Replacement of alcoholic OH by fluorine

Direct substitution of F for OH by means of HF has no preparative importance. All the methods of preparing alkyl fluorides from alcohols proceed in principle by way of esters the alcohol is converted into the alkyl chloride, bromide, iodide, or / -toluenesulfonate, and then the halogen atom (see page 204) or the tosyloxy group (see page 229) is replaced by fluorine. 

Alkyl and cycloalkyl fluoroformates decompose even at about 50° in presence of boron trifluoride dietherate, the reaction being represented by equation (a) 858 

Fluoroformic esters are obtained either from the corresponding chloroformates and thallium fluoride by halogen exchange859 or, if the expensive T1F is not available, from carbonyl bromide fluoride and alcohols which give only 

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