Halogen-exchange fluorination of aromatic halides using HF or HF-base solutions

Abstract

Heteroaromatic halides such as chloropyridines, or some chlorobenzenes such as 2,4-dinitrochlorobenzene underwent halogen-exchange fluorination by the use of HF or HF-base solutions to produce the corresponding aromatic fluorides. ▪ The reaction of heteroaromatic halides take place even at rather milder conditions ( 20 – 150 °C ) than those employed in the halogen-exchange aromatic fluorination using KF. The reaction in a closed container attains equilibrium fairly rapidly giving ArF in low yields. When using a more nucleophilic fluorinating reagent obtained by the addition of pyridine in HF, yields of ArF were not improved but decreased somewhat in the reaction of chloropyrimidines in particular. On the other hand, the reaction of chlorobenzenes such as 2,4- dinitrochlorobenzene need higher temperature than 180 °C to produce the corresponding ArF, and the presence of organic bases such as γ-collidine in HF enhanced the reaction remarkably to give ArF in good yields.