Oxyfunctionalization of Hydrocarbons. 17. Acid-Dependent High Regioselectivity Hydroxylation of Naphthalene with Hydrogen Peroxide Giving 1- or 2-Naphthol

Article abstract of DOI:10.1021/jo00021a035

The acid-catalyzed hydroxylation of naphthalene with 90percent hydrogen peroxide was investigated.Regioselectivity of the reaction depends on the acidity of the system and the solvent used.In anhydrous hydrogen fluoride or 70percent HF-30percent pyridine solution at -10 to +20 deg C 1-naphthol is the product formed in > 98percent selectivity.In contrast, 2-naphthol is obtained in hydroxylation in superacid (HF-BF3, HF-SbF5, HF-TaF5, FSO3H-SbF5) solution at -60 to -78 deg C in > 98percent selectivity.When 1-naphthol reacted under the latter conditions 1,5- and 1,7-dihydroxynaphthalene were obtained, while 2-naphthol gave 1,6-dihydroxynaphthalene (along with only minor amounts of 1,7-dihydroxynapthtalene).The mechanism of the reactions is discussed, contrasting electrophilic hydroxylation of naphthalene, giving predominantly 1-substitution, with reaction of protonated naphthalenes (i.e., naphthtalenium ions) with hydrogen peroxide.