Kinetic acidity function Hc.thermod.. 2. The scale in perchloric acid

1979 ◽  
Vol 44 (5) ◽  
pp. 753-757 ◽  
Author(s):  
C. David Johnson ◽  
Shaaron Rose ◽  
Peter G. Taylor
Keyword(s):  
Perchloric Acid ◽  
Acidity Function ◽  
Kinetic Acidity

Solvolysis kinetics and mechanism of substituted 3-acetyl-1,3-diphenyltriazenes in acid medium; Kinetic acidity function

1987 ◽  
Vol 52 (9) ◽  
pp. 2212-2216
Author(s):  
Oldřich Pytela ◽  
Martin Kaska ◽  
Miroslav Ludwig ◽  
Miroslav Večeřa
Keyword(s):  
Acid Medium ◽  
Sulphuric Acid ◽  
Rate Constants ◽  
Decomposition Kinetics ◽  
Acidity Function ◽  
Hammett Equation ◽  
Kinetic Acidity ◽  
Reaction Constant ◽  
Acid Catalyzed ◽  
Catalytic Rate

The decomposition kinetics has been measured of fourteen 3-acetyl-1,3-bis(subst. phenyl)triazenes in 40% (v/v) ethanol and sulphuric acid. The kinetic acidity function and catalytic rate constants have been determined from the rate constants observed. Mechanism has been suggested for the general acid-catalyzed solvolysis from comparison of the course of the kinetic acidity function and H0 function and from the reaction constant of the Hammett equation.

An acidity scale, [H+]hv, for proton quenching of excited states in aqueous perchloric acid

1989 ◽  
Vol 67 (4) ◽  
pp. 710-719 ◽  
Author(s):  
J. A. Pincock ◽  
P. R. Redden
Keyword(s):  
Excited State ◽  
Activity Coefficient ◽  
Excited States ◽  
Perchloric Acid ◽  
Acidity Function ◽  
Quenching Rate ◽  
Benzyl Alcohols ◽  
Fluorescent Indicator ◽  
Aqueous Perchloric Acid ◽  
Acidity Scale

An acidity scale for excited state protonation kinetics in aqueous perchloric acid has been developed using 1-cyanonaph-thalene as a fluorescent indicator. A comparison of the quenching rate constants obtained using this scale is made with both the more general excess acidity function, X, and the transition state activity coefficient approach. A variety of chromophores were studied including 1- and 2-cyanonaphthalenes, 1- and 2-methoxynaphthalenes, benzyl alcohols, toluenes, benzonitriles, and 2-vinylnaphthalene. Keywords: acidity scale, proton fluorescence quenching.

The Acidity Function of Perchloric Acid in Aqueous Acetic Acid

1954 ◽  
Vol 76 (14) ◽  
pp. 3853-3854 ◽  
Author(s):  
Frederick J. Ludwig ◽  
Kenneth H. Adams
Keyword(s):  
Acetic Acid ◽  
Perchloric Acid ◽  
Aqueous Acetic Acid ◽  
Acidity Function

Kinetic acidity function and solvolysis of 3-hydroxy-1,3-diphenyltriazenes

1986 ◽  
Vol 51 (3) ◽  
pp. 564-572 ◽  
Author(s):  
Oldřich Pytela ◽  
Stanislava Štumrová ◽  
Miroslav Ludwig ◽  
Miroslav Večeřa
Keyword(s):  
Sulphuric Acid ◽  
Substituent Effects ◽  
Acidity Function ◽  
Kinetic Acidity ◽  
Acid Catalyzed ◽  
Kinetics Of

Ten 3-hydroxy-1-(X-phenyl)-3-phenyltriazines have been synthesized, and kinetics of their solvolysis have been measured in 40% (v/v) ethanol and sulphuric acid. The concept of kinetic acidity function has been generalized, its construction has been suggested, and the procedure has been applied to the solvolysis of 3-hydroxy-1,3-diphenyltriazenes. The kinetic acidity function found has been confronted with the H0 acidity function. The substituent effects have been evaluated with respect to mechanism of the acid catalyzed solvolysis.

