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  4. The hydroxyl compound that gives a precipitate immediately when treated with concentrated hydrochloric acid and anhydrous zinc chloride is

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Q. The hydroxyl compound that gives a precipitate immediately when treated with concentrated hydrochloric acid and anhydrous zinc chloride is

KEAMKEAM 2011Alcohols Phenols and Ethers

Solution:

An equimolar mixture of cone. $ HCl $ and anhydrous $ ZnC{{l}_{2}} $ is called Lucas reagent. On treatement with Lucas reagent, tertiary alcohols gives precipitate immediately. This test is known as Lucas test.
$ \underset{\begin{smallmatrix} 2-methyl-2-butanol \\ \,\,\,\,\,\,\,\,(3{}^\circ alcohol) \end{smallmatrix}}{\mathop{C{{H}_{3}}-\underset{\begin{smallmatrix} | \\ C{{H}_{3}} \end{smallmatrix}}{\overset{\begin{smallmatrix} OH \\ | \end{smallmatrix}}{\mathop{C}}}\,-C{{H}_{2}}-C{{H}_{3}}}}\,\xrightarrow[+anhy.\,ZnC{{l}_{2}}]{HCl} $ $ \underset{\begin{smallmatrix} \,\,\,\,\,\,\,\,\,2-chloro-2-methylbutane \\ (Turbidity\text{ }appears\text{ }immediately) \end{smallmatrix}}{\mathop{C{{H}_{3}}-\underset{\begin{smallmatrix} | \\ C{{H}_{3}} \end{smallmatrix}}{\overset{\begin{smallmatrix} Cl \\ | \end{smallmatrix}}{\mathop{C}}}\,-C{{H}_{2}}-C{{H}_{3}}}}\, $