Fluorides, acyl compounds

Pubhcations have described the use of HFPO to prepare acyl fluorides (53), fluoroketones (54), fluorinated heterocycles (55), as well as serving as a source of difluorocarbene for the synthesis of numerous cycHc and acycHc compounds (56). The isomerization of HFPO to hexafluoroacetone by hydrogen fluoride has been used as part of a one-pot synthesis of bisphenol AF (57). HFPO has been used as the starting material for the preparation of optically active perfluorinated acids (58). The nmr spectmm of HFPO is given in Reference 59. The molecular stmcture of HFPO has been deterrnined by gas-phase electron diffraction (13). 

The perchloryl fluoride [7616-94-6] FCIO, the acyl fluoride of perchloric acid, is a stable compound. Normally a gas having a melting poiat of —147.7° C and a boiling poiat of —46.7°C, it can be prepared by electrolysis of a saturated solution of sodium perchlorate ia anhydrous hydrofluoric acid. Some of its uses are as an effective fluorinating agent, as an oxidant ia rocket fuels, and as a gaseous dielectric for transformers (69). 

Theperfluoroorganozmc compounds have limited application in organic syn thesis because of their lack of reactivity However, heptafluoro I methylethylzinc iodide reacts with acyl fluorides or anhydrides of carboxylic acids in the presence of pyndine to give the corresponding ketones [7S] (equations 28 and 29) In the presence of zinc fluoride, acyl chlorides can be used as substrates [7d]... 

The eliminaUon of carbon monoxide from nonfluonnated acyl fluorides, however, does not result in a fluonne compound Although it was claimed earlier that benzoyl fluoride can be converted into fluorobenzene by using tris(triphenyl-phosphme)rhodium chloride, recent studies proved that the product is benzene and not fluorobenzene [91]... 

Although acyl fluorides, bromides, and iodides are all known classes of organic compounds, they are encountered far- less frequently than are acyl chlorides. Acyl chlorides will be the only acyl halides discussed in this chapter. 

These reactions are most important for the preparation of acyl fluorides. " Acyl chlorides and anhydrides can be converted to acyl fluorides by treatment with polyhydrogen fluoride-pyridine solution" or with liquid HF at — 10°C. Formyl fluoride, which is a stable compound, was prepared by the latter procedure from the mixed anhydride of formic and acetic acids. Acyl fluorides can also be obtained by reaction of acyl chlorides with KF in acetic acid or with DAST. Carboxylic esters and anhydrides can be converted to acyl halides other than fluorides by the inorganic acid halides mentioned in 10-77, as well as with PhsPXa (X = Cl or but this is seldom done. Halide exchange can be carried out in a... 

Many aldehydes and ketones have been converted to g m-difluoro compounds with sulfur tetrafluoride (SF4), " including quinones, which give 1,1,4,4-tetra-fluorocyclohexadiene derivatives. With ketones, yields can be raised and the reaction temperature lowered, by the addition of anhydrous HF. Carboxylic acids, acyl chlorides, and amides react with SF4 to give 1,1,1-trifluorides. In these cases the first product is the acyl fluoride, which then undergoes the ge i-difluorination reaction ... 

Sodium or potassium phenoxide can be carboxylated regioselectively in the para position in high yield by treatment with sodium or potassium carbonate and carbon monoxide.316 14C labeling showed that it is the carbonate carbon that appears in the p-hydroxybenzoic acid product.317 The CO is converted to sodium or potassium formate. Carbon monoxide has also been used to carboxylate aromatic rings with palladium compounds as catalysts.318 In addition, a palladium-catalyzed reaction has been used directly to prepare acyl fluorides ArH — ArCOF.31 ... 

Polyfluorooxiranes rearrange to carbonyl compounds in the presence of a wide range of catalysts. The nature of the product carbonyl compound depends on the structure of the epoxide and the catalyst an overview is given in Scheme 8. Monosubstituted perfluorooxiranes generally give acyl fluorides with Lewis bases, and trifluoromethyl ketones with Lewis acids. Symmetrically 2,3-disubstituted perfluorooxiranes give ketones with either Lewis acids or Lewis bases. In the presence of Lewis acids, unsymmetrically 2.3-disubstituted perfluorooxiranes give a 1 1 mixture of the two possible ketones. 

Compounds which tend to eliminate hydrogen fluoride in the presence of a base are 1.2-difluoroalkancs, oqa -difluoro ethers, a,a -difluoro sulfides, /1-fluorocarbony] compounds, 1,1-diaryl- and 1,2-diarylpolyfluoroalkanes, 277-acyl fluorides and polyfluoroalkylammonium salts. Polyfluoroalkancs (see Table 2) are relatively labile towards basic reagents. If two elimination pathways are possible, such as in 1,1,2.3,3,3-hexafluoropropanc (1), hydrogen is eliminated from the carbon bearing fewer fluorines.11,2... 

Acetylenic carbonyl compounds Di-/x-carbonylhexacarbonyldicobalt, 99 Tributyltin chloride, 315 Acyl halides Acyl fluorides... 

One of the best known reactions of dialkyl cadmium compounds is that with acyl halides which results in the formation of ketones. The reactions of (CF3)2Cd glyme with CH, COBr and C6HhCOC1 were the third class of reactions of the trifluoromethylating reagent examined. However, the mixed trifluoromethylalkyl or -aryl ketones were not observed. The organic products obtained were the acyl fluorides (95% yield) along with difluorocarbene. The latter could be stereospecifically trapped at temperatures as low as -78°C. The addition of either lithium or magnesium halides to the reaction mixture did not affect the outcome (106). 

Sulfur tetrafluoride converts carboxylic acids, in the first reaction step, into the acyl fluorides, and in the second step into trifluoromethyl compounds. By selecting suitable reaction conditions, the acyl fluorides can be isolated. " Thus. /> ra-substituted benzoic acids react at 20 C to yield the acyl fluorides almost exclusively." Substitution of the carbonyl oxygen requires higher reaction temperatures. Similar findings have been made with a series of different cyclohcxanedicarboxylic acids. ... 

Molybdenum(VI) fluoride which is a liquid at room temperature (bp 35 C) converts carboxylic acids into trifluoromethyl compounds (Table 7).174- 75 No halogen exchange takes place in halogenated carboxylic acids.174 Benzoic acid could not be fluorinated using this method.174 With trifluoroacclic acid only the acyl fluoride has been obtained. 

Finally, among the various acyl halogen compounds, formyl fluoride, oxalyl chloride, oxalyl bromide, etc., are interesting possibilities as war gases. 

Selective anodic fluorination of aldehyde and cyclic ketones can be successfully carried out in Et3N-5HF to give the corresponding acyl fluorides and fluoroacyl fluorides, respectively, in good yields, as shown in Eqs. (10) and (11) [41]. In these reactions, fluoride salts such as Et3N-3HF lead to lower yields, reflecting the fact that this salt is discharged prior to oxidation of the carbonyl compounds. 

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