Transition-state activity coefficients-a new mechanistic tool in the investigation of acid-catalyzed reactions

1978 ◽  
Vol 11 (5) ◽  
pp. 190-196 ◽  
Author(s):  
Keith Yates ◽  
Tomasz A. Modro
Keyword(s):  
Transition State ◽  
Activity Coefficients ◽  
State Activity ◽  
Acid Catalyzed ◽  
Catalyzed Reactions

Transition state activity coefficients in the acid-catalyzed hydrolysis of esters

1975 ◽  
Vol 97 (18) ◽  
pp. 5223-5231 ◽  
Author(s):  
Robert A. McClelland ◽  
Tomasz A. Modro ◽  
Malcolm F. Goldman ◽  
Keith Yates
Keyword(s):  
Transition State ◽  
Activity Coefficients ◽  
State Activity ◽  
Acid Catalyzed ◽  
Hydrolysis Of Esters ◽  
Hydrolysis Of

Kinetic medium effects. IV. Transition state activity coefficients in mixed solvents

1972 ◽  
Vol 25 (4) ◽  
pp. 777 ◽  
Author(s):  
PT McTigue ◽  
AR Watkins
Keyword(s):  
Transition State ◽  
Activity Coefficients ◽  
Mixed Solvents ◽  
State Theory ◽  
Medium Effects ◽  
State Activity ◽  
Medium Activity ◽  
Solvent Systems ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of acid hydrolysis of a number of aliphatic acetals have been studied in dimethyl sulphoxide-water and dioxan-water mixtures. Where possible, experimentally measured medium activity coefficients for the acetals in the solvent systems have been used in order to calculate the transition state activity coefficients as a function of solvent composition. These activity coefficients are compared with those calculated for the transition states of other hydrolytic reactions, and with the known activity coefficients of some stable ions. The results show no features inconsistent with the assumptions of transition state theory.

Oxygen exchange in methanol in acid solutions. Transition state activity coefficients

1980 ◽  
Vol 58 (4) ◽  
pp. 393-398 ◽  
Author(s):  
Robert A. McClelland
Keyword(s):  
Sulfuric Acid ◽  
Activity Coefficient ◽  
Transition State ◽  
Activity Coefficients ◽  
Oxygen Exchange ◽  
Acid Solutions ◽  
Salting Out ◽  
Carbonium Ion ◽  
State Activity ◽  
Significant Difference

Rate constants for oxygen exchange of methanol in sulfuric acid and perchloric acid solutions are reported, along with activity coefficients of methanol in sulfuric acid. Transition state activity coefficients (f≠*) for methanol exchange and tert-butanol exchange have been calculated. Values of f≠* for the latter behave very similarly to those for tert-butyl acetate hydrolysis, consistent with a carbonium ion-like transition state. Values for methanol exchange show considerably more salting-out, consistent with an oxonium ion-like transition state. A significant difference with the AAc2 hydrolyses of esters and amides is noted. For the latter the transition state is salted-out relative to its protonated precursor, whereas for methanol exchange, there is little difference between the activity coefficient of the protonated alcohol and the transition state, with the latter actually being somewhat salted-in. It is pointed out that the transition state activity coefficient approach can be rigorously applied even in the absence of protonation data.

Kinetics of the hydrolysis of acetic anhydride and the reaction of 4-nitrophenyl acetate with imidazole in aqueous-organic mixed solvents

1974 ◽  
Vol 27 (7) ◽  
pp. 1423 ◽  
Author(s):  
DG Oakenfull
Keyword(s):  
Acetic Anhydride ◽  
Organic Solvent ◽  
Transition State ◽  
Activity Coefficients ◽  
Butyl Alcohol ◽  
Dimethyl Sulphoxide ◽  
Kinetics Of Hydrolysis ◽  
State Activity ◽  
Kinetics Of ◽  
Hydrolysis Of

With the general aim of elucidating the role of water structure in the kinetics of hydrolysis, a comparative study has been made of the kinetics of the hydrolysis of acetic anhydride and the reaction of 4-nitrophenyl acetate with imidazole in mixtures of water with ethanol, t-butyl alcohol, dimethyl sulphoxide and dioxan. Both rate constants were always reduced by the addition of organic solvent. Transition state activity coefficients were measured for both reactions in dimethyl sulphoxide-water mixtures and compared with the activity coefficient of phenylalanine (a model zwitterionic transition state). Activation parameters were measured for the hydrolysis of aceticanhydride in t-butyl alcohol-water and dimethyl sulphoxide-water mixtures. Semilogarithmic plots of rate constant against Winstein's Y-value were non-linear for some of the solvents and this fact, coupled with the effect of dimethyl sulphoxide on the transition state activity coefficients, leads to the conclusion that specific interactions of the solvent with the reactants and with the transition state could be of major importance in controlling the reaction rate.There was no obvious relationship between the effect of an organic solvent on the kinetics of hydrolysis of acetic anhydride and its effect on the structure of water.

