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Write a short note on Lucas test.


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Solution

Alcohols

  • A type of organic molecule with at least one hydroxyl -OH functional group attached to a saturated carbon atom is called an alcohol.
  • Primary, secondary, and tertiary alcohols are the three types of alcohol.
  • Examples: Ethanol C2H5OH and Butanol C4H9OH.

Lucas test

  • The Lucas test is used to distinguish between the many types of alcohol.
  • The Lucas reagent is used to distinguish between primary, secondary, and tertiary alcohols.
  • The Lucas test uses a solution of anhydrous zinc chloride ZnCl2 in concentrated hydrochloric acid HCl to distinguish and classify primary, secondary, and tertiary alcohols.
  • The Lucas reagent is a common name for this mixture.

Lucas test for tertiary alcohol

  • Tertiary alcohol reacts right away to create an oily layer and an insoluble compound called alkyl halide.
  • Examples: 2-methyl-2-butanol.

Lucas test for secondary alcohol

  • The reaction time of secondary alcohol is five minutes.
  • The solution becomes turbid in three to five minutes and produces an oily layer.
  • Example: 2-Pentanol.

Lucas test for primary alcohol

  • Primary alcohols don't seem to react at all.
  • Unless it is heated, the solution doesn't change color.
  • When heated, the solution generates an oily layer.
  • Example: 1-Pentanol.

Mechanism of Lucas test

  • SN1 nucleophilic substitution, a two-step reaction, is the reaction that takes place in this test.

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