scholarly journals Equilibrium constants and protonation site for N-methylbenzenesulfonamides

2011 ◽  
Vol 7 ◽  
pp. 1732-1738 ◽  
Author(s):  
José A Moreira ◽  
Ana M Rosa da Costa ◽  
Luis García-Río ◽  
Márcia Pessêgo
Keyword(s):  
Sulfuric Acid ◽  
Oxygen Atom ◽  
Electron Donor ◽  
Equilibrium Constants ◽  
Acidity Constants ◽  
Protonation Site ◽  
Protonation Equilibria ◽  
Vis Spectroscopy ◽  
Donor Character ◽  
Solvation Parameter

The protonation equilibria of four substituted N-methylbenzenesulfonamides, X-MBS: X = 4-MeO (3a), 4-Me (3b), 4-Cl (3c) and 4-NO2 (3d), in aqueous sulfuric acid were studied at 25 °C by UV–vis spectroscopy. As expected, the values for the acidity constants are highly dependent on the electron-donor character of the substituent (the pK BH+ values are −3.5 ± 0.2, −4.2 ± 0.2, −5.2 ± 0.3 and −6.0 ± 0.3 for 3a, 3b, 3c and 3d, respectively). The solvation parameter m* is always higher than 0.5 and points to a decrease in the importance of solvation on the cation stabilization as the electron-donor character of the substituent increases. Hammett plots of the equilibrium constants showed a better correlation with the σ+ substituent parameter than with σ, which indicates that the initial protonation site is the oxygen atom of the sulfonyl group.

scholarly journals Protolytic equlibria of bromazepam

2002 ◽  
Vol 67 (3) ◽  
pp. 187-195 ◽  
Author(s):  
Lidija Pfendt ◽  
Gordana Popovic ◽  
Tatjana Damjanovic ◽  
Dusan Sladic
Keyword(s):  
Heterogeneous System ◽  
Nmr Spectra ◽  
Equilibrium Constants ◽  
Heterogeneous Systems ◽  
13C Nmr Spectra ◽  
Acidic Media ◽  
Acidity Constants ◽  
Protonation Site ◽  
Pyridine Nitrogen ◽  
Ph Range

The protolytic equilibria of bromazepam, an ampholyte sparingly soluble in water, in homogeneous and heterogeneous systems were studied in the pH range 0?14 at 25?C and at ionic strength of 0.1 mol/dm3 (NaCl). On the basis of 13C-NMR spectra, the protonation site was predicted ? in acidic media the pyridine nitrogen of bormazepam is protonated. The acidity constants of bromazepam were determined spectrophotometrically (pKa1 2.83 and pKa2 11.60) and potentiometrically (pKa1 2.99). In the heterogeneous system the following equilibrium constants were determined: Ks0 =[HA]?(pKs0 3.44), Ks1 =[H2A+]/[H3O+](pKs1 0.61), and Ks2 =[A-][H3O+](pKs2 15.04).

scholarly journals Solvent extraction of Sc(III) from sulfuric acid solution by bis(2-ethylhexyl) phosphonic acid in toluene

2002 ◽  
Vol 67 (4) ◽  
pp. 265-272 ◽  
Author(s):  
Devendra Koladkar ◽  
Purshottam Dhadke
Keyword(s):  
Sulfuric Acid ◽  
Acid Solution ◽  
Sulfuric Acid Solution ◽  
Equilibrium Constants ◽  
Phosphinic Acid ◽  
Extraction Equilibrium ◽  
H2so4 Concentration ◽  
Liquid Liquid Extraction ◽  
Extraction Reaction ◽  
Reaction Proceeds

Liquid-liquid extraction of scandium(III) from sulfuric acid solution using bis(2-ethylhexyl) phosphinic acid (PIA-8) in toluene has been studied. The extraction of scandium(III) was found to be quantitative with 0.03 M PIA-8 in toluene in the acidic range of 0.1?0.5 M and 6.0?8.0 M H2SO4. The effect of the reagent concentration and other parameters on the extraction of scandium(III) was also studied. The stoichiometry of the extracted species of scandium(III) was determined on the basis of the slope analysis method. The extraction reaction proceeds via the cation exchange mechanism in the H2SO4 concentration range of 0.1?0.5M and the extracted species is ScR3.3HR. However, at higher acidity (6.0M?8.0M H2SO4) it proceeds by solvation. The extracted species is HSc(SO4)2.4HR. The temperature dependencies of the extraction equilibrium constants were examined to estimate the apparent thermodynamic functions (?H, ?S and ?G) for the extraction reaction.

Protonation Equilibria of Tertiary Anilines in Sulfuric Acid: Water as a Reactant

1983 ◽  
Vol 136 (136) ◽  
pp. 65-67
Author(s):  
Michael W. Lovell ◽  
Brian S. Vogt ◽  
Stephen G. Schulman
Keyword(s):  
Sulfuric Acid ◽  
Acid Water ◽  
Protonation Equilibria

Structure of a New Tetranuclear Iron(III) Complex with an Oxo-Bridge; Factors to Govern Formation and Stability of Oxo-Bridged Iron(III) Species in the L-Subunit of Ferritin

2006 ◽  
Vol 61 (1-2) ◽  
pp. 149-154 ◽  
Author(s):  
Yuichi Sutoh ◽  
Yuko Okawamukai ◽  
Satoshi Nishino ◽  
Yuzo Nishida
Keyword(s):  
Hydrogen Peroxide ◽  
Oxygen Atom ◽  
Electron Donor ◽  
Carboxyl Groups ◽  
Cavity Surface ◽  
Reaction Products ◽  
Ferroxidase Activity ◽  
Oxo Bridge

