Intramolecular nucleophilic participation by the thiol group during amide hydrolysis. Part 2. The imidazole catalysis dilemma

1992 ◽  
Vol 70 (1) ◽  
pp. 62-67 ◽  
Author(s):  
Robert S. McDonald ◽  
Patricia Patterson ◽  
June Rodwell ◽  
Ann Whalley
Keyword(s):  
Aqueous Solution ◽  
Thiol Group ◽  
Tetrahedral Intermediate ◽  
General Base ◽  
General Acid ◽  
Amide Hydrolysis ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Imidazole Catalysis

Catalysis by imidazole and N-methylimidazole buffers of the intramolecular thiolysis of N-n-propyl 2-mercaptomethylbenzamide (forming 2-thiophthalide) has been studied in aqueous solution at 40.0 °C, μ = 1.0. Unlike other buffers previously studied, imidazole and N-methylimidazole are able to catalyze, by a general base route, formation of neutral tetrahedral intermediate; this pathway is rate limiting at pH ≤ 7.5. At higher pH, the previously reported general acid-catalyzed breakdown of this intermediate is rate limiting. The relevance of these observations to the currently accepted pathway for the acylation of papain by amide substrates is discussed. Keywords: amide hydrolysis, intramolecular, thiol participation, imidazole, papain model.

Intramolecular participation by the thiol group in amide hydrolysis: the general acid-catalyzed pathway

1983 ◽  
Vol 61 (8) ◽  
pp. 1846-1852 ◽  
Author(s):  
Robert S. McDonald ◽  
Patricia Patterson ◽  
Ann Stevens-Whalley
Keyword(s):  
Thiol Group ◽  
General Acid ◽  
Amide Hydrolysis ◽  
Acid Catalyzed

Kinetics of cyclization of S-ethoxycarbonylmethylisothiouronium chloride to 2-imino-4-thiazolidone

1979 ◽  
Vol 44 (3) ◽  
pp. 912-917 ◽  
Author(s):  
Vladimír Macháček ◽  
Said A. El-bahai ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrochloric Acid ◽  
Dilute Hydrochloric Acid ◽  
Base Catalysis ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Kinetics Of Formation ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of formation of 2-imino-4-thiazolidone from S-ethoxycarbonylmethylisothiouronium chloride has been studied in aqueous buffers and dilute hydrochloric acid. The reaction is subject to general base catalysis, the β value being 0.65. Its rate limiting step consists in acid-catalyzed splitting off of ethoxide ion from dipolar tetrahedral intermediate. At pH < 2 formation of this intermediate becomes rate-limiting; rate constant of its formation is 2 . 104 s-1.

Deuterium exchange of C-methyl protons in lumazine derivatives

1970 ◽  
Vol 48 (2) ◽  
pp. 263-270 ◽  
Author(s):  
J. M. McAndless ◽  
Ross Stewart
Keyword(s):  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Acid Catalysis ◽  
Deuterium Exchange ◽  
Base Catalysis ◽  
Resonance Spectroscopy ◽  
Methyl Group ◽  
General Base ◽  
General Acid ◽  
Acid Catalyzed

Proton magnetic resonance spectroscopy has been used to examine the deuterium exchange of the methyl protons in two lumazine derivatives. The exchange occurs at the C-7 methyl group in 6,7,8-trimethyllumazine (2) and at the C-6 methyl group in 1,7-dihydro-6,7,8-trimethyllumazine (3). The former reaction is subject to both general acid- and general base-catalysis but the latter only to general acid-catalysis. Plausible mechanisms for the reactions of both compounds are advanced, involving in the case of 3, acid-catalyzed addition of water across the C6—N5 double bond.

Reaction kinetics of 1,2-diaminobenzene with ethyl 2-oxopropanoate and 2,3-butanedione

1988 ◽  
Vol 53 (12) ◽  
pp. 3154-3163 ◽  
Author(s):  
Jiří Klicnar ◽  
Jaromír Mindl ◽  
Ivana Obořilová ◽  
Jaroslav Petříček ◽  
Vojeslav Štěrba
Keyword(s):  
Reaction Kinetics ◽  
Acid Catalysis ◽  
Reaction Pathway ◽  
Hydroxide Ion ◽  
Tetrahedral Intermediate ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
General Acid ◽  
Rate Limiting ◽  
Kinetics Of

The reaction of 1,2-diaminobenzene with 2,3-butanedione is subject to general acid catalysis in acetate and phosphate buffers (pH 4-7). The rate-limiting step of formation of 2,3-dimethylquinoxaline consists in the protonation of dipolar tetrahedral intermediate. In the case of the reaction of 1,2-diaminobenzene with ethyl 2-oxopropanoate, the dehydration of carbinolamine gradually becomes rate-limiting with increasing pH in acetate buffers, whereas in phosphate buffers a new reaction pathway makes itself felt, viz. the formation of amide catalyzed by the basic buffer component and by hydroxide ion.

