and even

over-stoichiometric amounts of metal salts or complexes, recovery of catalyst and recycling are used for such oxidations

[1]. Several methods are available in literature to convert benzylic compounds to ketones employing metals such as

sodium bismuthate in acetic acid, and bismuth with pyridine, and picolinic acid [2]. Molybdenum (VI)-peroxo complex

[3], Mn salen complexes [4], Mn (III) porphyrins in ionic liquid [5], Mn (III) porphyrin (H2O2) [6], barium [7], N-

hydroxyphthalimide/ cobalt(II) [8], MCPBA, oxygen and molecular bromine at 758C with N-hydroxypthalimide as

oxidant [9]. J. Einhorn [28] reported aerobic oxidation of indan with Cu complex in acetonitrile with 62% conversion at

35 8C. Often many homogeneous systems which are applied for this transformation require tedious work ups. Aqueous

organometallic catalysis has recently received attention as another useful routes to overcome these limitations [1,2].

Heterogeneous catalysts have been developed for the oxidation of benzylic compounds to ketones with cobalt alkyl

phosphonate on silica [10], Ru exchanged K10 [11], ZnO [12], Fe/MgO [13], Co/Zeolite [14]. Hock [15] reported

oxidation of indan with Cu catalysts with isobutyraldehyde as co oxidant. The catalytic activity of zeolite-encapsulated

complexes of copper like copper acetate monohydrate [16], copper-phthalocyanines [17], and copper salens [18,19] for

the selective oxidation of alkalies like methane, propane, aliphatic and aromatic hydrocarbons. The choice of water

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Chinese Chemical Letters 22 (2011) 691–693

* Corresponding author.

E-mail address: ateeqr786@yahoo.com (A. Rahman).

1001-8417/$ – see front matter # 2010 Ateeq Rahman. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

doi:10.1016/j.cclet.2010.12.035

soluble Cu complex by author over Cu (TPIP)2 was linked to the observation by Murahashi et al. [20] who reported use of

Cu (II) salts for the conversion of indane to indanone in the absence or presence of external ligand crown ethers, together

with the formation of minor amounts of indanol [20]. A useful method is developed for the direct oxidation of indan with

water Cu complex in TBHP in this report.

1. Experimental

1.1. Typical procedure for the oxidation of indan

In a 25 mL round-bottomed flask charged with distilled water (5 mL), CuCl2, 2H2O (0.02 mmol), Na2CO3 (1

mmol), and BQC (0.02 mmol), and TBAC (0.06 mmol) were added. A green-blue solution thus formed was stirred for

5 min then the substrate (2 mmol) was introduced followed by aqueous 70% TBHP (6 mmol). The purple mixture was

allowed to stir for 17 h at room temperature. At the end of the reaction, a light purple mixture has resulted. The mixture

of insoluble products and substrate, were extracted three times with ethyl acetate (20 mL). After separation, the

organic phase was dried over (MgSO4), later filtered and the filterate was evaporated under vacuum to dryness

resulting into a solid which was further purified and found to match with authentic sample of 1-indanone by IR and

HPlC by comparison with standard sample. Similar experimental procedure was adopted for other substrates reported

in this report (Tables 1 and 2).

Cu complex (0.025 g) and TBAC, BQC, and Na2CO3 of known amount were stirred in 6 mmol of TBHP at room

temperature for 17 h. At the end of the reaction time the extent of decomposition of TBHP was estimated by standard

iodimetric method.

2. Results and discussion

The article demonstrates that the reaction is radical in nature, and the alcohols are not the primary products while

hydroperoxides are formed, which are decomposed to ketones. Recently Nait Ajjou and co-worker [1] reported oxidation

of alcohols to ketones in water solube Cu complex. The water soluble catalyst which is easily separated from the reaction

products by extracting with organic solvent like ethyl acetate. Indan was oxidized to 1-indanone with maximum

conversion and 100% selectivity. Ethyl benzene was selectively oxidized to acetophenone. Murahashi et al. [20] reported

oxidation of indan to hydroperoxide intermediate in the presence of Cu(TPIP)2, CuCl and crown ether, both at room

temperature and 70 8C. In all the cases the presence of hydroperoxide was established, [7]. In view of the work of

Murahashi et al. [20]. The authors designed the oxidation of indan to 1-indanone in the presence of water soluble copper

complex and TBAC, BQC ligand and Na2CO3 at room temperature. Tetralin was oxidized to 1-tetralone under similar

A. Rahman et al. / Chinese Chemical Letters 22 (2011) 691–693692

Table 1

Oxidation of alicylic and benzylic compounds to their corresponding ketones with CuCl2/BQC and Na2CO3, TBAC with 1 equivalent TBHP 70% for

17 h.

S.No Substrate Product Results conv %

1 Indan Indanone 98%

2 Ethyl benzene Acetophenone 100%

3 Tetralin 1-Tetralone 97%

4 Diphenyl methane Benzophenone 95%

5 Fluorene Fluorenone 95%

Table 2

Oxidation of indan to 1-indanone with CuCl2/BQC complex with various equivalent of TBHP 70%, 17 h.

S.No Equivalent Temperature Results conv %

1 1 RT 98

2 4 RT 85

3 4 80 8C –

4 4 55–60 8C –

5 2 60–65 8C –

conditions with 98% conversion, and diphenyl methane to benzophenone in 95%. While the oxidation of fluorene in these

conditions did not occur the solvent had to be changed to dichloromethane and resulted in 95% fluorenone. There is no

leaching of Cu catalyst during the extraction of aqueous layer. In the 2nd run the aqueous layer of Cu catalyst was tested

with the addition of indan and TBHP. Only starting material was recovered.

3. Conclusions

The water soluble Cu complex system comprising of 2,2-biquinoline-4,4-dicarboxylic acid potassium slat (BQC),

(TBAC), Na2CO3, is found to be highly efficient system for the selective oxidation of benzylic and alicylic

hydrocarbons to their corresponding ketones, with aqueous t-butyl hydroperoxide under normal conditions at room

temperature. These experiments showed that the Cu complex system is very effective for the oxidation of indan, ethyl

benzene, and benzylic compounds to their corresponding ketones. In the light of these results, and considering

environmental factors water as green solvent is largely advantageous in our methodology which is economical and

environmentally friendly system.

Acknowledgments

Authors acknowledge NSERC of Canada and Department of Chemical Engineering, King Saud University, Riyadh,

Kingdom of Saudi Arabia for their support.

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