Study of cyclization of 2-acetyl-3-methylamino-N-benzoyl-2-butenethioamide

1981 ◽  
Vol 46 (1) ◽  
pp. 256-261 ◽  
Author(s):  
Vladimír Macháček ◽  
Said El Bahaie ◽  
Vojeslav Štěrba
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Hydroxyl Ion ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Cyclic Intermediate

Kinetics has been studied of cyclization of 2-acetyl-3-methylamino-N-benzoyl-2-betenethioamide (Ia) and 2-acetyl-3-amino-N-benzoyl-2-butenethioamide (Ib) giving 5-acetyl-2-phenyl-1,6-dimethyl-4-(1H)pyrimidinethione (IIa) and 5-acetyl-2-phenyl-6-methyl-4-(3H)-pyrimidinethione (IIb), respectively, in aqueous buffers within pH 2 to 9. Formation of the cyclic intermediate is rate-limiting in the cyclization of Ib within the whole range. In the case of Ia the rate-limiting step consists in acid-catalyzed splitting off of water from the cyclic intermediate above pH 5 and in base-catalyzed splitting off of hydroxyl ion above pH 7.

Mechanism of base-catalyzed cyclization of ethyl N-(substituted aminocarbonyl)glycinates

1987 ◽  
Vol 52 (1) ◽  
pp. 156-161
Author(s):  
Jaromír Mindl ◽  
Vojeslav Štěrba
Keyword(s):  
Rate Constants ◽  
Ethoxy Group ◽  
Tetrahedral Intermediate ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid Catalyzed ◽  
Cyclization Rate ◽  
Rate Limiting ◽  
Cyclic Intermediate

The cyclization rate constants have been measured of substituted ethyl N-(phenylaminocarbonyl)-, N-(alkylaminocarbonyl)-, and N-(phenylaminothiocarbonyl)glycinates RNHCXNHCH2CO2.C2H5 (X = O, S). Logarithms of these constants increase with decreasing basicity of the amines down to the value of pKa(RNH2) = 5.5. The rate-limiting step of the reaction is formation of the tetrahedral intermediate. With ethyl N-(phenylaminocarbonyl)glycinates (whose pKa(RNH2) values are higher) this dependence, on the contrary, slightly decreases, and the acid-catalyzed splitting off of ethoxy group from the cyclic intermediate becomes rate-limiting. The cyclization rate of a series of ethyl N-(phenylaminothiocarbonyl)glycinates is practically independent of the pKa(RNH2) values, the change in the rate-limiting step would take place at pH about 9.

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.

A mathematical modelling of acid catalyzed decomposition of 3-methyl-1,3-diphenyltriazene

1987 ◽  
Vol 52 (10) ◽  
pp. 2492-2499 ◽  
Author(s):  
Oldřich Pytela ◽  
Petr Svoboda ◽  
Miroslav Večeřa
Keyword(s):  
Reaction Mechanism ◽  
Linear Regression ◽  
Organic Solvent ◽  
Mathematical Modelling ◽  
Aqueous Ethanol ◽  
Activation Parameters ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid Catalyzed ◽  
Rate Limiting

The effect of acids on the decomposition of 3-methyl-1,3-diphenyltriazene has been studied in aqueous ethanol (40% (v/v) ethanol). The dependences found between the rate constant and acid concentration have been analyzed by means of non-linear regression using models including the specific and general catalysis and formation of associates between the substrate and the buffer components. The substrate has been found to form electrostatic associates with the conjugated base of acid. The complex formed is decomposed with the assistance of the proton or a general acid in the rate-limiting step to form the product. The Bronsted coefficient α = 0.81 has been found. Investigation of the activation parameters supports the earlier conclusions, indicating a dependence between the reaction mechanism and composition of the aqueous organic solvent.

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 Cyclization of N-(2-Methoxycarbonylphenyl)-N-methylsulfonamide to 1-Methyl-(1H)-2,1,3-benzothiadiazine-4(3H)-one-2,2-dioxide

1992 ◽  
Vol 57 (6) ◽  
pp. 1282-1290 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Miloš Sedlák ◽  
Vojeslav Štěrba
Keyword(s):  
Potassium Hydroxide ◽  
Kinetics And Mechanism ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Conjugate Acid ◽  
Cyclization Kinetics ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Cyclic Intermediate

The cyclization kinetics of N-(2-methoxycarbonylphenyl)-N-methylsulfonamide to 1-methyl-(1H)-2,1,3-benzothiadiazine-4(3H)-one-2,2-dioxide have been studied in glycinamide, morpholine, and butylamine buffers and in solutions of potassium hydroxide. The rate-limiting step consists in splitting off of the proton from the cyclic intermediate formed from the anion of the starting substrate. The value of the Bronsted coefficient β decreases with increasing pKa value of the conjugate acid of buffer. The calculated pKa value of the cyclic intermediate is 9.3.

scholarly journals Circularity in Mixed Plastics Chemical Recycling Enabled by Variable Rates of Polydiketoenamine Hydrolysis

