Diprotic Acid Research Articles

Acids in dimethylformamide. III. Ionic equilibria of dicarboxylic acids

Dissociation and homoconjugation constants of succinic, malonic, and dimethylmalonic acids have been determined potentiometrically at 25°C. Conductometric studies on the tetraethylammonium salts of the acids permitted the evaluation of the corresponding dissociation constants, which allowed a better fit of calculated curves with experimental data. Homoconjugation of two monovalent anions with a divalent anion was pointed out in all cases. No appreciable homoconjugation of the monovalent anion with the diprotic acids was found. In order to standardize the glass electrode at high paH values, the dissociation constant of diethylbarbituric acid has also been determined.

Potentiometric Determination of Overlapping Dissociation Constants

The dissociation constants of polyprotic acids can be determined potentiometrically by defining a variable, P, as the average number of protons dissociated. The proton balance equation for the titration of these acids with base led to a general expression which could be solved graphically or through the use of linear regression or nonlinear regression analysis. Experimental data for a number of acids and for a series of simulated titration curves were analyzed using the three methods. The graphical solution was found to be applicable in all instances. As the ratio of K1 to K2 for diprotic acids increased from 50 to 1000, the value of K2 estimated by the use of linear regression became progressively worse and finally could not be determined at all. In all instances, the value of K1 was determined to within a relative error of 0.5%. In all instances in which nonlinear regression analysis was used, the values for K1 were determined to within 0.3% and those for K2 were determined to within 0.02%. This technique requires an initial estimate of each constant. These initial estimates are then refined in an iterative procedure until satisfactory convergence is obtained. The digital computer program used in this work is unique in that initial estimates are obtained within the computer program itself. The program also determines the total number of dissociable protons. This latter property can be extremely useful for compounds with an unknown number of acidic sites.

Solvent extraction of some diprotic nitroaromatic acids and of their complexes with some actinides—III: Extraction of tetravalent plutonium and thorium 3-nitro- p-cresol-5-sulphonate complexes with tributylphosphate

The extraction of tetravalent plutonium and thorium from 1 M (H, Na)Cl aqueous solution containing 3-nitro- p-cresol-5-sulphonic acid (H 2A) with a n-dodecane solution of tributyl-phosphate (TBP) at 25 ± 0·2°C has been studied. The experimenal data were explained in terms of the following extractable complexes: PuA(HA)Cl·3TBP and PuCl 4·2TBP; ThA(HA)Cl·2TBP, ThACl 2·2TBP and ThA 2·2TBP. The first nitroaromatic complex, MA 2+, was found in the aqueous phase in addition to the first chloride complex, MCl 3+, in both cases. The stability constants of these species have been calculated.

Solvent extraction of some diprotic nitroaromatic acids and of their complexes with some actinides — II: Extraction of uranyl 3-nitro- p-cresol-5-sulphonate complexes with tributylphosphate

Extraction of uranyl complexes from the 1M (H,Na)Cl solution containing 3-nitro- p-cresol-5-sulphonic acid (H 2A) with n-dodecane solution of TBP at 25°C has been investigated. The prevailing extractable species seems to be UO 2A·2TBP, the two-phase stability constant of which has been calculated to be (3·57 ± 0·37) × 10 6. The stability constant of the main aqueoue species, UO 2A, is (7·89 ± 2·35) × 10 5. The role of chloride complexes in the extraction equilibrium has been evaluated and their stability constants calculated.

Effect of pH on calcium binding by phytic acid and its inositol phosphoric acid derivatives and on the solubility of their calcium salts

