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31.5.1.1.9 Method 9: Substitution of Aryl Aldehydes

DOI: 10.1055/sos-SD-031-00236

González-Bello, C.; Castedo, L.Science of Synthesis, (200731290.

Both 2- and 4-hydroxybenzaldehydes can efficiently and economically be converted into phenols using alkaline hydrogen peroxide. This method, known as the Dakin oxidation,[‌83‌‌85‌] consists of the oxidation of an aromatic aldehyde via rearrangement of a hydroperoxide intermediate to a formyl ester, which is then hydrolyzed under basic reaction conditions to afford the corresponding phenol. However, this reaction is limited to 2- and 4-alkoxybenzaldehydes,[‌86‌,‌87‌] since nonactivated substrates usually give the corresponding benzoic acid. Hydrogen peroxide in acidic media (such as formic, acetic, or sulfuric acid) is a good alternative, affording, for example, the corresponding formate esters which are then hydrolyzed to the phenols. Thus, phenols 35 are prepared from their corresponding benzaldehydes 34 by acid-catalyzed hydrogen peroxide oxidation (Scheme 18).[‌88‌‌91‌]

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8-Meeee-8,8-eeeeeeeee-8-eeeeeeeeeeee (88); Meeeeee Meeeeeeee:[‌88‌]

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References