ABSTRACT
A number of reagents have been investigated for applications in the direct fluorination of aromatics, or for the electrophilic replacement at carbanionic aromatic centers such as aryl Grignards. Elemental fluorine itself has been used, although the reaction needs to be moderated by the use of diluted fluorine in inert solvents. Other fluorinating reagents are generally prepared from elemental fluorine, resulting in less reactive reagents and more selective fluorinations. Reagents of this class include high-valency metal fluorides (such as cobalt trifluoride and silver difluoride), xenon difluoride, trifluoromethyl hypofluorite, acetyl hypofluorite, and cesium fluoroxysulfate. Recently, a number of electrophilic fluorinating reagents, based on a N-F+ system have been developed for the selective fluorination of both aromatic and aliphatic systems. Although these reagents are derived from elemental fluorine, a number are commercially available, which has opened up the field of electrophilic fluorination to workers not practiced in the handling of the element.
