How is hydration used to convert alkenes into alcohols?

Hydration is used to convert alkenes into alcohols by adding water (H2O) across the double bond in the presence of an acid catalyst.

In more detail, the process of converting alkenes into alcohols through hydration is a type of addition reaction. This is because a molecule of water (H2O) is added to the alkene molecule across its carbon-carbon double bond. The reaction is facilitated by an acid catalyst, often sulphuric acid (H2SO4) or phosphoric acid (H3PO4).

The mechanism of this reaction involves three main steps. Firstly, the acid catalyst donates a proton (H+) to the alkene, forming a carbocation (a positively charged carbon atom) and a double bond between two carbon atoms. This is known as the protonation step.

Next, a water molecule attacks the carbocation, forming a bond with the positively charged carbon atom. This results in a molecule with an extra hydrogen atom and a positive charge on the oxygen atom, known as an oxonium ion.

Finally, another water molecule removes a proton from the oxonium ion, resulting in the formation of an alcohol. This step is called deprotonation.

The overall result of this reaction is the conversion of an alkene into an alcohol. For example, if ethene (C2H4) is hydrated using this method, the product is ethanol (C2H5OH).

It's important to note that the reaction is regioselective, meaning the elements of water add to the alkene in a specific manner. According to Markovnikov's rule, the hydrogen atom in water attaches to the carbon atom in the alkene that has more hydrogen atoms, while the hydroxyl group (OH-) attaches to the carbon atom with fewer hydrogen atoms. This rule helps predict the major product of the reaction.

In summary, hydration is a useful method for converting alkenes into alcohols, involving the addition of water across the double bond in the presence of an acid catalyst.