Fluorine-Containing Carboxylic Acids

Carboxylic esters, usually methyl or ethyl esters, can be converted into trifluoromethyl compounds by reaction with sulfur tetrafluoride in the presence of an excess of hydrogen fluoride. In comparison to carboxylic acids more vigorous conditions are needed." Substitution of the ester group carbonyl oxygen is observed with fluoroalkyP or phenyl esters " of polyfluorocarboxylic acids, fluorine-containing a-oxo esters,fluorine-containing a- and j -hydroxy esters, " and furancarboxylic esters. ... 

Abe, T. Hayashi, E. Fukaya, H. Baba, H. The electrochemical fluorination of nitrogen-containing carboxylic acids. Fluorination of methyl esters of cyclic amino-group substituted carboxylic acids. J. Fluorine Chem. 1990, 50, 173-176, and references therein. 

The discussion of acylation reactions in this chapter is focused on fluonnated carboxylic acid derivatives and their use to build up new fluorine-containing molecules of a general preparative interest Fifteen years ago, fluonnated carboxylic acids and their derivatives were used mainly for technical applications [/] Since then, an ever growing interest for selectively fluonnated molecules for biological applications [2, 3, 4, 5] has challenged many chemists to use bulk chemicals such as tnfluoroacetic acid and chlorodifluoroacetic acid as starting materials for the solution of the inherent synthetic problems [d, 7,, 9]... 

TABLE 8-2. Catalytic Hydrogenation of Fluorine-Containing ,/MJnsaturated Carboxylic Acids... 

Partly fluorinated or perfluorinated sulfonic and carboxylic acids are compounds with excellent surface activity combined with an extreme stability against chemical or physico-chemical attacks as also described for non-ionic fluorine containing surfactant compounds. The anionic surfactants are shown with their structural formulae in Fig. 2.11.24(1)—(III). A selected ESI-FIA-MS(-) spectrum of a partly fluorinated surfactant (CF3-(CF2)4-(CH2)8-S03H, m/z 461) is presented in Fig. 2.11.25. The FIA spectrum also contains ions of the by-products CF3-(CF2)2-(CH2)8-S03H (m/z 361) and CF3-(CF2)3-(CH2)8-S03H (m/z 411). 

Quinolone carboxylic acid antibacterials are synthetic compounds whose basic nuclear structure includes a quinolone ring and a carboxylic acid group. Fluoroquinolones are second-generation quinolones that contain in their molecule a fluorine and a piperazine ring. Quinolones are amphoteric compounds slightly soluble in polar solvents such as water, and insoluble in nonpolar solvents such as benzene and hexane. Most of these drugs are fluorescent and are quite stable in aqueous solution toward light, except miloxacin, which is reported to be unstable. 

The products of the electrochemical perfluorination of aliphatic or cyclic ethers are the corresponding perfluorinated ethers. Byproducts are perfluorinated ethers with shorter carbon chains, perfluoroalkanes, perfluorocarboxylic acid fluorides and oxygen difluoride. Cyclic perfluorinated ethers can be produced by electrochemical fluorination of alcohols,32 aliphatic carboxylic acids33 or of their acid halides34 containing not less than four carbon atoms in the chain. 

The reaction of furancarboxylic acids with sulfur tetrafluoride leads to the corresponding trifluoromethyl-substituted furans in good yields (see examples in Table 6). A number of furancarboxylic acids, mainly furan-2-carboxylic acids, and furan-2,5- and -3,4-dicarboxylic acids, show a different behavior. Here highly fluorinated dihydrofurans, e g. 25, are formed. This class of compounds is also obtained with the reagent system sulfur tetrafluoride/hydrogen fluoridc/chlorine or sulfur tetrafluoride/hydrogen fluoride/sulfuryl chloride. In some cases chlorine-containing products are found. 

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