The acid dissociation constants of 2,3-quinoxalinedithiol

Sodium salts of 2,3-quinoxalinedithiol have been prepared and used for determination of the acid ionization constants by potentiometric titration. The fully protonated form of the reagent was used in an alternative determination of the first ionization constant by a solubility method. The constants are pK(2), == 6.84 +/- 0.04 and pK(2) = 9.95 +/- 0.03.     

The dissociation constants of alizarin fluorine blue

Dissociation constants for the analytical reagent alizarin fluorine blue (3-aminomethylalizarin-N N-diacetic acid) have been determined by potentiometric titration at ionic strength 0.1, and are k(1) = 1.28 +/- 0.30 x 10(-5); k(2) = 2.82 +/- 0.24 x 10(-8); k(3) = 3.72 +/- 0.19 x 10(-11); k(4) = 6.39 +/- 0.12 x 10(-12).     

Electronic absorption spectrum of 4-methylindole

The near u.v. absorption spectrum of 4-methylindole has been recorded. The observed spectrum lying in the region λ 2960-2600 Å has been identified as a π* ← π transition, analogous to the λ 2850 Å system of indole. A vibrational analysis has been proposed for the band system.     

N-(间-取代苯基)氨基乙酸的离解常数

本文研究了N-苯基氨基乙酸中苯环间位不同取代基对氨基酸酸碱强度的影响。将按前文方法制得的N-(间-取代苯基)氨基乙酸乙酯用氢氧化钠水溶液皂化,然后用浓盐酸酸化即得N-间-取代苯基氨基乙酸。在0.1M NaClO_4存在下,于15±0.2,25±0.2,35±0.2℃,用配有231型玻璃电极和甘汞电极的PHS-2型酸度计测定了N-(间-取代苯基)氨基乙酸在30%(体积)乙醇中的离解常数。用氨基酸钠盐测定离解常数的方法业已报道。从所测得的氨基酸表观离解常数(表1)可以看出,如同N-(对-取代苯基)氨基乙酸一样,N-(间-硝基苯基)氨基乙酸(m-NO_2PhG)的pK_1值反而比N-(间-氯苯基)氨基乙酸(m-ClPhG)和N-(间-甲氧苯基)氨基乙酸(m-CH_3OPhG)的大。这是不能用诱导效应来解释的。一般说来,氨基酸具有两性离解的性质,存在下列平衡:     

Detection and separation of metal ions on paper impregnated with 4-hydroxybenzthiazole

Zinc, magnesium and cadmium ions in the presence of ammonia, form intense blue chelates on paper impregnated, with 4-hydroxybenzthiazole, 0.25 microgram, 1.0 microgram and 0.1 microgram respectively, of these metal ions can be detected by means of this test. Several cations interfere.Alumunium can be separated from zinc, cadmium, copper, nickel and cobalt on paper impregnated with 4-hydroxybenzthiazole, which acts as a chromatographic column.     

The microwave absorption spectrum of MgO

The microwave absorption spectrum of ²⁴MgO, ²⁵MgO and ²⁶MgO has been observed in the frequency range between 67 and 275 GHz. Quadrupole hyperfine structure of ²⁵MgO was partially resolved. The molecular constants derived from these measurements are two orders of magnitude more accurate than previous MODR results.     

The high temperature pyrolysis of 1,3-butadiene II: Pulsed laser flash absorption rate constants,and consideration of possible molecular dissociation pathways

Rate constants for the unimolecular dissociation of 1,3-butadiene have been measured with the pulsed laser flash absorption technique, following butadiene disappearance at 222 nm. The results are in excellent agreement with previous laser-schlieren measurements interpreted with a ΔH°₂₉₈ = 100 kcal/mol heat of dissociation. A new RRKM calculation agreeing with both sets of rate constants gives log k_∞(s^?1) = 17.03 ± 0.3 – 94(kcal/mol)/RT. These data and product measurements using ARAS, single-pulse product analysis, and time-of-flight mass spectrometry, in shock tubes, all provide independent evidence against any major participation by molecular reactions in the dissociation. The only dissociation channel, or combination of channels, consistent with all the measurements is C-C scission to two vinyl radicals. However, the extremely slow rate of H-atom formation seen in ARAS experiments then requires an unacceptably low rate of vinyl dissociation.     

