Substituent effects on azo coupling of indoles

1993 ◽  
Vol 71 (12) ◽  
pp. 2144-2149 ◽  
Author(s):  
Hassan A. Albar ◽  
Ahmad S. Shawali ◽  
Magda A. Abdaliah
Keyword(s):  
Diazonium Salt ◽  
Substituent Effects ◽  
General Mechanism ◽  
Coupling Reactions ◽  
Azo Coupling ◽  
Straight Line ◽  
Reaction Constant ◽  
Methyl Derivatives ◽  
Rate Limiting ◽  
Kinetics Of

The kinetics of the azo coupling of eight para-substituted benzenediazonium tetrafluoroborates 2a–h with indole and its 1-, 2-,and 3-methyl derivatives 1a–d, respectively, were studied in acetonitrile at 25 °C under pseudo-first-order conditions. The relation k1(obs) = k2[diazonium salt] was found applicable in all cases. The logarithms of the rate constants k2 for each reaction series were correlated by the Hammett equation. A plot of the values of the reaction constant, ρ, obtained against the acidity constants pKa of 1a–d gave a straight line: ρ = 2.97 – 0.15 pKa. These results indicate that the azo-coupling reactions of indoles 1a–d follow one general mechanism involving rate-limiting initial electrophilic attack at the 3-position for all four compounds, contrary to the previous conclusion of Jackson and Lynch that the final deprotonation step is rate limiting.

scholarly journals Kinetics of the diazotization and azo coupling reactions of procaine in the micellar media

2014 ◽  
Vol 18 (5) ◽  
pp. 632-637 ◽  
Author(s):  
Fawziah Faleh Al-Blewi ◽  
Hamad A. Al-Lohedan ◽  
M.Z.A. Rafiquee ◽  
Zuheir A. Issa
Keyword(s):  
Coupling Reactions ◽  
Azo Coupling ◽  
Micellar Media ◽  
Kinetics Of

Arenediazonium o-Benzenedisulfonimides: Some Kinetics of Azo Coupling Reactions with Naphthols

2002 ◽  
Vol 2002 (22) ◽  
pp. 3837-3843 ◽  
Author(s):  
Carla Boga ◽  
Jacopo Degani ◽  
Erminia Del Vecchio ◽  
Rita Fochi ◽  
Luciano Forlani ◽  
...  
Keyword(s):  
Coupling Reactions ◽  
Azo Coupling ◽  
Kinetics Of

Synthesis, kinetics and mechanism of cyclization of 1-(2-aryloxycarbonylphenyl)-3-phenyltriazenes

1990 ◽  
Vol 55 (11) ◽  
pp. 2692-2700 ◽  
Author(s):  
Oldřich Pytela ◽  
Zdeněk Bahník
Keyword(s):  
Kinetic Isotope Effect ◽  
Intramolecular Proton Transfer ◽  
Steric Effects ◽  
Aqueous Methanol ◽  
Kinetic Isotope ◽  
Reaction Constant ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Substituted 1

Twelve substituted 1-(2-aryloxycarbonylphenyl)-3-phenyltriazenes have been synthetized and kinetics of their reactions have been measured in 52.1% (by mass) aqueous methanol at pH 3 to 11. Plots of kobs vs pH show three regions: noncatalyzed cyclization (pH 4 to 7), acid-catalyzed splitting of the triazene chain, and base-catalyzed cyclization. The non-catalyzed cyclization exhibits a kinetic isotope effect, the reaction constant ρ = 2.69 (σ-p), and β1g = 1.02, which indicates a mechanism of E1cB type with intramolecular proton transfer and a transient formation of a ketene intermediate. The base-catalyzed cyclization, on the other hand, exhibits the reaction constant ρ = 1.05 (σ-p), β1g = 0.4, and distinct steric effects, which indicates a cyclization by BAc2 mechanism with rate-limiting formation of the tetrahedral intermediate.

