Acid dissociation equilibria

Clearly, it is also possible to synthesize benzylpenicillin by the reverse reaction. Two (relevant) acid dissociation equilibria are involved ... 

From the acid dissociation equilibria, we replace [H2L+] with [HL [H 1 IKX, and [L ] with [HL]AV[II+ ]. Also, we can always write [OH ] = KJ. Putting these expressions into the charge balance gives... 

Acid-dissociation equilibria for the coordinated water in [Co(III)-(H20)2(BDHC)]2+ and [Co(III)(H20)(CN)(BDHC)]+ are accompanied by the spectral changes shown in Figure 5 the pKa values are summarized in Table IV along with those for the corrinoid complexes (29). The pKa values are comparable with each other between these two complex systems. 

In the case of gases such as S02> which are anhydrides of weak acids (i.e., for SO2, sulfurous acid), assumption also of pertinent hydration and acid dissociation equilibria, which, together with the cloud droplet pH, determine the total solubility. This pH-dependent total solubility is conveniently expressed as an effective Henry s law coefficient, H. ... 

Plesch and collaborators have recently introduced this technique for the study of carbenium and oxonium ions and of Br nsted acid dissociation equilibria ° The ultimate aim of this work is of course to gain a better understanding of the mechanism of initiation in cationic polymerisation. For the moment however it is difficult to assess the real potential of polarography in that context and we feel that, althou it certainly possesses a hi sensitivity, the conditions required for meaningful measurements are still too distant from those employed in an actual polymerisation, in particular the high ionic strength of the medium. Its use is therefore still doubtful and one can only hope that more research will bridge the gap. 

A. Acid Dissociation Equilibria of Carboxymethyldextrans and Their Gel Analogs... 

The polyion domain volume can be computed by use of the acid-dissociation equilibria of weak-acid polyelectrolyte and the multivalent metal ion binding equilibria of strong-acid polyelectrolyte, both in the presence of an excess of Na salt. The volume computed is primarily related to the solvent uptake of tighdy cross-linked polyion gel. In contrast to the polyion gel systems, the boundary between the polyion domain and bulk solution is not directly accessible in the case of water-soluble linear polyelectrolyte systems. Electroneutrality is not achieved in the linear polyion systems. A fraction of the counterions trapped by the electrostatic potential formed in the vicinity of the polymer skeleton escapes at the interface due to thermal motion. The fraction of the counterion release to the bulk solution is equatable to the practical osmotic coefficient, and has been used to account for such loss in the evaluation of the Donnan phase volume in the case of linear polyion systems. 

The equilibria of metal (Mz+) complexation and H+ binding in weak acidic polyelectrolyte or weak basic polyelectrolyte solution can be treated equally, since both ions are cationic. However, conventionally H+ binding equilibria are expressed by acid dissociation. In this section, the acid dissociation equilibria of both weak acidic and weak basic polyelectrolytes are analyzed by the Gibbs-Donnan concept [5-7], and the fundamental aspects clarified up to the present time are presented. 

Though the phase boundary is not necessarily observable, the remarkable salt concentration (Cs/mol/dm3) dependence of the ion binding equilibria in polyion systems implies the phase separation nature of the polyelectrolyte solutions. A straightforward proof for this property can be gained by the careful examination of the acid dissociation equilibria of weak acidic polyelectrolytes, (HA) , and the conjugate acids of weak basic polyelectrolytes, (BH+) , respectively, expressed as the repeated functionalities of HA and BH+ ... 

