What will be the major product obtained on dehydration of propan-1,2-diol ?

I am not being able to understand which one among the 2 lone pairs (of 2 oxygen atoms) is going to attack the proton.

1 Answer
Jan 24, 2018

I predict the major product to be propanal.

Explanation:

The sulfuric acid protonates both oxygen atoms.

Protonation at #"C1"#

C1 Protonation

However, loss of water from #"C1"# produces a primary carbocation, which is quite unstable.

Protonation at #"C2"#

C2 protonation

Loss of water from #"C2"# produces a secondary carbocation, which is much more stable.

Loss of an α-hydrogen

Deprotonation

The cation loses a proton preferentially from #"C1"# to form an enol, which rapidly tautomerizes to the more stable aldehyde.