Facile and Selective Oxidation of Benzylic Alcohols to Their Corresponding Carbonyl Compounds with Sodium Nitrate in the Presence of Brønsted Acidic Ionic Liquids

Abstract

A chemoselective and effective procedure for the conversion of benzylic and allylic alcohols into the corresponding ­carbonyl compounds using sodium nitrate-3-methylimidazolinium hydrogensulfate is reported.

Brønsted acidic ionic liquids - oxidation - alcohols - aldehydes - ketones

References and Notes

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<A NAME="RG00407ST-21">21</A>

Preparation of [Hmim]⁺HSO₄ ^-: 1-methylimidazole (0.82 g, 0.01 mol) was placed in a two-necked flask with stirrer and was cooled to 0 °C. MeCN (10 mL) was added and then H₂SO₄ (0.98 g, 0.01 mol) was added slowly with stirring. The mixture was stirred for 30 min and the MeCN was removed by simple decanting.

<A NAME="RG00407ST-22">22</A>

General procedure: In a mortar a mixture of benzylic alcohol (1.0 mmol), sodium nitrate (0.085 g, 1.0 mmol), and [Hmim]⁺HSO₄ ^- (0.25 mmol) was ground with a pestle. The reaction times and temperatures are shown in Table [1] . After completion of the reaction (monitored by TLC, EtOAc-cyclohexane, 25:75), the mixture was cooled to r.t., extracted into Et₂O and washed with H₂O. The organic layer was dried over Na₂SO₄ and evaporated under reduced pressure. Purification of the residue using flash column chromatography (silica gel, EtOAc-cyclohexane, 20:80) provided the pure carbonyl compounds.

<A NAME="RG00407ST-23">23</A> Mudgal PK. Bansal SP. Gupta KS. Atmos. Environ.  2007,  accepted for publication