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.

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.

Kinetics and mechanism of cyclization of N-(2-methoxycarbonylphenyl)-N’-methylsulphonamide to 3-methyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide

1991 ◽  
Vol 56 (8) ◽  
pp. 1701-1710 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Miloš Sedlák ◽  
Vojeslav Štěrba
Keyword(s):  
Potassium Hydroxide ◽  
Acid Catalysis ◽  
Potassium Hydroxide Solution ◽  
Hydroxide Solution ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Cyclization Kinetics ◽  
Rate Limiting ◽  
Kinetics Of

The cyclization kinetics of N-(2-methylcarbonylphenyl)-N’-methylsulfonamide (IIb) into 3-methyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (Ib) has been studied in ethanolamine, morpholine, and butylamine buffers and in potassium hydroxide solution. The cyclization is subject to general base and general acid catalysis. The value of the Bronsted coefficient β is about 0.1, which indicates that splitting off of the proton from negatively charged tetrahedral intermediate represents the rate-limiting and thermodynamically favourable step. In the solutions of potassium hydroxide the cyclization of dianion of the starting ester IIb probably becomes the rate-limiting step.

Kinetics of reaction of 1,2-diaminobenzene with phenylglyoxal

1990 ◽  
Vol 55 (5) ◽  
pp. 1216-1222 ◽  
Author(s):  
Jiří Klicnar ◽  
Jaromír Mindl ◽  
Vojeslav Štěrba
Keyword(s):  
Reaction Kinetics ◽  
Cyclization Reaction ◽  
Amino Group ◽  
Ph Values ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Kinetics Of Reaction ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Aldehydic Group

The cyclization reaction kinetics of phenylglyoxal monohydrate with 1,2-diaminobenzene have been studied in formate, acetate, and phosphate buffers. At high pH values and low buffer concentrations the rate-limiting step consists in the protonation of the intermediate formed by addition of the first amino group to aldehydic group of phenylglyoxal. With increasing concentrations of formate and acetate buffers the rate-limiting step shifts to the formation of the intermediate. In phosphate buffers the catalysis by the basic buffer component makes itself felt, too. At higher concentrations of 1,2-diaminobenzene, the dehydration of phenylglyoxal monohydrate gradually becomes the rate-limiting step.

Kinetics of reaction of 5-phenyl-1,3,4-thiadiazol-2-diazonium ion with water

1979 ◽  
Vol 44 (10) ◽  
pp. 3102-3110 ◽  
Author(s):  
Jaromír Kaválek ◽  
Karel Janák ◽  
Vojeslav Štěrba
Keyword(s):  
Sulphuric Acid ◽  
Reaction Rate ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Mineral Acids ◽  
Diazonium Ion ◽  
Kinetics Of Reaction ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Sulphuric Acid Concentration

5-Phenyl-1,3,4-thiadiazol-2-diazonium ion (I) is transformed into 2-amino-5-phenyl-1,3,4-thiadiazol (II) in diluted mineral acids. The reaction rate measured in solutions of diluted sulphuric acid reaches its maximum at concentrations of 2 to 2.5M-H2SO4. The reaction intermediate is 5-phenyl-1,3,4-thiadiazol-2-diazo hydroxide (III). The rate-limiting step in formation of III consists in base-catalyzed reaction of the diazonium ion I with water; it is 4.3 times slower in 0.1M-D2SO4 than in 0.1m-H2SO4. Ratio of the rate constants of the transformation of the diazo hydroxide III into the diazonium ion I and into the amine II increases rapidly with increasing sulphuric acid concentration.

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.

scholarly journals A study of the oxidation of butan-1-ol and propan-2-ol by nicotinamide-adenine dinucleotide catalysed by yeast alcohol dehydrogenase.

1975 ◽  
Vol 147 (3) ◽  
pp. 541-547 ◽  
Author(s):  
C J Dickenson ◽  
F M Dickinson
Keyword(s):  
Alcohol Dehydrogenase ◽  
Ternary Complexes ◽  
Kinetics Of Oxidation ◽  
Yeast Alcohol Dehydrogenase ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Ph Range ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Flow Experiments

1. The kinetics of oxidation of butan-1-ol and propan-2-ol by NAD+, catalysed by yeast alcohol dehydrogenase, were studied at 25 degrees C from pH 5.5 to 10, and at pH 7.05 from 14 degrees to 44 degrees C, 2. Under all conditions studied the results are consistent with a mechanism whereby some dissociation of coenzyme from the active enzyme-NAD+-alcohol ternary complexes occurs, and the mechanism is therefore not strictly compulsory order. 3. A primary 2H isotopic effect on the maximum rates of oxidation of [1-2H2]butan-1-ol and [2H7]propan-2-ol was found at 25 degrees C over the pH range 5.5-10. Further, in stopped-flow experiments at pH 7.05 and 25 degrees C, there was no transient formation of NADH in the oxidation of butan-1-ol and propan-2-ol. The principal rate-limiting step in the oxidation of dependence on pH of the maximum rates of oxidation of butan-1-ol and propan-2-ol is consisten with the possibility that histidine and cysteine residues may affect or control catalysis.

Oxidation of 1- and 2-acetylnaphthalenes by iodate - a kinetic study

1990 ◽  
Vol 55 (6) ◽  
pp. 1535-1540 ◽  
Author(s):  
Prerepa Manikyamba
Keyword(s):  
Solvent Effect ◽  
Enol Form ◽  
Aqueous Methanol ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Carbonium Ion ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of oxidation of 1- and 2-acetylnaphthalenes by iodate in the presence of sulphuric acid in aqueous methanol has been studied. The reaction is first order with respect to both [iodate] and [acetylnaphthalene]. Solvent effect indicates a cation-dipole type of interaction in the rate limiting step. A mechanism is proposed with a slow attack of IO2+ on enol form of acetylnaphthalene forming an intermediate carbonium ion, which ultimately gives corresponding ω-hydroxyacetylnaphthalene. The higher reactivity of 2-acetyl isomer is attributed to the greater stability of the corresponding carbonium ion than that of 1-acetyl isomer.

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