Lucas Test for Primary, Secondary, and Tertiary Alcohols

CCA! Volume 5

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Lucas Test for Primary, Secondary, and Tertiary Alcohols

1-butanol, 2-butanol, and 2-methyl-2-propanol are treated with a solution of ZnCl₂ in concentrated aqueous HCl.

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Narrative
Three test tubes contain a solution of zinc chloride (ZnCl₂) in concentrated aqueous hydrochloric acid (HCl). The primary alcohol 1-butanol, the secondary alcohol 2-butanol, and the tertiary alcohol 2-methyl-2-propanol are added to separate test tubes. Immediately the tertiary alcohol forms a cloudy solution as the alcohol is converted to the water insoluble alkyl chloride by a S_N1 reaction. The primary alcohol, 1-butanol, does not react. The secondary alcohol, 2-butanol, reacts after about 6.5 minutes.

Discussion
In sequence, 1-butanol, 2-butanol, and 2-methyl-2-propanol are treated with a solution of ZnCl₂ in concentrated aqueous HCl. Immediately the tertiary alcohol forms a cloudy solution as the alcohol is converted to the water insoluble alkyl chloride by a S_N1 reaction. The secondary alcohol, 2-butanol, reacts after about 6.5 minutes. The primary alcohol, 1-butanol, does not react.