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The preparation of p-hydroxybenzene ether (4-methoxyphenol) from benzyl ether can be achieved through the following steps:
Method: Selective demethylation
BBr₃ demethylation:
Benzyl ether reacts with 1.2 equivalents of BBr₃ in anhydrous CH₂Cl₂ at -78°C for 2 hours. The C-O bond of the methoxy group is selectively broken to generate p-hydroxybenzene ether (J. Org. Chem. 1985, *50*, 5875).
Advantages: High regioselectivity (few ortho-products), yield up to 80% or more.
AlCl₃/EtSH reduction (alternative method):
Benzyl ether is refluxed with AlCl₃/ethyl sulfide (EtSH) to obtain the product through the hydrolysis of the thioether intermediate (Synlett 2006, *2006*, 3101). Notes:
BBr₃ requires strict anhydrous operation;
The product can be purified by column chromatography (PE/EA = 3:1). Application: This product is an intermediate for the synthesis of fragrances and drugs (such as guaiacol derivatives).
