Tetraalkylammonium hexafluorophosphate

As mentioned earlier, tetraalkylammonium hexafluorophosphate and tetra-fluoroborate salts are replacing the corresponding perchlorates for general use. There does not appear to be any reason to use the perchlorates in view of the potential safety (explosion) hazard that they present [42,71,72]. A number of methods for preparation of hexafluorophosphate and tetrafluoroborate salts have been reported [9-11,57,73]. 

This electrolyte provides the required conductivity to the solution, but its ions may themselves undergo redox reactions before the solvent does. The choice of the supporting electrolyte, in turn, depends not only on the resistance of its ions to being reduced or oxidized but also on its solubility in the solvent in question. Tetraalkylammonium ions are generally the preferred cations, otherwise alkali metal ions such as lithium or sodium may be employed, and perchlorate or hexafluorophosphate are commonly the anions of choice. 

Abstract This chapter discusses the potential usefulness of ionic liquids with respect to biocatalysis by illustrating the stability and activity of enzymes in ionic liquids in the presence or absence of water. Ionic liquids are a class of coulombic fluids composed of organic cations like alkyl-substituted imidazolium, pyrrolidin-ium, and tetraalkylammonium ions and anions such as halides, tetrafluoroborates, hexafluorophosphates, tosylates, etc. The possibility of tunable solvent properties by alternation of cations and anions has made ionic liquids attractive to study biocatalysis which warrants an understanding of enzyme stability and activity in ionic liquids. This chapter systematically outlines the recent studies on the stability of enzymes and their reactivity toward a wide range of catalytic reactions. A careful approach has been taken toward analysis of relationship between stabil-ity/activity of enzymes versus chaotropic/kosmotropic nature of cations and anions of ionic liquids. 

Among these anions, two are often used to form ionic liquids, namely, hexafluorophosphate PFg and bis(trifluoromethanesulfonyl)amide NTf2. In Table 2.3, the melting points of tetraalkylammonium and trialkylsulfonium salts formed with the NTf2 anion are indicated, clearly showing that a large variety of ionic liquids with low melting points can be prepared. 

In choosing the electrolyte for electropolymerization, an important requirement is that both the anion and cation are inert to electrochemical reactions at the potentials used for polymerization. Typical electrolytes used in nonaqueous solutions are tetraalkylammonium salts such as tetrabutylammonium hexafluorophosphate, tetrafluoroborate, perchlorate, and corresponding lithium salts. 

One of the most often overlooked variables in electrochemistry is the supporting electrolyte which is often selected on the basis of availability, cost, solubility, or perhaps just precedent (my electrochemical colleagues use a given salt, why shouldn t I ). The most commonly utilized salts in nonaqueous media have generally been tetraalkylammonium perchlorates, tetrafluoroborates or hexafluorophosphates and these are usually utilized in 0.05 to 0.2 M concentrations. Chemistry is sometimes a consideration in selection of the supporting electrolyte but in most cases the... 

Various cations and anions can be used to produce huge number of ILs. The most common are those composed of nitrogen or phosphorus-containing cations such as l-aIkyl-3-methylimidazolium, V-alkylpyridinium, W-dialkylpiperidinium, A(V-dialkylpyrrolidinium, tetraalkylammonium, or tetraalkylphosouium aud anions such as chloride, nitrate, hexafluorophosphate, tetrafluoroborate, ethyl sulfate, or bis-triflimide, as shown in Figure 5.4 and Table 5.6. The commercially available ILs are those based on l-butyl-3-methylimidazolium with hexafluorophosphate and... 

The electrolyte, added to enhance conductivity and to minimize double-layer and migration current effects, is chosen on the basis of solubility in a given solvent as well as inertness toward the electroactive substance and its electrolysis products. There are of course many choices of electrolyte for use in aqueous solution. The tetraalkylammonium salts are the most commonly used non-aqueous electrolytes. Tetrabutylammonium tetrafluoroborate (TBATFB) and tetrabutylammonium hexafluorophosphate (TBAHFP) are recommended by Fry and Britton, who note that TBAHFP in acetonitrile has a particularly large useful potential range of +3.4 to —2.9 V (vs. SCE). 

Cathodic reductions can be carried out at platinum electrodes if the measurement proceeds in aprotic media, e.g., in dimethylformamide or acetonitrile and with tetraalkylammonium salts (perchlorates, tetrafluoroborates, hexafluorophosphates) as supporting electrolytes. A sufficient electron affinity of the hydrocarbon is necessary. The process can be best exemplified by the reduction of 9,10-diphenyl-anthracene in n-Bui+NC10i+ at a Pt microelectrode ... 

The hexameric arene capsules 397 and 401 (Scheme 3.86) have been studied in [82] as potent caging ligands for the encapsulation of cobaltocenium cation. According to NMR data, these ligands form 1 1 cage complexes that result in substantial changes in the CVs the reversible wave characteristic of the free cobaltocenium cation disappears after caging. Tetraalkylammonium halides do not affect this encapsulation process. In the case of hexafluorophosphate, tetrafluo-roborate, and perchlorate salts of these cations. 

---