PFCA fluorides

Analogous to perfluoroalkanesulfonyl fluorides, PFCA fluorides are useful starting materials for the synthesis of PFCAs, flnorinated esters, amides, or other intermediates. These PFCA intermediates can subsequently be converted into numerous fluorinated surfactants. The industrial production pathways for these important intermediates are outlined in Figure As outlined in... 

Section 18.3.1, the key step is the preparation of PFCA fluorides by electrochenaical fluorination from the corresponding alkanoyl chlorides or fluorides. - Compared to perfluorooctanesul-fonyl surfactants (see Section 18.2), the production volume of PFCA fluorides by electrochemical fluorination was much smaller. For example, the U.S. production of ammonium perfluorooctanoate... 

APFO) by electrochemical fluorination was 227 t/year. Owing to environmental concerns, the 3M Company voluntarily began to phase out the production of PFCA fluorides at the end of the year 2000 and, with the exception of a small amount of perfluorooctanoic acid (PFOA) for internal use, production of PFCAs by electrochemical fluorination ceased in the United States in 2002. ... 

Similar to perfluoroalkanesulfonic acids, the yield of the fluorination reaction decreases with the increasing chain length of the starting material. For example, the electrochemical fluorination of acetyl fluoride yields 76% of perfluoroacetyl fluoride, whereas the fluorination of octanoyl fluoride yields only 10% of perfluorooctanoyl fluoride. The yield is also lower when the readily available acid chlorides, and not the fluorides, are employed as starting materials. A major side reaction of the fluorination of acid chlorides such as octanoyl chloride is the formation of cyclic products. Other by-products and impurities present in PFCA fluorides obtained by electrochemical fluorination include short-chain PFCA fluorides, perfluoroalkanes, COFj, and HF. Perfluorooctanoyl fluoride, the most important PFCA, was industrially synthesized from the corresponding chloride despite the lower yield and formation of cyclic by-products. ... 

PFCAs can also be synthesized by electrochemical fluorination of the corresponding alkanoic acid however, the yield of this reaction is only 10-20%. Slightly higher yields can be obtained by fluorination of the corresponding anhydrides. For example, acetic acid and acetic acid anhydride form perfluoroacetyl fluoride in a 17% and 32% yield, respectively. A major disadvantage of this approach is the formation of water that may form explosive oxygen difluoride. Simple alkanoic acids were, therefore, never useful starting materials for the industrial synthesis of PFCA fluorides. 

PFCA salts (e.g., the sodium and ammonium salts) are an industrially important class of anionic PFCA surfactants. Electrochemical fluorination has been employed to manufacture APFO, an emulsifier used in the production of fluoropolymers and other PFCAs. Hydrolysis of the acid fluorides obtained by electrochemical fluorination results either in the free carboxylic acids or the respective salts. A major problem associated with the hydrolysis of PFCA fluorides is the presence of HF from the electrochemical fluorination and the hydrolysis of the PFCA fluorides with water." The technical process of isolating fluoride-free PFCA derivatives has, therefore, been optimized to reduce the fluoride content of the final product to trace amounts. An example of such a process is shown in Figure 18.6. °... 

As shown in Figure 18.5, l//,l//-perfluoroalkanols are an important group of intermediates that can be obtained from PFCA fluorides obtained by electrochemical fluorination (or, alternatively, by a telomerization process ). These alcohols are readily converted into polydisperse nonionic polyoxyethylene surfactants by reaction with oxirane (or analogues) in the presence of a catalyst (Scheme 18.13). Borontrifluoride etherate is the classical catalyst for this oxyethylation reaction, but there are claims for the utilization of other catalysts such as aluminum alkoxides, sodium hydroxide, and acidic catalysts. ... 

Cationic PFCA surfactants are obtained through PFCA amides, which are readily obtained from the corresponding PFCA fluorides or chlorides and esters. The synthesis of these surfactants is typically simple and requires only a few synthetic steps however, the amide function of these per-fluorinated amides is relatively labile because of the strong electron-withdrawing effect of the CF2-group adjacent to the amide group, thus posing a limitation for the usefulness of these surfactants. " ... 

ECF can be used for the production of FSAs and both PFSAs and PFCAs [4]. Generally, starting materials such as afkanesulfonyl fluoride and alkanecarbonyl fluoride are converted to their perfluorinated counterparts using ECF ... 

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]. 

In the past years, elucidation of transformation products of per- and polyfluorinated compounds (PFC) has been a task frequently approached by analytical chemists. It has been estimated that biotransformation contributes to approximately 0.1-5% with respect to perfluorocarboxylic acid (PFCA) historical global emissions [1]. For perfluorooctanesulfonyl fluoride (POSF)-based compounds such as perfluorooctane sulfonic acid (PFOS), biotransformation products probably affect environmental burden marginally, although no distinct estimations have been made so far [2]. 

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