Effect of substituents in the gas‐phase elimination kinetics of β‐substituted ethyl acetates

Abstract

The kinetics of gas-phase elimination of 3-methyl-1-butyl acetate and 3,3-dimethyl-l-butyl acetate into acetic acid and the corresponding substituted butenes have been measured over the temperature range of 360-420°C and the pressure range of 63-250 Torr. The reactions are homogeneous in both clean and seasoned vessels, obey first-order law, and are unimolecular. The temperature dependence of the rate constants is given by the Arrhenius equation 3-methyl-1-butyl acetate:The points in a plot of log (klko) of P-alkyl and several ,@substituted ethyl acetates against E, values appear aligned in an approximate linear relationship. These results may be interpreted as a consequence of steric effects, namely, steric accelerations.

Effects of polar .beta.-substituents in the gas-phase pyrolysis of ethyl acetate esters

“…These groups gave a good linear relationship by plotting log k/k0 vs. £s values (r = 0.913). 19 Steric acceleration has been advanced elsewhere for d-substituted ethyl acetates.16…”

“…The semipolar transition state of these reactions led to the successful use of structure-reactivity relationships, especially with substituents in the benzene ring remote from the reaction center.2,5,12"18 Very few aliphatic series have been analyzed in this way, but of particular relevance here is the gas-phase elimination of ß-substituted ethyl acetates. 19 Plotting the log k/k0 vs. Es values (Taft equation)20 gave an approximately straight line (r = 0.913), indicating that steric acceleration is important in determining the rate. The overall interpretation required electronic effects as well: (a) Alkyl groups and several polar substituents insulated by at least three methylene groups from the Ca-0 bond enhance the rate of reaction.…”

Evaluation of the olefinic double bond influence in the unimolecular homogeneous gas phase elimination of alkenyl acetates

“…Such a point of view has already been advanced in a recent communication regarding the effect of alkyl groups and several polar substituents in the gas-phase pyrolysis of /3-substituted ethyl acetates. 25 Yet, the CH2=CH substituent at the ß carbon in 3-buten-l-yl acetate causes the rate of elimination to be significantly greater by a factor of 6.4 more than ethyl acetate (Table II) and 3.8 greater than the corresponding saturated ester butyl acetate (Table III). According to these estimated rate ratios, the vinyl substituent at the ß carbon of ethyl acetate does not seem to sterically enhance the pyrolysis reaction.…”

“…The point of the logarithm of the relative rate of this ester with respect to ethyl acetate against its EB value is beyond the correlation line reported before. 25 Consequently, another factor must be operating during the process of elimination.…”

Termólisis de Clorooxoacetato de Etilo en Fase Gas: Comparación con Oxoacetato de Etilo y Detalles del Sistema Estático para el Estudio Cinético

“…Por esta razón, las reacciones en fase gas no tienen limitaciones para que la obtención de los parámetros cinéticos y el estudio del comportamiento de la molécula aislada en el estado de transición puedan efectuarse con ayuda de modelos mecanocuánticos. Sin embargo, aunque las termólisis en fase gas son importantes por constituir un raro caso de reacciones de orden uno y, adicionalmente, esclarecer la relación estructura-reactividad de ciertos sustratos bajo estudio [1][2][3][4][5][6][7][8][9], el número de reacciones en fase gas no complejas es relativamente pequeño [10]. Los análogos del ácido oxálico han sido escasamente investigados en fase gas.…”