Kinetics and mechanism of acid catalyzed decomposition of substituted 1,3-diphenyltriazenes

1987 ◽  
Vol 52 (9) ◽  
pp. 2217-2224 ◽  
Author(s):  
Petr Svoboda ◽  
Oldřich Pytela ◽  
Miroslav Večeřa
Keyword(s):  
Diazonium Salt ◽  
Bond Formation ◽  
Reaction Constant ◽  
The Media ◽  
Acid Catalyzed ◽  
Reaction Constants ◽  
Kinetics Of ◽  
Better Than ◽  
Nitrogen Bond ◽  
Bond Splitting

The kinetics of acid catalyzed decomposition of 3-substituted and 1,3-disubstituted 1,3-diphenyl-3-methyltriazenes have been studied in 40% aqueous ethanolic buffers at 25 °C. The reaction constant for substitution of the phenyl ring at the 3 position of the triazene chain has been determined and the reaction constants of the protonation and bond splitting between the nitrogen atoms 2 and 3 have been estimated. By the covariance analysis it has been found that the standard constants of the Hammett relation are better than the constants determined in the media of organic solvents. Also estimated were the values of the slope β1g of the linear relation between the rate constants and the equilibrium between the diazonium salt and diazotate. The A-SE2 mechanism is suggested as probable, the bond between nitrogen atoms of triazene chain being more than half split in the transition state and the nitrogen-proton bond formation being more advanced than the nitrogen-nitrogen bond splitting.

Substituent effects in cooxidation: Cr(VI) – oxalic acid – sulfoxides systems

1987 ◽  
Vol 65 (10) ◽  
pp. 2421-2424 ◽  
Author(s):  
C. Srinivasan ◽  
P. Pandarakutty Jegatheesan ◽  
S. Rajagopal ◽  
N. Arumugam
Keyword(s):  
Oxalic Acid ◽  
Phenyl Ring ◽  
Substituent Effects ◽  
Aluminium Nitrate ◽  
First Order ◽  
Kinetic Information ◽  
Hammett Correlation ◽  
Analogous Manner ◽  
Reaction Constant ◽  
Kinetics Of

The kinetics of cooxidation of several substituted phenyl methyl sulfoxides and oxalic acid with Cr(VI) have been carried out in the presence of perchloric acid. The reaction is first order each in sulfoxide, oxalic acid, Cr(VI), and H+. The products of oxidation are sulfones and carbon dioxide. Electron-releasing groups in the phenyl ring accelerate the rate while electron-withdrawing groups retard it. The Hammett correlation yields a reaction constant of −0.927 ± 0.08 (r = 0.994) at 313 K. Addition of aluminium nitrate prevents the occurrence of cooxidation. Based on the kinetic information a suitable mechanism has been proposed. Diaryl sulfoxides behave in an analogous manner in the cooxidation.

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.

Kinetic analysis of mechanism of intestinal Na+-dependent sugar transport

1985 ◽  
Vol 248 (5) ◽  
pp. C498-C509 ◽  
Author(s):  
D. Restrepo ◽  
G. A. Kimmich
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Sugar Transport ◽  
Enzyme Kinetic ◽  
Steady State Distribution ◽  
State Distribution ◽  
Least Squares Fit ◽  
Coupling Stoichiometry ◽  
Rate Limiting ◽  
Kinetics Of

Zero-trans kinetics of Na+-sugar cotransport were investigated. Sugar influx was measured at various sodium and sugar concentrations in K+-loaded cells treated with rotenone and valinomycin. Sugar influx follows Michaelis-Menten kinetics as a function of sugar concentration but not as a function of Na+ concentration. Nine models with 1:1 or 2:1 sodium:sugar stoichiometry were considered. The flux equations for these models were solved assuming steady-state distribution of carrier forms and that translocation across the membrane is rate limiting. Classical enzyme kinetic methods and a least-squares fit of flux equations to the experimental data were used to assess the fit of the different models. Four models can be discarded on this basis. Of the remaining models, we discard two on the basis of the trans sodium dependence and the coupling stoichiometry [G. A. Kimmich and J. Randles, Am. J. Physiol. 247 (Cell Physiol. 16): C74-C82, 1984]. The remaining models are terter ordered mechanisms with sodium debinding first at the trans side. If transfer across the membrane is rate limiting, the binding order can be determined to be sodium:sugar:sodium.

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