Partially fluorinated perfluorinated

This reaction has often reached explosive proportions in the laboratory. Several methods were devised for controlling it between 1940 and 1965. For fluorination of hydrocarbons of low (1—6 carbon atoms) molecular weight at room temperature or below by these methods, yields as high as 80% of perfluorinated products were reported together with partially fluorinated species (9—11). However, fluorination reactions in that eta involving elemental fluorine with complex hydrocarbons at elevated temperatures led to appreciable cleavage of the carbon—carbon bonds and the yields invariably were only a few percent. 

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... 

Similarly, partially fluorinated and perfluorinated methylenecyclopropanes [57, 52], cyclopropenes [55, 84, 55], cyclobutenes [75, 56], and bicychc alkenes [57, 55, 59, 90] apparently denve dienophilic reactivity from relief of their ground-state strain during reaction Thus 2,2-difluoromethylenecyclopropane and perfluoromethylenecyclopropane undergo exclusive [244] cycloadditions [57, 52] (equations 72 and 73), whereas (difluoromethylene)cyclopropane undergoes only [24-2] cycloadditions [57]... 

Hexafluoroacetone and certain perfluorinated or partially fluorinated ketones, aldehydes, and imines react with a-functionalized carboxylic acids (e.g., a-amino, a-At-methylamino [S3, 84], a-hydroxy [S5], and a-mercapto [Sd] acids) to give five-membered heterocyclic systems (equation 13). 

Perfluorinated and partially fluorinated substituents directly bonded to hetero multiple bond systems lower the energies of FMOs Consequently, they are highly reactive in H0MO (l,3-dipole)-LUMO (dipolarophile)-controlled [3+2] cycload-... 

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]... 

An alternative approach to the use of partially fluorinated systems to reduce the cost of fluorinated PEMs has been developed by DeSimone et al. a perfluo-rinated vinyl ether is copolymerized with a hydrocarbon monomer (styrene), sulfonated, and then subsequently fluorinated to replace existing C-H bonds with C-E bonds (Eigure 3.18). Thus yields the perfluorinated, cross-linked sul-fonyl fluoride membrane that can then be hydrolyzed to give the PEM (7). Because the membranes are cross-linked, considerably higher acid contents (up to 1.82 meq/g) are possible for these materials in comparison to Nafion, leading also to higher proton conductivity values. 

The following test procedures reflect the experiences with the characterisation of perfluorinated and partially fluorinated compounds used as ocular endotamponades but should also be used for other, similar applications. A risk assessment shows that toxic effects from a completely water-insoluble substance can be caused by... 

The different PFCLs used as interoperative tools can be categorised as a group of compounds with more or less uniform behaviour. On the contrary, the partially fluorinated species have to be regarded as individuals each. This is due to the hybrid character of these compounds, which combine the behaviours of alkanes and perfluoroalkanes. Especially, the toxicological behaviour cannot be optimised by simple modifications of the degree of fluorination. If the two molecule parts are combined in the right balance, the cytotoxic behaviour of the alkyl chain can be overcompensated by the inert perfluorinated part of the compound. But each compound should be tested individually to ensure its suitability as a candidate for ophthalmic use. 

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. 

In the Liquid-Phase Photofluorination [39,44] process the reactant is injected at a very slow constant rate into an inert fluorocarbon solvent which is saturated by fluorine and under U.V. irradiation. Conditions are chosen to ensure that the concentration of fluorine and fluorine radicals is always much higher than the concentration of the substrate. This method is only suitable for the perfluorination of substrates, such as partially fluorinated ethers (see Section 2.5) and amines (see Section 2.7), that are both soluble in perfluorocarbon solvents and can withstand such vigorous reaction conditions. 

Perfluorinations of many partially fluorinated ethers have been carried out (Figs. 24-26) [39,55,65,79,80]. 

Typically, these reactions yield only partially fluorinated products, introducing one, two, or a maximum of four fluorine atoms into the organic substrate. This is in stark contrast to the other methods described later, which readily yield perfluorinated products. 

In a series of publications on the fluorination of amines and quaternary ammonium salts Rudiger and co-workers have reported their findings on the analyses of the three product containing phases from the reactions, the perfluorinated liquid phase, the gaseous phase, and the so-called HF-phase, which was shown to contain significant quantities of partially fluorinated material, some of which were considered as intermediates in the fluorination process, but also others which remained inert to further reaction [180, 181]. 

As the fluorination proceeds, solubilities, basicities, oxidation potentials, etc. of the successive products will alter such that new molecules formed will become competitors in the dynamic equilibrium between electrolyte and anode surface. It is supposed that this process continues until perfluorination takes place, unless, in the case of partially fluorinated compounds which are resistant to further fluorination by virtue of there structure, they remain in the HF-phase or in the perfluorinated phase depending upon the number and positions of remaining hydrogen atoms and the properties which this imparts. 

Figure 14.13. UV-visible transmission spectra of partially fluorinated (dFDA/TFDB), perfluorinated (10FEDA/4FMPD), and unfluorinated polyimide (PMDA/ODA) films. 

Table 14.5 lists the thermal, electrical, and optical properties of perfluorinated polyimides, along with those of partially fluorinated and unfluorinated polyimides. Because of die flexible structure of the lOFEDA component, the polymer decomposition temperatures and values of perfluorinated polyimides are slightly lower than those of conventional polyimides. This coincides with the results of Hougham et al. who reported that an increase in fluorine content in... 

Table 14.4. Mechanical Properties of Perfluorinated (10FEDA/4FMPD), Partially Fluorinated (6FDA/TFDB), and Unfluorinated (PMDA/ODA) Polyimide Films ...

Table 14.5. Thermal, Electrical, and Optical Properties of Perfluorinated, Partially Fluorinated, and Unfluorinated Polyimides...

These characteristics show that perfluorinated polyimides are promising materials for waveguides in integrated optics and optical interconnect technology. The thermal, mechanical, and optical properties of perfluorinated polyimides can be controlled by copolymerization in the same manner as partially fluorinated polyimides. ... 

In organo-fluorine chemistry many reactions are known where more or less stable ionic or radical intermediates are formed, for example, carbocations, carbanions. and partially fluorinated and perfluorinated radicals and carbenes. While some of these species are short lived, others are surprisingly stable and isolable. In the latter case electronic and steric arrangements often kinetically stabilize the intermediate. 

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. 

Apart from fragmentations, the main byproducts isolated are partially fluorinated compounds in which the remaining hydrogen atoms are attached to the most hindered carbon as demonstrated in the case of di-tert-butylmethane (l)11 and in the preparation of dimethyl bexa-fluorobicyelo[1.1.1]pentane-l,3-dicarboxylate(2, R = F). Apart from the perfluorinated products considerable amounts of polyfluoro derivatives are also obtained.12... 

---