Anchoring of the amide acidity function in dilute aqueous acid: a corrected HA scale

1977 ◽  
Vol 55 (13) ◽  
pp. 2492-2494 ◽  
Author(s):  
John T. Edward ◽  
Sin Cheong Wong
Keyword(s):  
Sulfuric Acid ◽  
Acidity Function ◽  
Aqueous Acid

Amide indicators ionizing over the range 0–30% sulfuric acid indicate that values of the HA scale established by Yates etal. (Can. J. Chem. 42, 1957 (1964)) should be corrected by +0.33 unit.

A Critical Test of the Hammett Acidity Function

1972 ◽  
Vol 50 (4) ◽  
pp. 581-583 ◽  
Author(s):  
Keith Yates ◽  
Stanley A. Shapiro
Keyword(s):  
Sulfuric Acid ◽  
Aromatic Amines ◽  
Acidity Function ◽  
Experimental Uncertainty ◽  
Critical Test ◽  
Hammett Acidity Function ◽  
Primary Aromatic Amines

The applicability of the H0 acidity function to primary aromatic amines in general has been tested by using a set of five aniline indicators bearing no nitro-substituents. Up to 45% sulfuric acid the scale generated by these bases is the same (within experimental uncertainty) as that based entirely on nitro-anilines.

Temperature variation of the H0 acidity function in aqueous sulfuric acid solution

1969 ◽  
Vol 91 (24) ◽  
pp. 6654-6662 ◽  
Author(s):  
Colin Douglas Johnson ◽  
A. R. Katritzky ◽  
S. A. Shapiro
Keyword(s):  
Sulfuric Acid ◽  
Acid Solution ◽  
Temperature Variation ◽  
Sulfuric Acid Solution ◽  
Acidity Function ◽  
Aqueous Sulfuric Acid

Protonation of polyacid organic bases. III. Hammett acidity function H+ for aqueous sulfuric acid

1968 ◽  
Vol 33 (6) ◽  
pp. 1687-1692 ◽  
Author(s):  
P. Vetešník ◽  
J. Bielavský ◽  
M. Večeřa
Keyword(s):  
Sulfuric Acid ◽  
Acidity Function ◽  
Organic Bases ◽  
Aqueous Sulfuric Acid ◽  
Hammett Acidity Function

scholarly journals Permanganate oxidation of aromatic alcohols in acid solution

1969 ◽  
Vol 47 (17) ◽  
pp. 3199-3205 ◽  
Author(s):  
Fariza Banoo ◽  
Ross Stewart
Keyword(s):  
Sulfuric Acid ◽  
Acid Solution ◽  
Acidity Function ◽  
Effect Of Substituents ◽  
Tertiary Alcohols ◽  
Permanganate Oxidation ◽  
Carbonium Ion ◽  
Aromatic Alcohols ◽  
Rapid Reaction ◽  
Rate Controlling Step

The mechanism of the permanganate oxidation of di- and tri-arylcarbinols has been studied in aqueous sulfuric acid. With both kinds of alcohols the rate-controlling step in solutions more acidic than H0 −0.50 was found to be the ionization of the carbinol to give the carbonium ion followed, it is believed, by rapid reaction with permanganate ion to form the ester which decomposes rapidly to products. In the case of the tertiary alcohols the decomposition probably proceeds via a 1,2-aryl shift. The effect of substituents is correlated with σ+ in both cases, ρ+ being −1.02 and −1.39 for the secondary and tertiary series. The acidity function which governs both reactions is H0. Tri(p-tolyl)carbinol is exceptional in that its oxidation in solutions more acidic than HR −2.6 is second-order and is governed by the HR acidity function.

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+.

An acidity function in ethanol – sulfuric acid based on the protonation of diphenylamines

1967 ◽  
Vol 45 (9) ◽  
pp. 903-910 ◽  
Author(s):  
Douglas Dolman ◽  
Ross Stewart
Keyword(s):  
Sulfuric Acid ◽  
Nitro Group ◽  
Strong Interaction ◽  
Acidic Solution ◽  
Sulfuric Acid Concentration ◽  
Substituent Effects ◽  
Solvent System ◽  
Acidity Function ◽  
Substituent Constants ◽  
Hammett Σ Constants

A Hammett H0 acidity function based on the protonation of 17 diphenylamines in 20 volume % ethanol – aqueous sulfuric acid has been established. The H0 value for the most acidic solution studied (11.2 M sulfuric acid) is −6.97. This acidity function differs from that based on the protonation of azobenzenes in the same solvent system; the latter diverges to more negative H0 values as the sulfuric acid concentration increases.The [Formula: see text] values for the protonation of the diphenylamines vary from +1.36 for 4-methoxy-diphenylamine to − 6.21 for 4,4′-dinitrodiphenylamine. A plot of [Formula: see text] versus the Hammett σ constants for five monosubstituted diphenylamines yields a ρ value of +3.36. The [Formula: see text] values for 4-methoxy-, 4-methyl-, 4-methylsulfonyl-, and 4-nitro-diphenylamine are all less (more negative) than expected from the Hammett substituent constants. The substituent effects on the basicities of aniline and diphenylamine are the same.The basicities of several nitro-substituted diphenylamines appear to vary regularly, and do not reflect the presence of a strong interaction between the nitro group and sulfuric acid.

Protonation of conjugated carbonyl groups in sulfuric acid solutions. III. α,β-Unsaturated ketosteroids

1970 ◽  
Vol 48 (16) ◽  
pp. 2538-2541 ◽  
Author(s):  
R. I. Zalewski ◽  
G. E. Dunn
Keyword(s):  
Sulfuric Acid ◽  
Spectral Data ◽  
Acidity Function ◽  
Additive Effects ◽  
Acid Solutions ◽  
Carbonyl Groups ◽  
Ultraviolet Spectrophotometry ◽  
Unit Slope ◽  
Straight Lines ◽  
Sulfuric Acid Solutions

Protonation of 20 α,β-unsaturated ketosteroids by sulfuric acid was studied by ultraviolet spectrophotometry. Plots of log [B]/[BH+] from spectral data against the amide acidity function, HA, gave straight lines with unit slope. The pKBH+ values thus obtained show the same additive effects of substituents as that reported previously for simple α,β-unsaturated alicyclic ketones.

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