Sulfur tetrafluoride alkyl alcohols

The result of the reaction of sulfur tetrafluoride with alcohols strongly depends on the structure of the alcohol. Simple aliphatic alcohols, such as methanol, ethanol and propan-2-ol, give alkyl ethers as the main product with only small amounts of fluoroalkanes.41 42 Yields of fluorinated products increase with increasing acidity of the hydroxy group and, in general, the reaction is only synthetically useful with alcohols equally or more acidic than tropolone (p K, = 6.42). 

With alcohols, mixtures of alkyl fluorides and alkyl ethers are obtained (100). Alcohols beating electron-withdrawiag groups can be converted to the corresponding fluorides ia high yield (101). Sulfur tetrafluoride replaces the carboayl oxygea with fluorine (100,102). 

Both aromatic and aliphatic fluoroformates 7 can be readily prepared from phenols or alcohols and carbonyl difluoride and treated with sulfur tetrafluoride without isolation. Hydrogen fluoride evolved in the reaction of hydroxy compounds with carbonyl di fluoride serves as a catalyst for the consecutive reaction with sulfur tetrafluoride.15<)-162 This provides a general, convenient, direct synthesis of aryl and alkyl trifluoromethyl ethers 5 from phenols and alcohols. When the intermediate fluoroformate 7 is isolated prior to treatment with sulfur tetrafluoride, at least one mole equivalent of hydrogen fluoride is necessary to promote the fluorination reaction. 159 163 Representative examples of the conversion of hydroxy compounds 6 into trifluoromethyl ethers 5 via intermediate fluoroformates 7 are given (for other examples 7 -> 5, see Houben-Weyl, Vol. E4, pp 628. 629). 

Reaction with phenols and alcohols. Carbonyl fluoride reacts with a phenol or alcohol (autoclave, 100-200°) to form the fluoroformate (10). In a second step the fluoroformate on reaction with sulfur tetrafluoride (150-200°) affords the aryl(alkyl) trifluoromethyl ether. ... 

Hydrogen fluoride (HF) fails to convert alcohols to the corresponding fluorides. Sulfur tetrafluoride or its derivative, diethylaminosulfur trifluoride (DAST (CH3CH2)2NSp3), is required for the conversion of alcohols to the corresponding fluorides. As with analogous proton-catalyzed reactions and as shown in Scheme 8.29, alkyl fluoride formation results from mixtures of SnI and Sn2 processes. 

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