Molecular iodine was used to catalyse the oxidation of several benzylic alcohols to the corresponding ketones under the microwave-irradiated method, and the role of iodine was explored.
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The acceleration of reaction rate under microwave irradiation method in open vessels was studied extensively by Bose and Manhas. For some examples, see: (a) BoseA.K., ManhasM. S., GhoshM., RajuV. S., TabeiK., and Urbanczyk-LipkowskaZ., Heterocycles, 1990, 30, 741.
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BanikB.K., BarakatK. J., WagleD. R., ManhasM. S., and BoseA. K., J. Org. Chem., 1999, 64, 5746. For some examples of various microwave-induced organic reaction in open vessels from other groups, see: (a) A. Boruah, B. Baruah, D. Prajapati, J.S. Sandhu, Tetrahedron Lett. 1997, 38, 4267.
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The kinetics of the oxidation of benzhydrols to benzophenone by iodine in alkaline methanol was reported, see: OgataY., and NaguraK., J. Org. Chem., 1974, 39, 3680.
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We thank a reviewer for suggesting the consideration of the hypoiodite path.
38.
It is convenient to irradiate the reaction mixtures under microwave periodically for 1- min intervals. The on–off cycle of the domestic microwave oven can be used to keep the temperature of the reaction mixture under 130° C. For better temperature control the use of a heat sink as described in the previous publications11 is recommended. The open glass-system used in this study is very convenient, safe and it can prevent explosions due to rapid rise of pressure and temperature.
39.
The compounds reported here gave satisfactory m.p., spectral data, and were compared with known authentic samples available from Aldrich chemical company. For the synthesis of 13-dibenzofluorenone (entry 2) see: HarveyR.G., PatakiJ., CortezC., Di RaddoP., and YangC., J. Org. Chem.1991, 56, 1210.
40.
Synthesis of these types of benzylic ketones was reported earlier by the oxidation of benzylic methylenes in alkali and acid media. For example see: (a) HarveyR. G., Abu-shqaraE., and YangC., J. Org. Chem.1992, 57, 6313.
41.
BanikB.K., VenkatramanM. S., MukhopadhyayC., and BeckerF. F., Tetrahedron Lett., 1998, 39, 7243 and references cited therein.