Calcium binding by phytic acid and its inositol mono-, di-, tri-, tetra- and pentaphosphoric acid derivatives was examined over the pH range of 2.0 to 12.0. Differences in pH when each compound was titrated with NaOH and with Ca(OH) 2 gave a measure of the calcium binding. A disphasic curve, typical of that for a diprotic acid, was obtained when IMP was titrated with either NaOH or Ca(OH) 2. The same type of curve was observed when phytic acid and the remaining inositol phosphoric acids were titrated with Ca(OH) 2, but not when tritrated with NaOH. As the P I ratio increased from 1 to 6, the NaOH curves, between 50 and 100 per cent neutralization, showed progressively larger deviations from the Ca(OH) 2 curves. The difference is attributed to the titratable hydrogens on the inositol phosphates other than IMP being bound between oxygen atoms of adjacent phosphate groups such that Ca 2+ can easily displace these hydrogens whereas Na + cannot. The results indicated that phosphates thus bound were more resistant to hydrolysis than phosphate groups that were not. The relation between pH and the solubility of each of the calcium salts of the different inositol phosphates was determined by noting, during each titration with Ca(OH) 2, the pH at which a precipitate first formed. With increase in their P I ratios, the pH required to precipitate the calcium salts of the various inositol phosphates decreased asymptotically.

Solvent extraction of some diprotic nitroaromatic acids and of their complexes with some actinides—I: Dissociation constants and solvent extraction of 3-nitro- p-cresol-5-sulphonic acid with tributyl-phosphate

The second dissociation constant, K 2 H= a H[A 2−]/[HA −], for 3-nitro- p-cresol-5-sulphonic acid (H 2A) in 1·0M (H, Na)Cl at 25°C has been determined by potentiometric titration and u.v.-visible spectrophotometry as (2·71 ± 0·07). 10 −7 and (2·72 ± 0·16). 10 −7, respectively. The solvent extraction of H 2A from 1M (H, Na)Cl with TBP in n-dodecane at 25°C has also been studied. The extractable species appears to be H 2A·3TBP, its apparent formation constant, K H 2 A .3 TBP=[ H 2 A·3 TBP]/a H [HA −][TBP] 3, is 2·27 ± 0·06. The value of the dissociation constan, K 1 H= a H[HA −]/[H 2A], has been calculated from the extraction data as 2·06±0·23.

Titration behavior of monoprotic and diprotic acids

Defines the conditions of concentration and pK for which an earlier published distinction between weak diprotic and monoprotic acids is valid.

Preparation-controlled forms of copper(II) and nickel(II) ethylenediaminetetraacetato complex diprotic acids

Preparation-controlled forms of copper(II) and nickel(II) ethylenediaminetetraacetato complex diprotic acids

Thermometric titration of some monoprotic and diprotic acids in aqueous and non-aqueous media

Some mono- and diprotic acids have been titrated thermometrically with strong alkalis in aqueous and non-aqueous media. Thermograms with sharp arrest points were obtained, from which heats of neutralization were measured. Heats of neutralization in the media used were compared and an effect attributable to hydrogen bonding was found.

The stability constants of polyvalent cations and aromatic arsonic acids—I The thermodynamic dissociation constants of aromatic arsonic acids

Potentiometric and spectrophotometric data obtained at 25±0·1°C have been used to evaluate thermodynamic dissociation constants for benzene arsonic acid, 2-hydroxybenzene arsonic acid, 4-hydroxybenzene arsonic acid, and 2,4-dihydroxybenzene arsonic acid. A method developed by Ernst and Menashi for the determination of low dissociation constants for diprotic acids has been extended to evaluate those for tri- and tetraprotic acids.

Non-aqueous titration of hydroxamic acids

Benzohydroxamic acid is titrated with 0.1M tetrabutyl-anunonium hydroxide in nine non-aqueous solvents with three different indicating electrodes. The best results are obtained using dimethylformamide as solvent and platinum-platinum electrodes. Four monoprotic and three diprotic hydroxamie acids and iron(III) benzohydroxamate have been successfully titrated with this system. The effect of quantitative additions of carbon dioxide to the titrant on its apparent molarity are found to be dependent on the amount added, the strength and sample size of acid titrated and the solvent used.

Equivalence Points and Inflexion Points in Acid-Base Titration Curves

General equations are derived for the relation between pH and stoichiometric degree of neutralization in the titration of monoprotic and diprotic weak acids (or bases) with strong acid or strong base. From these equations the number and position of inflexion points in the curves is derived, and their relation to the equivalence points is shown. Methods for determining ionization constants from inflexion points are discussed.