TRIFLUOROMETHANESULFONIC ACID - A NOVEL SOLVENT FOR THE ELECTROPHILICFLUORINATION OF FLUOROAROMATICS

Trifluoromethanesulfonic acid has been discovered to be an excellent n ew solvent for promoting the direct elemental fluorination of aromatic s. Fluorobenzene has been successfully fluorinated to a mixture of 1,4 -difluorobenzene (31%) and 1,2-difluorobenzene (7%) in CFCl3-CF3SO3H ( 5%), but no further improvement is observed by the addition of boron t rifluoride, When the reaction is carried out in only CFCl3, the main r eaction pathway is the 1,2- and 1,4-addition of fluorine to fluorobenz ene forming cyclohexenes of molecular formula C6H5F5, and only a small amount of 1,4-difluorobenzene is produced, Although both 1,2- and 1,3 -difluorobenzene are fluorinated to 1,2,4-trifluorobenzene in CFCl3-CF 3SO3H (10%), 1,4-difluorobenzene does not undergo the same electrophil ic substitution reaction.