What is the hydration of alkene

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H2O-addition to alkenes

The acids HBr and HCl add easily to alkenes. H2O can also be viewed as an HX reagent, as water can also split off a proton. So water should add to alkenes in the same way as e.g. HBr and should lead to hydration. H2However, O and alkenes only react with one another in the presence of an acid as a catalyst. The acids HBr (= -9) and HCl (= -7) have a much higher proton concentration than water (= 15.7). The presence of an acid during hydration opens up a new (completely different) reaction path that obviously has a much lower activation energy than that for direct hydration.

The addition of H takes place under acid catalysis2O to alkenes in 3 sub-steps.

Protonation is the slowest and therefore the rate-determining step in the reaction.

Acid catalysis of the addition
Only in the presence of an acid as a catalyst does water add to alkenes to form an alcohol.

However, directly acid-catalyzed hydration has two major disadvantages:

  • rearrangements can occur
  • the regiochemistry cannot be controlled.

For this reason, other methods such as oxymercuration and hydroboration are also used, especially for reactions on a laboratory scale.