Counterions tetrabutylammonium

The ionic or polar substances can be seperated without any reaction on specially treated chromatographic columns and detected refractometrically. This is necessary because alkyl sulfosuccinates show only small absorption in the UV-visible region no sensitive photometric detection can be obtained. Separation problems can arise when common steel columns filled with reverse phase material (or sometimes silica gel) are used. This problem can be solved by adding a suitable counterion (e.g., tetrabutylammonium) to the mobile phase ( ion pair chromatography ). This way it is possible to get good separation performance. For an explanation of separation mechanism see Ref. 65-67. A broad review of the whole method and its possibilities in use is given in an excellent monograph [68]. 

Inorganic bases have been also employed in this system. When Butcher first used alkali carbonates [50], it was reported that, in DMF and at ambient temperature, the carbamation of primary and secondary aliphatic amines (or also arylamines) with alkyl halides under a C02 atmosphere (0.1 MPa) was effectively promoted by Cs2C03 [50, 51]. The Cs+ cations in the solvent used (DMF) did not form ion pairs with counterions, and favored the formation of naked carbamate anions that were more reactive at the O-ends with alkyl halides. Jung further found that the addition of tetrabutylammonium iodide (TBAI) to the system RR NH/ C02/RX/Cs2C03/DMF promoted the carbamation process with a higher yield and selectivity with respect to N-alkylation [51]. The process has been successfully extended to the synthesis of carbamate functionalities on solid phases. In this case, resin-bound carbamates are readily released from the resin by treatment with LiAlH4 in THF, yielding the respective N-methyl secondary amines [51]. 

An alternative suggestion is that the coordinated monomer dissociates to give an oxyanion stabilized by the nucleophile s counterion, most commonly, tetrabutylammonium or cesium ions,69 by analogy to the mechanism proposed for activation of tributylstannyl ethers by nucleophiles.57 This proposal is summarized in Fig. 14, which also shows the product mixture obtained for methyl (2S,3R)-2,3-dihydroxybutanoate. For this compound, reaction on the oxygen atom of the inherently less acidic hydroxyl is favored. Both anions, E and F, are in equilibrium with the coordinated monomer, and the less populated (but more reactive) anion E reacts to a greater extent, or in other words, the difference in the rate constants for trapping is greater than the difference in equilibrium constants. 

In some systems it is necessary to add a large amount of salts to obtain polymers with low polydispersities. This happens when salts participate in ligand/anion exchange (special salt effect) and when they enhance ionization of covalent compounds through the increase of ionic strength. The special salt effect may either reduce or enhance ionization. Strong rate increases observed in the polymerization of isobutyl vinyl ether initiated by an alkyl iodide in the presence of tetrabutylammonium perchlorate or triflate can be explained by the special salt effect [109]. The reduction in polymerization rate of cyclohexyl vinyl ether initiated by its HI adduct in the presence of ammonium bromide and chloride can be also ascribed to the special salt effect [33]. The breadth of MWD depends on the relative rate of conversion of ion pairs to covalent species and is affected by the structure of the counterions. 

In extraction procedures using methylene chloride as organic phase, bromothymol blue has been used as an ion-pairing counterion for amfetamine, and picrate ions for atropine. Tetrabutylammonium ion has been used for the extraction of penicillins into chloroform. 

On the other hand, these values are dramatically modified if the presence of alkali-metal (sodium) counterions is taken into account, the ion-paired trianions becoming by far the most stable species (E = —4.5 eV). On this basis, it has been postulated that in the butoxide reduction of 65 and 67 formation of the potassium ion-paired trianions would be favored over that of the ion-paired monoanions, while reduction with tetrabutylammonium borohydride in THF or the electro-... 

The counterion employed also has a marked effect on the electropolymerization process in organic solvents. For example, the polymerization of poly(methyl carboxypyrrole) (PMCP) proceeds differently in para-tolucncsul Ionic acid (pTS), tetrabutylammonium perchlorate (TBAP), tetrabutylammonium tetrafluoroborate (TBABF4), and tetrabutylammonium hexafluorophosphate (TBAPF6).63 As reported in that work, the rate of polymerization (at constant potential) and the time required for the onset of polymer deposition varied with the counterion employed. 

Considering hydrocarbon tails, it seems that the minimal length to produce polysoap properties is about C8 [52, 191, 199, 200], Polysoap behaviour was reported even for some shorter chains, but then additional hydrophobic units in the backbone must be present (see below). Also, hydrophobic counterions such as tetrabutylammonium [252] or alkyltrimethylammonium ions [186,204] may induce hydrophobic aggregation for short chain polysoaps , but in such cases it... 

For cation systems, the suppressor membranes are anion exchange polymers, which allow anions to pass freely, but exclude cations. Dilute acids such as HCl are used in the mobile phase. In the suppressor, chloride counterions are replaced by highly conductive OH ions, neutralizing the acidic mobile phase. Tetrabutylammonium hydroxide is used as the regenerant because it is excluded from the anion exchange membranes."... 

The observed nanostructuration is not just due to the effect of a particular ion, but to the combined influence of the different ions present in solution. For example, the structuration effect of tetrabutylammonium salts is different for different counterions. The size of the bumps was larger for the case of iodide or bromide compared with nitrate or chloride. A more marked difference is observed for the case of lithium salts. While LiCl and LiSOq did not induce extensive surface structuration, substantial effect of Lil and LiBr solutions was... 

For the separation of anions of weak protolytes such as carboxylates, a pH close to neutral is chosen to ensure that the solutes are in ionic form. Quaternary ammonium ions such as tetrabutylammonium are most often used as counterions, as in the example given in Figure 5, which shows the separation of benzoic acid and three structurally related carboxylic acids. A mixture of acetonitrile and phosphate buffer of pH 6.0 is the mobile phase. These few applications illustrate the kind of phase systems being used with anionic or cationic counterions. The hydrophobicity... 

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