Monobasic acids titration

B10H14 can be titrated in aqueous/alcoholic media as a monobasic acid, pA a 2.70 ... 

It was found already by Cattelain that the 3-thioxo derivatives behave as monobasic acids that can be titrated on phenolphthalein and he considered them as more acid than the analogous 3,5-dioxo-triazines. This assumption was recently confirmed by determining the dissociation constants. Just as with 6-azauracil, it was possible to demonstrate, by comparing the dissociation constants of the V-methyl derivatives of all the thioxo analogs, that with the 3-thioxo compounds too, dissociation proceeds first at the NH group in position 3 122... 

Table 2 pA), values of various monobasic acids and aminium ions as determined by Hyperquad analysis of titration data at 1 x 10 3 M in anhydrous ethanol, T = 25.0 °C... 

The complexes with boric acid and borates have been of more interest. The ability of D-mannitol to render boric acid more acidic is well known and forms the basis of an anal3rtical method allowing boric acid to be titrated as a monobasic acid. The boric acid complexes have been... 

The identicalness of the ionization sites in a linear polyelectrolyte (Tanford, 1961) stimulated the interest of Walter and Jacon (1994) in a possible relationship between Kz and M of ionic polysaccharides displaying the characteristic titration curve of a weak, monobasic acid. Without any theoretical assumption, Eq. (S.4) was derived from simple algebra by combining elementary principles of the dissociation theory of weak acids with polymer segment theory ... 

When a monobasic acid is titrated, the titration curve is described completely by the pK. We know for instance that, when pH = pK —... 

Conclusion. If protein molecules exhibit no interactions that are not also present on smaller molecules, then the pK values of their titratable groups would be expected to be roughly those of Table I. Electrostatic forces may move them up or down by as much as 1.5 pK units, but relative values will be unaffected thereby. The pK changes during the course of titration, so that the titration curve for any one group will be broader than it would be for a monobasic acid. 

From a qualitative point of view, a minimum difference in ionization constants is to be expected, because even though a molecule contains two equivalent ionizable protons, once one proton has been lost, the second is retained more strongly by an energy amounting to e jOr (where e is the electronic charge, D is the dielectric constant, and r is the distance between the proton and the charge on the add anion). Thus, for oxalic acid, Ky is about 1000 21 for adipic add, Ky is only about SK2 (nearly the factor of 4). The titration curve of an add in which Ky = 415 2 can be shown to be-identical in every respect to the titration curve of a monobasic acid of one-half its molecular wdght and with dissodation constant Kyjl. 

Some phosphonic acids in alcohols or acetone behave as though they are monobasic when titrated potentiometrically. However, they give two well-defined deflections of the titrimetric curve when DMF is the solvent. The pjSTa values of the first ionization of alkylphosphonic acids (232) increased with... 

Prepared in situ by diazotization of p-aminobenzoic acid with sodium nitrite in an acid medium, the reagent reacts with an active methylene compound (at pH < 6 to avoid formation of a formazan derivative) to give a p-carboxyphenylhydrazone, which can be titrated with 0.1 )VN aOH as a monobasic acid. 

Carbohydrate SVI titrated as a monobasic acid, pK = 2.0, as expected for a phosphate diester, - and mild alkaline hydrolysis cleaved the labile, phosphate diester linkage, to produce a serologically inert monoester, [a]D -M06°, which was not precipitated by alcohol in the presence of calcium acetate. Acidic or enzymic hydrolysis of the monoester yielded a crystalline, nonreducing, chromatographically homogeneous tetrasaccharide which, after sequential methylation and acidic hydrolysis, yielded 2,3,4,6-... 

Figure 6.11 shows the titration curve for adipic acid, hexane-1,6-dioic acid with p Ti = 4.41 and pK2 = 5.28 at 25°C. Here the curve resembles that of a monobasic acid with one extended buffer region, and only one end-point. There is thus a clear distinction between this titration curve and those for malonic and phosphoric acids. The two dissociations for this acid cannot be treated as independent of each other, and analysis of the curve must consider both equilibria simultaneously. 

DL-Form, efflorescent prisms, platelets from water probably contg 1 mol water of crystn. Dec at about 245. Aq solns are acid to litmus. Behaves as a monobasic acid when titrated with NaOH and phenolphthalein. One gram dissolves in about 590 ml water at 20. therap CAT Thyroid inhibitor. 

The pH profiles in Fig. 6 may either show a change of a slope of 1 at the pif, if the incorrectly protonated form can not bind a molecule of substrate or a molecule of inhibitor at all. Thus, pH profiles for titration curves of monobasic acids have some simple properties which should be remembered. Functions (14.47) are decreasing in alkaline or in the add, with a slope of +1 or -1, respectively. Functions (14.48) are the mirror images of functions (14.47). 

In this enzymatic reaction, the catalytic constant, ftcati is the rate-limiting step in the propan-2-ol —> acetone direction a plot of log fccat versus pH has a shape of a titration curve for a monobasic acid with pKa value of 7.0, suggesting that a histidine residue is involved in catalysis in the ternary complex enzyme-NAD" -alcohol (Maret Makinen, 1991). However, this assignment is not unambiguous, since carboxyl groups are known to have pK s as high as 8, and lysines to have pita s as low as 6. 

Equation (18.63) has a form of a titration curve of a monobasic acid with a plateau in alkaline which is decreasing in the add over a single pJCa value (Fig. 6). Equation (18.64) has a form of a titration curve of a dibasic which is also decreasing in the add, but this time overtwo pii values, pKj and (Fig. 8). In this case, if p/E and pKi are not sufficiently apart, separate by at least two pH units, the titration curve may resemble that for the monobasic acid, with a single pK value, and Eq. (18.64) is reduced to Eq. (18.63) in such cases, even the statistical analysis can fail to detect the presence of two dissociating groups in the enzyme. 

Telluric acid can be titrated as a monobasic acid with standard sodium hydroxide using phenolphthalein as an indicator, if an equal volume of glycerol is added. If any nitric acid is present, it must be neutralized first with sodium hydroxide, using methyl orange as indicator. 

Certain hydroxy or halogenated aldehydes, and also some diketones, react with alkali like monobasic acids, and may be titrated in aqueous or alcoholic solution. In some cases the end-point depends on the indicator... 

In the case of sulphur trioxide-alcohol systems the conductivity-composition curve reveals a maximum at 1 4-5 sulphur trioxide/alcohol molar ratio showing that the adducts formed are highly solvated. There is no break in the curve at a molar ratio 1 3, There are, however, breaks at 1 2 and 1 1 sulphur trioxide/alcohol molar ratios. The potentiometric, conductomeuic and visual titrations show that sulphur trioxide solutions in these alcohols behave as monobasic acids against nitrogen bases and indicate that the stable species in alcohol solutions are the tetracoordinated alkyl hydrogen sulphates which are monobasic ionizable acids. 

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