Question

35.
The reaction of Lucas reagent is fastest with:
(a) Ethyl alcohol
(b) n-Butyl alcohol
(C) T-butyl alcohol
(d) Isopropyl alcohol​

Answer 1

Lucas Reagent reacts immediately and gives an oily layer or a cloudy white turbidity immediately with Tertiary alcohols in which the Carbon which is attached to the Hydroxyl group is itself attached to three other carbon atoms.

=> In ethyl alcohol, the carbon atom attached to the hydroxyl group is itself only attached to one carbon atom, it is a primary alcohol, so it does not react at room temperatures with Lucas Reagent.

=> n-Butyl alcohol is also a primary alcohol so it does not react with Lucas Reagent to give an oily layer at room temperature.

=> T-Butyl alcohol is a tertiary alcohol. The Carbon atom to which the Hydroxyl group is attached is itself attached to three other carbon atoms. So it immediately gives an oily layer with Lucas Reagent.

=> Isopropyl alcohol or 2-Propanol is a secondary alcohol, it gives a turbidity and an oily layer not immediately but after 3-5 minutes.

So, the correct answer is (c) T-butyl alcohol as it immediately gives an oily layer or a turbidity with Lucas Reagent as it is a tertiary alcohol and forms an alkyl chloride most easily , its carbocation is very stable.