ChemInform Abstract: NUCLEOPHILIC DISPLACEMENT IN POLYHALOAROMATIC COMPOUNDS. PART 9. KINETICS OF AZIDODEFLUORINATION AND METHOXYDEFLUORINATION OF SOME POLYFLUOROBENZONITRILES

1979 ◽  
Vol 10 (10) ◽  
Author(s):  
R. BOLTON ◽  
J. P. B. SANDALL
Keyword(s):  
Nucleophilic Displacement ◽  
Kinetics Of

Open-chain nitrogen compounds. Part XV. A kinetic study of the hydrolysis of 1-aryl-3-aryloxymethyl-3-methyltriazenes and related triazenes

1992 ◽  
Vol 70 (8) ◽  
pp. 2224-2233 ◽  
Author(s):  
Keith Vaughan ◽  
Donald L. Hooper ◽  
Marcus P. Merrin
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Buffer System ◽  
Open Chain ◽  
Nucleophilic Displacement ◽  
Ether Oxygen ◽  
Rate Of Hydrolysis ◽  
Electron Withdrawing Group ◽  
Ph Range ◽  
Kinetics Of

The kinetics of hydyrolysis of a series of 1-aryl-3-aryloxymethyl-3-methyltriazenes, Ar-N=N-NMe-CH2OAr′, was studied over the pH range 2–7.5. Reactions were followed by the change in UV absorbance spectra of the triazenes. The aryloxymethyltriazenes decompose more slowly at pH 7.5 than the hydroxymethyltriazenes, Ar-N=NMe-CH2OH; the hydrolysis is favoured by the presence of an electron-withdrawing group in Ar′. A mixed isopropanol/buffer system was developed in order to improve solubility of the aryloxymethyl triazenes. Lowering the pH caused an increase in the rate of hydrolysis and under strongly acidic conditions an electron-withdrawing group in Ar′ actually slows down the reaction. A Hammett plot of the pseudo-first-order rate constant, kobs, is curved, indicating that two or more mechanisms operate simultaneously and that the contribution of each mechanism is substituent-dependent. A plot of kobs vs. [buffer] is linear; the slope of the plot affords the rate constant, kb for the buffer-catalyzed reaction for each substituent. A Hammett plot of kb vs. σ is linear with ρ = +0.55, suggesting that the buffer-catalyzed reaction involves nucleophilic displacement of the phenoxy group by the buffer anion. Further analysis afforded the specific acid-catalyzed rate constants, [Formula: see text], for each substituent; this component of the reaction has a negative ρ, consistent with a mechanism involving protonation at the ether oxygen. The postulation that specific acid catalysis is a component of the reaction mechanism was confirmed by the observation of a solvent deuterium isotope effect, 2.28 > kH/kD > 1.60. Only the p-NO2 and p-CN phenyloxymethyltriazenes showed any spontaneous decomposition.

Kinetics of nucleophilic displacement of 2,5-disubstituted furans

1979 ◽  
Vol 44 (8) ◽  
pp. 2417-2420 ◽  
Author(s):  
Viera Knoppová ◽  
Rudolf Kada ◽  
Jaroslav Kováč
Keyword(s):  
Kinetic Data ◽  
Reaction Rate ◽  
Nucleophilic Reagent ◽  
Nucleophilic Displacement ◽  
Kinetics Of

5-Nitro- and 5-bromo-2-furfurylidenemalonitriles react with secondary saturated amines in an SN reaction to replace bromo or nitro groups. The effects of nucleophilic reagent, solvent and temperature on the reaction rate were investigated. The results were contrasted with kinetic data of the SN reaction of 5-(4-X-phenylsulfonyl- or phenylthio)-2-furfurylidenemalonitriles.

Electronic Effects of Aryl and Heteroaryl Groups on the Rate of Nucleophilic Displacement of Chlorine from 5-Heteroaryl(or Aryl)-2-chloropyrimidines by Piperidine

1980 ◽  
Vol 35 (4) ◽  
pp. 463-467 ◽  
Author(s):  
David W. Allen ◽  
David J. Buckland ◽  
Barrie G. Hutley
Keyword(s):  
Rate Data ◽  
Electronic Effects ◽  
Nucleophilic Displacement ◽  
Synthetic Routes ◽  
Kinetics Of

The kinetics of nucleophilic displacement of chlorine from a series of 2-chloro-5-heteroaryl( or aryl)pyrimidines by piperidine have been studied in order to assess the electronic effects of the 5-substituent. The observed order of reactivity is 5-(1-methylpyrrol-2-yl) < 5-p-anisyl < 5-p-tolyl < 5-phenyl < 5-(2-thienyl) < 5-(2-furyl) < 5-(m-chlorophenyl). The reactions are enthalpy-controlled and the rate data can be explained as a consequence of the electron-withdrawing or electron-donating ability of the 5-substituent. Synthetic routes to the compounds studied are also described.

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