Acids fluoride intermediates

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... 

The same acid fluoride intermediates may also be used to synthesize stable fluids. If the intermediates are decarboxylated in a protic solvent such as water at elevated temperature the carboxyl groups are replaced by a proton (Eq. 13.7). 

Treatment ot I,l,3,3-tetrafluoro-l,3-dihydroisobenzofuran with anhydrous hydrogen fluoride, followed by hydrolysis of the intermediate acid fluoride, gives a high yield of 2-trifluoromethylbenzoic acid [4] (equation 4). 

The acid fluoride TTF-COF has been introduced as an important intermediate for synthesis of substituted TTFs <99TL8611> and the preparation and properties of salts 54 have been described . The hexaTTF system 55 has been prepared and its X-ray structure and electrochemistry examined <00CC331> and the photochromic TTF derivative 56 has been reported <99CL1071>. 

The synthesis of 3-aryltetrahydroisoquinolines was accomplished by electrophilic aromatic substitution of polysubstituted phenols and phenyl ethers with Lewis acid-generated tosyliminium ions of 2-tosyl-3-methoxytetrahydroisoquinoline derivatives <00SL801>. In addition isoquinoline was reported to react with N-tosylated (R)- or (S)-amino acid fluorides to afford optically active dihydroimidazoisoquinolinones. The reaction proceeds via acylation followed by attack of the tosylamino group at Cl of the intermediate 2-tosylaminoacylisoquinolinium salt <00TL5479>. 

The fact that functionalization of polymers and small molecules is observed to occur predominately on terminal (methyl) carbon atoms does not imply that the oxyfluorination reaction is truly selective. Although the reaction mechanism has not been studied in detail, it is undoubtedly a free-radical process. Molecular oxygen reacts spontaneously with the fluorocarbon—hydrogen radicals generated by fluorine during the fluorination process. Acid fluorides are retained on terminal carbon atoms because they are stable in 1 atm of elemental fluorine. Hypofluorites, which may be short-lived intermediates of oxygen reactions with methylene radical sites along the carbon chain, are not observed in the functionalized polymers. It is probable that, if they are intermediates, they are cleaved and removed by the excess elemental fluorine. 

The photoanodic dissolution of n-silicon in acidic fluoride media provides an example of the complexity of multistep photoelectrochemical reactions [33, 34]. The reaction requires the transfer of four electrons, but it is clear that not all of the steps involve photogenerated holes because the photocurrent quantum efficiency is between 2 and 4. The explanation of the high quantum efficiencies is that the initial hole capture step can be followed by a series of steps in which intermediates with low electron affinity inject electrons into the conduction band. These intermediates can be assigned nominal oxidation states as shown in the following scheme. 

Several synthetic applications of these intermediates have been reported by J. F. Normant and coworkers. For instance, trifluorovinyllithium reacts with carbonyl compounds in the usual manner to give carbinols. When treated with concentrated sulfuric acid these primary adducts undergo allylic rearrangement to the corresponding acid fluorides which, in turn, can be converted to acids, esters or amides as outlined by reaction sequence (50) ... 

Instead to acid fluorides the reaction between trifluorovinyllithium and carbonyl compounds can lead to oc-fluoro-oc,0-unsaturated aldehydes and ketones by treating the intermediate lithium alkoholates either with a lithiumalkyl or lithium aluminium hydride, as the geminal fluoro atoms on the vinylic carbon in the alcoholates are susceptable to nucleophilic replacement by these reagents (reaction sequence (51)). Finally, rearrangement yields the a-fluoro-a,(J-unsaturated aldehydes and ketones 55). 

Mechanistic studies of the pyrolysis of disodium peifluoropentanedioate and derivatives have shown that the acid fluorides are formed during the reaction. The formation of dienes from the salts of halogcnalcd carboxylic acids with a terminal C = C bond is also possible. The thermal decomposition of sodium (Z)-6//-perfluoro 6-chlorohex-5-cnoate) gives (Z)-l//-perfluoro(l-chloropenta-l,4-diene) (7) in 75% yield.The decarboxylation of potassium 5H-pcrfluoropcnt-4-enoate, however, gives 1//-perfluorobut-2-yne (8) via the isomerization of the intermediate butadiene by potassium fluoride. ... 

Perfluoroalkoxide ions are postulated as intermediates in the mechanism leading to the hypohahtes from acid fluorides. Generally, organic hypofluorites can be prepared from acid fluorides by the action of metal fluorides and elemental flnorine... 

Review. New synthetic reactions based on the onium salts of aza-arenes have been reviewed (75 references). The reactions discussed involve activation of carboxylic acids or alcohols with 2-haIopyridinium, benzoxazolium, benzothiazolium, and pyridinium salts to afford 2-acyloxy or 2-alkoxy intermediates, which can be transformed into esters, amides, thiol esters, (macrocyclic) lactones, acid fluorides, olefins, allenes, carbodiimides, isocyanates, isothiocyanates, and nitriles under appropriate conditions. 

Perfluoroalkoxyanions are also generated by reaction of fluoride ion with acid fluorides and with epoxides (see Section niB, below). Reaction of the (CF3)2CO—CsF complex with tetrafluoroethene [135] gives alkoxide 8.34A, not a carbanion 8.34B (Figure 8.34). In the presence of iodine, however, ethers are formed [126], indicating the formation of intermediate hypoiodites, RpOI (Figure 8.35). 

A tandem intramolecular Michael/SN2 reaction was also used to produce pyrroli-done derivatives. Heating a mixture of KF, dichloroacetamides 370a,b and acetonitrile at reflux temperature produced bicyclic amides 372a,b in 85 and 30% yield, respectively (Scheme 70) (94T9943). In this reaction, the choice of fluoride ion as a base was critical. Also, the isolation of the conjugate acid of intermediate 371 provided confirmation that the reaction occurred by the tandem cyclization sequence, rather than simple cyclization of a carbene intermediate. 

Perfluoroalkylene telomer diiodide intermediates were purchased from the Thiokol Corp. Perfluoroalkylene ether dicarboxylic acid intermediates were purchased as a mixture of the acid fluorides from PCR, Inc. under an agreement with Dupont. Properties of distilled fractions are indicated in Table II. The discrepancy in observed and calculated equivalent weights results from the presence of close boiling mono acid fluoride by-products, C3F70(CFCF20)nCFCF3C0F. 

Beilstein Handbook Reference) AI3-19341 BRN 1809678 CCRIS 4386 EiNECS 206-397-9 Fluorad FC-26 Hexanoyl fluoride, 3,3,4,4,5,5,6,6,6-nonafluoro-2-oxo- NSC 95114 Octanoic acid, penta-decafluoro- Pentadecafluoro-1-octanoic acid Pentadeca-fluoro-n-octanoic acid Perfluorocaprylic acid Petfluor-octanoic xid Perfluoroheptanecarboxylic acid Per-fluorooctanoic acid PFOA. Intermediate for preparation of monomers and surfactants. Solid mp = 59-60° bp = 192° soluble in H2O (3.4 g/l), organic solvents. 3M Company. 

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