Solvent effects on kinetics and mechanism of acid-catalyzed decomposition of 1,3-bis(4-methylphenyl)triazene I. Reactions in alcohols

1990 ◽  
Vol 55 (1) ◽  
pp. 147-155 ◽  
Author(s):  
Taťjana Nevěčná ◽  
Oldřich Pytela ◽  
Miroslav Ludwig ◽  
Jaromír Kaválek
Keyword(s):  
Trichloroacetic Acid ◽  
Acid Catalysis ◽  
Acid Catalyst ◽  
Kinetics And Mechanism ◽  
Acid Catalysts ◽  
Effect Of Solvents ◽  
Protic Solvents ◽  
General Acid ◽  
Catalytically Active ◽  
Acid Catalyzed

The effect of protic solvents (methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, cyclohexanol) has been studied on the kinetics and mechanism of acid-catalyzed decomposition of 1,3-bis(4-methylphenyl)triazene, using trichloroacetic acid as the acid catalyst. Both the non-dissociated acid and the proton have been found to be catalytically active. The mechanism of splitting of the triazene substrate with the non-dissociated acid involves the general acid catalysis. Comparison of the catalytic rate constants of the two acid catalysts and effect of solvents on these values indicate that the general acid catalysis probably also operates in the reaction of the substrate with proton.

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.

The kinetics and mechanism of the oxidation of mercaptoethanol by riboflavin

1977 ◽  
Vol 30 (6) ◽  
pp. 1387 ◽  
Author(s):  
JW Holden ◽  
L Main
Keyword(s):  
Kinetic Study ◽  
Acid Catalysis ◽  
Kinetics And Mechanism ◽  
Alternative Mechanism ◽  
Semiquinone Radical ◽  
Radical Intermediate ◽  
General Acid ◽  
Elimination Mechanism ◽  
Ph Range ◽  
Kinetic Form

Kinetic study of the oxidation of mercaptoethanol (RSH) by riboflavin (FlH) over the pH range 8.5-10.5 establishes that the rate is given by the term 0.036[FlH][RSH][RS-]]2 mol-2 s-1, there being no buffer catalysis. Any reactivity of the N 3-ionized riboflavin species (Fl-) is sufficiently low to be kinetically undetected. The kinetic form and lack of general acid catalysis are consistent with a nucleophilic (thiolate) 4a-addition-elimination mechanism previously proposed, but a possible alternative mechanism involving a flavin semiquinone (radical) intermediate is suggested.

Solvent effects on kinetics and mechanism of acid-catalyzed decomposition of 1,3-bis(4-methylphenyl)-triazene II. Reactions in aprotic solvents

1990 ◽  
Vol 55 (1) ◽  
pp. 156-164 ◽  
Author(s):  
Oldřich Pytela ◽  
Taťjana Nevěčná ◽  
Miroslav Ludwig
Keyword(s):  
Rate Constant ◽  
Acid Catalyst ◽  
Kinetics And Mechanism ◽  
Aprotic Solvents ◽  
Catalytic Rate Constant ◽  
Negative Effect ◽  
Acid Catalyzed ◽  
Catalytic Rate ◽  
Positive Effect ◽  
Solvent Acidity

The effect of aprotic solvents (hexane, cyclohexane, dichloromethane, 1,2-dichloroethane, benzene, acetonitrile, acetone, 1,2-dimethoxyethane, ethyl acetate, dioxane) on kinetics and mechanism of acid-catalyzed decomposition of 1,3-bis(4-methylphenyl)triazene has been studied with trichloroacetic acid as the acid catalyst. It has been found that beside the non-dissociated monomer of the acid also its dimer acts as the catalytic species. With regard to the results obtained in protic solvents (the catalysis by proton and general acid) three cases can be encountered of the dependence of observed rate constant on analytical concentration of the acid. The effect of solvents (inclusive of the protic ones) on the catalytic rate constant of the reaction with the non-dissociated monomer of acid is best interpreted by the equation suggested by Koppel and Palm and by the solvent scale suggested by us earlier. The solvent acidity and polarity have positive effect, whereas its basicity has negative effect. The catalytic rate constant of the reaction with the acid dimer decreases with increasing solvent basicity and polarity, due predominantly to the decrease in the equilibrium constant of dimerization.

