Electrochemical Study of Acid-Base Properties of Some 2,5-Dihydro-1,3,4-thiadiazoles in Aqueous-Ethanolic Solutions

1998 ◽  
Vol 63 (1) ◽  
pp. 31-41
Author(s):  
Maria Turowska ◽  
Grzegorz Mloston ◽  
Pawel Krzyczmonik ◽  
Jacek Raczak ◽  
Jaroslaw Romanski
Keyword(s):  
Ionic Strength ◽  
Dissociation Constants ◽  
Mndo Method ◽  
Electrochemical Study ◽  
Acidic Properties ◽  
Acid Base ◽  
Weak Bases ◽  
Formation Enthalpies ◽  
Protonated Forms ◽  
Base Properties

The dissociation constants Ka for spherically crowded 2'- and 2,5-substituted thiadiazolines and their protonated forms in 45% (v/v) aqueous-ethanolic solutions (ionic strength m = 0.1) were determined using the pH-metric method. All the thiadiazoles are weak bases. Some of them showed also weak acidic properties. The formation enthalpies have been calculated using the MNDO method. On the basis of the obtained results the mechanism of the protonation process is discussed.

Acid-base properties of 1,3-diphenyl-5-(1H-tetrazol-2-yl)formazan and 1,3-diphenyl-5-(2H-1,2,4-triazol-3-yl)formazan

1982 ◽  
Vol 47 (11) ◽  
pp. 2882-2889
Author(s):  
Nadezhda Likhareva ◽  
Ladislav Šůcha ◽  
Miloslav Suchánek
Keyword(s):  
Computer Program ◽  
Dissociation Constants ◽  
Acid Base ◽  
New Compounds ◽  
Base Properties

Two new compounds from the formazan series, viz. 1,3-diphenyl-5-(1H-tetrazol-2-yl)formazan and 1,3-diphenyl-5-(2H-1,2,4-triazol-3-yl)formazan, were prepared, and the dissociation constants and molar absorptivities of all of their acid-base species were determined spectrophotometrically employing the SPEKTFOT computer program.

scholarly journals SPECTROPHOTOMETRIC STUDY OF ACID-BASE PROPERTIES OF SPATIAL-DISTORTED DERIVATIVES OF PORPHYRINS IN ACETONITRILE

2018 ◽  
Vol 59 (6) ◽  
pp. 49 ◽  
Author(s):  
Yulia B. Ivanova ◽  
Svetlana G. Puhovskaya ◽  
Nugzar Zh. Mamardashvili ◽  
Oscar I. Koifman
Keyword(s):  
Absorption Spectra ◽  
Molecular Form ◽  
Spectral Characteristics ◽  
Reaction System ◽  
Spectrophotometric Titration ◽  
Spectrophotometric Study ◽  
Acidic Properties ◽  
Acid Base ◽  
Electron Absorption ◽  
Base Properties

