Kinetics of the reaction of guanyl-O-methylisourea hydrochloride with dimethylformamide dimethylacetal

1986 ◽  
Vol 51 (9) ◽  
pp. 1964-1971
Author(s):  
Jaromír Kaválek ◽  
Josef Panchartek ◽  
Tomáš Potěšil ◽  
Vojeslav Štěrba
Keyword(s):  
Absorption Maximum ◽  
Base Catalysis ◽  
Dimethylformamide Dimethylacetal ◽  
Catalysis Mechanism ◽  
Kinetics Of

The reaction of guanyl-O-methylisourea hydrochloride (IV) with dimethylformamide (V) proceeds in two steps. The first step consists in the reaction of the imidoester with the imidatonium ion formed in a fast pre-equilibrium to give a conjugated system with the absorption maximum at 278 nm. The subsequent slower step consists in the cyclization to 2-amino-4-methoxy-1,3,5-triazine (VI). The rate of the first step is directly proportional to the concentrations of both hydrochloride IV and acetal V. Both the steps involve base catalysis. Mechanism of the whole reaction is suggested on the basis of the kinetic results.

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.

Kinetics and Activation Parameters for the Alkaline Aqueous Rearrangement of Trichorfon [O,O-Dimethyl-(2,2,2-Trichloro-1-Hydroxyethyl) Phosphonate] to Dichlorvos [O,O-Dimethyl-O-(2,2-Dichloroethenyl)Phosphate]

2001 ◽  
Vol 36 (3) ◽  
pp. 589-604 ◽  
Author(s):  
Julian M. Dust ◽  
Christopher S. Warren
Keyword(s):  
Activation Energy ◽  
High Pressure ◽  
Activation Parameters ◽  
Base Catalysis ◽  
Rearrangement Product ◽  
Exponential Factor ◽  
First Order ◽  
Pseudo First Order ◽  
Order Plot ◽  
Kinetics Of

Abstract The kinetics of the alkaline rearrangement of O,O-dimethyl-(2,2,2-trichloro-1- hydroxyethyl)phosphonate, (trichlorfon, 1), the active insecticidal component in such formulations as Dylox, was followed at 25±0.5°C by high pressure liquid chromatography (UV-vis detector, 210 nm). The rearrangement product, O,Odimethyl- O-(2,2-dichloroethenyl)phosphate (dichlorovos, 2), which is a more potent biocide than trichlorfon, undergoes further reaction, and the kinetics, consequently, cannot be treated by a standard pseudo-first-order plot. A two-point van't Hoff (initial rates) method was used to obtain pseudo-first-order rate constants (kѱ) at 25, 35 and 45°C: 2.6 × 10-6, 7.4 × 10-6 and 2.5 × 10-5 s-1, respectively. Arrhenius treatment of this data gave an activation energy (Ea) of 88 kJ·mol-1 with a pre-exponential factor (A) of 5.5 × 109 s-1. Kinetic trials at pH 8.0 using phosphate and tris buffer systems show no buffer catalysis in this reaction and indicate that the rearrangement is subject to specific base catalysis. Estimates are reported for pseudo-first-order half-lives for trichlorfon at pH 8.0 for environmental conditions in aqueous systems in the Corner Brook region of western Newfoundland, part of the site of a recent trichlorfon aerial spray program.

scholarly journals Evidence of a General Acid–Base Catalysis Mechanism in the 8–17 DNAzyme

Biochemistry ◽  
2018 ◽  
Vol 57 (9) ◽  
pp. 1517-1522 ◽  
Author(s):  
Marjorie Cepeda-Plaza ◽  
Claire E. McGhee ◽  
Yi Lu
Keyword(s):  
Base Catalysis ◽  
Acid Base ◽  
General Acid ◽  
Catalysis Mechanism

Pyridoxal and pyridoxal 5′-phosphate catalyzed β-deuteration of α-aminobutyric acid and homoserine. I. Metal-free systems

1986 ◽  
Vol 64 (10) ◽  
pp. 2053-2059 ◽  
Author(s):  
Kuniyasu Tatsumoto ◽  
Rabindra P. Reddy ◽  
Arthur E. Martell
Keyword(s):  
Amino Acids ◽  
Metal Ion ◽  
Initial Step ◽  
Proton Exchange ◽  
Base Catalysis ◽  
Aminobutyric Acid ◽  
Vitamin B ◽  
Metal Free ◽  
Amino Acid Moiety ◽  
Kinetics Of

As the initial step in the investigation of metal ion- and vitamin B6-catalyzed, β, γ-elimination in α-amino acids, the pyridoxal-and pyridoxal 5′-phosphate-catalyzed β-deuteration of α-aminobutyric acid and homoserine in D2O in metal-free systems has been studied by nuclear magnetic resonance. The reaction kinetics of α-H, β-H, and 4′-CH exchange rates were measured by following the rates of deuteration of these positions. The kinetic data obtained for these reactions lead to a proposed mechanism for β-deuteration. The relative rates of the deuteration reactions observed, and the order in which deuteration products were obtained are: α-H exchange > transamination (4′-CH exchange) > β-H exchange. The observed rates of β-proton exchange exhibit specific base catalysis and are dependent on the activation of the α-hydrogen of the amino acid moiety in the aldimine, and on the activation of the β-hydrogens of the amino acids in the ketimine.

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