Solvents fluorinated

In this short section, we focus mainly on four types of fluorinated solvents, traditional and new, which are available for ordinary organic synthesis. These are benzotrifluoride (BTF) 1, fluorous ether F-626 2, fluorous dimethylformamide (F-DMF) 3, and perfluorohexanes such as FC-72 4, whose physical properties are summarized in Table 3.5-1. The challenges to explore the green potentials of fluorous media have just begun but, no doubt, the concept is growing to constitute another important aspect of fluorous chemistry. 

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Like many organic solvents, including hexane, heptane, ben2ene, xylene, toluene, gasoline, and particularly some of the other chlorinated and fluorinated solvents, methylene chloride may cause cardiac arrhythmias in the presence of elevated epinephrine when inhaled at concentrations as high as 20,000 ppm (36). 

Trifluoromethyl-l-phenylethyl tosylate has been used to differentiate as shown in Table 1, the solvolytic power of three fluorinated solvents and to compare these with formic and acetic acids The three fluorinated solvents are trifluoroacetic acid, trifluoroethanol, and 1,1,1,3,3,3-hexafluoroisopropyl alcohol [55]... 

PSS SDV columns can be used for all applications requiring organic eluents. The exception to the rule is the exclusion of lower aliphatic alcohols (e.g. methanol) from the otherwise complete list (28). For fluorinated solvents such as TFE and HFIP, PSS recommends its specially designed PFG columns (cf. Section V1I,C), which have a much longer life in this kind of demanding eluents. Figures 9.13 through 9.19 show some unusual applications that illustrate the variety of solvents and the feasibility of the columns. 

In contrast with salen ligands, ionic liquids were used earlier than fluorinated solvents for biphasic liquid systems with bis(oxazoline)-based complexes. In... 

The choice of solvent may have a critical impact on efficiency too. In metathesis, dichloromethane, 1,2-dichloroethane and toluene are the solvents most commonly used. There are examples that show much higher yields in ring closing metathesis (RCM) when using fluorinated solvents [150]. An impressive effect of hexafluorobenzene as a solvent for CM is the modification of the steroid 93 the use of 1,2-dichloroethane leads to a very low yield and significant amounts of dimerisa-tion while the same reaction proceeds in 90% yield in C F (Scheme 3.14) [151]. 

Kho, Y.W., Conrad, D.C. and Knutson, B.L. (2003) Phase equilibria and thermophysical properties of carbon dioxide-expanded fluorinated solvents. Fluid Phase Equilibria, 206 (1-2), 179-193. 

Combinations of liquid chlorine trifluoride with several halocarbons except perfluo-rohexane exploded immediately when suddenly mixed at all temperatures between 25° and — 70°C. Poly(chlorotrifluoroethylene), below See Carbon tetrachloride, Fluorinated solvents, both above... 

Partially fluorinated components can be used either as electrolyte solvents (Fig. 12) or as electrolyte additives (Fig. 13). In many cases they show much superior SEI forming capabilities compared to their non-fluorinated counterparts. Moreover, fluorinated solvents are in general much less flammable as less hydrogen is available, which might contribute to cell safety [12, 23, 25]. 

Some of the disadvantages of the Stille reaction, e. g. the low reactivity of some substrates, separation difficulties in chromatography, and the toxicity of tin compounds, have been ameliorated by recent efforts to improve the procedure. Curran has, in a series of papers, reported the development of the concept of fluorous chemistry, in which the special solubility properties of perfluorinated or partly fluorinated reagents and solvents are put to good use [45]. In short, fluorinated solvents are well known for their insolubility in standard organic solvents or water. If a compound contains a sufficient number of fluorine atoms it will partition to the fluorous phase, if such a phase is present. An extraction procedure would thus give rise to a three-phase solution enabling ready separation of fluorinated from nonfluorinated compounds. 

In the solvolysis of secondary alkyl sulfonates, competition between nucleophilic solvation and electron donation by the substituents results in a significantly solvent-dependent p, which varies from — 9 to — 1 on going from the non-nucleophilic hexafluoro-2-propanol to 80% aqueous ethanol (Bentley et al, 1981). In contrast, the p -invariance for alkene bromination in H20, M70, MeOH and AcOH [equations (22)-(25)] seems to imply a perfect balance between the two types of charge stabilization. However, this conclusion is probably risky since the nucleophilicities of the solvents implied in (22)-(25) do not vary markedly. Data in non-nucleophilic fluorinated solvents would therefore help to fill the gap in our knowledge. 

Various other biphasic solutions to the separation problem are considered in other chapters of this book, but an especially attractive alternative was introduced by Horvath and co-workers in 1994.[1] He coined the term catalysis in the fluorous biphase and the process uses the temperature dependent miscibility of fluorinated solvents (organic solvents in which most or all of the hydrogen atoms have been replaced by fluorine atoms) with normal organic solvents, to provide a possible answer to the biphasic hydroformylation of long-chain alkenes. At temperatures close to the operating temperature of many catalytic reactions (60-120°C), the fluorous and organic solvents mix, but at temperatures near ambient they phase separate cleanly. Since that time, many other reactions have been demonstrated under fluorous biphasic conditions and these form the basis of this chapter. The subject has been comprehensively reviewed, [2-6] so this chapter gives an overview and finishes with some process considerations. 

Micelle formation of our block copolymers in fluorinated solvents indicates that these polymers might act as stabilizers or surfactants in a number of stabilization problems with high technological impact, e.g., the surface between standard polymers and media with very low cohesion energy such as short-chain hydrocarbons (isopentane, butane, propane), fluorinated solvents (hexafluoroben-zene, perfluoro(methylcyclohexane), perfluorohexane) and supercritical C02. As... 

The fluorous tin hydrides show a reactivity similar to that of tributyltin hydride,405 406 and the residues can be extracted into a fluorinated solvent. 

Interestingly, in fluorinated solvents where the solubility of the reagents is not compromised, for example hexafluorobenzene, the rate of reaction is not increased (Figure 7.2). This implies that there is an inverse relationship between solubility of reagents and the rate of reaction, and that this relationship may be exploited by the use of either water or suitable perfluorinated solvents. 

Fluorinated carbonates were also used by Smart et al. as low-temperature cosolvents (Table 12), in the hope that better low-temperature performances could be imparted by their lower melting points and favorable effects on SEI chemistry. Cycling tests with anode half-cells showed that, compared with the ternary composition with nonfluorinated carbonates, these fluorinated solvents showed comparable and slightly better capacity utilizations at room temperature or —20 °C, if the cells were charged at room temperature however, pronounced differences in discharge (delithiation) capacity could be observed if the cells were charged (lithiated) at —20 °C, where one of these solvents, ethyl-2,2,2-trifluoroethyl carbonate (ETFEC), allowed the cell to deliver far superior capacity, as Figure 63 shows. Only 50% of the capacity deliverable at room temperature was... 

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