scholarly journals The mechanism of the iodination of aminochromes

1967 ◽  
Vol 45 (15) ◽  
pp. 1721-1725 ◽  
Author(s):  
G. L. Mattok ◽  
D. L. Wilson
Keyword(s):  
Potassium Iodide ◽  
Molecular Iodine ◽  
Reactive Species ◽  
Base Catalysis ◽  
Ion Concentration ◽  
Zwitterionic Form ◽  
General Base ◽  
Rate Of Reaction ◽  
Reaction Proceeds ◽  
Kinetics Of

The kinetics of the iodination of several aminochromes by iodine in aqueous potassium iodide, to form the 7-iodo derivatives, have been studied. The rate of iodination is directly dependent on the concentrations of the aminochrome and iodine and varies inversely with the first power of the iodide ion concentration. The rate of reaction is independent of pH, but the reaction is subject to general base catalysis. A mechanism for the iodination of aminochromes is proposed. The reactive species are molecular iodine and the zwitterionic form of adrenochrome, and the reaction proceeds via a quinonoid intermediate. The rate-controlling process is the removal of the C-7 proton.

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.

Evidence for general base catalysis by protic solvents in a kinetic study of alcoholyses and hydrolyses of 1-(phenoxycarbonyl)pyridinium ions under both solvolytic and non-solvolytic conditions

2009 ◽  
Vol 74 (1) ◽  
pp. 43-55 ◽  
Author(s):  
Dennis N. Kevill ◽  
Byoung-Chun Park ◽  
Jin Burm Kyong
Keyword(s):  
Second Order ◽  
Base Catalysis ◽  
Substitution Reactions ◽  
Third Order ◽  
Methoxy Derivative ◽  
First Order ◽  
General Base ◽  
Protic Solvents ◽  
Kinetics Of ◽  
Pyridinium Ions

The kinetics of nucleophilic substitution reactions of 1-(phenoxycarbonyl)pyridinium ions, prepared with the essentially non-nucleophilic/non-basic fluoroborate as the counterion, have been studied using up to 1.60 M methanol in acetonitrile as solvent and under solvolytic conditions in 2,2,2-trifluoroethan-1-ol (TFE) and its mixtures with water. Under the non- solvolytic conditions, the parent and three pyridine-ring-substituted derivatives were studied. Both second-order (first-order in methanol) and third-order (second-order in methanol) kinetic contributions were observed. In the solvolysis studies, since solvent ionizing power values were almost constant over the range of aqueous TFE studied, a Grunwald–Winstein equation treatment of the specific rates of solvolysis for the parent and the 4-methoxy derivative could be carried out in terms of variations in solvent nucleophilicity, and an appreciable sensitivity to changes in solvent nucleophilicity was found.

scholarly journals The mechanism of the catalytic oxidation of ethylene - I. Experiments using a flow system

1946 ◽  
Vol 188 (1012) ◽  
pp. 92-104 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Ethylene Oxide ◽  
Catalytic Oxidation ◽  
Flow System ◽  
Oxidation Reactions ◽  
Direct Oxidation ◽  
Rate Of Reaction ◽  
Reaction Proceeds ◽  
Products Of Reaction ◽  
Kinetics Of

