Kinetics and mechanism of isobutene formation from T‐butanol in hot liquid water

Isobutene is the only product of the uncatalyzed and acid‐catalyzed dehydration of tert‐butanol in compressed liquid water at 250°C. The uncatalyzed dehydration reaction is fast: equilibrium is established after about 30 s. Only one of many chemically‐motivated kinetic models is able to fit all the experimental data. This model presumes a heterolytic dehydration mechanism that involves protonated alcohol, carbocation, di‐tert‐butyl ether, and protonated ether as intermediates. The model permits tert‐butanol to dissociate as both an Arrhenius acid and a Bronsted acid while catalyzing its dehydration to isobutene. The pK a of tert‐butanol at 250°C is predicted to be about 9, whereas its value at normal temperature and pressure is 18. This 10 9 increase in the K a value of tert‐butanol hints of the promising new world of reaction chemistry in near‐ and supercritical water.