Thermodynamic dissociation constants of N-phenylbenzohydroxamic acids and benzohydroxamic acid

Thermodynamic association constants of benzohydroxamic acid and several ortho-substituted N-phenylbenzohydroxamic acids have been determined by pH titration in aqueous dioxan media at 25 degrees and 35 degrees . Empirical pH corrections for mixed aqueous media have been applied. The pK(a) values do not vary linearly with the reciprocal of dielectric constant of the medium, but a plot of pK(a) vs. the mole fraction of dioxan is linear at a given temperature. Values of DeltaG degrees , DeltaH degrees and DeltaS degrees are tabulated.     

Reinterpretation of the absorption spectrum of UCl4 single crystal

The absorption spectra of UCl₄ single crystals have been measured from 4000 to 30 000 cm⁻¹ at temperatures ranging from 4.2 K to room temperature. The transitions were assigned by comparing the strong absorption features of UCl₄ to those of ThCl₄:U⁴⁺. The energy levels were fitted to a semiempirical Hamiltonian in D_2d symmetry.A r.m.s. deviation of 60 cm⁻¹ in the fit to 26 assigned levels was achieved using the following set of parameters (cm⁻¹): F² = 42 561 ± 235; F⁴ = 39 440 ± 634; F⁶ = 24 174 ± 185; ξ = 1805 ± 8; α = 31 ± 1; β = −576 ± 168; (γ = 1200); B²₀ = −903 ± 151; B⁴₀ = 766 ± 220; B⁴₄ = −3091 ± 185; B⁶₀ = −1619 ± 482; B⁶₄ = −308 ± 280.     

Determination of acidic dissociation constants of several vic-dioximes

The acidic dissociation constants of three vic-dioximes have been determined from spectrophotometric data. The results may be summarized as follows:

     

15.

Acid dissociation constants of some nitrogen-containing multinuclear systems     

E. I. Stankevich  Yu. Yu. Popelis  E. E. Grinshtein  A. Ya. Ozola  G. Ya. Dubur 《Chemistry of Heterocyclic Compounds》1970,6(1):116-118

The pK_a values have been determined spectrometrically of the 5, 8, 8-trimethyl-2, 4, 6-trioxo-1, 2, 3, 4, 5, 6, 7, 8, 9, 10-decahydropyrimido[4, 5-b]quinolines Ia–Ic, the 5, 8, 8-trimethyl-2, 4, 6-trioxo-1, 2, 3, 4, 6, 7, 8 9-octahydropyrimido [4, 5-b]quinolines IIa and IIb, the 2, 4, 6-trioxo-5-phenyl-1, 2, 3, 4, 5, 11-hexahydro-11-azapyrimido [4, 5-b]fluorenes IIIa–IIIc, and the 4-amino uracils IVa–IVc. The following sequences of the dissociation of the protons attached to the nitrogen atoms have been established: for I, N₍₁₎ > N₍₁₀₎ > N₍₃₎; for II, N₍₁₎ > N₍₃₎; for III, N₍₁₁₎ > N₍₁₎ > N₍₃₎; and for IV, N₍₃₎ > N₍₁₎.     

16.

Hexafluoroisopropylhydroxylamine and dissociation constants of some fluorinated hydroxylamines and oximes     

I. L. Knunyants  B. L. Dyatkin  E. P. Mochalina  L. T. Lantseva 《Russian Chemical Bulletin》1966,15(1):164-165

     

17.

On the dissociation constants of phenylazochromotropic acid derivatives     

Haruo Miyata 《Fresenius' Journal of Analytical Chemistry》1969,245(5):322

     

18.