Reactions of thiourea with chloro- and bromoacetic acids

1980 ◽  
Vol 45 (1) ◽  
pp. 263-268 ◽  
Author(s):  
Jaromír Kaválek ◽  
Said El-Bahaie ◽  
Vojeslav Štěrba
Keyword(s):  
Chloroacetic Acid ◽  
Hydroxyl Group ◽  
Salt Formation ◽  
Sulphur Atom ◽  
Bromoacetic Acid ◽  
Tetrahedral Intermediate ◽  
Acid Catalyzed ◽  
Rate Limiting

The reaction of chloroacetic acid with thiourea represents an SN2 substitution of chlorine by sulphur atom and is about two orders of magnitude slower than that of bromoacetic acid. Chloroacetate ion reacts slower than chloroacetic acid only about 30%. The acid catalyzed splitting off of hydroxyl group from the formed tetrahedral intermediate is rate-limiting in the cyclization of the S-carboxylatomethyleneisothiouronium salt, formation of the intermediate being rate-limiting below pH 2.

The proton activating factor and its application to acid and base catalysis of aldehyde hydration

1984 ◽  
Vol 62 (5) ◽  
pp. 907-910 ◽  
Author(s):  
Ross Stewart
Keyword(s):  
Nucleophilic Addition ◽  
Base Catalysis ◽  
General Base ◽  
Uncatalyzed Reaction ◽  
General Acid ◽  
Acid And Base ◽  
Alternative Means ◽  
Acid Catalyzed ◽  
Substituted Benzaldehydes ◽  
Class E

The data of McClelland and Coe for the general acid and general base catalyzed hydration of a series of substituted benzaldehydes has been analyzed in terms of the proton activating factor, paf, and concepts related thereto. Although the latter were derived for use with prototropic systems, the present work shows that they have application to nucleophilic addition as well. Three conclusions emerge from the analysis. 1. Alternative means of calculating paf from buffer catalytic data that were previously derived on theoretical grounds can be used in practice to give essentially the same results. 2. The mechanism of the general acid catalyzed pathway for aldehyde hydration is that favoured by McClelland and Coe and by Jencks, to wit the class (e) mechanism, rather than the class (n) mechanism. 3. Electron-withdrawing groups in the benzaldehyde ring cause the disparity between the contributions of alternative, kinetically equivalent, pathways for the uncatalyzed reaction to become greater.

Coupling Kinetics of Benzenediazonium Ions with 2,6-Dioxo-3-(p-substituted phenylhydrazono)-1,2,3,6-tetrahydropyridine-4-carboxylic Acid

1992 ◽  
Vol 57 (9) ◽  
pp. 1915-1927
Author(s):  
Jaroslava Horáčková ◽  
Vojeslav Štěrba
Keyword(s):  
Base Catalysis ◽  
Partial Replacement ◽  
Tetrahedral Intermediate ◽  
Buffer Solutions ◽  
General Base ◽  
Rate Limiting Step ◽  
Bisazo Compounds ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Derivatives Of

The kinetics have been measured of the reactions of 4-nitro-, 4-chloro-, and 4-methoxybenzenediazonium ions with substituted phenylazo derivatives of citrazinic acid in buffer solutions, and the pKa values of the corresponding monoazo and bisazo compounds have been estimated. The reactions of 4-nitrobenzenediazonium ion with 4-chloro- and 4-methoxyphenylazo derivatives and of 4-chlorobenzenediazonium ion with 4-methoxyphenylazo derivative were accompanied by a partial replacement of the substituted phenylazo group by the 4-nitro- and 4-chlorophenylazo groups, respectively. The reactions of 4-chloro- and 4-methoxybenzenediazonium ions are subject to general base catalysis, the rate-limiting step consisting in the splitting off of the proton from the tetrahedral intermediate; with 4-nitrobenzenediazonium ion the reaction rate is limited by the formation of the tetrahedral intermediate.

Change of Rate Limiting Step in General Acid-Catalyzed Benzo[a]pyrene Diol Epoxide Hydrolysis

1998 ◽  
Vol 120 (18) ◽  
pp. 4327-4333 ◽  
Author(s):  
Bin Lin ◽  
Nafisa Islam ◽  
Steve Friedman ◽  
H. Yagi ◽  
Donald M. Jerina ◽  
...  
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
General Acid ◽  
Diol Epoxide ◽  
Acid Catalyzed ◽  
Rate Limiting
Sign in / Sign up

Export Citation Format

Share Document