Carboxylic acid fluorides

Carboxylic acid fluorides, intermediates in the pathway to trifluoromethyl derivatives, are readily formed in reactions of all types of carboxylic acids with sulfur tetrafluoride derivatives (see Section 8.2.4.). Little attention has been paid to fluorination of other carboxylic acid halides. Aroyl chlorides are converted into aroyl fluorides by treatment with sulfur tetrafluoride, e.g. formation of l,41 or to (trifluoromethyl)arenes, e.g. 2 and 3. in the presence of hydrogen fluoride.45 Chlorination of the aromatic ring occurs in some cases.41... 

Similarly, salts of carboxylic acids are converted into carboxylic acid fluorides, e.g. 4,41 or trifluoromethyl derivatives, e.g. 5,113 by treatment with sulfur tetrafluoride, with or without hydrogen fluoride in the latter case a sufficiently large excess of hydrogen fluoride is required. 

Carboxylic acid fluorides undergo addition to fluoroalkenes in the presence of a fluoride ion catalyst, e.g. antimony(V) fluoride to give products 1, or cesium fluoride to give products 2 ... 

The acylation of alkenes can also be similarly effected with SbFs [32], For example, a,/3-unsaturated carboxylic acid fluorides react with perfluoroalkenes to form a,/3-unsaturated ketones (Eq. 16) [32b]. 

Carboxylic acid fluorides are more stable to water and other nucleophiles. They are readily prepared by the use of cyanuric fluoride and converted to amides by siiylated amines. In contrast to the chlorides, protected amino acid fluorides exert virtually no racemization in peptide coupling. ... 

The conversion of carboxyl groups into trifluoromethyl groups proceeds in two steps. The first step, exchange of the hydroxy group by fluorine, can be accomplished easily by use of less potent fluorination agents such as a-fluoroenamines or DAST. Subsequent conversion of the carboxylic acid fluoride into the trifluoromethyl group requires more drastic conditions and can be achieved only with SF4. The most convenient procedure is the one-step direct reaction of carboxylic acids with SF4 in aHF as solvent (Scheme 2.66). For most aliphatic and aromatic carboxylic acids, excellent yields can be obtained even at room temperature or below. 

Potassium hydrogen fluoride Carboxylic acid fluorides... 

Sulfonyl fluorides are readily obtained from sulfonyl chlorides and KF or KHF2j even in an aqueous medium.801"804 Carboxylic acid fluorides are formed when the acid chlorides are heated with dry KF and can be removed continuously from the reaction mixture by distillation through a column formyl and acetyl fluorides are thus obtained when the acid is heated with benzoyl chloride and KF.805,806 Xylene or acetamide may be used as diluent. Further, a>chloro and at-bromo fatty esters, nitriles, and amides react with KF at temperatures around 100-150°. 

Carboxylic acid fluorides are not of particular preparative importance since the reactions that can be carried out with them proceed analogously with the cheaper carboxylic acid chlorides. These fluorides are very stable, even towards hydrolysis. Formyl fluoride can be kept at room temperature for several hours before it decomposes into CO and HF. The preparation of carboxylic acid fluorides from the corresponding chlorides and KF was mentioned on page 204. If butyric anhydride is heated gradually to 180° with KHF2, butyryl fluoride, b.p. 67° 1167 mm, distils off, and benzoyl fluoride, b.p. 155-156°, can be obtained analogously from benzoic anhydride at 190-240°. KF can also be used in place of KHF2. Yields are around 80-90%.1079... 

Barbituric Acid + Pyridine-4-carboxylic acid Fluoride Alizarin Fluorine blue + Lanthanum(III) ion... 

Electrochemical fluorination of carboxylic acid fluoride and chloride or alkylsulphonic acid fluoride/ chloride is carried out in anhydrous hydrofluoric acid medium at t < 19 C (or t<35°C for n-C8Hi5S02F) at a voltage of 5-12 V and electric current density of 0.02 A/m ... 

Irradiation N,N-Difluoroamines from carboxylic acid fluorides Degradation with loss of 1 C-atom... 

Carboxylic acid fluorides from carboxylic acid chlorides with formation of cyclopropanes from halides... 

Carboxylic acid fluorides can be prepared from the free acids by treatment with hexafluoro-1,2-epoxypropane, and benzylidene chlorides are converted into the... 

Fluorocarbons. Fluorocarbons are prepared primarily by the electrolytic substitution of fluorine for hydrogen on the carbon chain of carboxylic acid fluorides or sulfonyl fluorides. They may be completely fluorinated (per-fluoro-) or have a terminal hydrogen atom. In that respect, it is important to know which type of chain is present in a material, since the properties of the two may differ significantly in critical applications. They are also prepared by the oligomerization of tetrafluoroethylene. Linkage to many hydrophilic groups is accomplished through a short-chain hydrocarbon unit. 

Most commercial fluorocarbon surfactants are produced by the electrolytic substitution of fluorine for hydrogen on the carbon backbone of a carboxylic acid fluoride or sulfonic acid fluoride... 

The electrochemical fluorination of the corresponding hydrocarbon carboxylic acid fluorides or chlorides follows the general reaction scheme ... 

Compounds, colored Colson, carboxylic acid fluorides according to —... 

M ercuryj nitrogen d i oxi d e I oxygen Preferential replacement of halogen by oxygen Carboxylic acid fluorides from polyhalides... 

Reactions with a,a-difluorotrimethylamine trihydrofluoride (CHg)2NCHF2,3HF Carboxylic acid fluorides from carboxylic acids COOH COF... 

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