Why is the reactivity of all the three classes of alcohols with conc. HCl and ZnCl2 (Lucas reagent) different?
The reactivity of all the three classes of alcohols with concentrated HCl and ZnCl2 (Lucas reagent) is different because of the steric hindrance of the alkyl groups and the stability of the carbocation.
We know, the stability of carbocation is in the following order:
Tertiary > secondary > primary
Primary alcohol does not show any reaction at room temperature because the 1° carbocation is least stable. Thus, they cannot form halides easily.
Secondary alcohol does not show any turbidly at room temperature but shows turbidity upon heating.
Tertiary alcohol immediately shows turbidity after addition of Lucas reagent as they can form halides easily due to the higher stabilityof the carbocation.