Perfluoroalkylation with perfluorocarboxylic acid

Direct perfluoroalkylation of electron poor aromatic and heterocyclic systems with perfluorocarboxylic acids is mediated by xenon difluonde [165] (equation 142)... 

Employment of Zn—Cu couple is representative of another approach. For example, reaction of perfluoroalkyl iodides with carbonates gives fluorocarboxylic esters (equation 107)132. Similarly, reaction of perfluoroalkyl iodides with Zn—Cu couple and C02 or S02 in DMSO affords the perfluorocarboxylic acids and sulfonyl chlorides, respectively133. A double methylene inserted product is formed when dibromomethane is used as a substrate (equation 108)134. 

In dissociating solvents, perfluoroalkyl iodides react with a zinc-copper couple to give perfluoroalkylzmc compounds, R Znl, which react with alkyl carbonates or pyrocarbonates to give perfluorocarboxylic acids or esters, respectively [55] (equations 47 and 48)... 

Like perfluorocarboxylic acid fluorides, perfluoroalkyl chlorosulfonates react with 2-aminophenols, 2-aminothiophenols, and 1,2-diaminobenzene to give A -acylated products. On subsequent heating ring closure occurs with formation of 2-perfluoroalkyl-substituted benzoxazoles, benzothiazoles, and benzimidazoles [90JFC(49)197] (Scheme 44). 

High-temperature oxidations with nitrogen dioxide or nitrogen dioxide and chlorine followed by treatment with water convert perfluoroalkyl hydrides and perfluoroalkyl iodides into perfluorocarboxylic acids. Perfluoroalkyl bromides and especially perfluoroalkyl chlorides do not react appreciably (equation 201) [455]. 

The condensation of imine 38 with anhydrides or chlorides of perfluorocarboxylic acids provides access to pyrimidines 46 bearing three perfluoroalkyl groups (Fig. 7.14). ... 

Nitriles themselves can be also used as acylating reagent for amidoximes in some cases. Subsequent heterocyclization involves loss of ammonia in the final step (Scheme 10). For this purpose, the reaction is carried ont in the presence of an ammonia acceptor reagent (e. g. the perfluorocarboxylic acid, or an excess of the nitrile). For example, from the reaction of benzamidoxime with perflnoroalkylnitriles, a series of 5-perfluoroalkyl-l,2,4-oxadiazoles 35 can be obtained [20]. 

Xenon difluoride has been used to initiate oxidative decarboxylation of perfluorocarboxylic acids for Rp generation and with aromatic and heterocyclic compounds the perfluoroalkyl groups can also become incorporated into the aromatic ring [59]. On the other hand, Sipyagin et al. [60] have employed this method for the perfluoroalkylation of thiols such as polychloropyridine thiols. Two different methods were used the action of preformed xenon carboxylates or treatment of a pyridinethiol solution in RpCOOH directly with xenon difluoride. A range of isomeric perfluoroalkyl sulfides was obtained (Scheme 27). 

The repellency of fluorocarbon finishes depends on the structures of the fluorocarbon segment, the nonfluorinated segment of the molecule, the orientation of the fluorocarbon tail, the distribution and the amount of the fluorocarbon moiety on fibers, and the composition and geometry of the fabric [101]. The relationship between repellency and the structure of the fluorocarbon segment is in accord with the critical surface tension concept developed by Zisman and co-workers (see Chapter 11). Shafrin and Zisman [102] determined the wettabilities and critical surface tensions of -perfluoroalkyl substituted 77-heptadecanoic acids synthesized by Brace [103]. Once the seven outmost carbon atoms are fully fluorinated x = 7), the wettability of monolayers of the acids F(CF2)a(CH2)i6COOH approaches that of the perfluorocarboxylic acid F(CF2).vCOOH (Fig. 12.2). This suggests that a terminal perfluoroalkyl chain of seven carbon atoms is sufficiently... 

Figure IV-G-2. Simplified oxidation mechanism for Cj F2x+iCHO illustrating the three possible mechanisms for perfluorocarboxylic acid formation A, reaction of hydrate with OH B, reaction of perfluoroacylperoxy with HO2 radicals and C, reaction of perfluoroalkyl peroxy with a-hydrogen-containing peroxy radicals (e.g., CH3O2).

---