Basic dissociation constants

Delphonine shows an unusually high basic dissociation constant, and that of aconine is only a little less. In the case of tertiary vinyl cyclic amines, which prove to be unexpectedly strong bases, Adams and Mahan suggested that they exist in solution as equilibrium mixtures consisting of the tertiary unsaturated base and a quaternary arrangement in which the double bond has moved to the nitrogen, which may be represented thus —. . . +. . . +... 

Otherwise expressed, bases are considered from the standpoint of the ionisation of the conjugated acids. The basic dissociation constant for the reaction... 

The base properties of the amine are represented by its basicity constant (basicity dissociation constant, Kh), which identifies the amount of the amine (in moles) that is ionized (i.e., available to raise pH) in liquid water-condensate at any given temperature and pressure. The dissociation reaction for a primary amine is shown in equation 1, and the value of the dissociation constant is shown in equation 2. 

Davidson and Hantzsch (1898) and later Engler and Hantzsch (1900) investigated this system on the supposition that it corresponds to that of the common dibasic acids. From conductivity measurements they calculated basic dissociation constants for the diazohydroxides, but it is now known that their assumptions were incorrect. In fact, at the turn of the century it was practically impossible to reach the right solution. On the one hand, Hantzsch did not have at his disposal the current poten-tiometric technique for protolytic equilibria, and on the other hand, the system of Scheme 5-1 is a special case for a dibasic acid, the principle of which was not grasped in Hantzsch s time. 

However, EU2O3 behaves as an amphoteric oxide and dissociates according to the two reaction schemes already proposed for all trivalent REE (cf. eq. 10.37 and 10.38). Denoting and respectively, as the acidic and basic dissociation constants, the Eu /Eu oxidation ratio varies with the silica amount in the melt (1 - Xmo) according to... 

Isoelectric casein Nag [(O ") Ca,] ->-Nas (C ") Na Cg,. Whether the complex salt [NusC" casein] must be regarded as a complex salt or an ionic micelle of the type investigated by McBain in his investigations on the soap solutions is not yet clearly established, whilst information on the acid and basic dissociation constants of the higher stages of dissociation of the complex protein is still lacking. 

In this case the basic dissociation constants K should follow the relation ... 

Hence the basic dissociation constant should follow the relation—... 

The value of h for p-aminobenzoic acid is 4.93 X whereas the basic dissociation constant (kb) of ethyl p-aminobenzoate is 2.8 X 10 . What conclusions may be drawn concerning the structure of p-aminobenzoic acid in aqueous solution ... 

The basic dissociation constant is a measure of the tendency of a ligand to coordinate with the hydrogen ion. Therefore, if a series of ligands of structural similarity are compared, a linear relation should be expected between log (where is the formation constant) and pAj or pKg for the ligand. Examples are the Ag(I) complexes of primary amines and the Cu(II) complexes of )S-diketones. There is a... 

This relationship is general for all conjugate acid/base pairs. Many compilations of equilibrium-constant data list only acid dissociation constants, since it is so easy to calculate basic dissociation constants by using Equation 9-14. For example, in Appendix 3, we find no data on the basic dissociation of ammonia (nor for any other bases). Instead, we find the acid dissociation constant for the conjugate acid, ammonium ion. That is,... 

Equation 9-14 confinns the observation in Figure 9-2 that as the acid of a conjugate acid/base pair becomes weaker, its conjugate base becomes stronger and vice versa. Thus, the conjugate base of an acid with a dissociation constant of 10 -will have a basic dissociation constant of 10 , whereas an acid with a dissoci ation constant of 10 has a conjugate base with a dissociation constant of lO". ... 

We have shown in the section on hydrolysis included in the first chapter that the reaction of salts derived from weak acids and weak bases is never strongly acidic or strongly alkaline, unless the difference between the acidic and basic dissociation constants is too large. The same explanation, applied to the acidic and basic functions of ampholytes, accounts for the fact that solutions of amphoteric compounds never react very strongly acid or alkaline. 

For the sake of simplicity we shall refer to the undissociated ampholyte as A, to the ampholyte cations as A+, and to the anions as A. We shall designate the dissociation constant of the acidic group by Ka, the basic dissociation constant by Kb, and the constant of water by The total ampholyte concentration will be taken as equal to c. 

In order to illustrate the hybrid ion theory, we shall compare ammonium acetate with an amino acid of which the acid and basic dissociation constants are respectively the same as those of acetic acid and ammonium hydroxide. We know that in 0.1 molar solution, ammonium acetate is 0.5% hydrolyzed and the salt is 99.5% ionized. If we employ the same equation (40 in Chapter One) to calculate the degree of hydrolysis of the amino acid, we find that it too is 0.5% hydrolyzed. Thus it appears logical to assume that the remainder of the ampholyte is present in the ionogenic form. 

Ka and Kb are the true acidic and basic dissociation constants of the ampholyte whereas Ka and Kb are merely the apparent dissociation constants. 

The true acidic dissociation constant of the amino acid is evidently identical with the hydrolysis constant of the basic group with an apparent dissociation constant Kb," the true basic dissociation constant corresponds to the value of the hydrolysis constant for the acid group on the older basis. 

The radical difference between the classical and modern views is readily seen from equations (17) and (18). The basic character, as defined by the older theory, actually is determined by the true acidic dissociation constant based on the hybrid ion conception. Conversely, the acidic nature is governed by the true basic dissociation constant. 

The fact that Walbltjm found a large temperature coefficient for the Ka of glycine supports the hybrid ion theory. The dissociation constants of carboxylic acids and of ammonia show small temperature coefficients. If Walblum s data are recalculated to yield the true basic dissociation constant, we find only a twofold increase in this constant between 10° and 70°. 

The catalytic power of a particular species is most conveniently specified by the catalytic constant (fcA or fcB), as shown in Eq. (8). The acid strength of a catalyst is usually described by its dissociation constant in water, KA. The basic strength of a catalyst may be measured by the conventional basic dissociation constant, but it is more convenient to use the reciprocal of the dissociation constant of the corresponding acid thus for the acetate ion we write = l/KHAe = [HAc]/[H+][Ac ], and for ammonia, K3 = 1/ANH4+ = LNH4+]/[H+][NH3]. Strictly speaking,... 

Because every base has a conjugate acid we can conveniently quote the acid dissociation constant of the conjugate acid instead of the basic dissociation constant of the base. Consider, for example, the ionization of the base NH3 in water ... 

Amines occur as gases (methylamine bp,—6.7 C), liquids (aniline bp, 184 C), and solids (1-naphthylamine mp, 50°C). Their basic characteristics are best illustrated by the list of basic dissociation constants (Kb) given in Table 6-1. 

Table 5-1. Basic Dissociation Constants of Primary Amines...

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