Question

5. Using the tests performed in this experiment, how could you distinguish between the following pairs of compounds? Tell what reagent or test you would use and what you would observe. 1-Butanol and 2-butanol a) b) C Isobutyl alcohol and tert-butyl alcohol 1-Propanol and 1-heptanol Cyclohexanol and cyclohexane d)

properties of alcohol

Answer 1

Only 2-butanol gives positive iodoform test whereas 1-butanol does not give iodoform test.

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)

Bromine and carbontetrachloride can be used since the red bromine reacts with colorless cyclohexene to give colorless 1,2-dibromocyclohexane. Bromine does not react with cyclohexane at room temperature and in the dark so the cyclohexane solution becomes red and stays red.