Determination of acid dissociation constants by capillary electrophoresis   总被引：2，自引：0，他引：2  

Poole SK  Patel S  Dehring K  Workman H  Poole CF 《Journal of chromatography. A》2004,1037(1-2):445-454

Capillary electrophoresis affords a simple, automated approach for the measurement of pKa values in the range 2-11 at a throughput of less than 1 h per sample per instrument. Agreement with literature values is usually within 0.20 log units with a precision better than 0.07 log units. The attractive features of capillary electrophoresis for pKa measurements are: (1) conventional instrumentation with a high level of automation are suitable for all measurements; (2) because it is a separation method samples need not be of high purity; (3) samples of low water solubility with suitable chromophores are easily handled (detection limits in the microM range); (4) sample consumption per measurement is in the microgram range; and (5) since only mobilities are measured, exact knowledge of concentrations is not needed. The general approach can be extended to pKa measurements in aqueous-organic solvent mixtures and non-aqueous solvents with suitable calibration. The widespread use of absorbance detection in capillary electrophoresis means that the sample must have a suitable chromophore for detection. The main source of controllable error is the accuracy of buffer standardization and their stability in use, and uncontrollable error, the retentive interactions of the sample with the column wall. The latter seems to be a rare problem in practice for typical operating conditions.     

19.

Thermodynamic dissociation constants of risedronate using spectrophotometric and potentiometric pH-titration     

Milan Meloun  Zuzana Ferenčíková  Hana Málková  Tomáš Pekárek 《Central European Journal of Chemistry》2012,10(2):338-353

Risedronate inhibits bone resorption in diseases like osteoporosis, Paget’s disease, tumor bone diseases or the malfunction of phosphocalcium metabolism. The acid-base properties of risedronate in an aqueous solution have been studied in a pH range from 2 to 12 and can be described in terms of four dissociation steps: pK _a,2, pK _a,4, pK _a,5 (related to the dissociation of POH groups) and pK _a,3 related to the dissociation of protonated amino group NH₃ ⁺. The mixed dissociation constants were determined at different ionic strengths I = 0.02 to 0.20 mol dm⁻³ KCl and of 25°C and 37°C using pH-spectrophotometric and pH-potentiometric titration methods. Determination of group parameters L ₀, H _T might lead to false estimates of common parameters p K _a;therefore, the computational strategy employed is important. A comparison between the two programs ESAB and HYPERQUAD demonstrated that the ESAB program provides a better fit of potentiometric titration curve. The thermodynamic dissociation constants pK _a^T were estimated by a nonlinear regression of (pK _a, I) data and a Debye-Hückel equation at 25°C and 37°C, pK _a,2^T = 2.37(1) and 2.44(1), pK _a,3^T = 6.29(3) and 6.26(1), pK _a,4^T = 7.48(1) and 7.46(2) and pK _a,5^T = 9.31(7) and 8.70(3) at 25°C and 37°C using pH-spectroscopic data and pK _a,2^T = 2.48(3) and 2.43(1), pK _a,3^T= 6.12(2) and 6.10(2), pK _a,4^T = 7.25(2) and 7.23(1) and pK _a,5^T = 12.04(5) and 11.81(2) at 25°C and 37°C. The ascertained estimates of three dissociation constants pK _a,3, pK _a,4, pK _a,5 are in agreement with the predicted values obtained using PALLAS      

20.

Potentiometric and spectrophotometric determination of the dissociation constants of cefetamet     

M. Kosanić  V. Kapetanović  L. Milovanović  N. Burić  D. Veselinovic 《Monatshefte für Chemie / Chemical Monthly》1997,128(2):137-146

Summary The dissociation constants of cefetamet-Na have been determined using potentiometric titrations and spectrophotometry. The investigations were carried on in water solutions at constant temperature and ionic strength, and at differentH ₀ andpH values. Potentiometric investigations were performed at three different temperatures and ionic strengths. The concentration dissociation constants and the corresponding thermodynamic dissociation constants were calculated by a computer program. The mixed dissociation constants (pK) of cefetamet-Na have been determined spectrophotometrically in theH ₀ range from -5.80 to 0.00 and atpH values from 0.00 to 12.70 and are in good agreement with values achieved by graphical methods as well as with those obtained by potentiometric methods. Based on the determined values, the thermodynamic parameters (G, H, S) were calculated atI=0.1M.

