Hydration reaction

[2] The general chemical equation for the hydration of alkenes is the following: A hydroxyl group (OH−) attaches to one carbon of the double bond, and a proton (H+) adds to the other.

In the "direct process," the acid protonates the alkene, and water reacts with this incipient carbocation to give the alcohol.

Acetylene hydrates to give acetaldehyde:[3] The process typically relies on mercury catalysts and has been discontinued in the West but is still practiced in China.

Conceptually similar reactions include hydroamination and hydroalkoxylation, which involve adding amines and alcohols to alkenes.

[4] Hydration is an important process in many other applications; one example is the production of Portland cement by the crosslinking of calcium oxides and silicates that is induced by water.