Fluorocarbon ions, reactions with

In Table I, we also estimate the probabilities that the collisions between these reactant pairs lead to reaction. Except for the reactions of CF2, we see that the F or F transfer reactions observed in perfluorinated alkanes are extremely inefficient. This low reaction probability is especially striking when compared with the efficiencies of the corresponding reactions in hydrocarbon systems ( ). The methyl ion reaction with ethane corresponding to reaction 4 occurs at every collision between the reactant pair the hydride transfer reactions from propane to vinyl ions or ethyl ions, corresponding to reactions 6 and 7, occur with efficiencies of about 0.5. These differences between the efficiencies of ion-molecule reactions in fluoroalkanes and alkanes can be explained in terms of the thermochemistry of these systems, remembering that endothermic or thermoneutral ion-molecule reactions are quite inefficient, and often can not even be seen on the time scale of ion collection in a mass spectrometer. The highly efficient hydride transfer reactions observed in hydrocarbon systems are all exothermic. In the fluorocarbon systems, o the other j hand, the F transfer reactions listed for 2 3 2 5 actually slightly endothermic, as... 

Addition of anionic nucleophiles to alkenes and to heteronuclear double bond systems (C=0, C=S) also lies within the scope of this Section. Chloride and cyanide ions are effieient initiators of the polymerization and copolymerization of acrylonitrile in dipolar non-HBD solvents, as reported by Parker [6], Even some 1,3-dipolar cycloaddition reactions leading to heterocyclic compounds are often better carried out in dipolar non-HBD solvents in order to increase rates and yields [311], The rate of alkaline hydrolysis of ethyl and 4-nitrophenyl acetate in dimethyl sulfoxide/water mixtures increases with increasing dimethyl sulfoxide concentration due to the increased activity of the hydroxide ion. This is presumably caused by its reduced solvation in the dipolar non-HBD solvent [312, 313]. Dimethyl sulfoxide greatly accelerates the formation of oximes from carbonyl compounds and hydroxylamine, as shown for substituted 9-oxofluorenes [314]. Nucleophilic attack on carbon disulfide by cyanide ion is possible only in A,A-dimethylformamide [315]. The fluoride ion, dissolved as tetraalkylammo-nium fluoride in dipolar difluoromethane, even reacts with carbon dioxide to yield the fluorocarbonate ion, F-C02 [840]. 

Either fusion with alkali metals or reaction with aUcali-metal complexes with aromatic hydrocarbons will break down most fluorocarbon systems, due to the high electron affinities of these systems. Such reactions form the basis of some methods of elemental analysis [13], the fluorine being estimated as hydrogen fluoride after ion exchange. Surface defluorination of PTFE occurs with alkali metals and using other techniques [14]. Per-fluorocycloalkanes give aromatic compounds by passage over hot iron and this provides a potential route to a variety of perfluoroaromatic systems (Chapter 9, Section IB). 

Carbanions, generated by reaction of fluoride ion with unsaturated fluorocarbons, may be trapped by reaction with activated polyfluoroaromatic compounds, resulting in the introduction of polyfluoroalkyl groups.303 307 These are, of course, reminiscent of familiar cationic processes and may be thought of as nucleophilic Friedel-Crafts reactions (Eqs. 80 and 81).307... 

That is, hydrocarbon carbonium ions will nearly always undergo exothermic hydride transfer reactions with alkanes having a larger number of carbon atoms, but this is apparently not the case In fluorocarbon systems. An examination of the thermochemistry of these reactions explains these di fering trends.Table X contrasts the nergy gained in going from R to RH for, and sec-... 

This explains the low probability that thermal fluorocarbon car-bonlum ions undergo F transfer reactions with fluoroalkanes (Table I). 

Ozone undergoes decomposition when irradiated with a-particles352, 353 or with y-rays354. The decomposition may proceed through a number of distinct reaction sequences354, such as negative ion chain decomposition reactions in allglass vessels and involvement of impurities in vessels fitted with fluorocarbon-lubricated stopcocks. 

