Aromatic Fluorinations Investigated in Micro Reactors

Cas/liquid reaction [CL 1] Direct fluorination of toluene using elemental fluorine 

Direct fluorinations with elemental fluorine still are not feasible on an industrial scale today they are even problematic when carried out on a laboratory-scale [49-53]. This is caused by the difficulty of sustaining the electrophilic substitution path as the latter demands process conditions, in particular isothermal operation, which can hardly be realized using conventional equipment. As a consequence, uncontrolled additions and polymerizations usually dominate over substitution, in many cases causing large heat release which may even lead to explosions. 

For this reason, industrial fluorinations of aromatics are performed by other routes, mostly via the Schiemann or Halex reaction [54, 55]. As these processes are multi-step syntheses, they suffer from low total selectivity and waste production and demand high technical expenditure, i.e. a need for several pieces of apparatus. 

Accordingly, for decades scientific investigations have been carried out to achieve the direct fluorination which would be attractive as a one-step synthesis alternative. Although the early reports concerned gas-phase direct fluorinations, the most relevant work in the last three decades was based on contacting fluorine gas with the aromatic compound dissolved in a liquid phase. These attempts at gas/liquid 

Cas/liquid reaction 2 [CL 2] Direct fluorination of 4-nitrotoluene using elemental fluorine 

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