How will you distinguish primary, secondary and tertiary alcohols by Lucas test?
The test is based upon the difference in reactivity of primary, secondary and tertiary alcohols with hydrochloric acid. This test consists of treating an alcohol with Lucas reagent, an equimolar mixture of conc. HCl and anhydrous ZnCl2 at room temperature, when turbidity due to the formation of insoluble alkyl chlorides is observed.
(i) If the turbidity appears immediately, the alcohol is tertiary.
R3COH R3CCl + H2O
(ii) If the turbidity appears in about five minutes, the alcohol is secondary.
R2CHOHR2CHCl + H2O
(iii) Primary alcohols do not react with Lucas reagent at room temperature and hence no turbidity is formed.
RCH2OH No reaction and hence no turbidity at room temperature