ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Thermodynamics of the solution equilibria of 3-hydroxypyridine and pyridoxine in water-dioxane mixtures (1995)
    Springer
    Journal of solution chemistry 24 (1995), S. 1293-1305 
    Details
    ISSN: 1572-8927
    Keywords: 3-Hydroxypyridine and pyridoxine ; thermodynamics of ionization ; thermodynamics of tautomerization ; water-dioxane mixtures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The thermodynamics of tautomeric and microscopic ionization equilibrium constants of 3-hydroxypyridine and pyridoxine have been determined in waterdioxane mixtures (0–70% weight fraction in dioxane) ranging from 10°C to 50°C. Generally, for both types of processes, the entropic contributions to the Gibbs energy predominate and this tendency increase concomitantly with the dioxane content in the media. The thermodynamic parameters are consistent with the corresponding values obtained from macroscopic ionization processes. An equation for the equilibrium constant K as a function of temperature and a solvent characteristic parameter is proposed to predict the K values throughout the whole range of the temperature and solvent compositions studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00972834
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Complete Resolution and Thermodynamic Parameters of the Ionization Equilibria of Pyridoxal in Water—Dioxane Mixtures (2000)
    Springer
    Journal of solution chemistry 29 (2000), S. 1123-1141 
    Details
    ISSN: 1572-8927
    Keywords: pyridoxal ; thermodynamic ionization equilibrium constants ; microscopic constants ; thermodynamics of ionization ; water—1 ; 4-dioxane mixtures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A potentiometric method has been used to determine the thermodynamicequilibrium constants for the macroscopic ionization processes of pyridoxal inwater—1,4-dioxane mixtures (0–70% weight fraction dioxane)at temperatures ranging from 10 to 50°C. These data, combined with the equilibrium constants for the tautomericand hemiacetalization processes, allow complete resolution of the microconstantsystem and calculation of the microscopic ionization equilibrium constants underall our experimental conditions. The standard thermodynamic function changesfor the macroscopic and microscopic ionization processes were obtained in variouswater—1,4-dioxane mixtures at 25°C. The values of any given microscopic pKfor the different solvents and temperatures fit very well to a single equation. Thefree energy, enthalpy, and entropy obtained for the different ionization processesin water—dioxane mixtures correlate with Kamlet and Taft's solvatochromicparameters π* and α, which are a measure of the dipolarity/polarizability andhydrogen-bonding capacity of the solvent, respectively. These correlations explainmore fully the mutual compensation between the contributions of enthalpy andentropy and the origin of the solvent effect on the pK.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005143217105
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Thermodynamics of the tautomeric, hydration and hemiacetalization of 5-deoxypyridoxal and pyridoxal in water-dioxane mixtures (1996)
    Springer
    Journal of solution chemistry 25 (1996), S. 667-679 
    Details
    ISSN: 1572-8927
    Keywords: 5-Deoxypyridoxal ; pyridoxal ; tautomeric hydration and hemiacetalization equilibria ; equilibrium constants ; water-dioxane mixtures ; standard thermodynamic functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The resolution of electronic spectra using log-normal curves has permitted a quantitative description of the equilibria of pyridoxal, one of the vitamin B6 molecules, and of the related 5-deoxypyridoxal in solution. Tautomeric, hydration and hemiacetalization equilibrium constants for water-dioxane mixtures of these compounds are reported (0–70% weight fraction in dioxane) at temperatures ranging from 10°C to 50°C. These results provide the standard thermodynamic function changes for the indicated processes in the different mixtures studied. The aldehyde content in the two compounds increases concomitantly with the dioxane content of the solution and also when it changes from the cationic to the anionic species. 5-deoxypyridoxal becomes significantly more hydrated in its more protonated form, K h (+a)/K h (±a)≈7–8, as do other aldehydes. Hemiacetalization in pyridoxal follow a similar pattern, K he (±a)/K he (−a)≈20–30, due principally to differences in the enthalpy contribution. Hemiacetalization is favored over hydration by ∼20.6 kJ-mol−1 in water solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00972681
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Kinetics of the formation and hydrolysis of the schiff's base of 4-pyridinecarboxaldehyde with N-hexylamine in water-dioxan mixtures (1989)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 21 (1989), S. 51-61 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have carried out a kinetic study of the 4-pyridinecarboxaldehyde plus n-hexylamine system, at 25°C, in water-dioxan mixtures (0-60% v/v) and in the pH range pKa + 1.5 〉 pH 〉 pKa - 1.5, where pKa is the pK value of the conjugate acid of the amine. The results obtained could be interpreted in terms of a rate constant for Schiff's base hydrolysis and a rate constant for the reaction between the nonprotonated n-hexylamine and the nonhydrated form of 4-pyridinecarboxaldehyde. Both constants decrease sharply as the dioxan content of the solvent increases, in a manner consistent with Marshall's model [J. Phys. Chem., 74, 346 (1970)]. It is suggested that the transition state of the rate-limiting step (carbinolamine dehydration) is highly solvated by water molecules and has a high separation of charges.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550210105
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...