Perfluoroalkanoates

Reduction of perfluoroalkanesulfonyl halides leads to sulfinic acids, which are unstable in aqueous acid and give perfluoroalkanoic acids [75] (equation 16) A variety of reducing agents can be used... 

Preparation of trimethyl perfluoroorthocarboxylates by the methyla-tion of the sodium methoxide addition products of methyl perfluoroalkanoates [192]. 

Esters 8 of perfluoroalkanoic acids and perfluorinated or highly fluorinated alcohols react with the sulfur tetrafluoride/hydrogen fluoride mixture without cleavage to give high yields of perfluorinated or highly fluorinated ethers 9.164-165... 

Iron (23-25). Ultrasound-promoted reactions were also applied to the syntheses and rate enhancements of fluorinated compounds such as perfluoroalkyl iodides in the presence of zinc and carbon dioxide to give perfluoroalkanoic acids (26,27). 

The electron-withdrawing properties of the RF-chains also activate COO groups to the attack of nucleophiles so that perfluoroalkanoates, especially those with phenols, are sensitive to hydrolysis and there are long term stability problems [163]. The same problems arise for the relatively reactive esters of l//,l//-perfluoroalkanoles. Hence such structures should be avoided if possible. 

Electrochemical oxidation of perfluoroalkanoic acids can lead to radical derived products, although the same problems apply to such oxidations as applied to the electrochemical reduction processes of perfluoroalkyl iodides. 

Electron transfer from perfluoroalkanoic acids to xenon difluoride was also reported to give perfluoroalkyl radicals which were found to add to benzene derivatives [63]. 

Perfluoroalkanoic acids also undergo Hunsdiecker reactions, with the greatest utility for such methodology being the preparation of perfluoroalkyl iodides, bromides and chlorides [64]. 

Hunsdiecker reactions of salts of perfluoroalkanoic acids are known primarily as perhaps the best way of making perfluoroalkyl halides [58,306,307], but there have been other synthetic uses found for the perfluoroalkyl radicals which are formed by this decarboxylative process [308]. 

Ethoxybut-3-en-2-ones and (E)-4-(dimethylamino)but-3-en-2-ones react with ethyl perfluoroalkanoates to form intermediate 728. Acid promoted cyclization of the intermediate 728 and subsequent elimination of HR1 affords 2-perfluoroalkyl-pyran-4-ones (Scheme 181) <1998T2819, 2000T7313>. 

In 1957, Anderson found that perfluoroalkanoic acids dehydrocondense with Et3GeH without catalyst to give Et3GeOOCR (R = CF3, C2F5, C3F7), whereas the reaction did... 

Similarly, with perfluoroalkanoic acids or the corresponding anhydrides, perfluoroalkyl groups can be attached to five-membered heterocyclic systems [81JFC( 18)243] (Scheme 42). 

The decarboxylation of perfluoroalkanoic acids may also be achieved via the 0-acyl thiohydtoxa-mates. When carried out in the presence of electron rich alkenes such as ethyl vinyl ether the perfiuoroal-... 

Perfluoroalkylcopper reagents are the most studied perfluoroalkyl organometallic reagents due to their unique combination of thermal stability and chemical reactivity. They are readily prepared by copper metal insertion reactions with perfluoroalkyl halides in a coordinating solvent (e.g., formation of decarboxylation reactions of perfluoroalkanoic acid salts and copper(I) halide (e.g., formation of 2 ), or metathesis reactions (e.g., formation of 4 via 3 ). (Trifluoro-methyl)copper (4) has also been recently accessed by decomposition of methyl 2,2-difluoro-2-(fluorosulfonyl)acetate (5) or methyl perfluoro [2-(fluorosulfonyl)ethoxy]acetate (6) in the presence of copper(I) iodide and by reaction of trimethyl(trifluoromethyl)silane (7) with fluoride and copper(I) iodide. ... 

Reaction of Perfluoroalkanoic Acid Chlorides 14 with TViethyl Phosphite (I) Giving Diethyl (Z)-l l(Di-cthoxyphosphinyl)oxy perfluoroalk-l-enylphosphonates IS General Procedure ... 

Heating ethyl perfluoroalkanoates with sodium ethoxide affords ]//-perfluoroalkanes 1 in 70% yield together with diethyl carbonate. ... 

A range of normal functional-group chemistry may be carried out with perfluoroalkanoic acids, little modified by the perfluoroalkyl group [2, 25, 26]. Acid chlorides are readily obtained with thionyl chloride or phosphoms chlorides and may be converted to the fluorides using potassium fluoride or, where a volatile product is obtained, by exchange with benzoyl fluoride (see Chapter 3, Section IIB) anhydrides are produced by reaction of the acid with phosphorus pentoxide [27]. To illustrate some of the chemistry of perfluoroalkanoic acids, a selection of reactions is contained in Table 8.3. 

Perfluoroalkanoic acid chlorides 14 react with two equivalents of triethyl phosphite (1) to afford diethyl (Z)-l-[(diethoxyphosphinyl)oxy]perfluoroalk-l-enylphosphonates 15.<,1( 2... 

Watanabe, H., Hashizume, Y. and Uneyama, K. (1992) Homologation of trifluoroacetimidoyl iodides by palladium-catalyzed carbonylation. An approach to a-amino perfluoroalkanoic acids. Tetrahedron Lett., 33, 4333 4336. 

When the dipyridylimines (104.4) are treated first with LDA at — 78 °C and then with benzophenone, a new imidazole ring is formed in good yield [3190]. An isomeric imidazopyridine is produced by reacting a perfluoroalkanoic nitrile with a pyridinium salt (104.5) at low temperature in the presence of a strong base [3175]. 

Condensation of 2-acetyloxiranes with ethyl perfluoroalkanoates gives 2,3-dihydro-3-hydroxy-6-perfluoroalkyl-4//-pyran-4-ones, which on dehydration form 5-substituted 2-perfluoroalkyl-4//-pyran-4-ones (98T2819) (Scheme 31). The dehydration of hydroxy dihydropyranones intermediates was performed by the action of a slight excess of thionyl chloride in dry pyridine. 

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