Perfluoroalkyl carboxylates

As Table 20 shows, the yields of the Rh(II)-promoted reaction are temperature-dependent. Furthermore, competitive experiments between pairs of alkanes revealed a marked dependence on the alkoxy group of the diazoester and on the perfluoroalkyl carboxylate part of the catalyst. The observed relative selectivities have been taken as evidence for the importance of lipophilic interactions between carbenoid and alkane. 

WITTIG OLEFINATION OF PERFLUOROALKYL CARBOXYLIC ESTERS SYNTHESIS OF 1,1,1-TRIFLUORO-2-ETHOXY-5-PHENYLPENT-2-ENE AND 1-PERFLUOROALKYL EPOXY ETHERS 1,1,1-TRIFLUORO-2-ETHOXY-2.3-EPOXY-5-PHENYLPENTANE (Oxirane, 2-ethoxy-3-(2-phenylethyl)-2-(trifluoromethyl)-, cis-(+)-)... 

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]. 

More recently, studies have demonstrated that UV irradiation (220-460 nm) of aqueous PFOA solutions at room temperature in the presence of oxygen resulted in the formation of shorter-chain perfluoroalkyl carboxylates, CO2, and F" [30]. The environmental significance for this photolytic pathway was not discussed, but it is not likely to be an important degradation route for PFOA in natural surface waters. PFOA absorbs UV mostly at wavelengths below 220 nm [30], and these energetic wavelengths are not present at the earth s surface. 

For many organic compounds that accumulate in lipids, bio accumulation potential can be estimated from the Kow. Since perfluoroalkyl compounds are inherently oleophobic, and do not partition preferentially to lipid rich tissues [67], the K0w is not a useful predictor of bioaccumulation and direct evidence derived from the laboratory or field is required. Additionally, tissue concentrations of perfluoroalkyl substances should never be lipid normalized. The dietary accumulation, bioconcentration, and biomagnification potential of various perfluoroalkyl carboxylates and sulfonates have been assessed in the laboratory and in the Great Lakes food web (Table 4). 

In the Great Lakes region, surface water samples were analyzed for PFAs in Lakes Ontario, Erie, and their tributaries, and various Michigan rivers (Table 11). Most reports are for PFOS and PFOA, whereas PFHxS and FOSA are often below method detection limits and no data exists for longer-chain perfluoroalkyl carboxylates. It can be generalized that the concentrations of PFOA slightly exceed the concentrations of PFOS at all background sites. 

Diketones are synthesized by Claisen condensation of appropriate acetyl methyl ketone and ethyl perfluoroalkyl carboxylate. For example, 4,4/-bis(l",l,/,l//,2//,2",3//,3//-heptafluoro-4//,6//-hexanedion-6"-yl)-chlorosulfo-o-terphenyl (BHHCT) was synthesized from o-terphenyl by three step reactions (scheme 3 (Yuan et al., 1998a, 1998b)). The o-ter-phenyl are acetylated by acetyl chloride with anhydrous aluminum chloride as a Lewis acid and 4,4 -diacetyl-e>-terphcnyl is obtained. Then, the 4,4/-diacetyl-o-terphenyl is reacted with perfluoropropionic acid ethyl ester with sodium methoxide as a base. Finally, 4,4,-bis(l", 1",l//,2,2,3,/,3"-heptafluoro-4//,6"-hexanedion-6//-yl)-o-terphenyl is chloro-sulfonylatcd by chlorosulfonic acid to form BHHCT. 

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]. 

Wittig Olefination of Perfluoroalkyl Carboxylic Esters Synthesis of... 

Benskin, J. P, Bataineh, M., Martin, J. W. Simultaneous characterization of perfluoroalkyl carboxylate, sulfonate and sulfonamide isomers by liquid chromatography-tandem mass spectrometry. Anal. Chem., 79 6455-6464 (2007). 

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]. 

The free-radical addition of TFE to pentafluoroethyl iodide yields a mixture of perfluoroalkyl iodides with even-numbered fluorinated carbon chains. This is the process used to commercially manufacture the initial raw material for the fluorotelomer -based family of fluorinated substances (Fig. 3) [2, 17]. Telomeri-zation may also be used to make terminal iso- or methyl branched and/or odd number fluorinated carbon perfluoroalkyl iodides as well [2]. The process of TFE telomerization can be manipulated by controlling the process variables, reactant ratios, catalysts, etc. to obtain the desired mixture of perfluoroalkyl iodides, which can be further purified by distillation. While perfluoroalkyl iodides can be directly hydrolyzed to perfluoroalkyl carboxylate salts [29, 30], the addition of ethylene gives a more versatile synthesis intermediate, fluorotelomer iodides. These primary alkyl iodides can be transformed to alcohols, sulfonyl chlorides, olefins, thiols, (meth)acrylates, and from these into many types of fluorinated surfactants [3] (Fig. 3). The fluorotelomer-based fluorinated surfactants range includes noiuonics, anionics, cationics, amphoterics, and polymeric amphophiles. 

The world of fluorinated surfactants is full of many useful and unique products tailored for specific end users who take advantage of their exceptional performance properties. Recently, major global manufacturers have made commitments to work toward eliminating the manufacture of long-chain perfluoroalkyl carboxylates and perfluoroalkyl sulfonates and substances that may break down to them in the environment [108-110]. As a result, commercial production has shifted to short chain alternatives [24] and new fluorinated moieties such as the per- and poly fluorinated ethers. Clearly, there remains a need for fluorinated surfactants in many industries to obtain the beneficial performance properties of these substances that cannot be achieved with other types of surfactants. 

PFCA Perfluoroalkyl carboxylic acid/Perfluoroalkyl carboxylate... 

Arsenault G, McAlees A, McCrindle R et al (2007) Analysis of perfluoroalkyl anion fragmentation pathways for perfluoroalkyl carboxylates and sulfonates during liquid chromatog-raphy/tandem mass spectrometry evidence for fluorine migration prior to secondary and tertiary fragmentation. Rapid Commun Mass Spec 21 3803-3814... 

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

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