Perfluorinated Aromatics

To the best of our knowledge, aromatic fluorinated macromolecules for PEMFCs may be prepared by direct radical (co)polymerization from two groups of functionalized aromatic perfluorinated monomers (i) a,, -trifluorostyrene (TFS) and... 

To solve some of the environmental problems of mixed-acid nitration, we were able to replaee sulfuric acid with solid superacid catalysts. This allowed us to develop a novel, clean, azeotropic nitration of aromatics with nitric acid over solid perfluorinated sulfonic acid catalysts (Nafion-H). The water formed is continuously azeotroped off by an excess of aromatics, thus preventing dilution of acid. Because the disposal of spent acids of nitration represents a serious environmental problem, the use of solid aeid eatalysts is a significant improvement. 

Chemical Properties. A combination of excellent chemical and mechanical properties at elevated temperatures result in high performance service in the chemical processing industry. Teflon PEA resins have been exposed to a variety of organic and inorganic compounds commonly encountered in chemical service (26). They are not attacked by inorganic acids, bases, halogens, metal salt solutions, organic acids, and anhydrides. Aromatic and ahphatic hydrocarbons, alcohols, aldehydes, ketones, ethers, amines, esters, chlorinated compounds, and other polymer solvents have Httle effect. However, like other perfluorinated polymers,they react with alkah metals and elemental fluorine. 

Another type of soHd supetacid is based on perfluorinated resin sulfonic acid such as the acid form of Du Font s Nafion resin, a copolymer of a perfluorinated epoxide and vinylsulfonic acid or soHd, high molecular weight petfluotoalkanesulfonic acids such as petfluotodecanesulfonic acid, CF2(CF2)qS02H. Such sohd catalysts have been found efficient in many alkylations of aromatic hydrocarbons (225) and other Friedel-Crafts reactions (226). 

Partial fluorination [50] and perfluorination [5/] of aromatic systems can be accomplished electrochemically. A number of other reagents add fluorine to benzene and its derivatives, as elaborated in equation 5 [52, 53, 54, 551... 

Fluorine has also been added successfully to perfluorinated aromatic compounds, as illustrated in equation 6 [57, 58, 59, 60, 61], Also bromine trifluoride adds fluorine to pentafluorophenol [56] and octatluoronaphthalene [62]... 

Polyfluoroalkyl- andperfluoroalkyl-substituted CO and CN multiple bonds as dipolarophiles. Dmzo alkanes are well known to react with carbonyl compounds, usually under very mild conditions, to give oxiranes and ketones The reaction has been interpreted as a nucleophilic attack of the diazo alkane on the carbonyl group to yield diazonium betaines or 1,2,3 oxadiazol 2 ines as reaction intermediates, which generally are too unstable to be isolated Aromatic diazo compounds react readily with partially fluorinated and perfluorinated ketones to give l,3,4-oxadiazol-3-ines m high yield At 25 °C and above, the aryloxa-diazolines lose nitrogen to give epoxides [111]... 

Ad layering (Fig. 16a). On the other hand, additional conformational entropy related to the sequenced hydrocarbon-perfluorinated chain prevents the crystallization of the aromatic parts of the molecules in the smectic layers as occurs for hydrocarbon analogues of the same tail length [4]. The stability of Cd phase in polyphilics is more delicate in nature and will be discussed below. 

Two nitrogen-containing polymeric materials with extended aromatic ladder structures have been chosen for direct fluorination studies (Figure 14.9).57 Pyrolyzed polyacrylonitrile (3) and paracyanogen (4) [poly(pyrazinopryazine)] have been subjected to direct fluorination to produce perfluorinated analogues. 

Membrane research is a rather diverse field, exploiting perfluorinated iono-mers, hydrocarbon and aromatic polymers, and acid-base polymer complexes. Polyether and polyketo polymers with statistically sulfonated phenylene groups such as sPEK, sPEEK, and sPEEKK or polymers on the basis of benzimidazole have been tested as well. Recent reviews on membrane synthesis and experimental characterization can be found in the literature. ... 

On the basis of their previous experiences with lithium borates coordinated by substituted ligands. Barthel and co-workers modified the chelatophos-phate anion by placing various numbers of fluorines on the aromatic ligands. Table 13 lists these modified salts and their major physical properties. As expected, the introduction of the electron-with-drawing fluorines did promote the salt dissociation and reduce the basicity of phosphate anion, resulting in increased ion conductivity and anodic stability. The phosphate with the perfluorinated aromatic ligands showed an anodic decomposition limit of 4.3 V on Pt in EC/DEC solution. So far. these modified lithium phosphates have attracted only academic interest, and their future in lithium ion cell applications remains to be determined by more detailed studies. 

The selective alkylation of a chemically distinct phenohc site on a perfluorinated aromatic has been achieved following a polymer assisted solution phase protection of an alternative o-hydroxybenzoic acid unit as the dioxin-4-one (19) (Scheme 2.45) [66]. A diverse set of 22 different alkyl and benzyl bromides were then attached to the free phenol using cesium fluoride as the base, followed by treatment with Amberlyst 15 and Amberlyst A-21 as the work-up. Subsequent hydrolysis of the dioxin-4-one group with NaOH proceeded smoothly and was quenched... 