Spectrophotometric titration method was used to study the acidic properties of: 5,10,15,20-tetrakis(thienyl-2-yl)-2,3,7,8,12,13,17,18-octaethylporphyrin (I), 5,10,15,20-tetrakis(4’-t-butylphenyl)-2,3,7,8,12,13,17,18-octaethylporphyrin (II), 5,10,15,20-tetrakis(3,5-di-t-butylphe-nyl)-2,3,7,8,12,13,17,18-octaethylporphyrin (III), 5,10,15,20-tetraphenyl-2,3,7,8,12,13,17,18-octaethylporphyrin (IV), 5,15-bis(4’-methoxyphenyl)-10,20-bis(4-nitro-phenyl)-2,8,12,18-tetrame-thyl-3,7,13,17-tetraarylporphyrin (V), 5,15-bis(4’-methoxyphenyl)-10,20-diphenyl-2,3,7,8,12,13, 17,18-octaethylporphyrin (VI), 5,15-bis(4’-methoxyphenyl)-2,8,12,18-tetramethyl-3,7,10,13,17,20-hexaethylporphin (VII), 5,10,15,20-tetrakis(4’-methoxyphenyl)-2,3,7,8,12,13,17,18-octaethylpor-phyrin (VIII) in the presence of a deprotonated agent, 1,8-diazabicyclo[5.4.0] undec-7-ene, in acetonitrile. Under deprotonation two families of spectral curves in the absorption spectra, having its own system of isobestic points, are formed. Electron absorption spectrum of molecular form transforms gradually into the spectrum of the final form of dianion with titrant concentration increase. Determination of the coordinates of the inflection (and the corresponding concentration of DBU) on the titration curve  allowed us to distinguish two areas in the electron absorption spectra of the reaction system, which are likely belong to the first and second steps of deprotonation, namely, to the formation of mono- and dianionic forms (HP–  and P2–) of the compound. Spectral characteristics of the ionized forms and combined ionization constant for the first and second steps (lgКа1 and lgКа2) were revealed. At the first step in the order of decreasing acidic properties of the ligands the compounds form a series of: III< V< VIII< VI < VII< II< IV < I; at the second step in decreasing order of the acidic properties of the ligands the compounds form a series of:.III < V < VI < II <VIII< VII < IV < I. The effect of structural and electronic properties of substituents on acid-base properties of porphyrins is analyzed. Thus, chemical modification of the macrocycle can lead to direct changes in acid-base properties of supramolecular macroheterocyclic ligands and can be a powerful tool to control the reactivity of compounds of the porphyrins class.

Some thermodynamic properties of dl-Tyrosine and dl-Tryptophan. Effect of the ionic medium, ionic strength and temperature on the solubility and acid–base properties

2012 ◽  
Vol 314 ◽  
pp. 185-197 ◽  
Author(s):  
Clemente Bretti ◽  
Francesco Crea ◽  
Concetta De Stefano ◽  
Silvio Sammartano ◽  
Giuseppina Vianelli
Keyword(s):  
Ionic Strength ◽  
Thermodynamic Properties ◽  
Acid Base ◽  
Ionic Medium ◽  
Base Properties

Synthesis, Acid-Base Properties, Kinetics and Mechanism of Cu2+ Incorporation into Water-Soluble Highly Substituted Porphyrins

2017 ◽  
Vol 21 (09) ◽  
pp. 611-621
Author(s):  
Hirofumi Konno ◽  
Jun Takeda
Keyword(s):  
Aqueous Solution ◽  
Ionic Strength ◽  
Kinetics And Mechanism ◽  
Water Soluble ◽  
Acid Base ◽  
Base Equilibrium ◽  
Absorbance Change ◽  
Acid Base Equilibrium ◽  
Kinetics Of ◽  
Base Properties

The synthesis, acid-base properties, and kinetics of Cu[Formula: see text] incorporation into water-soluble highly substituted porphyrins were studied. The basicity increased and the stepwise acid-base equilibrium was clarified by increasing the number of phenyl groups at the [Formula: see text] position, and the basicity of a dodeca-substituted porphyrin increased with the ionic strength. The metalation reaction of the dodeca-substituted porphyrin with Cu[Formula: see text] in aqueous solution revealed a biphasic absorbance change at 453 nm. Plots of [Formula: see text] or[Formula: see text] vs. the Cu[Formula: see text] concentration and of log ([Formula: see text] or[Formula: see text]/[Formula: see text] 0) vs. the ionic strength show that [Formula: see text] is dependent on the Cu[Formula: see text] concentration and ionic strength, while [Formula: see text] is independent of these parameters. These results confirm the stepwise metalation mechanism and the existence of an intermediate in aqueous solution, which is indicated by the biphasic absorbance change at 453 nm.

scholarly journals Analysis of acid-base properties of some p-substituted aromatic hydrazones in aqueous perchloric acid by spectrophotometric and semiempirical methods

