Tetraalkylammonium cations

A mild and effective method for obtaining N- acyl- and N- alkyl-pyrroles and -indoles is to carry out these reactions under phase-transfer conditions (80JOC3172). For example, A-benzenesulfonylpyrrole is best prepared from pyrrole under phase-transfer conditions rather than by intermediate generation of the potassium salt (81TL4901). In this case the softer nature of the tetraalkylammonium cation facilitates reaction on nitrogen. The thallium salts of indoles prepared by reaction with thallium(I) ethoxide, a benzene-soluble liquid. 

Among cations, potassium, acetylcholine, some cationic surfactants (where the ion-exchanger ion is the / -chlorotetraphenylborate or tetra-phenylborate), calcium (long-chain alkyl esters of phosphoric acid as ion-exchanger ions), among anions, nitrate, perchlorate and tetrafluoro-borate (long-chain tetraalkylammonium cations in the membrane), etc., are determined with this type of ion-selective electrodes. 

The crystals of (V) and (VI) (Table 1) are built from tetraalkylammonium cations and cluster anions [Tc6(/i-Br)6Br6]Br2] " , where n = 2 for (V) and n = 3 for (VI). The metal core of the cluster anions [Tc6(ju-Br)6Br6]Br2] 3-(Fig. Id) is a regular trigonal prism formed from technetium atoms. The vertical... 

For further contributions on the dia-stereoselectivity in electropinacolizations, see Ref. [286-295]. Reduction in DMF at a Fig cathode can lead to improved yield and selectivity upon addition of catalytic amounts of tetraalkylammonium salts to the electrolyte. On the basis of preparative scale electrolyses and cyclic voltammetry for that behavior, a mechanism is proposed that involves an initial reduction of the tetraalkylammonium cation with the participation of the electrode material to form a catalyst that favors le reduction routes [296, 297]. Stoichiometric amounts of ytterbium(II), generated by reduction of Yb(III), support the stereospecific coupling of 1,3-dibenzoylpropane to cis-cyclopentane-l,2-diol. However, Yb(III) remains bounded to the pinacol and cannot be released to act as a catalyst. This leads to a loss of stereoselectivity in the course of the reaction [298]. Also, with the addition of a Ce( IV)-complex the stereochemical course of the reduction can be altered [299]. In a weakly acidic solution, the meso/rac ratio in the EHD (electrohy-drodimerization) of acetophenone could be influenced by ultrasonication [300]. Besides phenyl ketone compounds, examples with other aromatic groups have also been published [294, 295, 301, 302]. 

When a tetraalkylammonium cation is used as a counterion in solvents of high polarity, such as AN or DME, the alkyl groups of the cation hinder the mutual approach of species with different charges. Ion pairs with the potassium cation are stable. This follows from a comparison of the polarographic behavior of the three isomeric dinitrobenzenes in the same solvent (DMF) using tetraethylammonium or potassium perchlorate as the carrier electrolyte (Todres 1970). The halfwave potentials corresponding to the conversion of p- and m-dinitrobenzenes into anion-radicals are independent of whether tetraethylammonium or potassium counterions are employed. The anion-radical is formed from o-dinitrobenzene at a potential that is less negative by almost 100 mV when... 

Table 4.3. They vary with the electrode material and with the tetraalkylammonium cation used. Early workers used mercury electrodes but mercury may be involved in the overall reaction. Glassy carbon is generally favoured as the electrode material. Reproducibility of data depends critically on methods used for cleaning the glassy carbon surface [33].

In basic tetraalkylammonium chloride ionic liquids, the active catalyst was suggested to form from the dissociation of the chloride ligand of RuCl2(PPh3)3 in the base. The effect of the cation became evident as the catalyst in tetraalkylammonium chloride was much more active than that in [BMIMJCl. It is known that the bulky tetraalkylammonium cation is weaker in its association with the chloride anion than a planar [BMIM] cation. Therefore, it was concluded that the ionic liquids giving the best catalytic activity appeared to be tetraalkylammonium hydroxide, which melts at approximately room temperature. 

Cabovska, B., Kreishman, G. R, Wassell, D. F., and Stalcup, A. M., Capillary electrophoretic and nuclear magnetic resonance studies of interactions between halophenols and ionic liquid or tetraalkylammonium cations,. Chromatogr. A, 1007,179-187, 2003. 

Abnormal relationships between the reactivities of the free ion and ion pair for the Na+ and K+ counterions were also obtained for the other model systems 174). Unfortunately, similar data for tetraalkylammonium cations are absent at present. 

The second important chain termination reaction characteristic of the catalysis of anionic polymerization of epoxy compounds by the TA consists in the abstraction of the hydrogen atom from the p-carbon atom in the tetraalkylammonium cation by the growing alkoxy anion (P-elimination reaction)I58 164). 

The largest silicate species in the extracts of the concentrated TEA system after 45 min, detected with GPC as a shoulder on the main peak, has a retention volume characteristic for dimer of tetracyclic undecamer (Fig.2). This indicates that the first steps of the TEOS polycondensation processes till the formation of (4) and (4 ) occur with TEA as well. This is in agreement with the proposed model in which TEOS hydrolyses at the TEOS-aqueous interfaces in the vicinity of the alkyl groups of the tetraalkylammonium cations (Fig.l). These alkyl groups favor the formation of the hydrophobic silica surfaces encountered already in the smallest species (l)-(3). The absence of trimers... 

Tetraalkylammonium fluoride (R4N 1 F ) is well known as being highly receptive to protic compounds such as hydrogen halides and water, affording non-stoichiometric hydrogen-bonded adducts, R N F (HY) , in non-polar solvents. This property reasonably accounts for the hygroscopic nature of ammonium fluorides. However, under strictly anhydrous conditions, intramolecular interactions are predominant and result in self-destruction of the tetraalkylammonium cation via Hoffman elimination to furnish tetraalkylammonium bifluoride, trialkylamine, and olefin (Scheme 9.12) [22]. Consequently, the resulting tetraalkylammonium bifluoride,... 

Kornienko et al. [32] have utilized wetproofed electrodes of acetylene black containing 40 wt.% PTFE to reduce CFC 113 to CTFE in 3 M LiCl at 35°C. The presence of tetraalkylammonium cations considerably facilitates the reduction process. It is assumed that CFC 113, like other halogenated compounds, forms a positively charged complex with the tetraalkylammonium cation, which is much more easily reduced than the CFC 113 itself. The largest effect was found for tetra-M-butylammonium ion (TBA+), giving a 96% yield of CTFE. The increase in CTFE current yield is explained by the shift of potential to less cathodic values and to the displacement of water molecules by organic cations in the layer next to the electrode because hydrogen evolution is slower. 

Figure 3.11 illustrates a scenario where OH ions are transported from the aqueous into the chloroform phase by tetraalkylammonium cations. There, the tetraalkylammonium hydroxide is the base and is available for deprotonation in the entire chloroform phase—a process that was previously limited to just the interface. The C13C so formed could undergo fragmentation to dichlorocarbene, which could then add to the alkene to be cyclopropanated. This scenario provides a plausible explanation of the reaction mechanism for dichlorocyclo-propanations, which in practice are usually performed under phase-transfer catalysis (cf. Figure 3.13 for an example). 

Adams [56] reported ion-pairs partition chromatography of mefenamic acid with tetraalkylammonium cations as an effort to develop an analytical method from the extraction data. Ion pairs of mefenamic... 

In spite of the large number of dithiolene palladium complex-based compounds with tetraalkylammonium cations that have been prepared, only a few... 

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