Abstract We have investigated the reaction products of several iron(III) compounds with hydrogen peroxide, and have found that hydrogen peroxide promotes the formation of an oxo-bridged iron(III) species in the presence of methanol (electron donor), and carboxyl groups of the ligand systems play a role to give the tetranuclear iron(III) compound containing a bent Fe- O-Fe unit (O: oxo oxygen atom). Based on the present results and the facts that L-chains of human ferritins lack ferroxidase activity, but are richer in carboxyl groups (glutamates) exposed on the cavity surface, it seems reasonable to conclude that (i) the hydrogen peroxide released in the H-subunit may contribute to the formation of a diferric oxo-hydrate in the L-subunit, (ii) the formation of a bent oxo-bridged iron(III) species is essentially important in the L-subunit, and (iii) rich carboxyl groups in L-subunits contribute to facilitate iron nucleation and mineralization through the capture and activation of the peroxide ion, and formation of a stable bent oxo-bridged iron(III) species

Stability constants of three iron(III) salicylates

1970 ◽  
Vol 48 (16) ◽  
pp. 2574-2586 ◽  
Author(s):  
W. A. E. McBryde ◽  
Janet L. Rohr ◽  
J. S. Penciner ◽  
J. A. Page
Keyword(s):  
Stability Constants ◽  
Equilibrium Constants ◽  
Background Electrolyte ◽  
Aminosalicylic Acid ◽  
Sulfosalicylic Acid ◽  
Spectrophotometric Measurement ◽  
Acidity Constants ◽  
Extinction Coefficients ◽  
The Stability ◽  
Improved Methods

Stability constants of the iron(III) complexes of salicylic acid, sulfosalicylic acid, and 4-aminosalicylic acid, together with several of the acidity constants of these, have been determined at 25 °C and in solutions with 0.5 M background electrolyte. For the spectrophotometric measurement of the stability constants improved methods for determining the extinction coefficients of the first and second complexes are described. Protonated species appear only with the aminosalicylate complexes, and the site of this protonation is discussed. Previous values of these equilibrium constants have been collected and critically assessed.

Study of electron donor-acceptor complexes in the group of local anesthetics. The use of equilibrium constants Kc in QSAR study

1993 ◽  
Vol 28 (9) ◽  
pp. 743-748
Author(s):  
M Bachratá ◽  
M Stankovičová ◽  
Ẑ Bezáková ◽  
M Blešová ◽  
J Čiẑmárik
Keyword(s):  
Electron Donor ◽  
Local Anesthetics ◽  
Equilibrium Constants ◽  
Qsar Study ◽  
Donor Acceptor

ChemInform Abstract: PROTONATION EQUILIBRIA OF KETONES IN AQUEOUS SULFURIC ACID

1974 ◽  
Vol 5 (52) ◽  
Author(s):  
ARRIGO LEVI ◽  
GIORGIO MODENA ◽  
GIANFRANCO SCORRANO
Keyword(s):  
Sulfuric Acid ◽  
Protonation Equilibria ◽  
Aqueous Sulfuric Acid

scholarly journals EQUILIBRIA PROCESSES IN AQUEOUS SOLUTIONS OF K2CrO4 – HNO3 – KNO3 – H2O AND K2Cr2O7 – NaOH – KNO3 – H2O SYSTEMS

2021 ◽  
Vol 26 (2(78)) ◽  
pp. 56-72
Author(s):  
Yu. A Oleksii ◽  
O. Yu. Mariichak ◽  
G. M. Rozantsev ◽  
S. A. Shyshkanov ◽  
S.V. Radio
Keyword(s):  
Mathematical Modeling ◽  
Aqueous Solutions ◽  
Equilibrium Constants ◽  
Equilibrium Concentration ◽  
Quantitative Composition ◽  
Anion Formation ◽  
Chromium Vi ◽  
Vis Spectroscopy ◽  
Pitzer Method ◽  
Quasi Newton

The equilibria processes in aqueous solutions of CrO42– – H+ – H2O and Cr2O72– – OH– – H2O systems were studied by pH‑potentiometric titration, mathematical modeling and UV–Vis. spectroscopy. It was established that in the CrO42– – H+ – H2O systems with acidity ZН = ν(H+)/ν(Cr(VI)) = 0–2.5 the processes of dichromate and hydrochromate anion formation and hydrolytic conversion of dichromate to hydrochromate take place, for which the logarithms of the equilibrium concentration constants were calculated by the quasi-Newton method (CLINP 2.1 software; 95 % confidence probability). The calculated values of the logarithms of the concentration equilibrium constants lgKC reliably agree with the literature data. The calculated lgKC were used to build of chromium(VI) anions distribution diagrams depending on ZH, and ZOH in solutions. For the first time, by the Pitzer method the thermodynamic equilibria constants of hydrochromate HCrO4– (lgK10 = 6,94), the dichromate anion Cr2O72– (lgK20 = 15,49) formation processes from the CrO4 2– and H+ ions, and the logarithm of equilibrium constant of the interconversion of the dichromate anion to the hydrochromate anion (lgK30 = –1,61) were calculated. Mathematical modeling and UV–Vis. spectroscopy show that the composition of anions in Cr2O72– – OH– – H2O solutions with alkality ZOH = ν(OH–)/ν(Cr(VI)) = 0–2.5 is identical to CrO42– – H+ – H2O systems. It is established that the experimental dependencies pH = f(Z) for the Cr2O72– – OH– – H2O system can be reliably reproduced by hydrolysis reactions of dichromate anion to hydrochromate anion and by subsequent neutralization to chromate anion with equilibrium constants calculated for processes in CrO42– – H+ – H2O solutions with same ionic strengths. The quantitative composition of chromium(VI) solutions was confirmed qualitatively by UV–Vis. spectroscopy.

Sign in / Sign up

Export Citation Format

Share Document