Acyl fluoride

My early work with acyl fluorides also involved formyl fluoride, ITCOF, the only stable acyl halide of formic acid, which was first made in 1933 by Nyesmeyanov, who did not, however, pursue its chemistry. 1 developed its use as a formylating agent and also explored formyla-tion reactions with CO and HF, catalyzed by BF3. 

The carbonylation of aryl halides under mild conditions in the presence of CsF afford.s the acid fluoride 490 in good yields. Unlike acyl chlorides, acyl fluorides are inert toward Pd(0) catalyst[345]. Benzenesulfonyl chloride (491) undergoes desulfonylation-carbonylation to give the benzoate 492 in the presence of titanium tetralkoxide at 160 °C[346]. 

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

The reaction of OF2 and various unsaturated fluorocarbons has been examined (35,36) and it is claimed that OF2 can be used to chain-extend fluoropolyenes, convert functional perfluorovinyl groups to acyl fluorides and/or epoxide groups, and act as a monomer for an addition-type copolymerization with diolefins. 

Hydrogen fluoride, HP, when used alone is a comparatively ineffective exchange agent and replaces only active halogens (13), eg, acyl fluorides from acyl chlorides and ben2otrifluoride [98-08-8] from hen2otrich1 oride (eq. 12). 

Perfluoropolyethers with the linear perfluoropropoxy repeat unit have been commercialized (28). They are prepared by the anionic oligomerization of tetrafluorooxetane followed by direct fluorination to remove the acyl fluoride end group as well as to fluorinate the remaining CH2 groups n can vary widely. 

The oxidation may be carried out with an inert solvent thermally (35), with a sensitizer such as bromine (36), with uv radiation (37), or over a suitable catalyst (38). Principal by-products of all these oxidation processes are the acyl fluoride products derived from oxidative cleavage of the perfluoroaLkene (eq. 

HFPO reacts with a large number of acyl fluorides in a general reaction to give 2-alkoxytettafluotoptopionyl fluorides which in turn may be converted to trifluorovinyl ethers (eq. 14). 

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). 

Preparation. The preparation of tetrafluoroethylene has been described previously. Perfluorovinyl ethers (4—7) are prepared by the following steps. Hexafluoropropylene [116-15-4] (HEP) is oxidized to an epoxide HEPO [428-59-1] (5) which, on reaction with perfluorinated acyl fluorides, gives an alkoxyacyl fluoride. 

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). 

H-Bond Acceptor (HBA) Acyl chlorides Acyl fluorides Hetero nitrogen aromatics Hetero oj gen aromatics Tertiary amides Tertiary amines Other nitriles Other nitros Isocyanates Peroxides Aldehydes Anhydrides Cyclo ketones Ahphatic ketones Esters Ethers Aromatic esters Aromatic nitriles Aromatic ethers Sulfones Sulfolanes... 

Acyl fluorides [256] and formaldehyde [257] add to fluorinated olefins, such as difluoroethene, under Lewis or Brijinsted acid conditions (equation 54). 

During electrochemical fluorination retention of important functional groups or atoms in molecules is essential. Acyl fluorides and chlorides, but not carboxylic acids and anhydrides (which decarboxylate), survive perfluorination to the perfluorinated acid fluorides, albeit with some cyclization in longer chain (>C4) species [73]. Electrochemical fluorination of acetyl fluoride produces perfluoro-acetyl fluoride in 36-45% yields [85]. Electrochemical fluorination of octanoyl chloride results in perfluorinated cyclic ethers as well as perfluorinated octanoyl fluonde. Cyclization decreases as initial substrate concentration increases and has been linked to hydrogen-bonded onium polycations [73]. Cyclization is a common phenomenon involving longer (>C4) and branched chains. a-Alkyl-substituted carboxylic acid chlorides, fluorides, and methyl esters produce both the perfluorinated cyclic five- and six-membered ring ethers as well as the perfluorinated acid... 

Carboxylic acids react both with fluoroaminosulfiiranes such as DAST and with sulfur tetrafluonde. Whereas DAST converts the acids to acyl fluorides only, sulfur tetrafluonde further fluorinates the primarily formed acyl fluorides and ultimately converts the carboxyl group to a trifluoromethyl group. 

Diazoalkanes react with ethyl fluoroformate [S7j and acyl fluorides [87, 55] to give ethyl ot-fluorocarboxylates and ot-fluoroketones, respectively (equation 22) Table 7 lists examples of hydrofluorination [6. 83, 89] and geminal difluori-nation [90] of aryldiazomethanes... 

Replacement of a hydrogen with bromine in the polyfluoroalkyl group of a ketone or acyl fluoride can be carried out with phosphorus pentabromide [i50] (equation 45)... 

Bis(dimethylamino)carboniiim bifluoride catalyzes the addition of acyl fluorides to perfluoroalkenes by the generation of readily acylated carbanions [4] (equation 4)... 

Perfluoro-y-butyrolactone can be prepared from 1,4 diiodoperfluorobutane by reaction with turning sulfuric acid (oleum) [7S] (equation 19) The yield depends on the concentration of sulfur trioxide One of the by-products, 4-iodoperfluo-robutyryl fluoride, can be recycled to increase the overall yield of the lactone Pure sulfur trioxide generates only perfluorotetrahydrofuran, the lodo acyl fluoride, and perfluorosuccmyl fluoride... 

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]... 

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]... 

TBAF has been used as a source of fluoride ions in a number of substitution reactions studied by Cox et al. [23]. Allcyl and acyl halides react with TBAF to give the corresponding allcyl or acyl fluoride in good yield. In the reaction between (R)-2-tosyloctane and TBAF, the product was (S)-2-fluorooctane, confirming an Sn2 mechanism for the reaction (Scheme 5.1-5) [18, 23]. 

Carbonsaure-fluoride zu Carbonsaureestern (S. 189) (die Alkohol-Komponente entstammt dem Acyl-fluorid) Aromatischc Aldehyde zu Kohlenwasserstoffen (S. 285)... 

Hydrolysis of acyl halides is not usually catalyzed by acids, except for acyl fluorides, where hydrogen bonding can assist in the removal of There are several methods available for the hydrolysis of acyl fluorides. ... 

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... 

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. Carbon-14 labeling showed that it is the carbonate carbon that appears in the p-hydroxybenzoic acid product. The CO is converted to sodium or potassium formate. Carbon monoxide has also been used to carboxylate aromatic rings with palladium compoimds as catalysts. In addition, a palladium-catalyzed reaction has been used directly to prepare acyl fluorides ArH —> ArCOF. ... 

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 ... 

---