Alcohols fluorides from

Just as in the case of aromatic compounds isoparaffins can be alkylated with sources of alkyl groups other than olefins. Alkyl halides, alcohols, ethers, mercaptans, sulfides, etc., can be used. When olefins are used some alkyl fluorides from a combination of olefin and hydrogen fluoride are always formed. The quantity of this in the product can be greatly reduced by providing conditions under which the alkyl fluoride is used in alkylation. The apparent paradox is provided, in that the fluoride content of the product is lessened by further treatment with hydrogen fluoride. A more thorough treatment of the details of the alkylation of isoparaffins with olefins is found elsewhere in this volume. 

The HF-pyridine reagent is an effective complement to di-methylaminosulfur trifluoride (DAST) reagent6 in the preparation of alkyl fluorides from alcohols. DAST is also useful for the conversion of carbonyl groups to difluoromethylene functions. The... 

Preparation of Tertiary and Secondary-Alkyl Fluorides from Alcohols with Hydrogen Fluoride-Pyridine Reagent... 

Furthermore, 41 % hydrogen fluoride/ polyvinylpyridine combined with jV-bromosuccinimide as coreagent has been used in the preparation of alkyl fluorides from alcohols (Table 18) in good yields. 

Carboxylates are stable to anhydrous hydrogen fluoride,30 but as described above, how ever, hemiacetal esters are readily cleaved and fluorinated by anhydrous hydrogen fluoride or 70% hydrogen fluoride/pyridine, this method has been widely applied in the synthesis of glycosyl fluorides from glycosyl esters for reviews see refs 29, 34, 277-279. 288, 289. Furthermore, p-toluene- or methanesulfonates (but not trifluoroacetates) of primary alcohols arc fluorinated by nucleophilic substitution using tctrabutylammonium hydrogen fluoride. This procedure is less suitable for secondary alcohols because of the considerable number of elimination products 306 for example, formation of 1 compared to 2.306... 

The first step in the hydrolysis in tert-butyl alcohol is probably nucleophilic displacement of fluorine in the reactive allylic position. Spontaneous elimination of hydrogen fluoride from the geminal fluorohydroxy compound yields perfluorocyclopent-2-en-l-one. 

Lead tricyclohexyl fluoride is obtained from the hydroxide by the action of hydrofluoric acid or Irotn the iodide by neutral potassium fluoride. From hot alcohol small lancets are deposited, which decompose at about 108° C. Its density at 16 5° C. is 1-79. 

The fluoFoalkylamine reagent (FAR) 2-chloro-l,l,2-trifluorotriethylamine gives alkyl fluorides from alcohols in one step and is known as the Yarovenko reagent." This reagent is less reactive than DAST but was used intensively before the introduction of DAST. Rearrangement and elimination are similar with FAR and DAST (equations 39 and 40)." " This may be explained by the similar mechanism. Activation of the alcohol by intermediate formation of ester-type derivatives is followed by 5N2-type displacement by fluoride ion (Scheme 32). 

Substitution. Activated aryl fluorides are converted into ethers on reaction with various alcohols released from (RO)4Si in situ by TBAF. The reaction is conducted in refluxing acetone. ... 

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. 

Salts of o-halogeno-N-heterocyclics, such as 2-fluoro-l-methylpyri-dinium tosylate, and related compounds have been used successfully in a variety of reactions, particularly as agents for esterification, lactoni-zation, and the preparation of amides and thiolic esters They have been used also for the preparation of iodides from alcohols and acid fluorides from the acids as well as for Beckmann rearrangements and reductions, e.g. of a-hydroxyketones to ketones . Various condensed heterocyclic salts have been prepared from l-acylmethyl-2-chloropyridinium salts 2-Dialkylaminopyridinium salts have been used as phase transfer catalysts... 

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