Perfluoroalkyl carboxylic acids

Transmission electron microscope ( ) images of such n-Al powders indicate the presence of a thin passivation layer of aluminum oxide (A1203) which provides stability to it in the air. Without this layer, A1 nanoparticles would be pyrophoric and also have tendency to agglomerate to form bulk A1 metal. In order to protect this n-Al powder further, some researchers have suggested its coating with self-assembled nanolayers using perfluoroalkyl carboxylic acid [90]. 

The precursor is generally a perfluoroalkyl iodide, and the preferred solvent dimethylformamide (DMF).21,22 Since a two-step Grignard process would give rise to difficulties, the one-step reaction was preferred giving good yields, which are still improved by sonochemical activation, minimizing 3-elimination.23,24 Perfluoroalkyl carboxylic acids can be prepared by running the reaction in the presence of carbon dioxide. 

Generally, treatment with electron-deficient olefins such as nitroethylene or vinyl sulfone is effective for radical addition reactions, since alkyl radicals derived from O-acyl esters (2) are nucleophilic and take SOMO-LUMO interaction. However, treatment of O-acyl esters ) derived from perfluoroalkyl carboxylic acids (RfC02H) generates electrophilic radicals, Rf, which react preferably with electron-rich olefins such as vinyl ether, as shown in eq. 8.16 [52]. 

The CO2 fixation into (perfluoroalkyl)iodoalkanes, (perfluoroalkyl)-iodoalkenes and (perfluoroalkyl)alkenes, catalyzed by electrogenerated nickel complexes, afforded perfluoroalkyl carboxylic acid derivatives. The electrocarboxylation of perfluoroalkyl olefins proceeded with double bond migration and loss of an allylic fluorine atom. 

We have been interested in tbe carbon dioxide fixation into organic substrates for tbe synthesis of speciality products of the carboxylic acid family. We focussed our attention on tbe formation of new carbon-carbon bonds between CO2 and perfluoroalkyl derivatives, particularly perfluoroalkyl olefins. The perfluorinated chain being highly hydrophobic, the expected perfluoroalkyl carboxylic acids are precursors of amphiphilic molecules, of interesting applicability in the field of surfactants and medicinal chemistry [1]. 

The electrocarboxylation of 1 took place under mild conditions (CO2 pressure of 1 atm, T = 20°C) in the presence of Ni(bipy>32+, 2BF4- as the catalyst precursor and a Mg/stainless steel couple of electrodes, to afford the corresponding perfluoroalkyl carboxylic acid 5 in 30% yield, together with the olefin 3 [20%, E/Z 90 10)] (eq. 1). 

Starting materials for the synthesis of all perfluoroalkyl iodonium reagents are the perfluoroalkyl iodides, which themselves play a central role as building blocks in fluoroorganic chemistry. The iodides are available either by pyrolysis of the silver salts of perfluoroalkyl carboxylic acids in the presence on iodine [14] or - on a more technical scale - by iodofluorination of tetrafluoroethylene [15] with the iodine-IFp system [16] and subsequent radical telomerization of tetrafluoroethylene with the resulting intermediate perfluoroalkyl iodides [17] (Scheme 2.143). 

Metzger, J.O., and U. Linker, Synthesis of Linear and Branched Perfluoroalkylated Carboxylic Acids by Radical Addition of PerfluoroaUcyl Iodides to Unsaturated Fatty Acids, Liebigs Ann. Chem., 209-216 (1992). 

Polyfluorinated compounds comprise hundreds of chemicals characterized by hydrophobic linear alkyl chains partially or fully fluorinated (as the perfluorinated compounds [PFCs]) and containing different functional groups. Polyfluorinated compounds include perfluoroalkyl sulfonamides (PFASAs), fluorotelomer alcohols (FTOHs), polyfluorinated alkyl phosphates (PFAPs), fluorotelomer unsaturated carboxylic acids (FTUCAs), perfluoroalkyl acids (PFAAs), and their salts. The most common PFAAs are perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFASs). In particular, PFASs contain one or more fluorinated alkyl chains bonded to a polar head, which at neutral pH can be charged (anionic, cationic, and amphiphilic surfactants) or noncharged (nonionic surfactants). 

Vestergren, R., UUah, S., Cousins, I. T., and Berger, U. 2012. A matrix effect-free method for reliable quantification of perfluoroalkyl carboxylic acids and perfluoroal-kane sulfonic acids at low parts per ttilhon levels in dietary samples. J. Chromatogr. A 1237 64-71. 

Fluorinated surfactants have been commercially available since the 1950s. The first available were perfluoroalkyl sulfonates (e.g., perfluorooctane sulfonate, CgFisSOs, PFOS) and perfluoroalkyl carboxylic acids (e.g., perfluorooctanoic acid, C7F15COOH, PFOA) manufactured using the electrochemical fluorination (ECF) process [10]. The unique properties (e.g., surface tension lowering in aqueous systems, high chemical and thermal stability) of these acids and their derivatives when used at low concentrations resulted in their widespread use in industrial processes and consumer uses [11-13]. The most common commercially produced perfluorinated surfactants are the perfluoroalkyl acids (PFAAs) ... 

In addition, perfluoroalkyl carboxylic acids (PFCAs) and their derivatives have also been synthesized using the ECF process. Typically, an alkyl carbonyl fluoride (for example C7H15COF) is transformed into the corresponding perfluoroalkyl carbonyl fluoride (for example C7F15COF). The carbonyl fluoride is then reacted to yield esters, amides, or carboxylic acid salts which are have all been commercially produced and used as surfactants [4]. The most widely known is the ammonium salt of perfluorooctanoic acid (C7Fi5COOH-NH3), whose major historical use has been as a processing aid in the manufacture of fluoropolymers [29]. 

PFCA Perfluoroalkyl carboxylic acid/Perfluoroalkyl carboxylate... 

Continuing his investigations on the fluorination of polyhydrofluoroethylenes, Shinohara has described the formation of perfluoroalkyl carboxylic acids on the... 

Wang L, Sun HW, Yang LR, He C, Wu WL, Sun SJ, et al. Liquid chromatography/ mass spectrometry analysis of perfluoroalkyl carboxylic acids and per-fluorooctanesulfonate in bivalve shells extraction method optimization. J Chromatogr A 2010 1217(4) 436-42. 

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