Ammonium counter-ion

Highly sensitive ammonium and methylammonium tetraazidoaurates(III) have been prepared according to different procedures depending on the ammonium counter ion [37] (Equations 2.2 and 2.3). 

Bortoletto et al. (1997) have used neutral and cationic triphenylphosphine trisulphonate or triphenylphosphine mono-sulphate Rh complexes. Monosulphonate is less readily oxidized and can replace trisulphonate in industrial processes. The presence of a quaternary ammonium counter ion associated with the trisulphonate confers phase-transfer properties to the catalytic. species, which makes use of co-solvents unnecessary. 

The addition of a surfactant counter-ion reduced the retention factor at low pH due to the surface modification of the stationary phase material. Covering the surface of the stationary phase with the surfactant reduces the hydro-phobicity of the stationary phase material. The addition of the tetrabutyl-ammonium counter-ion increased the retention factor at high pH. The pKa of the indole acetate was 5.15 without surfactant, 4.85 with octyl sulfate ion, and 5.60 with tetrabutylammonium ion. That is, the addition of a same-charged hydrophobic ion reduced the pKa value, and the addition of the counter-ion increased the pKa value. The difference in the pKa value on the addition of surfactant is not constant it is affected by the kind of ion and the concentration. It is difficult to estimate the pKa change. 

Initiation takes place by rapid reaction of an ammonium salt with the anhydride (Eq. (46)) whereby ammonium carboxylate is formed. In the propagation step, the carboxylate anion opens an epoxy ring and forms an ammonium alcoholate (Eq. (47)). The latter reacts with the anhydride to yield another ester bond, and ammonium carboxylate is recovered (Eq. (48)). Termination occurs through decomposition of the ammonium counter ion, the alkoxide anion abstracting a proton from the quaternary nitrogen with the formation of a deactivated tertiary amine. 

Figure 15. (i) Ion-pair channel former 39. (ii) Hypothetical half-channel structure, which is connected to another similar half-channel in the other half of the monolayer. The black and white columns represent the oligoether-carboxylate anion and the two-tailed hydrophobic ammonium counter ion, respectively. Adapted version of a figure reprinted from Kohuke, Y. Morita, K., Inorg. Chim. Acta 283, 173 with permission from Elsevier Science. 

The products thereby obtained are anionic silane surfactants exhibiting excellent surfactant properties dependent on the ammonium counter ion. Some specimen are real foam boosters, too. For example an 1 wt. % aqueous solution of isopropylammonium sulfatohexyl trimetyl silane shows a surface tension of 21 mN m and a spreading ability of 65 mm. As being familiar for the nonionics the aqueous solution of... 

Under the experimental conditions quaternary ammonium ions would not have been subject to Hofmann degradation. The growing anions must then have been partnered almost exclusively by tertiary ammonium counter ions. 

Jaacks40) has suggested that, while most chains initiated must be ion pairs, zwitterions could make up most of the polymer. An alkoxide ion will react rapidly with a tertiary ammonium counter ion and consequently the molecular weigth of chains initiated by hydroxide ion is probably quite low. 

The sulphoxide 4 is, as expected, an intermediate. The results indicate that the reaction proceeds fastest below pH5. At this pH and lower, TDA-1 is largely present in the protonated ammonium form, unavailable for complexation of sodium ions. We speculated that the transfer mechanism of TDA-1 in this reaction might be as an ammonium counter ion to peroxomolybdate. We evaluated this by testing three alternative... 

Anthracene and naphthalene radical anions, in the presence of quaternary ammonium counter ions, are moderately stable when proton donors are absent. If phenols are added, the radical ion K decomposes according to the scheme... 

Although the above polymerization method fulfills the requirements of an industrially viable process, it should be mentioned that we have developed a second method which is completely different. Accordingly, metal-free carbanions having ammonium counter ions (e.g., RC(C02Et)2N(n-Bu)4) are used as initiators at room temperature in the absence of catalysts. The ammonium ion "binds" the reaction components on the basis of electrostatic forces. 

Figure 5.9 Schematic drawing of the ion cluster structure of the fluorinated ion exchange polymers with (a) alkali metal counter ion and (b) alkyl ammonium counter ion forms (Reprinted with permission from Onishi, K., Sewa, S., Asaka, K. et al. The effects of counter ions on characterization and performance of a solid polymer electrolyte actuator, Electrochimica Acta, 46 (8), 1233-41. Copyright (2001) Elsevier).

Fig. 10. 360 MHz iR-NMR spectrum of CMP-Neu5Ac (as triethylammonium-salt) dissolved in 2H2O, recorded at p2R 8 and 25 °C. Multiplets at 81.3 and 3.2 represent ethyl groups of triethyl ammonium counter ions.

Fig. 1 shows WAXD data for PS/SPS/Na-Mmt composites as a function of alkyl chain length of the quaternary ammonium counter-ions in ammonium neutralized SPS. The original dooi spacing of Na-Mmt at room temperature is 1.03 run the difference is because of collapsing of the layers due to loss of water at high temperatures. The 150"C XRD pattern of Na-Mmt shows that the base gallery spacing for the clay was 0.96 nm. The PLNs were processed between 150 and 160"C, so it was assumed that the weakly bonded water in Na-Mmt was already lost from the clay. 

Takacs-Novak, K. Szasz, G., Ion-pair partition of quaternary ammonium drugs The influence of counter ions of different lipophilicity, size, and flexibility, Pharm. Res. 16, 1633-1638 (1999). 

Figure 3 shows the cathodic reaction. The counter ion, protonated trialkyl ammonium ion, migrate through the ion selective membrane to the cathode. Hydroxyl ions are generated at the cathode where they reduce the amine ions to free amines. 

The doso-clusters B Hn2-, B10H102-, and B6H62 are stable entities. Their alkali salts are very water soluble. Cesium as a counter-ion reduces the water solubility considerably, and ammonium ions (especially quaternary ammonium ions) precipitate the cluster anions quantitatively from aqueous solutions. The resulting tri- and tetraalkylammonium salts are usually soluble in organic solvents. This allows chemistry to be performed under conditions which are standard for organic... 

In the case of ionic species, which may be represented by the ammonium ion, the nitrogen chemical shift depends upon the nature of the counter ion as well as the concentration. 

Li", the covalent character predominates and further reduction is faster than ring closure. The covalent character decreases when quaternary ammonium cations are used as counter ions. Hence, the subsequent electron transfer is much slower than the cyclization step and only the cyclized product is obtained. 

Fluorhydroxyapatite can be synthesised by the traditional double-decomposition method generally used for apatite precipitation. An ammonium phosphate and fluoride solution (solution B) is added, dropwise, into a hot (generally at boiling temperature) calcium solution (solution A) at a basic pH level as previously published [122,123]. Fluorapatites close to stoichiometry are obtained (a = 2, see the following reaction equation) however, a very small residual amount of OH always seems to be present. Filtration and several washing operations are necessary to remove the counter-ions. The reaction is almost total due to the very low solubility of fluorhydroxyapatites. 

We have determined the ion-pair formation-partition equilibrium constant with picrate anion for a number of primary, secondary, tertiary and quaternary ammonium ions 23>. In aqueous media of pH 5-6, the ammonium ions and picrate are considered to exist almost completely as unpaired counter ions. When the aqueous solution is mixed with an immiscible organic solvent, the ions are partitioned into the organic phase as the ion pair. We expected that the steric effect of N-substituents in the ion-pair formation-partition equilibrium could be analyzed by a procedure similar to Eq. 24, and derived Eq. 27 for the set of quaternary ions 23). 

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