Perfluorinated organic solvents

Physical and chemical properties of perfluorinated organic solvents... 

The term fluorous was introduced by Horvath and Rabai to stress the conceptual similarity to aqueous biphasic catalysis (246). In this version of organic-organic two-phase systems one of the liquid phases is composed of a perfluorinated organic solvent, in most cases an aliphatic or cycloaliphatic hydrocarbon, ether or tertiary amine. Such solvents are used in the electronics industry as well as basic components of artificial blood and have several useful characteristics. Most importantly, at room temperature the mentioned perfluorinated... 

Many transition metal complexes dissolve readily in ionic liquids, which enables their use as solvents for transition metal catalysis. Sufficient solubility for a wide range of catalyst complexes is an obvious, but not trivial, prerequisite for a versatile solvent for homogenous catalysis. Some of the other approaches to the replacement of traditional volatile organic solvents by greener alternatives in transition metal catalysis, namely the use of supercritical CO2 or perfluorinated solvents, very often suffer from low catalyst solubility. This limitation is usually overcome by use of special ligand systems, which have to be synthesized prior to the catalytic reaction. 

Only a few years after the development of the homogeneous chiral Mn(salen) complexes by Jacobsen and Katsuki, several research groups began to study different immobiUzation methods in both liquid and soUd phases. Fluorinated organic solvents were the first type of Uquid supports studied for this purpose. The main problem in the appUcation of this methodology is the low solubility of the catalytic complex in the fluorous phase. Several papers were pubUshed by Pozzi and coworkers, who prepared a variety of salen ligands with perfluorinated chains in positions 3 and 5 of the saUcyUdene moiety (Fig. 2). 

Materials similar to Nation containing immobilized —COO- or —NR3+ groups on a perfluorinated skeleton were also synthesized. These are available in the form of solid membranes or solutions in organic solvents the former can readily be used as solid electrolytes in the so called solid polymer electrolyte (SPE) cells, the latter are suitable for preparing ion-exchange polymeric films on electrodes simply by evaporating the polymer solution in a suitable solvent. 

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. 

A very different route to soluble PPP derivatives was demonstrated by Yoshino and coworkers [586], who introduced perfluorinated alkyl substituents into PPP 471 by reaction with perfluorobutanoyl peroxide. The resulting modified polymer 475 was soluble in common organic solvents and a solution-fabricated PLED ITO/475/Mg In emitted blue to green light (depending on voltage) with band half-width of over 200 nm. 

It has recently been shown that the rates of certain Diels-Alder reactions are also accelerated dramatically when carried out in perfluorinated solvents [10]. When the reaction between A -ethylmaleimide and 9-hydroxymethylanthracene (Scheme 7.4) was examined in a range of solvents, significant rate enhancements were found in water and perfluorinated solvents compared to organic solvents. 

It would appear that water is a remarkable solvent for Diels-Alder reactions giving both rate and selectivity enhancements. There are now many examples of successful reactions being carried out in this solvent. However, water cannot be used for all reactions. Perfluorinated solvents have also been found to give beneficial rate enhancements over organic solvents as have ionic liquids. Interestingly, both ionic liquids and SCFs can be used to tune the selectivities of these reactions, ionic liquids by varying the solvent used and SCFs by altering the density of the solvent. 

From our cooperation partners. Profs. Gladysz and Dinjus, we received ligands with perfluorinated chains ( ponytails ), which show a thermomorphic solubility in organic solvents (P(et-Rf8)2(m-me-bz)) or maybe extracted with fluorous solvents (P(et-Rfs)3). P(et-Rf6)(z-pr)2 with only one perfluorinated... 

By treating Nafion (NR-50), a perfluorinated acidic ion exchanger based on sulfonic acid groups, with scandium(III) chloride hexahydrate Kobayashi et al. generated a solid scandium-derived catalyst (29) (Nafion-Sc) that proved to be effective in al-lylation reactions of carbonyl compounds with tetraallyltin (Scheme 4.15). Since the catalyst is stable in both organic solvents and water, even unprotected carbohydrates could be transformed directly in aqueous solvents. The resulting homo-allylic alcohols were separated by simple filtration [97]. 

Although PDMS is swollen by many organic solvents, it is unaffected by water, polar solvents (e.g., ethylene glycol), and perfluorinated compounds [367]. A detailed study of solvent compatibility of PDMS has been reported. It was found that non-swelling solvents include water, nitromethane, DMSO, ethylene glycol, acetonitrile, perfluorotributylamine, perfluorodecalin, and propylene carbonate [251]. The compatibility of PDMS to other organic solvents can be improved by coating the PDMS surface by sodium silicate [261]. 

As such, polar organic solvents like dichloromethane and propan-2-one are miscible with ionic liquids, solvents of low polarity show partial miscibility and non-polar solvents such as hexane are immiscible. The polarity of ionic liquids can be modified by incorporation of various groups onto the cation and, for example, perfluorinated chains have the effect of considerably lowering polarity such that the resulting ionic liquid is miscible with organic solvents of low polarity and immiscible with polar organic solvents. 

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