ortho-Effect on the acid-catalyzed hydration of 2-substituted α-methylstyrenes

2009 ◽  
Vol 74 (1) ◽  
pp. 85-99 ◽  
Author(s):  
Ondřej Prusek ◽  
Filip Bureš ◽  
Oldřich Pytela
Keyword(s):  
Sulfuric Acid ◽  
Benzene Ring ◽  
Rate Constants ◽  
Reaction Centre ◽  
Acidity Function ◽  
Isopropyl Group ◽  
Kinetic Acidity ◽  
Reaction Constant ◽  
Acid Catalyzed ◽  
Catalytic Rate

α-Methylstyrene and nine ortho-substituted analogs have been synthesized and the kinetics of their acid-catalyzed hydration in aqueous solutions of sulfuric acid at 25 °C have been investigated. The kinetic acidity function HS has been constructed from the dependence of the observed rate constants kobs on the sulfuric acid concentration. The catalytic rate constants of the acid-catalyzed hydration kortho have been calculated as well. The identical shape of the kinetic acidity functions for ortho- and para-derivatives confirms what the consistent mechanism A-SE2 of the acid-catalyzed hydration has already proved for the corresponding para-derivatives. The A-SE2 mechanism involves a rate-determining proton transfer of the hydrated proton to the substrate. From the dependence of the catalytic rate constants of the ortho-derivatives on the catalytic rate constants of the para-derivatives, it is seen that the logarithm of the catalytic rate constant for hydrogen as a substituent is markedly out of the range of the other substituents and, simultaneously, that the ortho-derivatives react significantly slower than the corresponding para-derivatives. In correlation with the substitent constants σp+, a reaction constant of ρ+ = –1.45 have been found. The constant is, in absolute value, considerably smaller than that for para-derivatives (ρ+ = –3.07). In parallel, the steric effects are enforced more significantly for the monoatomic substituents (slope of the Charton’s constants 3.92) than for substituents including more atoms (slope of the Charton’s constants 2.09). A small value of the reaction constant ρ+ has been elucidated due to the lower conjugation between the reaction centre and the benzene ring as a consequence of the geometric twist of the reaction centre out of the main aromatic plane accompanied by fading mesomeric interaction between the reaction centre and the substituents attached to the benzene ring. The isopropyl group in the carbocation is twisted less out of the aromatic plane for the monoatomic substituents and, therefore, also a small difference in the bulk of substituents has considerable steric influence on the conjugation between the carbocation and the benzene ring bearing substituents. On the contrary, the isopropyl group in the carbocations with polyatomic substituents is twisted to such a degree that changes in the bulk of substituents affect the resonant stabilization negligibly. Similar conclusions were also deduced from the correlations of the substitution constants σI and σR+.

Synthesis and cyclization kinetics and mechanism of 1-(2-ethoxycarbonylphenyl)-3-aryltriazenes. Kinetic acidity function of sodium methoxide in methanol

1990 ◽  
Vol 55 (10) ◽  
pp. 2468-2474 ◽  
Author(s):  
Oldřich Pytela ◽  
Vladimír Dlouhý
Keyword(s):  
Rate Constants ◽  
Sodium Methoxide ◽  
Substituent Effects ◽  
Acidity Function ◽  
Subsequent Reaction ◽  
Limiting Step ◽  
Kinetic Acidity ◽  
Substituent Constants ◽  
Catalytic Rate ◽  
Cyclization Kinetics

Eight 1-(2-ethoxycarbonylphenyl)-3-aryltriazenes have been synthetized and the rate constants of their sodium-methoxide-catalyzed cyclization have been measured in methanol at 25 °C. The experimental rate constants kobs have been adopted to construct the kinetic acidity function HKM which has been shown to be identical with the -log[CH3O-] values. Two mathematical procedures have been used to determine the catalytic rate constants and their dependence on the Hammett substituent constants. A closer dependence is obtained with the σ values than with the σp- values. The ρ value found (0.3) indicates a compensation of the substituent effects upon the dissociation of the starting triazene and upon the subsequent reaction of the conjugated base. Out of the two mechanistic alternatives - E1cB and BAc2 - the latter appears to be more probable, the splitting of tetrahedral intermediate being its limiting step.

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