70149-39-2Relevant academic research and scientific papers
Equilibration of N-(2-cyanoethyl)pyridinium cations with substituted pyridines and acrylonitrile. A change in rate-determining step in an E1cb reaction
Bunting, John W.,Toth, Andrea,Heo, Christina K. M.,Moors, Rodney G.
, p. 8878 - 8885 (1990)
The rates of equilibration of N-(2-cyanoethyl)pyridinium cations (1) with the corresponding pyridines and acrylonitrile have been measured in aqueous solutions of ionic strength 0.1 at 25 °C. Second-order rate constants (kOH) have been obtained for the hydroxide ion catalyzed elimination reactions of 16 ring-substituted 1 having pyridine leaving groups of pKBH in the range 1.5-9.7. Bronsted plots of log kOH vs pKBH are "concave down" with two distinct linear regions having β1g = -0.30 (for pKBH 1g = -0.93 (for pKBH > 5.8). This observation is consistent with a change in rate-determining step within an E1cb reaction mechanism from rate-determining deprotonation of 1 (i.e., (E1cb)irrev) for pKBH rev) for pKBH > 5.8. This interpretation is supported by 1H NMR spectral observations in basic D2O, which show no incorporation of deuterium into the acrylonitrile product for pKBH BH > 5.8. Rates of nucleophilic attack of pyridines and pyridinone anions (pKBH > 6) upon acrylonitrile have also been measured. These display a linear Br?nsted plot of βnuc = 0.20. Combination of β1g and βnuc gives βeq = 0.13 for the Michael-type addition of pyridinium cations to acrylonitrile to produce 1. Although the rates of the addition of pyridines of pKBH nuc = 0.20 for pyridines of pKBH > 5.8 to rate-determining protonation of the carbanionic intermediate with βnuc = 0.83 for pyridine nucleophiles of pKBH irrev region but is extremely weak under the current experimental conditions.
Kinetics and mechanism of the bromination of 4-pyridone and related derivatives in aqueous solution
Tee, Oswald S.,Paventi, Martino
, p. 2556 - 2562 (2007/10/02)
The kinetics of bromination of 4-pyridone and selected derivatives have been measured in aqueous solutions in the pH range 0-9, at 25 deg C.The tautomeric system 4-pyridone 4-hydroxypyridine (1a 2a) reacts with bromine via the predominant (pyridone) tautomer at pH 6. 3-Bromo-4-pyridone behaves similary.The kinetics also reveal that the facile dibromination of 4-pyridone occurs because at most pH's the monobromo derivative is actually more reactive towards bromine by virtue of its lower pKa values.From the point of view of reactivity the 4-pyridones and their anions behave as substituted phenoxide ions. 4-Methoxypyridine does not undergo bromination under comparable conditions, but rather forms a complex with bromine.