2014 ◽  
Vol 33 (1) ◽  
pp. 85 ◽  
Author(s):  
Mirjana Stojan Jankulovska ◽  
Ilinka Spirevska
Keyword(s):  
Perchloric Acid ◽  
Dissociation Constants ◽  
Protonated Form ◽  
Heat Of Formation ◽  
Semiempirical Methods ◽  
Acid Base ◽  
Spectrophotometric Methods ◽  
Aqueous Perchloric Acid ◽  
The Stability ◽  
Base Properties

<p>The acid-base properties of some <em>p</em>-substituted aromatic hydrazones were examined in aqueous perchloric acid medim by spectrophotometric methods. The possible site where the proton may take place and the stability of the protonated form was discussed using the values of the total energy, binding energy, heat of formation and proton affinity calculated according to the semiempirical methods AM1 and PM3. Furthermore, the stability of the protonated forms, as well as, the stability of the isomers (<em>E</em> and <em>Z</em>) was discussed. Electronic absorption studies were utilized for determination of the dissociation constants of the protonated form (p<em>K</em><sub>BH</sub><sup>+</sup>), numerically and graphically, at different ionic strength (0.1, 0.25 and 0.5 mol/dm<sup>3</sup>), as well as, thermodynamic dissociation constants.  The influence of the solvent on the appearance of the recorded spectra was compensated by the use of the method of characteristic vector analysis (CVA).</p><p> </p>

scholarly journals Acid-base properties of kaolinite, montmorillonite and illite at marine ionic strength

2018 ◽  
Vol 483 ◽  
pp. 191-200 ◽  
Author(s):  
Yuxia Liu ◽  
Daniel S. Alessi ◽  
Shannon L. Flynn ◽  
Md. Samrat Alam ◽  
Weiduo Hao ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Acid Base ◽  
Base Properties

On the interaction of phytate with proton and monocharged inorganic cations in different ionic media, and modeling of acid-base properties at low ionic strength

2015 ◽  
Vol 90 ◽  
pp. 51-58 ◽  
Author(s):  
Clemente Bretti ◽  
Rosalia Maria Cigala ◽  
Concetta De Stefano ◽  
Gabriele Lando ◽  
Demetrio Milea ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Acid Base ◽  
Inorganic Cations ◽  
Ionic Media ◽  
Low Ionic Strength ◽  
Base Properties

Quantitative description of the changes in the acid-base properties of bromocresol green in the presence of submicelle and micelle concentrations of cationic tenside-Septonex

1983 ◽  
Vol 48 (5) ◽  
pp. 1290-1304 ◽  
Author(s):  
Josef Havel ◽  
Irena Burešová-jančářová ◽  
Vlastimil Kubáň
Keyword(s):  
Dissociation Constant ◽  
Equilibrium Constant ◽  
Dissociation Constants ◽  
Quantitative Description ◽  
Polymeric Micelle ◽  
Bromocresol Green ◽  
Acid Base ◽  
Experimental Conditions ◽  
Spectrophotometric Methods ◽  
Base Properties

The effect of cationic surface-active substances - tensides - on the acid-base and optical properties of anionic organic analytical reagents was studied by spectrophotometric methods on the example of bromocresol green with Septonex in the submicelle and micelle tenside concentration regions. The acid-base properties of bromocresol green under the given experimental conditions depend on the concentrations of the tenside and reagent and on the type and concentration of the inert electrolyte. Changes in the conditional dissociation constant of the reagent were quantitatively described by equations that were derived from the relationships for the dissociation constant of the acid-base transition of the reagent LH/L-, the equilibrium constant for formation of the stoichiometric ion-associates between the tenside T+ and the anionic acid-base form of the reagent L- or the anion of the inert electrolyte X- and the equilibrium constant for formation of the polymeric micelle aggregates (T+)n. The experimental values of the conditional dissociation constants for bromocresol green for various tenside or inert electrolyte concentrations are in good agreement with these theoretically derived relationships.

Sign in / Sign up

Export Citation Format

Share Document