Fluorinations silver® fluoride

Uses. Silver fluoride has found many laboratory and special industrial appHcations. It is used as a soft (nHld) fluorinating agent for selective fluorination (7—17), as a cathode material in batteries (qv) (18), and as an antimicrobial agent (19). Silver fluoride is commercially available from Advance Research Chemicals, Inc., Aldrich Chemicals, Cerac Corp., Johnson/Matthey, PCR, Atochem, and other sources in the United States. The U.S. price of silver fluoride in 1993 was 1000— 1400/kg and the total U.S. consumption was less than 200 kg/yr. 

Silver Fluoride. Silver fluoride, AgF, is prepared by treating a basic silver salt such as silver oxide or silver carbonate, with hydrogen fluoride. Silver fluoride can exist as the anhydrous salt, a dihydrate [72214-21-2] (<42° C), and a tetrahydrate [22424-42-6] (<18° C). The anhydrous salt is colorless, but the dihydrate and tetrahydrate are yellow. Ultraviolet light or electrolysis decomposes silver fluoride to silver subfluoride [1302-01 -8] Ag2p, and fluorine. 

Alkyl fluorides have been prepared by reaction between elementary fluorine and the paraffins, by the addition of hydrogen fluoride to olefins, by the reaction of alkyl halides with mercurous fluoride, with mercuric fluoride, with silver fluoride, or with potassium fluoride under pressure. The procedure used is based on that of Hoffmann involving interaction at atmospheric pressure of anhydrous potassium fluoride with an alkyl halide in the presence of ethylene glycol as a solvent for the inorganic fluoride a small amount of olefin accompanies the alkyl fluoride produced and is readily removed by treatment with bromine-potassium bromide solution. Methods for the preparation of alkyl monofluorides have been reviewed. ... 

This topic has been reviewed [2, pp 94, 100-111, 130-134] All of the standard approaches to the synthesis of a compound like methyl 2-fluorostearate from methyl 2-bromostearate result mall yield of the 2-fluoro ester and the unsaturated esters. Although silver fluoride is not a new reagent, its use moist in wet acetonitrile to convert methyl 2-bromostearate to its fluoro ester is a departure from the traditional set of anhydrous conditions (Procedure 6, p 194) [71] In contrast, silver tetrafluoroborate converts a-chloroketones to their respective fluoroketones under anhydrous conditions. The displacement of less activated halogen groups by silver tetrafluoroborate to form their respective fluorides is novel Although silver tetrafluoroborate could not be used to convert an aliphatic terminal dichloromethyl or trichloromethyl group to its corresponding fluoro derivative, it is an effective fluorine source in other situations [72] (Table 8)... 

Rearrangement of fluorine with concomitant ring opening takes place in fluorinated epoxides Hexafluoroacetone can be prepared easily from perfluo-ropropylene oxide by isomerization with a fluorinated catalyst like alumina pre treated with hydrogen fluoride [26, 27, 28] In ring-opening reactions of epoxides, the distribution of products, ketone versus acyl fluoride, depends on the catalyst [29] (equation 7) When cesium, potassium, or silver fluoride are used as catalysts, dimenc products also are formed [29]... 

Because the fluoride ion is so small, the lattice enthalpies of its ionic compounds tend to be high (see Table 6.6). As a result, fluorides are less soluble than other halides. This difference in solubility is one of the reasons why the oceans are salty with chlorides rather than fluorides, even though fluorine is more abundant than chlorine in the Earth s crust. Chlorides are more readily dissolved and washed out to sea. There are some exceptions to this trend in solubilities, including AgF, which is soluble the other silver halides are insoluble. The exception arises because the covalent character of the silver halides increases from AgCl to Agl as the anion becomes larger and more polarizable. Silver fluoride, which contains the small and almost unpolarizable fluoride ion, is freely soluble in water because it is predominantly ionic. 

The type of reactivity shown by the formation of Chichibabin s hydrocarbon extends to the activation of substituents other than hydrogen as well. For example, molecular silver will not usually remove fluorine from organic compounds, not even from triphenylmethyl fluoride. Yet the radical parafluorophenyldiphenylmethyl reacts with molecular silver to give silver fluoride.88... 

Fluorination with Silver Fluoride from Glycosyl Bromide [17] A mixture of 2,3,4,6-tetra- O-acetyl-a-D-glucopyranosyl bromide (5 g) and anhydrous silver fluoride (5 g) in dry acetonitrile (25 ml) was shaken under argon overnight. The resulting solution was filtered and aqueous sodium chloride was added to precipitate any silver ions from the solution. The mixture was filtered and concentrated to a syrup that was... 

In this work on compounds containing the C—F link, it was obviously desirable to prepare 2-fluoroethanol, both for toxicity tests on the compound itself, and as a starting material for the production of other fluorine compounds. Swarts1 was unable to obtain 2-fluoroethanol by the action of silver fluoride or mercuric fluoride on either ethylene chlorohydrin or ethylene bromohydrin. He obtained acetaldehyde in each case. He ultimately obtained fluoroethanol in very poor yield by the indirect method of hydrolysing fluoroacetin (from bromoacetin and mercuric fluoride) for 80 hr. with dilute mineral acid. 

Carbonyl fluoride is prepared by the reaction of carbon monoxide with fluorine gas or silver fluoride ... 

Other nucleophilic fluorination processes in heterocycles have included displacement of bromine with potassium, cesium, or silver fluorides, but these failed to work for 4-bromo-5-nitroimidazole and ethyl 4-bromoimid-azole-5-carboxylate (73JA4619). Xenon hexafluoride was reported to convert 2,4,5-tribromoimidazole into the trifluoro analogue (79JGU1251). 

Organic compounds Organic fluorine compounds arc made by reaction of the corresponding alkane chloro-compounds with silver fluoride, mercurous fluoride, antimony trifluoride, titanium tetrafluoridc. and the arene fluoro-compounds by the diazo-reaction using hydrogen fluoride, and otherwise. The effect of the continued replacemenl of hydrogen atoms by fluorine atoms is an initial increase in reactivity, followed by a reversal of this effect, so lhal the highly substituted compounds arc relatively inert, See also Fluorocarbon. 

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