Basicity constant table

The basicity constants (Table 5) of the stepwise protonation of methylated tetramines (trienMeq and trienMeg) have been considered and compared with those of the unsubstituted parent triethylenetetramine (trien). 

The basicity constants (Table 6) of the stepwise protonation of polyazacycloalkanes have been determined. 

Gibbs transfer encryy or standard transfer potential of every component (basic constants tabled as mentioned in section II.C.I)... 

Various amines find application for pH control. The most commonly used are ammonia, morpholine, cyclohexylamine, and, more recently AMP (2-amino-2-methyl-l-propanol). The amount of each needed to produce a given pH depends upon the basicity constant, and values of this are given in Table 17.4. The volatility also influences their utility and their selection for any particular application. Like other substances, amines tend towards equilibrium concentrations in each phase of the steam/water mixture, the equilibrium being temperature dependent. Values of the distribution coefficient, Kp, are also given in Table 17.4. These factors need to be taken into account when estimating the pH attainable at any given point in a circuit so as to provide appropriate protection for each location. 

The value of Kb tells us how far the reaction proceeds to the right. The smaller the value of Kh the weaker is the ability of the base to accept a proton. Table 10.2 lists the basicity constants of some weak bases in aqueous solution. 

Ahrland et al. (1958) classified a number of Lewis acids as of (a) or (b) type based on the relative affinities for various ions of the ligand atoms. The sequence of stability of complexes is different for classes (a) and (b). With acceptor metal ions of class (a), the affinities of the halide ions lie in the sequence F > Cl > Br > I , whereas with class (b), the sequence is F < Cl" < Br < I . Pearson (1963, 1968) classified acids and bases as hard (class (a)), soft (class (b)) and borderline (Table 1.23). Class (a) acids prefer to link with hard bases, whereas class (b) acids prefer soft bases. Yamada and Tanaka (1975) proposed a softness parameter of metal ions, on the basis of the parameters En (electron donor constant) and H (basicity constant) given by Edwards (1954) (Table 1.24). The softness parameter a is given by a/ a - - P), where a and p are constants characteristic of metal ions. 

The basicity constants in water and micelles then have the same units (M 1), and values of K and Kb are not very different for arenimidazoles and nitroindoles under a variety of conditions (Table 10). The comparisons suggest that inherent basicities are not very different in water and cationic micelles, but, as with second-order rate constants of bimolecular reactions (Section 5), there is a limited degree of specificity because K /Kb is slightly larger for the nitroindoles than for the arenimidazoles, almost certainly because of interactions between the cationic micellar head groups and the indicator anions. 

The results of these investigations for forty-five aromatic compoimds are collected in Tables 19, 22 and 23. All figures for basicity constants were obtained in anhydrous hydrofiuoric acid as the solvent. This means that these values only apply to this solvent they are, however, precise. 

This means that the basicity constant measured in solution represents the total basicity of the dissolved aromatic substance. In order therefore to obtain the true basicity constant the measured figure evidently has to be divided by the number of active C-atoms in the molecule. This number, z, which is related to the symmetry of the molecule, is six for benzene, four for p-xylene, one for pentamethylbenzene, six for hexa-methylbenzene, fom for naphthalene, two for anthracene, etc. (see Tables 19 and 22). Thermodynamically, this correction can be justified as an entropy contribution (Mackor et al., 1958a). 

The values from (53) give the overall basicity constants relative to a standard substance. The last column of Table 27 gives the differences piTg — pJTJ calculated according to (52), since the p.K -values are known from the investigations of Mackor and collaborators (1958a, b). 

In calculating these relative basicity constants, the value of 0-34 e.v. was used for Sa. The results so obtained are listed in Table 28 in comparison with the values of Ehrenson (1961, 1962), Flurry and Lykos (1963) and the experimental values of Mackor and collaborators (1958a, b). 

The nickel oxide electrode is generally useful for the oxidation of alkanols in a basic electrolyte (Tables 8.3 and 8.4). Reactions are generally carrried out in an undivided cell at constant current and with a stainless steel cathode. Water-soluble primary alcohols give the carboxylic acid in good yields. Water insoluble alcohols are oxidised to the carboxylic acid as an emulsion. Short chain primary alcohols are effectively oxidised at room temperature whereas around 70 is required for the oxidation of long chain or branched chain primary alcohols. The oxidation of secondary alcohols to ketones is carried out in 50 % tert-butanol as solvent [59], y-Lactones, such as 10, can be oxidised to the ketoacid in aqueous sodium hydroxide [59]. 

For ammonia in water at 25°C, the experimental value of Kb is 1.8 X 105. This small value tells us that normally only a small proportion of the NH3 molecules are present as NH4+. Equilibrium calculations of the type we used in Section 9.7 and which we shall do in more detail later confirm this conclusion. They show that only about 1 in 100 molecules is protonated in a typical solution (Fig. 10.14). The basicity constants of some weak bases are given in Table 10.2. 

To predict the pH of mixtures of weak acids or bases and their salts quantitatively, we set up an equilibrium table, as described in Toolbox 10.1. Then we use the acidity or basicity constant to calculate the concentration of hydronium ions present in the solution. The only difference is that now the conjugate acid and base are both present initially, so the first line of the table must have their initial concentrations. For instance, in the mixed acetic acid/sodium acetate solution, both acetic acid and its conjugate base, acetate ions, are present initially. In the ammonia/ammo-nium chloride solution, both the base (ammonia) and its conjugate acid (the ammonium ions) are present initially. 

A very interesting observation was the decrease in basicity of the cyano group in a-sulphur-substituted nitriles in comparison with the corresponding sulphur-free compounds75. The basicity constants for the nitriles (Table 11) were corrected to give lg Kas + SEs values. These values consider the steric effects of the substituents. 

The diprotonation of the TV-benzoylthioureas is complete in 100% sulphuric acid. A comparison of the mono- and diprotonation constants (Table 24) shows that the oxygen and sulphur atoms of TV-benzoylthiourea and other A-acylthioureas have about equal basicities, but in spite of this fact protonation on oxygen requires much stronger acids than does protonation on sulphur. These results are caused by the fact that —Ha (which... 

Unfavourable intramolecular repulsions between NH+ groups are highly dependent on the distance between the protonation sites and thus the introduction of a longer, propylenic spacer generally increases the second and subsequent basicity constants as well as influencing the first by increased electron donation. Compare entries 3 and 4 in Table 3.16. The effect is also evident in the linear... 

Table 3.16 Basicity constants for some representative polyamines.

Table 17 Acidity constants in water and basicity constants in H2SO4/H2O mixtures (determined using H0 acidity function) of selected 5-R-tetrazoles at 25 °C <2006RJ01585>...

Some substances with very weakly basic properties are only partially ionized in sulfuric acid and it is possible to measure their degree of ionization and hence obtain their basicity constants by means of cryo-scopic, conductimetric, and spectroscopic measurements. A number of nitro-compounds have been carefully studied by several different methods. It may be seen in Table IX that the results obtained by the differ-... 

Thus either the acidity or basicity constant describes fully the protolysis properties of an acid-base pair. The stronger the acidity of an acid, the weaker the basicity of its conjugate base, and vice versa. For illustration purposes Table 3.2 lists a series of acids and bases in the order of their relative strength. 

Table 3.2. Acidity and Basicity Constants of Acids and Bases in Aqueous Solutions (25°C)... 

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