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Kinetics, Activation Parameters, and Mechanism of the Acid Hydrolysis of tert-Butyl Acetate in Aqueous DMSO

F. Y. Khalil ; Chemistry Department, Faculty of ,Science, Alexandria University, Alexandria, Egypt
M. T. Hanna ; Chemistry Department, Faculty of ,Science, Alexandria University, Alexandria, Egypt

Puni tekst: engleski pdf 7.435 Kb

str. 329-338

preuzimanja: 534



The rate of the acid-catalysed hydrolysis of tert-butyl acetate
was found to decrease pronouncly in the presence of increasing
amounts of DMSO. The observed activation energy decreased progressively
with increasing DMSO content of the medium and the
change was attributed to a gradual interconversion of the two
concurrent and competing reaction mechanisms AALl and AAc2.
The overall reaction rate was analysed theoretically as two individual
rate constants corresponding to the respective mechanisms.
The percentage contribution of each mechanism was then estimated
and found to be concordant with the values determined experimentally
by others using 180 tracer technique. The proportion of
the AALl mechanism was found to increase both with increasing
temperature and decreasing DMSO content. The relative abundance
of the transition state belonging to each of the involved mechanisms
was discussed in the light of the solvating power of the binary DMSO-H20 solvent system. The effect of the molar concentration of water as well as the dielectric constant of the medium on the reaction kinetics was studied. The thermodynamic parameters of activation showed strong dependence on solvent composition and their values were determined by the relative contributions of the two mechanistic routes of the reaction.

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