Chlorolysis of the corresponding disulfanes is a favorable procedure for the preparation of aliphatic, aromatic, and heterocyclic sulfenyl chlorides under not too demanding conditions [low temperature mild chlorinating agents, such as SO2CI2 14) or CH3SCI3 (15)]. Perfluorinated sulfenyl chlorides can also be prepared by this procedure in special cases a mixture of CF3SSCF3 and chlorine reacts in a Pyrex Carius tube imder UV irradiation to form sulfenyl chloride in an equilibrium reaction 84) ... 

The perfluoroacetamide catalysts, rhodium(II) trifluoroacetamidate [Rh2(tfm)4] and rhodium(II) perfluorobutyramidate [Rh2(pfbm)4], are interesting hybrid molecules that combine the features of the amidate and perfluorinated ligands. In early studies, these catalysts were shown to prefer insertion over cycloaddition [30]. They also demonstrated a preference for oxindole formation via aromatic C-H insertion [31], even over other potential reactions [86]. In still another example, rhodium(II) perfluorobutyramidate showed a preference for aromatic C-H insertion over pyridinium ylide formation, in the synthesis of an indole nucleus [32]. Despite this demonstrated propensity for aromatic insertion, the perfluorobutyramidate was shown to be an efficient catalyst for the generation of isomtinchnones [33]. The chemoselectivity of this catalyst was further demonstrated in the cycloaddition with ethyl vinyl ethers [87] and its application to diversity-oriented synthesis [88]. However, it was demonstrated that while diazo imides do form isomtinchnones under these conditions, the selectivity was completely reversed from that observed with rhodium(II) acetate [89, 90]. 

In a recent review, Tao etal. [34] describe the partial fluorination and the perfluorination of organics with particular emphasis on medically important compounds and pharmaceuticals. The selective electrofluorination (SEF) of olefins and active methylene groups is reviewed by Noel et al. [35] In the case of heterocycles, nuclear fluorination is known to be the predominant process. However, in aromatic compounds, nuclear substitution as well as addition proceeds simultaneously, leading to the formation of a mixture of products. The influence of solvents, supporting electrolytes, and adsorption on product yield and selectivity is summarized and evaluated. Dimethoxyethane is found to be a superior solvent for SEF processes. Redox mediators have been employed to minimize anode passivation and to achieve better current efficiencies. 

Perfluorination of unsaturated hydrocarbons such as alkenes, allenes (Fig. 7) [53] and aromatics (Fig. 8) [54,55] is also possible since the total energy released upon fluorine addition to a carbon-carbon double bond (typically between 251.4-292.9 kjmol-1) is not sufficient to break carbon-carbon single bonds. 

Clearly, Greek or Latin numeral roots in conjunction with numerical locants can be used to indicate the number and positions of fluorine substituents in any type of organo-fluorine compound or group, ranging from monofluorinated systems, e.g. 2-fluorobutane (1), to perfluorinated entities, e.g. l,l,l,2.2,3,4,4,4-nonafluoro-3-iodobutane(2). Fluorine locants may be omitted, and often are in non-indexing situations when naming simple and therefore easily visualized fully fluorinated aliphatic/cycloaliphatic or monocyclic aromatic compounds or groups, e.g. octafluoropropane (3), hexafluorocyclopropane (4), pentafluoropropanoic acid, (5). pentafluorophenyl (6). 

While aromatic amines are discussed in Section 5.2.14., various data for aliphatic amines are listed in Table 20. It is worthwhile remembering that tertiary perfluorinated amines, such as perfluorotributylamine. are completely stable, inert and nontoxic compounds, while some partially fluorinated tertiary amines tend to be unstable, eliminating hydrogen fluoride even at low temperature and are therefore toxie. Primary and secondary aliphatic fluorinated amines carrying CF,N groups have not, so far, been isolated due to their instability. 

The products of the electrochemical perfluorination of aromatic and heteroaromatic compounds are the corresponding perfluorinated cyclic and heterocyclic alkanes.28 and also per-fluorinated derivatives of the heteroaromatic compounds. Perfluorocyclohexane is the principal product from the electrochemical fluorination of benzene and fluorobenzene. Chloro derivatives of perfluorocyclohexane are produced from chlorobenzenes. Anisoles give fully saturated per-fluoro ethers, together with cleavage products. Extensive cleavage is observed in the fluorination of benzenethiols. Chloropyridines, fluorocarbons and sulfur hexafluoride or nitrogen trifluoride are characteristic byproducts from the above scries of reactions. 

There is only a small number of reactions known whereby a perfluorinated aromatic compound is formed by thermal disproportionation perfluorotoluene is disproportionated at temperatures above 500 C to form perfluorobenzene and perfluoroxylcnc.42 44 The perfluoroxylene itself can be dismutated at 550°C to yield perfluorotoluene and 1,2.4- and 1,3,5-perfluoro-... 

In polyfluorinated and especially perfluorinated aromatics, fluorine is hydrolyzed relatively easily. Perfluorochlorobenzene gives perfluoro-4-chlorophenol (2) on treatment with potassium hydroxide in tert-butyl alcohol.33... 

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