2021 ◽  
Author(s):  
jeremy demarteau ◽  
alexander epstein ◽  
Peter Christensen ◽  
Mark Abubekerov ◽  
hai wang ◽  
...  
Keyword(s):  
Sustainable Manufacturing ◽  
Molecular Engineering ◽  
Chemical Recycling ◽  
Recycling Process ◽  
Polymer Recycling ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid Catalyzed ◽  
Circular Design ◽  
Rate Limiting

<div>Footwear, carpet, soft furnishings, automotive interiors, and multi-layer packaging are examples of products manufactured from several types of polymers whose inextricability poses significant challenges for recycling at end-of-life. Here, we show that chemical circularity in mixed-polymer recycling becomes possible by controlling the rates of depolymerization of polydiketoenamines (PDKs) over several orders of magnitude through molecular engineering. Stepwise deconstruction of mixed-PDK composites, laminates, and assemblies is chemospecific, allowing a prescribed subset of monomers, fillers, and additives to be recovered in pristine condition at each stage of the recycling process. We provide a theoretical framework to understand PDK depolymerization via acid-catalyzed hydrolysis and experimentally validate trends predicted for the rate-limiting step. The control achieved by PDKs in managing thermal and materials entropy points to new opportunities for pairing circular design with sustainable manufacturing.</div>

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

scholarly journals Circularity in Mixed Plastics Chemical Recycling Enabled by Variable Rates of Polydiketoenamine Hydrolysis

2021 ◽  
Author(s):  
jeremy demarteau ◽  
alexander epstein ◽  
Peter Christensen ◽  
Mark Abubekerov ◽  
hai wang ◽  
...  
Keyword(s):  
Sustainable Manufacturing ◽  
Molecular Engineering ◽  
Chemical Recycling ◽  
Recycling Process ◽  
Polymer Recycling ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid Catalyzed ◽  
Circular Design ◽  
Rate Limiting

<div>Footwear, carpet, soft furnishings, automotive interiors, and multi-layer packaging are examples of products manufactured from several types of polymers whose inextricability poses significant challenges for recycling at end-of-life. Here, we show that chemical circularity in mixed-polymer recycling becomes possible by controlling the rates of depolymerization of polydiketoenamines (PDKs) over several orders of magnitude through molecular engineering. Stepwise deconstruction of mixed-PDK composites, laminates, and assemblies is chemospecific, allowing a prescribed subset of monomers, fillers, and additives to be recovered in pristine condition at each stage of the recycling process. We provide a theoretical framework to understand PDK depolymerization via acid-catalyzed hydrolysis and experimentally validate trends predicted for the rate-limiting step. The control achieved by PDKs in managing thermal and materials entropy points to new opportunities for pairing circular design with sustainable manufacturing.</div>

Kinetics and mechanism of solvolysis of substituted phenyl N-phenylbenzimidoesters

1987 ◽  
Vol 52 (5) ◽  
pp. 1285-1297
Author(s):  
Jaromír Kaválek ◽  
Ludmila Hejtmánková ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrochloric Acid ◽  
Kinetics And Mechanism ◽  
Reaction Products ◽  
Phenol Content ◽  
Aqueous Methanol ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of hydrochloric acid-catalyzed solvolysis of substituted phenyl and methyl N-phenylbenzimidoesters have been studied in methanol, 50 vol. % aqueous methanol, and 50 vol. % aqueous tetrahydrofurane, and the composition of the reaction products has been determined. The rate-limiting step consists in addition of water or methanol to the protonated substrate. The reaction of methyl N-phenylbenzimidoester with both water and methanol and that of substituted phenyl N-phenylbenzimidoesters with methanol produce aniline, the ester (or orthoester) and the corresponding phenol. The reaction of substituted phenyl N-phenylbenzimidoesters with water gives both the neutral tetrahedral intermediate (which is decomposed into phenol and anilide) and the protonated intermediate (which produces aniline and the ester). At the same proton concentration the phenol content increases with increasing value of the σ constant of the substituent.

The Meyer Reaction of Phenylnitromethane in Acid. III. The Tautomerization to the aci-Form

1971 ◽  
Vol 49 (21) ◽  
pp. 3493-3501 ◽  
Author(s):  
J. T. Edward ◽  
P. H. Tremaine
Keyword(s):  
Rate Increase ◽  
Isotope Effects ◽  
Dilute Acid ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid Catalyzed ◽  
Deuterium Isotope Effects ◽  
Rate Limiting ◽  
Hydrolysis Of ◽  
Competing Reactions

The rate-acidity profiles for the Meyer rearrangement–hydrolysis of phenylnitromethane in sulfuric, perchloric, and hydrochloric acid show a maximum near 3 M acid. Ring-substituted phenylnitromethanes also show a maximum in their rate profiles, at slightly different acid concentrations. These maxima arise because the slow formation of the aci-form is followed by two competing reactions: fast tautomerization back to the nitro-form, and fast rearrangement–hydrolysis to the Meyer products. The rearrangement is rate-limiting in dilute acid and is acid-catalyzed, causing the rate increase. In more concentrated acid, the rate-limiting step is the nitro to aci tautomerization, which is not acid-catalyzed, and which goes more slowly as the activity of water decreases.The tautomerization was studied by means of primary and solvent deuterium isotope effects, and was found to occur through proton abstraction by water, through a transition state closely resembling the products.

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