Kinetic acidity function Hc.thermod.. 1. Definition of the function in aqueous sulfuric acid and its applicability to acid-catalyzed hydrogen exchange of the ring protons of aromatic molecules, and protonation of carbon-carbon double and triple bonds

1979 ◽  
Vol 44 (5) ◽  
pp. 745-753 ◽  
Author(s):  
C. C. Greig ◽  
C. David Johnson ◽  
Shaaron Rose ◽  
Peter G. Taylor
Keyword(s):  
Sulfuric Acid ◽  
Hydrogen Exchange ◽  
Acidity Function ◽  
Aromatic Molecules ◽  
Triple Bonds ◽  
Aqueous Sulfuric Acid ◽  
Kinetic Acidity ◽  
Acid Catalyzed ◽  
Definition Of

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+.

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.

The decomposition of aliphatic N-nitro amines in aqueous sulfuric acid. Bisulfate as a nucleophile

1996 ◽  
Vol 74 (10) ◽  
pp. 1774-1778 ◽  
Author(s):  
Robin A. Cox
Keyword(s):  
Sulfuric Acid ◽  
Water Molecule ◽  
Rate Constants ◽  
Activation Parameters ◽  
Standard State ◽  
Aqueous Sulfuric Acid ◽  
Alkyl Groups ◽  
Different Temperatures ◽  
State Rate ◽  
Acid Catalyzed

In aqueous sulfuric acid, aliphatic N-nitro amines decompose to N2O and alcohols. An excess acidity analysis of the observed rate constants for the reaction shows that free carbocations are not formed. The reaction is an acid-catalyzed SN2 displacement from the protonated aci-nitro tautomer, the nucleophile being a water molecule at acidities below 82–85% H2SO4, and a bisulfate ion at higher acidities. Bisulfate is the poorer nucleophile by a factor of about 1000. Twelve compounds were studied, of which results obtained for nine at several different temperatures enabled calculation of activation parameters for both nucleophiles. The reaction appears to be mainly enthalpy controlled. The intercept standard-state rate constants are well correlated by the σ* values for the alkyl groups; the slopes are negative, with a more negative value for the slower bisulfate reaction. Interestingly the m≠m* slopes also correlate with σ*, although the scatter is bad. Key words: N-nitro amines, excess acidity, bisulfate, nucleophiles, acid-catalyzed, kinetics.

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.

ChemInform Abstract: Hydroxylamine Production via Hydrogenation of Nitric Oxide in Aqueous Sulfuric Acid Catalyzed by Carbon-Supported Platinum.

ChemInform ◽  
1987 ◽  
Vol 18 (51) ◽  
Author(s):  
S. POLIZZI ◽  
A. BENEDETTI ◽  
G. FAGHERAZZI ◽  
C. GOATIN ◽  
R. STROZZI ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Sulfuric Acid ◽  
Aqueous Sulfuric Acid ◽  
Supported Platinum ◽  
Acid Catalyzed

THE WALLACH REARRANGEMENT: PART II. KINETICS AND MECHANISM OF THE ACID-CATALYZED REARRANGEMENT OF AZOXYBENZENE

1965 ◽  
Vol 43 (4) ◽  
pp. 862-875 ◽  
Author(s):  
E. Buncel ◽  
B. T. Lawton
Keyword(s):  
Sulfuric Acid ◽  
Proton Transfer ◽  
Acid Concentration ◽  
Entire Range ◽  
Kinetics And Mechanism ◽  
The Other ◽  
Rate Data ◽  
Spectrophotometric Methods ◽  
Aqueous Sulfuric Acid ◽  
Acid Catalyzed

The rate of rearrangement of azoxybenzene to p-hydroxyazobenzene has been measured in 75.3–96.4% sulfuric acid at 25° and in 65.0–90.4% sulfuric acid at 75.5° by spectrophotometric methods. The pKa of azoxybenzene in aqueous sulfuric acid has also been determined. It is found that although azoxybesssnzene is almost completely protonated over the entire range of acid concentration studied, the rate increases by more than 1 000-fold. A two-proton process is therefore indicated and mechanisms are proposed involving a dication (II) as the key intermediate. The rate data do not allow differentiation between two proposed mechanisms, one involving two equilibrium protonations, and the other a single equilibrium protonation followed by rate-determining proton transfer. Past mechanisms of the Wallach rearrangement are discussed.

The Mechanism of Bromination of 2(1H)-Pyrimidinone, its N-Methyl and N,N′-Dimethyl Derivatives in Aqueous Acidic Solution

1974 ◽  
Vol 52 (3) ◽  
pp. 451-457 ◽  
Author(s):  
Oswald S. Tee ◽  
Sujit Banerjee
Keyword(s):  
Sulfuric Acid ◽  
Acidic Solution ◽  
Acid Solutions ◽  
Aqueous Sulfuric Acid ◽  
Acid Catalyzed ◽  
Aqueous Acidic Solution ◽  
Sulfuric Acid Solutions

Rates of bromination at the 5-positions of the title compounds have been measured in aqueous sulfuric acid solutions. The reaction involves a rapid irreversible formation of a 5-bromo-4,6-dihydroxy-hexahydro-2-oxopyrimidine which undergoes slow acid-catalyzed conversion to the corresponding 5-bromopyrimidinone. If excess bromine is present the latter product reacts further to produce a 5,5-dibromo-4,6-dihydroxyhexahydropyrimidine.

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