Retro-Halex reaction

However, water enhances dramatically this Retro-Halex reaction but only when performed on very activated substrates (ref. 17). 

An explanation could be found in the fact that the fluoride anion can be far more strongly solvated than the chloride anion hydration could thus be an effective driving force for the Retro-Halex reaction. 

It has been already reported that, with organosoluble ammonium chlorides, water favours the Retro-Halex reaction which competes with hydrolysis. Similar experiments showed that this process does not occur under heterogeneous conditions (aromatic fluoride and solid KC1 or CsCl in aprotic solvent), whatever are the substrates, the solvent and the source of inorganic chloride, provided that the water content of the latter remains around or below 1 % by weight. This point has been confirmed independently in a very recent paper (ref. 41). However, when 10 % wt of water is added to potassium chloride, the Retro-Halex has been observed, though hydrolysis was the major process (ref. 17) ... 

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See also in sourсe #XX -- [ ]

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