Replacement of halogen by fluorine

The particular importance of halogen exchange reactions lies in preparation of aliphatic fluoro and iodo compounds. 

HF is used only with particularly reactive halides, i.e., with acyl halides or allyl halides. Benzotrichloride between 0° and 140° has all its three Cl replaced by F.767-771 

Benzotrifluoride 767 A slow stream of hydrogen fluoride (200 g) is introduced in 72 h into benzotrichloride (500 g) which is stirred at 0° in a copper flask fitted with a copper gas inlet tube that reaches to the bottom, a gas outlet tube, and a copper stirrer. Initially only HC1 is evolved, but this includes HF and benzotrifluoride in increasing amounts as reaction proceeds they are condensed out in a copper receiver cooled in ice-salt. The product in the flask and the condensate in the receiver are united and warmed to room temperature, then shaken with sodium fluoride to bind the HF. Filtration and distillation of the filtrate gives benzotrifluoride (300 g), b.p. 102.3°. Higher-boiling distillate contains partially chlorinated benzotrichloride and can be used in a new batch. 

For preparation of benzotrifluoride in about the same yield by means of BF3 see Pouterman et al.16  

Dichlorodifluoromethane, b.p. —30°, is prepared industrially by passing HF (b.p. 19.4°) and CC14 (b.p. 76°) into a vessel containing SbF3 and a small amount of a Sb(v) halide. HC1 

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Replacement of Halogens by Fluorine with Antimony(IIl) Fluoride 12.1.1. In the Absence of Catalysts... 

Replacement of Halogens by Fluorine and Addition of Fluorine to C = C Bonds with Antimony(V) Fluoride and Fluoroantimonates... 

Replacement of Halogens by Fluorine in Carboxylic Acid Halides... 

Silver fluoride-calcium fluoride Replacement of halogen by fluorine s. 44, 408... 

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