In situ generation and synthetic applications of anhydrous hydrogen fluoride in a solid-liquid biphasic system

Abstract

The in situ generation of anhydrous HF by reaction of solid CaF₂ with H₂SO₄ in the presence of an organic phase containing the substrate is proposed as a simple and safe alternative to other fluorination methods. Using this method, the addition of HF to olefins to produce fluoroalkanes, the substitution of hydroxy and halide functional groups by F atoms, and the conversion of anilines to fluorobenzenes, proceed with good conversions and moderate yields. In the latter reaction, HF generation, diazotization and fluoro de-diazonization can all be carried out in one pot. Reactions can be performed at ambient temperatures and pressures. HF generation using NaF or KF as fluoride sources is less efficient due to formation of stable bifluorides. Lipophilic quaternary ammonium salts such as tetra-n-octylammonium bromide can be used to enhance the extraction of HF into the organic phase. The effects of solvent nature and reagent ratios are discussed.