Acetate, as ion-pair

Oxygen-containing solvents with a strong coordinating ability, such as diethyl ether, methyl /.so-butyl ketone and /.so-amyl acetate, form oxonium cations with protons under strongly acidic conditions, e.g. (R20) H. Metals which form anionic complexes in strong acid can be extracted as ion pairs into such solvents. For example, Fe(III) is extracted from 7 M hydrochloric acid into diethyl ether as the ion pair... 

From the other anticoccidial drugs, benzamides can be readily extracted as ion-pairs into dichloromethane at strong alkaline conditions (pH 11) using tetrabutylammonium as pairing ion (257). Imidocarb residues have been partitioned into chloroform from alkaline water extracts containing sodium chloride (409), while ethopabate can be partitioned into ethyl acetate from water extracts containing sodium chloride widiout pH adjustment (388). 

Figure 2.12 also shows a curve representing the relation between the values of log (cKa) and the degree of ion association (a). This curve shows that, for 10-2 M KC1 in EtOH (logKA = 2), log (cKA)=0 and 38% of KC1 exists as ion-pairs. For 0.1 M KC1 in acetic acid (log KA=6.2), 99.9% of KC1 exists as ion-pairs the fraction dissociated to free ions is only 0.1%. Usually, in solvents with er<10, the fraction of electrolyte that is dissociated into ions is small except in very dilute solutions. Conversely, in solvents with er>40, the fraction of electrolyte that forms ion-pairs is small except in fairly concentrated solutions.11 ... 

An acid may, rather arbitrarily, be called a strong acid in glacial acetic acid if HAjp - 1- Thus perchloric acid is a strong acid, and yet the pAT for the overall dissociation constant is only 4.87 because it exists largely as ion pairs. Hydrochloric acid has an overall pAT value of 8.55 ammonia, 6.40 pyridine, 6.10 sodium acetate, 6.68 potassium chloride, 6.88 and sodium perchlorate, 5.48. Perchloric acid is the strongest acid and the one used for titration of bases that may be too weak to be titrated in water as solvent. At first it appears that an attempt to titrate a base such as pyridine with perchloric acid would fail, since both have small overall dissociation constants. Critical to the success of such titrations is the small dissociation constant of the salt formed, which results in a large favorable equilibrium constant for the reaction. 

Acidity scales for highly acidic solutions in media of low dielectric constant have been proposed, such as for ethanol-water mixtures and glacial acetic acid-acetic anhydride. Ion pairing is a complicating factor in these solvents. The extent of formation of ion pairs and of free ions differs for various indicators and salts in particular, dissociation constants are sensitive to the size of the anion. The Hammett postulate therefore cannot easily be extended to include media of low dielectric constant. 

Storm et al. [74] evaluated various trialkylamines as ion-pairing agents for the LC separation of aromatic sulfonates. Tributylamine was preferred. In time-scheduled SRM, 19 aromatic sulfonic acids could be determined with detection limits of 3-74 pg/1. Socher et al. [75] demonstrated the applicability of ion-exchange chromatography with an ammonium acetate salt gradient up to 500 mmol/1 in combination with negative-ion ESI as well as APCI LC-MS. 

In solvents containing low concentrations of water in acetic acid, dioxane, or sulfolane, most of the alcohol is formed by capture of water with retention of configuradon. This result has been explained as involving a solvent-separated ion pair which would arise as a result of concerted protonation and nitrogen elimination. ... 

The ionization eonstant should be a function of the intrinsic heterolytic ability (e.g., intrinsic acidity if the solute is an acid HX) and the ionizing power of the solvents, whereas the dissoeiation constant should be primarily determined by the dissociating power of the solvent. Therefore, Ad is expeeted to be under the eontrol of e, the dieleetrie eonstant. As a consequenee, ion pairs are not deteetable in high-e solvents like water, which is why the terms ionization constant and dissociation constant are often used interchangeably. In low-e solvents, however, dissociation constants are very small and ion pairs (and higher aggregates) become important species. For example, in ethylene chloride (e = 10.23), the dissociation constants of substituted phenyltrimethylammonium perchlorate salts are of the order 10 . Overall dissociation constants, expressed as pArx = — log Arx, for some substanees in aeetie acid (e = 6.19) are perchloric acid, 4.87 sulfuric acid, 7.24 sodium acetate, 6.68 sodium perchlorate, 5.48. Aeid-base equilibria in aeetie acid have been earefully studied beeause of the analytical importance of this solvent in titrimetry. 

In contrast to bilateral triple-ion formation, unilateral triple-ion formation may also occur in solvents of high permittivity, when ion-pair association is increased by noncoulombic specific ion-ion interactions in solvents of low basicity such as PC or AN. Exclusive formation of anionic tripleions [A-C+A-] ", is observed in these solvents when large organic molecular anions A interact with small cations such as Li + or H+. For example, in contrast to lithium acetate in DMSO [97], where ion association is moderate, ion association as well as unilateral triple-ion formation is observed in the solvent PC [105] due to the much lower basicity of this solvent, (see Table 2)... 

If the diazonium acetate ion pair can lose a proton, it should also be possible to add a proton to the diazo-methylene compound 6.75. This hypothesis was checked experimentally by carrying out the indazole syntheses in the presence of D2S04. The result was not conclusive, as H/D exchange was observed to a small extent in two cases, but not in others. 

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