Kinetics and Mechanisms of the Acid-catalysed Hydrolysis of Tertiary Butyl Acetate

Abstract

The kinetics of the acid-catalysed hydrolysis of tertiary butyl acetate in water, in aqueous acetone, and in aqueous dioxan, over a range of temperature have been studied. The Arrhenius equation is not obeyed. In 40% water-60% acetone the energy of activation varies from 26-29 kcal mole^-1 for temperatures 48-97 °C. This is due presumably to simultaneous hydrolyses via the A_AL1 and the A_AC2 mechanisms. By combination of oxygen-18 tracer results and kinetic results the rate constants for reactions by these mechanisms in water have been separated. The observed percentage of alkyl-oxygen fission in water varies from 85 at 25 °C to 97 at 60 °C. Rate constants for reactions by the A_AL1 and the A_AC2 mechanisms are expressed by the equations : k (sec^-1 l mole^-1) = 10^l6.l exp (-27500/RT), and k (sec^-1 l mole^-1) = 10^7.9 exp (-l73OO/RT),respectively. However, the parameters of the latter equation may contain considerable errors because the extent of reaction by the A_AC2 mechanism is small. In water and in 80% water-20% acetone, tertiary butyl acetate undergoes an uncatalysed solvolytic reaction, involving presumably the B_AL1 mechanism. The variation of the rate of this reaction with temperature is expressed by the equation, k (sec^-1) = 10^12.3 exp (-26800/RT).