Common anion effect

The effect of common-anion salts and of added water showed, however, that ionic chain carriers must also be present in these systems. These observations, coupled with experiments where dilute solutions of the monomers were treated with excess of acid and the reactions followed by ultraviolet spectroscopy, produced sufficient information about the initiation reaction pattern and thus completed the overall kinetic and mechanistic approach. 

Type II refers to the case in which the isotherms for both cations increase with increasing concentration of the respective cations. Such isotherms have been found for (Li, K)F,j2 (Li, K)(S04)i/2, (Na, K)OH, (Ag, Cs)Br, - (Ag, Na)I, - (Ag, K)I, - " and (Ag, CS)I. In charge asymmetric systems such as (K, Ca 2)CI, such isotherms also usually appear. A common feature of these type II systems is the particularly strong interaction of one cation with the common anion compared with that of the second cation with the anion. The strongly interacting cation will retard the internal mobility of the second cation. This is called the tranquilization effect, and will be explained in Section III.5( 70-... 

In such systems as (M, Mj (i/2))X (M, monovalent cation Mj, divalent cation X, common anion), the much stronger interaction of M2 with X leads to restricted internal mobility of Mi. This is called the tranquilization effect by M2 on the internal mobility of Mi. This effect is clear when Mj is a divalent or trivalent cation. However, it also occurs in binary alkali systems such as (Na, K)OH. The isotherms belong to type II (Fig. 2) % decreases with increasing concentration of Na. Since the ionic radius of OH-is as small as F", the Coulombic attraction of Na-OH is considerably stronger than that of K-OH. 

Case I. No Double Salt Separates.—Let us suppose that the solubility of the compound A at a given temperature (say 20°) is represented (Fig. 18) by point A on the abscissa OX the solubility of the compound B, by the point B on the ordinate OF and let us further suppose that the two salts have a common anion, e.g., are both chlorides. If to the saturated solution A some salt B is added, the common ion effect will diminish the solubility of A, the line AC representing the diminishing solubility of A as increasing quantities of B are added. 

Effect of Cation. Of all alkali chlorides, only lithium chloride is sufficiently soluble in ethylenediamine to act as an electrolyte. On the other hand, all alkali iodides are soluble in ethylenediamine. Since the anion has a large effect on current efficiency, a common anion such as the iodide ion must be used to compare the effect of the various cations. The results of runs 6 and 7 show that the current efficiency was slightly higher and the percentage of octalin formed much greater when rubidium iodide was used instead of lithium iodide. The metallic cations Li and Rb give markedly better current efficiency than the organic cations (runs 6, 7, 8, and runs 5, 9, 10, 11). 

The most common electrochemical effects exerted in bulk solution are related to association (solvation, ion-pairing, complex formation, etc.) with the electroactive substance or electrochemically generated intermediates [4,19]. The importance of solvation can be gauged by comparing calculated and measured values of the parameter AE1/2 (defined as the difference, in volts between the half-wave potentials of the first and second polarographic waves) exhibited by polycyclic aromatic hydrocarbons (PAH) in dipolar aprotic solvents [46,47], It can be shown that AE1/2 is related to the equilibrium constant for disproportionation of the aromatic radical anion into neutral species and dianion, that is,... 

Dual-host approaches have also been used to good effect for CsN03 extraction. Nitrate is a common anion found upon nitric acid extraction of 137Cs+ in the nuclear industry. Cs+ is conveniently com plexed by a large crown ether such as tetrabenzo[24] crown-8 while simple tripodal amide hosts of type 5.31 (where R is a long alkyl group to impart lipophilicity) are effective at binding N03 . Extraction efficiency of Cs+ from water into 1,2-dichloroethane was found to be enhanced by a factor of up to 4.4 in the presence of the anion host.28... 

Wu et al. [818] have described a method for the derivatisation of iodide into pentafluorobenzyl iodide using pentafluorobenzyl bromide. The derivative was analysed at ig levels by gas chromatography with electron capture detection. The effects of solvent, water content, base or acid concentration, amount of pentafluorobenzylbromide, reaction time and reaction temperature were examined. Interferences by common anions were minimal. The method was applicable to iodide determination in spring water. 

But let us return to conventional IEC and consider the order of anion selectivities. It can be seen that an anion resin in the citrate form would be useless—citrate is the anion most strongly held, and it would not be appreciably displaced by any other anion in the list. To convert a citrate or sulfate resin to another form requires extensive washing with a mobile phase highly concentrated in the other ion in order to effect the displacement equilibrium. It is even difficult to convert completely a chloride resin to its hydroxide form. Thus, in purchasing a resin, it is important to note the counterion with which it is sold. Commonly anion resins are in the chloride form and cation resins in the hydrogen form. 

Antagonist actions in 4,5-epoxymorphinans are often substantially increased when oxygen is introduced into the molecule at C-14(264), and several explanations have been offered for this phenomenon. 265"268 In particular, the effect of a 14/3-OH function upon the JV-substituent and its directionality, 269 270 or upon molecular conformation, 271 153 has been given some consideration. The suggestion 272 that the 14-OH interacts both with the protonated tertiary nitrogen and with loW-energy conformers of the N-substituent at a common anionic site on the opioid receptor has been tested 273 by the... 

The dissociation constants of trityl and benzhydryl salts are KD 10 4 mol/L in CH2C12 at 20° C, which corresponds to 50% dissociation at 2-10-4 mol/L total concentration of carbocationic species (cf. Table 7) [34]. The dissociation constants are several orders of magnitude higher than those in analogous anionic systems, which are typically KD 10-7 mol/L [12]. As discussed in Section IV.C.l, this may be ascribed to the large size of counterions in cationic systems (e.g., ionic radius of SbCL- = 3.0 A) compared with those in anionic systems (e.g., ionic radius of Li+ 0.68 A), and to the stronger solvation of cations versus anions. However, the dissociation constants estimated by the common ion effect in cationic polymerizations of styrene with perchlorate and triflate anions are similar to those in anionic systems (Kd 10-7 mol/L) [16,17]. This may be because styryl cations are secondary rather than tertiary ions. For example, the dissociation constants of secondary ammonium ions are 100 times smaller than those of quaternary ammonium ions [39]. 

These KD values are much smaller than those of trityl and benz-hydryl salts (lO-MO-4 mol/L) (cf Tables 7 and 16). The KD values of trityl salts correspond to interionic distances of approximately 5 A. The smaller (Kd 107-10-6 mol/L) dissociation constants calculated from the common ion effect in styrene polymerizations with triflate and perchlorate anions correspond to interionic distances =4 A. However, perchlorate and triflate anions may not be spherical, and their dipole moments should therefore also be considered in calculating their interionic distances and dissociation constants. As discussed in Section II.D, specific interactions of counteranions with the ar-H atoms of the secondary carbenium ions may result in lower dissociation constants [39],... 

The common ion effect does not influence the kinetics of collapse of the ion pairs to dormant covalent species since it is a unimolecular reaction. In this case, however, deactivation of the ion pair can be increased by using less stable and more nucleophilic counteranions. The nucleophi-licity of both pure halides and complex anions with halide ligands increases in the order FOther examples of polymerizations which are well behaved because the equilibrium is favorable due to nucleophilic counteranions include Hl/I2 initiated polymerizations of vinyl ethers and polymerizations of isobutene and styrene using acetate-based initiators in the presence of BC13. 

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