In the preceding section, the remarkable salt concentration effect on the acid dissociation equilibria of weak polyelectrolytes has been interpreted in a unified manner. In this treatment, the p/( ,pp values determined experimentally are believed to reflect directly the electrostatic and/or hydrophobic nature of polyelectrolyte solutions at a particular condition. It has been proposed that the nonideality term (Ap/Q corresponds to the activity ratio of H+ between the poly electrolyte phase and the bulk solution phase, and that the ion distribution equilibria between the two phases follow Donnan s law. In this section, the Gibbs-Donnan approach is extended to the equilibrium analysis of metal complexation of both weak acidic and weak basic polyelectrolytes, i.e., the ratio of the free metal ion activity or concentration in the vicinity of polyion molecules to that of bulk solution phase is expressed by the ApAT term. In Section III.A, a generalized analytical treatment of the equilibria based on the phase separation model is presented, which gives information on the intrinsic complexation equilibria at a molecular level. In Secs. B and C, which follow, two representative examples of the equilibrium analyses with weak acidic (PAA) and weak basic (PVIm) functionalities have been presented separately, in order to validate the present approach. The effect of polymer conformation on the apparent complexation equilibria has been described in Sec. III.D by exemplifying PMA. 

Equation 22 predicts that the nonideality term for the acid dissociation equilibria of weak polyelectrolytes can directly be used to evaluate the (K mt function, i.e., if log( M)app is plotted against ApA, a straight line with the slope Z is expected, whose intercept at the y axis corresponds to log( [5-7], It should be noted again that (1) the concurrent measurement of pH and pM at each titration point is needed for this analysis and (2) the ratio of the total concentrations of metal ion to ligand polymer should be kept as low as possible for the perturbation due to complexation on acid dissociation equilibria to be neglected. 

By the systematic work on the complexation equilibrium analyses of both weak acidic and weak basic polyelectrolytes, the Gibbs-Donnan approach is validated to provide deep insights into the complexation behaviors of linear polymer ligands. This concept does not need any adjustable parameter it only uses the logic of phase separation of polyelectrolyte aqueous solutions. The electrostatic nonideality (polyelectrolytic effect) observed in the acid dissociation equilibria of a polyion can directly be used to correct for the electrostatic nonideality for metal complexation. The potentiometric titration technique with concurrent measurements of pH and pM is most suit-... 

M Mori, T Miyajima, S. Ishiguro. The influence of quaternary ammonium ions on the acid-dissociation equilibria of polyacrylic acid. J Colloid Interface Sci, in press. 

H Kodama, T Miyajima, M Mori, M Takahashi, H Nishimura, S Ishiguro. A unified analytical treatment of the acid-dissociation equilibria of weakly acidic linear polyelectrolytes and the conjugate acids of weakly basic linear polyelectrolytes. Colloid Polym Sci 275 938-945, 1997. 

The acid dissociation equilibria of the ligand coupled with the inclusion equilibria can be expressed in Schemes 1 and 2, where Kg - > a2>... 

The closeness of fit may be gauged from the experimental and theoretical rate vs. concentration curves for hydrolysis of p-nitrophenyl carboxylates catalysed by quaternary ammonium surfactant micelles (Figure 3). The shape of the curve is satisfactorily explained for unimolecular, bimolecular, and termolecular reactions. An alternative speculative model is effectively superseded by this work. Romsted s approach has been extended in a set of model calculations relating to salt and buffer effects on ion-binding, acid-dissociation equilibria, reactions of weakly basic nucleophiles, first-order reactions of ionic substrates in micelles, and second-order reactions of ionic nucleophiles with neutral substrates. In like manner the reaction between hydroxide ion and p-nitrophenyl acetate has been quantitatively analysed for unbuffered cetyltrimethylammonium bromide solutions. This permits the derivation of a mieellar rate constant km = 6-5 m s compared to the bulk rate constant of kaq =10.9m s . The equilibrium constant for ion-exchange at the surface of the micelle Xm(Br was estimated as 40 10. The... 

Mesmer RE, Baes CF (1974) Phosphoric acid dissociation equilibria in aqueous solutions to 3(X)°C. J Solution Chem 3 307-322... 

Table 21.1 Hydrolysis of thorium (/y) and uranium (iv) in solutions of various ionic strengths I and temperatures t. M ium NaJl)ClO, if not otherwise stated. Constants pPZm listed refer to the acid dissociation equilibria + n H2O M (OH) + IIH. ...

Table 21.3 Hydrolysis of uranyl (vi) in various aqueous media% at 25°C except when stated otherwise. Constants p/J listed refer to the acid dissociation equilibria mUOi + + nHjO (UO ) + H +.

---