Aerobic Oxidation of Secondary Alcohols with Nitric Acid and Iron(III) Chloride as Catalysts in Fluorinated Alcohol

Fluorinated alcohols as solvents strongly influence and direct chemical reaction through donation of strong hydrogen bonds while being weak acceptors. We used 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as the activating solvent for a nitric acid and FeCl3-catalyzed aerobic oxidation of secondary alcohols to ketones. Reaction proceeded selectively with excellent yields with no reaction on the primary alcohol group. Oxidation of benzyl alcohols proceeds selectively to aldehydes with only HNO3 as the catalyst, while reaction on tertiary alcohols proceeds through dehydration and dimerization. A mechanistic study showed in situ formation of NOCl that converts alcohol into alkyl nitrite, which in the presence of Fe3+ ions and fluorinated alcohol decomposes into ketone. The study indicates that iron(III) acts also as the single-electron transfer catalyst in regeneration of NOCl reactive species.