Microwave Chemistry tips Microwave Chemistry FAQ Dariusz Bogdall's Microwave Syntheses Miscellaneous information on clays MW-chem: Preparation of alkyl azides from alkyl bromides MW-chem: Reductive amination with NaBH4 MW-chem: Reduction of carbonyl compounds with NaBH4 MW-chem: Nitroalkene preparation from benzaldehydes (PDF) MW-chem: Benzaldehydes from alcohols using MnO2/Silica (PDF) MW-chem: Preparation of beta-nitrostyrenes from styrenes MW-chem: An introductory overview from New Scientist by Gavin Whittaker MW-Chem: Catalytic Transfer Hydrogenation MW-Chem: Ethers from alcohols and alkyl halides MW-chem: Theoretical and mechanistical background (PDF) MW-chem: Organic Chemistry Review (PDF) MW-chem: Wolff-Kishner reduction of ketones to hydrocarbons (PDF) MW-chem: Oxidation of Alcohols to Ketones MW-chem: High-yielding Azidation of Primary and Secondary Tosylates MW-chem: Solvent-Free Nucleophilic Aromatic Substitution of Inactive Aryl Halides
The oxidation of benzyl alcohol is representative of the general procedure employed. MnO2 'doped' silica (1.25 g, 5 mmol of MnO2 on silica gel, Selecto Scientific, 230-400 mesh with large surface area of 600m2/g) is thoroughly mixed with benzyl alcohol (108 mg, 1 mmol) and the material is placed in an alumina bath inside the MW oven and irradiated for 20 seconds. Upon completion of the reaction, monitored on TLC (hexane: AcOEt, 10:1), the product is extracted into methylene chloride, solvent removed and the residue passed through a bed of silica gel (4 cm) to afford exclusively benzaldehyde. The overoxidation to carboxylic acid is not observed. The same reaction could be completed in 2 h at a comparable temperature of 55 °C in an oil bath. CAUTION: In view of the hazards associated with an active oxidant due caution is recommended for its use at elevated temperatures; the localized temperature may be much higher than the bulk temperature of the bath in the microwave oven and we suggest that the oven be operated at a lower power and for a shorter duration of time.
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