Transition state activity coefficients in the acid-catalyzed hydrolysis of amides

1977 ◽  
Vol 55 (16) ◽  
pp. 3050-3057 ◽  
Author(s):  
Tomasz A. Modro ◽  
Keith Yates ◽  
Françoise Beaufays
Keyword(s):  
Transition State ◽  
Bond Cleavage ◽  
Protonated Form ◽  
State Activity ◽  
Alkyl Derivatives ◽  
Amide Hydrolysis ◽  
Conjugate Acid ◽  
Acid Catalyzed ◽  
Hydrolysis Of ◽  
Nitrogen Bond

The transition-state activity coefficient [Formula: see text] approach has been applied to the acid-catalyzed hydrolysis of benzamide and its N-alkyl derivatives. For all systems (with the exception of the N-tert-butyl derivative which reacts via carbon–nitrogen bond cleavage) a uniform type of medium dependence of [Formula: see text] is observed. The reaction shows a pronounced destabilization of S≠ over the whole region of acidity studied, practically identical to that found for the AAc-2 type of ester hydrolysis. This is interpreted in terms of an AoT2 mechanism of amide hydrolysis, that is the rate-determining formation of the oxonium-type tetrahedral intermediate from the O-protonated form of substrate conjugate acid.

Photoinduced rearrangement of hydroxymethylisoxazolines, a route to enaminoaldehydes

1986 ◽  
Vol 51 (10) ◽  
pp. 2167-2180 ◽  
Author(s):  
Lubor Fišera ◽  
Nadezhda D. Kozhina ◽  
Peter Oravec ◽  
Hans-Joachim Timpe ◽  
Ladislav Štibrányi ◽  
...  
Keyword(s):  
Thionyl Chloride ◽  
Quantum Yields ◽  
Acid Catalyzed ◽  
Catalyzed Reactions ◽  
Photoinduced Rearrangement ◽  
Condensed Heterocycles

3-Aryl-4-R-carbamoyl-5-hydroxymethylisoxazolines (IV) were synthesized by allowing R-NH2 amines with R = H, CH3, C3H7, C6H5C2H5, and NH2 to act on 3-(X-phenyl)-4-oxo-3a,4,6,6a-tetrahydrofuro[3,4-d]isoxazoles (III) with X = H, 4-CH3, 4-OCH3, 2-OCH3, 4-Cl, 2-Cl, 4-F, 2-F, 4-Br, 4-NO2, and 3-NO2. Exposed to radiation, the substances IV give Z-2-hydroxymethylamino-2-aryl-1-formylacrylamides (V) in good yields. The 4-Cl and 4-F substituted Z-derivatives V isomerize irreversibly to the E-derivatives VI if allowed to stand in solvent; the remaining derivatives V are stable. The quantum yields of the photoreaction are from 0.012 to 0.106 in dependence on the substituent X. In all cases where the compounds IV were used for the preparation of condensed heterocycles in conditions of acid-catalyzed reactions, lactones III were preferentially formed; the action of thionyl chloride on IV results in the formation of chloromethyl derivatives VIII, which do not undergo further cyclization.

Synthetic Scope of Brønsted Acid-Catalyzed Reactions of Carbonyl Compounds and Ethyl Diazoacetate

2021 ◽  
Author(s):  
Mizzanoor Rahaman ◽  
M. Shahnawaz Ali ◽  
Khorshada Jahan ◽  
Damon Hinz ◽  
Jawad Bin Belayet ◽  
...  
Keyword(s):  
Carbonyl Compounds ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Ethyl Diazoacetate ◽  
Brönsted Acid ◽  
Acid Catalyzed ◽  
Catalyzed Reactions

Kinetic modelling of reactions for the synthesis of 2-methyl-5-ethyl pyridine

2021 ◽  
Author(s):  
Emanuele Moioli ◽  
Leo Schmid ◽  
Peter Wasserscheid ◽  
Hannsjoerg Freund
Keyword(s):  
Kinetic Modelling ◽  
Acid Catalyst ◽  
Acid Catalyzed ◽  
Catalyzed Reactions ◽  
Kinetics Of

The kinetics of the acid catalyzed reactions of acetaldehyde ammonia trimer (AAT) and paraldehyde (para) to 2-methyl-5-ethyl pyridine (MEP) in the presence of an acid catalyst were investigated systematically. A...

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