Tetraalkylammonium ion

In spite of being ionic many quaternary ammonium salts dissolve m nonpolar media The four alkyl groups attached to nitrogen shield its positive charge and impart lipophilic character to the tetraalkylammonium ion The following two quaternary ammonium salts for example are soluble m solvents of low polarity such as benzene decane and halo genated hydrocarbons... 

Perhaps the best known example of adsorption effects in electrosynthetic reactions is the beneficial role of tetraalkylammonium ions in the hydrodimerization of acrylonitrile... 

A method for the development of a generic LC-electrospray-MS method for the analysis of acidic compounds using experimental design has been reported [5], From an HPLC perspective, this type of analysis often requires the use of an ion-pairing reagent to obtain separation however, many of these, such as tetraalkylammonium ions, are involatile and have undesirable effects on the performance of the mass spectrometer and more volatile alternatives have to be found - in this case, triethylamine was used. 

Wahl et al. have completed the first detailed isotopic study of this exchange reaction and have shown paths catalysed by cations ( , K", Ca, Ba, Ph4As and various tetraalkylammonium ions ) occur. The first order with respect to both Fe(CN)6 and Fe(CN) was confirmed, viz. 

The differences in pK values in the case of tetraalkylammonium ions as counterions can he explained by the size of the CH ) N ion in comparison with the ion and delocalization of the positive charge on the... 

D. Comparison of the Reactions of Protonated Amines and Tetraalkylammonium Ions... 

Fig. 7. Limiting single ion mobility-viscosity product vs. reciprocal of estimated crystallographic radii of tetraalkylammonium ions in various solvents. Stokes law plot shown as dashed line.

A fundamental improvement in the facilities for studying electrode processes of reactive intermediates was the purification technique of Parker and Hammerich [8, 9]. They used neutral, highly activated alumina suspended in the solvent-electrolyte system as a scavenger of spurious impurities. Thus, it was possible to generate a large number of dianions of aromatic hydrocarbons in common electrolytic solvents containing tetraalkylammonium ions. It was the first time that such dianions were stable in the timescale of slow-sweep voltammetry. As the presence of alumina in the solvent-electrolyte systems may produce adsorption effects at the electrode, or in some cases chemisorption and decomposition of the electroactive species, Kiesele constructed a new electrochemical cell with an integrated alumina column [29]. 

Drastic changes in the disproportionation constants occur when alkaK cations are used instead of tetraalkylammonium ions. Typically, the potentials of the radical anion formation are less affected than that of the dianion formation. In the presence of alkali cations, AE shifts may reach values of more than 600 mV, which correspond to an increase in the K constant of more than 10 orders of magnitude [52, 53]. 

Electrodimerization of activated alkenes in aprotic solvents occurs by radical-ion, radical-ion coupling. There is ample evidence for steric inhibition to this process. In contrast to the low reactivity of 11,4-methylbenzabnalononitriIe radical-ion dimeiises with a rate constant of 5.8 x 10 M s in dimethylformamide containing tetraalkylammonium ions [48]. Dimethyl maleate radical-anion diraerises faster than dimethylftimarate radical-anion by a factor of lO in dimethylformamide [49]. 

At very negative potentials, using a mercury cathode, tetraalkylammonium ions are deposited as a crystalline tetraalkylammonium amalgam. Tetramethylammo-nium amalgam slowly decomposes at 0 C to give trimethylamine and a methyl radical [30, 31]. The amalgam fomred by reduction of dimetfaylpyrrolidinium cation 7 is more stable and characterisation of this class of materials has centred on... 

Reversed-phase ion-pair chromatography is primarily used for the separation of mixtures of ionic and ionizable compounds. In this chromatographic mode, a pairing ion is added to the mobile phase in order to modulate the retention of the ionic solutes. The pairing ion is an organic ion such as alkylsulfonate, alkylsulfate, alkylamine, tetraalkylammonium ion, etc. Here, only a very brief description of the main ideas behind the electrostatic model for ion-pair chromatography is presented. For a complete discussion, the reader is referred to Ref. [7,8] and the references therein. 

Also, the deviations from a parabolic shape are greater with some solutions than with others. Electrocapillaiy curves show, for instance, a marked sensitivity to the nature of the anions present in the electrolyte (Fig. 6.63). In contrast, the curves do not seem to be affected significantly by the cations present unless they are large organic cations, e.g., tetraalkylammonium ions. 

Although tetraalkylammonium salts are most frequently used as supporting electrolyte in aprotic solvents, it should be noted that even tetraalkylammonium ions give significant influences on electrode reactions. An appropriate R4N+ should be selected for each measurement. 

One difference in behavior between the hydrophilic alkali halides and hydrophobic solutes like the larger tetraalkylammonium halides in water is expressed by the enthalpy. The enthalpies of solution of the larger tetraalkylammonium halides in water are more exothermic than those of the corresponding alkali halides but in other solvents, e.g., several amides, propylene carbonate (PC), and dimethylsulfoxide (DMSO), the reverse is true. Generally, this phenomenon is attributed to an enhanced hydrogen bonding in the highly structured solvent water in the vicinity of the tetraalkylammonium ions (hydrophobic hydration) (i). This idea is substantiated by the absence of the effect in solvents like N,N-dimethylformamide (DMF), PC, and DMSO (2), where specific structural effects are not present in the pure solvents. 

In view of the different behavior of n-Bu4NBr in mixtures of DMF and NMF and of DMF and water, we recently (6) derived an equation for the excess enthalpy of solution in the DMF-water mixture (AHE(M)) by use of a simple hydrophobic hydration model. Summarizing this derivation, we conceived the enthalpies of solution in the DMF-H20 system (AH°(M)) as being the result of two effects (a) When the hydrophobic hydration of tetraalkylammonium ions is absent, the corresponding enthalpy of solution in pure water AH K O) and in the mixture AHJ(M) should be correlated by ... 

Ion exchange between heparin and Cl associated with tetraalkylammonium ions in the membrane of the ion-selective electrode. Ion-selective electrodes described in this chapter reach an equilibrium electric potential... 

Performance of tetraalkylammonium ions during the formation of zeolites from tetraethylorthosilicate... 

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