Experiments have been made using a flow system to determine the mechanism of the catalytic oxidation of ethylene on a silver catalyst. The effects of time of contact of the gases with the catalyst, gas concentration, and temperature have been investigated. The products of reaction are ethylene oxide, and carbon dioxide and water. There appear to be two processes whereby the carbon dioxide is formed: (1) by direct oxidation of the ethylene not via ethylene oxide, and (2) by the further oxidation of the ethylene oxide. The isomerization of ethylene oxide to acetaldehyde by the catalyst in the absence of any oxygen has also been examined. By comparison with the oxidation of ethylene oxide, it has been shown that this latter reaction proceeds to a large extent, and possibly entirely, through a preliminary isomerization of the ethylene oxide to acetaldehyde. The rate of oxidation of acetaldehyde is extremely rapid and no trace of acetaldehyde is found during the oxidation of ethylene or of ethylene oxide. Ethylene oxide forms on the catalyst an involatile deposit, which is oxidized away by oxygen, so that during oxidation reactions the quantity of it on the catalyst is kept low. The kinetics of the oxidation of ethylene, i.e. rate of reaction proportional to the oxygen concentration and slightly dependent on the ethylene pressure, are consistent with the view that ethylene reacts with oxygen adsorbed on the catalyst and that the slowest step in the whole series of reactions is the rate of adsorption of the oxygen. An energy of activation of about 27 kcal. was found for the production of ethylene oxide, and slightly less for the production of carbon dioxide and consumption of oxygen.

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.

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.

Discreteness-of-charge effects in electrode kinetics. I. The electroreduction of tetrathionate anion in the presence of specifically adsorbed iodide anions

1982 ◽  
Vol 60 (15) ◽  
pp. 2038-2045 ◽  
Author(s):  
W. Ronald Fawcett ◽  
Kveta Markušová
Keyword(s):  
Ionic Strength ◽  
Electrode Potential ◽  
Ion Concentration ◽  
Electrode Kinetics ◽  
Charge Effect ◽  
Charge Effects ◽  
Potential Analysis ◽  
Rate Of Reaction ◽  
Kinetics Of ◽  
Outer Helmholtz Plane

The kinetics of electroreduction of tetrathionate anion have been studied at a Hg electrode in aqueous solutions of Nal + NaF and KI + KF with an ionic strength of 0.25 M. The rate of reaction was observed to decrease as the iodide ion concentration was increased, and when the cation was changed from K+ to Na+ at constant electrode potential. Analysis of the double layer effects on the basis of the Frumkin model results in an overestimation of the repulsive effect of the adsorbed iodide anions. This result is interpreted on the basis of the discreteness-of-charge effect and the possible non-coincidence of the reaction plane and outer Helmholtz plane.

Discreteness-of-charge effects in electrode kinetics. II. The electroreduction of hexamminocobalt(III) cation in the presence of specifically adsorbed nitrate anions

1983 ◽  
Vol 61 (12) ◽  
pp. 2821-2826 ◽  
Author(s):  
W. Ronald Fawcett ◽  
Kveta Markušová
Keyword(s):  
Ion Pairs ◽  
Electrode Reaction ◽  
Ion Concentration ◽  
Charge Effects ◽  
Interfacial Kinetics ◽  
Rate Of Reaction ◽  
Layer Effect ◽  
Kinetics Of ◽  
Nitrate Anions ◽  
Cation Nature

The kinetics of electroreduction of the hexamminocobalt(III) cation have been studied at a Hg electrode in aqueous solutions of NaNO3 + NaF and KNO3 + KF with an ionic strength of 0.2 M. The rate of reaction was observed to increase with increasing nitrate ion concentration but was independent of the cation nature. Analysis of the double layer effect for this system indicates that ion pairs formed between the reacting cation and anions of the base electrolyte also participate in the electrode reaction, and that attractive interactions between the reactant and adsorbed anions have a significant influence on the interfacial kinetics.

Reactions of free radicals with aromatic compounds in the gaseous phase. III. Kinetics of the reaction of methyl radicals with anisole (methoxybenzene)

1967 ◽  
Vol 20 (6) ◽  
pp. 1155 ◽  
Author(s):  
MFR Mulcahy ◽  
BG Tucker ◽  
DJ Williams ◽  
JR Wilmshurst
Keyword(s):  
Free Radicals ◽  
Gaseous Phase ◽  
Aromatic Compounds ◽  
Phase Iii ◽  
Methyl Radicals ◽  
Kcal Mole ◽  
Rate Of Reaction ◽  
Reaction Proceeds ◽  
Kinetics Of Reaction ◽  
Kinetics Of

