Autoprotolysis Constants Research Articles

Determination of acid—base constants in amphiprotic nonaqueous solvents by direct potentiometry

A direct potentiometric method for the determination of acid-base constants of protolytes in nonaqueous solvent is proposed. The method is based on the treatment of the data of a single potentiometric titration of a base or an acid in nonaqueous solvent. The titration is performed in a galvanic cell consisting of a glass and a silver-silver chloride electrode with liquid junction. Two alternatives are proposed by which at first, only the acid or only the base constant is directly determined. By the second alternative the acid, the base as well as the autoprotolysis constant are determined simultaneously from a single experiment. The method is checked with the determination of some acid-base constants in water as well as in some mixed water-alcoholic mixtures. The constants obtained coincide relatively well with the data of other investigators.

Determination of acid-base constants in amphiprotic nonaqueous solvents by direct potentiometry

A direct potentiometric method for the determination of acid-base constants of protolytes in nonaqueous solvent is proposed. The method is based on the treatment of the data of a single potentiometric titration of a base or an acid in nonaqueous solvent. The titration is performed in a galvanic cell consisting of a glass and a silver-silver chloride electrode with liquid junction. Two alternatives are proposed by which at first, only the acid or only the base constant is directly determined. By the second alternative the acid, the base as well as the autoprotolysis constant are determined simultaneously from a single experiment. The method is checked with the determination of some acid-base constants in water as well as in some mixed water-alcoholic mixtures. The constants obtained coincide relatively well with the data of other investigators.

Potentiometric methods for determination of autoprotolysis constants of amphiprotic nonaqueous solvents I. Titration of a weak protolyte with a strong one

Potentiometric methods for determination of autoprotolysis constants of amphiprotic nonaqueous solvents I. Titration of a weak protolyte with a strong one

Potentiometric methods for determination of autoprotolysis constants of amphiprotic nonaqueous solvents: I. Titration of a weak protolyte with a strong one

An independent potentiometric method is developed for the determination of autoprotolysis constants of nonaqueous amphiprotic solvents. The data of potentiometric titrations of a weak protolyte (base or acid) with a strong one are used for calculation of both autoprotolysis constant of the solvent and acid—base constant of the protolyte. The calculations are based on the method of least-squares in combination with the “pit-mapping” procedure developed by Sillén. The validity of the method was proved by the determination of the autoprotolysis constant of water. The method has no restriction concerning the strength of the weak protolyte, the latter being its main advantage. The autoprotolysis constants of methanol and ethylene glycol were determined by means of the proposed method too. The obtained values of p K MeOH=17.00 and p K EG=15.91 are in a good agreement with some recent data.

Acid-base equilibria in ethylene glycol—II: Autoprotolysis constants and acid-base properties of ethylene glycol and its mixtures

The acid-base behaviour of ethylene glycol and its mixtures with water (1, 5 and 10%), methanol, ethanol, isopropanol, nitromethane (each 10%) and ethyl methyl ketone-chloroform (5 + 5%) have been investigated by potentiometric titration, in a cell without liquid junction, equipped with a glass and a silver-silver chloride electrode. The autoprotolysis as well the protolysis constants of phthalic acid were determined for each mixture. The added solvents improve the properties of ethylene glycol, decreasing the viscosity without changing the acid-base behaviour of the ethylene glycol itself, which is favourable for the titration of weak bases. Water increases the basic, and nitromethane the acidic, properties of the mixture. Small quantities of water ( ca. 1%) do not impair the titration conditions.

ΔGθ, ΔHθ, ΔSθ de transfert de H2O et du couple H+, OH− de l'eau à ses mélanges contenant jusqu'à 40% de EtOH, tert-BuOH, DMSO, acétone et urée à 25 °C

We have measured the heat of neutralization of dilute solutions of HCl in aqueous–organic mixtures containing up to 40% by weight of t-BuOH, DMSO, acetone, and urea; autoprotolysis constants of the mixtures H2O–DMSO and H2O–urea also were determined. Thus the usual thermodynamic quantities ΔGθ, ΔHθ, and ΔSθ could be determined for the dissociation of water in these mixtures. The results for the H2O-urea mixtures must be accepted with caution because the dissociation of urea itself is not negligible compared to that of water. Using various literature data we have calculated values of the Gibbs free energy and the enthalpy for the transfer of a molecule of water from the pure liquid to the mixtures noted above. (We also have calculated for these mixtures the coefficients of isobaric expansion and those for the variation with temperature of the dielectric constant.) In addition, the values for the transfer of the ion pair H+, OH− have been determined as well as those for the transfer from water to H2O–EtOH mixtures. These are com pared to those already known for HCl and the alkali halides. It is not possible to establish a simple correlation between the differing variations of these quantities with the structural prop erties usually considered to exist in the media studied. [Journal translation]