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Potentiometrische und spektrophotometrische Bestimmung der Dissoziationskonstanten von Cefetamet

Zusammenfassung Die Dissoziationskonstanten von Cefetamet-Na wurden mittels potentiometrischer Titrationen und auf spektrophotometrischem Weg bestimmt. Die Untersuchungen wurden in wäßriger Lösung bei konstanter Temperatur und Ionenstärke und verschiedenenH ₀- undpH-Werten durchgeführt. Potentiometrische Messungen wurden bei drei verschiedenen Temperaturen und Ionenstärken vorgenommen. Die stöchiometrische Dissozation und die entsprechenden thermodynamischen Dissoziationskonstanten wurden mit Hilfe eines Computerprogramms berechnet. Die gemischten Dissoziationskonstanten (pK) wurden spektrophotometrisch imH ₀-Bereich von -5.80 bis 0.00 und impH-Bereich von 0.00 bis 12.70 bestimmt und stimmen sowohl mit Werten, die mit Hilfe der graphischen Methode erhalten wurden, als auch mit potentiometrisch bestimmten gut überein. Aus den ermittelten Werten der Dissoziationskonstanten wurden die thermodynamischen Parameter (G, H, S) fürI=0.1M berechnet.

     

pK1	pK2
2,3-butanedionedioxime	10.6 ± 0.1	11.9 ± 0.3
1,2-cyclohexanedionedioxime	10.6 ± 0.2	12.4 ± 0.5
1,2-cycloheptanedionedioxime	10.7 ± 0.2	12.3 ± 0.5

Acid dissociation constants of some nitrogen-containing multinuclear systems

The pK_a values have been determined spectrometrically of the 5, 8, 8-trimethyl-2, 4, 6-trioxo-1, 2, 3, 4, 5, 6, 7, 8, 9, 10-decahydropyrimido[4, 5-b]quinolines Ia–Ic, the 5, 8, 8-trimethyl-2, 4, 6-trioxo-1, 2, 3, 4, 6, 7, 8 9-octahydropyrimido [4, 5-b]quinolines IIa and IIb, the 2, 4, 6-trioxo-5-phenyl-1, 2, 3, 4, 5, 11-hexahydro-11-azapyrimido [4, 5-b]fluorenes IIIa–IIIc, and the 4-amino uracils IVa–IVc. The following sequences of the dissociation of the protons attached to the nitrogen atoms have been established: for I, N₍₁₎ > N₍₁₀₎ > N₍₃₎; for II, N₍₁₎ > N₍₃₎; for III, N₍₁₁₎ > N₍₁₎ > N₍₃₎; and for IV, N₍₃₎ > N₍₁₎.     

Determination of acid dissociation constants by capillary electrophoresis

Capillary electrophoresis affords a simple, automated approach for the measurement of pKa values in the range 2-11 at a throughput of less than 1 h per sample per instrument. Agreement with literature values is usually within 0.20 log units with a precision better than 0.07 log units. The attractive features of capillary electrophoresis for pKa measurements are: (1) conventional instrumentation with a high level of automation are suitable for all measurements; (2) because it is a separation method samples need not be of high purity; (3) samples of low water solubility with suitable chromophores are easily handled (detection limits in the microM range); (4) sample consumption per measurement is in the microgram range; and (5) since only mobilities are measured, exact knowledge of concentrations is not needed. The general approach can be extended to pKa measurements in aqueous-organic solvent mixtures and non-aqueous solvents with suitable calibration. The widespread use of absorbance detection in capillary electrophoresis means that the sample must have a suitable chromophore for detection. The main source of controllable error is the accuracy of buffer standardization and their stability in use, and uncontrollable error, the retentive interactions of the sample with the column wall. The latter seems to be a rare problem in practice for typical operating conditions.     

