Lucas Test disitinction of primary, secondary and tertiary alcohols

The difference in reactivity of primary, secondary and tertiary alcohols with HCl distinguishes them from one another. This test is known as Lucas test. In this method, the alcohol is treated with Lucas reagent (a mixture of conc. HCl and anhydrous ZnCl₂). The alcohol is converted into alkyl halides. Alcohols are soluble in Lucas reagent while their halides are insoluble. The formation of alkyl halide is indicated by the appearance of turbidity in the reaction mixture. As the reactivity of alcohols with halogen acids is in the order tertiary > secondary > 2primary, the time required for the appearance of turbidity will be different for primary, secondary and tertiary alcohols which helps to distinguish them from one another.

In the case of tertiary alcohols, turbidity is produced immediately at room temperature. Secondary alcohols give turbidity in few minutes while primary alcohols do not produce appreciable turbidity at room temperature, but give turbidity only on heating.

 Related post Chemical properties of Alcohols and Phenols