The kinetics of the reaction between methyl radicals and anisole have been studied at temperatures between 453 and 539�K and total pressures between 10 and 30 torr. The concentrations of methyl radicals ranged from 2 x 10-12 to 5 x 10-11 mole and those of anisole from 10-7 to mole cm-3. The reaction proceeds mainly by the mechanism ������������������ C6H5OCH3+CH3· → C6H5OCH2·+CH4���������������� (1)����������������� C6H5OCH2·+CH3· → C6H5OC2H5�������������������� (2)���������������� ���������C6H5OCH2· → C6H5CHO+H·������������������ (3) At 487�K attack on the aromatic ring to yield methyl anisoles is about twelve times slower than reaction (1). The Arrhenius parameters for reactions (1) and (8) are: log10(A1 cm3 mole-1 sec-1) = 11.7 � 0.3, and E1 = 10.5 � 0.8 kcal mole-1; log10(A8 sec-1) = 12.5, and E8 = 21 kcal mole-1. The last two values are based on the assumption that the kinetics of reaction (2) are similar to those of the recombination of methyl radicals. The rate of reaction (1) is about half that of the corre- sponding reaction with toluene and about five times that of the reaction with ethane in the above temperature range.

Acid and Base Catalysis in the Oxidation of 6,7,8-Trimethyllumazine. II. Kinetics and Mechanism

1974 ◽  
Vol 52 (23) ◽  
pp. 3884-3894 ◽  
Author(s):  
Ross Stewart ◽  
Kiyotaka Oyama
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Base Catalysis ◽  
Methyl Group ◽  
General Base ◽  
Kinetic Isotope ◽  
Conjugate Acid ◽  
Acid And Base ◽  
Rate Plot ◽  
Kinetics Of

The kinetics of the oxidation of 6,7,8-trimethyllumazine, 1, by permanganate in aqueous solution is examined. The pH–rate plot shows a minimum at pH 3.5 and there is catalysis by buffers. Above pH 3.5 the 7-keto compound, 5, is produced by a general base catalyzed route the rate of which is identical to that of the reaction that causes exchange at the 7-methyl group. The kinetic isotope effect for oxidation of the 7-CD3 compound is 6.89 at 31.4°.Below pH 3.5 scission of the pyrazine ring occurs, there is a small isotope effect, and the rate is somewhat faster than that observed for exchange of the 7-methyl group. There appear to be three routes leading to product; one, a permanganate-independent reaction catalyzed by general acids, a second which is also permanganate independent and involves hydration of the substrate, and a third which is permanganate dependent and involves attack by permanganate on the conjugate acid of the substrate.The utility of oxidation as a means of locating hydration sites in heterocyclic compounds is discussed and some comments are made on the mechanism of the enzymic oxidation of the ribityl analog of 1.

The Oxidation of Benzyldimethylamine by Bromine

1973 ◽  
Vol 51 (15) ◽  
pp. 2546-2554 ◽  
Author(s):  
Donald G. Lee ◽  
R. Srinivasan
Keyword(s):  
Acetic Acid ◽  
Hydrogen Atom ◽  
Base Catalysis ◽  
Slow Step ◽  
Aqueous Acetic Acid ◽  
General Base ◽  
Rate Determining Step ◽  
Rate Of Reaction ◽  
Electron Withdrawing Substituents

The rates of oxidation of several substituted benzyldimethylamines by bromine in 50% aqueous acetic acid have been determined spectrophotometrically. Electron-withdrawing substituents decrease the rate of reaction with the Hammett ρ value being −0.95. The reaction is subject to general base catalysis and substitution of deuterium in the α-position decreases the rate of reaction by approximately 30%, thus indicating that the α-C—H bond is cleaved in the slow step of the reaction. All results are consistent with a mechanism which involves, in the rate determining step, loss of an α-hydrogen atom as a proton with concomitant transfer of electrons from nitrogen to the oxidant.

Sign in / Sign up

Export Citation Format

Share Document