Aromatic protonation. IV. Activation parameters for acid-catalyzed aromatic hydrogen exchange in 1,3-dimethoxy-benzene and 1,3,5-trimethoxybenzene

1967 ◽  
Vol 89 (17) ◽  
pp. 4418-4424 ◽  
Author(s):  
A. Jerry. Kresge ◽  
Yvonne. Chiang ◽  
Yoshishige. Sato
Keyword(s):  
Hydrogen Exchange ◽  
Activation Parameters ◽  
Acid Catalyzed ◽  
Aromatic Hydrogen

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.

Hydrogen exchange and isomerization in ortho substituted benzamides. On the question of free rotation in an N-protonated amide

1979 ◽  
Vol 57 (22) ◽  
pp. 2896-2901 ◽  
Author(s):  
Robert A. McClelland ◽  
William F. Reynolds
Keyword(s):  
Exchange Reaction ◽  
Rate Constants ◽  
Hydrogen Exchange ◽  
Isomerization Reaction ◽  
Free Rotation ◽  
Bond Rotation ◽  
Diffusion Limited ◽  
Deprotonation Reaction ◽  
Substituted Benzamides ◽  
Acid Catalyzed

Rate constants have been obtained for the acid-catalyzed N–H exchange of N-methyl, 2,N-dimethyl, and 2,4,6,N-tetramethylbenzamide and the acid-catalyzed isomerization of the three corresponding N,N-dimethylbenzamides. The ratio [Formula: see text] increases significantly with increased number of ortho methyl substituents. This is explained in terms of a suggestion of Perrin, that C—N bond rotation is not completely free in the N-protonated amide, since it must compete with a diffusion limited deprotonation reaction. The isomerization reaction, which requires such a rotation, is therefore slowed by ortho methyl substituents which hinder rotation, relative to the exchange reaction, which does not require rotation.

Acid-Catalyzed Hydration of Prop-2-en-1-ol and 2-Methylprop-2-en-1-ol: Correlation of Reactivity

1989 ◽  
Vol 42 (8) ◽  
pp. 1345 ◽  
Author(s):  
KP Herlihy
Keyword(s):  
Activation Parameters ◽  
Relative Reactivity ◽  
Nucleophilic Attack ◽  
Alternative Mechanism ◽  
Catalysed Reaction ◽  
Acid Catalyzed ◽  
Solvent Isotope ◽  
Kinetics Of

The kinetics of the acid-catalysed reaction of prop-2-en-1-ol and 2-methylprop-2-en-1-ol have been measured. The relative reactivity, solvent isotope ( kH+/kD +) and change in acidity effects, and activation parameters, have been determined and found to be similar to those of other alkenes. While this correlation of results for the hydration of both these alkenols can be interpreted in terms of the conventional Ad-E2 mechanism, computed values for the lifetime of possible carbocation intermediates suggest that an alternative mechanism for the reaction of prop-2-en-1-ol, in which nucleophilic attack by the solvent is concerted with protonation, is feasible.

The acid-catalyzed decomposition of nitramide

1996 ◽  
Vol 74 (10) ◽  
pp. 1779-1783 ◽  
Author(s):  
Robin A. Cox
Keyword(s):  
Rate Constants ◽  
Activation Parameters ◽  
Cyclic Process ◽  
Dilute Acid ◽  
Acid Media ◽  
Dilute Acid Solution ◽  
Acid Catalyzed ◽  
Reaction With Water ◽  
Hydrochloric And Sulfuric Acids ◽  
Good Agreement

Much attention has been paid to the base-catalyzed decomposition of nitramide, but despite this it was not certain that a corresponding acid-catalyzed reaction even existed before the work described in this paper. The excess acidity method has been applied to nitramide decomposition rate constants obtained in aqueous perchloric acid media, and to a lesser extent in aqueous hydrochloric and sulfuric acids. This analysis shows that the decomposition in dilute acid solution is actually a base-catalyzed reaction, with water acting as the base (perhaps in a cyclic process involving two water molecules), with rate constants in good agreement with previous estimates. However, in more concentrated acid media a true acid-catalyzed reaction can be dissected out. Activation parameters are given for both mechanisms, and it is shown that the acid-catalyzed process is similar to the acid-catalyzed decomposition of alkylnitramines. In sulfuric acid the reaction is slightly faster than it is in the other acids, due to the presence of a base-catalyzed process involving sulfate. Key words: nitramide, excess acidity, acid-catalyzed, base-catalyzed, kinetics.

Clay catalysis of aromatic hydrogen-exchange reactions

1982 ◽  
Vol 46 (2) ◽  
pp. 219-222 ◽  
Author(s):  
Robert Alexander ◽  
Robert Ian Kagi ◽  
Alfons Valentino Larcher
Keyword(s):  
Hydrogen Exchange ◽  
Exchange Reactions ◽  
Clay Catalysis ◽  
Aromatic Hydrogen
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