Autoprotolysis Constants of Water–N-Methylacetamide Mixtures. A New Application of the Hammett Relationship to Acidity Constants

The hydrogen electrode can be used to measure proton activities of both acid and basic solutions in water–N-methylacetamide (NMA) mixtures, and hence to calculate autoprotolysis constants for the different mixtures. The intermediate acidities between the acid and basic regions are established by the use of buffer solutions of variously substituted phenols, whose acidities in the different water–NMA mixtures have been established. The diminution of the acidity constants with increasing concentrations of N-methylacetamide cannot be explained by the increased dielectric constants of the solution. Instead, we propose a new adaptation of the Hammett relationship (pKH − pKX = ρσX), which places N-methylacetamide between water and DMSO, and close to alcohols, which have a dielectric constant 5-fold smaller. Because of its precision, this method of analysis allows one to classify into one or more homogeneous families compounds having the same chemical function which would be classified together by the classical treatment of Hammett.

Potentiometric determination of autoprotolysis constants of solvents

A new method is proposed for determination of autoprotolysis constants by titration of a weak acid with strong base or strong acid with weak base, and applied to water and ethylene glycol (EG). The constants found were pK(w) = 13.90-13.97, and pK(EG) = 15.4 +/- 0.2.

Potentiometric Determination of the Autoprotolysis Constants of Water–Dimethylsulfoxide Mixtures at Different Temperatures and Related Thermodynamic Quantities

Potentiometric Determination of the Autoprotolysis Constants of Water–Dimethylsulfoxide Mixtures at Different Temperatures and Related Thermodynamic Quantities

IONIC EQUILIBRIA IN MIXED SOLVENTS. IX. THE AUTOPROTOLYSIS CONSTANTS OF MIXTURES OF WATER AND AN AMPHIPROTIC SOLVENT

Abstract A thermodynamic consideration is made for the autoprotolysis constant of a mixture of water and an amphiprotic solvent on the basis of equilibria of hydronium-lyonium and hydroxyl-lyate ions. The autoprotolysis constants of various water-methanol solutions are calculated and compared with those in literature. The calculated values of autoprotolysis constants of water-ethanol and water-n-propanol solutions are presented.

Autoprotolysis constants of water + dimethyl sulphoxide mixtures at 25°C and the related free energies of transfer of OH–

The autoprotolysis constants (Ks) of dimethyl sulphoxide (DMSO)+ water mixtures containing 10, 20, 40 and 60 percent of DMSO by weight have been determined at 25°C from e.m.f. measurements of the cell: Pt, H2(g, 1 atm)∣ NaOH(m1), NaCl(m2), solvent ∣ AgCl—Ag. These values were utilized to compute the standard free energy changes, ΔGt(H2O—H2O)sys accompanying the transfer of H2O molecules, acting as an acid as well as a base, from water to these mixed solvents, and thence ΔG°t(OH–)app values for these solvent mixtures using ΔG°t(H+) values reported in the literature. The observed increasingly positive values of ΔG°t(OH–)app and also of ΔG°t(OH–), as obtained by deducting the influence of the activity of H2O in the mixed solvents, i.e., RT ln (aH2O)sw, from ΔG°t(OH–)app, suggest that the acidity of the mixed solvents decreases with increasing proportion of DMSO, as is expected from the decreasing stabilization of OH– by H-bonding and the increasing desolvation of OH– due to weaker ion-dipole interactions in the resulting solvent mixtures.

Studies in ‘isodielectric’ media. Part II. Autoprotolysis constants of methanol–propylene glycol at 25 °C

The autoprotolysis constants (Ks) of a series of approximately ‘isodielectric’ media comprising methanol and propylene glycol (PG) have been determined at 25° from the e.m.f. measurements of the cell: Pt, H2(g, 1 atm)| NaS(m1), NaCl(m2), solvent|AgCl–Ag. Since the ‘electrostatic effect’ arising from the little difference in dielectric constant values is negligibly small, the standard free-energy changes accompanying the transfer of solvent molecules acting as an acid as well as a base, from methanol to the solvent, have been shown to be dictated by the intrinsic acidity and basicity of the solvents. The results suggest that the acidity of the mixed solvents increases and the basicity decreases, as the proportion of PG is increased.

