Acid-catalysed elimination (dehydration)

Step 1 of 3

1. 1.A lone pair on the alcohol's oxygen bonds to H⁺ (supplied by the concentrated acid).

The protonated alcohol (oxonium ion) forms.

Step 2 of 3

1. 1.The C–O bond breaks heterolytically: both electrons go to the positive oxygen and a molecule of water leaves.

Water leaves, leaving a secondary carbocation.

Step 3 of 3

1. 1.A C–H bond on the carbon NEXT to C⁺ collapses in to form the π bond — releasing H⁺, which regenerates the catalyst.

Propene forms and H⁺ is regenerated — dehydration complete.