Prop-2-en-1-ol in aqueous
acid solution gives propane-1,2-diol and propanal. At
100�C the amount of diol in this product ratio is
found to decrease from 65% in 1 M HClO4 to 50% in 4 M HClO4.
Pseudo-first-order kinetics are found to apply. The values obtained for the
activation parameters, Ea and ΔS‡ and for a Hammett acidity
plot, are similar to results reported for other alkenes. The relative rates of
partitioning between regeneration of the substrate and rearrangement for the pinacol rearrangement of optically active propane-1,2-diol
have been calculated previously. When these are compared with product ratios
obtained from the hydration of prop-2-en-1-ol, good agreement is found between
the respective values if it is assumed that the regenerated substrate has
undergone complete racemization of configuration.
This is interpreted to be evidence for a short-lived, but free ion-dipole as
the intermediate in the heterolysis of propane-1,2-diol.