Catalysis of the Reduction of Hydroperoxides by Triphenylphosphine

The reaction of hydroperoxides with triphenylphosphine is catalyzed by the addition of strong acid. Likewise in hydroxylic solvents, the log of the bimolecular rate constant increases linearly with the solvents' autoprotolysis constants. Soluble salts of molybdenum or vanadium are 104 to 105 times more effective catalysts than H+. The reaction shows promise as a method for quantitative comparison of the effectiveness of these compounds in augmenting the electrophilic character of hydroperoxides.

Hammett acidity functions (H–) of lithium, sodium, and potassium glycoxide solutions in ethylene glycol at 25 °C

H – scales have been set up for solutions of lithium, sodium, and potassium glycoxides in anhydrous ethylene glycol at 25 °C by use of nitro-substituted anilines and diphenylamines as indicators. The order of increase of H– with alkali concentration is Li < Na < K. This may be due to ion-pair formation which will be in the order Li > Na > K, and is reflected in the H– being in the reverse order, as expected. The H– scales for the three systems (i) NaOH in water, (ii) NaOMe in methanol, and (iii) Na glycoxide in ethylene glycol are compared. A comparison is also made of the aqueous and glycolic systems on a mole-fraction scale, which seems to indicate that, like the autoprotolysis constant, the H– scale in any amphiprotic solvent is largely a composite function of bulk dielectric constant of the solvent, as well as the intrinsic acidity and basicity of the solvent molecules.

Autoprotolysis constant of acetonitrile

Autoprotolysis constant of acetonitrile

Autoprotolysis constants of ethylene glycol–water mixtures at different temperatures and related thermodynamic quantities

Autoprotolysis constants (Ks) of glycol–water mixtures (containing 10, 30, 50, 70, and 90% by weight of glycol) were measured at different temperatures ranging from 5–45° using a cell of the following type: Pt, H2(1 atmosphere)|NaS| MBr, AgBr–Ag. where M stands for Na or Li, and S– stands for lyate ion.The experimental data can be fit in the form of equations of Harned–Robinson type using the least square method as given below: For 10%, pKs= [graphic ommitted] + 2·77 + 0·00329T. “ 30%, pKs= [graphic ommitted] + 1·49 + 0·00708T. “ 50%, pKs= [graphic ommitted] – 7·11 + 0·02271T. “ 70%, pKs= [graphic ommitted] + 4·38 + 0·00433T. “ 90%, pKs= [graphic ommitted] – 2·67 + 0·01711T.The value of pKs is found to pass through a minimum at a value of around 50% by weight of glycol. This has been interpreted in the light of the dielectric constant as well as the relative acidity and basicity of glycol and water.Thermodynamic quantities such as ΔH°, ΔG°, ΔS°, and ΔCp° for the processes have been evaluated for 25°.

Behaviour of glass and silver/silver chloride electrodes in some non-aqueous media

The stability of glass electrodes and silver/silver chloride electrodes in isopropanol, methyl ethyl ketone and a mixture of equal volumes of these has been measured, and found to be of the order of 1 mV. Changes in the electrode potential due to addition of water and to addition of supporting electrolyte have been investigated. The glass electrode responded reversibly to hydrogen ion activity changes in buffers of picric acid-tetraethylammonium picrate, and perchloric acid-di-isopropylamine. The autoprotolysis constants at 25° were calculated to be 2 × 10 −19 in isopropanol, 2 × 10 −26 in the ketone and 8 × 10 −19 in the mixture.

Autoprotolysis Constants of Ethylene Glycol and Propylene Glycol and Dissociation Constants of Some Acids and Bases in the solvents at 30° C.

Autoprotolysis Constants of Ethylene Glycol and Propylene Glycol and Dissociation Constants of Some Acids and Bases in the solvents at 30° C.

Equilibria in Acetic Acid: Ion Association Constants of Salts and the Autoprotolysis Constant of Acetic Acid at 105.7°C

The ion association constants KA=[M+A-]/[M+][A-] which have been measured conductimetrically at 105 7 �C in acetic acid are : perchloric acid 0.0644 X 106, sodium perchlorate 0.1346 x 106, and sodium acetate 0.752 x 106. The parameters 6, centre to centre distance between the ions at contact, which were calculated from Bjerrum's formula, are : perchloric acid 4.52 Ǻ, sodium perchlorate 4.20 Ǻ, and sodium acetate 3.61 Ǻ. The autoprotolysis constant, K = [H2+ Ac][Ac-]= 1.17 x 10-19, was calculated from the specific conductivity of acetic acid at 105.7 �C. The acetic acidium acetate ion pairs were calculated to be 100.0% dissociated.