Kinetics and mechanism of solvolysis of N-aryl sulfuric diamides

1990 ◽  
Vol 55 (1) ◽  
pp. 202-222 ◽  
Author(s):  
Jaromír Kaválek ◽  
Ulrika Králíková ◽  
Vladimír Macháček ◽  
Miloš Sedlák ◽  
Vojeslav Štěrba
Keyword(s):  
Acid Catalysis ◽  
Catalytic Effect ◽  
Kinetics And Mechanism ◽  
Base Catalysis ◽  
Reactive Intermediate ◽  
Hydrolysis Kinetics ◽  
General Acid ◽  
Acid And Base ◽  
Elimination Mechanism ◽  
Acid And Base Catalysis

The methanolysis and hydrolysis kinetics have been studied with the following sulfuric diamide derivatives: N-methyl-N-phenyl- (IIIa), N-methyl-N-(4-methoxycarbonylphenyl)- (IIIb), N-(4-methoxycarbonylphenyl)- (IIIc), N-methyl-N-(2-methoxycarbonylphenyl)- (IIId), N-(2-methoxycarbonylphenyl)- (IIIe), and N-methyl-N-(2,4-dibromophenyl)- (IIIf). The solvolyses of the neutral substrates IIIa and IIIb proceed by the addition-elimination mechanism. In the presence of the solvent lyate ions the solvolyses go by the E1cb mechanism. The solvolyses of the conjugated bases of compounds IIIa and IIIb are subject to general acid catalysis, the effects of the ring substituents being opposite to those in the addition-elimination mechanism. The solvolyses of compounds IIId and IIIf exhibit a distinct catalytic effect of neighbouring group; the reaction goes via a reactive intermediate, the transformation of the intermediate into the solvolysis product being subject to general acid and base catalysis.

Hydration of the carbonyl group — Acetic acid catalysis in the co-operative mechanism

2005 ◽  
Vol 83 (6-7) ◽  
pp. 769-785 ◽  
Author(s):  
Yih-Huang Hsieh ◽  
Noham Weinberg ◽  
Kiyull Yang ◽  
Chan-Kyung Kim ◽  
Zheng Shi ◽  
...  
Keyword(s):  
Acetic Acid ◽  
Carbonyl Group ◽  
Isotope Shift ◽  
Acid Catalysis ◽  
Water Molecules ◽  
Hydration Reaction ◽  
Water Solvent ◽  
General Acid ◽  
O Isotope ◽  
Acid Catalyzed

In a co-operative reaction, solvent molecules, specifically water molecules, participate actively in the mechanism to circumvent the formation of charged intermediates. This paper extends our earlier theoretical treatment of the neutral co-operative hydration of acetone to include general acid catalysis by acetic acid. As before, the predominant neutral channel employs three catalytic water molecules. The principal acetic acid catalyzed channels employ one catalytic water molecule and, in approximately equal proportions, one or both oxygens of the carboxyl group. The theoretical rate constant for general acid catalysis is calculated to be 0.49 M–1 s–1 at 298 K. This compares to an estimated experimental value of 0.30 M–1 s–1 for acetic acid catalyzed hydration of acetone at 298 K in water solvent, determined by using the 18O-isotope shift in the 13C NMR spectrum of 2-13C-labelled acetone as a kinetic probe. It is concluded that the notion of co-operativity can be extended to include general acid catalysis of the hydration of a carbonyl group in water solvent. This creates an obvious problem for the generally accepted view that multistep ionic mechanisms are operative in the low dielectric media that exist at the active sites of hydrolytic enzymes. The relevance of this finding to the mechanisms of action of β-lactam antibiotics has been noted.Key words: hydration, reaction mechanism, co-operativity, general acid catalysis, ab initio, SCRF, 18O-isotope shift.

Polyvinyl trisulfonate ethylamine based solid acid catalyst for the efficient glycosylation of sugars under solvent free conditions

RSC Advances ◽  
2015 ◽  
Vol 5 (127) ◽  
pp. 104715-104724 ◽  
Author(s):  
Avinash A. Chaugule ◽  
Amol R. Jadhav ◽  
Hern Kim
Keyword(s):  
Catalytic Activity ◽  
Solid Acid ◽  
Solid Acid Catalyst ◽  
Acid Catalyst ◽  
Solvent Free ◽  
Solid Acid Catalysts ◽  
Acid Catalysts ◽  
Solvent Free Conditions ◽  
Acid Catalyzed

We have synthesized Brønsted solid acid catalysts which exhibited effective catalytic activity for acid catalyzed glycosylation reactions.

A KINETIC STUDY OF THE HYDROLYSIS OF BENZALANILINE

1953 ◽  
Vol 31 (4) ◽  
pp. 361-376 ◽  
Author(s):  
A. V. Willi ◽  
R. E. Robertson
Keyword(s):  
Kinetic Study ◽  
Acid Catalysis ◽  
Catalyst Concentration ◽  
Effect Of Substituents ◽  
General Acid ◽  
Acid Catalyzed ◽  
Interesting Special Case ◽  
Hydrolysis Of ◽  
Special Case

The rates of the acid catalyzed hydrolysis of a series of para substituted benzalanilines have been studied in 50/50 methanol–water in the presence of acetate buffers. Special and general acid catalysis were observed. The effect of para substituents on the rate is different for the charged and uncharged catalyst, and Hammett's relation cannot be applied. Similarly the effect of substituents on the Arrhenius constants for the two cases is different. The para dimethylamino derivative provides an interesting special case. For low buffer concentrations and in unbuffered solutions certain deviations were observed which show that the dependence of the rate on the catalyst concentration is more complicated than the equation[Formula: see text]

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