Decomposition of some cyclic dithiocarbamates

1970 ◽  
Vol 48 (14) ◽  
pp. 2204-2209 ◽  
Author(s):  
Ronald R. Vandebeek ◽  
Serge J. Joris ◽  
Keijo I. Aspila ◽  
Chuni L. Chakrabarti
Keyword(s):  
Dielectric Constant ◽  
Dissociation Constants ◽  
Acid Dissociation ◽  
Acid Molecule ◽  
Decomposition Rates ◽  
Acid Dissociation Constants ◽  
Ring Strain ◽  
Relative Stabilities ◽  
Ph Values ◽  
The Stability

The stability of some cyclic N,N-disubstituted dithiocarbamates has been studied by the analysis of the decomposition rates at different pH values. It is concluded that the most important factors which determine the relative stabilities of three cyclic dithiocarbamates (DTC) are the solvation of the DTC acid molecule and the ring strain associated with the substituents. This has been proven by a study of (a) the decomposition rates as a function of the dielectric constant of the medium, (b) order of the stability, and (c) activation energy.The molar absorptivities and the apparent acid dissociation constants have been determined for pyrrolidine-, piperidine-, and hexamethylene-dithiocarbamates.

Article

1998 ◽  
Vol 76 (5) ◽  
pp. 576-582
Author(s):  
Patricia Gabriela Molina ◽  
María Alicia Zón ◽  
Héctor Fernández
Keyword(s):  
Dissociation Constants ◽  
Monomethyl Ether ◽  
Spectroscopic Studies ◽  
Acid Dissociation ◽  
Alternariol Monomethyl Ether ◽  
Acid Dissociation Constants ◽  
Ph Values ◽  
Acidic Constant ◽  
Acidic Constants ◽  
Good Agreement

The acid dissociation constants for alternariol monomethyl ether (AME), altertoxin-I (ATX-I), and alternariol (AOH), three of the Alternaria alternata genus mycotoxins, are estimated through conventional UV-VIS spectroscopic studies at different pH values. Experimental variations of absorbance as a function of pH at a given wavelength were fitted by using the exact equations that describe the systems studied. Good agreement between the experimental absorbance vs. pH plots and the curves generated by the fitting process was found. A comparison between the acidic constants for the first step of dissociation of these mycotoxins and the value for the acidic constant of phenol is discussed by assuming that phenolic structures are responsible for the acidity of these mycotoxins.Key words: mycotoxins, alternariol monomethyl ether, altertoxin-I, alternariol, acidic constants.

Solution speciation in the aqueous Na(I)–EDTA and K(I)–EDTA systems

1993 ◽  
Vol 71 (5) ◽  
pp. 763-768 ◽  
Author(s):  
Min Chen ◽  
R. Stephen Reid
Keyword(s):  
Potentiometric Titration ◽  
Ethylenediaminetetraacetic Acid ◽  
Dissociation Constants ◽  
Equilibrium Constants ◽  
Acid Dissociation ◽  
Equilibrium Models ◽  
Acid Dissociation Constants ◽  
Aqueous Sodium ◽  
Ph Values ◽  
Solution Speciation

Speciation in the aqueous sodium(I) – ethylenediaminetetraacetic acid and potassium(I) – ethylenediaminetetraacetic acid equilibrium systems was investigated by automated gravimetric potentiometric titration. It was found that in both cases, particularly below neutral pH values, speciation includes a previously uncharacterized diprotonated complex. All formation and acid dissociation constants were measured for the full systems. The validity of previous literature equilibrium constants, which are based on incomplete equilibrium models, is discussed.

Dihydroxyanthraquinone complexes of zirconium

1969 ◽  
Vol 22 (11) ◽  
pp. 2321 ◽  
Author(s):  
TM Florence ◽  
YJ Farrar ◽  
HE Zittel
Keyword(s):  
Dissociation Constants ◽  
Equilibrium Constants ◽  
Alizarin Red S ◽  
Acid Dissociation ◽  
Hydroxyl Groups ◽  
Acid Dissociation Constants ◽  
Alizarin Red ◽  
Zirconium Complexes ◽  
Voltammetric Techniques ◽  
The Stability

The nature of the zirconium complexes of alizarin red S (1,2-dihydroxy- anthraquinone-3-sulphonate), alizarin (1,2-dihydroxyanthraquinone), and hystazarin (2,3-dihydroxyanthraquinone) were studied using spectrophotometric, kinetic, and voltammetric techniques. In HClO4- NaClO4, 75% methanol media, these compounds form 1 : 1 complexes with zirconium. The equilibrium constants, KC, for the reaction of zirconium with alizarin red S, alizarin, and hystazarin were found to be 2.8 x 105, 3.0 x 103, and 6.9 x 102, respectively, at 25� and μ = 1.0M. The concentration acid dissociation constants, pKca, for the dihydroxyanthraquinones in 75% methanol were determined as: alizarin red S 6.71 and 11.35; alizarin 7.31 and 11.84; hystazarin 7.57 and 11.40; at 25� and μ 1.0M. Zirconium reacts slowly with alizarin red S and alizarin, and mainly via the hydrolysed Zr(OH)22+ species, whereas the reaction with hystazarin is rapid. Rate constants were determined for the first two reactions. The zirconium-alizarin red S complex includes two coordinated hydroxyl groups, the alizarin complex one, and the hystazarin complex contains none. It is suggested that these coordinated hydroxyl groups hydrogen-bond to the sulphonate and/or quinone groups and enhance both the stability and colour of the zirconium complexes.

Calculation of reference pH values for standard solutions from the corresponding acid dissociation constants

1990 ◽  
Vol 239 ◽  
pp. 129-137 ◽  
Author(s):  
M.J.Guiomar H.M. Lito ◽  
M.Filomena G.F.C. Camões ◽  
M.Isabel A. Ferra ◽  
Arthur K. Covington
Keyword(s):  
Dissociation Constants ◽  
Acid Dissociation ◽  
Acid Dissociation Constants ◽  
Ph Values ◽  
Standard Solutions
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