Structure-reactivity effects in the breakdown of hemiacetals of .alpha.-bromoacetophenone. Change in rate-limiting step for base catalysis

1988 ◽  
Vol 110 (15) ◽  
pp. 5118-5123 ◽  
Author(s):  
Poul E. Soerensen ◽  
K. J. Pedersen ◽  
P. R. Pedersen ◽  
V. M. Kanagasabapathy ◽  
Robert A. McClelland
Keyword(s):  
Base Catalysis ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

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.

Ketimine-enamine tautomerism of 2-ethoxycarbonylmethylene-4-methyl-3-oxo-1,2,3,4-tetrahydroquinoxaline: A kinetic study

1981 ◽  
Vol 46 (9) ◽  
pp. 2104-2109
Author(s):  
Jaromír Toman ◽  
Vojeslav Štěrba ◽  
Jiří Klicnar
Keyword(s):  
Carbon Atom ◽  
Solvent Effects ◽  
Title Compound ◽  
Base Catalysis ◽  
Methine Carbon ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid And Base ◽  
Acid Catalyzed ◽  
Rate Limiting

Tautomerism of the title compound in methanol in the presence of buffers is subject to general acid and base catalysis. The rate-limiting step of the acid-catalyzed reaction consists in addition of the proton to the methine carbon atom of the enamine form, whereas that of the base catalyzed reaction consists in protonation of the formed conjugated base of the enamine. Solvent effects on the equilibrium constant of the isomerization have been measured.

Kinetics and Mechanism of the Formation and Decomposition of Imidazolin-4-ones from 2-(N-Benzoylamino)alkanamides in Aqueous Medium

1999 ◽  
Vol 64 (10) ◽  
pp. 1629-1640 ◽  
Author(s):  
Miloš Sedlák ◽  
Jiří Hanusek ◽  
Radim Bína ◽  
Jaromír Kaválek ◽  
Vladimír Macháček
Keyword(s):  
Sodium Hydroxide ◽  
Aqueous Medium ◽  
Sodium Hydroxide Solution ◽  
Base Catalysis ◽  
Cyclization Reactions ◽  
Sodium Hydroxide Concentration ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Reaction Constant ◽  
Rate Limiting

The cyclization reactions of substituted 2-(N-benzoyl-N-methyl)aminoalkanamides 1a-1g have been studied in aqueous medium. The Hammett reaction constant is ρ = 1.4 for the cyclization reactions of compounds 1a-1e in sodium hydroxide solutions. 2-[N-Methyl- N-(4-nitrobenzoyl)amino]-2-(4-nitrophenyl)propanamide (1g) is cyclized to imidazolinone 2g in aqueous amine buffers of pH 9-11.5; the reaction is subject to specific base catalysis in these media, and the rate-limiting step is the formation of a tetrahedral intermediate. In sodium hydroxide solution, the primary cyclization product is hydrolyzed to give an intermediate M which is subsequently decomposed to sodium 4-nitrobenzoate and 2-methylamino- 2-(4-nitrophenyl)propanamide. At low sodium hydroxide concentration, the rate-limiting step of the opening of imidazoline ring of compound 2g is non-catalyzed decomposition of the intermediate. At higher sodium hydroxide concentrations, the other reaction path begins to make itself felt: hydroxide-ion-catalyzed decomposition of the intermediate. The dependence of observed rate constant of cyclization of compound 1f on sodium hydroxide concentration was used to determine kinetically the value of pKa = 13.5 ± 0.1. The kinetic deuterium isotope effect of cyclization of compounds 1f giving 2f (kCH/kCD = 1.7) was determined in solutions of NaOD in D2O.

Kinetics of Coupling of 4-Methoxybenzenediazonium Ion with 2,6-Dihydroxypyridine

1996 ◽  
Vol 61 (6) ◽  
pp. 951-956 ◽  
Author(s):  
Jaroslava Horáčková ◽  
Vojeslav Štěrba
Keyword(s):  
Methyl Ester ◽  
Steric Hindrance ◽  
Base Catalysis ◽  
Necessary Condition ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Kinetics Of Reaction ◽  
Rate Limiting ◽  
Kinetics Of

The kinetics of reaction of 4-methoxybenzenediazonium ion (3) with 2,6-dihydroxypyridine (1) has been studied in methoxyacetate, acetate, and phosphate buffers. The rate-limiting step is the formation of the reaction intermediate and not the splitting off of the proton (which was detected in the cases of citrazinic acid and its methyl ester). Therefrom it follows that for 2,6-dihydroxypyridine derivatives the steric hindrance to the formation of the Wheland intermediate exerted by CO2- and CO2CH3 groups represents a necessary condition for the rate-limiting splitting off of the proton and, hence, for the existence of general base catalysis.

ChemInform Abstract: Structure-Reactivity Effects in the Breakdown of Hemiacetals of α-Bromoacetophenone. Change in Rate-Limiting Step for Base Catalysis.

ChemInform ◽  
1988 ◽  
Vol 19 (46) ◽  
Author(s):  
P. E. SOERENSEN ◽  
K. J. PEDERSEN ◽  
P. R. PEDERSEN ◽  
V. M. KANAGASABAPATHY ◽  
R. A. MCCLELLAND
Keyword(s):  
Base Catalysis ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Abstract Structure ◽  
Rate Limiting

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting
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