Pinacol Rearrangement

the formation of ketones (pinacolones) by the action of acids (HCl and H₂SO₄), and also ZnCl₂, on pinacols, leading to dehydration of the pinacols accompanied by alteration of the skeleton of the molecule involving migration of a substituent to the adjacent carbon atom. The loss of the hydroxyl group and migration of the substituent take place synchronously (R is an organic radical):

The reverse rearrangement of the skeleton is called the re-tropinacolic rearrangement, and its mechanism is similar to that of the pinacolic rearrangement. An example is the formation of tetramethylethylene in the dehydration of pinacolyl alcohol in the presence of mineral acids:

The method for producing pinacolone from the simplest pinacol, (CH₃)₂C(OH)C(OH)(CH₃)₂, is used in industry. Processes similar to the retropinacolic rearrangement take place during cracking of higher olefins.