how can we distinguish between ethanol, isopropyl alcohol and tertiary butyl alcohol?
Answers
isopropyl alcohol is CH3-CH(OH)-CH3 ...a secondary alcohol..
t-butyl alcohol is (CH3)3C-OH ....a tertiary alcohol .....
the best way to distinguish between them is;' Lucas test'...this test is based upon the difference in reactivity of primary,secondary and tertiary alcohols with HCl...
in this test the alcohol is mixed with Lucas reagent (an equimolar mixture of conc.HCl and anhydrous ZnCl2) at room temperature when turbidity due to the formation of insoluble alkyl chloride is observed....
if the turbidity appears immediately ,the alcohol is tertiary...
if the turbidity appears in about 5 minutes alcohol is secondary..
a primary alochol however does not react with lucas reagent at room temperature and hence no turbidity is formed...
so (CH3)3-C-OH + HCl + ZnCl2(anhydrous) -----> (CH3)C-Cl + H2O (turbidity appears immediately)
CH3-CH(OH)-CH3 + HCl + ZnCl2(anhydrous) ----.>CH3-CH(Cl)-CH3 + H2O (turbidity appears in 5 minutes
Ethanol, isopropyl alcohol, and tertiary butyl alcohol can be distinguished by using the Lucas test.
- Ethanol is a primary alcohol, isopropyl alcohol is a secondary alcohol, and tertiary butyl alcohol is a tertiary alcohol.
- In this reaction, Conc. HCl and ZnCl2 are used as Lucas reagents.
- The three alcohols can be distinguished by the turbidity of the reaction.
- If the turbidity appears immediately in the reaction then it is tertiary butyl alcohol.
- If the turbidity appears in some times then it is a secondary alcohol.
- If the turbidity doesn't appear then it is a primary alcohol.
Hence, Ethanol, isopropyl alcohol, and tertiary butyl alcohol can be distinguished by using the Lucas test.