However, two important points should be noted. Firstly, that when one of the ions of an added electrolyte can interact with the surfactant to form an insoluble salt this reaction can remove the adsorbed layer from the particle (see Table I). Secondly, the hydrophobic chain of the surfactant must be compatible with the particle surface. This point is illustrated in Figure 10 which shows the adsorption of dodecanoic acid on to PTFE particles. The adsorption of the C11H23 hydrocarbon chain to PTFE is clearly much less favourable than the adsorption of the, C7F15, fluorocarbon chain in fact, a C7H15 chain, in the form of octanoic acid showed no apparent adsorption on to a PTFE surface. Thus, although both acids have hydrophobic chains, there is clearly a remarkable difference between their affinities for the substrate. 

The low energy collisions of Si+ with perfluorohexane have been studied in the search for analogies with the ion-surface reactions at fluorinated alkane monolayer surfaces. A fluorine atom abstraction product was observed, SiF+, in analogy to the corresponding ion/surface reaction, though its abundance was relatively low with respect to fluorocarbon fragment ions39. 

Polyfluoroalkylation Some of the chemistry of polyfluoroalkyl anions, generated by reaction of fluoroalkenes with fluoride ion, was discussed in Chapter 7, where the analogy between the role of fluoride ion in fluorocarbon chemistry and the role of the proton in hydrocarbon chemistry was emphasised. This analogy has been extended to include reactions of polyfluorinated anions, generated in the same way, with activated poly-fluoro-aromatic systems in what may be regarded as the nucleophilic counterpart of Friedel-Crafts reactions [119] (Figure 9.50). 

The F NMR spectra of the reaction products from the attack on C F AsFfi by show that the fluorocarbon products are C F and the 1,4-diene in a 1 1 molar ratio. These products are exactly the same as in the pyrolysis of the salt. The production of equimolar quantities of C Fg and the diene C Fg in both of these reactions is in harmony with rapid transfer of an electron from the addition product radical, C6p7, to another C F ion. ... 

The postulated primary chemical steps can be examined in the light of the mass spectroscopic fragmentation pattern of F-cyclobutane (14), which shows C2F/ as the parent peak (abundance 100 arbitrary units). A 1-3 split is also favorable C3Fr,+ has an intensity of 87 units, and CF3 25 units. These data are consistent with Steps 5b and 5c. Rupture of a C—F bond (Reaction 5a) must be more important in the radiolysis mechanism than indicated by the low abundance of 0.1 unit for the C4F7+ ion in the mass spectrum. However, this anomaly occurs not only in other fluorocarbon systems (1, 5, 10, 11, 22) but in most hydrocarbon systems studied to date. The intensities of CFL>+ and CF+ are also substantial in the mass spectrum, being 13 and 54 units respectively. These results, and the fact that CFL> has often been found under pyrolytic conditions (2,12), suggest the possibility that difluorocarbene plays a role in the mechanism, perhaps leading to a portion of the odd-carbon products. We have no evidence on this point, however. 

Above, the parameters necessary to solubilize important nitrogen ligands in fluorocarbon media have been established. In a concomitant manner, important metal complexes that are needed as precatalysts for many classical catalytic reactions require special attention with regard to fluorocarbon solubility, simply because of the polar and/or ionic nature of these complexes. Thus, we found in our experience that, in many cases, the counteranion also needed fluoro ponytails to ensure fluorocarbon solubility, even if the metal ion was coordinated to a fluorous-soluble ligand such as 1. Therefore, we [4, 5], and Pozzi et al. [6], have addressed this critical... 

In another example, the reaction of a Cu(I) complex, [CuCl], with ligand Rfg-TACN 1, provided a fully fluorocarbon-soluble complex 13 (fully characterized) [8b], without appended fluoroponytails on the Cu(I) metal ion [Eq. (2)], isolated from tri-fluoromethylbenzene. This appears to be a general phenomenon with Cu(I) complexes and fluorous ligands, and apparently is predicated on their hydrophobic properties that engender their solubility in hydrophobic solvents, such as fluorocarbons. 

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