Decarboxylative fluorination carboxylic acids

The pyrolytic decomposition of the sodium salts of various fluorinated carboxylic acids to give isomeric unsaturated compounds has also been reported. The products were identified as alkenes with the C = C bond inside the carbon chain, mainly alk-2-enes. This isomerization may be catalyzed by the coal-like products formed during the pyrolytic decarboxylation of the salts, but the metal fluoride formed in the reaction may also be responsible for the isomerization. When potassium perfluoro(5-chloropentanoate) is heated in a rocking autoclave at 300 C for 2 hours, perfluorobut-2-ene (2b) is isolated in 82% yield.This is only possible by migration of the double bond away from the terminal position after carbon dioxide elimination and halogen exchange to form potassium chloride. ... 

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 with xenon difluoride to produce unstable xenon esters The esters decarboxylate to produce free radical intermediates, which undergo fluorination or reaction with the solvent system Thus aliphatic acids decarboxylate to produce mainly fluoroalkanes or products from abstraction of hydrogen from the solvent Perfluoro acids decarboxylate in the presence of aromatic substrates to give perfluoroalkyl aromatics Aromatic and vinylic acids do not decarboxylate [91] (equation 51)... 

Decarboxylative fluorination, presumably via intermediate acyl hypofluorites, has been achieved in low yield by passing a dilute stream of fluorine in nitrogen into aqueous solutions of sodium carboxylates. A somewhat more promising method, tolerant of aryl groups, ketones and ethers, involves reaction of a dichloromethane solution of the acid with xenon difluoride and hydrogen fluoride (equation 23). ... 

Perfluoroalkylfuran Derivatives Fluorination of 2,4-furandicarboxylic acid by sulfur tetrafluoride results in the mixture of products 45-47." The carboxylic group in position 4 is more reactive than in position 2 and the yield of the compound 46 higher than that of the compound 47. Decarboxylation of the acid 46 in the presence of copper powder in quinoline gives 3-trifluoromethylfuran. 

For the simplest carboxylic acid, formic acid, this latter step leads to H + CO2. The reaction of S04 with acetate, however, leads predominately to decarboxylation 193]. Rate constants for the reactions of acetate 196] and several halo-genated acetates [97] have been measured, Substitution of a single chlorine or fluorine for a hydrogen makes little difference in the rate constant. Substitution of two chlorines reduces the rate constant by a factor of two, while two fluorines reduce it by a factor of 50. Three fluorines lower the rate constant by almost 3(X) the effect of three chlorines is significant, but uncertain. 

The decarboxylative fluorination of a wide range of aliphatic carboxylic acids with Selectfluor is achievable under silver catalysis (Scheme 4.83) [87]. 

Reactions, not being accompanied by the displacement of fluorine atoms are also important for functionalization of fluorinated quinolines. For instance, 6-substituted 5,7,8-trifluoroquinolines 148-153 were obtained from 6-trifluoro-methyl-5,7,8-trifluoroquinoline 147 (Scheme 67) through hydrolysis of the CF3 group in quinoline 147 followed by decarboxylation of 5,7,8-trifluoroquinoline-6-carboxylic acid 148 on heating in DMF [6]. From the acid 148 obtained is the acyl chloride 150, which gives with methanol the methyl ester 151 and with ammonia - the amide of... 

Common silver compounds such as silver nitrate catalyzed the decarboxylative fluorination of carboxylic acids (Schane 7.23 and Example 7.10) [36]. Selectfluor served as the fluorine source for this chanistry, and simply refluxing the reagents in acetone/water mixtures generated good to excellent yields of the fluorinated compounds. Not only was the reaction successful in the presence of water, but also water was a critical component of the... 

Electrochemical fluorination of dicarboxylic acid fluorides also gives a higher yield than fluorination of the parent acids. The lower yield given by the parent carboxylic acids has been attributed to decarboxylation, similar to the Kolbe reaction [31]. 

Selective hydrolysis of the 3-carboxylate with 6N-HCl/AcOH was unsuccessful and instead the 4-carboxylate hydrolyzed to the corresponding acid, however, heating of 432 at 50 °C caused its hydrolysis and decarboxylation in one step. Subsequent reaction with either MnO or DDQ gave 433. The fluorine atom at 8-position could be replaced by cyclic amines to give the 8-pyrrolyl or 8-[l-methyl-4-piperazinyl] derivatives 436 which upon hydrolysis using either acidic or basic conditions afforded the... 

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