Selective Monoetherification of 1,4-Hydroquinone Promoted by NaNO2
Catalytic amounts of NaNO2 are able to successfully promote the reaction between 1,4-hydroquinone and methanol under acidic conditions, affording selectively the corresponding mequinol in excellent isolated yields. According to the proposed reaction mechanism, the semi-quinone intermediate, generated in situ from the corresponding hydroquinone by NO2 oxidation, is the real reactive species, undergoing nucleophilic attack onto the alcoholic molecule. Experimental evidences emphasize the key role of NO2. After optimization of the reaction conditions, the scope of the proposed protocol is extended to a wider range of alcohols, providing the corresponding mono-ethers in good to excellent yields. Moreover, when substituted hydroquinones are selected as reactive substrates, monoetherification occurs with complete regio-selectivity towards the less hindered phenolic -OH group.
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