Thermodynamic dissociation constants of risedronate using spectrophotometric and potentiometric pH-titration

Risedronate inhibits bone resorption in diseases like osteoporosis, Paget’s disease, tumor bone diseases or the malfunction of phosphocalcium metabolism. The acid-base properties of risedronate in an aqueous solution have been studied in a pH range from 2 to 12 and can be described in terms of four dissociation steps: pK _a,2, pK _a,4, pK _a,5 (related to the dissociation of POH groups) and pK _a,3 related to the dissociation of protonated amino group NH₃ ⁺. The mixed dissociation constants were determined at different ionic strengths I = 0.02 to 0.20 mol dm⁻³ KCl and of 25°C and 37°C using pH-spectrophotometric and pH-potentiometric titration methods. Determination of group parameters L ₀, H _T might lead to false estimates of common parameters p K _a;therefore, the computational strategy employed is important. A comparison between the two programs ESAB and HYPERQUAD demonstrated that the ESAB program provides a better fit of potentiometric titration curve. The thermodynamic dissociation constants pK _a^T were estimated by a nonlinear regression of (pK _a, I) data and a Debye-Hückel equation at 25°C and 37°C, pK _a,2^T = 2.37(1) and 2.44(1), pK _a,3^T = 6.29(3) and 6.26(1), pK _a,4^T = 7.48(1) and 7.46(2) and pK _a,5^T = 9.31(7) and 8.70(3) at 25°C and 37°C using pH-spectroscopic data and pK _a,2^T = 2.48(3) and 2.43(1), pK _a,3^T= 6.12(2) and 6.10(2), pK _a,4^T = 7.25(2) and 7.23(1) and pK _a,5^T = 12.04(5) and 11.81(2) at 25°C and 37°C. The ascertained estimates of three dissociation constants pK _a,3, pK _a,4, pK _a,5 are in agreement with the predicted values obtained using PALLAS      

Potentiometric and spectrophotometric determination of the dissociation constants of cefetamet

Summary The dissociation constants of cefetamet-Na have been determined using potentiometric titrations and spectrophotometry. The investigations were carried on in water solutions at constant temperature and ionic strength, and at differentH ₀ andpH values. Potentiometric investigations were performed at three different temperatures and ionic strengths. The concentration dissociation constants and the corresponding thermodynamic dissociation constants were calculated by a computer program. The mixed dissociation constants (pK) of cefetamet-Na have been determined spectrophotometrically in theH ₀ range from -5.80 to 0.00 and atpH values from 0.00 to 12.70 and are in good agreement with values achieved by graphical methods as well as with those obtained by potentiometric methods. Based on the determined values, the thermodynamic parameters (G, H, S) were calculated atI=0.1M.

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Potentiometrische und spektrophotometrische Bestimmung der Dissoziationskonstanten von Cefetamet

Zusammenfassung Die Dissoziationskonstanten von Cefetamet-Na wurden mittels potentiometrischer Titrationen und auf spektrophotometrischem Weg bestimmt. Die Untersuchungen wurden in wäßriger Lösung bei konstanter Temperatur und Ionenstärke und verschiedenenH ₀- undpH-Werten durchgeführt. Potentiometrische Messungen wurden bei drei verschiedenen Temperaturen und Ionenstärken vorgenommen. Die stöchiometrische Dissozation und die entsprechenden thermodynamischen Dissoziationskonstanten wurden mit Hilfe eines Computerprogramms berechnet. Die gemischten Dissoziationskonstanten (pK) wurden spektrophotometrisch imH ₀-Bereich von -5.80 bis 0.00 und impH-Bereich von 0.00 bis 12.70 bestimmt und stimmen sowohl mit Werten, die mit Hilfe der graphischen Methode erhalten wurden, als auch mit potentiometrisch bestimmten gut überein. Aus den ermittelten Werten der Dissoziationskonstanten wurden die thermodynamischen Parameter (G, H, S) fürI=0.1M berechnet.