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6. Conclusions
5 (a) K. B. Sharpless and T. R. Verhoeven, Aldrichim. Acta., 1979, 12,
63; (b) R. A. Sheldon, In The Chemistry of Peroxides, ed. S. Patai,
Wiley, New York, 1983.
This is the first report of direct microwave assisted oxidation
of alkyl aromatics with aqueous TBHP without involving any
metal reagent. This oxidation of alkyl substituted aromatics to
ketones, mono-anddicarboxylic acids is also an environmentally
friendly green chemical process. It is free of heavy metals with
no added organic solvent. The only solvent involved is water12
that comes with TBHP. A tiny amount of ionic liquid which
is also viewed as a “green” reagent13,14 enhanced the oxidation
efficiency. Finally, focused microwave is also a “green” energy
source as compared to conventional heating.15–17
The oxidation of xylene isomers to the corresponding phthalic
acids opens up a green alternative to the synthesis of these
economically important fine chemicals. Of course, in order to
be commercially viable, the yields will need to be improved.
Using a continuous flow reactor18–20 may be a possibility. Under
a continuous flow system, the precipitated diacid can be filtered
off and the solution recycled back to the microwave reaction.
6 (a) C. O. Kappe, Chem. Soc. Rev., 2008, 37, 1127; (b) V. Polshettiwar
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H. Tashiro, G. K. S. Prakash and G. A. Olah, Chem. Commun., 2005,
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7 The term was first coined by Bose: A. K. Bose, B. K. Banik,
N. Lavolinskaia, M. Jayaraman and M. S. Manhas, Chemtech, 1997,
27, 18.
8 (a) T. Katsuki and V. Martin, in Organic Reactions, ed. L. A. Paquette,
1996, 48, 1-299; (b) R. M. Hanson and K. B Sharpless, J. Org. Chem.,
1986, 51, 1922.
9 (a) S. V. Ley, A. G. Leach and R. I. Storer, J. Chem. Soc., Perkin Trans.
1, 2001, 358; (b) N. E. Leadbeater and H. M. Torenius, J. Org. Chem.,
2002, 67, 3145; (c) N. E. Leadbeater, H. M. Torenius and H. Tye,
Tetrahedron, 2003, 59, 2253; (d) Y. Peng and G. Song, Tetrahedron
Lett., 2004, 45, 5313–5316; (e) Y.-H. Yen and Y.-H. Chu, Tetrahedron
Lett., 2004, 45, 8137–8140; (f) M.-C. Liao, X.-H. Duan and Y.-M.
Liang, Tetrahedron Lett., 2005, 46, 3469–3472; (g) A. Shaabani and
A. Rahmati, Synth. Commun., 2006, 36, 65–70; (h) Z.-Z. Zhou, F.-Q.
Ji, M. Cao and G.-F. Yang, Adv. Synth. Catal., 2006, 348, 1826–1830.
10 (a) R. K. Arvela and N. E. Leadbeater, Org. Lett., 2005, 7, 21012101
and references therein; (b) P. Appukkuttan, M. Husain, R. K. Gupta,
V. S. Parmar and E. Van der Eycken, Synlett, 2006, 1491–1496;
(c) G. S. Vanier, Synlett, 2007, 131–135; (d) M. Hosseini, N. Stiasni,
V. Barbieri and C. O. Kappe, J. Org. Chem., 2007, 72, 1417–1424.
11 Homogeneous Catalysis, G. W. Parshall and S. D. Ittel, Wiley,
New York, 2nd edn, 1992.
Acknowledgements
This work was supported by Faculty Research Grants of Hong
Kong Baptist University (FGR/03-04/II-36 and FRG/05-
06/II-32) and a CERG Grant from the Hong Kong Research
Grant Council (HKBU 201006). We thank Professor Tak-hang
Chan of the Hong Kong Polytechnic University for the gift of
ionic liquid samples.
12 (a) C.-J. Li and L. Chen, Chem. Soc. Rev., 2006, 35, 68–82; (b) S.
Narayan, S. Muldoon, M. G. Finn, V. V. Fokin, H. C. Kolb and K. B.
Sharpless, Angew. Chem., Int. Ed., 2005, 44, 3275; (c) C. I. Herreras,
X. Yao, Z. Li and C.-J. Li, Chem. Rev., 2007, 107, 2546–2562.
13 U. M. Lindstro¨m and F. Andersson, Angew. Chem., Int. Ed., 2006,
45, 548–551.
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