Hydration of alkenes.

https://www.youtube.com/watch?v=Njasv7Fdpao

What is hydration reaction

The electrophilic addition of water to alkenes to make alcohols.

Water is in form of steam, phosphoric acid used as catalyst, temp is 300 and pressure is 60 atm

Structure of phosphoric acid

Three hydrogen atoms, each bonded to oxygen (very electronegative , so phosphoric acid is polar )

Oxygen atoms have partial negative charge, hydrogen atoms have partial positive charge

First stage of reaction

The pair of electrons in pi bond of ethene are attracted to one of the positive hydrogen atoms in thew phosphoric acid.

So pos hydrogen atom is acting as electrophile.

The pair of electrons in pi bond form a covalent bond to pos hydrogen atom, at same time covalent bond between hydrogen and oxygen breaks, pair of electrons move completely onto oxygen atom

So at end of stage 1, there is carbocation intermediate with pos charged carbon atom

Also dihydrogen phosphate ion with neg charged oxygen atom

Stage 2 of reaction

The carbocation intermediate reacts with molecule of water in form of steam

Oxygen atom in water molecule has two lone pairs of electrons ( one pair forms cov bond between oxygen and pos carbon atom in carbocation intermediate)

At end of stage 2 , we have intermediate molecule containing pos oxygen atom

Stage 3 of teaction

Involves dihydrogen phosphate ion produced earlier

This ion forms covalent bond to a hydrogen in intermediate molecule

At same time , covalent bond in intermediate breaks by heterolytic fission, pair of electrons in bond now move completely onto the oxygen,

End of this stage , product molecule ethanol made and phosphoric acid catalyst has been regenerated.