The acid dissociation constant of triphenylethenethiol, a simple thioenol, and that of its oxygen-enol analog

1998 ◽  
Vol 76 (6) ◽  
pp. 657-661 ◽  
Author(s):  
Yvonne Chiang ◽  
A Jerry Kresge ◽  
Norman P Schepp ◽  
Vladimir V Popik ◽  
Zvi Rappoport ◽  
...  
Keyword(s):  
Flash Photolysis ◽  
Spectrophotometric Titration ◽  
Acid Dissociation ◽  
Acid Dissociation Constant ◽  
Acidity Constant ◽  
Dilute Acid ◽  
Acidity Constants ◽  
Oxygen Analog ◽  
Vinyl Halide

The acidity constant, pQaE = 8.49, for the stable thioenol, triphenylethenethiol, was determined by spectrophotometric titration, and that, pQaE = 11.37, for its unstable oxygen analog, triphenylethenol, was determined by analysis of its ketonization rate using enol generated flash photolytically from triphenylvinyl bromide. (These acidity constants are concentration quotients applicable at 0.10 M ionic strength in 50 vol.% aqueous methanol.) This appears to be the first determination of the acid strength of a simple thioenol. Triphenylethenethiol was unreactive in dilute acid or base, but in concentrated perchloric acid solutions it was slowly transformed into diphenylacetophenone and 2,3-diphenylbenzo[b]thiophene; the mechanisms of these reactions are believed to involve rapid equilibrium protonation of the enol on the beta -carbon followed by rate-determining capture of the cation so formed, either externally by solvent or internally by one of the beta -phenyl groups of the ion.Key words: enol ketonization, thioenol, flash photolysis, vinyl halide.

Dissociation of imino proton(s) of a highly water-soluble metal-free phthalocyanine and determination of its pKa value in water

2013 ◽  
Vol 17 (06n07) ◽  
pp. 447-453 ◽  
Author(s):  
Hiroaki Isago ◽  
Harumi Fujita
Keyword(s):  
Aqueous Media ◽  
Thermal Reaction ◽  
Water Soluble ◽  
Acid Dissociation ◽  
Acid Dissociation Constant ◽  
Metal Free ◽  
Imino Proton ◽  
Pka Value ◽  
Triton X

Dissociation of imino proton(s) in the cavity of the macrocycle of a highly water-soluble, metal-free phthalocyanine ( H 2( H 4 tsppc ); where H 4 tsppc denotes tetrakis{(2′,6′-dimethyl-4′-sulfonic acid)phenoxy}phthalocyaninate) in ethanolic and aqueous solutions has spectrophotometrically been investigated. The spectral changes associated with reaction with NaOH have been found to involve one-proton transfer process in aqueous media while two-protons process in ethanolic media. The acid-dissociation constant of the first imino proton in water (in the presence of Triton X-100) has been determined to be 12.5 ± 0.2 (as pKa) at 25 °C. The doubly deprotonated species in EtOH has been easily converted to its corresponding cobalt(II) derivative by thermal reaction with anhydrous CoCl 2.

Chromatographic Determination of Thermodynamic Acid Dissociation Constants of Tetracycline Antibiotics and Their Epimers

2019 ◽  
Vol 57 (8) ◽  
pp. 745-750
Author(s):  
İlkay Konçe ◽  
Ebru Çubuk Demiralay ◽  
Hülya Yılmaz Ortak
Keyword(s):  
Experimental Data ◽  
Dissociation Constant ◽  
Binary Mixtures ◽  
Dissociation Constants ◽  
Reversed Phase ◽  
Acid Dissociation ◽  
Acid Dissociation Constant ◽  
Chromatography Method ◽  
Ph Values

Abstract The presented study describes the development of reversed-phase liquid chromatography method using a core-shell particle column with a pentafluorophenyl stationary phase for the dissociation constant (pKa) determination of the tetracycline group antibiotics (tetracycline, oxytetracycline, chlortetracycline) and their epimers (4-epitetracycline, 4-epioxytetracycline, 4-epichlortetracycline). The pH values were measured in the acetonitrile (ACN)–water binary mixtures, used as mobile phases, instead of in water and take into account the effect of the activity coefficients. Thermodynamic acid dissociation constant (pKa1) values of studied antibiotics and their epimers were calculated using retention factor (k) at different mobile phase pH values in studied binary mixtures with ACN percentages of 20, 25, 30 and 35% (v/v). Experimental data were analyzed by using an Origin 7.0 program to fit experimental data to the nonlinear expression derived. From calculated pKa1 values, the aqueous pKa values of studied compounds were calculated by different approaches and these values were compared.

scholarly journals Development of Methods for the Determination of pKa Values

2013 ◽  
Vol 8 ◽  
pp. ACI.S12304 ◽  
Author(s):  
Jetse Reijenga ◽  
Arno van Hoof ◽  
Antonie van Loon ◽  
Bram Teunissen
Keyword(s):  
Dissociation Constant ◽  
Conceptual Development ◽  
Acid Dissociation ◽  
Acid Dissociation Constant ◽  
Future Developments ◽  
Research Fields ◽  
Current State ◽  
Wide Range ◽  
Pka Determination

The acid dissociation constant (pKa) is among the most frequently used physicochemical parameters, and its determination is of interest to a wide range of research fields. We present a brief introduction on the conceptual development of pKa as a physical parameter and its relationship to the concept of the pH of a solution. This is followed by a general summary of the historical development and current state of the techniques of pKa determination and an attempt to develop insight into future developments. Fourteen methods of determining the acid dissociation constant are placed in context and are critically evaluated to make a fair comparison and to determine their applications in modern chemistry. Additionally, we have studied these techniques in light of present trends in science and technology and attempt to determine how these trends might affect future developments in the field.

Solution scanometry, a new method for determination of acidity constants of indicators

2015 ◽  
Vol 7 (8) ◽  
pp. 3551-3558 ◽  
Author(s):  
Ardeshir Shokrollahi ◽  
Fereshteh Zarghampour ◽  
Sima Akbari ◽  
Ayda Salehi
Keyword(s):  
New Method ◽  
Acidity Constant ◽  
Inexpensive Method ◽  
Acidity Constants

Solution scanometry, a new, simple, fast, available and inexpensive method for the determination of the acidity constant, pKa, of indicators.

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