Question

Explain lucas test , briefly

Answer 1

Lucas Test is a test which is used to distinguish between primary, secondary and tertiary alcohols. This test is carried out with the help of Lucas reagent, which is an equimolar mixture of Zinc Chloride and hydrochloric acid (ZnCl2+ HCl). It is based on the difference between the reactivity of primary, secondary and tertiary alcohols with hydrogen halides. The general equation for the reaction isROH + HCl + ZnCl2→ RCl + H2OWhen the reagent is added to tertiary alcohol, a turbidity or cloudiness appears in solution instantaneously. This occurs because the alkyl halide so formed is not water soluble. When the reagent is added to secondary alcohol, turbidity appears after 4-5 minutes. However, with primary alcohols, no turbidity appears, suggesting that no reaction occurs with primary alcohol at room temperature.Example(CH3)3-OH + HCl + ZnCl2→ (CH3)3-Cl + H2O.................turbidity appears instantaneouslytertiary butanolCH3-CH(OH)-CH2-CH3 + HCl + ZnCl2→ CH3-CH(Cl)-CH2-CH3.......turbidity appears after 5 minutessecondary butanolCH3-CH2-CH2-CH2OH + HCl + ZnCl2→ X........................no turbidity appearsprimary butanol